Effect of Acoustic Excitation on R134a/Al2O3 Nanolubricant Mixture Boiling on a Reentrant Cavity Surface
Mark A. Kedzierski, Steven E. Fick
This paper quantifies the influence of acoustic excitation of Al2O3 nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a commercial (Turbo-BII-HP) 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 high frequency 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 was approximately 12 % and 2 % for 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 pool boiling model for refrigerant/nanolubricant mixtures was modified to include the effect of acoustic excitation. For heat fluxes greater than 25 kWm-2, the model was within 4.5 % of the measured heat flux ratios for mixtures at all applied power levels. The average agreement between measurements and predictions was approximately 1 % for all power levels.