| Vertical-component density flow water-sediment gill-piece separation device (Hereinafter referred toas "gill-piece separation device"), which consists of gill-pieces and gill-duct, is a kind of new-type deviceusing for water-sediment separation.This article uses physical model experiment, numerical simulation andpilot experiment respectively, on the basis of the achieved research results about gill-piece separationdevice (GPSD) to further prove the two-phase flow field of water-sediment, reveal the mechanism ofwater-sediment separation, optimize its structure， and determine how GPSD is applied in practicalengineering.(1)The static water settlement experiments were carried out in the GPSD and in a common tubewithout gill-piece in order to study the influence of sediment concentration and gill-piece spacing on theefficiency of water-sediment separation in the GPSD. Through the physical experiment, the results areobtained as follows: Firstly, the average sediment settling velocity in the GPSD is bigger when thesediment concentration of muddy water is in the range of10~80kg/m3. So, the efficiency ofwater-sediment separation is higher. The average sediment settling velocity in the GPSD is about1.65times that of the common tube without gill-piece under the same concentration sediment of muddy water.Secondly, the average sediment settling velocity in the GPSD is biggest when the gill-piece spacing is5cm.So, the efficiency of water-sediment separation is highest. The efficiency of water-sediment separation inthe GPSD under different gill-piece spacing is higher than the common tube without gill-piece, and theaverage sediment settling velocity in the GPSD is1.4~3.25times that of the common tube withoutgill-piece.(2)The flow field of water-sediment was simulated in the GPSD through using Eulerian model andMixture model provided by fluent software. It is concluded that the Eulerian model is more suitable thanMixture model in simulating the flow field of water-sediment two phase in the GPSD by comparing withPIV measurement results qualitatively and quantitatively. And than the distribution characteristics of sediment and velocity in the GPSD was analyzed by using Eulerian model results. It is shown that averagesediment concentration and velocity distribution, which is on the upper surface and the lower surface of thegill-piece, is relevant with gill-piece location and time. The variation of average sediment velocity withtime in sediment channel is consistent with average water velocity in the water channel. And averagesediment velocity is generally bigger than average water velocity.The method of numerical simulation was used to study the effect of velocity flow field and theefficiency of water-sediment separation under the sediment concentration of muddy water, the tilt angle ofgill-piece, the gill-piece spacing and sediment grain size. Through the numerical simulation, the results areobtained as follows: Firstly, the sediment concentration of muddy water has no effect on velocity flow fieldof the GPSD. The smaller the sediment concentration of muddy water is, the higher the efficiency ofwater-sediment separation. Secondly, Velocity flow field is different in the GPSD under different tilt angleof gill-piece. Sliding tilt angle and azimuth angle of sediment on the upper surface of gill-piece are derivedaccording to the geometrical relationship under different tilt angles of gill-piece. The effect of angle β forthe efficiency of water-sediment separation in the GPSD is the largest, followed by the tilt angle α. Thirdly,the smaller gill-piece spacing is, the smaller the effect of velocity flow field comes from sediment flow inthe sediment channel and clear water flow in water channel. The optimal gills spacing is chosen as5cmconsidering water-sediment separation with high efficiency and velocity flow field of fewer disturbancesbetween the gill-piece, the result is consistent with physical model experiment result. Fourthly, the velocityflow, when sediment grain size is0.0001mm, is different with sediment grain size as0.005mm to0.035mm.(3) This article, which is according to the three aspects of structure type, characteristics of the flowfield and average sediment concentration in height direction, have revealed the mechanism to acceleratewater-sediment in the GPSD combining with the experiment and simulation results.(4)The experiment of water-sediment separation, which was in gill-piece separation device in closetype sedimentation tank (GPSDCTST), gill-piece separation device in open type sedimentation tank(GPSDOTST) and the sedimentation tank of no the GPSD respectively, was studied by using pilotexperiment method under the static and dynamic water. It can be seen that change of effluent turbidity with time in the static water precipitation can be divided into two stages, which turbidity diminishes quicklystage and turbidity slowly decrease stage. Hydraulic loading has great effect on the turbidity change indynamic water settlement. The smaller hydraulic loading is, the smaller the value of effluent turbidity is.Meanwhile the higher the efficiency of water-sediment separation is. When the hydraulic loading reaches athreshold value, the GPSD in two new sedimentation tanks is useless. The efficiency of water-sedimentseparation is the same as the sedimentation tank of no GPSD. The efficiency of water-sediment separationin GPSDCTST is higher than other two sedimentation tanks on the whole. |
PDF Full Text Request