Tanks Left in Sun

[scubatoys]

I know you guys are all just trying to have a bunch of fun with math... but basically an Aluminum 80 increases (or decreases as the case may be) about 5 psi for every degree F. So even if it goes up by 100 degrees... that's about 500 psi. This ball park number is close enough for most calculations.

 

[MikeFerrara]

I have a book (I'll look it up when I get home) that said that the plastic in your car would melt before your tank blew. Certified Divers Handbook maybe, yeah, thats it.

Mark

Don't need a book. If volume remains constant there is a linier relationship between temp and pressure.

75 deg F = 535 R....right? F + 460 = R That's our absolute temp scale. We could also convert from C to K by adding 273? if I remember.

535 R/3000 psi = x R/4000 psi

Solving for x above will tell us what temp is needed to take a tank from 300 psi up tp 4000 psi

I get about 713 R which is (713 R - 460) = 253 F

the change in temp was 178 F and the change in pressure was 1000 psi so there is a change of about 5.6 psi for each deg F of change.

 

[mccabejc]

Cool. So I guess the 400 deg. F they quoted wasn't far off. Thanks.

 

[rje634]

Thats why valves have burst disks.

And, yes, they do blow (the burst disks).

Yes they do!! I was at Dutch Springs this weekend and while I was dropping off my tanks for a fill one of the tanks that was in the filled section popped it's burst disk. Scared the S#$% out of me having never heard a burst disk pop before..
So, just goes to show it does happen....

 

[Boogie711]

I too, have seen a burst disk blow... I was at Gilboa waiting for a fill when a HP steel tank blew. Suffice it to say everyone was wearing their brown shorts for a while.

Talk to Soggy on this board. He left his doubles in his trunk and lost a fill when a burst disk went on him.

It can and does happen. Just because a disk is rated for 5000 psi, keep in mind we're talking about a small, tiny piece of copper here that can and will fail. After all, that's what they're designed to do.

 

[Ontario Diver]

I've seen enough pictures of blown tanks in cars. There are other factors like direct sunlight, overfilling et al.

Remember -

In theory, there is no difference between theory and reality.
In reality, there is.

 

[lamont]

As my Thermo professor used to say when he didn't feel like going thru the calculations, "I'll leave it to you guys to crunch the numbers".

The writeup I found seems to indicate that a 67% increase in pressure would require a 533% increase in temperature. So as jhelmuth says, delta P = (nR/V) * delta T.

Which means nR/V must be .67/5.3.

I'll leave it to you guys to crunch the numbers.

Actually, if you have this equation for a constant linear relationship between P and T:

P1 = k T1

Then if you go to T2 = 5.33 * T1 you get:

P2 = k 5.33 * T1
P2 = 5.33 * k * T1
P2 = 5.33 * P1

In other words, a 533% increase in the temperature results in a 533% increase in the pressure.

Gotta remember that its absolute temperature though. So at around 300 kelvin you're going to have to go to 600 kelvin to double the pressure.

Like some other poster said, the typical pressure variation due to temperature variation is going to be order of 10%.

 

[matt_unique]

Is it really a risk of explosion if you leave aluminum tanks in a hot car, or is that just a superstition? I would think that since most diving is probably done in very hot locations, and tanks are always left in the hot sun in some form or another, and there seem to be very few reports of tanks actually exploding, the conditions would have to be just right and extreme before you had a problem.

Though I found out that Aluminum has about 5 times the thermal conductivity as Steel, so maybe AL is more susceptible to transferring the heat into the tank than steel. Although the walls of the AL tank are thicker than the steel tank, so maybe not. Or maybe a reflective paint on the outside of the tank keeps the metal from heating up in the first place.

Geesh, this is giving me a headache...

Ha ha ha - why quantify the paradigm and over inundate with superfluous data? (Stolen from a Dilbert sketch).

I just make a point to keep my full tanks out of the trunk for the day if it is hot.

--Matt

 

[teknitroxdiver]

And remember to replace the disks now and then.

 

[pasley]

Jim,
Last year one of the local divers, Hmmm, let's see, can I remember his name? No. Oh well, it will come to me. Anyway, he had his tank in his car all day. On the way to the dive site in Malibu after a hard day work, the safety plug let go. Made a mess of his car and scared the you know what out of him. So he was a tad updset. A hour of driving, no diving and a mess in his car (and elsewhere I bet) to clean up. Nope, still can't think of the name. Hmm, was it Macheck? Maybe, maybe not. Not sure. But anyway it seems it is one of the sandeater crowd, but that takes in so many. Anyway, he posted it on one of the other forums as a first hand account.