Chapter 11
Estimating Thermal Black—Body Temperature of the Night Sky for Radiation Heat Transfer Calculations


My reference for the following equations is an excellent engineering text for practicing engineers entitled Heat Transfer Professional Version by Lindon C. Thomas, 1st edition, Prentice-Hall, Englewood Cliffs, New Jersey, 1993. The equations themselves are based upon work by Duffie and Beckman, published in Solar Energy Thermal Processes, John Wiley & Sons, New York, 1974.

I have found this data quite handy for making accurate estimates of the thermal equilibrium temperature of outdoors surfaces exposed to the night sky. For example, will an exposed surface temperature drop below the dew point during the night? Is it possible that a surface might drop below the freezing point even though the surrounding air temperature is above freezing?

First we shall see the equations, with a bit of explanation. Then we shall demonstrate their use via a copy of the hand calculated solution of a simple illustrative problem. The example problem answer checks the solution to the same problem published as Example 5–27, pp. 322–323 of Thomas's text.

  • Sky Temperature Equations

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