REVIEW | doi:10.20944/preprints201612.0097.v2
Subject: Life Sciences, Microbiology Keywords: pathogens; Legionella; amoeba; protozoa; biofilm; antibacterial; antimicrobial; cooling towers; biocides; polyvalent metals
Online: 20 December 2016 (10:26:22 CET)
Application of toxic antibacterial agents is considered necessary to control prevalent fresh water microorganisms in evaporative cooling water systems, but these agents can adversely affect the environment and human health. Alternatively, natural antibacterial water chemistry has been applied in industrial cooling water systems for over 10 years with excellent results. The tower water chemistry method concentrates natural salts in highly-softened water to produce elevated pH and dissolved solids, with low calcium and magnesium. This practice conserves water while generating only a small volume of non-toxic natural salt concentrate for cost efficient separation and disposal if required. This review presents a novel perspective of natural antimicrobial chemistry for inhibiting parasitic microbiome functional relationships within the bio-triad of Legionella outbreaks, "Trojan Protozoans" and biofilms. The review further examines practical application and function of polyvalent metal ions in the inhibition of biofilms. Reducing global dependence on toxic antibacterial agents discharged to the environment is an emerging concern due to their impact on the natural microbiome, plants, animals and humans. Discharge of antibacterial agents also contributes to development of pathogen resistance. Use of natural antibacterial chemistry can play a key role in managing the cooling water environment in a more ecologically sustainable manner.
ARTICLE | doi:10.20944/preprints202102.0566.v1
Subject: Physical Sciences, Acoustics Keywords: ultra-fast cooling; vitrification; glass transition; fast scanning calorimetry; liquid cooling
Online: 25 February 2021 (07:56:23 CET)
The liquid droplet cooling technique for fast scanning chip calorimetry (FSC) is introduced, increasing the cooling rate for large samples on a given sensor. Reaching higher cooling rates and using a gas as the cooling medium, the common standard for ultra-fast temperature control in cooling, requires reducing the lateral dimensions of the sample and sensor. The maximum cooling rate is limited by the heat capacity of the sample and the heat exchange between the gas and the sample. The enhanced cooling performance of the new liquid droplet cooling technique is demonstrated for both metals and polymers, on examples of solidification of large samples of indium, high-density polyethylene (HDPE), and poly (butylene 2,6-naphthalate) (PBN). It was found that the maximum cooling rate can be increased up to 5 MK/s in room temperature environment, that is, by 2 orders of magnitude, compared to standard gas cooling. Furthermore, modifying the droplet size and using coolants at different temperatures provide options to adjust the cooling rate in the temperature ranges of interest.
REVIEW | doi:10.20944/preprints202012.0304.v1
Subject: Biology, Anatomy & Morphology Keywords: Vitrification; cooling; abiotic; biotic; stress; browning
Online: 14 December 2020 (08:17:26 CET)
Recent developments in the cryopreservation space has increased the trend in germplasm collections established through cryopreserved in vitro material. Cryopreservation of recalcitrant seeds through embryos and embryonic axes, is not uncommon. Tropical and sub-tropical plants are not acclimated to the cold season, therefore have no in-built natural resilience to the cold. Also, larger seeds from trees, such as avocado (Persea americana Mill.), mango (Mangifera indica) and durian (Durio zibethinus L.) are sensitive to desiccation, chilling and freezing stress, making them unsuitable for seed banking or cryopreservation. Alternatively, as seeds do not carry the same genetic make-up as the mother plant, especially in the context of woody rainforest species of which the cross-pollination is dominant; seed conservation does not serve the purpose of germplasm preservation. Other plant material and methods are needed for these plants to be successfully stored in liquid nitrogen (LN). One such method commonly used is shoot-tip cryopreservation which ensures the clonal fidelity of germplasm. There are many problems when using shoot tips of tropical recalcitrant-seeded species. These include: 1) the toxic effects of cryoprotective agents towards structural integrity; 2) optimum developmental stage for success and 3) oxidative stress associated with excision injury leading to necrosis triggering cell death and hindering regeneration for the shoot tips in culture. A pre-requisite for any cryopreservation system is the availability of an established tissue culture regeneration platform. This review will outline conservation strategies for avocado with special emphasis on attempts and improvements made in the cryopreservation space for storing this horticulturally important crop ‘avocado’ at ultra-low temperatures.
Subject: Physical Sciences, General & Theoretical Physics Keywords: quantum thermodynamics; laser cooling; cavitation; sonoluminescence
Online: 7 February 2020 (03:13:02 CET)
In this paper, we design a quantum heat exchanger which converts heat into light on relatively short quantum optical time scales. Our scheme takes advantage of collective cavity-mediated laser cooling of an atomic gas inside a cavitating bubble. Laser cooling routinely transfers individually trapped ions to nano-Kelvin temperatures for applications in quantum technology. The quantum heat exchanger which we propose here is expected to provide cooling rates of the order of Kelvin temperatures per millisecond and is expected to find applications in micro and nanotechnology.
ARTICLE | doi:10.20944/preprints202105.0727.v1
Subject: Engineering, Automotive Engineering Keywords: absorption cycle; Kalina cycle; absorption power cycle; LiBr; combined power and cooling; ab-sorption cooling; salt solution
Online: 31 May 2021 (10:10:38 CEST)
Combined systems for power production and thermally activated cooling have a high potential for improving the efficiency and utilisation of thermal systems. In this regard, various configurations have been proposed and are comprehensively reviewed. They are primarily based on absorption systems and the implementation of multiple levels of complexity and flexibility. The configuration of the absorption power and cooling combined cycle proposed herein has wide commercial applicability owing to its simplicity. The configuration of the components is not new. However, the utilisation of aqueous salt solutions, the comparison with ammonia chiller and with absorption power cycles, the focus on parameters that are important for real-life applications, and the comparison of the performances for constant heat input and waste heat recovery are novel. The proposed cycle is also compared with a system based on the organic Rankine cycle and vapour compression cycle. An investigation of its performance proves that the system is suitable for a given range of boundary conditions from a thermodynamic standpoint, as well as in terms of system complexity and technical feasibility. New possibilities with regard to added power production have the potential to improve the economics and promote the use of absorption chiller systems.
ARTICLE | doi:10.20944/preprints201912.0312.v1
Subject: Engineering, Civil Engineering Keywords: thermal comfort; draught; cooling period; open office
Online: 24 December 2019 (08:42:03 CET)
Local thermal comfort (TC) and draught rate (DR) has been studied widely. There has been more meaningful research performed in controlled boundary condition situations than in actual work environments involving occupants. TC conditions in office buildings in Estonia have been barely investigated in the past. In this paper, the results of TC and DR assessment in five office buildings in Tallinn are presented and discussed. Studied office landscapes vary in heating, ventilation and cooling (HVAC) system parameters, room units and elements. All sample buildings were less than six years old, equipped with dedicated outdoor air ventilation system and room conditioning units. The on-site measurements consisted of TC and DR assessment with indoor climate questionnaire (ICQ). The purpose of the survey is to assess the correspondence between HVAC design and the actual situation. Results show, whether and in what extent the standard-based criteria for TC is suitable for actual usage of the occupants. Preferring one room conditioning unit type or system may not guarantee better thermal environment without draught. Although some HVAC systems observed in this study should create the prerequisites for ensuring more comfort, results show that this is not the case for all buildings in this study.
ARTICLE | doi:10.20944/preprints202301.0104.v1
Subject: Engineering, Civil Engineering Keywords: Engine Overheating; Cooling System; Cylinder Head; Cylinder Blok
Online: 5 January 2023 (10:51:33 CET)
Engine Overheating is a condition where the engine temperature has increased above the working temperature. This analysis aims to analyze the damage, determine the factors causing the damage, identify corrective steps and prevent engine overheating. The inspection procedure is carried out by checking the cooling system's components, cylinder head, and cylinder block. Further analysis using a fishbone diagram to analyze the causes of engine overheating troubleshooting. Damage analysis results Engine overheating occurs because the thermostat is damaged, namely, the thermostat valve which cannot open when the temperature reaches the standard temperature (71oC), and also due to damage to the cylinder gasket which causes bubbles due to compression leaks and mixing of radiator coolant and oil. Repair steps are taken in the form of replacing damaged components with new ones. Preventive measures are taken by not using the unit on an over-running basis, checking coolant levels, carrying out daily checks properly and correctly, and carrying out preventive maintenance regularly.
ARTICLE | doi:10.20944/preprints202002.0369.v1
Subject: Engineering, Energy & Fuel Technology Keywords: Solar Cooling; Adsorption; Evacuated tube collectors; Experimental testing
Online: 25 February 2020 (11:12:51 CET)
The high environmental impact of conventional methods of cooling and heating has increased the need for renewable energy deployment for covering thermal loads. Towards that direction, the proposed system aims at offering an efficient solar powered alternative, coupling a zeolite-water adsorption chiller with a conventional vapor compression cycle. The system is designed to operate under intermittent heat supply of low-temperature solar thermal energy (<90 °C) provided by evacuated tube collectors. A prototype was developed and tested in cooling mode operation. The results of separate components testing showed that the adsorption chiller was operating efficiently, achieving a maximum coefficient of performance (COP) of 0.65. With respect to the combined performance of the system, evaluated on a typical week of summer in Athens, the maximum reported COP was approximately 0.575, mainly due to the lower driving temperatures at a range of 75 °C. The corresponding mean energy efficiency ratio (EER) obtained was 5.8.
