Air Sparging

[Picky]

I'm doing some calculations on an air-sparging system and have come across a confusing input (I'm not very familiar with air sparging systems). The input required is the "Bleed-off Flow rate". Apparantly, there are formulas for computing this value this using a pitot tube or a velocity reading. I would be grateful for any advice.

Thanks.

 

[DeltaCascade]

So you want to measure air flow rate in pipe?

 

[Picky]

I would assume so since the values are obtained via a pitot tube or velocity meter. However, my question more relates to the source of this required input value. Are compressor bleed-offs routinely done in air-sparging? If so, how are these values normally recorded? Thank you.
Jack

 

[gtrainor]

I used to design sparge systems and I have never heard that term. But I am certain it pertains to the bleed off rate of air once you shut off the compressor. In other words; when you shut off the compressor, the pressure just doesn't instantly go to zero. The residual pressure under water and in soil fights its way to the atmosphere. Eventually the pressure in your supply line will go to zero (gauge). This would be an indication of how tight the soils are and the depth of water your in. But in terms of using a pitot tube to obtain the bleed off doesn't make sense. You would have to be underground measuring the air flow through each bubble port. I would think of it more in terms of knowing the volume of your piping, temperature, and the start pressure at shut off. Solve for v in PV=nRT (ideal gas law) when it's under pressure. This will tell you the volume of air in your piping system at the instant of shut down. Then observe how many seconds the pressure went to 0 psi. In a no pressure case, the volume of air at 0 psi (gauge) is simply the volume of the pipe. The difference will be in cubic feet or liters. So now you have a volume of air bleeding off at a time interval. And that is a bleed off rate in cubic feet per second or liters per second. But I could be wrong.