Study on the optimum mixing throat length for drive nozzle position of the central jet pump

The present paper describes a numerical prediction of optimum mixing throat length for various drive nozzle positions of the central jet pump. The flow pattern and pressure distribution in the pump for various positions of the drive nozzle are investigated by three-dimensional numerical analysis using the RNG k-epsilon turbulent flow model. Numerical analysis was carried out for values of the nozzle throat ratio d/D of the jet pump of 0.5, 0.6 and 0.7, respectively. The static pressure in the flow field of the jet pump is calculated for the following conditions: (1) drive nozzle position from the entrance of the throat l/D = 0 similar to 2.0, (2) flow rate ratio M= 0 similar to 1.2, and (3) Reynolds number Re = 3.6x10(5). These calculations revealed that (1) the optimum length of the mixing throat for l/D = 0 similar to 1.0 is Lm/D = 2.0 similar to 3.5, (2) the length of the mixing throat for l/D = 0 and M = 0 (suction flow rate ratio = 0) is approximately Lm/D= 3.5, and (3) the maximum efficiency is obtained for d/D= 0.6 at l/D= 0.5. Moreover, the flow pattern in the mixing throat is clarified through a spark tracing experiment. The results obtained in the visualization experiment and the numerically obtained mixing length agreed well.