Effect of Concentration on R134a/Al2O3 Nanolubricant Mixture Boiling on a Reentrant Cavity Surface with Extensive Measurement and Analysis Details
Mark A. Kedzierski
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-2, the model was within 0.5 %, 21 %, and 16 % of the measured heat flux ratios the 1AlO (99.5/0.5), the 1AlO (99/1), and the 2AlO (99/1) mixture mixtures, respectively. For the 1AlO (99/1) and the 2AlO (99/1) mixtures, it is possible that particle agglomeration may have reduced the nanoparticle surface density contributing to the deviation of the model from the measurements.