ARTICLE | doi:10.20944/preprints201905.0084.v1
Subject: Materials Science, Metallurgy Keywords: GTD222; nickel based superalloy; solidification behavior; cooling rate
Online: 8 May 2019 (08:57:20 CEST)
The microstructure and solidification behavior of nickel based GTD222 superalloy at different cooling rates are studied. The solidification of the GTD222 superalloy proceeds as follows: L→L+γ, L→L+γ+MC, L→L+(γ/γ ′)-Eutectic and L→η phase. The temperature of liquidus of GTD222 superalloy is 1360 °C while the solidus is slightly lower at 1310 °C, which due to the alloying elements redistribution. It was found that the dendrite arm spacing of the alloy decreased with the increase of cooling rate (From 200 μm at 2.5 K/min to 100 μm at 20 K/min).
ARTICLE | doi:10.20944/preprints201811.0343.v1
Subject: Engineering, Energy & Fuel Technology Keywords: film cooling; conjugate heat transfer; radiation; syngas; TBC
Online: 15 November 2018 (05:30:44 CET)
The future power equipment tends to take hydrogen or middle/low heat-value syngas as fuel for low emission. The heat transfer of film cooled turbine blade shall be influenced more by radiation. Its characteristic of conjugate heat transfer is studied experimentally and numerically in the paper by considering radiation heat transfer, multi-composition gas and TBC. The Weighted Sum of Gray Gases spectral model and Discrete Transfer Model are utilized to solve the radiative heat transfer in the multi-composition field, while validated against the experimental data for the studied cases. It is shown that the plate temperature increases significantly when considering the radiation and the temperature gradient of the film cooled plate becomes larger. It is also shown that increasing percentage of steam in gas composition results in increased temperature on the film-cooled plate. The normalized temperature of the film-cooled plate decreases about 0.02, as the total percentage of steam in hot gas increases per 7%. As for the TBC effect, it can smooth out the the temperature distribution and insulate the heat to a greater extent when the radiative heat transfer becomes significant.
ARTICLE | doi:10.20944/preprints201805.0098.v1
Subject: Engineering, Energy & Fuel Technology Keywords: condensation; non-condensable gas; experimental study; containment cooling
Online: 7 May 2018 (05:09:47 CEST)
According to the operation conditions of time unlimited passive containment heat removal system (TUPAC), a separate effect experiment facility was established to investigate the heat transfer performance of steam condensation in presence of non-condensable gas. The effect of wall subcooling temperature, total pressure and mass fraction of the air on heat transfer process was analyzed. The heat transfer model was also developed. The results showed that the heat transfer coefficient decreased with the rising of subcooling temperature, the decreasing of the total pressure and air mass fraction. It was revealed that Dehbi’s correlation predicted the heat transfer coefficient conservatively, especially in the low pressure and low temperature region. The novel correlation was fitted by the data obtained in the following range: 0.20~0.45 MPa in pressure, 20% ~ 80% in mass fraction, 15°C ~ 45°C in temperature. The discrepancy of the correlation and experiment data was with ±20%.
ARTICLE | doi:10.20944/preprints201709.0083.v1
Subject: Engineering, Civil Engineering Keywords: asphalt mixture; cooling; basic oxygen furnaces (BOF) slag
Online: 18 September 2017 (16:45:41 CEST)
The basic oxygen furnace slag (BOF) was wide used in road construction, but there was a lack of characteristics in different asphalt mixtures. This study investigates the properties of hot-mixed asphalt (HMA) containing stone mastic asphalt (SMA), porous asphalt (PA) and dense-graded BOF as a partial substitution for natural aggregates. The purpose of this study is to evaluate various BOF slag contents in the asphalt mixtures would affect the cooling behavior after compaction. Asphalt mixture specimens contained 0%, 20%, 40% and 60% BOF slag, respectively, as coarse aggregate. Test results showed that BOF slag has a lipophilic property, so it can be adsorbed by asphalt cement, thereby reducing the cost of asphalt. The stability value of all asphalt mixtures increases with the proportion of BOF slag replacement. In addition, the voids in the mineral aggregate (VMA) value variable exhibited significant differences among asphalt mixtures, and could determine the deviation of the cooling trend of asphalt mixtures. Furthermore; it was found that the cooling procedure of the BOF slag used in dense-graded asphalt mixture takes about 100 min, and that the temperature tends to be moderate; however, it took about 120 min of cooling the SMA and PA mixture with BOF slag. In addition, the voids distribution of dense asphalt mixture was not uniform. It would result in various locations of thermal energy temperature on asphalt mixtures that were inconsistent.
ARTICLE | doi:10.20944/preprints202103.0615.v1
Subject: Physical Sciences, Acoustics Keywords: quantum chromodynamics; confinement; center vortex model; vacuum structure; cooling
Online: 25 March 2021 (12:47:31 CET)
The center vortex model of quantum-chromodynamics can explain confinement and chiral symmetry breaking. We present a possible resolution for problems of the vortex detection in smooth configurations and discuss improvements for the detection of center vortices.
ARTICLE | doi:10.20944/preprints202101.0411.v1
Subject: Engineering, Automotive Engineering Keywords: Energy performance; Cooling load prediction; Neural network, Metaheuristic optimization.
Online: 21 January 2021 (09:23:04 CET)
Regarding the high efficiency of metaheuristic techniques in energy performance analysis, this paper scrutinizes and compares five novel optimizers, namely biogeography-based optimization (BBO), invasive weed optimization (IWO), social spider algorithm (SOSA), shuffled frog leaping algorithm (SFLA), and harmony search algorithm (HSA) for the early prediction of cooling load in residential buildings. The algorithms are coupled with a multi-layer perceptron (MLP) to adjust the neural parameters that connect the CL with the influential factors. The complexity of the models is optimized by means of a trial-and-error effort, and it was shown that the BBO and IWO need more crowded spaces for fulfilling the optimization. The results revealed that the internal parameters (i.e., biases and weights) suggested by the BBO generate the most reliable MLP for both analyzing and generalizing the CL pattern (with nearly 93 and 92% correlations, respectively). Followed by this, the IWO emerged as the second powerful optimizer with mean absolute errors of 1.8632 and 1.9110 in the training and testing phases. Therefore, the BBO-MLP and IWO-MLP can be reliably used for accurate analysis of the CL in future projects.
Subject: Engineering, Automotive Engineering Keywords: Digital twin; Simulation; District heating; District cooling; 4GDH; DHC
Online: 15 January 2021 (13:21:41 CET)
Dynamic simulation of district heating and cooling networks has an increased importance in the transition towards renewable energy sources and lower temperature district heating grids, as both temporal and spatial behavior need to be considered. Even though a lot and research and development has been performed in the field, there are several pitfalls and challenges towards dynamic district heating and cooling simulation for everyday use. This article presents the experiences from working with district heating and cooling projects, along with relevant research, corresponding research gaps and proposed research directions.
ARTICLE | doi:10.20944/preprints202012.0073.v1
Subject: Engineering, Automotive Engineering Keywords: lubrication; wear; cooling-lubrication system; valve forging; 3D scanning
Online: 3 December 2020 (07:36:43 CET)
TThe paper presents the results of research on the influence of the settings of lubrication and cooling system parameters (solenoid valve opening time and lubricant feed pressure in terms of its quantity) in order to select the optimal lubricating conditions and thus reduce the wear of the dies used in the first forging operation of the valve forging made of high-nickel steel. Based on the observation of lubrication in the industrial process, it was found that a significant part of the lubricant fails to reach the die cavity, reaching the outside of it, which causes die wear due to seizure resulting from adhesion of the forging material to the tool surface, as well as high lubricant consumption and dirt in the press chamber. The authors proposed their own mobile lubricating and cooling system, which allows for a wide range of adjustments and provided with automatic cleaning procedures of the entire system, unlike the fixed lubrication system used so far in the industrial process. First, tests were carried out in laboratory conditions to determine the highest wettability and the lubricant remaining inside the tool cavity. These tests determined the lubrication system parameter settings which ensured that the greatest amount of lubricant remains in the cold die cavity without the forging process. Then, to verify the obtained results, tests were carried out in the industrial process of hot die forging of valve forgings, for short production runs of up to 500 forgings. The results were compared with the measurement of changes in the geometry of tools and forgings based on 3D scanning and surface topography analysis with the use of SEM. For best results (the variant of the setting of the dose and the time of exposure to lubricant), the forging process was carried out with the use of a new tool, up to the maximum service life.
REVIEW | doi:10.3390/sci1020037
Subject: Keywords: thermoelectric; figure-of-merit; Peltier; Seebeck; thermoelectric generator; cooling
Online: 9 July 2019 (00:00:00 CEST)
Thermoelectrics, in particular solid-state conversion of heat to electricity and vice versa, is expected to be a key energy harvesting and temperature management solution in coming years. There has been a resurgence in the search for new materials for advanced thermoelectric energy conversion applications and to enhance the properties of existing materials. In this paper, we review recent efforts on improving figure-of-merit (ZT) through alloying and nano structuring. As heatsink characteristics dictate the performance of thermoelectric modules, various types of heatsink designs has been investigated. Several reported strategies for improving ZT are critically assessed. A notable increase in figure-of-merit of thermoelectric materials (TE) has opened up new areas of applications especially in the medical field. Peltier cooling devices are widely employed for patient core temperature control, skin cooling, medical device and laboratory equipment cooling. Application of these devices in the medical field both in temperature control and power generation has been studied in detail. It is envisioned that this study will provide profound knowledge on the thermoelectric based materials and its role in medical applications.
