Simulation Of Condensation Phase Change For Moist Air And Pure Steam Flowing Over Cold Wall Surface

The use of heat exchangers in today's industrial production and life is very wide.From aerospace power industry to air conditioning,it reflects an important effect.Therefore,there is a significant meaning studying thermal performance of heat exchanger and improving the heat transfer efficiency.Fin-and-tube heat exchanger is one of the main structural forms.The main heat resistance of the heat exchanger is in the air side.So changing the structure of the fins can reduce the thermal resistance.The common shapes are wavy finned,strip type,blinds and so on.In this paper,the physical and mathematical models of wavy finned tube heat exchanger are established,and condensing heat transfer processes of moist air are studied.On this basis,the two-phase heat and mass transfer processes are analyzed.In this research,a reasonable assumption is made for the heat and mass transfer when the moist air flows through the wavy finned tube heat exchanger.The rationality of the model and the independence of the grid are verified.The condensation and heat transfer processes of 1~4 rows of wavy finned tube heat exchanger are studied when the moist air inlet velocity is 1~6 m/s and its relative humidity is 30%~90%.The influences of inlet moist air parameter,heat exchanger tube row numbers and wall temperature on the quantity and coefficient of heat and mass transfer and analogy analysis of heat and mass transfer are analyzed.The results show that when the fin surface is under partly dehumidifying conditions,non-condensed area near the entrance increases with the increase of inlet air velocity while the non-condensed area at leeward side of the tube decreases.The heat transfer rate and condensation amount on the fin surface increase with the increase of the inlet velocity of the moist air,relative humidity,and the tube row numbers.Compared with the front tube,the heat transfer rate and the condensation amount of the back tube show a decreasing trend.At higher speed,the condensing amount of the second row tube is close to that of the first row tube.The VOF method is used for pure vapor phase change condensation,and the distribution of velocity,temperature and liquid volume fraction is obtained.The variations of heat transfer coefficient,liquid film thickness,and condensation quantity with the mass transfer rate ? are analyzed.The liquid film thickness is less than the Nusselt theoretical solution and the error is less than 27%.