On all my inverted canister winter stoves I have managed to avoid running a vaporizing tube over the flame. While such a thing is necessary for white gas stoves and essential for kerosene stoves, my theory was that there was enough heat around that the liquid propane/butane mix coming from a canister could look after itself with just a little feedback from the flames.
Mind you, in the cases of V1 and V2 temperatures of the heat shunt (HS), stove body (body), and water for low/medium power they were vortex burners and my main job was to prevent the stove body from getting far too hot. The feedback from the flame vortex inside the burner was intense. In the cases of V1 and V4, I ran a heat shunt, a strip of aluminum, from the flames back to the fuel inlet.
The idea is that the flame would heat the end of the heat shunt, heat (or energy) would flow down the strip of metal to where it joined the stove body near the fuel inlet. There the energy would be absorbed by the incoming liquid fuel which would vaporize, go up and out the burner head, to make the flame.
By and large, this idea works fine. However, a recent customer for the V4 (Ian) reported some problems. He would prime his stove so everything was hot, then invert the canister for a liquid feed, and run it for a while. Then sometimes, after a while, the stove would start to hiccup and flare, and the stove body was found to be cold. What was going wrong?
I suggested various things by email, but none of them worked well enough. This was not good. A more detailed investigation was required. Fortunately, Ian was technically minded and was able to play with his stove a bit. Between us, we worked out what was going wrong and how to fix it. This is the story.
Details of the Problem
The problem did not happen under what I would call normal use. The stove had to be turned up to full power before the problem started. I do not run any stove that hard, and I recommend you don't either, as it is rather inefficient in fuel usage. Full power normally means the flames are visible beyond the edge of the pot and a lot of heat is lost/wasted up the side of the pot. You can see this below and that was not really full power.
Now when the incoming fuel vaporizes, it uses up a fair bit of energy to go from liquid to vapor. Veryoften this energy comes from the canister or the fuel in the canister. This is why you may find that a canister will develop frost on the surface and stop giving off gas: it has lost so much energy that it has ceased boiling off vapor. (The use of the word boiling here is deliberate and correct.) In fact, this is why we use an inverted canister stove in winter, to prevent the canister from freezing up. Instead, the energy for boiling is meant to come from the stove and the flames.
So what this means is that the vaporizing fuel is sucking so much energy out of the stove body that the stove body is chilling to below the boiling point of the fuel. But surely the heat shunt is meant to be keeping the stove body and the fuel inlet warm, if not hot? Obviously not in this case.
You might wonder whether sticking more of the heat shunt into the flame might work. It might—until the aluminum melted. I do have one heat shunt with a slightly cooked end. This is not a good solution.