Thermophysical performance enhancement of vapor‐compression chiller systems via metal oxide nanofluid integration

Abstract This study examines the effect of CuO and Al 2 O 3 nanoparticles as heat transfer enhancers to increase the thermal performance of the chilled water refrigeration system. An experimental test rig was built that consisted of three parallel evaporator circuits that were immersed in three different water basins with CuO‐water, Al 2 O 3 ‐water nanofluids and pure water as reference. The system consisted of a reciprocating compressor, air‐cooled condenser, capillary expansion valve and air handling unit with copper coil heat exchanger. Nanofluids were produced by ultrasonic homogenization at mass fractions of 0.1%, 0.3% and 0.5% wt. Experimental measurements indicate that the optimal performance occurs for CuO‐water nanofluid at 0.5% wt. Reasons for this are that the coefficient of performance is increased by 22%, the compressor power consumption by 31% and the heat rejection ratio by 0.8% compared to pure water. Large drops in temperature were observed at evaporator and condenser outlets. The performance improvement mechanisms are a result of the high thermal conductivity of nanofluids that increases the heat convection mechanism at the evaporator surfaces. Subcooling effects at the condenser outlet decrease the refrigerant enthalpy entering the expansion device to improve the refrigeration effect and minimize the work input of the compressor. These results prove the metal oxide nanofluids as efficient passive enhancement techniques for energy‐efficient HVAC applications.