Sterno Inferno model 70138 High-tech Sterno?

[Roger Caffin]

You can’t dry bake with any HX pot. At all. ever.
Why not?
Just keep the heat down surely?

Cheers

[Ryan Smith]

“You can’t dry bake with any HX pot. At all. ever.”

I assume you mean shouldn’t as opposed to can’t.  I’ve done it about 30x by now, so obviously you can. Long term problem?

[DAN-Y]

Interesting! When a canister overheats, does the gas come out from under the O-ring or thru the needle valve?

[Kevin B]

I stand corrected on the hx pots.  For fear or damaging the fins, I’d never run my 14 year old jetboil pots empty/dry (that’s the limit of my experience with hx pots) and when I dry bake in my evernew 1300 I’m usually worried about the bottom deforming, though it hasnt happened yet.

[DAN-Y]

Am I correct to say that Sterno is the first to advocate using alcohol with the exchange fins? I was always in the mind set that canister stoves were the only ones to use that kind of pot.

I’m well pleased that I could boil 2 cups with 1/3 ounce of fuel. There are some that can do that with a non fin grease pot but they are the exception to the rule.

[Ryan Smith]

Kevin – I wouldn’t think there would be too much of an issue with the hx fins given the low flame. It’s not much more than the size of a candle when I dry bake. I can agree there could be long term issues or definitely if it got too hot.

Dan – I’m not too familiar with canister terminology. I just know the valve was hardly open, but the flame was coming out of the burner like it was wide open and the canister was pretty hot to the touch. I closed the valve and out went the flame.

[Stormin]

Thermal feedback caused the gas to expand, thereby increasing the stove pressure and excessive heat output. You were lucky this time, remember to always watch your pot when using canister top stoves and unsecured windshields.

[Roger Caffin]

Hi Dan

When a canister overheats, does the gas come out from under the O-ring or thru the needle valve?

Obviously some gas will be coming out the needle valve, but that is not the answer you are looking for. When a canister overheats most of the gas will come out the bottom, after the bottom has blown off. This tends to happen extremely abruptly and with a very (I mean VERY) loud noise. It is also usually accompanied by a rather large ball of fire as the gas meets oxygen and flame.

In other words Ryan was very lucky he was not killed or covered in deep burns. Imho, stoves should never be left unattended.

Cheers

[DAN-Y]

Roger, what do you make of Ryan’s description of what had taken place. What is you best guess as to where the gas leak was coming from?

Dan – I’m not too familiar with canister terminology. I just know the valve was hardly open, but the flame was coming out of the burner like it was wide open and the canister was pretty hot to the touch. I closed the valve and out went the flame.

 

[Ryan Smith]

Danger is my middle name.  <in my best Austin Powers voice>

[Roger Caffin]

Hi Dan

For a start, I do NOT think there was any gas leak. If there had been, Ryan would have seen a cloud of flame.

Now, what actually happened requires some guessing. OK, I’m game. One would need Ryan to comment on the following.

I think that Ryan’s canister was cold at the start – it IS winter in America after all. So the canister pressure would have been low. If the temperature of the canister was low then the butane may not have been doing very much: the stove may have been running mainly on the propane, and still cooling down to even colder.

I also know that most inexpensive upright canister stoves have a very small control range – you would be lucky to get 90 degrees rotation between off and full bore – 45 degrees on some of them. This was one of the reasons I turned to making my own control valves for my stoves: to get better control: a bigger angle of rotation.

This means that the valve might have been open a bit more than you might otherwise think, just to get a low simmer flame.

Now allow the windshield to close in on the pot. This would trap a lot of very hot air around the canister – air at several hundred degrees. The canister starts to heat up, and the butane starts to add it’s bit to the supply. The pressure inside the canister rises as the temperature rises – a factor of >4x in the pressure would be quite possible. Now you have a much bigger flame!

Incidentally, the ratio between pressure drop and flow through a tiny orifice is unlikely to be linear. At low flows the boundary layer effect will block a lot of the jet area. At high flows that boundary layer will thin down, making for a larger effective jet area. Even more flow and a bigger flame.

My 2c

Cheers

[Ryan Smith]

“I think that Ryan’s canister was cold at the start – it IS winter in America after all. ”

Temp was 42-43F. Canister had been outside and functioning off and on for about 30 mins.

