Dear Forum friends,
I run a support group for people afflicted with a unique nerve condition whereby people's feet get really hot (flare as we call it). I keep hoping that we could come up with a shoe insert or specially designed shoe that would keep feet cool using a battery operated thermoelectric cooling appliance. A lot of these people sleep with their feet outside of the covers; take portable fans to restaurant, flights etc. to manage this not so well.

I would appreciate any wisdom/guidance on this?
Thanks,
PK

 

That's going to be a pretty significant challenge. Not only do you need to carry the intended heat away, but also all of the waste heat from the battery. Unless your shoe design can efficiently dissipate this heat into the surroundings, you are going to experience the opposite effect and effectively be putting their feet in an oven. Shoes designed with the necessary heatsinking to the ambient air may be pretty heavy and/or bulky unless you are willing to run fluid down to the shoes and back up to a suitable heat exchanger.

Most TECs are not flexible, which will be another issue you will have to content with if they are to be rugged and reliable. There are some new flexible TEC materials that have been developed, but I don't know how expensive they are or even if they have made it to commercialization yet.

 

To expand on post #2, the thermo-electric devices are heat pumps, meaning that they transfer heat , and in addition, they also dissipate power, generating heat. Unfortunately, with thermo-electric devices that means moving heat between two metal plates, with forced air cooling one of them. Picture shoes with an aluminum insole, with the heat transfer diodes bonded to the underside of the insole, and then bonded to the bottom sole, also aluminum, or copper, below that. Not nearly as comfortable as a poorly fitting combat boot/safety shoe.
So using a heat transfer scheme that is able to move the heat farther away and at the same time, flex with walking, would be more comfortable and be much more effective.
Sorry to deliver sad news, but TE cooling would have a lot of problems.
I can provide a suggestion in another post so that this one is not too long.

 

HI WBahn and MisterBill2,
Thank you so much for your sage wisdom. For the people with this medical condition, even a not so elegant solution would be better because it would allow a degree of normalcy to their life. So here are some design thoughts based on your input:

1. We move to battery away from the shoe, strapped to the leg etc., hidden by the pants.
2. We carve out/indent the underside of a heavy insole to embed three to four 1"x 1" x 2 mm thick TEC's. Make channels in the insole toward the back or side of the shoe to allow for heat to escape. Make some riveted holes in the side and back of the shoe to allow for air to escape out. Also make some holes in the insole between the top of the TEC and top part of the insole to allow for cooling effect for the foot. Place the TEC's in the insole where the shoes don't flex - heel, arch and near the toes should be fine
I would greatly appreciate your thoughts?
Thanks.
PK

 

I suggest a discussion with the device manufacturer regarding the external structures needed for heat transfer away from the TE device. I am not tryin to be negative, it is just that the hardware aspect of heat transfer is actually quite demanding, and a lot of things do not work once they are made into physical devices instead of just concepts. Also, the performance numbers on heat transfer are rather brutal.

 

HI WBahn and MisterBill2,
Thank you so much for your sage wisdom. For the people with this medical condition, even a not so elegant solution would be better because it would allow a degree of normalcy to their life. So here are some design thoughts based on your input:

1. We move to battery away from the shoe, strapped to the leg etc., hidden by the pants.
2. We carve out/indent the underside of a heavy insole to embed three to four 1"x 1" x 2 mm thick TEC's. Make channels in the insole toward the back or side of the shoe to allow for heat to escape. Make some riveted holes in the side and back of the shoe to allow for air to escape out. Also make some holes in the insole between the top of the TEC and top part of the insole to allow for cooling effect for the foot. Place the TEC's in the insole where the shoes don't flex - heel, arch and near the toes should be fine
I would greatly appreciate your thoughts?
Thanks.
PK

Have you done ANY quantitative analysis on the thermal issues involved? Just having a some small channels for heat to escape is going to be a very poor way to move the heat, requiring the bottom of the TEC to be well above ambient temperature -- and the cools side is at a temperature drop relative to the hot side, not ambient. Then, your holes in the insole is going to be a poor thermal coupling to the person's foot, especially if they are wearing socks.

Just get some TECs and take some material similar to a shoe sole and insole and do some experiments to see if you can get anything close to an acceptable cooling effect and how extreme you have to be to get it.

 

The very first thing to look at is the thermal conductivity of the materials involved. ALL metals conduct heat energy hundreds of times better than any common shoe material. The first attempt could be an aluminum sole for the shoe, because aluminum will be required to conduct the heat pumped out by the thermo-electric element in any cooler arrangement.

 

1) Air Conditioned shoes are already sold so let's see how it's being done.
https://cyberbackpack.com/blogs/cyberbackpack-general-topics-2/air-conditioned-shoes

From the website,
The air within the shoe is cooled by a fan that is driven by a battery or by a refrigeration unit, depending on the type of air conditioned shoe. The foot is then maintained at a comfortable temperature while remaining dry thanks to the circulation of the cool air through vents or ducts in the shoe. In order to achieve the highest possible level of cooling performance, several models even employ a mix of refrigeration and fan technology.

2) Another company
https://arpa-e.energy.gov/sites/default/files/8. SRI Pitch for ARPA-E_DELTA SEPT-2017 public.pdf

3) This project uses thermoelectric cooling
https://dallasinnovates.com/how-coo...m-utsw-scientists-could-heal-diabetics-heels/

4) Thanko foot cooler
https://www.japantrendshop.com/thanko-usb-shoe-foot-cooler-p-1449.html

 

Shoes designed with the necessary heatsinking to the ambient air may be pretty heavy and/or bulky unless you are willing to run fluid down to the shoes and back up to a suitable heat exchanger.

That would be my approach. Forget TE and instead use a thin liquid-filled sole with a circulation pump and flexible remote radiating surfaces to dump heat to ambient.