Effect of TiO₂ and SiO₂ Nanoparticles on Traction, Wear, and High Shear Viscosity of PAG Lubricants Under Elastohydrodynamic (EHL) Conditions for Refrigeration Systems

This study tests TiO₂ and SiO₂ nanolubricants in PAG oil using a Mini Traction Machine and an Ultra Shear Viscometer. The loads were 20 N and 40 N. The entrainment speeds ranged from 2.5 to 500 mm per second. The slide to roll ratio ranged from 25 to 150 percent. The nanoparticle concentrations were 0.01, 0.03, and 0.05 percent. The ball size was 19.05 mm, and the disk was 46 mm. All tests ran at 40°C. Only 0.05% of samples lowered traction compared with PAG at fixed SRR. TiO₂ at 0.05% showed the largest drop, up to 4.89 percent at 20 N and 2.99 percent at 40 N. However, lower concentrations increased traction. All nanolubricants reduced wear. TiO₂ at 0.03 percent gave the lowest wear, with a reduction of about 35 µm at 40 N. Nanolubricant samples stayed between 40.2 and 40.5°C while PAG reached about 41.0°C. TiO₂ produced slightly lower temperatures than SiO₂. Ultra shear tests from 40 to 100°C showed shear thinning. TiO₂ at 0.05% kept the highest viscosity at 40 and 60°C, up to 12 percent above PAG. SiO₂ showed smaller changes. TiO₂ delivered better friction, wear, temperature, and viscosity performance. Overall, both nanolubricants at 0.03% suits refrigerations applications while the 0.05% suits high load or high shear use.