thermal conductivity

(noun)

the measure of a material's ability to conduct heat

Examples of thermal conductivity in the following topics:

  • Conduction

    • (The matter is stationary on a macroscopic scale—we know there is thermal motion of the atoms and molecules at any temperature above absolute zero. ) Heat transferred from an electric stove to the bottom of a pot is an example of conduction.
    • Some materials conduct thermal energy faster than others.
    • Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact.
    • Lastly, the heat transfer rate depends on the material properties described by the coefficient of thermal conductivity.
    • where Q/t is the rate of heat transfer in Joules per second (Watts), k is the thermal conductivity of the material, A and d are its surface area and thickness, and (T2−T1) is the temperature difference across the slab.

  • Infrared Waves

    • This range of wavelengths corresponds to a frequency range of approximately 300 GHz to 400 THz, and includes most of the thermal radiation emitted by objects near room temperature.
    • Unlike heat transmitted by thermal conduction or thermal convection, radiation can propagate through a vacuum.
    • This is a property of a surface which describes how its thermal emissions deviate from the ideal of a black body.
    • The range of wavelengths most relevant to thermally emitting objects on earth is often called the thermal infrared.
    • Many astronomical objects emit detectable amounts of IR radiation at non-thermal wavelengths.

  • Thermal Stresses

    • Solids also undergo thermal expansion.
    • What are the basic properties of thermal expansion?
    • What is the underlying cause of thermal expansion?
    • Thermal stress is created by thermal expansion or contraction.
    • Another example of thermal stress is found in the mouth.

  • The Zeroth Law of Thermodynamics

    • The Zeroth Law of Thermodynamics states that systems in thermal equilibrium are at the same temperature.
    • Systems are in thermal equilibrium if they do not transfer heat, even though they are in a position to do so, based on other factors.
    • If A and C are in thermal equilibrium, and A and B are in thermal equilibrium, then B and C are in thermal equilibrium.
    • Temperature is the quantity that is always the same for all systems in thermal equilibrium with one another.
    • The double arrow represents thermal equilibrium between systems.

  • A Review of the Zeroth Law

    • The Zeroth Law of Thermodynamics states: If two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C.
    • Two systems are in thermal equilibrium if they could transfer heat between each other, but don't.
    • Indeed, experiments have shown that if two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system C, then A is also in thermal equilibrium with C.
    • The answer lies in the fact that any two systems placed in thermal contact (meaning heat transfer can occur between them) will reach the same temperature.
    • The objects are then in thermal equilibrium, and no further changes will occur.

  • Thermal Radiation

    • $\displaystyle \text{Another Kirchoff's Law: }S_\nu = B_\nu(T) \text{ for a thermal emitter}$
    • Because $I_\nu=B_\nu(T)$ outside of the thermal emitting material and $S_\nu=B_\nu(T)$ within the material, we find that $I_\nu=B_\nu(T)$ through out the enclosure.
    • If we remove the thermal emitter from the blackbody enclosure we can see the difference between thermal radiation and blackbody radiation.
    • A thermal emitter has $S_\nu = B_\nu(T)$,$B_\nu(T)$ so the radiation field approaches $B_\nu(T)$ (blackbody radiation) only at large optical depth.

  • Thermal Pollution

    • Thermal pollution is the degradation of water quality by any process that changes ambient water temperature.
    • Thermal pollution is the degradation of water quality by any process that changes ambient water temperature.
    • Some fish species will avoid stream segments or coastal areas adjacent to a thermal discharge.
    • Some may assume that by cooling the heated water, we can possibly fix the issue of thermal pollution.
    • Identify factors that lead to thermal pollution and its ecological effects

  • Overview of Heat

    • Conduction is heat transfer through stationary matter by physical contact. ( The matter is stationary on a macroscopic scale—we know there is thermal motion of the atoms and molecules at any temperature above absolute zero. ) Heat transferred between the electric burner of a stove and the bottom of a pan is transferred by conduction.
    • A less obvious example is thermal radiation from the human body.

  • Linear Expansion

    • Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.
    • Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.
    • This kind of excitation is called thermal motion.
    • The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion; it generally varies with temperature.
    • Thermal expansion of long continuous sections of rail tracks is the driving force for rail buckling.

  • Thermal Bremsstrahlung Emission

    • The most important case astrophysically is thermal bremsstrahlung where the electrons have a thermal distribution so the probablility of a particle having a particular velocity is
    • ${\bar g}_{ff}$ is the thermally averaged Gaunt factor.
    • Thermal bremsstrahlung spectra for two temperatures that differ by a factor of ten