Study On Natural Convection Heat Transfer Characteristics Of Turbulent Flow In Enclosure With Different Heat Source Structure

Natural convection is widely used in engineering practice,such as electronic equipment heat dissipation,aviation,construction engineering,aerospace systems and other fields.With the continuous development of electronic equipment towards multi-function and small volume,the problem of heat dissipation becomes more and more difficult.Natural convection heat exchange has become the main focus of research on heat dissipation due to its advantages of low energy consumption and low noise.Reducing the heat dissipation problem of electronic equipment to the heat exchange problem with internal heat source in the cavity is the main method for scholars to study the heat dissipation problem of electronic equipment.In this paper,numerical methods were used to study the effects of heat source shape,heat source quantity,heat source location,heat source size,cavity aspect ratio(H/W),air-wall coupled radiation heat transfer,heat source emissivity and temperature,and three-dimensional structure on turbulent natural convection in closed cavity.The influence of various factors on velocity,temperature,Nu number,turbulent viscosity and wall shear stress in the closed cavity was analyzed,so as to provide theoretical support for improving the cooling efficiency of electronic equipment.The main work of this paper is as follows:(1)Consider the influence of heat source structure,heat source size(r/H),heat source location,heat source quantity and aspect ratio(H/W)on turbulent natural convection heat transfer in the cavity.The results show that when a semicircular heat source is placed in the closed cavity,the average Nu number of hot wall and cold wall is the largest.The heat source size(r/H)increases gradually,and the average Nu number of the hot wall decreases gradually.When the heat source is located at the bottom of the cavity and near the hot wall,the average Nu number of the hot wall is the lowest,with a value of 38.2.When the heat source is located at the top of the cavity near the cold wall,the average Nu number of the hot wall is the highest,with a value of 59.8.The closer the heat source is to the cold wall,the better the heat transfer strength of the fluid in the cavity.The number of heat sources increased,and the average Nu number on the hot wall decreased,which reduced the fluid heat transfer efficiency in the cavity.As the cavity size(H/W)gradually increases,the average Nu Number on the hot wall first decreases and then increases.when the cavity aspect ratio(H/W)reaches2,the average Nu number on the hot wall and the cold wall are the largest,with values of 82.2and-953.6 respectively.(2)The effects of absorption coefficient and scattering albedo on turbulence parameters in a closed cavity were analyzed when the radiation heat transfer of absorbent and emitting medium was considered.The results show that as the absorption coefficient increases,the heat flux density and velocity on the hot wall surface decrease,which weakens the radiation heattransfer of fluid in the cavity.When considering isotropic scattering medium,with the increase of scattering albedo,the heat flux density and velocity on the hot wall surface decrease,which weakens the heat transfer efficiency of fluid in the cavity.Compared with considering the wall radiation,the pure natural convection increases the average Nu number of the hot wall by73%.Compared with the wall radiation,the average Nu number of the hot wall is reduced by20.5%,which is due to the absorption and scattering of the air medium weakening the heat exchange capability of the fluid in the cavity.(3)The effects of different heat source temperatures and heat source radiance on turbulent natural convection in a closed cavity are studied.The results show that the horizontal velocity of isoline increases with the increase of heat source temperature,but the heat source temperature has little effect on vertical velocity.With the increase of heat source temperature,the local shear stress in the top region of the hot wall gradually increases.The turbulent viscosity increases with the increase of heat source temperature,and the closer the heat source is to the top of the cavity,the smaller the turbulent viscosity is.The average Nu number of hot wall decreases with the increase of heat source temperature.As the emissivity of the heat source wall increases,the radiant heat flux density of the hot wall decreases,and the heat flux density of the cold wall gradually increases.The average Nu on the hot wall shows a downward trend,but the average Nu on the cold wall increases with the increase of the emissivity of the heat source ?=0.1 Compared with ?=0.9,the average Nu of hot wall decreased by 11.2%,and that of cold wall increased by 9.6%.The emissivity of the heat source has little influence on the horizontal and vertical velocity of the isoline,but from the data,the velocity increases with the increase of emissivity,Compared with ?=0.9,the speed is increased by 0.83% when ?=0.1.(4)The coupled heat transfer characteristics in a three-dimensional rectangular cavity with a built-in heat source are numerically studied.The calculation results show that the local Nu number of the hot wall under the three-dimensional condition is larger than that under the two-dimensional condition.On the cold wall surface,the local Nu number decreases gradually along the wall height direction under the two-dimensional and three-dimensional conditions.Compared with the two-dimensional results,the calculated results of the cold wall surface,the hot wall surface and the heat source surface decrease 35.4%,4.2% and 50.9%respectively.The three-dimensional effect has little influence on the local shear stress of the cold wall.