Design of circulation pumps
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As shown in the figure below, the pump draws fluid from the buffer tank and sends it to the highest point, and then circulates it back to the buffer tank from that highest point. Throughout the process, the pump head is designed based on the pressure drop from the pump outlet to the end point (the inlet of the buffer tank), assuming that the potential energy is the same from the starting point to the end point; however, the impact of the height at the highest point on pump selection is not taken into account, which seems to be a problem. If the pump’s head is not sufficient to lift the fluid to the highest point, then there are no further calculations possible. What is the issue with the entire process?
Friend, take a look at this post and you should understand: http://bbs.hcbbs.com/thread-1400529-1-1.html
Thank you for the help. This of mine is a bit different from the post I provided to you. 1. I mentioned this example to illustrate the process of transporting low-temperature brine over mountains to supply cooling capacity to downstream areas, after which it returns to the refrigeration plant, in a cycle like this. 2. The highest elevation of the mountain is 250 meters; in accordance with the relevant standards, the flow velocity of cold saline water is taken as 1.5 m/s, with a frictional pressure drop of approximately 1.5 MPa. If a head of 150 meters is used, then the head at zero flow is approximately 1.2 * 150 meters, which still does not meet the required head at the highest point. If a head of 220 meters is selected, fluid can be transported to the highest point using a low flow rate. 3. However, since the entire conveying system is a closed loop without any open containers, there is no siphoning effect; therefore, even during normal operation, it is still necessary to meet the pressure requirements at the highest points at the rated flow rate. So, the second point mentioned above seems incorrect. 4. Further consideration shows that the fluid pressure remains very high when the low-temperature brine returns to the buffer tank; based on a height difference of 250 meters from the highest point to the buffer tank, the pressure is as high as 2.5 MPa. It is necessary to reduce this pressure before the fluid enters the buffer tank. To save energy, medium-pressure nitrogen can be used to raise the pressure in the buffer tank to 2.5 MPa. In this way, a pump head of 150 meters can be selected; during startup, the inlet pressure of the low-temperature brine can be increased to 2.5 MPa. Since the inlet pressure is higher than the pump’s head, is this acceptable?