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Two bodies at differing temperatures (and within sight of each other) will exchange heat energy via thermal radiation.

To calculate the radiation heat transfer between 2 bodies, enter the parameters below. The two bodies are assumed to be fully enclosed by a third nonconducting body, such that all radiation energy hitting this third surface will immediately re-radiate back into the cavity.

To simulate a single hot object fully surrounded by a large cavity (such as a hot brick sitting in a room), enter a View Factor of 1, and make sure that the second body has a much larger surface area than the first.

The default calculation is for a situation experienced by many living in cold winter climes. Ever wonder why a cloudless night sky feels so much colder than a cloudy night? The reason is that more body heat is lost to the cold clear sky; a cloud layer acts as a radiation barrier. Default values are for a hatless head at 95 deg F radiating to a cold clear sky at -150 deg F, with answers rounded to 3 significant figures.

Inputs
  Temperature of Object 1, T1:    
  Surface Area of Object 1, A1:    
  Surface Emissivity of Object 1, e1:    
  Temperature of Object 2, T2:    
  Surface Area of Object 2, A2:    
  Surface Emissivity of Object 2, e2:    
  View Factor of Object 1 to 2, F12:    
Answers
  Heat Flow from 1 to 2, Q:  11.6  W
 
Equations Behind the Calculator
This calculator assumes that both bodies are graybodies, whereas the third surface is needed for conservation of energy reasons. The heat transfered from Object 1 to Object 2 in this case is described by,
This equation is subject to the reciprocity condition for the 3-body problem,
which guards against non-physical problems. Reciprocity requires that, if Object 1 is larger than Object 2, the surface area of Object 2 seen by Object 1 must be less than unity. This means that the view factor must be less than 1 (or more exactly, less than A2/A1).
Glossary
Mechanical Engineers Outlook

Guide for those interested in becoming a mechanical engineer. Includes qualifications, pay, and job duties.

STEM Career Outlook

Wages, employment opportunities, and growth projections for STEM jobs.

3D Scanners

A white paper to assist in the evaluation of 3D scanning hardware solutions.

Selecting the Right 3D Printer

Discover how to choose the right 3D printer for your needs and the key performance attributes to consider.