3 replies to this topic

[Limesun]

Hello,

 

 

I have to estimate the pressure drop on a system such as the one described in the attachment.

The flow after the pump is divided in two different paths, both of them are open (one has a flow control valve in A and the rest of the flow is recirculated).

 

Could do you please help me calculate the pressure in the point A? or recommend me a good pressure drop calculator program/excel template?

 

I am finding a lot of confusing or misleading information.

 

Thank you very much

Attached Files

•  pressure drop.JPG   27.31KB   1 downloads

[Bobby Strain]

You should not rely on us to provide you with such calculators. Instead, you should use your text book, lecture notes, and other resources. Your job is to learn the basics of fluid flow. You won't learn much if we provide the tools that you requested.

 

Bobby

[Limesun]

Yes, you are absolutely right.

 

But maybe I should have set out my question differently.

In this case, the pressure drop caused by the division on the right is almost neglectible (I have studied the pressure drop in other pieces of piping after A and since we have such a low flow we have also a very small pressure drop).

 

My question then is not only about this example, but in general. How do we study this type of system in which the flow is not directed on one way but split unequally.

Is it correct to consider that the pressure at the 2 "ends" of T is the same, and then study the two different pieces of piping separately?

 

Once again thank you very much for your question... and I apologise if I was too direct.  

[samayaraj]

Hi,

 

Your sketch is not clear to me. It seems the pump you have shown is centrifugal pump. You have to size the main line for maximum flow and recirculation line for pump's min flow. During normal operation, less flow will pass through recirculation line. If the normal flow is less than pump's minimum flow, recirculation line will see the pump's min flow.

 

Pressure at the other two point in T branch is nearly same. With this you can study the two different pieces of piping separately.

 

Following steps shall be followed for carrying our pressure drop calculation.

 

1. Find pressure drop upto T branch (Total flow = Flow in line A + Recirculation flow)

2. T Branch pressure (for same elevation) = Pump's discharge pressure - Drop upto T branch

3. Pressure at point A = pressure at T branch - pressure drop up to point A - (static head x rho x g)

4. Pressure drop in recirculation line = pressure at T branch - pressure drop in rec. line - (static head x rho x g) - receiver system pressure

 

Alternatively, you can find the pressure at point A in reverse. Pressure in point A = receiver pr + pressure drop from receiver to point A + (static head x rho x g)

Edited by samayaraj, 17 August 2016 - 12:26 AM.