[Roger Caffin]

Hi Ryan

In which case the fuel was probably very close to 0 C.
I think you were lucky.

cheers

[DAN-Y]

I think that Ryan’s canister was cold at the start – it IS winter in America after all. So the canister pressure would have been low. If the temperature of the canister was low then the butane may not have been doing very much: the stove may have been running mainly on the propane, and still cooling down to even colder.

I also know that most inexpensive upright canister stoves have a very small control range – you would be lucky to get 90 degrees rotation between off and full bore – 45 degrees on some of them. This was one of the reasons I turned to making my own control valves for my stoves: to get better control: a bigger angle of rotation.

This means that the valve might have been open a bit more than you might otherwise think, just to get a low simmer flame.

Now allow the windshield to close in on the pot. This would trap a lot of very hot air around the canister – air at several hundred degrees. The canister starts to heat up, and the butane starts to add it’s bit to the supply. The pressure inside the canister rises as the temperature rises – a factor of >4x in the pressure would be quite possible. Now you have a much bigger flame!

Incidentally, the ratio between pressure drop and flow through a tiny orifice is unlikely to be linear. At low flows the boundary layer effect will block a lot of the jet area. At high flows that boundary layer will thin down, making for a larger effective jet area. Even more flow and a bigger flame.

Thank you Roger, that was a good explanation, easy to understand ;-)

[DAN-Y]

Wow, the Infernos are on sale for 19.99 and free shipping.

[Gary Dunckel]

Well, it is free shipping IF you spend $25. So one has to buy something else. Still it IS a good buy for what I consider to be an inferior HX pot.

[DAN-Y]

It’s a great deal, especially when you team it up with the Starlyte XL3. I had super boil tests published this thread. Great combination for a fast weekend jaunt. Take the kids, make them carry the gear ;-)

http://www.woodgaz-stove.com/starlyte-xl3.php

[David Thomas]

“the ratio between pressure drop and flow through a tiny orifice is unlikely to be linear”

The flow rate across an orifice is proportional to the square root of the pressure differential until it isn’t.

Double the pressure across an orifice (and most valves) and the flow rate goes up 41% (i.e. x 1.41 = x SQR(2) ).
Quadruple the pressure across an orifice and the flow rate doubles

Nine times the pressure drop and you get 3 times the mass flow rate.

Or, conversely, to double the mass flow rate, the pressure difference must be 4 times as much.

Until you get to a critical mass flow rate corresponding to the speed of sound in the orifice.  Then decreasing pressure downstream of the valve won’t increase gas flow at all and increasing pressure inside the pressure vessel will increase the mass flow only slowly (due to increased gas density).  This is something we were warned about in Chem Eng classes – to not assume “as the pressure increases, my pressure-relief valve will vent more gas” because it is a very weak effect.

(From memory) that critical pressure difference is about one atmosphere / 15 psi across the orifice for common gases – an operating condition we often have in canister stoves.

 

[Roger Caffin]

Hi David

The flow rate across an orifice is proportional to the square of the pressure differential until it isn’t.
Did you mean the square root of the pressure differential? (per your examples.)

Cheers
Roger

[David Thomas]

Roger, Yup.  Sorry.  I’ve edited it.

[Roger Caffin]

Being acutely interested in fuel flow rates through small jets, it did seem a bit strange.

Cheers

[DAN-Y]

Something else to consider is flames in axisymmetric laminar coflow jets. Take into consideration moderately large values of the Reynolds number, when the boundary-layer approximation can be used to describe the slender mixing region that extends between the jet exit and the flame, providing the profiles of velocity and mixture fraction that exist immediately upstream from the flame front region. The description of the nonslender flame front region, which provides the front propagation velocity as an eigenvalue, requires integration of the Navier-Stokes Equations with account taken of the reaction and thermal expansion effects. The limiting formulations corresponding to cases of practical interest, including large values of the air-to-fuel stoichiometric ratio, are briefly discussed. Illustrative numerical results are given for flames lifted or propagating at distances small compared with the jet development length, where the mixing layer is nearly planar.

just kidding ;)

[Roger Caffin]

Hi Dan

You are quoting maybe? But from where? Sounds like an interesting source.

Cheers

[DAN-Y]

I just wanted to fit in… :-)))  You got me interested in a comment you made about flame front. I googled flame front and this came up:

https://www.tandfonline.com/doi/abs/10.1080/00102200590926932

[Roger Caffin]

Ah, I see. But CST is paywalled, and they want US$50 for the full PDF. I refuse to pay as that represents pure profit to the publisher and does NOT serve either science or the public.

Cheers

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