Pressure drop through a slice/slot

[MariusChE]

Friends

I want to calculate the pressure drop of a fluid that flows out through a slotted opening. The slot is exactly 10 feet wide and 0.637 inches high. The flow is 5107 USGPM and the pressure (total head) is 9.427 PSIG. If I now reduce the slot opening to 0.433 inches, what would the required head be, and how would one calculate that?

I have done a calculation, obtaining the equivalent circular diameter. Doing a straight square edge pressure drop calc I found the required pressure to be around 22 PSIG.

Any comments and help would be appreciated.

Marius

remove.marius_che@yahoo.com

 

[speco]

Marius,

I ran your problem from the Eng-Tips.com posting as I would a nozzle pressure drop in a heat exchanger. Based on a liquid density of 62.4#/ft^3, I came up with a pressure drop of 3.1 psi in the first case and 6.7 psi in the second case. This is based on a sharp-edge sudden expansion only. I would multiply if by 1.5 if there is also a sudden contraction, as in a slot through a plate.

I don't know why my answers are so different from yours, but they seem to be consistent with other's results for nozzle drops.

Regards,

speco (

http://www.stoneprocess.com)

 

[hacksaw]

are you modeling the head box of a pulp machine?

 

[psafety]

If dealing with a paper machine slice opening, I can help with the headbox flow.

Don Coffman

 

[MariusChE]

Yes, it is the headbox for a paper machine.

remove.marius_che@yahoo.com

 

[psafety]

Marius,
I have sent you a email at remove.marius_che@yahoo.com
Don Coffman

 

[MariusChE]

Thanks. Got it. Will respond with my co. e-mail addr.

Best
M

remove.marius_che@yahoo.com

 

[MariusChE]

Speco

What is the discharge coefficient that you used/obtained?

Marius

remove.marius_che@yahoo.com

 

[speco]

Marius,

Here's what I used:
G^2
Pressure drop (psi) = -------------------------------
1.2E11 * Rho

where: G = mass velocity through the opening in #/hr-ft^2

Rho = density in #/ft^3

Regards,

speco (

http://www.stoneprocess.com)

 

[hacksaw]

we performed disch coef measurements on a slice with a contoured inlet; we got Cd=0.99+. pretty much what you'd expect.

what consistency are you running through the slice?

 

[MariusChE]

Gentlemen and Ladies

Thank you for your assistance. Especialy to Don for the XL sheet.

What we found out is that Bernoulli applies. The reason why it was not obvious is because the mass balance cast doubt on the accuracy of the pressure indicator. I tried the calc but it failed against the mass balance - which is why I asked for a coefficient - Thanks. The PI was faulty, in the end, as well.

Thanks a lot, guys. Let me know if I can help you in future.

Marius

If you can't calculate you can't engineer.

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