Hey!!! Hey!!! Hey!!!
Introduction
Pumps are no different when it comes to those moments where we say "THIS SUCKS!!!" Well, before tearing apart what cavitation &NPSH really are it is important that we are ready with things like "Bernoulli equation" ,"Head"and "Frictional losses" in our armour .Let me give you little insights of above mentioned weapons😜.....
Bernoulli equation is simple conservation of energy (Where the energy transitions among kinetic , potential ,Pressure ) this equation exists in different forms 1.Energy form 2.Energy per unit volume form,3.Energy per weight form(Mostly used and is also commonly called THE "Head form"....
If you did peek into my previous blog (51milesair) you should have noticed me writing pressure in the dimensions of meter/feet/miles (h=(P/rho*g)). Well, it is the head form. Frictional losses are something that engineers shouldn't ignore as they account for major losses for any fluid which is flowing..................Now its time for the intro of Our Anti -hero NPSH(net positive suction head)
NPSH & Cavitation
The equation is simple... if NPSH is positive Cavitation maintains social distance from the pump😂......If not it's a day to mourn for your pump(R.I.P).
Factual stuff:
-->It is a known fact that boiling point of water at 1atm is 100c and the boiling point gradually decreases when the surrounding pressure decreases this is the core cause for cavitation .
-->Any fluid boils when vapor pressure = atmospheric pressure
When a fluid enters a pump on the suction side the pressure at the suction is derived based on net head at the suction side which mainly depends on loss in pressure due to friction and gain in pressure due to static head and operating pressure, if the difference between net suction head and vapor pressure of the process fluid is negative cavitaion occurs.........
NPSH=Net head at suction side -Vapor pressure(also in head form).........(1)
What is cavitation?????
Cavitation is the collapse of vapor bubbles at sonic velocities on the impeller of the pump......you might be wondering why would they collapse🥴 its simple you need pressure for the bubbled vapor to change back its phase ...Well, pump provides that pressure resulting in collapse of water bubbles on the impeller......
NPSH A &NPSH R
NPSH available and required are parameters that always drown students in confusion because these can be better understood when you know how to design a pump( Will make a blog very soon).....For now NPSH available is just the value obtained from equation (1) and NPSH required is specified by the Vendor based on the process fluid operating conditions.........
Will soon meet you with an example 🙋♂️🙋♂️🙋♂️ ......
KUDOS TO BERNOULLI,NEWTON,DENIS....
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