Convection heat transfer coefficients for a hot hori- zontal surface facing upward may be determined by a gage whose specific features depend on whether the temperature of the surroundings is known. For con- figuration A, a copper disk, which is electrically heated from below, is encased in an insulating mate- rial such that all of the heat is transferred by convec- tion and radiation from the top surface. If the surface emissivity and the temperatures of the air and sur- roundings are known, the convection coefficient may be determined from measurement of the electrical power and the surface temperature of the disk. Con- figuration B is used in situations for which the tem- perature of the surroundings is not known. A thin, insulating strip separates semicircular disks with independent electrical heaters and different emissivi- ties. If the emissivities and temperature of the air are known, the convection coefficient may be determined from measurement of the electrical power supplied to each of the disks in order to maintain them at a com- mon temperature.
what is the temperature of the heat spreader when Too = Tsur = 23°C? Which thermal resistance (contact, conduction, radiation, or free convection) is the largest?
Consider the roof of the refrigerated truck compartment
Tsur
q
D
T, e
Tsur
T1, e1
D
q1 q2
T2, e2
described in Problem 7.20, but under conditions for which the truck is parked (V = 0). All other conditions remain unchanged. For aS = s = 0.5, determine the outer surface temperature, Ts,o, and the heat load imposed on the refrigeration system. Hint: Assume Ts,o > Too and RaL > 107.