HP air Bottle Sizing Problem?

[tribleprince]

Senario-1
I have a tank of Volume = 4.19 Cubic meter which is filled with water. Thank has an opening of 200 mm (0.2M) at the bottom of the tank also known as Flood ports. I want to empty the tank by giving a HP air blow at 10 Bar. How much air is required to empty the tank completely.
If someone can give any formula or any reference that can help me.
Senario-2
I have a tank of Volume = 4.19 Cubic meter which is filled with water and the tank is dipped in water at a depth of 5 meter depth. Thank has an opening of 200 mm (0.2M) at the bottom of the tank also known as Flood ports. I want to empty the tank by giving a HP air blow at 10 Bar. How much air is required to empty the tank completely.
If someone can give any formula or any reference that can help me.

 

[JohnGP]

The old P₁V₁/T₁=P₂V₂/T₂ should do it. Temperature effects probably don't come into it, so that would simplify it a bit.

You want to displace 4.19m³ of water, so that's how much air you need - final pressure will be whatever head you are pushing against - in the second scenario approx 0.5Bar if the bottom of the tank is at 5m below water surface. You can work that back to determine what volume of 10Bar air you require. You would need to allow to lose a bit of air to get the last of the water out.

That's it in very simple terms anyway.

Cheers,
John

 

[prex]

As the port is at bottom, you don't need any overpressure to empty the tank.
You need to specify more data to define your problem: pressures and deltap in lines upstream and downstream, required maximum time to empty the tank and perhaps more (e.g.how is the port closed before starting? in how much time will it be opened?).
And of course your tank needs to be stamped for a design pressure of 10 bar, unless you can calculate a lower pressure will be reached at the maximum rate of air inlet. The tank could also require a safety valve.

prex

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[JohnGP]

prex,

In the scenarios described, an overpressure is required otherwise you would just be able to drain the tank by gravity in Scenario-1. As you point out though there is not really enough information provided to give meaningful advice - on reflection it seems to more the sort of problem one may get in high school.

 

[tribleprince]

Thanks for the reply friends

Let me elaborate a little bit more.

I have a tank of Volume = 4.19 Cubic meter which is filled with water. Thank has an opening of 200 mm (0.2M) at the bottom of the tank which will remain open always.
There is a vent opening at the top which can be controlled by a solenoid valve. When the vent is open the tank will sink and reaches 5 meter depth below surface and at that time vent is closed by a solenoid valve.
Then there is a pipe for blowing at 10 bar inside the tank for blowing out the water in tank and to raise it to surface.
Outer pressure or back pressure at 5 meter depth is 0.5 bar.
I want to repeat the process for 2 or 3 times so how much volume of air will be required ?

 

[JohnGP]

Well, it's not a simple problem anymore -
Will the tank be actually full of water when it has sunk to 5m depth?
Will it start to rise before all the water is expelled (and so reduce the back pressure experienced by the air)? Tank weight will play a part there.

Each cycle will consume less air than would be calculated by the method described in my first post though, if the tank is not full of water when it is at 5m depth, and starts to rise before empty. Depends how accurate you need to know.

Cheers,
John

 

[tribleprince]

Thanks John
The Tank will be completely filled at 5m depth.
and it will start rising as air will be blown into it.

 

[Eltron]

I guess I'm confused at the intent of the question. If your bobbing tank is 4.19 m^3 then that is the volume of gas you will need to evacuate the water from the tank at whatever your working pressure is - in this case 10 bar. You say you'll need to do this a couple of times, so 4.19*3=12.57m^3 of gas at least. Again, this is at your working pressure. A standard compressed air cylinder holds an internal volume of .049m^3 at ~2500psi, so you would need around 16 cylinders to perform the task at the specified pressure with cylinders of air. So, I imagine you're going need to use a compressor to provide the air unless you have a manifold system. Either way, you'll need to use a regulator to deliver whatever pressure it takes, and heed the safety warning of the gents above.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[JohnGP]

You won't actually use the total volume of 10bar air - as soon as it is introduced into the "tank" (as a regulated supply per Eltron's response) it will displace water out the bottom. The air pressure will depend on the tank depth - it should start to rise when buoyancy effects kick in, and the air already in the tank will continue to expand as the tank rises. Speed of ascent depends on the rate air is introduced. As I indicated above, tank weight also plays a part.

Not sure what shape the opening is in the bottom, but overpressure is not likely if it's a round or square 200mm hole.

Cheers,
John

 

[tribleprince]

thanks to all of you
you people did add a valuable knowledge to me.
its really a serious problem. may be we are missing something which may cause problem during practical demonstration.

thanks