Radiation at certain distance

[stern]

All,

How to calculate the temperature of air at a certain distance from a heating panel?

I have a temperature in the Nichrome wires of the heating elements and the emissivity.

Im trying to heat a part but need to determine the distance from the panel, how the air temperature decreases with distance..

Thanks

 

[Compositepro]

Radiation does not heat the air. All you can calculate is a heat flux (watts/sq. meter) at a given distance.

 

[IRstuff]

"Radiation does not heat the air"

It can, but only VERRRRY SLOWLY. A typical atmospheric absorption might be 10% over a kilometer

As for heating the part, it'll depend on the absorptivity of the part, as well as the distance, and for sufficiently large distances, the radiation will fall off as 1/r^2

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[stern]

Yes I know about heat flux and the absoption of the part.

My point is, I put a thermometer near the panel and I read T1, then I put it at more distance, about 50 cms and I have a T2.

T2 is higher than that of surounding air temp, so this heating comes definitely from radiation.

How to measure or to relate if I have certain KW of power the temp of air at any distance from the panel?

 

[IRstuff]

"Yes I know about heat flux and the absoption of the part."

Apparently, you don't. What's heating up is the thermometer, not the air.

In any case, ~1/r^2, for short distances, there's some error due to your source being extended.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[stern]

Thanks to both

 

[willard3]

Radiation is a trancendal heat transfer function both for distance and temperature. Distance to the second power, temperature to the fourth power.

You should take a course in thermodynamics.

 

[stern]

I understand the inverse-square law will do with heat flux and I remembered the fact of air not absorbing heat from radiation.

I suscribed to this forum with the idea of getting and giving some practical responses to technical doubts in our fields.

The suggestion "You should take a course in thermodynamics" is not appropriate in my opinion. Here there are lots of doubts and I dont see much of hey you should take a course in astrophysics or anything like that.

But thanks anyway.

 

[IRstuff]

"I understand the inverse-square law will do with heat flux and I remembered the fact of air not absorbing heat from radiation."

You continued referring to "air temperature," even after correction, which suggests to me that you do not clearly understand the physics. If you know all this stuff, then just what exactly is your question?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[flash3780]

Well, what's happening as you move the thermometer farther from the source is the view factor is reduced. If you think of radiation as vectors whose direction follows a half-sine distribution from any particular point, it's clear that as you move farther away from a surface, the amount of energy entering that object is reduced.

As was noted above, radiation pretty much shines right through the air (though not entirely).

 

[stern]

No im not. I said I got it with the 1/r2 law. Im not referring to air temperature.

Thx,

 

[IRstuff]

So, is there still a question?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[stern]

No, thank you IRstuff