Flow boiling heat transfer of R134a: Effect of heat flux and Dry-out characteristics

Abstract

- This study presents an experimental analysis of flow boiling heat transfer of R134a refrigerant in a smooth horizontal stainless-steel tube with the goal of investigating the effect of heat flux on heat transfer coefficient and dry-out characteristics. The experiment was performed for heat fluxes ranging from 7.2 kW/m 2 to 47.4 kW/m 2 , mass flux of 300 kg/m 2 s and saturation pressure of 460 kPa. At low heat flux, the heat transfer is predominantly controlled by convection boiling with a higher slope of heat transfer coefficient. As heat flux increases, nucleate boiling begins to predominate the heat transfer. The predominance of nucleate boiling is strongly experienced at low vapor quality when the higher slope in convective boiling begins to disappear as nucleate boiling dominates. Dry-out vapor quality incipience ( 𝑥𝑥 _ 𝑑𝑑𝑑𝑑 ) is not highly affected by heat flux. All the dry-out vapor quality incipience correlations investigated predicted well the vapor quality for which dry-out begins and ends.