oven surface temperature

[phbalance]

My heat transfer is rusty at best. We are designing an oven that has 600 F internal cavity temperature. The oven door is constructed of stainless steel with 2 glass panes. The glass panes are seperated apart by 1/2" air gap. We want to solve for the surface temperature of the outer glass pane, assuming ambient room temperature of 75 F. The glass panes are 1/4" thick.
We want to know the temp for both a vented and a sealed air gap between the glass panes.

I'm making some assumptions on the heat transfer coefficients of the air, but my answer is about 390 F on a sealed door. When I increase the h value for a vented door, the temperature rises!

Can somebody enlighten me on how to calculate this and verify my result? Maybe do a quick hand calculation and post me the results?

Thank you.

 

[MechEng2005]

Depending on you assumptions, 390 F might not be too far off. Picture the situation as a single box, perfectly isoloated from everything else (Closed system). We divide the box in two equal halves with your 2 panes of glass with 1/2" air gap, and then ensure one side starts at 600 F and the other at 75 F. In theory, the box will eventually reach a steady state where everything is at a temperature mid-way between the two starting temperatures, at:

((600+75)/2)+75 = 337.5 F

Unfortunately, I only do heat transfer calcs occasionally, and it takes me a long time to work things out (Dust off the reference books, look everything up, ect). Therefore, I'll leave it up to somebody else to give you more input on the correct direction to go from here.

-- MechEng2005

 

[zekeman]

"We divide the box in two equal halves with your 2 panes of glass with 1/2" air gap, and then ensure one side starts at 600 F and the other at 75 F. In theory, the box will eventually reach a steady state where everything is at a temperature mid-way between the two starting temperatures...."

Exactly not the way you do it. I don't think so.

 

[IRstuff]

I don't quite get that, but it's still pretty high, about 158°F

TTFN

FAQ731-376