Way to equalize pressure in parallel pipes

[linkin1990]

This question might have been asked before but still can someone please answer it.There is a main header pipe from which two lines emerge and along each line there are three reactors.My question is that how to get equal flow of water to all the reactors.Attached is a simple schematic.
Cheers!!

 

[katmar]

The easy way is to make the piping oversized so that there is effectively no pressure drop along the pipe to each reactor. The supply pressure at each reactor is then the same and you can control the flow rate with a simple restriction orifice.

In practice, this may mean using only one standard pipe size larger than what you normally would because the friction pressure drop is inversely proportional to the 5th power of the diameter - for example a 4" pipe will have only 25% of the friction drop that a 3" pipe would.

Alternatively you could put a flow meter and control valve in each line and control it exactly.

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[linkin1990]

Thanks!!
But I forgot to specify one thing that this system is already in place and i cant change the pipe diameter.What i was thinking of is that putting pipes at an angle across two reactors as shown in the attachment.But i do not know at what angle to place them so as to enable equal flow to all the pipes.
Cheers!!

 

[zdas04]

There absolutely is not an "easy way" to do this. Two pipes as nearly identical as man can make them, in parallel will always have different flow. In a cooling water system it is simply impossible. Ever opened the tube side of a sea water cooled steam condenser? I found a 3 pound octopus (we found at least 5 legs stopping up tubes) in one once. Barnacles, shells, and silt are normal. So if the flow had coincidentally been perfectly balanced at some point, they rapidly diverged when Squidward decided to commit suicide. Freashwater coolers aren't much better, but tend to smell better.

Even with control valves and orifices they will never be equal. They shouldn't be. A reasonable goal would be to set control valves to give you an equal (or constant) process outlet temp, but each heat exchange is going to require different flow rates to extract the same heat from the process. Trying to match flow is just pointless.

David

 

[Latexman]

Refering to your first attachment, one way would be to provide another supply header to the two subheaders from the opposite end/side (the top). This would reduce the flow in each individual header and subheader supplying the single pipe to each reactor, and the resulting pressure drop would be reduced, thus improving the current maldistribution concern.

I do wonder about the economic justification to remedy the current maldistribution issue though. Can you give us some insight on this?

Good luck,
Latexman

 

[BigInch]

If you can feed each header from near center, you'll be better off, and if you have clean feed lines, and you can keep your reactors from clogging, or clog them equally, this may not be as much a problem as you think.

Feed the first header through a T between 4 and 5 and the second with a T between 2 and 3.

What line diameters are we talking about and what's the target flowrate through one reactor?

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[Robster1us]

I'm not sure how hot the water is you're talking about, but if it's cooling jacket water below 200°F, then you can probably use circuit setters (also called circuit balancing valves) in each line going to the equipment. These valves are settable and have known characteristics along their range so that, for a given upstream pressure and pressure drop through the valve (measured with probes through integral ports on the valve), you know what the flow rate is. The handle has numbers on it so you know what the setting is.
It would be helpful to know the line sizes and some more information on the water, temperature, pressure, is the upstream pump a constant speed pump, etc.
Any hydronic pump rep can point you to a good source for these valves.

 

[emanoelman]

You didn't try the simplest way, just put flow meter and measure total flow from each line. It might be enough, so you wouldn't need to make any adjustment.
If there is a big difference in flow, you will know which pipe needs to be adjusted. Use appropriate valve, restriction oriface etc...