Experimental study of the mouth ring gap on the influence of centrifugal pump performance
|School||Lanzhou University of Technology|
|Course||Fluid Machinery and Engineering|
|Keywords||centrifugal oil pumps performance wear ring clearance disk friction loss CFD|
This research issues is one part of a project, which was fully supported by the Key Research and Development Program for Outstanding Groups at Lanzhou University of Technology in 2002.The wear-rings of impeller are one of important components of centrifugal oil pumps. The rings not only have negative influence on operation reliability but also affect hydraulic performance of the pumps. However, the effects of the clearance of wear-rings on centrifugal pump performance have been attacked only while handling water, the effects of clearance on centrifugal oil pump performance never have been done currently. Nevertheless, We know nothing about effect of the clearance on centrifugal oil pump performance when pumping viscous oils.The centrifugal oil pump of type 65Y60, which is widely utilized in oilfields and refineries, is selected as a test model here. The effects of wear-ring clearance on the pump and hydraulic parameters variations at best efficiency points have been investigated more systematically via experiments when pumping water and viscous oil with various viscosities. When the experiments were performed, the clearances of wear-rings on shroud, on hub as well as on both shroud and hub were enlarged from original 0.25mm to 0.45mm, 0.65mm and 0.85mm respectively. Meanwhile, the two-dimensional, rotating flow fields of viscosity liquids in spaces between impeller shrouds and casing have been computed numerically by using Fluent, a CFD code, and this caused a flow mechanism, which was associated with the clearance how to affect the pump performance, to be analyzed. The aim of those investigations is to set up guidelines to design and operation of the centrifugal oil pumps and to provide deeper insight into flow theory and performance features of the pumps. Through detailed study, the following conclusions can be made:(1) The influence extent of clearance of wear-rings on shroud on the performance differs from that on hub. The clearance of wear-rings on shroud affects the performance stronger than that on hub. As a result, this clearance should be controlled strictly. When both clearances of wear-rings on shroud and hub are enlarged simultaneously, the performance greatest drops, therefore this situation must be avoided.(2) The effect of the clearance on the performance is concerned with the viscosity of handling liquid. The increase in viscosity will lead to the effect to be weakened, vice verse.(3) The hydraulic parameters at best efficiency point can be influenced by the clearances. Under current experimental conditions of the thesis, the increase in the clearances will cause the maximum changes of +2m3/h or -3.5m3/h in flow rate, -11% in head, +13% in shaft power and -8% in efficiency respectively at best efficiency point.(4) The pump performance would be affected by the two clearances in such a way that the clearance alters both volumetric leakage power loss and mechanical power loss (dick friction loss of impeller). The numerical and analytical results show that the volumetric power loss increases significantly, and the mechanical power loss decreases a little as the clearance being enlarged. However, the net decrease value in the mechanical power loss is less than the net increase in the volumetric power loss. Thus, the pump efficiency will descend while the two clearances increase together.