Performance Simulation Of Boiling Heat Transfer Of R417A Inside Horizontal Smooth And Internally Grooved Tubes

As the complexity of multiphase flow and lack of micro-understanding and quantitative description of the interface heat transfer and dynamic behavior, multiphase flow and boiling heat transfer has become an important issue on multiphase flow research. As the alternative to R22 at present, there are some differences between ternary non-azeotropic refrigerant R417A and R22 in the flow and heat transfer performance and study of boiling heat transfer on R417A in the evaporator can provide the theoretical basis for the development of replacement refrigerants and the corresponding evaporators in the future.This article has conducted the numerical simulation and theoretical analysis on boiling heat transfer performance of the refrigerant R417A in horizontal tubes.Firstly, based on flow and heat transfer mechanism of gas-liquid two-phase flow in tubes, the computing models of a horizontal smooth tube and an internally grooved tube were built using Fluent software, and meshed. The boundary conditions were set and turbulence model and the multiphase flow model were selected through the analysis of thermodynamics and fluid dynamics.Secondly, through simulation, obtained the distribution and variation law of the temperature field, velocity and heat transfer coefficient on flow boiling heat transfer of refrigerant R417A in tubes. By changing the boundary conditions, simulated the influence laws of the mass flow rate, heat flux, evaporating temperature and dryness on the boiling heat transfer : As the increase of the refrigerant mass flow rate and heat transfer density, the heat transfer coefficient increased significantly; the influence of evaporation temperature on the heat transfer coefficient was not very obvious; with the increased dryness, heat transfer coefficient firstly increases to a maximum, and when wall turned dry, heat transfer coefficient fell quickly and heat transfer performance deteriorated. There was a trend that peak of heat transfer coefficient moved to the corresponding peak dryness in the internally grooved tube.Thirdly, heat transfer performance and pressure drop were compared in the smooth tube and the internally grooved tube and the results were analyzed. The reasons that the internally grooved tube can enhance heat transfer are not only area increase caused by micro-fin, but the thread structure can increase wetting area increases, the boiling point and vaporization core, effects of disturbance and turbulence, capillary and wetting phenomena and rotating fluid. The increased pressure drop is mainly due to the secondary flow, friction increases and the effects of boiling heat transfer flow caused by the formation of the internally grooved tube.Finally, numerical simulation and experimental results were compared and the causes of errors are analyzed. The results showed that simulation results coincided with the experimental results, and further verified the reliability of the numerical simulation.