Water flow calculation through tee pipes

[Renie]

Hi

I need help calculating water flow through a few tee pipes.

Water flows to the plant through a 36” diameter pipe @3500m3/h and 220kPa for 9m before teeing out to a 24’’ pipe (1.5m high with butterfly valve). The original 36’’ than immediately encounters a 90 degree bend before it is reduced to a diameter of 24’’. The water flows from the bend for another 10 meter before reaching another t pipe which is 12’’ in diameter and for 2m teeing into a16’’ diameter pipe(1.5m high with butterfly valve) . After another 6m it ties out to an 8’’ pipe level @1.5m long (with butterfly valve). The 8’’ pipe that elevates to a height of 20m going to a Nitrogen /water tower. The rest of the water that came from the original 36’’ pipe flows through an 8’’ plant to the rest of the plant

I need to calculate the flow of water to each tee pipe in order to get the water flow to Nitrogen/Water tower to do an efficiency calculation

Thanks

 

[Q_Goest]

Hi Renie, welcome to the board. I'm afraid your system has too many unknowns right now. There is 1 inlet and 5 outlets. For each of the outlets, you need to know either the pressure at some point or the flow rate through the branch. For example, pressure at a point in your piping network may be determined by a valve such as a pressure regulator and flow might be controlled using a flow control valve. Those are just examples. So each branch has to have a flow rate or pressure. Also, if there are any elevation changes, you'll need to know that. Along with that information, you'll need to define the geometry of each system including the flow coefficients for any valves you have.

The way this has to be done is by iteration. You'll need to set up an equation for each unknown and iterate till your system pressure and flow rates all match. If you're not familiar with the Crane Technical Paper 410, you should get a copy. There is a similar document I posted online years ago here:
https://www.physicsforums.com/showthread.php?t=179830

Page 15 of this document starts to discuss networks of systems. But before you can get to that point, you really need to understand how to determine the flow through pipe, bends, valves and reducers and how to account for elevation changes in a single piping run. I'm afraid there's no easy answer to your question.

 

[Renie]

Thanks for the reply

I actually need the water flow through the 8'' pipe to a nitrogen/water tower in order to calculate the efficiecy of the tower. Is there a way this can be done.

 

[Q_Goest]

Have you ever performed a pressure drop/flow analysis like this before? Are you familiar with the Darcy Weisbach equation or Bernoulli equation?

The flow out the branches reduces the pressure along the main line up to that T where the flow branches off. The higher the flow through any length of pipe, the more the pressure drop, so if the water is going out the other branches, the flow through the pipe up to that branch will be unknown and you can't do an analysis of the pressure drop. The only thing you could do is neglect the flow out the other branches altogether.

If you completely neglect the flow into the other branches and assumed the pressure at the inlet of the 36" pipe was also the pressure at each of the T's, you could at least come up with an estimate for the flow out of that particular branch. But if that pipe is free flowing with no regulators or valves to control flow, doing this would result in a flow rate that's higher than actual.

 

[Renie]

From the original data available, is possible to calculate the flow through the first tee branch, 24'' diameter?

 

[Q_Goest]

From the original data available, is possible to calculate the flow through the first tee branch, 24'' diameter?

Unfortunately not. The flow rate through the first T is unknown so the irreducible pressure drop (as calculated by the Darcy Weisbach equation) is also unknown. The flow rate through each part of the system needs to be known in order to determine the pressure drop through that portion. The flow rate through each point of the system is a sum total of the flow rate going out through each of the branches downstream of that point.