# Materila paramters

## Main Question or Discussion Point

Hi everyone...

I am doing a heat transfer simulation problem related with silicon, silicon dioxide and Nickel.... I would like to get some parametres like heat transfer coeffecient(h), emmisivity (e) etc of these materials .....has anyone got this data or can anyone suggest me a link to get these data...

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minger
Those aren't really material properties, they are more geometry and actual problem based. You'll need way more information.

hi minger
thanks for responding.....so how will i get those values??? is heat transfer coeffecient a geometry based function??? i am actually interested in microns and nanometre scale values...

Heat is transferred by a)conduction, b)convection. and c)radiation. Is there any other way?

minger
Yes, often times heat transfer coefficients are described in terms of the Nusselt number
$$Nu_l \equiv \frac{h_l l}{k}$$
Where l is a characteristic length, h is the convection coefficient and k is the thermal conductivity.

Now, the Nusselt number is something that can be found either experimentally, or empirically. For example, for a cylinder in cross-flow, the Number can be:
$$\bar{Nu_D} = 0.3 + \frac{0.62 Re_D^{1/2}Pr^{1/3}}{[1+(0.4/Pr)^{2/3}]^{1/4}}\left[1+ \left(\frac{Re_D}{282,000}\right)^{5/8}\right]^{4/5}$$
This is just a big function which is based on two simple non-dimensional parameters, Reynolds and Prandlt. From calculating this, one can go and back calculate the convection coefficient.

However, on nano-scale things break down. You'll have to find number/results that not only apply to your geometry, but on small scale as well. I wish you luck,

thanks minger..
so u mean to say that i cant rely on the formula which u gave nw....ok then my hard time starts nw to find on the nano scale...can you tell me what those above equations will be if my crss section is a cuboid? and lso any source to find reynolds and prandlt's parametre?

Mapes