Mud flow state and the corresponding critical flow rate in the sludge discharge pipe
Mud flow state in the sludge discharge pipe is an important factor causing the head loss in the discharge pipe, which has close relationship with the flow rate in the discharge pipe and the mud composition, the particle size as well. According to the flow rate and the different particle size, the mud flow state in the discharge pipe can be divided into four kinds:
(1) uniform flow-Vh
(2) Quasi-uniform flow-Vsu;
(3) non-uniform flow, the upper suspension, bottom transport-Vc;
(4) Non-uniform flow with a silt layer at the bottom-Vd.
Schematic diagram of flow velocity, particle size and flow state
(1) Principle of selecting practical flow rate
The actual flow rate used in the dredging pipe is called practical flow rate, which should be carefully selected from the perspective of economic rationality.
That is,whether the selection is appropriate or not has a great influence on the dredging efficiency. When drainage pipe in the selection of the flow rate is too large, beyond the Vh value is too much, although the mud to achieve a uniform flow state, but the mud pump power consumption increases a lot, suction and discharge of mud in the pipe resistance head loss increases, and because of the lift of mud with the specific gravity of the head of water caused by the lack of slurry concentration. If discharge pipe flow rate is too small, to reach or less than Vd , discharge pipe silt base to silt blockage, resulting in production reduction or stoppage. Therefore, the practical flow rate in the mud discharging pipe should be selected between Vc and Vsu , depending on the thickness of sediment particles, pipeline layout. For the grain suction dredger and poop suction dredger,it should make the flow rate and mud concentration to get the maximum earth as the principle.
Select practical flow rate
Influence upon pipeline slurry movement comes from many factors, which makes movement mechanism very complex. Although there have been many studies, but are concentrated in the laboratory range.Laboratory test is under test conditions such as pipe diameter can not be too large and other limitations, which coupled with other factors affecting the mud movement characteristics in the process of the actual evacuation more complicated than the laboratory limitations or assumptions of the conditions, so the results of the laboratory research from the quantitative application is quite different from actual situation, the practical selection of flow rate to a greater extent depends on the accumulation of practical information and experience.
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