Flow rates

[dizzlesizzle]

Not sure if anyone can help me here.

It is something im trying to work out for my job and i use this site so much for my diy i thought i would give it a shot.

Does anyone know how to calculate water flow rates through pipe sizes.

All i know is the pipe is 1"1/2 the water pressure is 4 bar and 20 C. Im yet to know the length of pipe but the water is being used as a cooling application on a large compressor.

If anyone has any calculations or sites i can visit i would really appreciate it.

Many thanks.

Dizz

 

[Breesey]

You can't work out a flow rate from pipe diameter and fluid pressure. You could have 100 bar but still no flow. You need to know fluid velocity.

You should be able to find a simple flow weir to check it.

 

[giblets]

The flow rates will depend on the resistance to flow of the pipework & fittings. All pipe flow charts have equivalent lengths shown which is a combination of actual pipe length plus an allowance for the resistance to flow of the fittings. In order to work out the actual flow rate for a given size of pipework you will need to know the actual pipe run length and fittings used. You also need to know the required fluid quantity for the bit of kit.

How do you know the pipe is 1.1/2"?

 

[gas4you]

boxbasher is the one you need to answer this. he has posted spreadsheets on here in the past giving loads of info like this

 

[Onetap]

Not sure if anyone can help me here.

It is something im trying to work out for my job and i use this site so much for my diy i thought i would give it a shot.

Does anyone know how to calculate water flow rates through pipe sizes.
Dizz

You need to get a book on fluid dynamics. I know how to do it, but the method covers several chapters of a textbook and any effort to explain it here would be simplified to the extent of being fairly useless.

However;

1) When the fluid flows in a pipe, there is a pressure loss due to friction.

There are numerous theories which you could use to estimate the pressure loss (D'arcy et al) , but you'd usually use a chart of empirical data from experimental measurements, e.g., CIBSE's Flow of Fluids in Pipes and Ducts, pipe manufacturer's data, etc.. At a given flow rate you get so much pressure loss per metre for a given pipe type (steel, copper, uPVC) and diameter. Each type of pipe fitting (gate valves, globe valves, elbows, bends, tees, etc) will have a pressure loss, which is usually expressed as an equivalent length of pipe.

2) There is a pressure difference across the pipe which drives the flow, e.g., a pump in a circulating system, a head of water in a water supply system, etc..

3) At equilibrium, the pressure loss due to friction (1 above) is equal to the pressure difference driving the flow (2 above).

What you'd do is, knowing the available pressure difference, the pipe sizes and number of fittings guesstimate a flow rate and calculate the pressure loss due to friction at that flow rate.

From the guesstimated flow rate and calculated pressure loss (P) at that flow rate (Q), you calculate Kv, where;

P = Q^2/Kv^2

Then, knowing Kv for that system, you then calculate the actual flow rate at the available pressure difference, i.e.,

Q= Squ. root of (P x Kv^2)

See? Easy.

PS The above assumes that the flow is turbulent in both cases, you could get laminar flow at values of Re<2000.

PPS You may find it more cost esffective to employ someone who already knows the calculation method, rather than spend your time in learning it.

 

[corgiman]

Not sure if anyone can help me here.

It is something im trying to work out for my job and i use this site so much for my diy i thought i would give it a shot.

Does anyone know how to calculate water flow rates through pipe sizes.
Dizz

You need to get a book on fluid dynamics. I know how to do it, but the method covers several chapters of a textbook and any effort to explain it here would be simplified to the extent of being fairly useless.

However;

1) When the fluid flows in a pipe, there is a pressure loss due to friction.

There are numerous theories which you could use to estimate the pressure loss (D'arcy et al) , but you'd usually a chart of empirical data from experimental measurements, e.g., CIBSE, Flow of Fluids in Pipes and Ducts. At a given flow rate you get so much pressure loss per metre for a given pipe type (steel, copper, uPVC) and diameter. Each type of pipe fitting (gate valves, globe valves, elbows, bends, tees, etc) will have a pressure loss, which is usually expressed as an equivalent length of pipe.

2) There is a pressure difference across the pipe which drives the flow, e.g., a pump in a circulating system, a head of water in a water supply system, etc..

3) At equilibrium, the pressure loss due to friction (1 above) is equal to the pressure difference driving the flow (2 above).

What you'd do is, knowing the available pressure difference, the pipe sizes and number of fittings guesstimate a flow rate and calculate the pressure loss due to friction at that flow rate.

From the guesstimated flow rate and calculated pressure loss (P) at that flow rate (Q), you calculate Kv, where;

P = Q^2/Kv^2

Then, knowing Kv for that system, you then calculate the actual flow rate at the available pressure difference, i.e.,

Q= Squ. root of (P x Kv^2)

See? Easy.

well it would have been One if you had not forgotten to carry the one

sheesh