ARTICLE | doi:10.20944/preprints201905.0181.v1
Subject: Engineering, Mechanical Engineering Keywords: annular cooling fan; outer ring; structure parameters; aerodynamic performance
Online: 15 May 2019 (10:05:43 CEST)
We studied the effect of the structure parameters of engine annular cooling fan with outer ring on the aerodynamic performance by means of experiments and model simulation in fluent®. Firstly, based on the experiment, a computational model is developed to calculate and analyze the aerodynamic performance of the tested annular fan. The model is validated by comparing the test results with the calculated data. Besides, the aerodynamic performance differences between two types of fans (common fan without outer ring and annular fan with outer ring) are discussed. Based on the computational model, the relation between aerodynamic performance and the outer ring structure parameters are investigated. The results show that the relative parameter on the axial direction has great influence on the aerodynamic performance; while the effect of radial relative parameter is minor. In addition, the outer ring with arc chamfer structure in the downstream side can improve its static pressure efficiency effectively.
ARTICLE | doi:10.20944/preprints201809.0353.v1
Subject: Earth Sciences, Environmental Sciences Keywords: cooling water shortage; thermal power; economic consequence; climate change
Online: 18 September 2018 (14:10:25 CEST)
Abstract: Currently, thermal power is the largest source of power in the world. Although the impacts of climate change on cooling water sufficiency in thermal power plants have been extensively assessed globally and regionally, their economic consequences have seldom been evaluated. In this study, the Asia-Pacific Integrated Model Computable General Equilibrium model (AIM/CGE) was used to evaluate the economic consequences of projected future cooling water insufficiency on a global basis, which was simulated using the H08 global hydrological model. This approach enabled us to investigate how the physical impacts of climate change on thermal power generation influence economic activities in regions and industrial sectors. To account for the uncertainty of climate change projections, five global climate models and two representative concentration pathways (RCPs 2.6 and 8.5) were used. The ensemble-mean results showed that the global gross domestic product (GDP) loss in 2070–2095 due to cooling water insufficiency in the thermal power sector was −0.21% (−0.12%) in RCP8.5 (RCP2.6). Among the five regions, the largest GDP loss of −0.57% (−0.27%) was observed in the Middle East and Africa. Medium-scale losses of −0.18% (−0.12%) and −0.14% (−0.12%) were found in OECD90 (the member countries of the Organization for Economic Co-operation and Development as of 1990) and Eastern Europe and the Former Soviet Union, respectively. The smallest losses of −0.05% (−0.06%) and −0.09% (−0.08%) were found in Latin America and Asia, respectively. The economic impact of cooling water insufficiency was non-negligible and should be considered as one of the threats induced by climate change.
ARTICLE | doi:10.20944/preprints202211.0390.v1
Subject: Materials Science, Metallurgy Keywords: A5N aluminum; Cooling; Convection; Thermal radiation; Size effect; Temperature dependence
Online: 21 November 2022 (11:52:13 CET)
The results of the study of the influence of the size of cylindrical samples of A5N aluminum on the time and rate of their cooling are presented. According to experimental data, the temperature dependence of the heat transfer coefficient for pure metals is calculated. It revealed that the process of cooling of the aluminium and its alloys has a relaxation behavior. It has found that the main mechanisms of natural air cooling are convection heat transfer and radiation. The characteristic cooling time due to radiation is less than due to convection. The contribution of thermal radiation is noticeable at high temperatures. It was found that the characteristic times of cooling due to radiation and convection increase with increase in volume to area ratio of the sample.
ARTICLE | doi:10.20944/preprints202110.0419.v1
Subject: Engineering, Energy & Fuel Technology Keywords: liquid cooling; phase-change loop; pressure difference; heat transfer enhancement
Online: 27 October 2021 (15:11:16 CEST)
To overcome the two-phase flow instability of traditional boiling heat dissipation technologies, a porous wick was used for liquid-vapor isolation, thus realizing efficient and stable boiling heat dissipation. A pump-assisted capillary phase-change loop with methanol as working medium was established to study the effect of liquid-vapor pressure difference and heating power on its start-up and steady-state characteristics. The results indicated that the evaporator undergoes four heat transfer modes including flooded, partial flooded, thin film evaporation and overheating. The thin film evaporation mode was the most efficient one with the shortest start-up period. Besides, the heat transfer modes were determined by liquid-vapor pressure difference and power. The heat transfer coefficient could be significantly improved and the thermal resistance could be reduced by increasing liquid-vapor pressure difference as long as it did not exceed 8 kPa. However, when the liquid-vapor pressure difference exceeded 8kPa, its influence on the heat transfer coefficient weakened. In addition, a two-dimensional heat transfer mode distribution diagram considering both liquid-vapor pressure difference and power was drawn through a great number of experiments. During engineering application, the liquid-vapor pressure difference can be controlled to maintain efficient thin film evaporation in order to achieve the optimum heat dissipation effect.
ARTICLE | doi:10.20944/preprints202101.0133.v1
Subject: Engineering, Automotive Engineering Keywords: Energy-efficiency; HVAC system; Neural network; Cooling load; Metaheuristic search.
Online: 8 January 2021 (10:20:07 CET)
Early prediction of thermal loads plays an essential role in analyzing energy-efficient buildings' energy performance. On the other hand, stochastic algorithms have recently shown high proficiency in dealing with this issue. These are the reasons that this work is dedicated to evaluating an innovative hybrid method for predicting the cooling load (CL) in buildings with residential usage. The proposed model is a combination of artificial neural networks and stochastic fractal search (SFS-ANN). Two benchmark algorithms, namely the grasshopper optimization algorithm (GOA) and firefly algorithm (FA), are also considered to be compared with the SFS. The non-linear effect of eight independent factors on the CL is analyzed using each model's optimal structure. Evaluation of the results outlined that all three metaheuristic algorithms (with more than 90 % correlation) can adequately optimize the ANN. In this regard, this tool's prediction error declined by nearly 23, 18, and 36 % by applying the GOA, FA, and SFS techniques. Also, all used accuracy criteria indicated the superiority of the SFS over the benchmark schemes. Therefore, it is inferred that utilizing the SFS along with ANN provides a reliable hybrid model for the early prediction of CL.
ARTICLE | doi:10.20944/preprints202008.0489.v1
Subject: Earth Sciences, Atmospheric Science Keywords: urban bioclimate; urban cooling; urban wetland; riparian shading; inversion layer
Online: 22 August 2020 (04:27:59 CEST)
Climate change and rapid urbanization are adversely affecting the urban environment by exacerbating the widely reported Urban Heat Island effect in Dhaka, Bangladesh. Two wetland areas with variable riparian shadings in the warm-humid conditions of urban Dhaka had been investigated through field campaigns on microclimatic parameters for their cooling potential on the surrounding urban fabric. It was observed that an inversion layer of fully saturated air develops over the water surface of wetland, suppressing evaporation from the wetland water surface layer, which was effectively reducing the heat exchange between the water surface and the air layer above it through its action as an insulating vapor blanket. Because of this effect, the wetland was unable to render as a source of coolth for the surrounding overheated urban area. This effect of the inversion layer was more pronounced in the urban wetland without riparian shading either by urban form or tree canopy. A Multiphysics simulation study conducted on the selected urban wetlands indicates the effect of differential shading pattern on the relation between fetch and inversion layer thickness. This research hypothesizes that the wetland can act as an urban adaption measure against the urban heat island effect by potentially transforming them into Urban Cooling Island (UCI) towards a favorable urban bioclimate.
ARTICLE | doi:10.20944/preprints201905.0354.v1
Subject: Keywords: Solar cooling; Absorption chiller; LiBr-H2O; Operating conditions; Climatic conditions
Online: 29 May 2019 (15:17:28 CEST)
The study carried out by simulation, concerns the thermal behavior of an office building’s solar fresh air cooling system, based on a LiBr-H2O absorption chiller in different climatic conditions. The coefficient of performance (COP) and the solar fraction were considered performance parameters and were analyzed with respect to the operating limits: risk of crystallization and maintaining at least a minimum degassing zone. A new correlation between the required solar hot temperature and the cooling water temperature was established and then embedded in another new correlation between the COP and the cooling water temperature that was used in simulations during the whole cooling season corresponding to each location. It was found that: the solar hot water should be maintained in the range of (80-100) °C depending on the cooling water temperature, the COP of the solar LiBr-H2O absorption chiller with or without cold storage tank can reach (76.5-82.4) % depending on the location, and the solar fraction can reach (29.5-62.0) % without cold storage tank and can exceed 100 % with cold storage tank, the excess cooling power being available to cover other types of cooling loads: through the building envelope, from lighting, from occupants, etc.
ARTICLE | doi:10.20944/preprints202208.0113.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: Liquid metal; Additive manufacturing; Thermal management; Temperature gradient; Cooling rate; Crack
Online: 4 August 2022 (16:23:19 CEST)
How to effectively suppress thermal cracks in the metal laser additive manufacturing process is still one of the key issues to be solved in the field of laser additive manufacturing. Metal tin, with wide liquid phase working temperature range, high boiling point, low viscosity, high thermal conductivity and excellent electrical conductivity. The use of tin as an auxiliary thermal management material in the metal additive manufacturing process is expected to achieve effective regulation of the temperature field and stress field of the formed part, thereby inhibiting the initiation of cracks and obtaining formed parts with the target grain structure and high reliability. This paper presented a novel liquid metal-assisted laser additive manufacturing method (LMAAM). A numerical model for the laser additive manufacturing of tin-assisted titanium alloys was established. The differences of the flow field, temperature field and stress field of the formed parts with tin and without tin were compared and analyzed. The influence of the interaction position between the tin liquid level and the forming part on the temperature field and stress field of the forming part was deeply studied. The laser additive manufacturing experiment of tin-assisted titanium alloy was carried out, and the experimental results were basically consistent with the simulation results, which verified the validity of the model. LMAAM technology has proven to be an effective method for additive manufacturing of highly reliable formed parts.
