Pool boiling of HFO-1336mzz(Z) on a reentrant cavity surface

This paper quantifies the pool boiling performance of R1336mzz(Z) on a flattened, horizontal Turbo-ESP surface for air-conditioning and industrial heat recovery applications for heat fluxes between roughly 10 kWm-2 and 120 kWm-2. The R1336mzz(Z) pool boiling curve was measured for three saturation temperatures and exhibited the best performance with respect to saturation temperature near the middle saturation temperature of 298.1 K. The study showed that the boiling performance of R1336mzz(Z) on the Turbo-ESP did not differ statistically from that of R123 for heat fluxes between 13 kWm-2 and 59 kWm-2. For heat fluxes larger than 59 kWm-2, the R123 boiling heat flux was up to 5% larger than the heat flux for R1336mzz(Z). A pool boiling model was modified to include a convective term and was used to predict boiling heat transfer for the test refrigerants on the Turbo-ESP surface, mostly, to within ±0.5 K.

Horizontal convective boiling of R1234yf, R134a, and R450A within a micro-fin tube

This paper presents local convective boiling heat transfer and Fanning friction factor measurements in a micro-fin tube for R134a and two possible low global warming potential (GWP) refrigerant replacements for R134a, namely R1234yf and R450A. Test section heating was achieved with water in either counterflow or in parallel flow with the test refrigerant to provide for a range of heat fluxes for each thermodynamic quality. An existing correlation from the literature for single and multi-component mixtures was shown to not satisfactorily predict the convective boiling measurements for flow qualities greater than 40%. Accordingly, a new correlation was developed specifically for the test fluids of this study so that a fair comparison of the heat transfer performance of the low GWP refrigerants to that of R134a could be made. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting example comparison, for the same operating conditions, showed that the heat transfer coefficient of the multi-component R450A and the single-component R1234yf were, on average, 15% less and 5% less, respectively, than that of the single-component R134a. Friction factor measurements were also compared to predictions from an existing correlation. A new correlation for the friction factor was developed to provide a more accurate prediction. The measurements and the new models are important for the evaluation of potential low-GWP refrigerants replacements for R134a.