This paper quantifies the influence of Al2O3 nanoparticles on the pool 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 by suspending 20 nm diameter Al2O3 particles in a synthetic ester to roughly a 1.6 % volume fraction. The nanoparticles enhanced the boiling heat transfer relative to that for R134a/polyolester mixtures without nanoparticles for the three lubricant mass fractions that were tested. The enhancement occurred for the lowest heat fluxes, which gives the opportunity for designing chillers for lower approach temperatures. 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) as large as 400 % for the lowest tested heat flux. The average heat flux improvement for heat fluxes less than 40 kW/m2 was approximately 105 %, 49 %, and 155 % for the 0.5 %, the 1 %, and the 2 % mass fractions, respectively. The heat flux enhancement for all of the mixtures increased with respect to decreasing heat flux. Due to the good quality of the nanolubricant suspension, the performance of the (99.5/0.5), and the (98/2) nanolubricant mixtures was stable over time.
Citation: Technical Note (NIST TN) - 1663Report Number:
NIST Pub Series: Technical Note (NIST TN)
Pub Type: NIST Pubs
additives, boiling, Al2O3, enhanced heat transfer, nanotechnology, refrigerants, refrigerant/lubricant mixtures