Study On The Phase Change Heat Transfer Inside The Tube Of Cryogenic Finned-tube Vaporizer

Finned-tube vaporizer，as a common heat exchange device in cryogenic engineering, isoften used to vaporize liquid oxygen, liquid nitrogen, liquid argon, liquefied natural gas andother cryogenic fluids. The cryogenic fluids often associate with phase transition process intube. It is more complex in working process, more drastic in change of thermal physicalproperties, and more difficult to determine the whole physical process. On the other hand, it’salso difficult to achieve the visualization experiment of boiling heat transfer in vaporizer tube,so through experimental method to describe the phase change heat transfer process from themicro perspective becomes more unpractical. It possesses an important practical andengineering significance to carry out the study on phase change heat transfer in thefinned-tube vaporizer tube for further accurately analyzing and forecasting the heat transferperformance of vaporizer.The phase change heat transfer characteristic of cryogenic liquid nitrogen in thefinned-tube vaporizer tube was studied through theoretical analysis and numerical simulationin this paper.Firstly, on the basis of a large number of domestic and foreign literature, thecharacteristics of cryogenic liquid phase change heat transfer was summarized in thefinned-tube vaporizer. The process of cryogenic liquid boiling heat transfer in vaporizer wasdivided into four heat transfer zones, including sub-cooled boiling heat transfer zone,saturated boiling heat transfer zone, two-phase forced convection heat transfer zone and lessliquid heat transfer zone, and the heat transfer calculation formulas were established for allzones.Secondly, by using CFD software FLUENT, three-dimensional steady-state numericalsimulation on phase transition flow and heat transfer of cryogenic liquid nitrogen in thefinned-tube vaporizer was carried out with different inlet velocities. The main work is asfollows:(1) Physical model&numerical model of finned-tube vaporizer were set up. Mixturemodel was applied to the calculation of multiphase flow, and RNG k ε model was used todescribe the turbulent flow of fluid. User-Defined Function (UDF) to express the phasechange process of liquid nitrogen in the vaporizer tube was embedded to fluent.(2) Through the numerical simulation, the distribution of temperature, pressure, total heat transfer, pressure drop, gas fraction, gasification volume and so on was given in different inletflux. And the distribution of nitrogen gas fraction along the tube with different inlet velocitieswas also given. The change reasons were explained. The conclusions provide some guiding significance for heat transfer calculation and design optimization of the finned-tube vaporizer.