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Hi Jim
> having the preheat tube inside the mixing chamber will change the dynamics inside the chamber.
That one I can answer. Yes, very likely. That mixing chamber looks so simple … It AIN'T!
I did succeed in making and testing a mixing chamber that actually gave a better flame and lower CO when I *blocked off* two of the four air inlet holes. I was a shade startled at first.
Cheers
Mark Rash wrote: > In your article on the BernzOMatic propane can, you point out that upside down feeding liquid propane, a preheat tube might be needed. Have you tried using an inverted BernzOMatic propane canister with a stove like the MSR Windpro that already has a preheat tube?
Mark,
I haven’t tried it, but there’s no reason to: It will work without a problem. The reason I’ve been trying stoves without a preheat mechanism is that there might be a problem.
If you like, I can test it, but there won’t be any problem.
Ken Larson wrote: > Thank you for your inquiry. Unfortunately, the Powercell / Ultra Blue (8oz) line was discontinued in 2009.
Ken,
Is Worthington the same as Bernzomatic?
Even if not, though, I suspected that the PC8 line was discontinued which is why I didn’t make a special thread for it. There are cans out there. I’ve found them, and I’ve talked to others who have found them, but once the cans that are out there are gone, that’s it.
David Thomas wrote: > Jim: I’ll ask the propane guy next time I’m in town, but maybe you know:
Are there retail-level, liquid-feed propane tanks? Like 20-, 40- or 100-pound sizes?
I honestly don’t know. I don’t think even I could fit one of those in my backpack, so I haven’t investigated them.
Stuart Robb wrote: > There is a degree of confusion here. As you were using the Brunton stand, you have a flow control valve at the canister end of the fuel line as well as the one in the stove itself.
You mentioned after my post that you were operating the valve at the stove, whereas I was assuming that you were using the valve at the canister to limit the flow/pressure to at least some degree. Was the valve at the canister just partially or fully open?
OK, so you’re talking to an old stovie here. I’m accustomed to operating dual valves with liquid fuel all the time: The MSR Dragonfly and the Primus Omnifuel. The way the D’Fly and the Omnifuel are generally operated when using white gasoline or kerosene is that you open the at-the-bottle valve all the way, and then control the flame with the at-the-burner valve.
What’s the difference between a liquid fueled stove and a gas stove in liquid feed mode? Not much really. You’ve got liquid hydrocarbons under pressure flowing down a fuel line until they pick up enough heat, typically from the burner, to vaporize. As they vaporize, the expand greatly (over 200X as I recall), and gaseous vapor rushes out the orifice of the jet. The process is the same, only the means of pressurization differs. With liquid fuel, a hand pump pressurizes the fuel reservoir. With liquified gas, the vapor pressure of the gas itself pressurizes the fuel reservoir.
So, long answer to a short question, I run with the at-the-canister valve fully open (or 95%, close enough), and then control things by means of the at-the-burner valve.
Recall my photos from earlier in this thread. Liquid feed 100% propane, GS-100 stove, no flaring.
Liquid feed, some mix of propane and isobtane (starting mix was 85/15, but canister was 2/3 empty), MicroRocket stove, flaring.
There has been some discussion as to why there was flaring with the one but not the other.
I went out for a brief hike this afternoon. I took along 100% propane again, but this time I took along a Markill HotRod stove (looks very much like a Kovea SupaLite or SnowPeak LiteMax). No flaring.
Guys, it’s the fuel. The 100% propane has such a low boiling point that it vaporizes at the drop of a hat. Recall also that the surface area to mass matters. A small tube like the fuel line that connects one end of a Brunton Stove stand to the other has quite a bit of surface area compared to the amount of fuel flowing down the line. Given the length of the line, there’s plenty of time for liquid propane to warm up enough to vaporize. Today, it was nice weather here. Probably 50F/10C when I was testing, maybe slightly warmer. All the heat in the world if you’re propane and are willing to boil below -40 on either scale.
I did feel the canister, the fuel line, and the adapter I was using. The fuel line and adapter were quite cold. The canister was cold, but not as cold as I would have expected had vapor feed been occurring. The canister by the way was propped up by rocks. I am certain that liquid feed was occurring.
