2007 Volume 2 Issue 1 Pages 238-247
This study focuses on the mixing process of the driving jet and the induced flow in the throat to improve the efficiency of jet pumps used in Boiling Water Reactors. The effect of nozzle and throat shapes on the performance of jet pumps are examined experimentally under normal temperature and small-scale model conditions using three kinds of nozzles (i.e., circular, notched, and flower-shaped) and two kinds of throats (i.e., conventional straight throat and diverging throat with a very gentle gradient). A nozzle throat area ratio, which influences the flow rate ratio at peak efficiency, is kept constant to avoid significantly changing the flow rate ratio. The velocity profile and local skin-friction coefficient in the throat are investigated experimentally to evaluate the effect of nozzle and throat shapes on the mixing process. The following results are obtained. The diverging throat reduces skin-friction loss and improves efficiency for all three nozzles. The efficiency curve of the circular nozzle with eight notches slightly shifts to higher flow rate region by the reduction of the jet size compared with the circular nozzle. The flower-shaped nozzle decreases efficiency owing to the increase of the skin-friction loss caused by enhanced mixing. The circular nozzle with a diverging throat improves the peak efficiency about 2% without changing the nozzle throat area ratio.
