Evaporation heat transfer characteristics of R410A inside horizontal three-dimensional enhanced tubes

Abstract

An experimental investigation was conducted for flow boiling inside three horizontal stainless-steel tubes with a series of newly-developed three-dimensional enhanced surfaces. Both the inner and outer surfaces of the 1EHT tubes were composed of dimples in different sizes and depths, and with an array of rectangular cavities for the 3EHT tube. These enhanced tubes have the same outer and inner diameters of 9.52 mm and of 8.32 mm, respectively. The evaporation experiments were performed using R410A as the working fluid at a constant saturation temperature of 279 K. The mass fluxes varied from 160 to 390 kg/m2s, with inlet and outlet vapor qualities of 0.2 and 0.8, respectively. As the mass velocity increased, the heat transfer coefficient and pressure drop penalty increased accordingly. Experimental results showed that the pressure drop of the 1EHT-1 tube is larger than those of the 1EHT-2 and 3EHT tubes, while the 1EHT-2 tube has the highest evaporation heat transfer coefficient.