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Old May 29th 2017, 12:20 AM   #1
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Head Loss in Pipe Network

Consider an overhead tank with a constant head (some mechanism maintains the constant head) kept at a height H from a reference line. Through a vertical pipe the fluid is brought down to the reference line and ejected into a glass tank as a horizontal jet.

I need to find the Height H required to obtain a very low Reynold's Number (=100) jet.
I am using the bernoulli's equation with head loss:

p1/rho*g + v1^2/2g + H = p2/rho*g + v2^2/2g + 0 + Head_loss

1 is the free surface of overhead tank and 2 is pipe exit in a glass tank. Now, I am writing Head loss as Head_Loss = (64/Re)*(H/D)*(Vavg^2/2g)

All the other terms are fine. But the issue is that the Head Loss depends on the unknown height H, which on simplifying the equation gives me a term:

(1 - (64*Vavg^2/2g*D)/Re)*H = (1 - k/Re)*H = Other P and V terms

for changes in Reynolds Number sometimes I am seeing that this coefficient is becoming zero or negative giving me a singularity or a negative height for the tank placement.

How is this physically possible, what am I doing wrong?
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Old Jun 17th 2017, 04:49 PM   #2
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Here's what I know

I'd suggest you should find the equation for height in terms of all other factors, and also find an equation for flowrate(or velocity or dynamic head) in terms of all other factors. If you get a negative or very small value of height in that case, it'd suggest that your losses are too great, you will then have to find out your favorable flow rate using the height you need and vary other factors to check. Remember that you might wanna change the diameter of the pipe, speed(flow rate), material of the pipe(f) and static head(pressure) too to obtain your height.
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