Optimal design and experiment of submerged grinder pump grinding device

Abstract: With the rapid development of industry and agriculture, more and more fiber and other impurities are doped in the sewage, but the ordinary sewage pump is easy to be blocked in operation and has been unable to meet the requirements of transport medium which contains high fiber impurities, so the sewage pump with auxiliary cutting grinding device (i.e., non-jamed submerged grinder pump) has been widely applied. How to ensure the grinding effect and high efficiency has become one of the hotspots in the research field of submerged grinder pump. This paper uses the software ANSYS-CFX to conduct steady and unsteady calculations for the non-jammed submerged grinder pump. Combined with the features of submerged grinder pump, the hydraulic design and the three-dimensional modeling are conducted for the main flow passage components of the grind pump, the structured hexahedral mesh and the grid-independent test for the model, and also numerical simulation and experimental verification are made for the external characteristics of non-jammed submerged grinder pump. The paper analyzes the most important factors which affect the external characteristics of non-jammed submerged grinder pump to search the optimization method of the grinder pump, and the results show that the installation of grinding device has great influence on hydraulic performance of the submerged pump, there is a decline in the grinding pump lift, the point of maximum efficiency shifts to the low flow rate condition, the pump efficiency is reduced, and the shaft power consumption increases about by 40% compared with that without grinding device. Through the study of submerged grinder pump model with 3 different radial clearances of dynamic and static cutter which are 1, 1.5 and 2 mm, it is found that the better grinding effect goes along with the smaller cutter radial clearance, and with the decrease of the dynamic and static cutter's radial clearance, the submerged grinder pump lift drops and especially under the large flow condition, the shaft power increases, the highest efficiency values decline and the high efficiency area is narrowed, but no overload performance of the submerged grinder pump improves. Through the study of submerged grinder pump model with 3 different cutter head numbers which are 2, 3 and 4, it is found that the cutter head number has greater effect on the hydraulic performance of the submerged grinder pump compared with the dynamic and static cutter's radial clearance; the increase of cutter head number and crowding coefficient at the pump inlet will increase the hydraulic loss, and coupled with cavitation intensified at the cutter heads of the grinding device, the loss at the grinding device increases significantly, resulting in the drop of pump lift, the overall efficiency decline and the overall shaft power increase, so under the premise of guaranteeing cutting grinding effect, it should try to use less cutter head number as far as possibly, and the optimum number is 2. Through comprehensive analysis, the optimal design of GSP-22-type non-jammed submerged grinder pump is that its dynamic and static cutter's radial clearance is 1.5 mm and its dynamic cutter head number is 2, which takes the ground pump hydraulic performance and grinding effect into account, and provides theoretical guidance for the optimal design of submerged grinder pump.