Preheat tube run up centre of burner column ?

Hi, Alan,

Sorry. Missed this post. There are a variety of ways to accommodate sufficient thermal feedback to facilitate liquefied gas vaporization. I suppose one could run the fuel line up the burner column, but at some point, generally, the fuel line needs to be exposed to the flame.

Interestingly, the other day I was experimenting with 100% propane for a backpacking stove. At 40F/5C, no thermal feedback at all was required to vaporize liquid feed. See 100% Propane for Backpacking.

HJ
Adventures in Stoving

The preheat tube would emerge into the flame at burner end but would be protected (from knocks etc) for most of its length within the column.

100% Propane for Backpacking:
I wonder if liquid worked because it hit the hot top of stove, vaporised, then out the unusual horizontal side vents of the snow peak as gas, unlike the micro rocket where the liquid gas came straight out vertically and flared.

I wonder does that can have thicker walls than normal for propane.

Alan,

I think the main difference between my run with the GS-100 on 100% propane and the MicroRocket on a 85/15 iso/pro mix is the fuel itself. Propane has such a low boiling point (below -40 in either Fahrenheit or Celcius), that it vaporizes with extreme haste.

The 85/15 mix doesn’t have nearly the same propensity to boil. The canister I was using was also only about 1/2 to 1/3 full, meaning that a lot off the pro has already burned off. It was also a fairly cold day, although the cold would be partially offset by the fact that I was at 8038 feet/2450m in elevation.

I don’t believe the Bernzomatic Powercell 100% propane canisters have substantially thicker walls. An empty snow peak 220g canister weighs 4.7oz/133g. An empty Bernzomatic Powercell weighs 4.9oz/139g. There’s only a difference of about 0.2oz/6g. The Bernzomatic Powercell does have a much smaller diameter which may give it the strength that it needs to withstand the greater internal pressure of 100% propane.

HJ
Adventures in Stoving

>"100% Propane for Backpacking:
I wonder if liquid worked because it hit the hot top of stove, vaporised, then out the unusual horizontal side vents of the snow peak as gas, unlike the micro rocket where the liquid gas came straight out vertically and flared."

That seems unlikely to me. Jim knows stoves and I think he would have reported the sizzle/roar of liquid fuel boiling on contact with the hot stove top a la a Svea 123 or any other old stove with a spreader plate to vaporize liquid fuel. And the mass flow of a jet of liquid would have been greater than for a gas so you'd get flaring, right? I've burped liquid fuel into a variety of gas burners over the years and the 2 to 20-foot column of flame is hard to miss.

What if the orifice was functioning as an expansion valve as in a refridgeration cycle? Than the liquid would flash to vapor at the beginning of the orifice but continue through the orifice as a cold gas and therefore be limited to the same mass flow as when in vapor mode. The "expansion valve" would get cold, but that's okay – there's not water vapor in the fuel to freeze (as there is in a carburated gasoline engine). Just a cool liquid coming up to the orifice and a very cold gas leaving it.

Jim: Was there icing on the orifice assembly?

In a classic expansion valve, you assume no heat transfer – it gets cold, but you don't try to balance that with ambient heat. It just gets cold and stays cold.

David,

There were no detectable odd characteristics or phenomena as I ran the GS-100 on 100% propane. I believe vaporization was happening prior to entry into the final burner head area. If vaporization were occurring too late in the process, then flaring would occur — and none did.

Contrast this photo (100% propane)

With this photo (85/15 iso/pro)

The burn in the first is completely normal. The second is quite irregular.

Jim: Was there icing on the orifice assembly?

None that I could detect.

Interesting idea though. The heat to vaporize has to come from somewhere. The body of the stove should get quite cold.

HJ
Adventures in Stoving

>"The heat to vaporize has to come from somewhere."

No it doesn't. At least not from anything else. The propane gas can just get cold. This is what the freon does going through the expansion valve in your refrigerator.

In the canister, yes, the heat has to come from somewhere and usually from multiple sources: (1) the sensible heat of the can and contents, causing it to cool down, (2) sensible heat conducted from the environment, (3) latent heat of water vapor as it condenses, and (4) latent "heat of fusion" when liquid water freezing to ice. (3) and (4) can and do occur together when the canister is below 0C – gaseous water condenses into ice, releasing both of those heats at once. I've iced up 500-gallon propane tanks in the cool and humid environment in SF when running some equipment flat out.

In an expansion valve, the heat of vaporization is taken from the fluid itself. The liquid/gas gets cold such that its delta T x Cp x mass flow = Hvap x mass flow.

