Calculating Leak Rate Through a Crack

Is the medium a liquid or a gas?

If it's a liquid, can you simply place a bucket of known volume under the joint to catch the fluid, and measure the time it takes to fill the known volume, thus giving you the flowrate?

If the Medium is a gas it will be much more difficult, and you may need to employ some special instrumentation, such as transducers to measure a pressure differential, or flowrate before and after the crack.

Could you maybe enclose the joint area with a sealed bag or something to actually capture the gas as it escapes, and measure the volume in the bag after a given time?

It is flue gas from a coal fired boiler. I have static measurements for the duct and it is venting to atmosphere so I'm good there. The leak is actually theroretical and does not exist. I'm assuming an area that would account for a buch of small leaks. I'm just doing this calcuation to estimate how much flue gas is leaking out based on the assumed area. I'm needing to try to find a way to estimate a discharge coeffeicent that would be representative of a small crack rather than an orifice.

The amount of leakage is not only dependent on the duct static pressure, but the flue gas velocity, crack geometry, crack opening roughness, and duct thickness where the crack occurs. These last two may be negligible.

What's the purpose of this focus?

It is to submit what sort of emissions (particulate, CO2 etc..) could potentially be unaccounted for in the stack. Based on the crack geometry, roughness I'm trying to either figure out what sort of discharge coefficient would be applicable or some other method of finding the flow rate.

For a given area, I don't think there'd be much difference between a crack and an orifice, and in any case the area you select appears to be completely arbitrary.

Flow is C*A*√(2*ΔP/ρ) (in consistent units) where C = discharge coefficient, 0.62 should be OK.

Codey

Thanks; That was the big question - whether or not treating it like an orifice is sound. I was thinking it would be vastly different, but was not sure.

Get a cfm meter from Bacharach. I cannot understand what the hell are you going to accomplish even after getting the volume of the escaping flue gases (apart from CO that can cause harm). You should be working on how to utilize the flue gas for further waste heat recovery.

change the expansion joint and help save us the nonsense exercise.