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What are the best materials and methods to keep the internal temperature of a device lower then the ambient temperature outside of the device? Based on the following information:

  • Starting temp of device is 20°C
  • Ambient temperature around the device is 200°C
  • The time in this environment would be one hour (1hr), after which it would be removed
  • The electronics in the device would be very low powered
  • The size of the device would be 2" square
  • The device would be re-usable
  • The device is in an oven, hot air surrounding it
  • Inside the device is also air
  • It is a simple sensor outputting readings to a bluetooth module

The goal would be to keep the internal components below 125°C

Any suggestions on how to achieve this would be helpful.

Mahendra Gunawardena
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Dave
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    I'm not sure what you're trying to do. If your gadget is in a 200C environment, it will eventually reach a uniform temperature of at least 200C, more if there's internal heat generation. How long it will take to reach the surrounding temperature depends a lot on the material surrounding the gadget, its insulating properties, size, internal structure, etc. You need some kind of cooling mechanism; coatings, insulation, etc. might slow the rate of heating but won't keep the temperature below 200C. – Carlton Mar 17 '16 at 14:57
  • @Carlton Thanks for the comment. I've added in the fact that the device would then be removed from the heat after an hour. As you said, it would be the goal to slow the heat down until the device is removed from the heat. – Dave Mar 17 '16 at 15:49
  • What's the medium inside the environment? Air? Water? Oil? Steam? What's the device doing? What's in contact with the device? There's so much missing information here. – DLS3141 Mar 17 '16 at 17:41
  • @DLS3141 I tried to fill in some of this info. This is not a finalized device, so I can only provide so much info. I am trying to find out ways that this could potentially be achieved so I can continue research on those ideas. – Dave Mar 17 '16 at 18:09
  • @Dave it's hard to give anything other than a general overview of heat transfer without that kind of information. – DLS3141 Mar 17 '16 at 18:14
  • If this is a meat thermometer (meater, etc.), the typical solution is to put all the electronics inside the meat where the temperature stays below 100 C. Antenna can be made with silicone cable. – jpa Mar 21 '16 at 12:51
  • @jpa Thanks for the info. I was wondering how the Meater achieved this. Very helpful. – Dave Mar 21 '16 at 19:48

2 Answers2

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I can think of three ways you could solve this problem:

  1. Insulate the device
  2. Add thermal mass to the device, e.g. make the case overly large and dense.
  3. Use some kind of cooling system, like a simple coil of tubing inside the device with coolant circulated through it.

Insulation and thermal mass will slow the rate of heating. If the device has a finite operating time in the hot environment, then there is certainly some amount of insulation/mass that can be added such that its internal temperature will not exceed 125 ℃ during that time. The type and amount of material depends on a lot of factors; you'll need to provide more specifics about your setup for a more detailed answer.

The cooling system approach may be overkill for what you need, but it has the advantage that it can extend your operating time indefinitely, and it is also easier to adjust on-the-fly. I'm thinking cold water circulating through a tube, so you can just increase the water flow rate if you need more cooling.

You'll of course want to minimize the power consumption of the electronics as much as possible, too, though I imagine you don't have much leeway there.

Fred
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Carlton
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  • thanks for your help. I think options 1 and 2 are possible for what I'm thinking. Very good info! – Dave Mar 18 '16 at 13:45
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There are drawer sized data safes available that are fire rated for 30 - 60 minutes. Perhaps you could inspect one of these for ideas on insulation /thermal mass. I think that they utilise some sort of cheap ceramic like concrete. Although 200 degrees isn't that much. I would have thought that some form of fire rated foam might work. It comes in spray cans like the common polyurethane foam filler stuff. You'd just need a suitable (metal?) container to fill.

Paul Uszak
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  • "Organic foam insulation, regardless of whether the foam contains fire retardants, should be considered combustible and handled accordingly." -- https://polyurethane.americanchemistry.com/Sustainability/Fire-and-Combustibility – Mathieu K. Mar 21 '16 at 02:49