Characteristic of heat transfer degradation during flow boiling of low GWP refrigerant R1336mzz(Z) in an enhanced channel

Abstract

The decreasing heat transfer coefficient with an increase in vapor quality, which is termed heat transfer degradation, commonly exists during flow boiling in channels. Experimental investigations have been conducted on the characteristics of heat transfer degradations for a low GWP refrigerant R1336mzz(Z) in an enhanced channel. The heat transfer degradations occur in both low mass flux and high mass flux. In the analysis of the mechanisms for heat transfer degradations, the effects of heat flux and saturation temperature are taken into account. Additionally, a comparison with the heat transfer characteristics of another refrigerant (R245fa) with different thermophysical properties is also included to reinforce the analysis. The heat transfer degradation at low mass flux is accelerated by increasing the heat flux or saturation temperature, and R245fa shows an earlier heat transfer degradation than R1336mzz(Z). However, a completely reverse phenomenon appears at high mass flux. The heat transfer degradation can be delayed or even eliminated as the saturation temperature and heat flux increase, and the degradation does not show up for R245fa under the same operating conditions. The mechanisms of heat transfer degradations at low mass flux and high mass flux are explored to be different. Dryout is the cause of heat transfer degradation at low mass flux, whereas suppression of nucleate boiling is the inducement at high mass flux.