Condensation Characteristics of Flows Inside the Three-Dimensional Enhanced Tubes

This paper presents experimental condensation characteristics of R134a inside two three-dimensional enhanced heat transfer tubes (1EHT1 and 3EHT) and one equivalent smooth tube. The 1EHT1 tube has the primary elliptical dimples and secondary petal arrays, and the 3EHT tube has the grooves and square bulge. All the tested stainless-steel tubes have the same outer diameter of 15.88 mm. The test tubes are installed in a horizontal test section with an effective length of 2 m. In these experiments, condensation temperature is kept constant at 318K. The refrigerant qualities at the test section inlet and outlet are 0.8 and 0.2. Mass flux is varied from 70 kg/(m²s) to 170 kg/(m²s). In a comparison of condensation heat transfer performance, the 1EHT1 tube has the best heat performance followed by the 3EHT tube. Condensing coefficients of the 1EHT1 tube and the 3EHT tube are about 1.45 times and 1.16 times that of the smooth tube, respectively. The experimental results in this study are compared with other experiments conducted by R410A under similar experimental conditions to evaluate the thermal performance.