This paper quantifies the influence of copper (II) oxide (CuO) nanoparticle concentration on the boiling performance of R134a/polyolester mixtures on a roughened, horizontal flat surface. Nanofluids are liquids that contain dispersed nanosize particles. Two lubricant based nanofluids (nanolubricants) were made with a synthetic polyolester and 30 nm diameter CuO particles to a 4% and a 2% volume fraction, respectively. As reported in a previous study for the 4% volume fraction nanolubricant, a 0.5% nanolubricant mass fraction with R134a resulted in a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) of between 50% and 275%. The same study had shown that increasing the mass fraction of the 4% volume fraction nanolubricant resulted in smaller, but significant, boiling heat transfer enhancements. The present study shows that use of a nanolubricant with half the concentration of CuO nanoparticles (2% by volume) resulted in either no improvement or boiling heat transfer degradations with respect to the R134a/polyolester mixtures without nanoparticles. Consequently, significant refrigerant/lubricant boiling heat transfer enhancements are possible with nanoparticles; however, the nanoparticle concentration is an important determining factor. Further research with nanolubricants and refrigerants are required to establish a fundamental understanding of the mechanisms that control nanofluid heat transfer.

This content is only available via PDF.
You do not currently have access to this content.