is this conduction convection hybrid?

[pakalolo]

I'm not trying to stir shit or anything, as I said I'm just trying to understand better. It's just that on one side, @OF once said: "Heat transfer by radiation is generally very poor at the temperatures we're dealing with and it only happens in significant amounts (like we need to make vapor) when the temperature differences between source and load are big."

Then on the other side, a quick search for "radiant" on the forum reveals plenty of different opinions (including from moderators), and if I'm not mistaken I might even have read the term on some product brochures...

I know one should not generalize, all vapes are designed differently and sometimes a tiny change can have a big impact, it's really not trivial... And well, in the end heat is heat, whatever the source it's the repartition and flow that are important.

I have done this experiment and I get vapour, so clearly there is enough IR under the conditions I describe.

 

[Stu]

I've done similar experiments with the FV myself. In standard mode (3.2V bats, load sitting directly on heat source/screen) when engaging the battery, there is a mist of vapor that almost immediately emerges in the chamber (not unlike the MFLB as they share a similar functional design). Some might assume that this vapor is being created by true conduction.

Now if you use it in S2 mode (3.7V bats, load separated from direct contact of heat source) you get a very similar emergence of vapor filling the chamber even before you draw. Since the load is not in direct contact with the heat source, we can rule out conduction as a means of energy transfer. We can also rule out convection at this point since airflow has not been entered into the equation (yet). Convection requires flow, and conduction requires contact, so it's pretty clear (to me) the radiation is the (main) form of energy transfer to the load - at least in the beginning of the hit.

This led me to re-think exactly how much true conduction is going on in S1 (standard) mode. Which led me to ask the same question about the MFLB. Magic Flight has always acknowledged that IR was in play as the diagram earlier illustrates, it just wasn't widely discussed in the past.

At the end of the day we get our vapor and that's what really matters IMO.

Edit: After (proof)reading this post I have (suddenly) realized that I (often) use parentheses (just a little) too much.

 

[pakalolo]

I've done similar experiments with the FV myself. In standard mode (3.2V bats, load sitting directly on heat source/screen) when engaging the battery, there is a mist of vapor that almost immediately emerges in the chamber (not unlike the MFLB as they share a similar functional design). Some might assume that this vapor is being created by true conduction.

Now if you use it in S2 mode (3.7V bats, load separated from direct contact of heat source) you get a very similar emergence of vapor filling the chamber even before you draw. Since the load is not in direct contact with the heat source, we can rule out conduction as a means of energy transfer. We can also rule out convection at this point since airflow has not been entered into the equation (yet). Convection requires flow, and conduction requires contact, so it's pretty clear (to me) the radiation is the (main) form of energy transfer to the load - at least in the beginning of the hit.

This led me to re-think exactly how much true conduction is going on in S1 (standard) mode. Which led me to ask the same question about the MFLB. Magic Flight has always acknowledged that IR was in play as the diagram earlier illustrates, it just wasn't widely discussed in the past.

At the end of the day we get our vapor and that's what really matters IMO.

Edit: After (proof)reading this post I have (suddenly) realized that I (often) use parentheses (just a little) too much.

I've repeated my test and this time I did it properly. It confirms your timings. I wondered why it took so long in the previous test (~30 seconds). Then it struck me—I used partially vaped material and I guess it was more than partially done. With fresh buds, it takes about 5-7 seconds before vapour starts.

I think conduction is the major source of vapour in standard mode but I have no idea how to separate that effect from radiant heat.

 

[lwien]

Now if you use it in S2 mode (3.7V bats, load separated from direct contact of heat source) you get a very similar emergence of vapor filling the chamber even before you draw. Since the load is not in direct contact with the heat source, we can rule out conduction as a means of energy transfer.

Or is it still conduction even in S2 mode with the difference just being that the heat that is generated is a bit less being that it's a bit further away from the heat source.

After (proof)reading this post I have (suddenly) realized that I (often) use parentheses (just a little) too much.

I have the same issue with commas and ellipsis.

I think conduction is the major source of vapour in standard mode but I have no idea how to separate that effect from radiant heat.

Maybe we need to define the difference between conduction and radiant heat. In the FV, as an example, it could be said that the ceramic heater is also a heat source, just less of one than the heater screen on which it sits.

 

[pakalolo]

Or is it still conduction even in S2 mode with the difference just being that the heat that is generated is a bit less being that it's a bit further away from the heat source.

This is what I think happens to some degree, but I have no way to measure how much. A temperature probe on the elevated screen would be an interesting test. What we do know is that the FV still gives vapour inverted, which moves the load far enough away from the heater that IR can't be playing any part.

Maybe we need to define the difference between conduction and radiant heat. In the FV, as an example, it could be said that the ceramic heater is also a heat source, just less of one than the heater screen on which it sits.

The ceramic doesn't really get hot enough to come into the picture. It has way too much thermal mass. You can heat the FV for 20 seconds and within 10 seconds touch the ceramic wall (and the heater screen for that matter). I just did. Also, with the load sizes you and I use, not much comes in contact with the ceramic.