Help with Heat Flux, Power and the whole sub-ohm thing

[Caterpiller]

I'm going to make this short:

My preferred coil in a kayfun v4:
28g, 3mm, 6.5wraps, 1.46 Ohms, gives a Heat Flux (HF) of 122 at 10 watts.

I'd probably be firing this at 9watts most of the time (juice dependent).

A:
28g, 3mm, 4.5 wraps, 1 ohm, would give a HF of 178 at 10w

I thinks this would probably be a bit hot for me and most of my juice, but by the by.

B:
26, 3mm, 4.5 wraps, 0.5 ohms, gives a HF of 177 at 10w.

So apart from a little more surface area from the 26g (due to wire diameter) what's the difference?

Would coil A and B not behave almost identically?

Part 2:

If I'd stuck to the 28g for coil B it would have a HF of 355! Surely that's not a pleasant vape?

I ask as I've just purchased my first RDA, haven't set it up yet, and trying to get my head round sub-ohms is a world with high power VV VW regulated devices.

 

[Tmg666]

If you did 28g for B, it would be the same as A as you did same [HASHTAG]#wraps[/HASHTAG] same sized wrapping diameter.

To get .5ohms on that diameter would take 2 wraps vs 4.

And if your getting a vv/vw device subohm isnt always better then 1+ohm.

 

[Alien Traveler]

Wicks and airflow. With good wicks and proper airflow you'll have enough liquid to evaporate and thus dissipate heat flux at lower temperature; result - more vapor, more juice consumption by vaper.

 

[itskohler]

Wait a second...same amount of wraps, same internal diameter, should not give the .5ohm difference in coils...

 

[Caterpiller]

Wait a second...same amount of wraps, same internal diameter, should not give the .5ohm difference in coils...

Did someone say it did?

 

[itskohler]

A:
28g, 3mm, 4.5 wraps, 1 ohm, would give a HF of 178 at 10w
B:
26, 3mm, 4.5 wraps, 0.5 ohms, gives a HF of 177 at 10w.

Ya, you did.

 

[Caterpiller]

Wicks and airflow. With good wicks and proper airflow you'll have enough liquid to evaporate and thus dissipate heat flux at lower temperature; result - more vapor, more juice consumption by vaper.

I'm sure you're absolutely right, but I don't think I've got a handle on the relationships between HF, Power, and Ohms in terms of vapor production and temperature.

 

[Caterpiller]

Ya, you did.

Yes I did, didn't I.

But for different gauges of wire.

 

[itskohler]

Yes I did, didn't I.

But for different gauges of wire.

You're missing what I am saying, the math doesnt add up. At 4 1/2 wraps of 26 your resistance is .7, all I am saying. Putting your heat flux at ~125F at 10 watts. Just wanted to make sure you had your ducks in a row. If you wanted the resistance to be .5 and the same heat flux, all other things equal, you need a little more than 3 wraps.

 

[Baditude]

You're missing what I am saying, the math doesnt add up. At 4 1/2 wraps of 26 your resistance is .7, all I am saying.

All the more reason to actually measure one's coils on an ohm reader, and not depend upon a coil building guide's estimate or what a You Tube person says. In the real world, there are too many variables.

 

[itskohler]

That's the truth, Truth.

 

[Rabbit Slayer]

Wait a second...same amount of wraps, same internal diameter, should not give the .5ohm difference in coils...

28g wire in the first, 26g in the second, are you saying those different gauge wire should give the same resistance?

 

[itskohler]

No, I am saying he had his resistance off in the first place, which would not allow for the same kind of heating, which would give skewed results when comparing the 2.

 

[Rabbit Slayer]

Nothing in the OP looks wrong to me
If they made a .5Ω coil out of the 28g wire instead of the 26g wire, it would take only 2 wraps and the HF would be 355 at 10w

 

[itskohler]

His post was asking if 2 coils (A and B) would behave the same. But his calculations are off if you do the math, so they would not behave the same at all because what he is assuming is wrong from the get-go.

Re-read the whole thing, and where he talks about coils A and B, you will see what I mean.

 

[Kahina]

A 26 coil at 0.5 (as above, your wrap count is off) and a 28 coil at 1.0 will have the same surface area. The 28 will reach temp quicker and there will be less waste through the legs. Other than that, with the same surface area and heat flux via equivalent applies watts, they will function the same.

You'll need to bring your target resistance for the 26 up to 0.65 for the same wraps, at which point your surface area rises and heat flux drops with the same 10w. They are then different beasts.

I'm getting a kick out of learning this stuff. Unregulated forces you to.

 

[mrcoolbp]

I agree the OPs wrap count is off, everything else could be sane. Let's see on steam engine:

Coil wrapping | Steam Engine | free vaping calculators

Here's 28AWG at 1 ohm "A" coil: Coil wrapping | Steam Engine | free vaping calculators
Wraps are 4.44 (HeatFlux: 178mW/mm²)
Here's 26AWG at .5 ohms "B" coil: Coil wrapping | Steam Engine | free vaping calculators
Wraps are 3.29 (HeatFlux: 177mW/mm²)

 

[Caterpiller]

I did make an error, it should have read:

A:
28g, 3mm, 4.5 wraps, 1 ohm, would give a HF of 178 at 10w

B:
26, 3mm, 3.5 wraps, 0.5 ohms, gives a HF of 177 at 10w.

The heat flux of coil A and B are almost identical at any given watts, so don't these coils produce the same heat, vapor, results?

If anything I'd think coil A has a larger surface area and would produce more vapour?

Why would I choose coil B over coil A? There must be a reason as Sub-ohming is so popular.

I'm not trying to cause debate, I really want to know the answer

 

[VictorViper]

Short answer: Still more surface area.

There are lower gauges of wire, different build techniques, etc. I'm not into super-sub-ohm builds personally, but I do enjoy the vape more - generally speaking, when I have at least six wraps on my coils. Since I don't care to use anything higher than 26awg, down goes the resistance. My best builds are usually around 0.5-0.7ohms (for single coils) for me to get the heat and wattage I'm looking for.