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RTAs & Heat Flux

JohnnyAce

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Heat Flux via Steam Engine is something I've only just started looking into & it's fascinating me

Usually, if the vape was too warm, I'd turn the wattage down, if it felt too cool, I'd turn it up

Now, my usually MTL setup is 1.2 ohms, 2.5mm rod, 6 wraps on 28g Kanthal build. Vape that at 12w, 178 mW/mm2 & it's a cool vape, about what I like

Now, over to a more airier tank. A duel coil 0.70 ohm, 3mm rod, 10 wraps on 26g Kanthal build. To vape that at the same Heat Flux would take 55w but the vape & tank gets too warm, even with more airflow & a larger chamber than the MTL RTA

That's the first thing, I can't get my head around

Secondly, if I were to build a 1.20 ohm coil on at 2.5mm rod, 8 wraps on 26g Kanthal build to get the 178 mW/mm2 Heat Flux you'd need to vape that at 24w. On the same RTA, how would that vape compared to the first coil?

I am overthinking stuff too much here? It's not something I see crop at all, so is it not worth bothering with? Are there too many variables here? Maybe I'm just not getting it

Think I need to add another tab to my nerdy spreadsheet
 
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Maybe ask this guy? I heard he knows his stuff when it comes to flux capacitors
 
Heat Flux via Steam Engine is something I've only just started looking into & it's fascinating me

Usually, if the vape was too warm, I'd turn the wattage down, if it felt too cool, I'd turn it up

Now, my usually MTL setup is 1.2 ohms, 2.5mm rod, 6 wraps on 28g Kanthal build. Vape that at 12w, 178 mW/mm2 & it's a cool vape, about what I like

Now, over to a more airier tank. A duel coil 0.70 ohm, 3mm rod, 10 wraps on 26g Kanthal build. To vape that at the same Heat Flux would take 55w but the vape & tank gets too warm, even with more airflow & a larger chamber than the MTL RTA

That's the first thing, I can't get my head around

Secondly, if I were to build a 1.20 ohm coil on at 2.5mm rod, 8 wraps on 26g Kanthal build to get the 178 mW/mm2 Heat Flux you'd need to vape that at 24w. On the same RTA, how would that vape compared to the first coil?

I am overthinking stuff too much here? It's not something I see crop at all, so is it not worth bothering with? Are there too many variables here? Maybe I'm just not getting it

Think I need to add another tab to my nerdy spreadsheet
Your airier tank coil has way more surface area than your MtL tank coil. That is why you have to deliver way more Watts to get the same heat flux. Steam engine has defined the heat flux as the milliwatts per unit of area (in this case mm^2).

The heat flux for the entire of your wire (and not per mm^2 of your wire) is really easy to calculate: It is the wattage that you set (minus a bit of loss due to imperfect conductivity in your rta etc). So your airier tank feels hotter because you are delivering more energy per second (=watts) out of the coil, into the e-liquid, then into your mouth/lungs.
 
Your airier tank coil has way more surface area than your MtL tank coil. That is why you have to deliver way more Watts to get the same heat flux. Steam engine has defined the heat flux as the milliwatts per unit of area (in this case mm^2)..

Yep, the first bit is what I've got my head around


The heat flux for the entire of your wire (and not per mm^2 of your wire) is really easy to calculate: It is the wattage that you set (minus a bit of loss due to imperfect conductivity in your rta etc). So your airier tank feels hotter because you are delivering more energy per second (=watts) out of the coil, into the e-liquid, then into your mouth/lungs.

Second part I'm not so clear :D So is it as simple as more wattage = more heat, even with the same Heat Flux on both tanks?
 
Yep, the first bit is what I've got my head around




Second part I'm not so clear :D So is it as simple as more wattage = more heat, even with the same Heat Flux on both tanks?
Pretty much, I'll try to explain some more:
Heat (temperature) is defined as being proportional to the average kinetic energy of particles in a system. The wattage setting of a device tell us how much energy is being delivered per second into this system, which increases temperature. So more wattage in means more heat. There is one other factor controlling heat of the vape though: airflow.

You can reduce the temperature of your vape by increasing airflow. This simply mixes heated stuff (vapour) with unheated stuff (air). This reduces the average temperature of what goes into your mouth. If you increase wattage but don't increase airflow then your vape gets too hot. However, if you open up your airflow enough, it will cool things down. Your airier tank just isn't quite airy enough to compensate for the increased wattage.

I don't think the heat flux measurement is there to give you an idea of how hot or cold your vape will be. I think that the heat flux measurement given by steam engine is there to help you figure out a rate of heat flux that doesn't burn your juice but still vapourises it. What I mean is that if you ran your mtl setup at 55w you would burn the crap out of it, because the heat flux would be very high. However, when you use a thicker wire with more turns you can run the thing at 55w but not get a dry hit (so long as your wick keeps up). I personally never think about heat flux when I'm building, but I guess you could think of it that way.
 
Cheers @jjde, you've cleared that up a treat!

So, in an RDA, that build must most likely be cooler (bags of airflow)

Airy RTA not quite enough air to cool it

MTL tank, much less air not worth thinking about
 
Cheers @jjde, you've cleared that up a treat!

So, in an RDA, that build must most likely be cooler (bags of airflow)

Airy RTA not quite enough air to cool it

MTL tank, much less air not worth thinking about
Glad I could help. I'm going to investigate this a bit. I'm wondering if there is a "goldilocks" zone (not too high not too low) for heat flux (as defined by steam engine), so that tootle puffing setups are basically running with the same heat flux as monster 100w+ builds. I'm going to guess that they are.
 
Glad I could help. I'm going to investigate this a bit. I'm wondering if there is a "goldilocks" zone (not too high not too low) for heat flux (as defined by steam engine), so that tootle puffing setups are basically running with the same heat flux as monster 100w+ builds. I'm going to guess that they are.

Yeah, I've been looking into it & playing with Steam Engine, checking the Heat Fluxes of different coils. That's why I was so confused comparing the two tanks in my opening post

Let me know how you get on :2thumbsup:
 
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