How to calculate local losses in drainage inspection wells
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I would like to ask the experts: when calculating the pipe losses in a plant’s drainage network, what values should be used for the local head loss coefficients when water flows into and out of inspection wells? Should the ξ value be determined based on a sudden expansion/contraction of the cross-section, or based on the inlet/outlet? The drainage network designed by the design unit for the existing factory site has a total length of 280 meters, with a height difference of 1.9 meters between the upstream and downstream sections. HDPE pipes with a diameter of 500 mm are used for this network, and there are 15 drainage inspection wells in total. The drainage flow rate is 680 m3/h. How can I determine whether the existing elevation difference is sufficient to account for friction losses along the pipeline?
Drainage network? Based on the known conditions, there is a height difference, so it should be a gravity flow pipeline. The ratio of the elevation difference to the total length of the pipeline network suggests that the slope is 0.6%, which is greater than the minimum slope requirement for that pipe diameter. With sufficient slope, the liquid can flow by gravity, and it is not necessary to calculate the elevation difference to determine whether the friction losses along the pipeline will be sufficient. As far as I remember, only pressure flow pipelines require the calculation of friction losses along the pipeline in order to determine the head required by pumps and other equipment. Actually, the original poster can estimate the flow velocity; after all, with the drainage volume known, as well as the pipe diameter and length, it’s possible to calculate the flow velocity roughly. Under full-flow conditions, the flow velocity is less than 0.004 m/s, so it’s definitely a gravity flow, and there’s no need to consider friction losses along the pipe