Analytical Study of Heat Transfer to Liquid Metals Flowing In-Line Through Closely Packed Rod Bundles

Circumferential variations of temperature and local heat transfer coefficients were obtained for sodium flowing in-line through a staggered rod bundle. The conditions of the study were: turbulent flow, uniform heat flux from the surfaces of all rods, and fully developed velocity and temperature profiles. The rods were spaced in an equilateral triangular array, and the pitch:diameter (P:D) ratio was varied down to 1.10. It was shown that the annulus model is satisfactory for estimating average heat transfer coefficients for P:D ratios down to about 1.3, but below this, it gives increasingly high results, e.g., at P:D = 1.10, an annulus-model coefficient can be high by about a factor of 2. It was found that circumferential temperature variations are not large, e.g., at P:D = 1.10, this variation is about twice the average temperature drop from the rod surface to flowing metal. Compared to the P:D ratio, the Peclet number has little influence on the reduction in the average heat transfer coefficient, or the circumferential variation of the surface temperature. At a P:D ratio of 1.40, the local coefficient is estimated to vary by a factor of only 1.2; at 1.20, by a factor of 1.7; and at 1.10, by a factor of ≈ 100.