Study On Water Block Characteristics For Feculence-Blocking Of Pumping Station

The effect of Feculence-blocking and Feculence-clearing on safe and economic operation of pumping station and hydropower station is great. The applied fundamental research of water blocking characteristics for Feculence-blocking of pumping station was developed under the financial of Project Supported by National Natural Science Foundation of China (No:51079125) and "333high-level talents training project" Foundation of Jiangsu province and so on.The type, composition, geometrical, ups and downs and flow characteristics of river trash were researched. The laboratory was converted, and the feculence-blocking experimental setup was designed and maked. The feculence-blocking experiment was conducted by changed combinations of trash kinds, flow rate, water depth and so on, and feculence-blocking resistance and flow regime were measured. The motion and aggregation feature of different kinds of trash in front of trash rack were revealed, and the relationship of feculence-blocking resistance with related factors was established. The formation mechanism of feculence-blocking resistance was initially revealed. The main research works and results are as follows:(1) River trash can be divided into three main types, they are aquatic plants class, flexible sheet class, hard floating class. In local place, these trashes are respectively given priority with alternanthera philoxeroides and grass; old clothes, plastics and polypropylene woven bags; dead branches, foam plastics and plastic bottle. Usually, the specific gravity of aquatic plants is0.5～1.0; and for flexible sheet trash, the specific gravity of plastics and polypropylene woven bags is less than0.5and the specific gravity of old clothes is slightly greater than1.0; the specific gravity of hard floating trash is less than0.5. Trash which specific weight is much less than1.0raft on the surface of water and move with flow, and trash which specific weight near1.0suspension in the water and move with flow.(2) Flexible sheet trash which suspension in the water are easy to accumulate the trash rack surface, their resistance effect is strong. Hard floating trash have no resistance effect essentially because they raft on the surface of water and are hard to descent. But for wide ranged and large quantity of aquatic plants, they raft on the surface of water and spread towards upstream when flow rate is smaller than critical velocity, they only block a small part of upside surface, and feculence-blocking resistance is very small; the subsequent trash descent with flow and block big part trash rack surface superincumbently when flow rate is greater than critical velocity, the flow section decreases gradually, and its upper limb far away from water surface, feculence-blocking resistance increase rapidly still the subsequent trash can not descent, and resistance reach its limits. Trash that gather at the upside surface are easy to be observed and salvaged. Trash which have big specific weight block surface bottomup. Trash that gather at the downside surface are not easy to be observed and salvaged, and the harmfulness they made is great.(3) The resistance effect of flexible sheet trash is greater than aquatic plants. The resistance of blocking polypropylene woven bags is greatest, The resistance of bloceing jean and cotton cloth takes second place. The resistance of blocking grass is greater than blocking alternanthera philoxeroides. For aquatic plants, the feculence-blocking resistance increases on open up parabola with trash quantity when flow rate is greater than critical velocity. Parabola linetype can be related to the characteristics of trash. The intercept trash resistance increases on open down parabola with flow rate at first, then growth rate slowing down. For flexible sheet trash, the feculence-blocking resistance increases on parabol with flow rate. The feculence-blocking resistance decreases on straight line or parabola with water depth, then it intends to straight line when water depth increases to certain value, resistance changs little with water depth.(4) Trash that have small specific weight block upside trash rack surface, for section that in front of trash rack, flow rate in upper been decreased and flow rate in lower been increased, orientation of flow rate been deflected toward downward, for section that in behind of trash rack, flow rate in upper been decreased and flow rate in lower been increased similarly, but the differences are greater, severe cases can appear obvious back-flow and tumbling, flow regime been seriously got worse. Trash that have big specific weight block downside surface, flow rate in upper been increased and flow rate in lower been decreased for section that in front and in behind of trash rack, orientation of flow rate been deflected upward for section that in front of trash rack and orientation of flow rate been deflected downward for section that in behind of trash rack.