Water Bath Fills

[RETIRED 11]

the weight of the aluminum is
about 1.5 times the weight of the
steel. What the above means is that
it will take about three times as
much heat to warm the aluminum
tank as it will take to warm the steel
tank. Because the transmission
ability of the metal of the two tanks
is about the same, the differences
noted above are reflected in time. It
will take longer for the aluminum
tank to be warmed by the air inside
it, and it will take longer for the
aluminum tank to give up that heat
to its surroundings. The aluminum
tank has a higher “storage factor”.
What this means is that typically
(because we’re all in a hurry) the
aluminum tank is out of the bath and
out of the dive store before all the
heat gets to the outside surface. The
preceding describes the principal
components relative to the difficulty
in “cooling” aluminum tanks versus
steel tanks

Thermal conductivity of material indicates the number of Joules (a measurement of energy) which will be transferred in 1 second through 1 square metre of the material being 1 metre thick given that the opposing faces have a delta t of 1 degree celcius. Thermal conductivity of steel is 45, Al is 140-160 (SAIT thermodynamics 3)
this shows that in reality Al transfers heat 4 to 4.5 times quicker than steel
Just one flawed statement.

[Tegg]

http://www.fillexpress.com/library/dryfills.pdf

They don't overfill, and as such don't heat the tanks nearly as much as going from 1K - 3600psi... If you want to see the difference a "water bath" makes... go to Bill's on a winter day and fill one of your tanks in the water bath and one in the truck. When you get to the dive site, you'll see the difference.

[Greenwood_60]

They don't overfill, and as such don't heat the tanks nearly as much as going from 1K - 3600psi... If you want to see the difference a "water bath" makes... go to Bill's on a winter day and fill one of your tanks in the water bath and one in the truck. When you get to the dive site, you'll see the difference.

psi seems like it would be an accurate figure to base comparisons off of (if the heat will be a factor of volume of gas pumped/volume of tank), except that the heat will be dissipated by the surface of the tank. Since the volume of the tank will increase at a higher rate than the surface area, a bigger tank will be harder to cool. The surface of the big tank will also be hotter, with a higher temperature difference between it and ambient. I would assume it is not enough to make up for the difference in total heat and lack of surface area, but I have no data.

They are also going from 500psi to 3000psi, and we should be doing no worse than 1200psi to 3600psi, pressure wise they are similar changes. Is the increase in heat going from 2500 - 3000 the same as say 3000 - 3500? Or does pressure or compressibility (or some other factor?) come in to play?

Is there a steel cylinder that holds 77ish cuft at 3000psi? You will again loose some surface area compared to the aluminum tank because of wall thickness... who cares. A side by side comparison would be interesting... steel vs aluminum, wet vs dry, all with cylinder wall temperatures taken at say 1 minute intervals. A IR non-contact thermometer is cheap at Harbor Freight.

Anyone have any real data on the effects of filling tanks in a water bath versus not in the water bath?

In short, no.

[gschaut]

Gschaut, your reply was good as well, don't be intimidated by the "PE" in that link.

Thanks, but I made the mistake of typing before I had my morning brew. It was a bit argumentative.

Short version:

There are TWO SEPARATE arguments going on here:

Slow fill vs fast fill.

And wet fill vs dry fill.

The two arguments should be debated individually, as they are separate variables.

For the record, our Fire Dept uses a dry filling station for SCBA tanks. BUT we are using composite
(fiberglass over AL) tanks, and thermal benefits of wet filling are not significant due to low thermal conductivity of epoxy resin. And we do fill slow. We maintain a sufficient supply of tanks (3 per airpack) that we do not need to fill during anything short of multiple alarm fires. All filling is done at our leisure, back at the hall, after the fire is over.

For AL and steel tanks, I've always felt that wet filling helps dissipate (whatever amount of) heat is generated in the fill cycle.

[RETIRED 11]

Temp equals pressure. That is a constant. Fast or slow changes nothing related to the temp.slow in water just dissapates the heat quicker, thus reducing stress on the tank, which over a considerable period could lead to metal fatigue. This time period would be most likely far greater than the working life of the tank.

[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.

[Sludge]

I work at two shops, one with a water bath, one without. (The one without is PSI-trained, hence the lack of a water bath.) I see a major difference in fills between the two shops. At one, I throw my stages in the water, fill them, and take them home. At the other, I fill them, leave them overnight, then come back the next day and top them off and take them home.

[Greenwood_60]

The back pressure in the tank should help too... since there is less drop in pressure (and lowering of temperature) in the lines on the way to the tank. Which would then seem like you would "produce" more heat filling the greater the difference in pressure between the bank and cylinder being filled.

[RETIRED 11]

The only relative number is the pressure you fill your tank to. This is why dive shops no longer fill 6351. The tanks are made with inferior aluminum alloy

[loquat149]

The back pressure in the tank should help too... since there is less drop in pressure (and lowering of temperature) in the lines on the way to the tank. Which would then seem like you would "produce" more heat filling the greater the difference in pressure between the bank and cylinder being filled.

HUH?

Raphael, can you translate?

Dave