Water Bath Fills

[DA Aquamaster]

Taking that one step farther - the outer surface of a steel tank *feels* hotter becaue it *is* hotter. That higher temperature however also increases the temperature gradient between the tank and the air or water it is in contact with. A larger temperature gradient would then improve the heat transfer - the question would be whether the difference is significant, and that then would partially detemrine whether the tank material makes a difference.

The deeper you dig, the more variables you'll find and that's a frustrating waste of time when a simple experiment would meaure the net effect of most of them on a tank fill.

[TobinGeorge]

Taking that one step farther - the outer surface of a steel tank *feels* hotter becaue it *is* hotter. That higher temperature however also increases the temperature gradient between the tank and the air or water it is in contact with. A larger temperature gradient would then improve the heat transfer - the question would be whether the difference is significant, and that then would partially detemrine whether the tank material makes a difference.

The deeper you dig, the more variables you'll find and that's a frustrating waste of time when a simple experiment would meaure the net effect of most of them on a tank fill.

What is the metric of success (or improvement)? Tank Temps or gas temps?

I'd say gas, in which case do we care if the heat moved from the compressed gas to the tank material to the outside air (or water)/ of just from the compressed gas into the tank?

The short answer is if I'm in a hurry and have to fill a tank *now* or blend something *now* is use a water bath (or cold towels) It helps. How? Enough to make the effort worth it.

Better is to plan ahead, that make require more cylinders but that's the least of my worries.

Tobin

[skip]

Guess the empirical approach is the only one left now! No one really knows how much of a difference, if any, a water bath makes. We all know that water transfers heat faster than air, but is it enough faster to really have an effect on tank fills? My thinking is that the difference between a tank filled in a water bath and one not filled in a water bath is very little and not worth adding a water bath to a fill station. In real life, the water is getting heated and with more tanks to fill in less time, the water gets as warm, maybe warmer than the air, and at this point it makes no sense to put the tanks in the water to fill them. I talked Bill High about this and the one thing he said that stuck in my memory is that scuba is full of "tribal knowledge." That's the kind of "knowledge" we all agree is knowing (whether true or not)! So time for the experiment! I'll give it a try next week at the LDS and post the results. Maybe some others can do the same, and we can all compare data!

skip

[Sludge]

No one really knows how much of a difference, if any, a water bath makes.

Have you even read this thread? Several experienced, trained, intelligent people have all said it makes a difference. (Bill High has never shown to have much of a command of logic, but he's the only one you've listened to.)

[Gene Powell]

Have you even read this thread? Several experienced, trained, intelligent people have all said it makes a difference. (Bill High has never shown to have much of a command of logic, but he's the only one you've listened to.)

Most actually said that it "can" make a difference. It all depends on the variables. But, I too am perplexed by the conclusion drawn. He did say he was going to experiment with it, and that's what I would do.

[gschaut]

Ok, here's an idea...

Instead of using pre-mix Nitrox...

Or instead of blending air with oxygen gas to produce your nitrox fill...

You fill your tank with liquid oxygen direct from the cryo dewar (-297 degrees) and compressed air.

Would that keep your tanks cool enough during filling to produce a solid cave fill?

[jcr]

In real life, the water is getting heated and with more tanks to fill in less time, the water gets as warm, maybe warmer than the air, and at this point it makes no sense to put the tanks in the water to fill them.

Remember, water conducts heat much better than air so unless the water is nearly as hot as the tanks, it will still cool the tanks better than air.

I'm not sure what kind of answer you're looking for. Your "experiment" has been repeated for nearly 50 years and the overwhelming conclusion of experienced fill operators is that a wet fill keeps tanks cooler than a dry fill at a given fill rate. It makes a bigger difference with steel tanks than aluminum tanks. Sure, it's certainly possible to fill a tank so painfully slow that they don't heat up significantly. But why do that? A water bath is a simple and effective method of keeping tanks cool during filling. A few simple precautions will prevent water entry, which is the only legitimate argument against wet fills.

[DA Aquamaster]

What is the metric of success (or improvement)? Tank Temps or gas temps?

I'd say gas, in which case do we care if the heat moved from the compressed gas to the tank material to the outside air (or water)/ of just from the compressed gas into the tank?

The short answer is if I'm in a hurry and have to fill a tank *now* or blend something *now* is use a water bath (or cold towels) It helps. How? Enough to make the effort worth it.

Better is to plan ahead, that make require more cylinders but that's the least of my worries.

Tobin

Tobin, I'm agreeing with you - hotter tank = greater gradient = more benefit from a water bath.

[skip]

My steel tanks today went from 88.2 F to 113.7 F filling from 1100 psi to 3500 psi at 5psi per second (300psi per minute). No water bath. 25.5 increase in temp. at 5psi per degree F that's 127.5 psi, so when they cool back to 88 F they should be at 3372.5psi. (I bought one of those gadgets that reads temp via laser.) Air Temp today was 97F, I was in the shade and no breeze. so how much more would a water bath help? I don't know, but I'm planning a test of that next week....I'll fill both al80's and steel 85's (and pst 119's) in and out of water and let you know. any suggestions on varying fill rate? or final pressure?

skip

[TobinGeorge]

My steel tanks today went from 88.2 F to 113.7 F filling from 1100 psi to 3500 psi at 5psi per second (300psi per minute). No water bath. 25.5 increase in temp. at 5psi per degree F that's 127.5 psi, so when they cool back to 88 F they should be at 3372.5psi. (I bought one of those gadgets that reads temp via laser.) Air Temp today was 97F, I was in the shade and no breeze. so how much more would a water bath help? I don't know, but I'm planning a test of that next week....I'll fill both al80's and steel 85's (and pst 119's) in and out of water and let you know. any suggestions on varying fill rate? or final pressure?

skip

Sounds good.

(BTW, the laser just makes the IR detector easier to aim, the laser doesn't measure temps)

Tobin