Water Bath Fills

[Greenwood_60]

The "friction" generated by the gas rushing at high speed thru the tubing generates heat. Even gasses are subject to friction when in motion. That's one reason slow fills produce less heat, slower gas movement produces less friction, and less heat.

I am more familiar with sub-sonic gas flow dynamics. Which this inherently is not. My point was based on adiabatic heating/cooling being 0 loss/gain. Based on my calculations (which are most certainly flawed, but should be conceptually correct) we are only looking at a few degrees difference if there is say a 1 degree Fahrenheit rise in the lower pressure section of the piping.

Much more importantly it seems, would be some way of keeping the difference between the bank and tank to below the sonic threshold... some sort of decompressor, to expand the gas, not allowing it to do so on it's own. It wouldn't have to be a whole lot slower, and it should make a huge difference.

[TobinGeorge]

Anyone have any real data on the effects of filling tanks in a water bath versus not in the water bath? Something more than opinion and hearsay? Something with graphs, charts, tables? Empirical, not theoretical or mathematical (but that too is ok, just not sufficient on its own).

skip

Skip,

What is the goal? Filling reliably to a known pressure? Filling faster? More accurate PP blending? Faster more accurate PP blending?

In my experience all of the above are improved with a cold water bath for the cylinders.

Equally or perhaps more useful is banked gas that has been allowed to cool to ambient vs hot gas straight from the filter towers.

Even better is active cooling of the gas below ambient.

There are so many variables that any examination of the water bath question would need to specify which are fixed and which are to be reached.


Tobin

[TobinGeorge]

I am more familiar with sub-sonic gas flow dynamics. Which this inherently is not. My point was based on adiabatic heating/cooling being 0 loss/gain. Based on my calculations (which are most certainly flawed, but should be conceptually correct) we are only looking at a few degrees difference if there is say a 1 degree Fahrenheit rise in the lower pressure section of the piping.

Much more importantly it seems, would be some way of keeping the difference between the bank and tank to below the sonic threshold... some sort of decompressor, to expand the gas, not allowing it to do so on it's own. It wouldn't have to be a whole lot slower, and it should make a huge difference.

?? Decompressor? Any flow restrictor will 1) Drop the pressure 2) Allow the gas to expand and cool. Unless you want uncontrolled fill rates there will always be a restriction in the flow path.

Hard to see "friction" in any system plumbed with 1/4 or larger tubing unless *very* high gas transfer rates are involved.

If you want to "capture" the cooling by expansion the banked gas generates as it passes the flow restriction 1) insulate the flow control valve 2) Locate it close the cylinder being filled 3) insulate the flow path between the valve and tank.

Tobin

[RETIRED 11]

QUOTE : Adiabatic is NOT a transfer of heat. It is the property of gasses to self-heat when compressed. Can you say "Diesel Engine"? End Quote


"Energy cannot be created or destroyed it can onle be transferred from one form to another"
can YOU say the first law of the conservation of energy?
Self heat?

First law of using the internet " Verify your sources, and ensure you understand what you see before you try to apply it to make yourself appear educated"


In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which the net heat transfer to or from the working fluid is zero. Such a process can occur if the container of the system has thermally-insulated walls or the process happens in an extremely short time, so that there is no opportunity for significant heat exchange[1]. The term "adiabatic" literally means impassable[2], coming from the Greek roots ἀ- ("not"), διὰ- ("through"), and βαῖνειν ("to pass"); this etymology corresponds here to an absence of heat transfer. Conversely, a process that involves heat transfer (addition or loss of heat to the surroundings) is generally called diabatic. Although the terms adiabatic and isocaloric can often be interchanged, adiabatic processes may be considered a subset of isocaloric processes; the remaining complement subset of isocaloric processes being processes where net heat transfer does not diverge regionally such as in an idealized case with mediums of infinite thermal conductivity or non-existent thermal capacity.

[Greenwood_60]

?? Decompressor? Any flow restrictor will 1) Drop the pressure 2) Allow the gas to expand and cool. Unless you want uncontrolled fill rates there will always be a restriction in the flow path.

My statement was based on friction being of any significance. Even "uncontrolled" fills will have some sort of a restriction somewhere... just not a valve in that case. If friction is not an issue, than my statement is pointless.

If you want to "capture" the cooling by expansion the banked gas generates as it passes the flow restriction 1) insulate the flow control valve 2) Locate it close the cylinder being filled 3) insulate the flow path between the valve and tank.

