Discharge Cavitation

Discharge Cavitation

discharge cavitation - pump-minDischarge cavitation occurs when the pump discharge pressure is extremely high or when the discharge flow is restricted and cannot leave the pump (e.g. caused by closed outlet valve). An extremely high discharge pressure results in the majority of the pumped fluid circulating inside the pump.

This type of cavitation originates from two sources. First, this internal circulation (from high-pressure zones into low-pressure zones) is forced through the clearance between the impeller and the pump housing at high velocity resulting in the formation of a low pressure region (as a result of Bernoulli’s principle) in which cavitation can occur. Second, the liquid is circulating inside the volute of the pump and it rapidly overheats.

In both cases, cavitation have similar consequences. The implosion of bubbles trigger intense shockwaves, causing premature wear of the impeller tips and pump housing. In extreme case, discharge cavitation can cause the impeller shaft to break.

Typical causes of discharge cavitation:

  • Pump is running too far left on the pump curve
  • Blockage in the pipe on discharge side
  • Clogged filters or strainers
  • Inappropriate piping design
Source: Wikipedia, CC BY 2.5, https://commons.wikimedia.org/wiki/File:Turbine_Francis_Worn.JPG
Source: Wikipedia, CC BY 2.5,
https://commons.wikimedia.org/wiki/File:Turbine_Francis_Worn.JPG
 
References:
Reactor Physics and Thermal Hydraulics:
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  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. White Frank M., Fluid Mechanics, McGraw-Hill Education, 7th edition, February, 2010, ISBN: 978-0077422417

See above:

Cavitation