Ian, your formula is functionally equivalent to the ones I used, the difference being that I posted two equations to show where pressure head comes from. Your "q" is what I referred to as "rho", or water density. The value difference is just round-off error (this, unfortunately, stacks, which is why my notes get filled with numbers to a ridiculous number of decimal places, and then reduced to an approximation at the end), and the fact that the discharge coeffecient (my "K", your "C") was ignored in my calc, and assumed to be thin-wall, round hole, laminar flow in yours. Neither assumption is correct, but the reality is that the exact conditions are not known, so you can approach the problem either by determining the exact worst-case conditions for every possible variable and run through the derivation, or just make some assumptions to simplify. Erring on the side of caution, I would tend to assume a higher K value, but in any case, we are both in the ballpark, which is about as close as we can expect without experimental results.
-Sean
On Feb 5, 2009, irox@ix.netcom.com wrote:
Hi,
he's how I tackled the same question. Definitely not ideal, but
probably good enough to get the idea.
(A)area of leak = (outer hole area) - (inner shaft area)
A = pi * .0127254^2 - pi * 0.127^2
= 0.00000203 m^2
(P)pressure = 500psi
= 3447378pa
(q) Water density = 1000 Kg / meter^3
(C) flow coefficient (guessing at 0.62, 1 would be frictionless)
(V) volume (GIECK Engineering formulas)
V = C * A * sqrt( 2 * P / q )
= 0.62 * 0.00000203 * sqrt ( 2 * 3447378 / 1000 )
= 0.000088055 m^3 per second
= 0.088 liters per second
= 5.28 liters per minute.
Please feel free to check my calcs. If I've done something wrong,
I would very much like to know where.
Cheers,
Ian.
-----Original Message-----
>From: "Smyth, Alec" <Alec.Smyth@compuware.com>
>Sent: Feb 5, 2009 8:43 PM
>To: personal_submersibles@psubs.org
>Subject: [PSUBS-MAILIST] formula for leak volume?
>
>I'm trying to calculate something but haven't found the right formula. Let's say the seal on my 1" prop shaft disintegrates. Just inboard of the seal, the shaft goes through an opening that is 1.002". This opening is not of any significant length The ambient pressure is 500 psi. How many gallons or liters per minute would come in?
>
>I'd really appreciate any pointers!
>
>
>thanks,
>
>Alec
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