Stefan's law for radiation between body and surroundings

AI Thread Summary
The discussion focuses on Stefan's law regarding radiation heat transfer between two bodies. It clarifies that a single value of emissivity (ε) is applicable for both heat exchange directions due to Kirchhoff's law, which states that absorptivity equals emissivity. The necessity for the body to be small compared to its surroundings is emphasized to simplify calculations. When considering two bodies, the geometry of the second body must be factored into the heat transfer calculations. The conversation also briefly critiques the use of imperial units like ft² and °R.
Remusco
Messages
30
Reaction score
3
My PE handbook describes how to calculate the "Net Energy Exchange by Radiation Between Two Bodies", as shown below:

1733092199642.png




How can a single value of epsilon be used for heat transfer in both directions? Why does the body need to be small compared to the surroundings?
 
Last edited:
Engineering news on Phys.org
Remusco said:
My PE handbook describes how to calculate the "Net Energy Exchange by Radiation Between Two Bodies", as shown below:

View attachment 354010



How can a single value of epsilon be used for heat transfer in both directions? Why does the body need to be small compared to the surroundings?
There is one ##\varepsilon## because the absorptivity of the body is the same as its emissivity per Kirchhoff's law of thermal radiation. You are calculating the heat on the body due to surroundings. If the surroundings are instead another body then you have to take into account the geometry of the second body.

Edit: not important, but who in their sane minds uses ft2 and °R?
 

Thread 'Bubble formation in 4 mm gap vessel'

How did you find PF?: Via Google search Hi, I have a vessel I 3D printed to investigate single bubble rise. The vessel has a 4 mm gap separated by acrylic panels. This is essentially my viewing chamber where I can record the bubble motion. The vessel is open to atmosphere. The bubble generation mechanism is composed of a syringe pump and glass capillary tube (Internal Diameter of 0.45 mm). I connect a 1/4” air line hose from the syringe to the capillary The bubble is formed at the tip...
View full post »
Thread 'Physics of Stretch: What pressure does a band apply on a cylinder?'

Thread 'Physics of Stretch: What pressure does a band apply on a cylinder?'

Scenario 1 (figure 1) A continuous loop of elastic material is stretched around two metal bars. The top bar is attached to a load cell that reads force. The lower bar can be moved downwards to stretch the elastic material. The lower bar is moved downwards until the two bars are 1190mm apart, stretching the elastic material. The bars are 5mm thick, so the total internal loop length is 1200mm (1190mm + 5mm + 5mm). At this level of stretch, the load cell reads 45N tensile force. Key numbers...
View full post »

Thread 'Find 3D Printer & Software Resources for Prototype Creation'

I'd like to create a thread with links to 3-D Printer resources, including printers and software package suggestions. My motivations are selfish, as I have a 3-D printed project that I'm working on, and I'd like to buy a simple printer and use low cost software to make the first prototype. There are some previous threads about 3-D printing like this: https://www.physicsforums.com/threads/are-3d-printers-easy-to-use-yet.917489/ but none that address the overall topic (unless I've missed...
View full post »

Similar threads

Radiation heat transfer between parallel plates
Replies
30
Views
6K
Differences between these materials for absorbing and radiating heat?
Replies
2
Views
2K
The Second Law of Thermodynamics and the Stefan-Boltzmann Law
Replies
6
Views
2K
Power Radiated From a Copper Cube
Replies
3
Views
835
Questions About Stephan's Law of Thermal Radiation
Replies
5
Views
2K
Clarification about Heat Conduction equations
Replies
1
Views
2K
I Energy Redistribution in Lorentz Oscillator Model with Pure Radiation Damping
Replies
2
Views
641
Molar Specific heat of Blackbody radiation
Replies
15
Views
1K
How Does Newton's Law of Cooling Affect Heat Loss Calculations?
Replies
2
Views
2K
B Understanding the Stefan-Boltzmann Law (when the surroundings are hotter)
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top