there should be some difference between these two different materials. i remember some testing done before for one natural convection application case. in the early stage, i used plastic material to build fixture, and thereafter, aluminium alloy used to shape its fixture. of course, these two case shared the same MLB, the only differene lied in their chassis material. as I remember, metal chassis is better than plastic one, I mean the surface temperature is lower when metal chassis is applied. but the feeling is different when you touch your finger onto the surface. it should feel worse when metal surface is used. you can build one model and do simulation in software to check out if I said is right or not.
thanks for ggliang and Rosicky sharing. actually i have done simulation for plastic and metal. metal surface temperature is very even and have no large temp gradient. but Plastic surface has big gradient. in my case, enclosure dimension is 40mmx200mmx68mm total power is 12W. metal surface temp is 60C@ Ta=40C, Plastic is about 72C(Maximum)..
i just don't know how to analysis from heat transfer theory?/ i don't think heat transfer coefficient has large difference between METAL and non-metal.
作者: 阳光下 时间: 2011-5-1 09:03
To bertfan, I think, for metal enclosure case, the total series thermal resistance from heat source to ambient is much smaller compared to non-metal one, which will result in the smaller temperature difference between the heat source and ambient, and also the smaller Delta T between enclosure surface to ambient.
作者: cliffcrag 时间: 2011-5-1 09:03
hi, Eggliang. i agree. but could you show some quantized calculation bewteen metal and non-metal?
作者: icepak 时间: 2011-5-1 09:03
it's easy, right? for example, we assume thermal resistance from ambient to surface is Theta_sa=6C/W, and conduction resistance is Theta-con=2C/W, and from inner surface to case is 8C/W. and for non-metal case, from ambient to enclosure surface is Theta-sa=6C/W, and conduction resistance is Theta-non=4C/W, and from inner surface to case is 8C/W. and we assume the total power is 5W, and ambient temp is 35C. so we can get below calculation:
(1) for metal enclosure:Tc=35+5*(6+2+8)=115C, and Ts=35+5*(6+2)=75C.
(2) for non-metal enclosure: Tc=35+5*(6+4+8)=125C, and Ts=35+5*(6+4)=85C.
from the above, we can see the difference from these two cases.
from thermal theory, if the two enclosure is same except for their material, the differene of their surface temperature should lie in their conduction thermal resistance. I think the convection and radiation heat tranfer should be identical.
if you anyone have the better understanding on this problem, please share with us.