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Answers to Readers' Questions on Physical Science:

Thermal Insulation

The following 134 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• Insulation of Extreme Temperature Electronics
• Want to know if I'm making a thermos correctly
• What factors determine the compressor to use?
• We have to build a thermos
• Radiation and conduction from a black body material
• Teaching 7 and 8 year olds about insulation
• Confused about thernal radiation
• I don't understand insulation
• What would insulate a 12 oz aluminum can?
• How can a stainless steel coffee mug hold heat?

Next 10

Insulation of Extreme Temperature Electronics

Question

August 20, 2010

I am working for GE, Hyderabad. I am in to Hardware electronics design group, we are working in temperature environment of -80 to +140 deg C. I need to protect my electronic circuitry on the printed circuit board from this harsh temperature environment. Please suggest some heat insulation material for my application.
Early reply is appreciable.

Thanks and Regards,

Vandana - India

20266

Answer

The follow website gives a good background on Extreme Temperature Electronics:
http://www.extremetemperatureelectronics.com/tutorial1.html

They reference sources for companies dealing in such electronics. You may be able to find a company or information on insulation to use:
http://www.extremetemperatureelectronics.com/sources.html

For general insulation information:
http://www.techlib.com/reference/insulation.html

I hope that helps.

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Want to know if I'm making a thermos correctly

Question

May 11, 2010

I am making a thermos and I have a glass bottle around it is aluminum foil and over that is bubble wrap and another coat of styrofoam. Then at the bottom of the thermos is stryofoam and all around the thermos is duct tape. My question is the insolator there or in the right place? PLEASE REPLY I NEED HELP

Project due - MAY,12TH, 2010

- Canada

19705

Answer

It sounds like you have done a good job. Don't forget to insulate the cover too.

Try it out by putting in some hot water to see how long it takes to cool down. Or you can put in some ice cubes to see how long they stay frozen.

Best wishes in your project.

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What factors determine the compressor to use?

Question

April 9, 2010

What factors determine the compressor to use in a refrigerator desighn.
Do compressors have specific climatic conditions for use.

Kim - Kenya

19520

Answer

I'm sorry, but we do not have that information available.

Best wishes in finding your answer.

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We have to build a thermos

Question

March 23, 2010

We have to build a thremos, and I was wondering how I could make the lid of the thermos. What materials must I use, and how do I make it?

S - Canada

19423

Answer

See the lesson on Thermos at:
http://www.school-for-champions.com/science/thermos.htm

Also, look at the Reader Feedback on the page to see what other students have done.

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Radiation and conduction from a black body material

Question

February 25, 2010

Case A: If a perfect vacuum exists between two, non-touching, "black bodies" that are at uniform but different temperatures, heat transfer between the bodies can only occur via radiation. Integrating Planck's law over all frequencies (zero to infinity) and including the Lambertian nature of black-body radiation from a planar surface (i.e., the radiation into a solid angle is proportional to the COSINE of the angle the solid angle direction makes with the normal to the black-body surface), provided two differential unit areas (one on each body) have line-of-sight visibility, one can generate a formula for the net power radiated between a differential unit of area on one black body to a differential unit of area on the other black body. By applying this formula over the entire surface areas of both bodies, one can in principle generate a formula for the heat flow between the two bodies. Suppose by hook or by crook we correctly generate such a formula.

Case B: Now fill the "vacuum of space" that existed between the two black bodies with a fixed material such as concrete. The fixed material will support heat transfer between the bodies via conduction but not convection. The formulas for conduction heat flow and radiation heat flow between two bodies are different. However, assume again by hook or by crook we can generate a formula for the conductive heat transfer between the bodies.

My question is this: To compute the "Case B" total heat transfer, do we algebraically sum (i) the "vacuum" radiative heat transfer formula of Case A...and... (ii) the conductive heat transfer formula of Case B? Put another way, when the vacuum is filled with a non-convective substance, are the radiative heat transfer properties affected by the substance? The follow-up question is: "If the radiative heat transfer properties are different for "vacuum" versus "fixed substance" conditions, how should the radiative transfer formula be modified?