ARTICLE | doi:10.20944/preprints202104.0568.v1
Subject: Engineering, Automotive Engineering Keywords: hot streak; swirl; turbine vane; thermal barrier coatings; overall cooling effectiveness
Online: 21 April 2021 (10:32:23 CEST)
This paper studied the combined influences of the hot streak and swirl on the cooling performances of the NASA C3X guide vane coated with or without TBCs. The results show that: (1) Even under uniform velocity inlet conditions, the hot streak core can be stretched as it impinges the leading edge which causes higher heat load on the suction side of the forward portion. (2) The swirl significantly affects circumferential and radial migration of the hot streak core in the NGV passage. On the passage inlet plane, positive swirl leads to a hotter tip region on the suction side. In comparison, negative swirl leads to a hotter hub region on the pressure side. (3) Under the influence of swirl, migration of coolant improve the coverage of film cooling close to the midspan, while in the regions close to the hub and tip end-wall, the overall cooling performance decrease simultaneously. (4) In the regions with enough internal cooling, the cooling effectiveness increment is always larger than that in other regions. Besides, the overall cooling effectiveness increment decreases on the region covered by film cooling for the coated vane, especially in the region with negative local heat flux.
ARTICLE | doi:10.20944/preprints201808.0290.v2
Subject: Materials Science, Nanotechnology Keywords: chemical modification; electronics cooling; thermal management nanocomposites; thermal conductivity; silver nanoparticles
Online: 25 October 2018 (10:33:13 CEST)
Polymer composites with high thermal conductivity have a great potential for applications in modern electronics due to their low cost, easy process, and stable physical and chemical properties. Nevertheless, most polymer composites commonly possess unsatisfactory thermal conductivity, primarily because of the high interfacial thermal resistance between inorganic ﬁllers. Herein, we developed a novel method through silver functionalized graphene nanosheets (GNS) and multiwalled carbon nanotube (MWCNT) composites with excellent thermal properties to meet the requirements of thermal management. The effects of composites on interfacial structure and properties of the composites were identiﬁed, and the microstructures and properties of the composites were studied as a function of the volume fraction of fillers. An ultrahigh thermal conductivity of 12.3 W/mK for polymer matrix composites was obtained, which is an approximate enhancement of 69.1 times compared to the polyvinyl alcohol (PVA) matrix. Moreover, these composites showed more competitive thermal conductivities compared to untreated fillers/PVA composites applied to the desktop central processing unit, making these composites a high-performance alternative to be used for thermal management.
ARTICLE | doi:10.20944/preprints201805.0187.v1
Subject: Materials Science, Metallurgy Keywords: ferrite; carbide; bainite; continuous cooling transformation (CCT) curve; charpy impact test
Online: 14 May 2018 (10:29:18 CEST)
2.25Cr-1Mo steel with high strength at high temperatures and good hydrogen resistance is widely used for power generation boiler material in high temperature and pressure use environments. Following the test evaluation of the ASME Boiler and Pressure Vessel Code, specimens from the base metal of a boiler pipe were found to have impact toughness values of 285 and 21 ft-lb, which are drastically different values. The analysis of the fracture surface of the 21 ft-lb test specimen revealed MnS inclusions, and it was found that cracks initiated at the inclusions. Observation of the cross-section of the crack propagation front revealed that cracks propagated along the ferrite regions and precipitate voids. Inclusions were also found in the 285 ft-lb impact specimen; however, the volume fraction of the inclusions was significantly less than that of the 21 ft-lb specimen. It was also found that the ferrite and carbide content of the 285 ft-lb specimen was less than 21 ft-lb specimen. The reason that the inclusions, ferrite, and carbide content differed in the two adjacent impact test specimens was analyzed. The effects of micro-segregation, such as MnS inclusions on ferrite and carbide, were compared and analyzed.
ARTICLE | doi:10.20944/preprints201701.0021.v1
Subject: Engineering, Energy & Fuel Technology Keywords: capacity; cooling and heating; fin-tube heat exchanger; pressure drop; turbulator
Online: 5 January 2017 (09:07:14 CET)
This study presents the comparison of heat transfer capacity and pressure drop characteristics between a basic fin-tube heat exchanger and a modified heat exchanger with the structural change of branch tubes and coiled turbulators. All experiments were carried out using an air-enthalpy type calorimeter based on the method described in ASHRAE standards, under heat exchanger experimental conditions. 14 different kinds of heat exchangers were used for the experiment. Cooling and heating capacities of the turbulator heat exchanger were excellent, compared to the basic one. As the insertion ratio of the coiled turbulator and the number of row increased, the heat transfer performance increased. However, the capacity per unit area was more effective in 4 rows than 6 rows, and the cooling performance of the 6 row turbulator heat exchanger (100% turbulator insert ratio) was down to about 6% than that of 4 row one. As the water flow rate and the turbulator insertion ratio increased, the pressure drop of the water side increased. This trend was more pronounced in 6 rows. In the cooling condition, the pressure drop on the air side was slightly increased due to the generation of condensed water, but was insignificant under the heating condition. The power consumption of the pump was more affected by the water flow rate than the coiled turbulator. The equivalent hydraulic diameter of a tube by the turbulator was reduced and then the heat transfer performance was improved. Thus, the tube diameter was smaller, the heat flux was better.
ARTICLE | doi:10.20944/preprints202207.0299.v1
Subject: Engineering, Energy & Fuel Technology Keywords: battery thermal management; biodiesel fuel; hybrid vehicle; Li-ion battery; cooling technology
Online: 20 July 2022 (09:01:45 CEST)
This paper focuses on the comparative analysis of lithium-ion batteries (LIB) thermal management with aim to maintain working temperature in the range 15 ℃ – 35 ℃. This is to prevent thermal runaway and high temperature gradients. The proposed approach is to employ the biodiesel, situated inside the diesel/LIB powered hybrid electric vehicle, to supply as fuel and coolant. A 3S2P LIB module is simulated using Ansys-Fluent CFD software tool. The system without a coolant shows that LIB has exceeded the optimum maximum temperature, which leads to shortened life-cycle and poor performance. Four fatty acid methyl ester biodiesels are used as coolants, namely palm, karanja, jatropha, and mahua oils. When compared with conventional methods of cooling, using air and 3M Novec liquid, the palm biodiesel coolant proves to be the best option to maintain LIB temperature within the optimum working range. With the use of palm biodiesel, the system is estimated to lightweight the BTMS by 43%, compared to the case when 3M Novec is used to maintain the same temperature range.
ARTICLE | doi:10.20944/preprints201909.0155.v1
Subject: Earth Sciences, Environmental Sciences Keywords: cooling effect; urban park; thermal comfort; physiological equivalent temperature; perceived thermal comfort
Online: 16 September 2019 (01:17:53 CEST)
This empirical study investigates large urban park cooling effects on the thermal comfort of occupants in the vicinity of the main central park, located in Madrid, Spain. Data were gathered during hot summer days, using mobile observations and a questionnaire. The results showed that the cooling effect of this urban park of 140 ha area at a distance of 150 m is able to reduce temperature by an average of 0.63°C and 1.28°C for distances of 380 m and of 665 meters from the park. Moreover, the degree of the Physiological Equivalent Temperature (PET) index at a distance of 150 meters from the park is on average 2°C PET and 2.3°C PET less compared to distances of 380 m and 665 m, respectively. Considering distance from the park, the correlation between occupant Perceived Thermal Comfort (PTC) and PET is inverse. That is, augmenting the distance from park increases PET, while the extent of PTC reduces accordingly. The correlation between these two factors at the nearest and furthest distances from the park is meaningful (P-value <0/05). The results also showed that large-scale urban parks generally play a significant part in creating a cognitive state of high-perceived thermal comfort spaces for residents.
ARTICLE | doi:10.20944/preprints201906.0108.v1
Subject: Engineering, Mechanical Engineering Keywords: Blade cooling; Gas turbine efficiency; TIT-pressure ratio correlation for optimal efficiency
Online: 12 June 2019 (15:36:03 CEST)
Modern gas turbines firing temperatures (1500-2000K) are well beyond the maximum allowable blade material temperatures. Continuous safe operation is made possible by cooling the HP turbine first stages -nozzle vanes and rotor blades- with a portion of the compressor discharge air, a practice that induces a penalty on the cycle thermal efficiency. Therefore, a current issue is to investigate the real advantage, technical and economical, of raising maximum temperatures much further beyond current values. In this paper, process simulations of a gas turbine are performed to assess HP turbine first-stage cooling effects on cycle performance. A new simplified and properly streamlined model is proposed for the non-adiabatic expansion of the hot gas mixed with the cooling air within the blade passage, which allows for a comparison of several cycle configurations at different TIT (turbine inlet temperature) and max (total turbine expansion ratio) with a realistically acceptable degree of approximation.. The calculations suggest that, at a given max, the TIT can be increased in order to reach higher cycle efficiency up to a limit imposed by the required amount and temperature of the cooling air. Beyond this limit, no significant gains in thermal efficiency are obtained by adopting higher max and/or increasing the TIT, so that it is convenient in terms of cycle performance to design at lower rather than higher max. The small penalty on cycle efficiency is compensated by lower plant cost. The results of our model agree with those of some previous much more complex and computationally expensive studies, so that the novelty of this paper lies in the original method adopted on which the proposed model is based, and in the fast, accurate and low resource intensity of the corresponding numerical procedure: all advantages that can be crucial for industry needs. The presented analysis is purely thermodynamic, with no investigation on the effects of the different configurations on plant costs, so that future work addressing a thermo-economic analysis of the air-cooled gas turbine power plant is the next logical step.
