Water flow rate split

[TheUnknownw]

Hello everyone,

I have a temperature control unit which provides cold water for my system. I have a hard time calculating the flow rate in the system.
So i have 6 devices that use this cold water. The flow comes out of the Temperature Control Unit and splits in 6 via a distributor.
The pipe going to distributor is around 25mm inside diameter while each of the 6 pipes comming out of the distributor are around 10mm inside diameter.
The system end with the cold water going back through another distributor which collects all 6 into 1 pipe again and to the TCU.
How do i calculate the flow rate required by the TCU to have a lets say 2l/min flow rate on each of the 6 pipes?
Also, should the split be equal to the main pipe flow rate divided by 6? My test shows 2l/min in each pipe with a flow rate of 20l/min for the TCU output pipe.

Attached a small representation of the system.

Regards.

[Brian_UK]

If you haven't made the distributors yet and your process items are the same have a look at using a reverse return system.

This is where the supply manifold is fed in at one end and branches 1 to 6 come out sequentially. The return manifold would be identical but the outlet pipe would be adjacent to branch 6.

Balancing valves would still be recommended however.

[TheUnknownw]

I already made the distributors. But that is not the problem. The distributor splits the flow rate evenly, without any probpens.
My question is why i have at the inlet of my distributor 20l/min and on each of the 6 outlets, 2l/min
And i dont have 20l/min split by 6 -> 3,3?
Or what i would really like to know, is how to actually calculate the flow rate and the flow rate splitting.

Thanks

[Brian_UK]

How are measuring the flow rates and to what accuracy?

Commissioning valve sets would allow branch flow measuring/adjustment.

[frank]

You could always disconnect each individual pipe and use this to accuratly measure the flow rate

https://www.ebay.co.uk/itm/TODAYS-TOOLS-FLOWMATE-WEIR-GAUGE-WATER-FLOW-METER-CUP-ABS-Dual-Gallon-Litre-/112635530658

[TheUnknownw]

I think i did not make myself clear.

I am not interested in measuring the flow rate. I am already measuring the flow rate with high tech ultrasonic devices.

I am interested in how to calculate the flow rate. At this very moment i have a distributor with the flow rate values from above.
I want to make another distributor, but i dont know how to calculate the flow rate splitting.
And i am also wondering why a flow split in 6 ways, dont add up to the initial flow.

[TheUnknownw]

Or to put the question in a problem like example:
I have a pipe with 20mm diameter. In this pipe flows water at 25°C at a flow rate of 20l/min at a 0.40 bar pressure.
I split this branch in 6 other branches, each of 10mm in diameter. What would be my flow rate in the small branches?

[Brian_UK]

Without knowledge of calibrated pressure drops across each branch it would be guesswork.

It might be possible with knowledge of the temperature changes and heat inputs at each branch to achieve some results.

[Brian_UK]

You could always disconnect each individual pipe and use this to accuratly measure the flow rate

https://www.ebay.co.uk/itm/TODAYS-TOOLS-FLOWMATE-WEIR-GAUGE-WATER-FLOW-METER-CUP-ABS-Dual-Gallon-Litre-/112635530658

Only if used at the return manifold so that branch resistance is included.

[Brian_UK]

I think i did not make myself clear.

I am not interested in measuring the flow rate. I am already measuring the flow rate with high tech ultrasonic devices. ...

Yes, you say that you have high tech equipment but you have proved that it cannot be giving you the correct results.

If 20l/m is going in then 20l/m must be coming out unless you have a leaking manifold.

[TheUnknownw]

I did not say that i am getting 20l out, since i dont know that, because the flow rate on the main return line is not measured, since i dont care about it.

I am only interested on the flow rate on the small branches.
So at this very moment i have 20l/min going out of my Temp Control Unit (measured with an in-line flow rate measuring device at the exit from my Temp Control Unit). This main line splits into 6 other lines. The flow rate measured at each of the 6 small lines is 1,5l/min at entry and 1,5l/min at return (measured with ultra-sonic devices on each line). The water returns back to the TCU via another 6 way distributor which collects all the 6 lines back into 1 single line (here i am not measuring the flow on the single line).

The pressure on the main before the 6 way distributor is 0.45bar. The pressure on the small lines is not known.

So, why if i split 20l/min into 6 lines, i get 1.5l/min?
And how do i calculate this "split" if i want to design another distributor?

Ill make a drawing and add it up in a moment

[TheUnknownw]

And again, with added Drawing

Its not the best drawing, but it is exactly the system that i am facing right now.
Dimensions:
- Main line diameter 20mm
- Small 6 lines diameter: Each 10mm
- Length of the main line 2000mm
- Length of the small lines: each 1000mm
- Liquid: Water
- Temperature 25 C

I dont have a problem with this system, the system works perfectly and the cooling is good. I just have the following questions which will help me design my own system and help me understand the splitting of the lines.

Why is a flow rate of 20l/min split into 6 going to 2l/min?
And how to calculate the split of 20l/min into 6 other lines?

[nike123]

(R1ˆ2xπ)/(R2ˆ2xπ) is ratio of pipes surfaces (where R1 i s main pipe internal radius, and R2 is branch pipe radius)

((25÷2)^(2)×π)÷((10÷2)^(2)×π)=6,25

Therefore one pipe off 25mm internal diameter is aproximatly same surface as 6 pipes of 10mm internal diameter surfaces combined.

And that is how you should calculate pipes by calculating pipe crossection surface and not diameter.


So at this very moment i have 20l/min going out of my Temp Control Unit (measured with an in-line flow rate measuring device at the exit from my Temp Control Unit). This main line splits into 6 other lines. The flow rate measured at each of the 6 small lines is 1,5l/min at entry and 1,5l/min at return (measured with ultra-sonic devices on each line).

One or both measuring devices are not measuring corectly.

If you precisely measure temperature difference at unit inlet/outlet and you have known cooling capacity you could calculate flow at cooling device.

https://theengineeringmindset.com/chiller-cooling-capacity-calculate/