Thermodynamics of a Box
Thermodynamics of a Box
(OP)
Does anyone have a simple equation to calculate the steady state temperature inside a box knowing the insulation qualities of the box, the initial temp, surrounding temp as well as the heating source?
I am trying to do a rough calculation on what temperature will be achieved inside this sealed box if I have a know heat source and box insulation qualities. I am not looking at accurate numbers, just a comparison of different possible heat sources and what effect they might have. I will be going some experimentation on the current heating source so I have a basic understanding on what to expect if I change the heating source.
The box materials are a simple polypropylene, the heat source is a lighting ballast 50watts and the outside temperature is 72F.
Any help would be appreciated.
I am trying to do a rough calculation on what temperature will be achieved inside this sealed box if I have a know heat source and box insulation qualities. I am not looking at accurate numbers, just a comparison of different possible heat sources and what effect they might have. I will be going some experimentation on the current heating source so I have a basic understanding on what to expect if I change the heating source.
The box materials are a simple polypropylene, the heat source is a lighting ballast 50watts and the outside temperature is 72F.
Any help would be appreciated.





RE: Thermodynamics of a Box
Thickness of wall = 1 in
Take the surface area of the box = 10 ft2
heat out = 0.2 x 10 x 1 ft2-in Btu/h-ft2-Fº/in
heat out = 0.2 x 10 x 1 Btu/h-Fº
heat out = 0.2 x 10 x 1 Btu/h-dT Fº
heat out = 2 Btu/h-dT Fº
heat out/Fº = 2 Btu/h x dT Fº
heat in = 50 W x 3.412 Btu/h-W
heat in = 170.6 Btu/h
Temp stabilizes when heat in = heat out
170.6 Btu/h = 2 Btu/h x dT
170.6/2 = dT
dT = 85.3 ºF
T = 72 + 85.3
T = 157.3ºF
lesson: use a smaller box if you want to boil water with 50 W.
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