Subject: Engineering, Civil Engineering Keywords: transient heat conduction; cooling; theoretical models; analytical solutions; ice rinks; energy efficiency
Online: 7 May 2019 (10:23:36 CEST)
The energy efficiency of ice hockey arenas is a central concern for the administrations, as these buildings are well known to consume a large amount of energy. Since they are composite, complex systems, solutions to such a problem can be approached from many different areas, from managerial to technological to more strictly physical. In this paper we consider heat transfer processes in an ice hockey hall, during operating conditions, with a bottom-up approach based upon on-site measurements. Detailed heat flux, relative humidity and temperature data for the ice pad and the indoor air are used for a heat balance calculation in the steady-state regime, which quantifies the impact of each single heat source. We then solve the heat conduction equation for the ice pad in transient regime, and obtain a generic analytical formula for the temperature profile that can be used in practical applications. We then apply this formula to the resurfacing process for validation, and find good agreement with an analogous numerical solution. Since it is given with implicit initial condition and boundary conditions, it can be used not only in ice hockey halls, but in a large variety of engineering applications.
ARTICLE | doi:10.20944/preprints201807.0212.v1
Subject: Physical Sciences, Atomic & Molecular Physics Keywords: time variation of constants; proton-electron mass ratio; molecular ion; laser cooling
Online: 12 July 2018 (08:04:03 CEST)
Molecular overtone transitions provide optical frequency transitions sensitive to variation in the proton-to-electron mass ratio (μ = mp/me). However, robust molecular state preparation presents a challenge critical for achieving high precision. Here, we characterize infrared and optical-frequency broadband laser cooling schemes for TeH+, a species with multiple electronic transitions amenable to sustained laser control. Using rate equations to simulate laser cooling population dynamics, we estimate the fractional sensitivity to μ attainable using TeH+. We find that laser cooling of TeH+ can lead to significant improvements on current μ variation limits.
ARTICLE | doi:10.20944/preprints201712.0002.v1
Subject: Engineering, Mechanical Engineering Keywords: Cruciform joint; fatigue; semi-elliptical crack; cooling; weld magnification factor; Fracture Mechanics
Online: 1 December 2017 (06:52:06 CET)
The objective of this research is to develop an experimental-theoretical analysis about the influence of the cooling medium and the geometry of the welding bead profile in fatigue life and associated parameters with structural integrity of welded joints. A welded joint with cruciform geometry is considered using SMAW, plates in structural steel ASTM A36 HR of 8 mm of thickness and E6013 electrode input. A three-dimensional computational model of the cruciform joint was created using the finite element method. For this model, the surface undulation of the cord and differentiation in the mechanical properties of the fusion zone were considered, the heat-affected zone (HAZ) and base material, respectively. In addition, an initial residual stress field which was established experimentally was considered. The results were a set of analytical expressions for the weld magnification factor Mk. It was found that values for the latter decrease markedly in function of the intensity of the cooling medium used in the post welding cooling phase, mainly due to the effect of the residual compressive stresses. The obtained models of behavior of the weld magnification factor are compared with the results from other researchers with some small differences, mainly due to the inclusion of the cooling effect of the post weld and the variation of the leg of the weld bead. The obtained analytical equations in the present research for Mk can be used in management models of life and structural integrity for this type of welded joint.
ARTICLE | doi:10.20944/preprints202110.0437.v1
Subject: Engineering, Energy & Fuel Technology Keywords: heating cycles; thermodynamic cycles; thermodynamics; temperature difference utilization; heating; cooling; cogeneration; thermal science
Online: 28 October 2021 (13:00:46 CEST)
Thermodynamic cycles are not only the core concepts of thermal science, but also key approaches to energy conversion and utilization. So far, power cycles and refrigeration cycles have been the only two general classes of thermodynamic cycles. While diverse types of systems have been developed to perform thermodynamic cycles, no new general classes of thermodynamic cycles have been proposed. Based on the basic principles of thermodynamics, here we propose and analyze a new general class of thermodynamic cycles named class 1 heating cycles (HC-1s). Two basic forms of HC-1s are obtained by connecting six essential thermodynamic processes in the proper order and forming a thermodynamic cycle. HC-1s present the simplest and most general approach to utilizing the temperature difference between a high-temperature heat source and a medium-temperature heat sink to achieve efficient medium-temperature heating and/or low-temperature cooling. HC-1s fill the gaps that have existed since the origin of thermal science, and they will play significant roles in energy conservation and emission reduction.
ARTICLE | doi:10.20944/preprints202107.0033.v1
Subject: Chemistry, Analytical Chemistry Keywords: Raman intensity; anharmonicity; conformational isomerism; chain folding; jet cooling; rotational band contour; esters
Online: 1 July 2021 (14:22:39 CEST)
The conformational preferences of the ester group have the potential to facilitate the large amplitude folding of long alkyl chains in the gas phase. They are monitored by Raman spectroscopy in supersonic jet expansions for the model system methyl butanoate, after establishing a quantitative relationship to quantum-chemical predictions for methyl methanoate. This requires a careful analysis of experimental details, and a simulation of the rovibrational contours for near-symmetric top molecules. The technique is shown to be complementary to microwave spectroscopy in quantifying coexisting conformations. It confirms that a C-O-C(=O)-C-C chain segment can be collapsed into a single all-trans conformation by collisional cooling, whereas alkyl chain isomerism beyond this five-membered chain largely survives the jet expansion. This sets the stage for the investigation of linear alkyl alkanoates in terms of dispersion-induced stretched-chain to hairpin transitions by Raman spectroscopy.
ARTICLE | doi:10.20944/preprints202102.0477.v1
Subject: Physical Sciences, Acoustics Keywords: Pulsating self-organization; Metric monism; Geodesic cooling/warming; Continuous mass; Bi-vertex energy
Online: 22 February 2021 (14:29:41 CET)
Due to the fact that negative energies have no existence in physical reality, the advanced mechanics of purely positive energies should describe gravitational interactions and collisions in monistic terms of extended kinetic energies and their local stresses. Such non-Newtonian mechanics of continuous inertial densities reinforces the Cartesian concept of matter-extension in the metric formalism of Einstein-Grossmann with a supplemental (dark, aether) fraction of bi-vertex mass-energy distributions. Local accelerations or decelerations of mono-vertex material densities in a multi-vertex distribution of complete kinetic energy arise under its constant integral due to nonlocal organization of continuous densities. Such integral conservation of the distributed mass-energy occurs instantaneously throughout the whole continuum of correlated densities and metric stresses despite the time-varying contributions of complementary mono-vertex and bi-vertex fractions. Under the nonlocal organization of purely kinetic (positive) mass-energy, geodesic self-heating and self-cooling of the pulsating space-matter conserve the integral energy in the two-fraction virial theorem for the averaged motion of visible mono-vertexes in the presence of invisible bi-vertex (interference, dark) mass-energy. Metric stresses of such material space are subordinate to nonlocal self-government of continuously distributed kinetic energy, including the relativistic rest-energy of General Relativity. These mutually consistent or correlated stresses in inertial space-time-energy create timelessly coordinated self-accelerations, observed for dense material volumes as distant gravitational pulls. In order to falsify/verify the nonlocal self-organization of adaptive kinetic energy, the monistic mechanics of self-consistent inertial densities and metric stresses can suggest moderate field changes in the temporal redshift, cycles of geodetic falls and takeoffs in pulsating kinetic organizations, and the calculated acceleration of the expanding Metagalaxy in its current phase of geodesic self-cooling.
ARTICLE | doi:10.20944/preprints201805.0041.v1
Subject: Engineering, General Engineering Keywords: ecological farming system; dynamic numerical simulation; evaporative cooling system; treated wastewater; temperature; humidity
Online: 2 May 2018 (12:56:15 CEST)
The United Arab Emirates (UAE) is significantly dependent on desalinated water and groundwater resource, which is expensive and highly energy intensive. Despite the scarce water resource, only 54% of the recycled water was reused in 2015. In this study, an “Oasis” complex comprised of Sustainable Farming Compartments (SFCs) was proposed for reusing treated wastewater to decrease the ambient temperature of the SFC via an evaporative cooling system. A prototype SFC with half the original scale (width = 1.8 m, depth = 1.5 m, front height = 1.2 m back height = 0.9 m) was designed, built, and tested in an environmentally controlled laboratory and field site to evaluate the feasibility and effectiveness of the SFC under the climatic conditions in Abu Dhabi. Based on the experimental results, the temperature drops obtained from the SFC in the laboratory and field site were 5 ̊C at initial relative humidity of 60% and 7- 15 ̊C at initial relative humidity of 50%, respectively. An energy simulation using dynamic numerical simulations was performed in comparison to the results of the experiment. The energy-based dynamic simulation shows good agreement with the experimental results. The total power consumption of the SFC system was approximately three and a half times lower than that of an electrical air conditioner.
