Influence Mechanism and Effect of Rotary Shell Speed on Roto-Jet Pump Performance

Abstract

The roto-jet pump mainly features the synchronous rotation of the impeller and the rotary shell as the structure, which is beneficial to reduce the friction loss of the disc and improve the pump efficiency. The synchronous rotation state of the impeller and the rotary shell, however, does not represent the optimal operating condition of the roto-jet pump. In order to examine the mechanism and the effect of the rotary shell speed on the performance of the roto-jet pump, an experimental research was carried out under two states, namely, rotating and fixed rotary shell, using the open test bench of the roto-jet pump as the research object. A simulation test was performed at rotating shell speed ratio i = 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6. The results show a relatively high entropy production and dissipation at the inlet of the collecting pipe and the outlet of the impeller at each operating point, and a large energy loss. In addition, the energy loss in the wall area of the rotary shell is basically proportional to the rotational speed of the rotary shell. The collecting pipe has a significant influence on the vortex structure inside the rotary shell, and the surrounding vortices are mainly generated on the upstream surface and the wake area of the collecting pipe. At constant impeller speed, the radial pressure gradient of the liquid in the rotary shell can be increased by increasing the rotary shell speed. The liquid pressure in the area of relative radius s smaller than 1 corresponds inversely to the rotary shell speed, while the liquid pressure in the area of s larger than 1 corresponds proportionally to the rotary shell rotating speed. The minimum value of the total disc friction loss for this pump occurs at position i = 0.8. At this point, the friction loss of the impeller disc is 83.8% of the total loss. The friction loss of the rotary shell disc is 16.2%, and the pump efficiency has the highest value, 1.3% higher than that of the rotary shell synchronous rotation operating point. The optimum rotating speed ratio between the rotating shell and the impeller is 0.8, and the research results can be a reference for the differential operation of the impeller and rotary shell of the roto-jet pump.