(1) When Z (2) Critical conditions for sediment to start to suspend When Z = kU≥5, the sediment basically moves in the form of traverse, otherwise, the suspending motion begins to appear.
(3) There are many critical flow rates U0 corresponding to the lowest value in the Jm ~ U relationship curve. Researchers believe that the lowest point of the Jm ~ U relationship line is equivalent to the critical situation when sediments appear at the bottom of the pipeline. From Figure 1, the criticality There are some differences between the flow rate UL and the critical deposition flow rate Uc, but the difference is not large.
(4) Critical non-silt flow rate In the pipeline water delivery system, in order to prevent pipeline blockage caused by sediment deposition in the pipe bed during the water delivery process, the concept of critical non-silt flow rate was proposed. The critical non-silt flow rate is the minimum average flow rate at which no sediment appears at the bottom of the tube. So, how to define and judge the critical non-silting flow rate of pipeline water conveying system? Because the sediment content in pipeline water conveying irrigation system is generally low (less than 15%), pipeline clogging is a gradual accumulation process. In the experiment, Jm-U The concave point of the relationship curve is not obvious. Therefore, based on this point of view, the graphical method is used to determine the non-silt flow rate of the pipeline, which is not suitable for the determination of the non-silt flow rate of the pipeline water delivery irrigation system.
According to the test data, referring to the formulas of Schuk and Durand, through regression analysis, the empirical formula for the critical non-silt flow rate of muddy water pipelines is: Uc = 0.2799S0.1847v1 / 24gds-where: Uc is the critical non-silt flow rate (m / s); g is the acceleration of gravity; Sv is the sand content (volume ratio%); s is the sediment density (g / cm3); d is the pipe diameter (mm); is the free sedimentation velocity of sediment (m / s); it is the water Density (g / cm3).
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