ARTICLE | doi:10.20944/preprints201712.0063.v1
Subject: Engineering, Energy & Fuel Technology Keywords: Capacity; Cooling and heating; CO2; Cycle performance; , EEV; Heat pump; Internal heat exchanger
Online: 11 December 2017 (12:30:52 CET)
Developing high performance HVAC system using natural refrigerants including carbon dioxide (CO2) has been important in respect of environmental preservation and associated technologies. Thus studies to optimize the HVAC (heating ventilation air conditioner) system using natural refrigerants through clarifying the cycle performance characteristics are necessary. The CO2 heat pump system using air and water sources was consisted to examine its performance characteristics, and by varying conditions of several factors that affect or characterize the system performance like the amount of refrigerant charge, EEV (electronic expansion valve) opening, and internal heat exchanger under cooling mode. The performance characteristics of CO2 heat pump system were tested by using an air enthalpy calorimeter. In the case of the CO2 heat pump system without internal heat exchanger, the opening of #3 EEV and #4 EEV was 60% and refrigerant charge amount was 5,600g. However, in the case of that with internal heat exchanger, the best performance was obtained when the opening of #2 EEV is 20%. From the present studies, it was observed that the performance variation and operational characteristics of the CO2 heat pump system were affected by design factors like refrigerant charge amount, EEV opening, and internal heat exchanger and thereby, the configuration on an optimal operation conditions of the system was enabled.
ARTICLE | doi:10.20944/preprints201712.0076.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: additive manufacturing; laser metal deposition; hot stamping; die and mold; conformal cooling; design optimization.
Online: 12 December 2017 (15:24:24 CET)
Hot stamping dies include cooling channels to treat the formed sheet. The optimum cooling channels of dies & molds should adapt to the shape and surface of the dies, so that a homogeneous temperature distribution and cooling are guaranteed. Nevertheless, cooling ducts are conventionally manufactured by deep drilling, attaining straight channels unable to follow the geometry of the tool. Laser Metal Deposition (LMD) is an additive manufacturing technique capable to fabricate nearly free-form integrated cooling channels and therefore shape the so-called conformal cooling. The present work investigates the design and manufacturing of conformal cooling ducts, which are additively built up on hot work steel and then milled in order to attain the final part. Their mechanical performance and heat transfer capability has been evaluated, both experimentally and by means of thermal simulation. Finally, conformal cooling conduits are evaluated and compared to traditional straight channels. The results show that LMD is a proper technology for the generation of cooling ducts, opening the possibility to produce new geometries on dies & molds and, therefore, new products.
ARTICLE | doi:10.20944/preprints202206.0249.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: rolled flat products; accelerated cooling; temperature; mathematical model; oxide scale; Ther-mo-Mechanical Controlled Process
Online: 17 June 2022 (05:14:37 CEST)
To verify the authors’ mathematical model for water jet cooling of steel sheet, the previously performed experimental studies of temperature of the test plate in the roller quenching machine (RQM) were used. The calculated data of steel temperature evolution along the RQM length were compared with the readings of thermocouples inserted in the center of the test plate and at its surfaces. The core of the model is the dependence of the temperatures of film, transition and nucleate boiling regimes on the thickness of the oxide scale layer on the cooled surface. It was found that the model correctly takes into account the oxide scale on the sheet surface, flow rates and combinations of the RQM banks used, water temperature and other factors. For all experiments the calculated metal temperature corresponds well to the measured one. In the experiments with interrupted cooling, the calculated temperature plots repeat the characteristic changes in the experimental curves. The main uncertainty in the modeling of cooling in a wide temperature range can be contributed by the random nature of changes in the oxide scale thickness during water cooling. In this regard, the estimated thickness of the oxide scale layer should be considered as the main parameter for adapting the sheet temperature control process. The obtained data confirm the possibility of effective application of the model in the ACS of industrial TMCP (Thermo-Mechanical Controlled Process) systems.
Subject: Engineering, Mechanical Engineering Keywords: large-scale additive manufacturing; interlayer cooling time; tool path optimization; part deformation; Ti-6Al-4V
Online: 10 November 2019 (09:04:24 CET)
Laser metal deposition with wire (LMD-w) is a developing additive manufacturing (AM) technology that has a high deposition material rate and efficiency, and is suitable for fabrication of large aerospace components. However, control of material properties, geometry, and residual stresses is needed before LMD-w technology can be widely adopted for the construction of critical structural components. In this study, we investigated the effect of interlayer cooling time, clamp constraints, and tool path strategy on part distortion and residual stresses in large-scale laser additive manufactured Ti-6Al-4V components using finite element method (FEM). The simulations were validated with the temperature and the distortion measurements obtained from a real LMD-w process. We found that a shorter interlayer cooling time, full clamping constraints on the build plates, and a bidirectional tool path with 180⁰ rotation minimized part distortion and residual stresses and resulted in symmetric stress distribution.
ARTICLE | doi:10.20944/preprints201808.0276.v1
Subject: Earth Sciences, Oceanography Keywords: typhoon; sea surface temperature; sea surface height anomaly; sea surface cooling; warm eddy; cold eddy
Online: 15 August 2018 (15:41:28 CEST)
Studying the interaction between the upper ocean and the typhoons is crucial to improve our understanding of heat and momentum exchange between the ocean and the atmosphere. In recent years, the upper ocean responses to typhoons have received considerable attention. The sea surface cooling (SSC) process has been repeatedly discussed. In the present work, case studies were examined on five strong and super typhoons that occurred in 2016—LionRock, 1610; Meranti, 1614; Malakas, 1616; Megi, 1617; and Chaba 1618—to search for more evidence and new features of typhoon’s impact on the sea surface environment. The typhoon monitoring data from the Central Meteorological Observatory, the sea surface temperature (SST) data from satellite microwave and infrared remote sensing, and the sea surface height anomaly (SSHA) data from satellite altimeters were used to analyze in detail: the SSC features caused by typhoons, the relationship between the SSC and the typhoon travelling speed, and the variations in cold and warm eddies during typhoon passage. Results showed that: (1) SSC generally occurred during typhoon passage and the degree of SSC was always determined by the strength and the travelling speed of the typhoon, as well as the initial SST. (2) One day before or on the day of typhoon passage, the SSHA slightly increased due to low surface pressure. After the typhoon passed, the SSHA obviously decreased along with the SSC. The pre-existing positive SSHAs, which always represent warm eddies, decreased or disappeared during typhoon passage, whereas negative SSHAs or cold eddies were enhanced. (3) New cold eddies were generated, especially at the turning points of the typhoon path. The presence of warm eddies is suggested to have a strengthening effect on the typhoons.
ARTICLE | doi:10.20944/preprints202008.0284.v1
Subject: Engineering, Other Keywords: Park cooling effect; Urban Heat Island; Thermal comfort; Perceived Thermal Comfort; Physiological Equivalent Temperature; Cognitive Maps
Online: 12 August 2020 (11:32:18 CEST)
The combined effects of global warming and increasing urban heat islands (UHIs) on air temperature and heat stress in cities are notable physical and mental health implications for citizens. With research having shown the effective role of urban green spaces in decreasing urban heat, this study investigated the cooling effect of a large urban park on thermal comfort outside the park area, from psychological and physiological perspectives. The studied park is located in the center of Madrid and adjacent to UHI. The study was performed by conducting field measurements and a survey with questionnaires. The measurements made on six summer days (with two-week intervals) showed that the park’s cooling effect could decrease the air temperature by 2.4-2.8°C right up to the edge of the heat island (600m), and decrease the physiological equivalent temperature (PET) by about 3.9°C. By decreasing air temperature and PET, this park was also shown to increase the perceived thermal comfort (PTC) of the citizens from the psychological perspective in the defined area of effect. This perceived thermal comfort was found to have a significant inverse relationship with PET (P-value <0.05). The examination of cognitive maps drawn by citizens showed that out of the 145 respondents, 68.3% marked the park as the area that they perceive as having the greatest thermal comfort, and prefer as the place to spend time enjoying thermal comfort, irrespective of its distance from their location.
ARTICLE | doi:10.20944/preprints201812.0034.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: personal cooling system; heat and mass transfer; environmental temperature; relative humidity; phase change materials; thermal management
Online: 3 December 2018 (16:11:11 CET)
The hybrid personal cooling system (HPCS) consisted of ventilation fans and phase change materials (PCMs) covered with insulation pads is a promising wearable cooling system to mitigate heat strain and heat-related illnesses of occupational workers with heavy labor in hot environments. Effects of clothing characteristics (e.g., thermal resistance of insulation pads, latent heat and melting temperature of PCMs) on the thermal performance of the HPCS have been investigated in detail in our previous study. Apart from the aforementioned factors, environmental conditions, i.e., environmental temperature and relative humidity, also significantly affect the thermal performance of the HPCS. In this paper, a numerical parametric study was performed to investigate the effects of the environmental temperature and relative humidity (RH) on the thermal management of the HPCS. Five levels of air temperature under environmental RH=50% were chosen (i.e., 32, 34, 36, 38 and 40 ºC) to study the impact of environmental temperature on the HPCS’s cooling performance. In addition, four levels of environmental RH at ambient temperatures of 36 and 40 ºC were selected (i.e., 30, 50, 70 and 90%) to examine the effect of RH on cooling performance of the HPCS. Results show that high environmental temperatures could accelerate the PCM melting process and thereby weaken the cooling performance of HPCS. In the moderately hot environment (36 °C), the HPCS presented good cooling performance with the maximum core temperature at around 37.5 °C during excise when the ambient RH≤70%, whereas good cooling performance could be only seen under RH≤50% in the extremely hot environment (40 °C). Thus, it may be concluded that the maximum environmental RH for the HPCS exhibiting good cooling performance decreases with the increase in the environmental temperature.
