Sizing electrical heater to meet required temperature on heater surface

[RadovanML]

Greetings,


I work a part-time project, it is e-cigarette. I am a mechanical engineer working on the design of atomizer, sealing, airflow, practically entire unit. It's out of my area I know but I need to do sizing of heater and I am kinda stuck. Here is the problem:

A heater is round wire, winded around the cylinder (idealized) base diameter 2,7mm.

Something like this:

http://i62.tinypic.com/a4r9jr.jpg

Battery: 3V, 10W, 0.9 Ω

Target temperature wire heater: 180C (this is what I need)

Heater:
Kantal wire diameter of 0.4mm. Resistance 0.011 Ω / mm
The total length: 146mm (this will probably be shortened)
R = 1.61 Ω
P = V ^ 2 / R = 5.59 W

Operating time 10sec.

Here is where I begin to lose myself. According to my research the following applies:

The specific heat of air is 716 J / kg K. The density of air is 1.3 kg / m ^ third 1 watt is 1 J / sec. So.
In 60 seconds, the temperature rise of: 100 * 60/716 / 1.3 = 6.5 C

Now when I apply my values it goes like:
5.59 * 10/716 / 1.3 = 0.06C / m3 (if I'm not mistaken per cubic meter?)

But I need the temperature to the heater and not in a volume of air. I tried to share this value with my volume (heater is placed in cylinder diameter of 4 mm, height 10mm) and I got an abnormal value.

Something is missing here. So my question is what will be the temperature on the surface of the heater - wire temperature, for know battery and if the heater is in a small volume 4mm diameter 10 hegiht cylinder.

I thank in advance, any help is welcome.

 

[MacGyverS2000]

You need to know the thermal resistance of your wire to the fluid it will be immersed in...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[RadovanML]

Hi there, thanks for quick answer!

It will not be immersed in oil, I use a porous ceramic wick and seal to prevent oil flooding atomizer. So configuration is as on the picture, wick with coil.
So for the purpose of calculation I take it as coil is in contact with air. I will use Solidworks to analyse heat transfer to wick.

 

[VEBill]

Experiment.

The problem with analysis in such circumstances is that if you do it correctly, that is bringing along all of the ± uncertainties of every input data point and assumption and then flowing the uncertainties through the math to the output, then you'd almost certainly prove the need to do the experiment anyway.

(^- Pure opinion based on instinct. For your consideration only.)

 

[waross]

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Thanks

Bill
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"Why not the best?"
Jimmy Carter