Again, I believe the lack of flaring is due to the use of 100% propane in relatively warm weather. In colder weather, I believe heat would have to be conducted from the burner to the fuel for proper vaporization. How cold would that be with 100% propane? I’m not sure. Perhaps Stuart, David, or Roger would have an insight here.
David: Are there retail-level, liquid-feed propane tanks? Like 20-, 40- or 100-pound sizes?
Jim: I honestly don't know. I don't think even I could fit one of those in my backpack, so I haven't investigated them.
My interest is in refilling with 100% propane at home, not BPing with large canisters. :-)
Jim
You have perhaps forgotten one important point: the _only_ reason to run a stove with an inverted canister is to prevent the propane part of the normal propane/butane fuel mixture from being used up more quickly than the butane part. Well ok, it also avoids evaporative cooling of the canister contents, but that is a relatively minor issue and easily overcome.
So, when you have a canister of 100% propane, there is absolutely no need to have the canister inverted – there is no mixture and no component to use up faster. Evaporative cooling is a non-issue with a BP of -42C.
Use the canister upright and it should work perfectly with no chance of a flare up.
BTW, what kind of adapter did you get for the canister?
>"the (fuels) expand greatly (over 200X as I recall)"
I love the number 231. I teach it to junior engineers. Because:
231 cubic inches is a gallon
2.31 feet of water column equals one psi
231 mph was the world record wind speed at ground level set on Mount Washington in 1934.
Now I have another reason.
Fuel gases expand about 231 times from liquid to vapor.
Specifically, using vapor densities from Perry's Chemical Engineering Handbook and liquid densities from Roger Caffin's site on fuel efficiency:
iso-butane expands 225 times
n-butane 233 times
propane 266 times
They are slightly different because the size of the molecule doesn't effect its volume as a gas – only the number of molecule does. But the larger molecules do take up more space in a liquid. Expansion ratios are based on atmospheric pressure and standard temperature. Typically our fuels are colder than that which will increase liquid density a bit and increase gas density somewhat more.
Hi Stuart
> when you have a canister of 100% propane, there is absolutely no need to have the
> canister inverted – there is no mixture and no component to use up faster.
> Evaporative cooling is a non-issue with a BP of -42C.
Of course, if you are sitting at -40 C it might be worth while using liquid feed (ie canister inverted) to prevent the canister from cooling down! Allowing a bit of radiant heat to hit the canister could also be 'useful'.
My understanding is that there are places, like Finland, where one has to cater for -40 C. Hum … a bit cool.
Cheers
>"there are places, like Finland, where one has to cater for -40 C"
And like my house. We've had -41C. But I wasn't camping.
I do notice the propane-fired grill doesn't get as hot at -20F (-29C). Certainly there are more losses off the sides and top. But I think I've also got a lower flame, although it could be a fuel/air ratio issue as well. Anyway, I've learned that below -20/-29, it's just easier and mroe comfortable to cook dinner inside.
Fairbanks usually sees -40 each winter. And -50F sometimes. That's just crazy, stupid cold.
I know people who've been camping in -40 and a very few who had -50F during an Iditarod dog mushing race. Except at that point, it wasn't a race, it was about survival.
And Roger, I know you're not too keen on alcohol stoves, but they use bigger versions to melt ice for the dogs. I'll be asking to see their rigs.
HJ said:
"Poor Alan…"
That's OK. I wonder if the little 170 cans could hold propane and meet regs, but maybe more conventionally thick walls: probably no market anyway.
HJ said
" How hard is it to run a tube up the column (from a manufacturing standpoint)? Looks tricky to me"
" also have a concern that having the preheat tube inside the mixing chamber will change the dynamics inside the chamber. "
Roger Caffin said
"That one I can answer. Yes, very likely. That mixing chamber looks so simple … It AIN'T!"
A simpler alternative would to be to just run the preheat tubes close to the outside of the conventional burner column, so that they are tucked in, and braced against it, rather than more exposed to knocks out on their own.
That cheap $16 remote stove (with tubing of unknown quality) seemed to use the pot stand to protect the tubes, which seemed neat. Some branded remote stoves seem to have more preheat tubing that would seem necessary (e.g. the primus spider): surely that's just extra weight?
