Optimization of pumping power of gas-cooled fuel element

For each specified permissible rod-surface temperature (theta), the optimum ratio of pin pitch to rod diameter P/d was obtained, which gives minimum pumping power in a rod bundle. Assuming uniform heat flux, a 9-rod square bundle and a 7-rod circular bundle were analyzed on the basis of the similar method used in the previous work by the authors. As for the 9-rod bundle, the results of heat transfer experiment by Marek et al. were used. A series of equations was developed to obtain the pumping power as a function of P/d. The results showed that the optimum P/d ratio is between 1.64 and 1.71 for a realistic range of theta of gas-cooled reactors. In case of the 7-rod circular bundle, the coefficient of friction obtained from the experiment by the authors was used instead of Rehme's equation. The results of experiment are shown by taking P/d as a parameter, and compared with the results with Rehme's equation. The authors' results are about 30 or 40% larger than those with Rehme's equation. The curves representing the relation between pumping power and P/d are also shown for both two friction coefficients mentioned above. Both curves have a minimum at P/d of 1.51 and 1.42, respectively. (Aoki, K.)