difference between thermal diffusivity and temperature diffusivity

[MetalEng]

in metals solidification theory, there are two technical idioms,as follows:
thermal diffusivity of the solid crystal
heat diffusivity of the mold
I want to have physical sensing of these parameteres.

thank you in adv.

 

[mdighe]

I am not a guru in solidification theory, but from what I know,

The thermal diffusivity if the crytal is a measure of the rate at which heat is carried from the center of the crystal to the surface of the crystal.

Once this heat energy reaches the surface of the crystal, it has to be conducted out the mold. The rate at which this happens is the diffusivity of the mold.

A low duffision through the mold will make it act like a insulator, locking in all the heat.

A low diffusivity of the crystal will result in very steep temperature gradient within the crystal leading to effects such as coring.

Hope that helps

 

[NickE]

Thats right as far as I remember. Also the diffusivity of the crystal is anisotropic (spelling and term) IE it is dependant upon x-tal direction. (111 etc...)

For bulk, non-collumnar, multicrystal castings an approximation is used to remove or mitigate the directional effect on diffusivitiy.

The directional dependancy of the heat extraction is a cause of dendritic structure formation.



Nick
I love materials science!