Comparison of Two Heat Transfer Enhancing Tubes for Boiling Heat Transfer

• Main Authors: Cheng-Chieh Huang, 黃正杰
• Other Authors: Jung-Yang San
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/17835341280418242435

碩士 === 國立中興大學 === 機械工程學系所 === 100 === This work investigated the heat transfer performance of two tubes. One is with a fin-module insert and the other is with internal micro-carved cross helical threads. In the experiment, R-22 refrigerant was the working fluid. The boiling heat transfer characteristics of the two test tubes were measured respectively. The external surfaces of the test tubes were wrapped with silicone electric-resistance heating wires for achieving a constant surface heat flux condition. The diameter of the wires is 3 mm. At the evaporation temperature in the range -12℃~-13℃and the volumetric flow rate of the refrigerant at 0.15、0.25、0.35、0.43 l/min, the heat transfer performance of the two tubes were tested. The acquired heat transfer data were compared to those of a smooth tube. The result shows that, at all the considered volumetric flow rates, the temperature differences between tube wall and refrigerant for the two test tubes are smaller than that for the smooth test tube. This means the heat transfer coefficients of both test tubes are higher than that of the smooth tube. The average heat transfer coefficients of the tube with fin-module insert are in the range 1.76～2.4 times of those of the smooth tube and the tube with internal micro-carved cross helical threads are in the range 1.36～1.73 times. Thus the heat transfer is enhanced for both test tubes. This implies that the two test tubes can be used to improve heat transfer performance of evaporators in refrigeration systems.