Hi Roger
"Of course, if you are sitting at -40 C it might be worth while using liquid feed (ie canister inverted) to prevent the canister from cooling down! Allowing a bit of radiant heat to hit the canister could also be 'useful'."
As I alluded to, there are other ways to overcome this, such as convective heating :-0
But I admit it: I am soft, I don't go camping when it's -40C
Stuart Robb wrote: > You have perhaps forgotten one important point: the _only_ reason to run a stove with an inverted canister is to prevent the propane part of the normal propane/butane fuel mixture from being used up more quickly than the butane part. Well ok, it also avoids evaporative cooling of the canister contents, but that is a relatively minor issue and easily overcome.
Absolutely correct.
But what’s the problem with running like this (below)?
Well, it’s not very stable for one thing. Possible thermal conduction for another — not something I was willing to experiment with! Not with 100% propane.
OK, so use the Brunton Stove Stand but have it upright, yes?
Well, better, but that canister still wants to fall over. Not very stable.
The canister wants to do this:
Now that is stable.
But is a side laying propane canister safe when running the stove? With 100% propane, I thought it might be. So, very cautiously, I tried it. Perfectly safe. Absolutely no flaring of any kind.
So, why didn’t I just leave it on it’s side? Curiosity really. I completely inverted the canister because I wanted to be sure that I was really getting 100% liquid feed. Clearly, I am. There is, however, no practical reason I can think of to invert the canister although at extremely low temperatures perhaps there might be in that the canister would be subject to less evaporative cooling. Also, just as a practical matter, it’s relatively more difficult to invert a big propane canister like the one I used in these last few photos or a PC8 Powercell type canister than it is to invert a dome shaped 100g or 200g canister. Side laying is the way to go with these 100% propane canisters.
Stuart Robb wrote: > BTW, what kind of adapter did you get for the canister?
That is a Kovea “LPG” adapter.
Fuel gases expand about 231 times from liquid to vapor.
This is what I was really worried about in my side laying liquid feed 100% propane set up. That expansion is occurring in the fuel line. That’s a lot of pressure, small diameter or no.
This is also why I absolutely refuse to experiment with cheap knock off remote canister stoves. The consequences of a burst fuel line could be grave indeed.
>"That expansion is occurring in the fuel line. That's a lot of pressure, small diameter or no."
Ah, we've covered this before.
1) small tubing has inherently very high burst strength.
2) the pressure in the small tube CAN'T be higher than the pressure in the canister.
3) Propane has whatever vapor pressure it has at ambient temps. It can't be a higher pressure or it will return to a liquid.
IF you closed both valves with liquid propane in the middle and let it warm up – well then you could get that tubing to a higher pressure. I suggest you not do that only because it's connected to a heat source (the stove). But EVEN if you did that – closed both valves – you can't get propane vapor to exceed propane's vapor pressure for the ambient temperature. If you did, some vapor would return to a liquid. As happens in the canister EVERY TIME it cycles in temperature: day and night, hot and cold, car trunk to mountain trail, etc.
That big diameter canister contains propane liquid and vapor just fine up to 120F / 50C and probably beyond because of safety margins. That very small diameter line can handle much higher pressures than the canister can.
Don't think about expansion of liquid to vapor. It may or may not go to vapor.
Think vapor pressure. The vapor can't exceed it's vapor pressure*.
*You can get the LIQUID to exceed the propane's vapor pressure by overfilling the canister. The liquid expands thermally more than the metal and too much liquid in a rigid container can go to VERY high pressures. That's the huge risk in refilling canisters – they'll take more than is safe if you don't go strictly by weight and never exceed factory fills.
Hi Jim
I'll repeat what David wrote:
You cannot get more pressure in the fuel line than is in the canister while one valve is open. Vapour, liquid, it does not matter!
I'll also repeat his warning: do not shut off both valves (at each end of the line) together. That could create a problem under extreme conditions (which are unlikely in practice). Always shut off the canister valve and let the fuel line empty.
In short, you can place a 100% propane canister at any angle you want. Generally doesn't matter.
