PERFORMANCE STUDY OF A JET PUMP

Abstract

Theoretical and experimental study on the jet pump has been carried out in this work. The contribution of the theoretical study primarily includes derivation of the governing equations for jet pump with different primary and secondary fluids, analysis of the effects of different density ratios of primary to secondary fluids on the pump performance, and estimation of the ideal pump efficiency. By using the common energy loss equation of the diffuser, one-dimensional theory was used to predict the jet pump performance with the same and different primary and secondary fluids. The results indicate that the maximum pump efficiency and the corresponding flow rate ratio increases with increase in density ratio. The energy loss in the jet pumps was analyzed in detailed by dividing it into friction loss, jet loss and mixing loss.

The jet pump ideal efficiency was systematically analyzed and also compared with those reported for jet pumps with the same primary and secondary fluids. The jet pump ideal efficiency was derived under three different conditions: for the same density of the primary and secondary fluids, for different densities of the primary and secondary fluids, and for liquid-jet gas-liquid (LJGL) pump. The results show that the ideal efficiency increases with the velocity ratio of the secondary to primary flow streams at the mixing throat entrance. It approaches to a maximum value of 100% for liquid jet gas liquid pump and liquid-jet liquid pump with density ratio of the primary to secondary fluids not less than unity at velocity ratio of unity. The maximum value of the ideal efficiency of liquid-jet liquid pumps with the density ratio less than unity is the value of density ratio and it occurs when the velocity ratio is equal to the density ratio.

The experiments were also conducted to verify the effects of different area ratios of nozzle to mixing throat ranging from 0.15 to 0.40 on the jet pump performance. Then, the effects of different nozzle exit shapes of circle, triangle, and square, on the jet pump performance were studied. The results show that the jet pump with circular nozzle exit and the area ratio of about 0.3 is the most efficient.

Based on the one-dimensional theory, the individual energy losses occurring in the jet pump were also calculated. It is clearly shown that the mixing loss and friction losses in the mixing throat and diffuser, respectively, are primarily responsible for the low jet pump efficiency. This experimental study on the limiting flow condition confirms that the limiting flow condition may occur in the jet pump when the jet velocity increases or when the delivery pressure decreases. The experiments also show that the effect of suction pressure on the limiting flow condition is indirect, and the limiting flow condition results in a sharp drop in the jet pump performance. However, the jet pump operation is still stable under the limiting flow condition. Visual observations in the mixing throat reveal that bubbly flow occurred well before the limiting flow condition. The experimental results on the effect of suction pressure on the limiting flow condition and of stable pump performance under the limiting flow condition are added contributions to the jet pump literature.