Simulation On R290 In-tube Flow Boiling Heat Transfer Characteristics

HCFCs have a high GWP and ODP is not zero,and large-scale use will cause global warming and ozone holes.Previously,as a typical representative of HCFCs,R22 was extensively used in refrigeration,air conditioning and heat pumps.R290 is one of the typical alternative working fluids for R22 with excellent physical property.Research on the heat transfer characteristics of R290 in the evaporator can make using of R290 more efficiently and safely.In this paper,the most commonly used finned tube evaporator in household air conditioners was used as the application background,the utilization of R290 was regarded as the actuating medium,meanwhile,the methods of numerical simulation were in use to seek the boiling heat transfer characteristics in a 9.52 mm pipe diameter horizontal tube.The effect of flow pattern,mass flow and heat flux on heat transfer,pressure drop and overall performance in the tube was studied.The main conclusions are as follows:(1)The average deviation value between the average heat transfer coefficient of the simulation results and the experimental results is8.8%,and the average deviation value between the pressure drop and the experimental is 22.7%.The flow pattern of the simulation results is in good agreement with the Baker flow pattern.From the inlet to the outlet,bubbly flow,block flow,slug flow,elongated slug flow,and agitated flow are obtained in sequence.(2)The mass flow rate and heat flux density affect the heat transfer condition of the round tube by influencing the flow pattern.Under the influence of gravity,the two phases in the tube form a distinct stratified flow,with the gas phase at the top and the liquid phase at the bottom.The air film above the pipe will severely obstrcut the heat exchange effect of the pipe,whose upper end is not so good as the lower part.(3)The increase in mass flow,heat flux and dryness will increase the local heat transfer coefficient and pressure drop.The increase in pressure drop loss in the slug flow and stirring flow stages is greater than that in the bubbly flow stage.(4)Due to the enhancement of mass flow and heat flux,the average heat transfer coefficient of flow boiling will be increased,on the other hand,the augment of the heat flux will accelerate the general performance factor.For every 10W/㎡ increase in heat flux,the overall performance factor will increase by 1.16 W /㎡·K·Pa,the overall performance factor will decrease by 3.75 W/㎡·K·Pa every time the mass flow increases by 1kg/(㎡·s).When optimizing the heat transfer of the heat transfer tube in the fin-tube evaporator,the heat flux should be considered first,and the heat flow density should be maximized while ensuring a small mass flow.