TABLE OF CONTENTS A furnace is to be located next to a dense complex of cryogenic propane piping. To protect the cold equipment from excessive heat loads, reflective aluminum radiation shielding sheets are to be placed between the piping and the 400 F (477 K) furnace wall. The space between the furnace wall and the cold surface is 2 ft (0.61 m). The facing surfaces of the furnace and the piping array are each 25 40 ft (7.6 12.2 m). With the ice-covered surface of the cold equipment at an average temperature of 35 F (275 K), how many 25 40 ft aluminum sheets must be installed between the two faces to keep the last sheet at or below 90 F (305 K)? Emittances of the furnace wall and cryogenic equipment are 0.90 and 0.65, respectively; that of the aluminum shields is 0.1.
1. Analyze the arrangement to assess the type(s) of heat transfer involved. The distance separating the hot and cold surfaces is small compared with the size of the surfaces. The approximation can thus be made that the furnace wall, the dense network of cryogenic piping, and the radiation shields are all infinitely extended parallel planes. This is a conservative assumption, since the effect of proximity to an edge is to introduce a source of moderate temperature, thus allowing the hot wall to cool off. Convection is omitted with the same justification. So the problem can be treated as pure radiation.
Radiant heat transfer between two parallel, infinite...
