1,4 • RADIANT EXCHANGE 



A convection coefficient of about 22 BTU/ft^ hr °F would produce the 

 same transfer rate. 



Radiation from other gases. Gas radiation plots similar to those for 

 CO2 and H2O have been prepared for SO2, CO, and NH3 [5, Chap. 4]. 

 Infrared spectroscopic data available on many gases can serve as a basis 

 for estimating radiant heat transfer although the data, particularly on 

 the effects of temperature and total pressure, are often found to be in- 

 adequate. For a discussion of the methods of calculation the reader is 

 referred to Sec. H, 



1,4. Radiant Exchange in an Enclosure of Source-Sink and 

 No-Flux Surfaces Surrounding a Gray Gas. One of the most complex 

 problems of heat transmission is the evaluation of heat transfer in a com- 

 bustion chamber, where all of the mechanisms of radiation so far dis- 

 cussed are operating simultaneously. Allowance is to be made for the 

 following: (1) the combined actions of direct radiation of all kinds from 

 the flame to the heat sink, (2) radiation from flame to refractory sur- 

 faces, thence back by reradiation or reflection through the flame (with 

 partial absorption therein) to the sink, (3) multiple reflection of all non- 

 black surfaces, (4) convection, (5) external losses, and (6) for the fact 

 that the refractory surfaces take up equilibrium temperatures which vary 

 continuously over their faces. Allowance for space variation in temper- 

 ature and emissivity of the gas introduces major complications, and the 

 problem is here limited to consideration of a gas mass of uniform concen- 

 tration and temperature equal to some set of mean values (see, however, 

 the last part of Art. 4). The problem is otherwise capable of a solution 

 free from seriously limiting assumptions. It will be convenient to group 

 surface zones into two classes. Source-sink zones, such as a fuel bed, a 

 carborundum muffle, a row of electric resistors, a liquid- or air-cooled 

 surface and stock on a furnace hearth are designated by subscripts 1, 2, 

 3, . . . ; surface 1 has area *Si, temperature Ti, emissivity ei. Completing 

 the enclosure are the insulating refractory connecting walls, which are 

 heat sinks only to the extent that they lose heat by conduction through 

 the walls. If the difference between gas convection to the inside of such 

 a wall and conduction through the wall to the outside is small compared 

 to the radiation incident on the wall inside, then the assumption that the 

 net radiant heat transfer at the wall surface be zero is an excellent one. 

 It enormously simplifies the problem of source-to-sink heat transfer and 

 the effect thereon of the refractory surfaces. All such zones will be re- 

 ferred to hereafter as no-flux surfaces, with the understanding that refer- 

 ence thereby is to radiant heat transfer alone, and the letter subscripts 

 R, S, T, . . . will be appended to their properties. 



Several restrictions are imposed at this point, some of them to be re- 

 moved later. (1) All of the sources and sinks, including the gas as well 



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