Help with fluid flow ...

[Spedley]

I have a basic understanding of pressure and flow but nowhere near enough to find the answers I need.

I have water flowing at a high rate through a pipe (80L/m) and I want to divert some of this through a heat exchanger (30 L/m) whilst keeping the total flow rate as high as possible.

I've included a diagram of roughly what I hope will work but I'm not totally sure how to get rough calculations of the dimensions required.  Currently I have a single pipe diameter and a valve between the input and output to the heat exchanger (C and E) to create a pressure differential but this slows the flow and is very sensitive to any slight adjustment.

In the diagram below, my idea is that the water flows in through A and out through F.  At B there will be a higher pressure (I think) than D causing water to flow through the heat exchanger G and H.  My hope is that flow will not be significantly affected and there should be a more stable flow through the heat exchanger.

Firstly, I'm not sure this will work?  Secondly, I don't know how to calculate the sizes for B and D or if the return flow at E will affect the pressure drop or if the pipe needs widening again at E to cope with the increased flow. 

Basically, I know very little and thought someone here may be able to point me in the right direction.

(Also, there is significant resistance through the heat exchanger - lots of narrow passages and turbulence)
(I've included a picture of the current setup, ignore the hot pipes to the heat exchanger behind it - the letters are from elsewhere and do not correlate to this post )
 

Edited June 16, 2018 by Spedley

[Endy0816]

I'd probably try a couple of elbows leading into/out of the heat exchanger instead.

Right now your fluid is going to want to shoot straight through, avoiding a 90 degree turn and bypass your heat exchanger altogether.

sketched this out with an optional bypass if it proves necessary.  A different valve type may help ease flow rate as well.

[Spedley]

Thanks, I did consider that kind of setup originally but for other reasons.  I'll try it.

[Bender]

Is the pressure drop over the heat exchanger specified in the data sheet? That is the pressure difference you are aiming for. 

Besides a valve, there are other ways to get a pressure difference. Bernouilli is an option, if you use a very large diameter (slow flow speed) T for the input and a small diameter (large flow speed) for the output.

Another option could be that you direct the output of the exchanger to another part in your circuit where the pressure is lower, or the input to where it is higher.