Experimental Studies On Evaporation Heat Transfer In Three-dimensional Stainless Steel Surface Enhanced Tubes

Enhanced heat transfer technology can improve the efficiency of heat exchangers,alleviate energy crisis and reduce environmental pollution.Thus,it has attached importance to find efficient intensifying tubes.Ripple tubes are newly developed three-dimensional enhanced tubes.The surface of two kinds of enhanced tubes can be called mixed surface.The convex or groove structures can increase the heat transfer area and the flow turbulence.In this article,the literatures of two-phase flow heat transfer are collected and summarized,and the research methods and conclusions are summarized.1EHT-1,1EHT-2 and 4LB tubes were investigated on a high-precision,multi-refrigerant heat transfer test rig.Finally,the evaporation heat transfer characteristics of the three-dimensional enhanced tubes were studied and concluded.The experimental conditions are as follows: the mass flow rate of refrigerant varied from 30kg/h to 70kg/h,the saturation temperature of 279 K,the inlet vapor quality of 0.2,and the outlet vapor qualities of 0.4,0.6 and 0.8,respectively.The outer diameter and inner diameter stainless steel tube are 9.52-mm-OD and 8.32-mm-ID,respectively.The Wilson enhancement ratio of three enhanced tubes(1EHT-1,1EHT-2 and 4LB)is 2.05,1.23 and 1.85,respectively.In single-phase experiment,the heat transfer coefficients of four tested tubes increase with the increase of refrigerant mass flow rate of three enhanced tubes.According to the experimental results,the heat transfer coefficients of 1EHT-1 tube,1EHT-2 tube and 4LB tube are 1.54-1.62,1.21-1.40 and 1.2-1.32 times than that of smooth tube.Analyzing the single-phase friction pressure drop,it is found that the frictionpressure drop of 1EHT-1 tube is the largest,while the pressure drop of the other two enhanced tubes is slightly larger than that of smooth tube.During the evaporation experiments,the evaporation heat transfer coefficients of the four tested tubes increase with the increase of vapor quality and refrigerant mass flow rate.However,1EHT-2 and 1EHT-1 tubes show better heat transfer performance in the low vapor quality,while 1EHT-2 and 4LB tubes have better heat transfer performance in the high vapor quality.By comparing the evaporation heat transfer models,it is found that Kandlikar correlation can not accurately predict the evaporation heat transfer coefficients of smooth tube,while Wojtan et al,Liu and Winterton,Gungor and Winterton correlations can accurately predict the evaporation heat transfer coefficient in this evaporation experiments,which can predict 90% of the data points within an error range of ±15%.The evaporation frictional pressure drop of 1EHT-1 tube is the largest and that of smooth tube is the smallest.