Influence of Gas-Liquid Multiphase-Flow on Acoustic Behavior and Performance of Side Channel Pumps

Abstract

Side-channel pumps (SCP) are a niche product, able to deliver relatively high heads at low flow rates, which corresponds in a low specific speed. They are closing the gap between classical radial centrifugal pumps and positive displacement pumps, combining the advantages of both without having all the negative effects. The hydraulic efficiency of SCP seems low at first sight. But classical centrifugal pumps are often working under part load conditions, when working at this volume flow and specific speed range, which means they are not able to perform at their BEP. This reduces the efficiency of centrifugal pumps and creates a major benefit of SCP, which are able to work in their BEP. The acoustic behavior and the characteristic pulsations and vibrations of a side channel pump are measured with various measurement methods, such as vibrometry, sound level measurement and sound cartography using an acoustic camera. The characteristic vibrations are shown and compared to the characteristic pressure-pulsations of the working fluid. The two-phase liquid-gas flow has, beside the effects on the characteristic curves such as head drop and efficiency reduction, many side effects on the behavior of the pump. This could be acoustical and vibrational effects. When gas is present in the working fluid, the emitted noise from the pump reduces significantly. This effect is shown by sound intensity measurements as well as measurements with an acoustic camera and laser vibrometry and compared to the results for single-phase flow. The maximum amount of gas for the test pump is measured at different rotational speeds. Some theories to improve the maximum amount of gas in the working fluid are presented and the modifications are tested on a test rig. These modifications consist of the idea that a pump without NPSH-impeller could process higher amounts of gas in multiphase-flow conditions. An additional gas outlet hole is added to the pump to allow a phase separation and therefore a better two-phase flow handling of the pump. The effect of these changes on the maximum amount of gas are presented and evaluated.