Why are there still bubbles after the pump?

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SUMMARY

The discussion centers on the persistence of bubbles in a centrifugal pump system, specifically a backward fan centrifugal pump. Key factors contributing to this issue include cavitation due to low pressure, temperature increases from throttled discharge, and potential aspiration from leaking gaskets or shaft seals. The presence of dissolved gases coming out of solution due to pressure drops or temperature increases within the pump is also identified as a significant cause for bubbles appearing downstream of the pump.

PREREQUISITES
  • Centrifugal pump operation principles
  • Cavitation effects in fluid dynamics
  • Understanding of pressure and temperature relationships in fluids
  • Knowledge of pump components, including impellers and seals
NEXT STEPS
  • Investigate centrifugal pump cavitation mitigation techniques
  • Learn about the effects of temperature on fluid behavior in pumps
  • Study the design and function of backward fan impellers
  • Explore methods for detecting and preventing aspiration in pump systems
USEFUL FOR

Engineers, fluid dynamics researchers, and maintenance technicians involved in pump design, operation, and troubleshooting will benefit from this discussion.

Guybob
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Hi everyone,
Got a question I'm trying to solve here. It is for an experiment I'm running at achool.

I got a pipe system with a centrifugal pump. There is cavitation in front of the pump due to the pressure falling below the water Vapor pressure. When the water flow enters to the backwards fan centrifugal pump, the Vapor/bubbles should collapse due to the high pressure at that location. But there are a few bubbles that passes through the pump. Why is this the case and what is happening?

Thanks for viewing!
 
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Best guesses: Temperature increase in the pump caused by low flow conditions (throttled discharge). Vane pass (impeller tip passing too close to the cutwater). Aspiration, basically leaking gaskets and/or shaft seals.

Describe the "backward fan" please.
 
It might be possible that some dissolved gases are coming out of solution due to the pressure drop (and/or temperature increase) within the pump. This would then show up as bubbles in the flow.
 
On the downstream side that occurs if the flow is throttled so much that the fluid heats up in the pump. First in my list above. Note that the original post says the bubbles are downstream from the pump.
 

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