What is flux?

[mattrix]

I'm confused!!
What area is being used?
On this page there are 2 examples.
1. a 8 ohm 32 gauge coil at 8000mW and Surface area=23.95mm^2: flux is said to be 317 mW/mm^2
2. two 0.8 ohm 27 ga coils in parallel at 40000mW and SA=61.55mm^2 : flux is said to ba 313 mW/mm^2
but
8000/23.95 = 334
40000/61.55 = 650

 

[93gc40]

Heat flux is a representation of potential coil surface temperature. .... how hot the coil can get dry.......
HEAT Capacity tells how much heat will be transmitted by the coil.and how fast it will heat and cool......

A good vape requires balancing of the 2 factors.

I try to shoot for a Heat Flux of 200..... others go in the 100s and some even vape in the 300 to 400 ranges. The number to shoot for is individual.. based on you prefered vapor,the gear you are sing and the juice.

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[mattrix]

Thanks 93gc40,

Isn't that the other way around?
ie flux represents the heat energy the coil will provide (J/mm^2/sec), and capacity (J/K) represents the temperature of the (dry) wire?

Also whats going on with the maths?

 

[93gc40]

Thanks 93gc40,

Isn't that the other way around?
ie flux represents the heat energy the coil will provide (J/mm^2/sec), and capacity (J/K) represents the temperature of the (dry) wire?

Also whats going on with the maths?

IDK or care about the math. ... that's why I use steam-engine. ....

Regarding proper terms...... You could be right .... as... that's what I said is my first response. FLUX THE Energy Capacity more like the affect felt by the energy.

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[mattrix]

Heat flux is ...
HEAT Capacity tells ...
A good vape requires balancing of the 2 factors

Is heat capacity (of the wire) really a consideration?

Using data from Steam Engine* heating the wire only takes 5 to 10% of the applied energy.
--------------------------------------------------------------------------
*the math, 6t of 03ga kanthal on 3mm, has a heat capacity of 11.36 mJ/K (or 4t of 26ga kanthal on 2.2mm has 18.04 mJ/K) The TC people tell us they use 360-460F (180-237C), a change of 220C. So this requires about 2500 mJ (or 4000 mJ) but requires 11000mW for a heat flux of 200 J/mm^2/sec.

 

[93gc40]

Is heat capacity (of the wire) really a consideration?

Using data from Steam Engine* heating the wire only takes 5 to 10% of the applied energy.
--------------------------------------------------------------------------
*the math, 6t of 03ga kanthal on 3mm, has a heat capacity of 11.36 mJ/K (or 4t of 26ga kanthal on 2.2mm has 18.04 mJ/K) The TC people tell us they use 360-460F (180-237C), a change of 220C. So this requires about 2500 mJ (or 4000 mJ) but requires 11000mW for a heat flux of 200 J/mm^2/sec.

Heat capacity affect heating and cooling speak and how hot you have to get the coil to transmit the heat to tbe juice . Thus creating vapor....
Too high it take too long to get hot and produce vapor.. then takes too long to cool back down.... wicks can get burned AFTER you release the fire button. Slow cooling also promotes gunk buildup.
Too low the coil heats too fast and cools too fast... low capacity can't overcome cooling affect of juice and airfliws.

There's more to consider than electricity and math.....

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[93gc40]

I kinda use the KISS principle with Heat Flux and Capacity....
.. flux is how hot the coil gets and capacity how much affect that will have on the environment around it.
Heat produced the flux vs usable heat the capacity.




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[mattrix]

capacity [is] how much affect [the wire] will have on the environment around it.

So, if you wanted more vapor, you would build a coil with greater capacity?

 

[mcclintock]

Looking at the math, the surface area you list is of the coil, vs. the wire which includes legs. The higher power one is also dual coil, and the area you show is per coil. (The example was Coil wrapping )

The heat flux is simply the heat power divided by the surface area of the whole energized part of the wire. If part of it is wick'd, and the ends are in posts, those will be cooler so some of the heat from hotter parts of the wire will flow down the wire into those sinks, but otherwise it isn't just during dry fire. It's essentially how much heat "wants out" of the wire vs. how big a window it has to go through. It's also steady state and doesn't take into account increasing or decreasing temperatures.

 

[mattrix]

Oh yeah, your brilliant! Thank you, mcclintock.
I took all the figures off of the page I linked.

So now the surface area of the 40W setup IS 5X that of the 8W setup.
I like it when things make sense.