Experimental Investigation Of Connective Single And Condensation Heat Transfer In Enhanced Tubes

Heat transfer in tubes plays a very important role in refrigeration system,air conditioning and heat pump equipment,and the heat transfer efficiency of heat exchanger is also a necessary factor in heat transfer process.At present,with the increasing heat load of heat exchangers,all kinds of heat transfer intensifying pipes have been developed.It has become a hot research topic to study the high performance heat transfer performance,the inner surface strengthening tube and the compact heat transfer component.Firstly,the literature review and built of two-phase flow in tubes were completed,followed by copper material enhanced tubes(1EHT,2EHT-1,2EHT-2),stainless steel bellows(1EHT-1,1EHT-2)and square tube(4LB)as the research object.The experiments were conducted to study the heat transfer characteristics of convection single and condensation in different saturation temperature,mass flow rate,heat flow,vapor quality and density.According to the existing two-phase flow correlation model to optimize and predict experimental data.The experimental conditions are as follows: all the data based on the smooth tube and R410 A is working fluid;Copper Tubes outer diameter are 12.7 mm,inter diameter are 11.5 mm,stainless steel tubes outer diameter are 9.52 mm,inter diameter are 8.32mm;at condensation saturation temperature of 45℃,and the single-phase temperature is 6℃;with an outlet quality of 0.8;outlet quality of 0.8.the stainless steel tubes reinforcement ratio is 1.92,1.86 and 1.23 by Wilson graphic method.In single-phase experiments,with the increase of mass flow rate,the heat transfer coefficients of 1EHT-1,1EHT-2 and 4LB tubes increase but larger than equivalent ofsmooth tubes.The enhancement rate of 1EHT tube is the largest,followed by 2EHT-2tube and 2EHT-1 tube is the smallest.For copper tubes,with the increase of mass flow,the heat transfer coefficient ratio of the 1EHT tube gradually decreases and the 2EHT tube increases gradually.The maximum ratio of the 2EHT-1 tube is 1.06,the average value is 1.04,and the maximum value of the 2EHT-2 tube is 1.29,the average value is1.15.The friction pressure drop increases with the mass flow rate increasing,so the trend of pressure drop loss is similar to the heat transfer coefficient.For condensation,the heat transfer coefficient increases with the increase of mass flow rate,and 1EHT tube has the largest heat transfer coefficient,followed by 2EHT tube,and the heat transfer coefficient of smooth tube is the lowest.Two 2EHT tubes showed a similar heat transfer performance,2EHT-2 tube heat effect is better than the2EHT-1 tube,the heat transfer coefficient ratio of three copper pipes is 1.3-1.95 times that of smooth tube.The heat transfer coefficient ratio of stainless steel tube is1.07-1.30 times of that of smooth tube,The Friedel correlation has a better prediction accuracy for the enhancement of tube condensation pressure drop.