搅拌槽中垂直列管外壁表面传热系数的模拟计算

Numerical Simulation of External Heat Transfer Coefficient of Vertical Heating Tubes in a Stirred Tank

使用计算流体力学(CFD)软件CFX对搅拌槽内垂直列管外壁的温度场进行了数值模拟,根据温度分布计算了不同高度处列管外壁的局部表面传热系数和列管外壁的平均表面传热系数.搅拌槽直径D=500mm,4组对称垂直加热列管兼作挡板,搅拌桨为四斜叶桨(PBT),以甘油为工作物料,计算中雷诺数为232.研究结果表明,背向流体的列管外壁的局部表面传热系数最小,在同一列管、相同位置、不同离底高度下的最大局部表面传热系数与最小局部表面传热系数之比达到6.23;列管外壁各点局部表面传热系数沿轴向的分布差别很大,在同一离底高度、同一列管的不同位置,其最大与最小值之比达4.48,且均随着轴向离底高度的增加而减小;每根列管外壁的平均表面传热系数的最大与最小值之比为2.35,将4根列管外壁的平均表面传热系数模拟结果与文献进行了比较,发现二者基本吻合.

The commercial software CFD code CFX was used to simulate temperature profiles in a φ500 mm stirred vessel with a pitched-blade turbine （PBT）. The liquid （glycerol） was heated by four sets of vertical heating tubes symmetrically fixed in the tank and the tubes also served as baffles. The simulation of liquid flow field at the Reynolds number of 232 was used to compute the local external heat transfer coefficient on the outer surface of vertical heating tubes （hL） at different heights. The results showed that hj at the downwind side surface was the smallest, and hLmax/hLmin reached 6.23 at different off-bottom clearances of the same position on the same tube. hL varied greatly along the axis, and hLmax/hLmin reached 4.48 at the same off-bottom clearance of different positions on the same tube, it decreased as the off-bottom clearance increasing. The ratio of the maximum and minimum average surface heat transfer coefficient values of the tubes was 2.35. The CFD predictions were in good agreement with the literature.