Why does a high-speed motor require more power than a low-speed motor under the same operating conditions?
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I personally believe it is because the flow channel of a pump equipped with a high-speed motor is narrower than that of a pump equipped with a low-speed motor, resulting in greater pressure loss; hence, a higher motor power is required.
The original poster is incorrect; they got it backwards. Generally speaking, for centrifugal pumps with the same performance, those operating at higher speeds have a higher specific speed as well as higher efficiency; therefore, they consume less power.
Nothing is absolute. It can be calculated using the formula.
Under the same conditions of flow rate and head: Pumps equipped with high-speed motors have a smaller outer diameter of the impeller, resulting in lower disk friction losses and higher pump efficiency. Low-speed impellers have a larger outer diameter, and their efficiency is lower compared to those of high-speed impellers. Low-speed pumps have high torque; generally, their pump shafts and bearings are larger than those of high-speed pumps, and the mechanical losses are also somewhat higher. Last edited by tzpump on 2009-3-20 11:49.]
For centrifugal pumps, those with higher rotational speeds have a greater specific speed as well as higher efficiency; moreover, they consume less power. High-speed motor pumps have a small outer diameter of the impeller, resulting in low disk friction losses and high pump efficiency.
The section on the 2nd floor analyzes the relationship between speed and mechanical efficiency using specific speed, which is indeed very good. However, centrifugal pumps compared using specific speed must be geometrically similar or identical pumps; for pumps with different specific speeds, it is not possible to compare the mechanical efficiency based on speed. Under the same operating conditions, in order to achieve the same flow rate and pressure, the diameter of a pump driven by a high-speed motor must be smaller than that of a pump driven by a low-speed motor. In pumps driven by high-speed motors, the flow velocity is high, the diameter is small, resulting in greater frictional resistance (including within the chamber), and thus higher energy losses. In contrast, pumps driven by low-speed motors have a larger diameter and lower flow velocity, leading to less frictional resistance and consequently lower energy losses. Total work = useful work (when flow rate and pressure are the same, the useful work is the same) + loss work. Therefore, I believe that under the same operating conditions, the power required for a low-speed motor is less than that required for a high-speed motor.