Yeah, I know, it's not quite Cp because we don't have constant pressure. Nor is it Cv because we don't have constant volume. Really, it is at constant enthalpy and you flow an iso-enthalpy line on a P-T-Enthalpy diagram and see what temperature it leads you to.

You ever checked out how a propane-powered fridge works? I'm pretty good with this stuff and yet I have squint my eyes, think hard, and kind of twist my mind to follow the PFD (process flow diapgram, not a life jacket nor the free money Alaskans get) on one.

Hi Jim

Long hose there. Sometimes you got gas out the jet, and sometimes you got liquid.

My guess is that the GS100 is sending a bit of energy back down the column and into the end of the hose (it does), and more energy is coming in through the walls of the long hose, so that a lot of the time the liquid is evaporating either at the constriction in the canister coupling or along the hose. Yep, seen that.

Cheers

Hi, Roger,

Thanks for your insights. If I get a chance, I may re-test the GS-100 (er, well, I believe mine is the GST-100, but whatever) and look for thermal conductivity just as I did with my MicroRocket set up.

I was actually quite surprised that I got no flaring, even though I was using 100% propane. If I do more tests, I’ll use a big 16.4oz/465g propane bottle with an adapter. The backpacking stove compatible ones like the one shown in my photo are too hard to find (discontinued I believe) to justify using them up for testing!

HJ
Adventures in Stoving

David,

Your “Explaining a fridge to a stove guy” left me a little cold. (sorry. Got off work at about 0500 this A.M. Exhaustion does not improve my jokes apparently)

I’m a little fried right now from overwork, but I’ll re-read your post in a bit. It’s been a looong time since I took Chemistry 201 and Physics 301, so be patient.

HJ
Adventures in Stoving

Hi Jim

Yeah, mine are GST-100s as well. Benchmark stoves, both of them.

I'll add one other observation, which might help as well. When the stove is flaring the burner does not get all that hot compared to proper operation. That means there is a bit of a vicious circle there: if it flares it lacks sufficient thermal feedback to vaporise the fuel and start burning properly. Yes, I have seen this myself while developing winter stoves.

Preachy at rest of world: using 100% propane means the available pressure at the jet is much higher than with any of the 30% propane mixes. At such higher pressures there is a real potential for the flame to lift off the burner head and 'blow out'. That means the burner is then spewing out a fuel/air mix which could lead to a fire ball and loss of eyebrows (or more) …
Be Careful! And experiment outdoors.

Cheers

David – you are right in principle, but the main pressure drop occurs across the flow control valve, as the pressure drop across the jet/orifice is really quite small.

My own observations are that if liquid fuel comes out of the jet, insufficient air is drawn into the mixer tube and this is the cause of the yellow flare.

So, the propane vapourises in the fuel hose. Because the boiling point of propane is so low, you just get cold gas.

So, the propane vapourises in the fuel hose. Because the boiling point of propane is so low, you just get cold gas.

Thank you, Stuart. I thought that was what was happening. On liquid propane, the stove behaved as a gas stove normally would. There were no odd noises, flares, or inconsistent flames. I surmised that vaporization was happening in the long fuel line.

One might worry that with vaporization occurring in the fuel line that the pressure in the line might be so great as to burst the line. However, I found no evidence of extreme high pressure while operating the valve at the stove. I did not open the valve 100% (I don’t normally). I think the length of the fuel line, which as Roger noted, is quite long, allows enough room for vaporization without creating extreme high pressure. I’ve seen indications of greater pressure change when inverting the canister on a WindPro for example (surge in flame, etc.).

HJ
Adventures In Stoving

I see Suart's point about most pressure drop occurring across the control valve, at least in vapor-phase operation (otherwise, the control valve wouldn't offer any control). But a slightly opened valve, that would give a small mass flow of vapor, would correspond to a high mass flow of liquid.

Test of that: Jim, could you regulate the flame with the control valve (on the fuel bottle?) during liquid-feed operation? Versus if the orifice functioned as an expansion valve, it would define a set mass-flow of propane.

My trouble with assuming vaporization in the tubing is that it there is so little surface area to absorb the BTUs to provide the Heat of Vaporization – I'd expect that small diameter line to get quite cold and noticeable ice up.

Jim: I wouldn't fret about bursting pressures in a small diameter line. I'll teach you that calc someday, but small diameter lines are inherently high-pressure rated. You can't make them thin enough or you'd puncture, bend them, and any minimal tubing thickness provides huge burst strength. Especially compared to that thin-walled Benzomatic canister of MUCH great diameter.

And remember, the pressure is greatest in the tank, then in the tubing, and lowest right at the orifice. Otherwise, flow wouldn't happen.

