From: Ken Smith
Subject: Emissivity


Emissivity is a measure of the objects ability to radiate or absorb energy.  A
perfect emissivity 1.0 is given to a black body that will absorb all of the ene
rgy radiated on to its surface.  A black body is a theoretical object.  Real ob
jects absorb a fraction of the energy radiated on it surface, emissivity <1.0.
The formula for radiation heat transfer in its simplest form is

q=e(T1**4-T2**4)

Where q is the heat flux
e is the emissivity
T1 is the temperature of the radiating body
T2 is the temperature of the absorbing body

For lists of emissivities for different materials, consult your CRC handbook of
chemistry and physics.

Because you will never truly know the emissivity of your target you will never
have the correct temperature reading on your IR gun.  I recommend using a conta
ct pyrometer.  You should be able to buy one from you regular thermocouple supp
lyer.

Ken Smith                               Phone (416) 448-6311
Process Engineering                        Tie Line 778-6311
Celestica Inc.                          [log in to unmask]

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