Cheers
PS: David's comment that the thin fuel lines are very strong is also very appropriate. Errr … cheap Chinese hoses which shed black powder … may be an exception!
Gentlemen:
Thank you for those reassurances. I know that smaller diameters are inherently stronger for such applications, but it’s nice now to have a sense of just how strong.
By the way, it wasn’t so much that I was worried that the pressure in the fuel hose would be greater than the pressure in the tank, which as David points out would prevent any flow, but rather that the pressure in the fuel hose would be greater than the bursting strength of the hose. The hose was intended for vapor feed and has been successfully used for liquid feed, but I was doing something a bit different: I was using the hose as the generator. Most stoves have a brass or steel generator. First stove I know of where the fuel hose has been used as the generator.
I find your input very reassuring. I just hate trips to the hospital you know, and perish the thought that I might mess up one of my nice stoves. ;)
Thank you both for the science education. It is extremely appreciated. And in particular I will not close off both ends of the fuel line when working with propane.
I’ll put all this, including my little friend below, into a blog post when I get time.
Screw vapor pressures, equations of state and heat of vaporization. Tell me something important:
WHERE DO YOU GET THOSE PROPANE TO THREADED CANISTER ADAPTORS?!?
If it ain't Walmart or Home Depot, tell me anyway, I'm in LowCal 5-6 times a year.
>"I know that smaller diameters are inherently stronger for such applications, but it's nice now to have a sense of just how strong."
And I'll make it quantitative:
For the same burst strength, the wall thickness must increase linearly with the diameter.
e.g. if the tubing is 1/8" and the canister is 2" diameter, the canister must have 16 times the wall thickness of the tubing (if they are of the same alloy).
Conversely, the tubing COULD, burst-strength-rating-only, have 1/16 the wall thickness of the canister. See what I meant? The tubing CAN'T be too thin-walled for burst-strength reasons – it wouldn't resist simple handling.
David, it would be nice if you had your PM set up so we could ask you other related/nonrelated questions that might not be related to this/other threads without derailing the particular thread. I know Jim wouldn't be offended by this post, so I posted it here.
Your call, thanks.
>"I know that smaller diameters are inherently stronger for such applications,
You know what sort of tubing we use for ultra-high pressure applications in Physics?
Small-bore COPPER tubing!
It's bendable, but the small bore makes it unburstable.
Cheers
Screw vapor pressures, equations of state and heat of vaporization. Tell me something important:
WHERE DO YOU GET THOSE PROPANE TO THREADED CANISTER ADAPTORS?!?
lol. Yeah, those are pretty slick, aren’t they? Stainless steel, though, so pretty heavy. In light of the weight of a 465g canister of propane, well, not so bad. Very nice build quality.
I got mine on eBay. I don’t remember which seller. I see one here on eBay. I have no idea if that seller is good or bad, but that is the correct product.
P.S. You want to see a stovie really salivate? Adapters from Japan Yipes! I think I need a cold shower.
Tad: I just updated my profile with a email address. I tried to do a human-readable form:
Dthomas (shift2) (largest US state) period net
but it wouldn't let me. Any tricks to doing that, anyone?
>"I know Jim wouldn't be offended by this post, so I posted it here."
Agreed. (1) this wasn't his or my thread to begin with and we've shamelessly hijacked a stove design question to wander into canister availability, vapor pressures, and pressure vessel design calcs. (2) Bob's sensibilities have already been throughly tested this week and asking me for an email address is quite minor in comparison!
But in general, if you can pose your question by starting a thread, then more people might benefit from the answers, including me. I'm learning stuff all the time and it's always good to have others checking one's answers.
David Thomas wrote: > I’ll make it quantitative:
For the same burst strength, the wall thickness must increase linearly with the diameter.
e.g. if the tubing is 1/8″ and the canister is 2″ diameter, the canister must have 16 times the wall thickness of the tubing (if they are of the same alloy).
Ah, specifics. Specifics good. Wow, that’s a radical difference.
David Thomas wrote: > Conversely, the tubing COULD, burst-strength-rating-only, have 1/16 the wall thickness of the canister. See what I meant? The tubing CAN’T be too thin-walled for burst-strength reasons – it wouldn’t resist simple handling.
Got it!
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