Thank you for your time,

Reed - USA

19292

Answer

What this comes down to is the question of whether there is any radiation heat transfer between two materials in contact to add to the conduction heat transfer.

Conduction is caused by molecules in one material striking molecules in the other, transferring kinetic energy. However, the black body molecules are also emitting radiation, which is also providing thermal energy to the concrete material.

Neither the conduction heat transfer from a black body material to concrete nor the radiation heat transfer is very efficient. I'm not sure which is more efficient. I assume the total heat transfer would be the total of the two.

The black body emits radiation independent of the other material. However, the loss of energy due to conduction would lower the temperature of the balk body and reduce the amount and form of its radiation.

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Teaching 7 and 8 year olds about insulation

Question

January 17, 2010

Hi,
Your information on insulation was very helpful.

I am teaching 7 and 8 year olds about insulation and wanted to role play the effect of insulation and materials that are poor or good insulators, do you have any suggestions on how to show it?I was using the children to be a warm or cold product and then some to be a material and show effect.
Thanks for any ideas you might suggest.

jennie - UK

19069

Answer

The role of clothing in protecting you from heat or cold is one good exercise for the children. Putting on a pair pf gloves and then holding an ice cube or getting near to a heater can show the insulation effect. Then try to same thing with a thin cotton cloth wrapped around the hand.

Likewise, holding a paper cup with warm or cold water in it can be compared to holding a better insulating cup.

I hope this helps. Best wishes in your demonstration.

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Confused about thernal radiation

Question

September 25, 2009

Hi,
I found you page on thermal insulation very helpful, so thank you but I am confused about how you say that "thermal radiation (heat) cannot pass through a vacuum", but if we receive heat from sun, through space, which I have been told is a vacuum.
Thanks for your help,

Anna - UK

18382

Answer

The paragraph where I mention that heat cannot pass through a vacuum was on thermal conduction, which requires matter. This form of heat comes from moving molecules.

The paragraph on "Insulation from radiation" concerns thermal radiation, and that can pass through a vacuum. However, the reflective coatings in a thermos are used to reflect thermal radiation.

Note that heat can be transferred by convection, conduction and radiation.

Perhaps I should clarify the paragraph on heat, so there is no misunderstanding.

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I don't understand insulation

Question

May 20, 2009

i don't anderstand the ideas about insulation system

hamza - Ethiopia

17778

Answer

Thermal insulation is preventing the flow of heat through a material. Metal conducts heat from one end to another quickly. But good insulators don't/

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What would insulate a 12 oz aluminum can?

Question

March 13, 2009

okay so i have a project coming up and i was wondering what would insulate a 12 oz aluminum can? would duck type wrapped in pencils work or paper or foil??
what would work the best
we want the highest heat posible so ideas please
thank you

courtney - USA

17439

Answer

You could wrap the can with something that does not conduct heat very well. There are Styrofoam cup holders that are very good. You could wrap it in layers of newspaper, as long as the layers are thick enough. Even wrapping a wool scarf around the can could be good to insulate it.

Look at our Reader Feedback to see what other students are doing. Also see:
http://www.school-for-champions.com/science/thermos.htm
http://www.school-for-champions.com/science/heat_transfer_coffee.htm

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How can a stainless steel coffee mug hold heat?

Question

February 25, 2009

Hi I was wondering, since metals that conduct electricity have poor insulation why do they use stainless steel in thermos coffee mugs? Doesn't stainless steel conduct electricity?

- USA

17333

Answer

Stainless steel is a strange metal. Although it is an alloy of steel and nickel, it is not usually magnetic. It does conduct electricity, but also, the rate that it conducts heat is only 20% of that of steel. To add to its ability to hold heat, a stainless steel coffee mug has a shiny surface which does not radiate away heat as would a dark dull surface.

Although a stainless steel coffee mug is not as efficient as a ceramic mug in holding heat (except for the fact that you can put a cap on it), the stainless steel mug is more convenient to use.

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