2 replies to this topic

[Aseem]

Hi

I have been trying to calculate the pump discharge flow rate for one of the recirculation lines.

1. I calculated the system curve using the energy balance in the following way:

P1/sp.gr. + V1^(2)/2g + z1+ hp = P2/sp.gr. +V2^(2)/2g + z2 +f(L/D)(V^2/2g) + Sum(KL)(V^2/2g)

where: P1 and P2 - Pressure above liquid surface at suction and discharge
V1 and V2 - velocity at liquid surface at suction and discharge
z1 and z2 - hieght of liquid at suction and discharge

All the above are assumed to cancel out because it is a recirculation and suction and discharge same location

f was calculated by using friction coefficient and Moody diagram.
KL was assigned for each valves and elbows in the line.

2. Therefore I got an equation of hp vs Q (after converting V to Q)

3. This was plotted in the pump performance curve and the intersection determined the flow rate.

However my hp was in the order of 10^-3 for each Q value and therefore was bound to intersect with the pump curve only at a flow rate of infinity!!!

Please help me to check if the above method is correct and if so why my pump flow rate is being calculated as infinity.

Thanks
Aseem

[breizh]

Hi Aseem ,
Let you check this resource :
http://www.gouldspum...at_pf_0001.html

Or try to get acccess to Crane technical paper

or use the search button on this forum ( numerous documents issued by Art Montemayor)

Hope it helps
Breizh

[marthin_was]

Please provide us your sketch of pump circulation line. Is there any restriction orifice or valve in that line?

If there is no restriction devices at the line, what you should do is to measure the pressure differential between P2 (discharge) and P1 (suction --> the point where recirculation line tied-in), from P2-P1, pipe roughness, pipe length, pipe size, pipe internal diameter, fluid properties information, and you can calculate the flow rate.