Estimating heat load of small area of human skin

[Iriso]

Hi,

For a project that I am doing, I am using a device to cool a small area of the skin. The device would be in contact with the skin, and I am unsure how to calculate the heat load transferring to the device from the skin for different goal temperatures. Does anyone know of a good way to estimate this, or a resource that can help?

Thanks,
Iriso

 

[IRstuff]

Depends on what the human behind the skin is doing. How accurate a number do you need, and what temperatures are you trying to achieve?

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[Iriso]

The subject would be sitting throughout application. It doesn't have to be incredibly accurate, just a justifiable estimate for the report. 5C is the lowest I'm looking to go for the device's output. The heat load would be higher at the start, I would think, so this highest value is the most important.

 

[Iriso]

Should also note a contact area of 30x30mm

 

[IRstuff]

OK, so what's the basal metabolic rate you think you'll see? If you assume that only exposed skin can transfer heat to the environment, that would give you a worst-case, wouldn't it?

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[btrueblood]

I'd make a fea model, with the body part in question modelled as a solid with thermal properties equivalent to salt water at 98.6 F...model a fairly large chunk of this simulated body with boundary conditions of fixed temperature, and then do a transient analysis where your cooling device is applied. Yes, there is a certain degree of heat output from a human body, roughly 100 Watts, and you could ratio that down and include a certain amount of source heat in your model volume, but I'd think it to be of little significance to the end result. A bigger issue probably is estimating any thermal resistance at the interface from device to skin...but that could probably be reduced to a trivial amount by wetting the skin with a bit of saline or something.

 

[LittleInch]

I think the 100 W though includes breathing warm air shout to the environment. The human body and skin is a complex ever changing thing capable of emitting heat or shutting down heat loss depending on local temperature and many other factors. The outside of your hand will give a lot less heat than your arm pit.

So for a postage stamp sized element you must be talking mW.

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[IRstuff]

These may help figure out how much exposed skin there is. The last talks about heat balance, and might be a good place to start.

http://www.etoolsage.com/Calculator/TBSA_Calculation.asp?toolsort=1500

https://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=458975

https://www.calculator.net/body-surface-area-calculator.html

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2409965/pdf/pone.0002464.pdf

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[MintJulep]

Take a block of copper or aluminum 30 x 30 x a few mm.

Embed a few thermocouples.

Insulate 5 sides.

Chill to known temperature.

Slap the uninsultated side on your arm.

Watch temperature vs time.

 

[hendersdc]

For a worst case scenario and rough first pass I think btrueblood has it right. Just give a large volume the properties of salt water at 98.6F and see what your numbers look like. If your device is unable to cool the contact area as much as you want you can work on a more accurate model.