Seeking guidance from the supervisor regarding import and export volume issues
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I have a question: In a company’s circulating water main and brine water main, the outlet diameter is one size larger than the inlet diameter (for example, the inlet main is DN300 while the return main is DN350). Is this done to reduce the resistance in the return flow? Or other reasons? I asked the company’s employees, and they said it was designed in the past; they’re not sure. I’ve seen the blueprints of several companies, and the inlet and outlet pipes are the same there as well
The pressure and flow rate of the water entering the system are high, while the pressure and flow rate of the water returning are low; therefore, larger pipes are required. In smaller systems, for the sake of ease of piping installation and without sacrificing any money that could be saved by using smaller pipes, it might be necessary to make the inlet as large as the outlet
This has nothing to do with outlet resistance. The supply pressure is generally about 0.1 MPa higher than the return pressure; as a result, the flow velocity of the supply stream is higher. The flow velocity of the return stream is reduced by the control of the outlet valve. With a constant flow rate, flow velocity = flow rate/area, so if the area increases, the pipe diameter also increases
I think this is related to the pressure loss in the water supply pipes. If the length of the pipes is short, and pressure drop losses can be ignored, the diameters of the inlet and outlet pipes can be set to be the same. However, if the pipes are long and a pump with high head isn’t desired, then it’s necessary to consider increasing the pipe diameter to reduce flow velocity and thus lower the pressure drop; in this case, the diameter of the outlet pipe should be larger than that of the inlet pipe