4 replies to this topic

[Venkat @89]

Hello everyone,

 

I would like to know why does the velocity head term is incorporated in the calculation of Net positive suction head calculations, even though velocity is not pure form of pressure?  Please let me know.Thank you.

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[breizh]

Hi ,

Consider these  resources to support your work.

 

http://centrifugal-p...definition.html

 

Hope this helps

Breizh

Edited by breizh, 27 December 2014 - 08:26 AM.

[fallah]

Chalapathi,

 

All parameters can generate a lot of head at the pump suction will be incorporated in calculation of NPSHA. Liquid velocity can generate dynamic pressure and subsequent velocity head; then the term of velocity head is incorporated in NPSHA calculation. Of course, it's often small value and in most cases not to be included in NPSHA calculation...

[Venkat @89]

Dear fallah sir,

 

Thank you all for the responses.

 

Even though liquid coming to suction might have velocity head which causes dynamic pressure, but the vaporization of liquid depends on the pure pressure i.e static pressure in moving liquid but not dynamic pressure. Am I right?

 

I mean to say if the static pressure for the moving liquid is 4kgf/cm2 and dynamic pressure is 5 kgf/cm2 and total pressure is 9kgf/cm2. The boiling point of the liquid is seen with respect to 4kgf/cm2 or 9kgf/cm2? 

 

Please help me. Thank you.

[samayaraj]

Chalapathi,

 

At any condition, the available pressure (i.e. Total pressure + static head - losses) at the pump suction should not fall bellow the vapor pressure of liquid at given temperature. If happens so, cavitation will occur. Always we have to keep at least +1m difference between head available at the pump suction and vapor pressure head of the liquid at operating temperature (i.e. NPSH A > NPSH R by at least 1m)

 

 

#Samayaraj

Edited by samayaraj, 01 January 2015 - 10:43 PM.