And, for completeness: Could there be some crazy pick-up tube inside the Benzomatic canister? The reverse of a chainsaw fuel pick-up tube? You can operate a chainsaw sideways and upside down because the fuel pick-up is a flexible tube with a weight on it. So when the fuel falls to a different side of the fuel tank, the end of the pick-up tube falls with it and settles at the lowest point within the liquid fuel. You could make a tank with a tube with a float so it was vapor-feed in any position. Seems like a bother, but it would allow you to operate in any position and that would add a lot of safety for some applications. Any rattling if you shake the Benzomatic can?

(Sorry, I know you want to save those 100% propane canisters, but) the clearest test might be to run it for a while in "liquid-feed" mode and check tank temp before and after. If it is truly liquid-feed, there won't be any temp drop. If it is phase-feed – if it is vaporizing in the tank – the temp temp will drop noticeable over time. My non-contact IR thermometer would be handy for detecting that temp drop quickly. Image the bottom of the tank where the liquid feed is, it will get the coldest. But you knew that.

Editted to add: Oops, I couldn't see the photos while composing that. The valve is on the STOVE, not the tank. And you couldn't get flare-up on 100% propane but you could on a butane mix? Hmmmm. I'm liking the idea of a floating pick-up tube more – give it a shake and listen. And/or cut one open once exhausted.

I need to get me some of those Benzomatic canisters. For all sorts of reasons.

David,

Re:

How a Propane Fridge Works

If you follow the link scroll down three quarters of the way towards the bottom of the page or .75 of the page facing. My shilling’s worth. LOL ;-)

Heat is produced by the burning propane below the “generator” in the fridge that contains the water, ammonia and hydrogen solution. It is the ammonia that evaporates and absorbs the heat to produce the cooling effect in the fridge.

I have however experienced first hand the refrigeration effects that are possible with a fuel gas both in my canister stove and in larger control valve / orifice plate applications.

The keys are flow, differential pressure, expansion and absorption. In the fridge there is one more step, cooling, where the ammonia releases its absorded heat to complete and begin the cycle again.

I’ll go lie down now because my brain hurts. ;-)

Party On,

Newton

Hi Jim

> One might worry that with vaporization occurring in the fuel line that the pressure
> in the line might be so great as to burst the line. However, I found no evidence of
> extreme high pressure while operating the valve at the stove.
Misunderstanding here.

The pressure in the line is going to be very close to the pressure in the propane tank, especially if the propane is in liquid state. There might be a *small* pressure drop at the canister connector if what is going through is gas, just because of the higher flow rate. But if liquid is going through the canister connector, then you can safely say the pressure in the line is FULL pressure.

In addition, you cannot get a higher pressure anywhere in the system than is found in the propane tank. Yes, that IS going to be high, but nothing gets higher.

Those little hoses are quite strong, so I would not worry about them. Unless of course the hose is shedding black powder … That was just Chinese cheap and very nasty.

Cheers

Jim
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?

The propane info is interesting but here is a diagram of my
"Preheat tube run up centre of burner column" idea;
protects tube from damage, might allow thinner(lighter) metal for burner column:

David Thomas wrote: > Could there be some crazy pick-up tube inside the Benzomatic canister? The reverse of a chainsaw fuel pick-up tube? You can operate a chainsaw sideways and upside down because the fuel pick-up is a flexible tube with a weight on it. So when the fuel falls to a different side of the fuel tank, the end of the pick-up tube falls with it and settles at the lowest point within the liquid fuel. You could make a tank with a tube with a float so it was vapor-feed in any position. Seems like a bother, but it would allow you to operate in any position and that would add a lot of safety for some applications. Any rattling if you shake the Benzomatic can?

I just took out one of my Bernzomatic PC8 Powercell canisters. There is no rattling or any other sound that would indicate the presence of a vapor feed tube (as in a restaurant type 100% butane canister). Nor, during use, was there any observable indication of something that would imply anything like that.

The instructions say:

DURING USE
1. Use upright to prevent flare-ups or flashes. Never drop or throw cylinder.
2. If torch sputters or flares up, turn cylinder upright and turn off torch. Vent area to remove unburned gas. Slowly turn on. After hearing slight hiss, re-light.
3. Never use near pilot lights, flames, sparks, or other possible ignition sources. They can ignite leaking gas.

Emphasis original.

Based on the instructions and my observations during use, I’d say there is no dip tube, float, or vapor feed tube (or similar).

My trouble with assuming vaporization in the tubing is that it there is so little surface area to absorb the BTUs to provide the Heat of Vaporization – I’d expect that small diameter line to get quite cold and noticeable ice up.

