Water Bath Fills

My point is that when the pressure drops, the temperature does too equally. So the pressure drops at some point to match the tank, from that point all the way to the tank, the lines will be cooler. If that cool is "lost" to ambient, you will be pumping extra heat in to the tank that is easily prevented.

AND... if that is a significant factor, the lower the pressure difference between the bank and the tank, the smaller the difference between the cool hard lines and ambient will be, and thus less needless heat will be pumped in to the tanks.

It would also then seem to reason that a higher pressure bank system would make cooler hard lines (higher difference between bank and tank), and if you could keep that cool in the lines, and keep the banks cool (getting rid of heat produced by filling them, keeping them out of the sun, etc.), you would have cooler fills.

The heat is only significant in the tank. Heat moves from hot to cold therefore ambient temp is not a factor as the temp/pressure will be far greater than ambient

I fill our tanks in a wet bath (Small Animal Troft). I fill them at a rate of 6 SCFM because that is the max for my filters. I used to fill dry and would have to fill to 37-3800ish to get to Lake Mead and have a 35-3600ish fill. Now that I am using a wet bath I usually always have the psi I filled to when arriving at the lake. Las Vegas heat doesnt help

When I fill my tanks. They again pressure. Is pics.

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Originally Posted by Greenwood_60

Wouldn't some insulation of the hard lines make a huge difference then? All that cold they "lose" on the way to the tank, gets pumped in as extra heat.

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Only partially true.

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.


The other cause of heat is "adiabatic" heating. You can read about it on the link.

http://en.wikipedia.org/wiki/Adiabatic_process

Adibaitic does not apply as the tanks are not insulated and heat transfer does actually occur. Friction is partially for the heat increase. But any matter when compressed will gain potential energy which manifests itself as heat. The heat in fact comes from the energy required to compress the matter.In this case gas which is a fluid. Adibaitic actually means the lack of ability to transfer heat.

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

The OLD gas in your tank, prior to filling is at a given pressure (say 1200psi?).

The new gas you add to the tank, comes from a cascade bank at, say 3500psi.
The new gas cools (adiabatic cooling) as it enters your tank and drops from 3500 to 1200psi.
But as the tank comes up to fill pressure (3500psi), the NEW gas re-compresses, is subject to adiabatic heating.
And returns to it's original temperature (plus heat from friction of motion thru cascade bank plumbing).

Net sum temperature change (for NEW gas) of zero, and the laws of thermodynamics are preserved.

BUT... in the process of filling your tank from 1200 to 3500psi, the OLD, EXISTING gas that was in the tank (prior to filling)
is compressed as well, and exhibits adiabatic heating.

http://en.wikipedia.org/wiki/Adiabatic_process

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Originally Posted by Boru

Adibaitic does not apply as the tanks are not insulated and heat transfer does actually occur....

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Originally Posted by gschaut

Adiabatic is NOT a transfer of heat. It is the property of gasses to self-heat when compressed...

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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 :-)

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Originally Posted by Reddiver

When I fill my tanks. They again pressure. Is pics.

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There was a dive shop in Branford many years ago that put ice in the water tank. They pumped my tanks way up in that ice water. Then I went out in 100 degree heat, with the tanks in the back of my truck, and the sun shining on them. By the time I got to the divesite, the burst disks blew, and I had zero pressure :-(

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Originally Posted by gschaut

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

The OLD gas in your tank, prior to filling is at a given pressure (say 1200psi?).

The new gas you add to the tank, comes from a cascade bank at, say 3500psi.
The new gas cools (adiabatic cooling) as it enters your tank and drops from 3500 to 1200psi.

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No not really. The "new gas" cools where it encounters a pressure drop. Unless you are using the tank valve to regulate flow (baad idea IMO) this cooling happens elsewhere, at needle valve, or at the regulator if one is used.

The "new gas" won't enter the tank being filled without 1) Compressing the gas already in the tank, and 2) Without compressing itself. This compression is what heats the gas and eventually heats the cylinder.

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Originally Posted by gschaut

But as the tank comes up to fill pressure (3500psi), the NEW gas re-compresses, is subject to adiabatic heating.

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See above. As the pressure nears stasis the cooling at the restriction drops.

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Originally Posted by gschaut

And returns to it's original temperature (plus heat from friction of motion thru cascade bank plumbing).

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Heating from "friction" is a very low order effect, particularly for a compressible fluid, much less important than cooling by expansion. This is easily demonstrated, the point of greatest friction (the flow restriction) and greatest cooling (again the flow restriction) gets *cold* not hot.

(Friction heating is notable phenomena in hydraulic and high pressure water systems, but these involve largely incompressible fluids. For example if my water jet plumbing (~65K psi) starts a small leak the fitting will reach several hundred degrees F in less than a minute.)

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Originally Posted by gschaut

Net sum temperature change (for NEW gas) of zero, and the laws of thermodynamics are preserved.

BUT... in the process of filling your tank from 1200 to 3500psi, the OLD, EXISTING gas that was in the tank (prior to filling)
is compressed as well, and exhibits adiabatic heating.

http://en.wikipedia.org/wiki/Adiabatic_process

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The heat gain from filling a tank is a function of the mass of the gas transferred, compressibility of that gas and the and the change in pressure of the transferred gas.

The temperature change depends on the fill rate, temperature of the supply gas, ambient temps, temperature of any cooling medium and the thermal conductivity of the cylinder.

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