Temperature rise in an alum enclosure 3

[SolSurfer1]

Hello all,
I searched through the forums ("temperature rise") and did not find an applicable thread (or at least one that I thought would help) for my question. My apologies, if I missed a previous thread that addresses my question.
My question is: What is the formula for estimating the rise in temperature within an enclosure, having no internal airflow and mounted outdoors?
The enclosure is constructed of aluminum; having dimensions of 0.7mX0.5mX0.4m and a wall thickness of 0.005m
The power dissipation inside the enclosure is 50w
The ambient (outside) temperature is 40°C
Thank you,
SolSurfer

 

[Twoballcane]

For steady state: q=(1/R)deltaT

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[SolSurfer1]

Sorry, but I'm confused.
I would have expected something that factors T2 (outside), the area and thickness of the surfaces, the coefficient of conductivity of those surfaces and the power dissipated inside; resulting in the DeltaT .
Can you please explain?
Thx.

 

[IRstuff]

The same basic relationship applies to each heat transfer interface, i.e., board to internal air, internal air to enclosure, enclosure to external air. The simultaneous solution to the three equations results in the enclosure surface temperature, the internal air temperature, and the temperature of the boards.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[IRstuff]

Seems to me that you need to consult an HT textbook.
This one is free to download:

http://web.mit.edu/lienhard/

http://www/ahtt.html

But there are plenty of HT resources on the web. The one that hosts Electronics Cooling Magazine has a library of older articles which include the subject you're interested in.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[SolSurfer1]

IRStuff, thank you for the links, I'll go through them.
Unfortunately, this is not my area of expertise, and I was hoping that that there was a straightforward first-order estimate equation that one might use to acquire a ROM estimate for the temperature rise in an enclosure(knowing the size of the enclosure, the material of the enclosure, that the fluid within the enclosure was air, the power dissipated in the enclosure and the ambient temperature outside the enclosure). At least to the point that I could begin to understand if it was 2 degrees or 20 degrees.
Again, thank you for your time and links.
Regards.

 

[amorrison]

This is like a single glazed house window where the glass is aluminum.
The aluminum will have an effective "R" value of zero -ie. no thermal resistance.
All the thermal resistance will come from the air films. There is one on the inside of the box probably about 0.68 in Imperial units (btu/hr/ft2/degF). The thermal resistance on the outside of the box will ~ the same unless there is a fan to provide air movement.

Unknowns 1. There will be "natural convection" of air inside the box - but imo won't change things much.

2. The viscosity of the air inside the box will change with the heating - but imo this won't affect much either -unless things are really hot.

3. You are unlikely to get a film coefficient accuracy better than +-20% so consider this.

4. There will be another film coefficient to consider - the one around your heat source in the box - but if you are only interested in the air temperature of the box provides no information of utility.

Good textbooks can provide a more "accurate" answer for these "heat source in an enclosure problems" but with the +-20 % in the "R" value - is it worth the effort for a standard analysis where nothing is "strange".

Then its Btu/hr = area x deltaT/(Total R)

 

[ione]

Just to give you a rough idea

http://www.westernextralite.com/resources.asp?key=72

 

[kjoiner]

SolSurfer,

Also check with some of the enclosure companies like Hoffman. Here is a link to their technical page. If you scroll down, there is a section on thermal management.

http://www.hoffmanonline.com/produc...&cat_2=139055&SelectCatID=139055&CatID=139055

Kyle

 

[kjoiner]

Here is another link on the Hoffman site that features thermal management software.

http://www.hoffmanonline.com/produc...?cat_1=34&cat_2=375&SelectCatID=375&CatId=375

You might be able to make it work for your appliation.

Kyle