Didn’t see any, but I’ll try running for a while on liquid feed and see what happens. I’ve been sparing thus far (for obvious reasons).

I wouldn’t fret about bursting pressures in a small diameter line. I’ll teach you that calc someday, but small diameter lines are inherently high-pressure rated. You can’t make them thin enough or you’d puncture, bend them, and any minimal tubing thickness provides huge burst strength. Especially compared to that thin-walled Benzomatic canister of MUCH great diameter.

Ah! Of course (slaps forehead). Duh.

I’m just a Nervous Nellie when using fuels that a stove wasn’t designed for. I turn everything down really really really low before I light a match. Really low. I run things for a while before turning anything up. I’ve tried all kinds of arrangements with various gasses, kerosene, gasoline, etc with various stove components. Just call me “Dr. FrankenStove.” :) Never had a problem, but, still, best to err on the side of caution. Schtuff happens.

Oops, I couldn’t see the photos while composing that. The valve is on the STOVE, not the tank.

Both, actually.

I need to get me some of those Benzomatic canisters. For all sorts of reasons.

Yeah, they’d be nothing short of ideal for use in your location. There is an eBay seller in Boise, ID that is selling packages comprised of a torch and one Bernzomatic Powercell for $12/pkg. Just one catch: Local pick up only.

HJ
Adventures In Stoving

>> David: I need to get me some of those Benzomatic canisters. For all sorts of reasons.

>Jim: Yeah, they'd be nothing short of ideal for use in your location."

Jim, Thanks for the reply. And yeah, since I wouldn't cross state lines with it and I'm unaware of any Alaskan regs against refilling, a few canisters could last a long time when in rotation. There's no shortage of 20-pound (net) propane cylinders around my place and I'm not afraid to do a little plumbing.

When I get any fuel canister, I weigh it and write the full weight on the bottom. Then when I use it all up, I weigh and record again ON THE CANISTER itself. Then I can check partials for how much fuel they have remaining. And, coincidentially, if someone were inclined to do a little refilling. . .

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've assumed that the new OPD over-fill protection devices preclude inverting the modern 20-pound cylinders, but I suppose I should try that first.

But it's 15F, gusting to 30 mph and a bull moose (with one antler, a left-winger perhaps?) just bedded down next the garage. Maybe this afternoon!

Poor Alan, we’ve hijacked your preheat tube thread haven’t we?

Good diagram. The question I have is: How hard is it to run a tube up the column (from a manufacturing standpoint)? Looks tricky to me.

I also have a concern that having the preheat tube inside the mixing chamber will change the dynamics inside the chamber. I can’t say how, but I doubt it would be good.

I don’t see the utility outweighing greater manufacturing costs and the necessity of redesigning the mixing chamber. Just one layman’s opinion.

HJ
Adventures In Stoving

When I get any fuel canister, I weigh it and write the full weight on the bottom. Then when I use it all up, I weigh and record again ON THE CANISTER itself. Then I can check partials for how much fuel they have remaining. And, coincidentially, if someone were inclined to do a little refilling. . .

I’ve been refilling my own BP’ing canisters for a couple of years now. It has worked great so far. I pay $1.25 for 230g of 100% butane in the “spray can” style canisters that are used for table side cooking in restaurants. Compare that to $5.00 for 110g of butane/isobutane/propane mix in a small backpacking canister.

In warm weather (fuel temperature above 40F/5C), there is no discernible difference between the performance of 100% butane vs. the butane blends sold in backpacking canisters.

Basically, in the summer months (and a lot of late spring/early fall), I have really cheap gas. It’s the equivalent of going into a store and seeing a sign: “Backpacking gas canisters, 75% off”. It’s easy, but I am very careful to as you say record weights. ON THE CANISTER. I weigh before, during and after. I’m just using 100% butane which has a relatively low vapor pressure, so not too much worry, but still, I don’t want to overfill.

I haven’t tried propane. Whole ‘nother ball of wax, as they say.

HJ
Adventures In Stoving

Jim:

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?

Thank you for your inquiry. Unfortunately, the Powercell / Ultra Blue (8oz) line was discontinued in 2009.

There are no direct replacements or fuel cylinders.

We apologize for the inconvenience & appreciate your feedback.

Warm regards,

Armando G. Castillo

INSIDE SALES

WORTHINGTON CYLINDERS

A DIVISION OF WORTHINGTON INDUSTRIES

(P) 800.654.9011

(F) 614.840.4943

(D) 614.840.4928

Armando.Castillo@Worthingtonindustries.com