Natural Convection Heat Transfer from Horizontal Rod Bundles in Liquid Sodium

本文通过实验和理论计算，得到了在0 ~ 90 °范围内，垂直方向与两圆柱轴线所在平面之间的夹角γ对两平行水平圆柱在液体钠中自然对流换热系数的影响。两个试验圆柱体的直径为7.6 mm，加热长度为50 mm，每个圆柱体轴线之间的距离与圆柱体直径的比值S/D为2。采用PHOENICS程序对水平双圆柱层流自然对流换热的理论方程进行了数值求解，计算条件与实验条件相同。在修正的瑞利数R_f范围为0.0637 ~ 63.1（q=1*10^4-7*10^6 W/m^2）时，每个圆柱体的表面热通量相等。将实验得到的圆柱体平均努塞尔数Nu与相应的理论值进行了比较，得到了Nu与修正瑞利数R_f [=Gr^**>Pr^]的关系曲线。 ...更多信息 2/（4+ 9 Pr ^<1/2>+10Pr）]图。除γ =0时R_f<4外，其它两个圆柱体的Nu理论值与实验值在各γ下均符合，偏差小于15%。基于理论解，得到了两个圆柱体的相关性作为S/D和γ的函数。在双圆柱相关式的基础上，提出了一种垂直排列五圆柱的组合相关式。对于R_f为4.7 ~ 63的五个圆柱体，计算值与理论值相差10%以内。对水平排列的Nx*Ny（Nx，Ny=5-9）棒束的自然对流换热进行了数值模拟，分析了3种不同排列方式（顺排和2种交错排）下棒束的自然对流换热。棒束的S_x/D和S_y/D（横坐标和纵坐标上的中心轴之间的距离与棒直径的比值）在每种棒束几何形状下的范围为1.6 ~ 2.5。计算<av>了不同S_x/D和S_y/D的三种管束几何形状的平均努塞尔数Nu_，考察了管束尺寸、S/D和R_f对换热的影响。Nu_f<av>随R_f值的减小而减小，随S_x/D和S_y/D值的增大而增大<av>。在<av>（S_x/D）*（S_y/D）=4的条件下，通过改变S_x/S_y的比值，研究了高Nu值的丛几何。在<av>考虑S_x/D和S_y/D影响的情况下，建立了上述三种几何形状的Nu_（？）该关联式可描述<av>Nx*Ny（Nx，Ny=5-9）阵列中三种束几何结构的Nu_（？）理论值，S_x/D和S_y/D在1.6 - 2.5之间，相差不超过10%。少

Natural convection heat transfer coefficients on two parallel horizontal test cylinders in liquid sodium were obtained experimentally and theoretically for various setting angles, gamma, between vertical direction and the plane including both of these cylinder axis, over the range of zero to 90ﾟ. Both test cylinders are 7.6 mm in diameter and 50 mm in heated length with the ratio of the distance between each cylinder axis to the cylinder diameter, S/D,of2. Theoretical equations for laminar natural convection heat transfer from the two horizontal cylinders were numerically solved for the same conditions as the experimental ones by using the PHOENICS code. The surface heat fluxes for each cylinder were equally given for a modified Rayleigh number, R_f, ranging from 0.0637 to 63.1 (q=1*10^4-7*10^6 W/m^2). The average Nusselt numbers Nu on the cylinders obtained experimentally were compared with the corresponding theoretical values on the Nu versus modified Rayleigh number R_f [=Gr^<**>Pr^ … More 2/ (4+9Pr^<1/2>+10Pr)] graph. The theoretical values of Nu on two cylinders except those for R_f<4at gamma=0ﾟ are in agreement with the experimental data at each gamma with the deviations less than 15 %. Correlations for two cylinders were obtained as functions of S/D and gamma based on the theoretical solutions. A combined correlation for five cylinders in a vertical array based on the correlations for two cylinders was developed. The values by the correlation agree with the theoretical solution for the five cylinders for R_f ranging from 4.7 to 63 within 10% difference. Natural convection heat transfer from horizontal rod bundles in Nx*Ny arrays (Nx, Ny=5-9) was numerically analyzed for three types of the bundle geometry (in-line rows, two kinds of staggered rows). S_x/D and S_y/D for the rod bundle which are ratio of the distance between center axs on the abscissa and the ordinate to the rod diameter were ranged from 1.6 to 2.5 on each bundle geometry. The average value of Nusselt number, Nu_<av>, for three types of the bundle geometry with various values of S_x/D and S_y/D were calculated to examine the effect of the array size, S/D and R_f on heat transfer. The Nu_<av> becomes lower with the decrease in the value of R_f and higher with the increase in the value of S_x/D and S_y/D.The values of Nu_<av> with the same combinations of S_x/D and S_y/D values are almost in agreement independent of the bundle geometry. The bundle geometry for the higher Nu_<av> value under the condition of (S_x/D) * (S_y/D)=4 was examined by changing the ratio of S_x/S_y. A correlation for Nu_<av> for three types of bundle geometry above mentioned including the effects of S_x/D and S_y/D was developed. The correlation can describe the theoretical values of Nu_<av> for three types of the bundle geometry in Nx*Ny arrays (Nx, Ny=5-9) for S_x/D and S_y/D ranging from 1.6 to 2.5 within 10% difference. Less