Effect of IF-WS2 Nanolubricant on R134a Boiling on a Reentrant Cavity Surface

This report quantifies the influence of inorganic fullerene-like tungsten disulfide (IF-WS₂) nanoparticles on the pool-boiling performance of R134a/polyolester mixtures on a commercial (Turbo-ESP) boiling surface. Tungsten disulfide nanoparticles, of roughly 150 nm, were used at a 15% mass fraction in a base polyolester lubricant to produce the test nanolubricant. The nanolubricant was mixed with R134a at a 1% mass fraction. The study showed that the nanolubricant caused an average 37% degradation in the boiling heat flux as compared to R134a/neat-lubricant boiling on a reentrant cavity surface at the same superheat. Similarly, boiling with R134a/neat-lubricant caused, on average, a 27% degradation in the boiling heat flux as compared to pure R134a boiling and the same superheat. An analysis was presented which showed that the nanoparticles were too large and too dense to promote a boiling enhancement. In addition, the fullerene-like structure and the large size encouraged nanoparticle settling, which presumably filled cavities of the boiling surface leading to additional boiling degradations.

Pool Boiling of Low-GWP Replacements for R134a on a Reentrant Cavity Surface

This paper quantifies the pool boiling performance of R134a, R1234yf, R513A, and R450A on a flattened, horizontal reentrant cavity surface. The study showed that the boiling performance of R134a on the Turbo-ESP exceeded that of the replacement refrigerants for heat fluxes greater than 20 kWm^-2. On average, the heat flux for R1234yf and R513A was 16 % and 19 % less than that for R134a, respectively, for R134a heat fluxes between 20 kWm^-2 and 110 kWm^-2. The heat flux for R450A was on average 57 % less than that of R134a for heat fluxes between 30 kWm^-2 and 110 kWm^-2. A model was developed to predict both single-component and multi-component pool boiling of the test refrigerants on the Turbo-ESP surface. The model accounts for viscosity effects on bubble population and uses the Fritz (1935) equation to account for increased vapor production with increasing superheat. Both loss of available superheat and mass transfer resistance effects were modeled for the refrigerant mixtures. For most heat fluxes, the model predicted the measured superheat to within ± 0.31 K.