Numerical Study Of Free Surface Jet Impingement Heat Transfer By Molten Salt

Jet impingement has been widely studied and applied as an efficient and enhanced heat transfer method for extreme operating conditions such as high temperature and high heat flow.Molten salt as a new type of heat transfer and heat storage mass is used in solar thermal power generation and industrial waste heat utilization due to its advantages of wide applicable temperature range,low working pressure and low viscosity,but the research and understanding of its heat transfer characteristics are still relatively lacking.In this paper,the flow heat transfer characteristics of molten salt under free surface jet impingement are studied by means of numerical simulation,which provides a reference for the application of molten salt heat transfer enhancement technology.Firstly,according to the basic characteristics of the jet impingement process,seven different turbulence models are selected for the numerical simulation of heat transfer performance,and the simulation results are compared with the experimental results in the literature to analyze the characteristics of different turbulence models,and the Standard k-εturbulence model is determined as the numerical simulation model in this paper.Secondly,according to the determined turbulence model,numerical simulations of the heat transfer characteristics of single hole jet impingement under different operating conditions were carried out to investigate the effects of geometric parameters and flow parameters on the flow heat transfer using molten salt as the working medium.The results show that the stagnation point region Nusselt number and radial Nusselt number increase with the increase of the jet Reynolds number.When the jet Reynolds number is constant,the distribution of the local Nusselt number is almost independent of the nozzle-to-plate spacing;Other conditions being constant,the impact pressure on the heat transfer surface at the stagnation point region gradually increases with the increase of Reynolds number.When the nozzle-to-plate spacing is small,The dimensionless velocity u/u₀ of the"direction"of the jet centerline and dimensionless radial velocity v/u₀ is almost independent of the jet Reynolds number,while the turbulent kinetic energy k/u₀~2 at the jet centerline decreases with and the radial turbulent energy k/u₀~2 near the wall decreases with as the jet Reynolds number increases.In addition,within the study range of this paper,as the molten salt temperature increases,its Prandtl number decreases and the jet impingement heat transfer performance gradually decreases.finally,based on the above study,a numerical simulation study of molten salt array jet impingement heat transfer was conducted to investigate the effects of nozzle-to-plate spacing,jet Reynolds number,and nozzle spacing on the jet impingement heat transfer performance.The results show that the local Nusselt number and pressure on the heat transfer surface increase with the increasing of jet Reynolds number at the same other conditions.As the nozzle-to-plate spacing increases,the average Nusselt number on the heat transfer surface gradually increases,but the increase becomes slower,and has relatively good heat transfer intensity and temperature uniformity at nozzle-to-plate spacing of 3d to 5d and nozzle spacing of 3d to 4d.In addition,the nozzle spacing has a great influence on the distribution structure of the jet flow field.In the nozzle spacing of 2d,before the jet impinges on the heat transfer surface,the mutual interference between the two jets is strong,and the jet in the downstream deflection occurs significantly,with the increase in nozzle spacing,this interference effect gradually diminished.