Subject: Engineering, Automotive Engineering Keywords: Energy Efficiency; Emissions; Tribology; Lubrication; Battery Electric Vehicles; Hybrid Electric Vehicles; Life Cycle Analysis; Thermal Cooling Fluids
Online: 17 June 2021 (10:46:41 CEST)
The motivations for the move to electrified vehicles are discussed with reference to their improved energy efficiency, their potential for lower CO2 emissions (if the electricity system is decarbonized), their lower (or zero) NOx/particulate matter (PM) tailpipe emissions, and the lower overall costs for owners. Some of the assumptions made in life-cycle CO2 emissions calculations are discussed and the effect of these assumptions on the CO2 benefits of electric vehicles are made clear. A number of new tribological challenges have emerged, particularly for hybrid vehicles that have both a conventional internal combustion engine and a battery, such as the need to protect against the much greater number of stop-starts that the engine will have during its lifetime. In addition, new lubricants are required for electric vehicle transmissions systems. Although full battery electric vehicles (BEVs) will not require engine oils (as there is no engine) they will require a system to cool the batteries – alternative cooling systems are discussed, and where these are fluid based, the specific fluid requirements are outlined.
ARTICLE | doi:10.20944/preprints202104.0697.v1
Subject: Earth Sciences, Atmospheric Science Keywords: heating degree-day (HDD), cooling degree-day (CDD), climate change, projections, energy demand of residential buildings, Portugal
Online: 26 April 2021 (21:18:06 CEST)
Climate change is expected to influence cooling and heating energy demand of residential buildings and affect overall thermal comfort. Towards this end, the heating degree-day (HDD), the cooling degree-day (CDD) and the HDD+CDD were computed from an ensemble of 7 high-resolution bias-corrected simulations attained from EURO-CORDEX under RCP4.5 and RCP8.5. These three indicators were analyzed for 1971-2000 (from E-OBS) and 2011-2040 and 2041-2070, under both RCPs. Results show that the overall spatial distribution of HDD trends for the 3 time-periods points out an increase of energy demand to heat internal environments in Portugal's northern-eastern regions, most significant under RCP8.5. It is projected an increase of CDD values for both scenarios; however, statistically significant linear trends were only found for 2041-2070 under RCP4.5. The need for cooling is almost negligible for the remaining periods, though linear trend values are still considerably higher for 2041-2070 under RCP8.5. By the end of 2070, higher amplitudes for all indicators are depicted for southern Algarve and Alentejo regions, mainly under RCP8.5. For 2041-2070 the Centre and Alentejo (North and Centre) regions present major positive differences for HDD(CDD) under RCP4.5(RCP8.5), within the 5 NUTS II regions predicting higher heating(cooling) requirements for some locations.
ARTICLE | doi:10.20944/preprints202009.0221.v1
Subject: Engineering, Energy & Fuel Technology Keywords: air shaft; air well; solar chimney; field measurement; natural ventilation; tropical climate; terrace house; passive cooling design
Online: 10 September 2020 (04:46:23 CEST)
The provision requirement of 10% openings of the total floor area stated in the Uniform Building by Law 1984 Malaysia has been practiced by designers for building plan submission approval. However, the effectiveness of thermal performance in landed residential buildings, despite the imposition by the by-law, has never been empirically measured and proven. Although terraced houses in Malaysia have dominated 40.9% of the total property transaction in 2019, such mass production with typical designs hardly provides its occupants with thermal comfort due to the static outdoor air condition and lack of external windows, where the conventional ventilation technique does not work well, even for houses with an air well system. Consequently, the occupants need to rely on mechanical cooling, which is a high energy-consuming component contributing to outdoor heat dissipation and therefore urban heat island effect. Thus, encouraging more effective natural ventilation to eliminate excessive heat from the indoor environment is critical. Since most of the research focuses on simulation modelling lacking sufficient empirical validation, this paper drawing on field measurement investigates natural ventilation performance in terraced housing with an air well system. More importantly, the key concern as to what extent the current air well system serving as a ventilator is effective to provide better thermal performance in the single storey terraced house is to be addressed. By adopting an existing single storey air welled terrace house, the existing indoor environmental conditions and thermal performance were monitored and measured using scientific equipment, namely HOBO U12 air temperature and air humidity, the HOBO U12 anemometer and the Delta Ohm HD32.3 Wet Bulb Globe Temperature meter for a six-month duration. The findings show that the air temperature of the air well ranged from 27.48°C to 30.92°C, while the mean relative humidity were from 72.67% to 79.25%. The mean air temperature for a test room (single sided ventilation room) ranged from 28.04°C to 30.92°C with a relative humidity of 70.16% to 76%. These empirical findings are of importance, offering novel policy insights and suggestions to potentially revising the existing building code standard and by laws; since the minimum provision of 10% openings has been revealed to be less effective to provide a desired thermal performance and comfort, mandatory compliance with, and the necessity for, the bylaw requirement should be revisited and further studied.
ARTICLE | doi:10.20944/preprints201903.0026.v1
Subject: Materials Science, General Materials Science Keywords: Nickel-based single crystal alloy; Heat treatment; Heating and cooling rate; Precipitation and dissolution of γ´ phase
Online: 4 March 2019 (09:45:06 CET)
The effects of heating rate before solution treatment and cooling rate after solution treatment on the morphological distribution and evolution of precipitation phase of nickel-based single crystal superalloy were studied. The dissolution, precipitation and growth of precipitation phase and matrix phase during heat treatment were analyzed by means of high power scanning electron microscopy. The results show that the morphology of precipitated phase has nothing to do with the distribution of precipitated phase and the heating rate in the heating process, but the cooling rate in the cooling process affects the shape, size and distribution of precipitated phase. The faster the cooling rate, the smaller the precipitated phase is, the more irregular the shape is, the smaller the equivalent edge length is, and the smaller the channel width of matrix phase is.
ARTICLE | doi:10.20944/preprints202110.0253.v1
Subject: Engineering, General Engineering Keywords: thermal management; electronics cooling; thermal energy storage; TES; duty cycle; phase change materials; PCM; cold finger technique, CFT.
Online: 18 October 2021 (15:27:08 CEST)
Miniaturization of electronics devices is often limited by the concomitant high heat fluxes (cooling load) and maldistribution of temperature profiles (hot spots). Thermal energy storage (TES) platforms providing supplemental cooling can be a cost-effective solution, that often leverages phase change materials (PCM). Although salt hydrates provide higher storage capacities and power ratings (as compared to that of the organic PCMs), they suffer from reliability issues (e.g., supercooling). ‘Cold Finger Technique (CFT)’ can obviate supercooling by maintaining a small mass fraction of the PCM in solid state for enabling spontaneous nucleation. Optimization of CFT necessitates real-time forecasting of the transient values of the melt-fraction. In this study artificial neural network (ANN) is explored for real-time prediction of the time remaining to reach a target value of melt-fraction based on the prior history of the spatial distribution of the surface temperature transients. Two different approaches were explored for training the ANN model, using: (1) transient PCM-temperature data; or (2) transient surface-temperature data. When deployed in a heat sink that leverages PCM based passive thermal management systems for cooling of electronic chips and packages, this maverick approach (using the second method) affords cheaper costs, better sustainability, higher reliability and resilience.
ARTICLE | doi:10.20944/preprints202007.0233.v1
Subject: Engineering, Energy & Fuel Technology Keywords: cooling; heating and power (CCHP) microgrid; kernel learning machine (KELM); particle swarm optimization (PSO); shuffled frog leaping algorithm (SFLA)
Online: 11 July 2020 (09:00:22 CEST)
An optimal scheduling strategy for cooling, heating and power (CCHP) joint-power-supply system is proposed to improve energy utilization and minimize costs in this paper. Firstly, the mathematical model of CCHP system is established. Particle swarm optimization (PSO) is used to optimize the regularization coefficient C and the kernel parameter λ which can affect the prediction accuracy of KELM(PSO-KELM). Then PV generation and load prediction model are established by PSO-KELM. In order to jump out of local optimal solution, Cauchy variation is introduced in SFLA local update, and adaptive mutation operation is carried out on SFLA individuals. The predictions of PV generation and load power by PSO-KELM are imported into the objective function, and the microgrid dispatching model is solved by the improved SFLA algorithm. Compared with the traditional GA-KELM and KELM, PSO-KELM has faster convergence and prediction accuracy. Compared with the power supply division, the operation cost of the power grid is reduced by the proposed optimization dispatching strategy of CCHP micro-grid.
