Heat

[LuckyHobo]

A flat 24" OD x 2" thk. steel surface is heated to and maintains a 400F temp. on side #1.

On the opposite side (side #2) is a 24"ID x 5" tall x 1/2" thk. steel enclosure. The enclosure has a 1/2" thk. steel cover.

I need to know the estimated temperature inside this steel enclosure.

The ambient temperature surrounding the enclosure is 78F.

 

[stanlsimon]

I think that you are talking about a 2" thick steel plate standing vertical with another metal box on one side, 400degF on the other. Need to know how much air space is between the metal enclosure and the 2" thick plate.


Because of the high thermal conductivity you can assume the back side of the 2" plate will be close to 400deg as an approximation. Are there any fans moving air or strictly gravity convection? Also would need to know surface finishes as these change absorptivity and emissivity.

 

[IRstuff]

Is this schoolwork?

TTFN

FAQ731-376

 

[LuckyHobo]

stanlsimon,

The 24"ID x 5" tall X 1/2" thick steel enclosure is welded to side #2 of the heated 2" thk. steel plate. There is stagnant air inside the steel enclosure but there is no airspace between the metal enclosure and the 2" thk. plate. The is a 125 finish on the plates.

 

[stanlsimon]

Just doing a quick shot from the hip, not 100% sure if I understand the geometry, but you have four film resistances, calling each one equal, this makes the Delta T's equal, neglecting the resistances of the steel, and not including radiative heat transfer, take your (400-78)/4=80.5, this will be the drop in temp on each side of each piece of steel. Therefore the inside temperature will be 78+80.5+80.5=239F. It sounds like there may be 1/2" air space? Just neglect that for now. I don't know what the emissivity of that 125 surface would be, but let's just assume that the increase in heat transfer caused by the radiation across the two parallel plates is counteracted by the r value of the air space. Note that this assumes no fans or forced air venting.

Can you stick a thermometer in there to verify? Empirical data is something to hang your hat on.

 

[LuckyHobo]

stanlsimon,

Attached is a sketch of the heated enclosure.

LuckyHobo

 

[stanlsimon]

Based on the drawing there would be a notable increase in the temperature inside due to the 1/2" ring around the edge. This is getting to be more than a simple hand calculation. Do you have some software that can do thermal finite element analysis?

 

[LuckyHobo]

stanlsimon,

No, unfortunately I do not have any software.

LuckHobo

 

[IRstuff]

What composition of steel, particularly, carbon, nickel, and chrome? There's a about 7:1 variation in thermal conductivity in the different types of steel.

Do you want the highest temperature it can be or the lowest temperature it can be?


TTFN

FAQ731-376

 

[LuckyHobo]

IRstuff,

The 2"thick heated plate is steel SA105 (SA105 is the steel used for making "pipe flanges"). The enclosure is made of low carbon steel SA-36.

I am looking for an estimated "high temperature" inside the enclosure.

LuckyHobo

 

[LuckyHobo]

IRstuff,

I made a mistake on the thickness of the heated plate - it is 2 13/16" thk and not 2" thk.

LuckyHobo

 

[stanlsimon]

Drill a 1/4" hole and stick a thermometer in.

 

[IRstuff]

I think that you'll find that the steel short-circuits the air thermal path and the net result is that the air is going to mighty HOT.

TTFN

FAQ731-376