Fall 2004
Radiation Worksheet Key
1. What is a photon? (1 pt)
An energy packet that is carried by electromagnetic waves.
2. Under what conditions is radiation heat transfer important? (1 pt)
When large temperature differences are present and/or the other modes of heat
transfer are very weak.
3. Write an equation that represents the Stefan-Boltzman law. (1 pt)
q = T4
4. What is transmissivity? (1 pt)
The ratio of radiation heat flow leaving a medium to that entering the medium.
5. A radiant heater may be considered a gray surface and the room it is occupying
may be considered black surrounds. If the heater is at 200C with emissivity 0.85
and the room walls are at 22C, determine the radiative heat flux away from the
heater. (2 pts)
For a gray surface in black surrounds,
q = Tsurf4 - Tsurf4] = (.85)(5.670 x 10-8)(4734-2954) = 2047 W
6. Solar radiation of 300 W/m2K is incident the outside surface of a window with
solar transmissivity of 0.78. What is the value of the radiation heat flux the leaves
the inside surface of the window? (2 pts)
q = (q)solar = (0.78)(300) = 234 W/m 2
7. What types of measurements will need to be made to determine the transmissivity
of a non-opaque material? (2 pts)
Will need to measure radiation heat flow into the medium on one side and
radiation heat flow out of the medium on the other side. The transmissivity will be
the ratio of out to in.
1