Air conditioning compressor lubricant enhancement using carbon-based nanomaterials for hot climates

Abstract

This study evaluates the impact of carbon-based nano-lubricants on air conditioning (AC) systems in hot climates, focusing on thermophysical, tribological, and stability properties. Nano-lubricants were formulated using POE32 oil with short single-walled carbon nanotubes (short-SWCNTs), short multi-walled carbon nanotubes (short-MWCNTs), and graphene (GN) at concentrations from 0.01 to 0.10 vol.%. A two-step mixing approach was employed, and properties were analyzed across 10 °C to 100 °C. Results showed negligible density changes with concentration but up to a 6% variation with temperature. Specific heat capacity decreased with higher nanomaterial concentrations, with a 6.85% reduction at 0.1 vol.% short-SWCNTs, at 100 °C. Thermal conductivity enhancements were minimal at 0.01 vol.% but reached 2.21% with 0.10 vol.% GN. Dynamic viscosity increased significantly at 0.05 and 0.10 vol.%, peaking at 15.31%. Tribological analysis revealed optimal coefficient of friction (COF) reductions at 0.025, 0.05, and 0.01 vol.% for short-SWCNTs, short-MWCNTs, and GN, respectively. In terms of dispersion stability, using three different analyses for verification, all as prepared nano-lubricants exhibited good physical stability up to 5 days, and then loses their static stability condition with time. The figures of merits (FOMs) analysis showed that optimized carbon-based nano-lubricant concentrations can enhance heat dissipation and compressor performance with minimal energy impact. These findings provide valuable insights for selecting optimal nano-lubricants for AC systems. Future work will focus on evaluating their compatibility with refrigerants and assessing their impact on compressor performance under high ambient conditions.