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What exactly happens when an insulating material comes in contact with heat through any mode (conduction, convection, or radiation). Something like aluminized mylar will reflect the heat back. How exactly does it block the transfer of heat?

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    $\begingroup$ How does a vacuum stop heat transfer? think of a vacuum flask... $\endgroup$
    – Solar Mike
    May 12, 2022 at 11:26
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    $\begingroup$ Metal surfaces (like your aluminized mylar) look like a mirror when viewed in IR. They reflect the photos instead of absorbing them. $\endgroup$
    – Drew
    May 13, 2022 at 19:45
  • $\begingroup$ An insulator is nothing more than a bad conductor. $\endgroup$ Feb 9, 2023 at 10:15

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The difference between an "insulator" and a "conductor" is subjective. All materials transfer heat and reflect some heat at a boundary. Insulating materials are chosen because their reflectivity is high, their thermal conductivity is low, or both.

Note that some materials are chosen because they reflect (or absorb) photons, while others are chosen for their properties related to phonons.

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Heat transfer is the process of energy transfer due to a temperature difference between objects or materials. There are three primary modes of heat transfer: conduction, convection, and radiation.

Conduction is the transfer of thermal energy between neighboring particles in a material due to their contact or close proximity. The thermal conductivity (k) of a material is a measure of its ability to conduct heat. High thermal conductivity materials (like metals) are good conductors of heat, whereas materials with low thermal conductivity (like insulators) impede heat transfer. Examples of insulating materials include plastics, rubber, and glass wool.

Reflectivity is a measure of a material's ability to reflect radiant energy, such as light or heat, without absorbing it. A high reflectivity means that a material reflects a large portion of the incident radiant energy, which can help to minimize heat transfer through radiation. Reflective materials such as polished metals, aluminum foil, or reflective coatings can be used to enhance the insulating properties of a system.

Vacuum is a space devoid of matter, and it is an excellent insulator because there are no particles to transfer heat through conduction or convection. Heat transfer in a vacuum can only occur through radiation, so vacuum-insulated systems often employ reflective surfaces to minimize this heat transfer.

Regarding the difference between an insulator and a conductor, you are correct that it is subjective. The distinction is based on the relative values of the material's properties, such as thermal conductivity and reflectivity. Insulators typically have low thermal conductivity and high reflectivity, while conductors have high thermal conductivity and may have low or high reflectivity, depending on the material.

As for the properties related to photons and phonons, photons are particles of electromagnetic radiation, and materials that reflect or absorb photons are chosen for their interaction with radiant heat. Phonons, on the other hand, are quasiparticles that represent the vibrational energy within a solid lattice. Materials that have low thermal conductivity impede the transfer of phonons, making them good insulators.

Sources:

  • Incropera, F. P., DeWitt, D. P., Bergman, T. L., & Lavine, A. S. (2007). Fundamentals of Heat and Mass Transfer (6th ed.). John Wiley & Sons.
  • Çengel, Y. A., & Ghajar, A. J. (2014). Heat and Mass Transfer: Fundamentals and Applications (5th ed.). McGraw-Hill Education.
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    $\begingroup$ Please answer the specific question. Do not post a wall of text about the topic, but not the question. I.e. please write and answer, and don't use an AI tool. $\endgroup$
    – hazzey
    Mar 18, 2023 at 13:03
  • $\begingroup$ No sure what you mean. I addressed the question and all concerns in the comments. $\endgroup$
    – user13416
    Mar 18, 2023 at 13:36
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If you see at molecular level the mechanism responsible for heat transfer,the adjacent molecules transfer vibration energy with their neighboring molecules,which results in heat transfer.

Condition in insulating material

The molecules of a typical insulating material are held in place rigidly as compared to heat conducting material,this hinders the heat transfer in insulating materials.

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    $\begingroup$ Not necessarily. vacuum, for one, is a good insulator. $\endgroup$ May 12, 2022 at 12:29
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    $\begingroup$ And diamond is a great conductor, and the only things not 'held rigidly' are phonons $\endgroup$ May 12, 2022 at 12:31

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