Numerical Study Of Supercritical Fluid Natural Convection In A Closed Cavity Based On The Lattice Boltzmann Method

The heat transfer of natural convection in a cavity is widely existed in nature and industrial fields,such as the heat preservation of envelope structure,the thermal management of nuclear reactor,the diffusion of indoor smoke and the cooling of electronic components.In recent years,since the heat transfer of closed cavity has many complex mechanism and influencing factors,more and more researchers have paid attention to its heat transfer characteristics.On the other hand,supercritical fluid has been widely used in the field of heat transfer in recent years due to its superior thermal properties near critical points.At present,many researchers have carried out studies on natural convection of supercritical fluid in the closed cavity,such as the critical circulation in refrigeration system and heat exchange in nuclear reactors.Compared with traditional numerical simulation methods,Lattice Boltzmann Method(LBM)has been widely used in recent years due to its clear physical meaning and high accuracy.However,applying Lattice Boltzmann Method to supercritical fluid in a square cavity is rare at home and abroad.Therefore,the Lattice Boltzmann Method is introduced to simulate the flow and heat transfer of natural convection of supercritical fluid in the closed cavity,which is expected to make up for the deficiency of this field.On the basis of detailed description of Lattice Boltzmann Method,this paper firstly uses LBM to simulate the flow and heat transfer of natural convection including atmospheric fluid and supercritical fluid.And the effectiveness of method is verified.The difference of heat transfer between supercritical fluid and atmospheric fluid is analyzed.The result shows that pressure and Rayleigh number have obvious influence on the flow and heat transfer of natural convection of supercritical fluid.The pressure value with good heat transfer performance is obtained.The flow and heat transfer at the low temperature wall have a significant effect on natural convection of supercritical fluid.Secondly,considering that the change of inclined angle disperses the buoyancy force and affect the heat transfer,the flow and heat transfer of supercritical fluid in an inclined cavity is simulated based on LBM.The influence of parameters on natural convective heat transfer of supercritical fluid is mainly analyzed,such as inclined angle and pressure.It is found that the heat transfer performance of natural convection of supercritical fluid in the inclined cavity is the best when the inclined angle is equal to 30°.The general characteristic correlation is fitted,which has reference value for the study of natural convective flow and heat transfer of supercritical fluid in the inclined cavity.Thirdly,given that the size of internal heat source can affect the flow and heat transfer,LBM is applied to simulate the flow and heat transfer of supercritical fluid in the inclined cavity containing the internal heat source.And the influence of width ratio and other factors on natural convective heat transfer are analyzed.The results show that although the increase of width ratio limits the flow area of the supercritical fluid,it obviously enhances the heat transfer on the right low temperature wall.According to the calculated Nusselt number,the characteristic correlation of Nusselt number,inclined angle and width ratio is fitted applying fitting software,such as 1st OPT.The results of this paper can provide useful references for scholars in natural convection of supercritical fluid,fluid flow and heat transfer in a square cavity,other similar research fields and engineering practice.