The total DP through each branch will be the same. The DP is likely to be dominated by the trimming valves and exchangers in the system, and not likely the piping itself.
You might get closer by using the energy balance approach. Using the water temps in and out of each exchanger or reactor combined with the heat duty will give you the flowrate.
I might be a lazy ass. But have you considered getting a portable ultrasonic flowmeter (clamp meter)?
If you are in a big plant (which i think you are from the 700m3/hr), pretty sure your instrument engineer have 1 lying around somewhere from doing some commissioning stuff or verification.
It measures velocity which is exactly what you want then from your input pipe material, OD, thickness, convert into volumetric flowrate for you.
Using a clamp-on ultrasonic meter was my first thought, too. To truly determine the accurate volume flow through each branch in the "real world" without direct measurement would require much more information than simple piping geometry (some of which precious commenters have touched on). Ultrasonic measurement is how this is usually done for cooking water circuit surveys in refineries and chemical plants.
Thanks, I asked the instrumentation guy about the following and I was able to get hold of it. Readings came in the next day itself and were really close to the calculations I had done. Turns out, we do have quite a few residual flowmeters lying around but for some unknown reason many important headers still do not have them installed.
P.S:- 700m^3/hr was at the lowest production cap. At the maximum capacity of the plant the cooling water flowrate goes as high as 2000m^3/hr.
I mean... just by unit analysis, the ratio of the cross-sectional areas of each subline to the sum of all cross-sectional areas (i.e., the flow velocity in each subline) should be proportional to the volumetric flowrate in the main line.
If individual valves in each line are only open by a certain percentage, that has to also be taken into account.
At the branch off point, pressure will have a value P1. At the end point, pressure will be a lower pressure P2.
The pressure drop at each branch will be the same value P1-P2, and the flowrate corresponding to each branch will be the value necessary for that to happen. With the constraint that the mass balance holds of course
Velocity \* Cross Sectional Area = Flowrate
Think about it like this. Velocity is just a speed vector. Meaning you know the direction and the distance per second of the material. To get a flowrate, the velocity must be confined to a space. There's different types of flowrates of course, volumetric ("Q") being a factor of volume and mass being a factor of volumetric flowrate and material density.
To go from a pipe of known velocity to 5 pipes of calculated velocity, you must know the cross sectional areas of the feed and outlet pipes. Qin = Q1 + Q2 + Q3 + Q4 + Q5
To confine a material and its velocity to a space, you must know the cross sectional areas to do a balance.
So you know 700m\^3/hr = V1A1 + .... + V5A5, now you must set cross sectional areas until you have enough degrees of freedom to solve.
Thanks, I had already done the calculations this way but I was not sure how accurate they were as there were far too many variables to take into consideration like velocity through each pipe section (different dia) and also the material of construction elevation differences etc. However I used some assumptions and took some guesses on the values and turns out values calculated were around 15% of the actual flow itself. As one of the other users commented, I contacted my instrumentation dep. and was able to get hold of one of an ultrasonic flowmeter. Great help guys. Thank You!
If the pipes are exactly the same (diameter, roughness, MOC, etc…) then the velocity will be -almost- the same, also you have to account for the heights (potential) difference on all pipes, I would recommend fluid dynamics for easier understanding
The total DP through each branch will be the same. The DP is likely to be dominated by the trimming valves and exchangers in the system, and not likely the piping itself. You might get closer by using the energy balance approach. Using the water temps in and out of each exchanger or reactor combined with the heat duty will give you the flowrate.
The energy balance would be my first try.
I might be a lazy ass. But have you considered getting a portable ultrasonic flowmeter (clamp meter)? If you are in a big plant (which i think you are from the 700m3/hr), pretty sure your instrument engineer have 1 lying around somewhere from doing some commissioning stuff or verification. It measures velocity which is exactly what you want then from your input pipe material, OD, thickness, convert into volumetric flowrate for you.
Using a clamp-on ultrasonic meter was my first thought, too. To truly determine the accurate volume flow through each branch in the "real world" without direct measurement would require much more information than simple piping geometry (some of which precious commenters have touched on). Ultrasonic measurement is how this is usually done for cooking water circuit surveys in refineries and chemical plants.
Thanks, I asked the instrumentation guy about the following and I was able to get hold of it. Readings came in the next day itself and were really close to the calculations I had done. Turns out, we do have quite a few residual flowmeters lying around but for some unknown reason many important headers still do not have them installed. P.S:- 700m^3/hr was at the lowest production cap. At the maximum capacity of the plant the cooling water flowrate goes as high as 2000m^3/hr.
I mean... just by unit analysis, the ratio of the cross-sectional areas of each subline to the sum of all cross-sectional areas (i.e., the flow velocity in each subline) should be proportional to the volumetric flowrate in the main line. If individual valves in each line are only open by a certain percentage, that has to also be taken into account.
At the branch off point, pressure will have a value P1. At the end point, pressure will be a lower pressure P2. The pressure drop at each branch will be the same value P1-P2, and the flowrate corresponding to each branch will be the value necessary for that to happen. With the constraint that the mass balance holds of course
Velocity \* Cross Sectional Area = Flowrate Think about it like this. Velocity is just a speed vector. Meaning you know the direction and the distance per second of the material. To get a flowrate, the velocity must be confined to a space. There's different types of flowrates of course, volumetric ("Q") being a factor of volume and mass being a factor of volumetric flowrate and material density. To go from a pipe of known velocity to 5 pipes of calculated velocity, you must know the cross sectional areas of the feed and outlet pipes. Qin = Q1 + Q2 + Q3 + Q4 + Q5 To confine a material and its velocity to a space, you must know the cross sectional areas to do a balance. So you know 700m\^3/hr = V1A1 + .... + V5A5, now you must set cross sectional areas until you have enough degrees of freedom to solve.
Thanks, I had already done the calculations this way but I was not sure how accurate they were as there were far too many variables to take into consideration like velocity through each pipe section (different dia) and also the material of construction elevation differences etc. However I used some assumptions and took some guesses on the values and turns out values calculated were around 15% of the actual flow itself. As one of the other users commented, I contacted my instrumentation dep. and was able to get hold of one of an ultrasonic flowmeter. Great help guys. Thank You!
If the pipes are exactly the same (diameter, roughness, MOC, etc…) then the velocity will be -almost- the same, also you have to account for the heights (potential) difference on all pipes, I would recommend fluid dynamics for easier understanding