Natural Convection Heat Transfer Of A Cylinder And Array Of Cylinders Based On Laser Shearing Interferometry

Natural convection heat transfer exists in situations that there is no forced velocity and it is induced by buoyancy force resulting from the temperature dependent density gradients in the fluid.It is commonly encountered in industrial and environmental applications.The natural convection heat transfer of single cylinder and an array of cylinders have attracted many researchers'attention.Large lateral shearing interferometry,as a kind of laser interferometry with simple output fringes and strong anti-interference ability,has been widely used in the detection of temperature fields.The rapid development of computer technology and numerical algorithms has promoted the advancement of computational fluid dynamics.Using numerical simulation to predict fluid heat transfer has become an indispensable part of heat transfer research.These two research methods were used to analyze the natural convection heat transfer of single elliptical cylinder,three elliptical cylinders,single horizontal cylinder and double horizontal cylinders.A numerical study has been carried out in order to investigate natural convection heat transfer from an elliptical cylinder.Two structures of infinite space and confined space were considered.Natural convection heat transfer of the elliptical cylinder under different deflection angles was investigated.The results show that the maximum heat transfer of the elliptical cylinder is always located on the major axis away from the plume flow side and the minimum is near the plume flow.The natural convection of a confined elliptical cylinder at different inclinations has been studied over the range of Rayleigh number 10~3~10~5.The results show that the maximum heat transfer increases obviously with the increase of Rayleigh number,but the minimum was basically unchanged.A numerical study was carried out to investigate natural convection heat transfer from a vertical array of three elliptic cylinders in a rectangle enclosure.The effect of distance between the upper wall and the uppermost cylinder,the distance between the cylinders and the axis ratio of each cylinder were considered.It was found that the effect of the uppermost cylinder was the most affected by the upper wall and had a maximum influence distance;The blocking effect was the main factor when the cylinder spacing was relatively close,and the Nusselt number of the cylinder directly contacting with plume increases significantly with the increase of cylinder spacing;Reducing the axis ratio of elliptic cylinder can increase the heat transfer but when the axis ratio is less than 0.25,the heat transfer cannot continue to increase.Large lateral shearing interferometry was conducted for the natural convection heat transfer of a single horizontal cylinder with the Rayleigh number in the range of2.4×10~4~1.2×10~5.The local Nusselt number and the average Nusselt number were calculated.The experimental results were compared with many existing results,and the range of Rayleigh number in previous experimental research results was broadened,which provides an experimental reference for the natural convection of the horizontal cylinder under the large Rayleigh number.Large lateral shearing interferometry was conducted for the natural convection heat transfer from two horizontal cylinders set in a horizontal array with the Rayleigh number in the range of 10~3~10~4 and the cylinder spacing S/D=1.3,1.8 and 2.7.The local Nusselt number and the average Nusselt number of the cylinders under different conditions were calculated.The results were also compared by using numerical method.The effects of cylinder spacing and Rayleigh number on the heat transfer from the individual cylinder and the array were investigated.In summary,this paper expects to lay a theoretical foundation for heat transfer research of cylinder structures and provide reference for engineering applications.