Pipe network pressure drop analysis 2

[dmeet]

Hello everyone.

I have a question for pipe network analysis. This can be done by computer programs but I would like to know if there is a hand calculation (spreadsheet) method available.

Even if someone can point me to a reference book, I would be greatful.

I tried searching for this on internet but was unsuccessful.

My question is.

1. If we have a pipe network, how do we find the total head developed so that the pump can be selected.

2. If we have heat exchangers in parallel, how do we find out the pressure drop in each line (is it similar to electrical resistance in parallel) and afterwards the total head developed for the pump calculation.

3. If a pump is pumping to a single pipe which then splits in to two lines going to two tanks (open to atmosphere) how do we know what will be the flow rate in each tank if these lines dont have a flow control valve. How can we find out the total head developed by the pump. To make this question interesting what if the pipe size going to these tanks are different and that the fittings are also different for both the pipes and that the tanks are at different elevations.

4. For a cooling tower there are several discharge points for a single line, how do we find out the pressure drop and the flow rate in each outlet if these outlets dont have a flow control valve or even a butterfly valve.

Till date I was using Crane technical paper 410 to do the calculations for pressure drop, but that was for a single input and single output pipe with just one pump connected. there were cases of 2 x 100% pumps, but I simplified the calculation by neglecting one pump. I took the additional tee in the calculation for pressure drop.

The reason for asking all these questions is that they were in my head for a long time and now that client has asked us to perform similar calculation, I thought it is the best time to ask other questions too.

Thanks

Dharmit

 

[KernOily]

There are commercial software packages like PipePhase that work well for this. They are pricey. No relationship, just a satisfied user.

You can hire the publisher of PipePhase to do this for you, or hire an engineering contractor who has the software to do it.

The original poster's problem is a liquid problem so it should be fairly straightforward to solve using one of the copmuter methods. No density change and no heat transfer simplifies things a whole lot.

zdas - 0.05 psi is a preeety tough convergence criterion, especially in a compressible flow problem. One good thing about Pipephase is it lets you adjust all the convergence criteria/parameters of the solver engine to help stabilize the solution. A lot of times a model will start to converge but then it suddenly runs off to bo-bo land, so you can adjust the various criteria to get the thing to solve. A lot of this is a function of your initial guesses and the network granularity. Pipephase has a lot of tricks to help you get a solution. Even with that I have built quite a few models that just would not solve, usually due to looping. Owners tend to build systems that defy analysis... it's "Ehhh, what's one more jumper gonna hurt?" One learns to make a lot of simplifying assumptions in order to get a reasonably representative solution. That, and you talk the owner into installing more block valves.

 

[BigInch]

Stoner Pipeline Simulator has very good convergence algorithms... built in. No fuss. If it doesn't reach a solution, you've really screwed up.

Actually (I was holding my tounge there zdas) and think 0.05 is expecting a little too much from hydraulic analysis. The typical deviations of the actual values of other variables in the field vs their typ. input values in an analysis would not allow confidence in an answer depending on convergence at 0.05 psi. A liter of water could get picked up somewhere, a valve at 99.5% open, or a temperature change of 2ºF and you'd be flowing from the other direction again.

http://virtualpipeline.spaces.msn.com

 

[dmeet]

Thanks vzeus,

These books are for gases but will be of great help.

They make a good start

Thanks

Dharmit

 

[waterengineer1]

Try using the Haaland equation within a spreadsheet this allows you to write a simple spreadsheet that then does not require a goal seek like the Colebrook equation.

 

[KernOily]

You don't have to use the Colebrook equation. There are plenty of formulae that explicitly calculate f. Maybe I missed your point?

 

[BigInch]

Discounting the discussion of the iteration that is required by some equations to solve f, there is another iterative step. Hydraulic networks are not like DC electricity, where a network can be solved by direct solution of n equations with n unknowns. Current is linearly proportional to voltage difference allowing a direct solution, but flow is nonlinearly proportional to the pressure/head differential, so an iterative solution technique needs to be applied to solve the nonlinear hydraulic network equations. It does not make for a small spreadsheet (w/o VBA) for anything more than a few loops composed of a minimum number of pipes.

http://virtualpipeline.spaces.msn.com