Study On Heat Transfer Performance Of Horizontal Condenser Tube Under Water Film

Evaporative condenser has a good application prospect because of its advantages of saving energy,saving water resources,good condensation effect,compact structure and small floor area.As a basic heat exchange unit,heat exchange tube directly affects the heat transfer performance of evaporative condenser.Based on the current domestic and foreign scholars’ research mainly focuses on the falling film outside the horizontal tube,and the condensation heat transfer in the tube also has a certain impact on the whole heat transfer process.Therefore,this paper studies the heat transfer characteristics of horizontal condenser tube under the action of water film.Firstly,by analyzing the heat and mass transfer process of horizontal condensation heat exchange tube under the action of water film,the mathematical model of heat transfer process of horizontal condensation tube under the action of water film is established,and the simulation calculation is carried out by using EES software.Comparing the simulation value with the experimental value,it is found that the simulation value is higher,the heat transfer error is less than 7%,and the total heat transfer coefficient error is less than 15%,which basically meets the engineering accuracy requirements It shows that the mathematical model and simulation calculation accuracy meet the requirements.Then,the effects of pipe diameter,condenser length,condensing temperature,refrigerant mass flow rate and refrigerant working medium on the heat transfer performance of horizontal condenser under water film were simulated by EES software,which provided reference for the design and performance optimization of evaporative condenser.The simulation results show that:(1)With the increase of pipe diameter,the heat transfer coefficient,total heat transfer coefficient and heat flux density under different refrigerant mass flow conditions show a decreasing trend,while the heat transfer first increases and then decreases,and the outlet dryness of condenser tube decreases first and then increases.That is to say,there is a diameter under different mass flow rates,which makes the heat transfer maximum and the outlet dryness minimum.When the mass flow rate of refrigerant is 0.0044kg/s,0.0050kg/s and 0.0056kg/s,the pipe diameters are 15.9mm,17 mm and 18 mm respectively.(2)With the increase of the length of the condenser tube,the heat transfer rate increases,while the heat transfer coefficient,total heat transfer coefficient,heat flux density and outlet dryness decrease.For the outlet dryness,the larger the mass flow rate,the longer the tube length required to reach 0.When the mass flow rate of refrigerant is 0.0044kg/s,0.0050kg/s and0.0056kg/s,the length of the pipe should be at least 5.6m,6.0m and 6.5m,and the outlet dryness can reach 0.(3)With the increase of condensation temperature,the heat transfer coefficient and total heat transfer coefficient decrease,while the heat transfer and heat flux increase.When the condensing temperature is reduced,the refrigeration performance is improved,but the outlet dryness of the condenser tube will increase.Therefore,in order to meet the requirements of condensation,it is necessary to increase the length of the tube to make up for the increase of the outlet dryness caused by the decrease of the condensation temperature.(4)With the increase of refrigerant mass flow rate,the heat transfer coefficient,total heat transfer coefficient,heat transfer capacity and heat flux density in the tube increase.The increase of mass flow rate is conducive to the enhancement of heat transfer effect,but at the same time,the dryness of condenser tube outlet will also increase.Therefore,in order to achieve the dryness of condenser tube outlet to 0,the greater the refrigerant mass flow rate,the longer the condenser tube length is required.(5)Under the same working conditions,the heat transfer coefficient,total heat transfer coefficient,heat transfer rate and heat flux density of the condenser tube with R290 working fluid in the tube are higher than that of R22 working fluid;however,the outlet dryness of the condenser tube with R290 working fluid in the tube is higher than that of R22.Therefore,in order to meet the outlet dryness of 0,R290 working fluid needs a longer condenser tube length.