Study On The Heat Transfer Characteristics And Numerical Simulation Of Air-Heating Cryogenic Finned-tube Vaporizer

Air-heating cryogenic finned-tube vaporizer is a kind of heat exchangercommonly used in cryogenic engineering. The heat source of the vaporizer is thenatural convective air, so the working efficiency of the vaporizer is heavily influencedby the environment. Besides, the surface of the vaporizer has lower temperature, sothe frosting is unavoidable, which directly lowers heat transfer performance. Underthe influence of various complex factors, the heat transfer performance of thevaporizer is difficult to analyze and forecast, and the accurate design of vaporizer isalso difficult to implement.In order to deeply understand the heat transfer characteristic of the air-heatingfinned-tube vaporizer under the frosting condition, this thesis applied theoreticalanalysis and numerical simulation methods study three aspects: frosting on thefinned-tube surface, natural convective heat transfer and designing calculation offinned-tube vaporizer.Firstly, on the basis of summarizing the mechanisms and characteristics of frostgrowth, the models of frost growth rate and physical property calculation wereestablished according to the basic heat and mass transfer theory, and an experimentabout frost layer growth on cryogenic surface and physical property change with theenvironment and time was designed.Secondly, utilizing the SST k Z turbulence model and SIMPLEC arithmetic,The three-dimensional numerical simulation of air side natural convection heattransfer was performed with different structural parameters and inner walltemperatures under. According to the numerical results, a correlation of Nusseltnumber for natural convection heat transfer was fitted. The correlative expression ismuch accurate, and the mean square error relative to numerical simulation results isless than 12%. So the formula can be applied in the design calculation of vaporizer.Additionally, the numerical simulated result shows that: 1) the outside naturalconvection heat transfer of the finned-tube mainly occurs in the viscous bottom layerand jet flow layer, in which the selection of physical property has a certain influenceon the numerical simulation results, 2) increasing the quantity of the fins on thefinned-tube can obviously improve the heat transfer efficiency, but the frost bridge caused by little space between fins should be avoided, which will dramatically reduce heat transfer performance.Lastly, the heat-transfer characteristics of the vaporizer were comprehensively analyzed. The outside heat transfer area of the finned-tube vaporizer is divided into frost working condition, wet working condition and dry working condition. The inside heat transfer of the finned-tube is divided into liquid-phase area, gas-liquid two-phase area and gas-phase area. Furthermore, a heat transfer calculation model is respectively established for each area and an experiment about the dynamic heat-transfer characteristics of the finned-tube vaporizer under the frosting working condition is designed.