Numerical Simulation Of Flow Condensation Heat Transfer Of R290 In Horizontal Smooth Pipe

HCFCs refrigerants have a high GDP(Global Warming Potential)and the ODP(Ozone Depletion Potential)is not zero.The extensive use of HCFCs refrigerants lead to severe environmental problems such as global warming and ozone hole.In the field of refrigeration,air conditioning and heat pump,R22 is the most widely used HCFCs refrigeration.Therefore,the replacement of R22 refrigerant is very urgent.The study found that R290 is an excellent alternative to R22.The primary problem that R290needs to solve in applications is the flammability problem.It is necessary to reduce the amount of R290 in the system.It is a good choice to use a small-diameter heat transfer tube while maintaining the original cooling capacity of the system.Therefore,this paper mainly uses the combination of numerical simulation and experimental research to study the condensation heat transfer characteristics of R290 in small diameter horizontal tubes.In this paper,the CFD software FLUENT19.0 is used to numerically simulate the condensation heat transfer characteristics of R290 in a 4mm pipe horizontal copper pipe.In the simulation process,the appropriate turbulence model and multiphase flow model were selected,and UDF was compiled to simulate the condensation heat transfer characteristics of R290 in a 4mm horizontal tube.The velocity field,temperature field,pressure field and gas-liquid phase distribution law are analyzed.It is concluded that the higher the mass flow rate or the heat flux,the higher the condensation heat transfer coefficient of R290 and the higher the quality,the higher the condensation heat transfer coefficient of R290 in the operating range of mass flow rate 180-250 kg/(m~2·s),heat flow density 5-8kW/m~2 and quality 0.1-0.9.Then,the condensation heat transfer characteristics of R290 in the horizontal tube were tested under the same working conditions,and the experimental results were obtained.Comparing the experimental results with the calculated values of six classical correlations of condensation heat transfer coefficients of pure refrigerants in horizontal tubes,it is concluded that Cavallini A and Bohdal T calculation values agreed well with those of the experimental of condensation heat transfer coefficients of R290 in horizontal tubes,with 79.05%and 86.67%data points within 30%error lines,respectively.In addition,by comparing the experimental results with the numerical simulation results,it is found that the absolute deviation of the simulation value is less than 17%in the comparison of mass flow rate,heat flux density and saturation temperature.The model is considered reasonable and the paper attempts to explain the causes of the errors.Finally,the effects of mass flow rate and pipe diameter are simulated.It is found that the higher the mass flow rate in the range of 330~480 kg/(m~2·s),the greater the condensation heat transfer coefficient.According to the above modeling method,the3,5 and 7 mm pipe diameter condensation models were established respectively.The condensation heat transfer characteristics of R290 in the above pipe diameter horizontal pipe were studied by numerical simulation method.It is pointed out that in the range of pipe diameter(3-7mm),the decrease of pipe diameter leads to the advance of the transition from non-annular flow to annular flow and the enlargement of annular flow area.Therefore,under the same conditions,the condensation heat transfer coefficient is larger in smaller pipe diameter.