This paper quantifies the influence of CuO nanoparticles on the boiling performance of R134a/polyolester mixtures on a roughened, horizontal, flat surface. Nanofluids are liquids that contain dispersed nano-size particles. A lubricant based nanofluid (nanolubricant) was made with a synthetic ester and 30 nm diameter CuO particles stably suspended in the mixture to a 4 % volume fraction. For the 0.5 % nanolubricant mass fraction, the nanoparticles caused a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) of between 50 % and 275 %. A smaller enhancement was observed for the R134a/nanolubricant (99/1) mixture, which had a heat flux that was on average 19 % larger than that of the R134a/polyolester (99/1) mixture. Further increase in the nanolubricant mass fraction to 2 % resulted in a still smaller boiling heat transfer improvement of approximately 12 % on average. Consequently, significant refrigerant/lubricant boiling heat transfer enhancements are possible with nanoparticles. Thermal conductivity measurements and a refrigerant\lubricant mixture pool-boiling model were used to suggest that increased thermal conductivity is responsible for only a small portion of the heat transfer enhancement due to nanoparticles. Further research with nanolubricants and refrigerants are required to establish a fundamental understanding of the mechanisms that control nanofluid heat transfer.
Citation: International Journal of Refrigeration-Revue Internationale Du Froid
Pub Type: Journals
additives, boiling, copper (II) oxide, enhanced heat transfer, nanotechnology, refrigerants, refrigerant/lubricant mixtures