Material Parameters: Heat Transfer Coeffecient & Emissivity

[rr00053]

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...

 

[minger]

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

 

[rr00053]

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...

 

[Bob S]

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,

 

[rr00053]

thanks minger..
so u mean to say that i can't 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]

A good start might be Ozsun et al.'s, "On heat transfer at microscale with implications for microactuator design," J Micromech Microeng 19 (2009).