Abstract:The influence of reducing nD value on hydraulic performance of a large pump system with low head was discussed from the point of view of pump type selection,energy performance and cavitation performance,and the design idea of reducing nD value for the pump system was put forward.The consistent relationship between reducing nD value and increasing impeller diameter and reducing pump speed was derived according to the affinity law of pumps.If the pump diameter increases by 5% under the condition of a certain design discharge,the pump speed and nD value will decrease by 13.6% and 9.3%,respectively.The effect of reducing nD value on increasing pump system efficiency was analyzed from the point of view of influence of impeller diameter on the conduit hydraulic loss.Based on the relation between nD value and pump head,it was put forward to reduce nD value for selecting the more excellent axial pump hydraulic model under the condition of low head.According to the cavitation affinity law of pumps,the influence of reducing nD value on the cavitation performance of the pump system was analyzed.Meanwhile examination index for the cavitation performance of the pump system and the influence of increasing impeller diameter and reducing pump speed on the conduit control sizes and equipment investment were also discussed.The research results indicate that if the pump diameter increases from 2.9 m to 3.1 m for a pump system with the average head of 4 m and single pump design discharge of 33.5 m3/s the conduit efficiency will increase by 2.9%.If the nD value decreases from 435 to 387.5 under the condition of a certain design discharge,the pump head at the high efficiency zone of the hydraulic model TJ04-ZL-06 will lower from 5 m to 4 m and the pump NPSHR will reduce by 20.6%.It suggests that a lower nD value should be adopted for a large pumping station with low head and long running operation time.
梁金栋, 陆林广, 徐磊, 陈伟. 大型低扬程泵装置nD值的选取[J]. 排灌机械工程学报, 2011, 29(3): 236-240.
Liang Jindong,Lu Linguang,Xu Lei,Chen Wei. Selection of nD value for low head pump system of large pumping station. Journal of Drainage and Irrigation Machinery Engin, 2011, 29(3): 236-240.