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Flow rate from head loss.

by EthanAnderson
Tags: flow, head, loss, rate
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EthanAnderson
#19
Feb6-13, 02:11 PM
P: 15
Just to be sure, the tank will be filled from the top. Like filling a glass of water. So tank pressure, volume shouldn't matter?
Travis_King
#20
Feb6-13, 02:18 PM
P: 823
Sorry, that was worded strangely. I meant exactly that. The tank is at atmospheric pressure. Feel free to ask me to clarify anything you might like elaboration on in post #18.
EthanAnderson
#21
Feb6-13, 02:56 PM
P: 15
So how can I find the exact flow rate? The formula from engtoolbox.com is only for water with detailed properties. How did you arrive at the conclusion of being higher than 81 gpm?
Travis_King
#22
Feb6-13, 03:32 PM
P: 823
Yea, friction losses for viscous fluids is a different process, but I figured that would help to at least show you the general viscinity you are in. A specific gravity of 1.53 is not that much more than water, relatively speaking.

Here's a link that shows you the expected losses in sch. 40 pipe for various viscous fluids. 50.97 CentiStokes is roughly 260 SSU (conversion), so bear that in mind when looking at the lines.

Viscous Fluid Friction Losses

I have a fluid dynamics program for process plants, running a quick simulation put it in the 130 gpm range. Some online calculators suggest around 100 gpm. When I said significantly higher, I didn't mean that it would be like 600 gpm, I just mean that it was a measurable and physically significant difference.

The thing to take from this, though, is that if you are going to use the method you used. What you want to do is make an initial guess (say 81.5 gpm) and figure out what the discharge pressure is. In this case you got over 7 psi. So you know your flow is too low. So you increase it to 150, you'll get a negative pressure, so it's too high. Keep doing these iterations, with logical progressions, and you will hone in on the correct answer.

Or, you can use the Darcy-Weisbach equation and do all the math:
Helpful link on that
However, because you don't know the flow, this becomes an iterative process for you anyway...
The table you are referring to likely used the D-W equations.

Unluckily for you, this scenario seems to be in the transition zone (Reynolds number in the 2000's), making an accurate calculation using the D-W equation difficult.
EthanAnderson
#23
Feb6-13, 04:14 PM
P: 15
Thank you for your help Travis! Greatly appreciated!
jim hardy
#24
Feb6-13, 05:10 PM
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Years ago where i worked, before computers, the "Crane Handbook" was regarded as "The Source" and was on every ME's desk.

I see it's on the web now.

http://www.craneengineering.net/prod...esFittings.pdf

hope it's some help. I downloaded one to my 'desktop'.

old jim
russ_watters
#25
Feb6-13, 09:49 PM
Mentor
P: 22,243
Quote Quote by EthanAnderson View Post
Would you like for me to email you the spreadsheet so you can see the formulas I used in the cells?
Can you attach it to the thread?

For a first pass by a co-op, that's a really good start. Adding-up all the components and then guess-and-check the flow rate vs the friction loss is the way to go if you can get accurate information on the friction loss.

Travis has given some good help -- more than I could have given. Your solution being far different from water really threw me. I probably would have used software for that.

Stupid question though: Does the railcar or tank have a sight-glass or other way to measure the volume of fluid in the tank? That plus a stop-watch equals a flow meter...


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