Distribution Point-of-Use Flow Calculations

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Johnny Two-Guns Participant Join Date: Jul 2009 Posts: 3	Distribution Point-of-Use Flow Calculations 07/14/2009 11:06 AM
	Hello, I have a 140F water distribution loop that spans my plant with a discharge pump and buffer tank. The distribution line is 1.37" id and has a discharge pressure of 100 psi at the pump outlet as well as a static (no consumption) return pressure of 25 which is regulated with a back-pressure valve. The loop has multiple 0.87" id points-of-use "tees" that I have recently choked to limit use flow. I was wondering what is the theoretical method for calculating the flow rate from a Point-of-use "tee" assuming no choking of additional orifice other than the reduction of the "tee's"s diameter. We can assume the pressure at the point of use for the example would be 70 (after -30psi due to equivalent length and exchangers). Let's assume only this point would be used. I am sure this has been discussed and I did try to find it however they all reduce to orifice calculations, which I don't think apply because my case involves a distribution loop and some flow will not pass through the point-of-use orifice (tee). Right?? even a point in the right direction would be appreciated. Thanks, John
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cingold Guru Join Date: Nov 2007 Posts: 519 Good Answers: 11	#1 Re: Distribution Point-of-Use Flow Calculations 07/15/2009 6:32 AM
	The Bernoulli equation is the general governing equation for fluid flow. Because of the branches you have in your problem, you will have to use an iterative method to solve this. Outside of computer programs, the only method I've used for piping networks is the Hardy-Cross Method. Check the Crane Technical Paper 410 (I think that's the right one). It may have some other methods for solving these type of problems. My college book for this is Analysis and Design of Energy Systems by B.K. Hodge and Robert Taylor. This book pulls from the Crane Paper and other similar sources.
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Johnny Two-Guns Participant Join Date: Jul 2009 Posts: 3	#2 In reply to #1 Re: Distribution Point-of-Use Flow Calculations 07/15/2009 8:35 AM
	Thanks for the feedback. I will read up on the Hardy-Cross method. I was hoping someone had figured out an equation to break the problem down to a kind of vector analysis of the non-compressible flow whereby the inbound flow would split into the two directions (point of use & downstream) as a function of the orifice sizes and back pressures. I guess I'm over simplifying. Thanks again, John
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cingold Guru Join Date: Nov 2007 Posts: 519 Good Answers: 11	#3 In reply to #2 Re: Distribution Point-of-Use Flow Calculations 07/15/2009 9:06 AM
	That's basically what the Hardy-Cross Method does. Fluid flow is pretty much the same as electrical current. If you have a circuit with multiple branches and each branch with a different resistance, you will have a different current flow in each branch as long as it can overcome the resistance. Unfortunately, fluid flow is dependant on resistance and resistance is dependant on fluid flow so there is no easy way to solve branch problems. At least none that I know of.
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woodygb Power-User Join Date: Mar 2009 Location: United Kingdom Posts: 308 Good Answers: 28	#4 Re: Distribution Point-of-Use Flow Calculations 07/15/2009 9:44 AM
	This calc might help. http://www.lmnoeng.com/Pipes/PipeNetwork.htm#Hardy Cross Regards Woody
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Johnny Two-Guns Participant Join Date: Jul 2009 Posts: 3	#5 Re: Distribution Point-of-Use Flow Calculations 07/15/2009 3:41 PM
	Thanks for the help. I'll crunch the numbers to see if they match my empirical info. John
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