If although regulating flow valve is used does flow rate remains constant since as per continuity equation A1V1=A2V2 for incompressible fluid?
Dear Gaurav,
It is a good question. It seems somehow confusing but the answer is simple.
The discharge must decrease due to the excess head loss of the valve.
Your equation is for ideal flow. Incompressible pipe flow is also a function of wall friction and temperature (density).
Equation is f1*Rho1*U1*A1 = f2*Rho2*U2*A2
See Darcy's Law.
Paul
To Mohammad Bijankhan
Sir,
does that mean if pump of flow rate 10 lpm is used, then at the downstream the discharge has to be 10 or less than 10 lpm?
Dear Gaurav
No. For each pump there is a H-Q curve available by the factory. The operating point of the pump will be chosen based on the system Head-Loss. In other word, when you close the valve the associated system head loss increases. Then the operating point of the pump will be changed in a way that the pump will produce sufficient head to overcome the system head loss. For such a case the discharge must be decreased.
You can find these fundamental concepts in many hydraulic books. Google operating point of pumps.
Have a look please on the attached file.
Yours,
M.Bijankhan.
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