Numerical Simulation Of Large-temperature-difference Natural Convection In The Enclosed Cavity

Natural convection heat transfer of large temperature difference has a very wide range of applications background in practical engineering. With the development of the miniaturization and high energy density of the device as well as to improve the energy efficiency requirements, the study of large temperature difference natural convection is becoming increasingly urgent problem. Due to the limited of high temperature conditions, it is difficult for the current experimental study of large temperature difference natural convection. Most of the existing research on numerical simulation method, but the select of the numerical calculation method effect on the accuracy of the results in a large temperature difference natural convection, so this paper investigate numerical simulation method to study the heat transfer of large temperature difference natural convection.In this paper, numerical simulations are conducted by the software of Fluent. Due to the fluid properties with temperature changes larger in the large temperature difference natural convection, there is a large deviation of calculation accuracy using the a given physical properties. Firstly, with three density treatment methods, including Boussinesq approximation, incompressible ideal gas and piecewise-linear density, the steady natural convection problem is simulated, which is driven by the large temperature difference the enclosed cavity. Meanwhile, numerical simulation of natural convection was carried out by two different physical parameters treatment methods for the thermal conductivity and viscosity coefficient. Next, we consider further the impact of the shape factor, which the cylindrical cavity of actual project is widely used to analyze the effect of curvature of the cylindrical surface of natural convection heat transfer. Finally, the transient characteristics of the large temperature difference natural convection is be studied preliminarily.The results show that the relative deviation of Boussinesq approximation with the other two methods is small in the small temperature difference(40K~200K). The maximum relative deviation does not exceed 5%. Meanwhile, Boussinesq approximation can reduce computation cost and accelerate the convergence. In a larger temperature difference(200K ~ 1000K), The maximum relative deviation of Boussinesq approximation with the other two methods has reached 18% so that it can not accurately describe the flow of fluid, because the gas compression and density changes can not be ignored. Meanwhile,the numerical simulation of natural convection need to consider separately the impact that the varies of thermal conductivity and viscosity coefficient with temperature. In addition,the surface curvature is one of the important factors to affect the natural convection of cylindrical cavity. With the decrease of surface curvature, the average Nusselt number Nuave at hot wall will approach to that of square cavity gradually. At the same time, when surface curvature and temperature difference are very large, Boussinesq approximation will bring about the greater relative deviation. Finally, the numerical simulation of transient show natural convection heat transfer characteristics with time-dependent properties.Numerical simulation of natural convection research in a closed cavity for different physical properties treatment methods helps to provide a frame of reference in numerical simulation,and has great significance in engineering applications and practices.