Effect of Acoustic Excitation on R134a/Al2O3 Nanolubricant Mixture Boiling on a Reentrant Cavity Surface

Abstract

This paper quantifies the influence of acoustic excitation of Al2O3 nanoparticles on the poolboiling performance of R134a/polyolester mixtures on a commercial (TurboBIIHP) boiling surface. A nanolubricant with 10 nm diameter Al2O3 nanoparticles at a 5.1% volume fraction in the base polyolester lubricant was mixed with R134a at a 1% mass fraction. The study showed that highfrequency ultrasound at 1 MHz can improve R134a/nanolubricant boiling on a reentrant cavity surface by as much as 44%. This maximum enhancement occurred for an applied power level to the fluid of approximately 6 W and a heat flux of approximately 6.9 kW/m2. Applied power levels larger and smaller than 6 W resulted in smaller boiling heat transfer enhancements. In total, five different applied power levels were studied: 0 W, 4 W, 6 W, 8 W, and 12 W. The largest and smallest enhancement averaged over the tested heat flux range were approximately 12% and 2% for the applied power levels of 6 W and 4 W, respectively. In situ insonation at 1 MHz resulted in an improved dispersion of the nanolubricant on the test surface. An existing poolboiling model for refrigerant/nanolubricant mixtures was modified to include the effect of acoustic excitation. For heat fluxes greater than 25 kW m−2, the model was within 4.5% of the measured heat flux ratios for mixtures, and the average agreement between measurements and predictions was approximately 1% for all power levels.