Pipeline resistance calculation

1. In the aforementioned circuit, the operating point of the pump still follows the principle that it lies at the intersection of the pump’s characteristic curve and the pipeline’s characteristic curve. 2. In the pipeline running from the pump outlet to the upper part of the ground tank, although the distance is short and thus the pipe resistance is low, there is a height difference between the center of the pump and the highest point of the pipeline. This liquid column represents the back pressure in the pipeline and is also part of the pipe resistance. Therefore, a situation in which the pipe resistance becomes infinitesimally small while the flow rate becomes infinitely large does not occur

Well, if I simply remove the pipe at the pump outlet, then the pipeline resistance will be 0

The energy relationship is described by Bernoulli’s equation. Here, we can imagine the following: 1. Without a pump casing, the fluid enters at the inlet of the closed impeller; as the impeller rotates, it generates centrifugal force on the fluid. Assuming the outlet is directed upward, when there is a pipe in place, the height that the liquid can reach at the outlet is higher than that in the case of no pipe, but this does not mean that there is no head loss. 2. For a pump with a fixed design, the flow channels of the impeller are fixed, so the flow rate cannot increase indefinitely. 3. Due to factors such as internal recirculation, the efficiency of a pump includes mechanical and hydraulic losses, and it is always less than 100%. When the pump operates under extreme conditions, it deviates from its optimal efficiency point, resulting in very low efficiency

Yes, that’s exactly what I want to ask: is there any theoretical explanation for determining the maximum flow rate that a specific pump can achieve? When the liquid exits the impeller, does it have no static head, with only a velocity component along the tangent to the impeller?

1. When designing a pump, flow rate is one of the parameters used to calculate values such as specific speed, efficiency, shaft power, speed, and structural dimensions. 2. Regarding the maximum flow rate issue for a specific pump that interests you, you might choose one of the parameters; for example, use shaft power as the conditional variable, and different values of shaft power can be used to determine the corresponding flow rates. It’s actually quite easy to understand: in simple terms, you do as much work as you eat. If the strength of the impeller and the pressure-bearing capacity of the casing are not taken into account, increasing the input energy can boost the flow rate; however, there are many limitations in practice, making it impossible to implement this in engineering applications. 3. Friends have a wide range of interests; rather than posting occasional messages on forums, it’s better to read a specialized book – for in books lies true knowledge.

In engineering, due to the limitations imposed by the power of the driving motor, even if the resistance in the pipeline is low, the flow rate cannot be unlimited. If the motor is used for driving, this will result in excessive current flowing through the motor; either the motor’s built-in protection system will activate or the motor will get damaged. :D:D:D

For this type of pump, the head calculated is relatively low. The key is to determine what the purpose of this pump setup is, what the required flow rate is, and to clarify the input conditions for the pump design. I have encountered similar pump setups before; they are used for stirring the liquid inside reactors, featuring high flow rates and low head pressure. There is also a circulation pump used in a type of crystallizer; the circulating fluid is intended to suspend the crystalline solids, and axial flow pumps with high flow rates and low head pressure are chosen for this purpose.

This post was last edited by henglinkou on 2020-4-11 at 11:21. It is a pump calculation table I created for trial use.