ARTICLE | doi:10.20944/preprints201904.0191.v1
Subject: Keywords: ducted photovoltaic; buoyancy cooling; vertical shafts; energy generation; efficiency of photovoltaic; temperature of photovoltaic; CFD simulations of buoyancy; BIPV
Online: 16 April 2019 (13:10:55 CEST)
A ducted photovoltaic façade (DPV) unit Studied using experimental Prototype and simulated in a full scale Computational Fluid Dynamics CFD Model. The Study comes in two parts; This is Part I with the title detailed above and Part II titled ‘A Ducted Photovoltaic Façade Unit with Buoyancy Cooling: Part II CFD Simulation’.. The process adopted in the experimental study is replicated in the simulation Part. The aim was to optimize the duct width behind the solar cells to allow for maximum buoyancy-driven cooling for the cells during operation. Duct widths from 5 to 50 cm were tested in a Proto-type. A duct width of 45 cm had the maximum calculated heat removed from the duct; however, the lowest cell-operating temperature was reported for duct width of 50 cm. It was found that the DT between ducts' inlets and outlets range from 5.47 °C to 12.32 °C for duct widths of 5–50 cm, respectively. The ducted system enhanced module efficiency by 12.69% by reducing PV temperature by 27 °C from 100°C to 73 °C. The maximum calculated heat recovered from the ducted PV system is 422 W. This is 47.98% from the incident radiation in the test. Total summation of heat recovered and power enhanced by the ducted system is 61.67%.
ARTICLE | doi:10.20944/preprints201901.0230.v1
Subject: Materials Science, Metallurgy Keywords: thin slab casting direct rolling, austenite grain coarsening, grain growth control, liquid core reduction, secondary cooling, two phase pinning
Online: 23 January 2019 (08:44:19 CET)
Thin Slab Casting and Directing Rolling (TSCDR) has become a major process for flat- rolled production. However, the elimination of slab reheating and limited number of thermomechanical deformation passes leave fewer opportunities for austenite grain refinement resulting in some large grains persist in the final microstructure. In order to achieve excellent Ductile to Brittle Transaction (DBTT) and Drop Weight Tear Test (DWTT) properties in thicker gauge high strength low alloy products, it is necessary to control austenite grain coarsening prior to the onset of thermomechanical processing. This contribution proposes a suite of methods to refine the austenite grain from both theoretical and practical perspective including: increasing cooling rate during casting, liquid core reduction, increasing austenite nucleation sites during the delta ferrite to austenite phase transformation, controlling holding furnace temperature and time to avoid austenite coarsening, and producing new alloy with two phase pinning to arrest grain coarsening. These methodologies can not only refine austenite grain size in the slab center, but also improve the slab homogeneity.
ARTICLE | doi:10.20944/preprints201709.0137.v1
Subject: Physical Sciences, Fluids & Plasmas Keywords: electrothermal flow; rotating electric field; out-of-phase smeared structural polarization; electrode cooling; external natural convection; co-field flow rotation
Online: 27 September 2017 (12:11:34 CEST)
In this work, we focus on investigating electrothermal flow in a rotating electric field (ROT-ETF), with primary attention paid to the horizontal traveling-wave electrothermal (TWET) vortex induced at the center of the electric field. The frequency-dependent flow profiles in the microdevice are analyzed using different heat transfer models. Accordingly, we address in particular the importance of electrode cooling in ROT-ETF as metal electrodes of high thermal conductivity while substrate material of low heat dissipation capability are employed to develop such microfluidic chips. Under this circumstance, cooling of electrode array due to external natural convection on millimeter-scale electrode pads for external wire connection occurs and makes the internal temperature maxima shift from the electrode plane to a bit of distance right above the cross-shaped interelectrode gaps, giving rise to reversal of flow rotation from a typical repulsion-type to attraction-type induction vortex, which is in good accordance with our experimental observations of co-field TWET streaming at frequencies on the order of reciprocal charge relaxation time of the bulk fluid. These results point out a way to make a correct interpretation of out-of-phase electrothermal streaming behavior, which holds great potential for handing high-conductivity analytes in modern microfluidic systems.
ARTICLE | doi:10.20944/preprints201803.0140.v1
Subject: Materials Science, Surfaces, Coatings & Films Keywords: laser surface glazing; Ti6Al4V alloy; FEA; thermal model; biomedical application; heating and cooling rates; depth of modified zone; hardness; wear resistance
Online: 19 March 2018 (06:42:48 CET)
Ti64 alloy plays a significant role in the biomedical applications such as bioimplants for its excellent biocompatibility. Its usage can be further extended by improving the surface hardness and wear resistance. In this respect, laser surface glazing (LSG), an advanced surface modification technique, is very useful which can produce thin hardened surface layer and strong metallurgical bonding. Investigation of temporal and spatial temperature distributions of laser glazed surface of materials are essential because temperature plays significant role in achieving required surface properties. Therefore, in this study, a 3D Finite element analysis has been developed to perform transient thermal analysis of LSG for Ti64 alloy. The model investigated temperature distribution, depth of modified zone and heating and cooling. The results show that the peak temperature is attained 2095 K for 300 W laser power, 0.2 mm beam width and 0.15 ms residence time. Since this temperature is above the melting point (1933 K) of Ti64 alloy, the melt depth is calculated 22.5 μm. Furthermore, from the simulation results, the average heating and cooling rates are estimated 1.19×107 Ks-1 and 2.71×106 Ks-1 respectively which indicate the presence of hard phases in the modified zone.
ARTICLE | doi:10.20944/preprints202101.0417.v1
Subject: Engineering, Industrial & Manufacturing Engineering Keywords: heating and cooling of injection mold; melt flow control; carbon fiber reinforced semi-aromatic polyamide; fiber orientation; bending strength; weld line; crystallization
Online: 21 January 2021 (12:29:40 CET)
Fiber reinforced thermoplastics (FRTP), which is reinforced with glass or carbon fibers, are used to improve the mechanical strength of injection-molded products. However, FRTP has problems such as the formation of weld lines, the deterioration of the appearance due to the exposure of fibers on the molded product surface, and the deterioration of the strength of molded products due to the fiber orientation in the molded products. We have designed and fabricated an injection mold capable of melt flow control and induction heating and cooling that has the functions of both heating and cooling the injection mold as well as the function of controlling the melt flow direction using a movable core pin. In this study, the above-mentioned mold was used for the molding of carbon fiber reinforced semi-aromatic polyamide. As a result, we found that increasing the heating temperature of the mold and increasing melt flow control volume contribute to the prevention of the generation of a weld line and the exposure of fibers on the molded product surface, as well as to the formation of a flat surface and increased bending strength. The relationships of these results with the carbon fiber orientation in the molded products and the crystallization of semi-aromatic polyamide were also examined in this study.
ARTICLE | doi:10.20944/preprints202105.0288.v1
Subject: Engineering, Automotive Engineering Keywords: effect of temperature; exposure time; steel microstructure; residual mechanical properties; high-strength steel bolts; heat treatment of steel; phase transformation; fire; cooling method
Online: 13 May 2021 (12:53:32 CEST)
The article presents results of research consisting in an attempt to assess the influence of temperature, heating time and cooling method on microstructure and residual strength properties of steel previously tempered during the production process. Simulated environmental conditions to which high-strength bolts, commonly used in steel construction, were subjected, were intended to reflect conditions of a natural fire that may occur in public facilities where the obligation to ensure safety of users and rescue teams is of key importance, also required by law. Furthermore, the tests carried out also comprised a simulated effect of a rescue and firefighting operation using shock, rapid cooling of some of the heated bolts. Samples cut out from the tested bolts, after they were properly prepared, were subjected to microstructural tests using light microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), phase analysis with the use of an X-ray diffractometer (XRD) and quantitative analysis of the microstructure involving, inter alia, measuring the surface area of grains, their equivalent diameter and mean diameter. As a result of the tests, considerable microstructure changes were identified occurring in the bolt material as a result of exposing it to fire conditions, leading to a change in key, from the point of view of structural safety, mechanical properties. The results of the microstructure tests were compared with the results of previous strength tests, including hardness of the material after the heat treatment and the residual tensile strength of the material Rm. A conducted comparative analysis showed a significant effect of all such factors as the temperature level of the simulated fire, its duration and the fire-fighting method on the mechanical properties of bolts. Results obtained were provided with required comments and the concept of using the microstructure for the post-fire assessment of steel structures was referred to.
ARTICLE | doi:10.20944/preprints202205.0183.v1
Subject: Engineering, Energy & Fuel Technology Keywords: Energy geostructure; ground source heat pump (GSHP); sustainable urban drainage system (SUDS); sector integration; 5th generation district heating and cooling; permeable asphalt; rainwater retardation; full-scale demonstration; numerical modelling; analytical modelling
Online: 13 May 2022 (08:06:39 CEST)
This paper proposes and demonstrates, in full scale, a novel type of energy geostructure (“the Climate Road”) that combines a ground source heat pump (GSHP) with a sustainable urban drainage system (SUDS) by utilizing the gravel roadbed simultaneously as energy source and rainwater retarding basin. The Climate Road measures 50m x 8m x 1m (length, width, depth) and has 800 m of geothermal piping embedded in the roadbed, serving as the heat collector for a GSHP that supplies a nearby kindergarten with domestic hot water and space heating. Model analysis of operational data from 2018-2021 indicates sustainable annual heat production levels around 0.6 MWh per meter road, with a COP of 2.9-3.1. The continued infiltration of rainwater to the roadbed increases the amount of extractable heat by an estimated 17% compared to the case of zero infiltration. Using the developed model for scenario analysis we find that draining rainwater from three single family houses and storing 30% of the annual heating consumption in the roadbed, increases the predicted extractable energy by 56% compared to zero infiltration with no seasonal energy storage. The Climate Road is capable of supplying three single family houses with heating, cooling and rainwater management year-round.