This is EXACTLY what I was talking about earlier. I am under the impression that under ideal circumstances that (other than friction, which I can not quantify) the equation is balanced. As in the only heat the cylinder will gain is the heat the bank lost. Based on that I was trying to get a feel for where this extra heat came from. The gas in the bank (that ends up in the cylinders) is at a higher pressure than in the cylinders, thus the cylinders SHOULD end up cooler than the banked gas. Of course it doesn't, and I would like to know why.

My theory was that you could stop a lot of the heating by not losing the cool. Ever had a paintball CO2 cylinder filled? Mine typically come back icy. Why?

[FW]

...Tobin (who uses a water cooled 6000 psi tube heat exchanger to cool his gas and fills slowly using banked gas through a regulator)

Do you fill tanks in a water bath as well?

[TobinGeorge]

Do you fill tanks in a water bath as well?

Of what benefit would a water bath be for slow fills using cool gas?

If I need to jack some O2 into deco bottles in a hurry I'll lput them in a 5 gallon bucket with some ice water, but I very seldom do that. (I try to plan ahead)

The major benefit is see is for fast fills and or hot gas. The water bath allows the fill station operator to reach the desired fill pressure with less overfill, or with fewer top offs.

Tobin

[TobinGeorge]

This is EXACTLY what I was talking about earlier. I am under the impression that under ideal circumstances that (other than friction, which I can not quantify) the equation is balanced. As in the only heat the cylinder will gain is the heat the bank lost. Based on that I was trying to get a feel for where this extra heat came from. The gas in the bank (that ends up in the cylinders) is at a higher pressure than in the cylinders, thus the cylinders SHOULD end up cooler than the banked gas. Of course it doesn't, and I would like to know why.

It's the mass, the compressibility and the delta P that determines the heat gained or lost, the absolute pressures are not important.

My theory was that you could stop a lot of the heating by not losing the cool. Ever had a paintball CO2 cylinder filled? Mine typically come back icy. Why?

CO2 is transferred as a incompressible liquid, some of which will flash into a vapor as it enters the empty tank, think refrigeration cycle. The latent heat of evaporation is huge.

Tobin

[DA Aquamaster]

Y'all quit squabbling, you agree on the main point, filling tanks in a water bath is better. Now just come up with some numbers

I agree with you forrest - I like a good theoretical discussion as much as any one, but in the end, what matters is how more or less efficient the fill is in a water bath.

Which takes us back to a simple experiment controlling for as many variables as possible and requiring the following equipment:

1) 2 AL tanks and 2 steel tanks, all four with comparable tank factors -AL 80s (TF= 2.5) and steel 72s (TF= 2.8) are close, another option would be a 3300 psi AL 100 (TF= 3.0) and a 3442 psi X7-100 (TF=2.9).

2) a four whip fill manifold

3) a water bath with the water at ambient temperature

The procedure would be simple:

Start with 4 empty tanks with 1 steel and 1 AL in the water bath, and 1 steel and 1 AL out of the water bath. Fill all four tanks off the four whip manifold at the same fill rate of 600 psi per minute. Fill all four tanks to the same end pressure (3000 or 3300psi to reflect the service pressure of the AL tanks used (I've never blown up a steel 72 with a 3000 psi fill, and its a non problem if a 3442 psi tank is used, but if it others you stop the fill for all four tanks at 2250 psi.) Stop the fill, close all the valves to isolate the tanks, disconnect them and let the tanks cool. When cooled to room temp, record the pressure in each tank. That will tell you the difference between wet and dry fills for both steel and AL tanks compared to one another and when comparing steel to steel and AL to AL.

Since we are pumping roughly the same volume of gas into empty tanks to the same pressure, the details like wall thickness, heat transfer properties of the materials, surface area of the tanks, etc, don't matter as we are just measuring the effect of the water bath on the same AL and steel tanks as well as between steel and AL tanks of comparable internal volume.

[Brian Kakuk]

When I took my PSI course with Bill High back in 85, the argument for non-water bath filling was simply that the DOT did not recommend it as it promoted over-filling. He stated that contrary to popular belief, water actually increases kinetic energy during a catastrophic rupture rather than buffers it...I'm not a mathematician, nor physicist, but seemed to make sense to me. I've used both ways at different military and civilian facilities. Water baths "usually" keep you from over filling too much during filling (unless you are a cave supporting facility), while non-water baths require me to take my steel 85's to 3800 psi in order to have 3500/3600 in them when they leave the shop.
I’m not sure if DOT standards have changed…maybe someone who has taken a recent PSI update can chime in there. Safe filling,
Brian