EPSILON ENGINEER
  • NEWS
  • Calculators/Tools
    • Inch To Metric Conversion Table
    • Thermal Expansion Calculator
    • Stress, Strain and Young's Modulus
    • Beam Deflection Calculators >
      • Single Load Cantilever Beam Deflection Calculator
      • Single load supported beam deflection calculator
      • Even load cantilever beam deflection calculator
      • Even load supported beam deflection calculator
    • Cutting Speed, Spindle, Feed Rate MRR Calculators
    • Pressure Calculator
    • MTBF, MTTR and Reliability
    • Ohm's Law Calculator
    • Laws of Thermodynamics
    • Heat Transfer >
      • Radiation, Absorbance, Emissivity and Reflectivity
    • Theory of Constraints
    • Entropy and Specific Entropy Calculators
    • Alloying Elements of Steel
  • About
  • Contact Us

Radiation, Absorbance, Emissivity and Reflectivity​

Home>Tools>Radiation Calculators

Radiation, Emissivity, Absorbance and Reflectance

Thermal radiation is the made of electromagnetic waves emitted due to agitation of the molecules in the substance. The electromagnetic waves behave in a similar way to light, in that they travel linearly and at the speed of light

​Black Body Radiation

When radiation hits a body, it can be absorbed, reflected or transmitted through the body. In order to conserve energy, the following must then be true
radiation total equals reflectivity absorbance and transmittance
Where:
 p equals reflectivity t equals transmissivity alpha equals absorbtivity
Picture
​For most materials, transmissivity is 0, therefore it is a common assumption that the following is true:
absorbance relfectance equal to 1
​A Black Body is a body with absorbance of 1 and therefore reflectivity and transmissivity of 0. 
​

Emissivity

​The emissive power of a body is defined as being the absorbance of the material over the equivalent black body materials emissive power:
Picture

Where:
Picture

By rearranging the above equation, we can see that Absorbance is in effect the emissivity of the grey body, or ε.

Grey Body Radiation

A grey body is a body where some of the energy is reflected, and some of the energy is absorbed. As reflectivity and absorbance are linked they will always add up to or close to 1 and therefore can be thought of as a ratio.

Emissivity

​Emissivity, Absorbance, reflectance and radiation in general, are all dependant on surface finish, temperature and wavelength. The following table shows some  example materials and their emissivity:
Surface Material/Finish
Emissivity
White Paint
0.95
Black Glossy Paint
0.95
Brick
0.97
Concrete
0.85
Rough Machined Steel
0.87
Well Finished Steel
0.39
Polished Steel
0.07
Gold
0.05-0.2
Silver
0.01-0.1
Aluminium Foil
0.07
Carbon
0.96
Cast Iron​
0.3
Copper (Polished)
0.02
Copper (Oxidised)
0.6
Wood
0.95
Asbestos
0.95
Asphalt
0.95
*Unless otherwise stated, Emissivity vaules given for room temperature (293K)

Services

Home
News

Tools
​

Company

About
​
Media

Support

Contact
Whats Next
Disclaimer
© COPYRIGHT 2015. ALL RIGHTS RESERVED.
  • NEWS
  • Calculators/Tools
    • Inch To Metric Conversion Table
    • Thermal Expansion Calculator
    • Stress, Strain and Young's Modulus
    • Beam Deflection Calculators >
      • Single Load Cantilever Beam Deflection Calculator
      • Single load supported beam deflection calculator
      • Even load cantilever beam deflection calculator
      • Even load supported beam deflection calculator
    • Cutting Speed, Spindle, Feed Rate MRR Calculators
    • Pressure Calculator
    • MTBF, MTTR and Reliability
    • Ohm's Law Calculator
    • Laws of Thermodynamics
    • Heat Transfer >
      • Radiation, Absorbance, Emissivity and Reflectivity
    • Theory of Constraints
    • Entropy and Specific Entropy Calculators
    • Alloying Elements of Steel
  • About
  • Contact Us