Understanding Choked Flow: How Pump Speed Affects Mass Flow and Velocity Changes

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In summary, the conversation discussed the relationship between the speed/flow of a pump and the resulting changes in mass flow, velocity, and density. It was noted that at a certain point, known as choked conditions, the mass flow is at its highest and any further increase in pump speed does not result in an increase in mass flow. The conversation also mentioned the observation of pressure drops across the pipe, which become non-linear after a certain point. The question of when the velocity and density begin to change was also raised.
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There is a long pipe connected to the inlet of a pump (air). As the speed/flow of the pump increases, according to the mass flow equation (pVA) something has to give. At what point does the velocity begin to increase? Ambient conditions have an infinite cross sectional area. Density has to change, but I keep wondering when it starts to change. Obviously the change occurs with velocity.

And then, mass flow is highest at choked conditions. If you continue to speed up the pump it appears to not flow any more mass. What happens?
 
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and to add, I notice pressure drops across the pipe to a certain point in a linear fashion as volumetric airflow rate increases to a point and then becomes non-linear. How close are you to choked flow when it becomes non-linear?
 

FAQ: Understanding Choked Flow: How Pump Speed Affects Mass Flow and Velocity Changes

1. What is choked flow with a pump?

Choked flow with a pump is a phenomenon that occurs when the flow rate of a fluid through a pump reaches its maximum limit. This is also known as the critical flow rate or the choked flow rate.

2. How does choked flow affect the performance of a pump?

When a pump is operating under choked flow conditions, it is unable to increase the flow rate even if the pump speed is increased. This can significantly reduce the performance of the pump and may even cause damage to the pump or other components in the system.

3. What causes choked flow with a pump?

Choked flow with a pump is caused by a restriction in the flow path, such as a narrow pipe or a valve that is partially closed. This restriction creates a backpressure on the fluid, limiting the flow rate that the pump can achieve.

4. How can choked flow be prevented?

To prevent choked flow with a pump, it is important to ensure that the flow path is free of any restrictions. This can be achieved by using properly sized pipes and valves, and by avoiding excessive bends or obstructions in the flow path.

5. What are the consequences of operating a pump under choked flow conditions?

Operating a pump under choked flow conditions can lead to a decrease in efficiency, increased energy consumption, and potential damage to the pump and other components in the system. It is important to monitor the flow rate and avoid operating a pump at or near its choked flow limit.

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