Simulation Study Of Thermo-Fluid-Solid Coupling Considering Subcooled Flow Boiling Based On OpenFOAM

In order to meet the goal of high efficiency,energy saving and low emission,a lot of advanced technologies have been adopted.The structure becomes more compact,and the heat flux in the local narrow space sharply increases,which brings huge challenges for cooling system of internal combustion engine(ICE).Boiling heat transfer has attracted wide attention due to its high efficiency and temperature uniformity.The structure of water jacket is very complex,nowadays,most of numerical studies on boiling heat transfer process are analyzed by commercial software.On the one hand,the effect of solid side heat transfer boundary conditions on the fluid domain is neglected,on the other hand,the functions of commercial software are limited,which result in the calculation accuracy need to be improved.In this paper,a computing simulation platform of boiling heat transfer was established based on the framework of open source CFD software(OpenFOAM).Aiming at the phenomenon of subcooled flow boiling in water jacket of ICE,an improved Lee interphase mass transfer model was proposed,and a subcooled flow boiling heat transfer solver was developed suitable for operating conditions of ICE.Based on the theory of heat-fluid-solid coupling,the solid conductivity equations were introduced into the above solver,and a coupled boundary condition was proposed.Then a subcooled flow boiling thermo-fluid-solid solver for solid-liquid-gas three-phase was developed,which promoted development of boiling phase change heat transfer theory and numerical simulation methods in ICE.The main contents are as follows:(1)On the basis of VOF method,the Lee interphase mass transfer model describing evaporation and condensation was introduced.The source term of volume fraction equations was reconstructed due to phase transition.The effect of evaporation and condensation were introduced into the pressure equation,and the standard PIMPLE algorithm was used to solve the pressure-velocity coupling process.The whole frame and phase change model library were designed,a numerical simulation platform for boiling heat transfer was built based on OpenFOAM.The validation was accomplished by one-dimensional Stenfan and two-dimensional film boiling problems.(2)Under typical operating conditions of ICE,the cooling method in water jacket is subcooled flow boiling heat transfer.During this process,the ratio of vapor phase and liquid phase changes due to the effect of evaporation in high temperature zone and condensation in the bulk.The effects of superheat,saturation temperature,subcooling and Reynolds number on mass transfer between two phases were considered under different operating conditions.Thus,time relaxation parameter()of Lee mass transfer model was revised,and a modified interphase mass transfer model was developed.The error between the experimental and predicted superheat by modified interphase mass transfer model is less than 20%,which is smaller than that of original Lee's mass transfer model.For other papers,the modified model also shows a good accuracy,within 25%.Finally,a subcooled flow boiling heat transfer solver was developed and it was suitable for operating conditions of ICE,which achieved accurate simulation for complex subcooled flow boiling heat transfer process.(3)The effect of different flow parameters on heat flux was investigated under typical operating conditions of ICE by subcooled flow boiling heat transfer solver.At low velocity,the growth rate of heat flux is faster than that of wall superheat.At high velocity,a considerably large quantity of heat in heating zone is taken away by fluid,and the energy required for growth bubble growth decreases.Meanwhile,the boiling phenomenon is restrained,and the slope of boiling curve increases gradually.With the increase of wall superheat,the slope of boiling curve increases gradually.The higher the inlet temperature is,the fluid only need to absorb less heat to achieve boiling requirements,the earlier the slope rises.The system pressure directly changes the saturation temperature and physical properties of fluid,boiling heat transfer is suppressed by high pressure.(4)On the basic of subcooled flow boiling heat transfer solver,some equations on solid conductivity were introduced,and the physical fields and grids of fluid and solid domain were marked with special keywords,respectively.According to the principle of domain decomposition and boundary coupling,a boundary condition for fluid-solid coupled heat transfer was built.Finally,a subcooled flow boiling thermo-fluid-solid solver(chtEvaConFoam)for solid-liquid-gas three-phase was developed.By comparing the simulated and experimental values of boiling heat transfer curves and gas-phase distribution in two cases,it was verified that chtEvaConFoam could accurately simulate boiling heat transfer process in the fluid domain and temperature distribution in solid domain.