摘要
离心油泵的叶轮口环是离心油泵的重要零件之一。它不但影响离心油泵运行可靠性，而且还影响其水力性能。但目前仅研究了输送清水时口环间隙对离心泵性能的影响情况，对离心油泵还没有。输送粘油时，口环间隙对离心油泵性能的影响更是一无所知。
本文以油田和炼油厂常用的65Y60型为研究对象，分别改变叶轮前口环、后口环和同时改变前后口环间隙，较为系统地研究了不同粘度下，口环间隙分别由原来的0.25mm增加到0.45mm、0.65mm和0.85mm时，对离心油泵性能的影响情况和变化规律。另外，还采用CFD软件Fluent对叶轮和泵壳体之间的粘性旋转液流进行二维数值计算研究，从理论上分析了口环间隙对泵性能影响的流动机理。这些研究旨在为离心油泵设计、实际运行提供指导，丰富离心油泵工作理论。通过详细研究，取得了以下研究成果：
(1)前后口环间隙对离心油泵性能影响的程度不同。前口环对泵性能的影响比后口环大，前口环间隙需重点控制。前后口环间隙同时增大时，性能下降最多，应尽量避免。
(2)口环间隙对离心油泵性能影响与被输送液体粘度有关。粘度增高，会使口环间隙对离心油泵性能的影响减弱，反之，则增强。
(3)口环间隙影响离心油泵最优工况参数。在本文试验条件下，口环间隙增大后，最多可使最优工况流量增加2m~3／h或减少3.5m~3／h，使最优工况扬程最多下降11％，使最优工况轴功率最多增大13％，使最高效率最多降低8％。
(4)口环间隙通过改变离心油泵的容积损失功率和机械损失功率(叶轮圆盘摩擦损失)影响离心油泵性能。计算表明，容积损失功率随口环间隙而大幅度增加，机械损失功率随口环间隙而减小，但其减小值小于容积损失功率的增加值，所以口环间隙增大后，泵效率下降。
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.
引文
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