封闭方腔内叉排管间熔融盐自然对流换热

Natural Convection Heat Transfer of Molten Salt in a Closed Square Cavity with Staggered Tube Bundle

以硝酸锂熔融盐为流体介质,对封闭方腔内交叉排布的四根热管间的介质自然对流换热进行了数值模拟,研究了热管不同位置和不同瑞利数对方腔内介质自然对流换热特性的影响。结果表明:管间距ε=0.5时,腔体内温度场和流场的对称性开始打破;ε=0.4和0.5时,下管及左右两管产生的热羽流冲刷上管热边界层,使上管局部Nu_φ分别在圆周角φ=180°、φ=280°和φ=80°处出现增强;ε=0.6时,上管不再受下管羽流影响。随着管间距增大,上管平均Nu_m越来越小,下管Nu_m越来越大;ε=0.4~0.6时,管间距对左右两管Nu_m影响很小,但ε=0.7时,左右两管平均换热均明显增强。

A numerical simulation was carried out to investigate natural convection heat transfer around four heating tubes positioned in a closed square cavity with the staggered array. With the molten salt lithium nitrate as working fluid,the effects of the heating tubes location and the Rayleigh number on the heat transfer and fluid flow in the cavity were studied. The numerical results showed that the symmetry of the temperature and flow fields in the square cavity is broken with the tube pitch ε = 0. 5. For ε = 0. 4 and 0. 5,the thermal boundary layer around the upper tube isscoured by the up-welling plumes produced by the ambient tubes,and the local Nusselt number on the upper tube surface has a local high peak at circumferential angle φ = 180° due to the plume of the lower tube. Meanwhile,the upper tube has two local high values of local Nusselt number at around φ = 280° and φ = 80° by the plumes of the left and right tubes,respectively. When the tube pitch increases to 0. 6,the upper tube is no longer affected by the plume of the lower tube. The averaged Nusselt number of the upper tube decreases and that of the lower tube increases with the tube pitch. When ε = 0. 4-0. 6,the tube pith has little effect on the averaged Nusselt number of the left and right tubes,while,for ε = 0. 7,the averaged Nusselt number of the left and right tubes has a clear enhancement.