Question

What is difference between thermal conductivity and thermal diffusivity

Answer 1

Thermal conductivity is a thermophysical measure of how much heat is transferred through a material by the conductive flow. ...

Thermal diffusivity controls the time rate of temperature change as heat passes through a material.

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Answer 2

Explanation:

Thermal conductivity as can be seen by the fourier law of heat conduction, tells about the rate of heat transfer per unit area through a wall of unit thickness and temperature diff maintained at 1deg. celsius between the 2 surfaces of the wall.

In short it tells about the rate of heat transfer through a surface ie. how fast the heat will flow through the surface.

where as thermal diffusivity is defined as ratio of thermal conductivity to the product of density and specific heat capacity of a material.

specific heat capacity tells about the energy req. to raise the temp of a substance of unit mass by 1 deg. where as product of specific heat capacity and density tells about the amount of heat req. to raise the temp of a substance of unit VOLUME by 1 deg.

So coming back to the thermal diffusivity, it tells about the rate of heat transfer through a body but also takes care of the temp raised by that heat. low value of thermal diffusivity show the high value of the denominator that is the product of density and specific heat capacity, which means more heat req. to raise the temp by unit degree celsius.

So thermal conductivity tells about the rate of heat transfer only but thermal diffusivity tells about the rate of heat transfer and also the effect on the temp change of the body due to this heat conduction.

Suppose you want to have a material that is a good conductor of heat but does not heat up easily that is its temperature increases slowly. For this type of material thermal conductivity will tell about the materials ability to transfer heat quickly, for temp part you need to concern the thermal diffusivity. If a material have high thermal conductivity but low thermal diffusivity, then that material will transfer heat fast as can be seen by thermal conductivity but will heat up easily as can be seen by the low value of thermal diffusivity.

So in whole thermal conductivity just tells the rate of heat transfer through a medium, but thermal diffusivity also incorporates the change in tempof the body due to this heat transfer.