
Radiation Heat Transfer 349
PROBLEMS
13.1 What is a gray surface? What is a diffuse surface? How do these sur-
faces differ from a blackbody?
13.2 An opaque surface does not reect any radiation incident on it. What
are its absorptivity and emissivity values?
13.3 A piece of glass reects 20% and absorbs 40% of the radiation inci-
dent on its surface. What percentage of the incident radiation is trans-
mitted through the glass?
13.4 The emissivity of an opaque surface is 0.35. What are its absorptivity
and reectivity?
13.5 If the view factor between surfaces 1 and 2, F
12
, is 0.3, and the absorp-
tivity of surface 2 is 0.8, what fraction ...