Effect of Acoustic Excitation on R134a/Al2O3 Nanolubricant Mixture Boiling on a Reentrant Cavity Surface with Extensive Measurement and Analysis Details

Abstract

This paper quantifies the influence of Al2O3 nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a Turbo-BII-HP boiling surface. Nanolubricants with 10 nm diameter Al2O3 nanoparticles of various volume fractions (1.6 %, 2.3 %, and 5.1 %) in the base polyolester lubricant were mixed with R134a at two different mass fractions (0.5 % and 1 %). The study showed that nanolubricants can improve R134a boiling on a reentrant cavity surface as long as the nanoparticles remain well dispersed in the lubricant and are at sufficiently large concentration. For example, three of the refrigerant/nanolubricant mixtures with the smallest nanoparticle mass fraction exhibited average enhancements over the entire heat flux range of approximately 10 %. However, when the nanoparticle mass fraction was increased to a point that likely encouraged agglomeration, an average heat transfer degradation of approximately 14 % resulted. An expression for the nanoparticle surface density was developed for the Turbo-BII-HP surface for use in an existing model for predicting refrigerant/nanolubricant boiling. For heat fluxes greater than 35 kWm, the model was within 0.5 %, 21 %, and 16 % of the measured heat flux ratios for mixtures with increasing nanoparticle surface density, respectively. The correspondence between the increases in the model deviation with the increase in nanoparticle surface density may be due to the increased propensity for agglomeration at greater nanoparticle surface density.