1 • ENGINEERING CALCULATIONS OF RADIANT HEAT EXCHANGE 



field of view of an element of radiation-receiving surface enormously 

 complicates the problem; see end of Art. 4. 



Application of the principles discussed is illustrated in the following 

 example: Nonluminous combustion products of a hydrocarbon fuel, con- 

 taining 10 per cent CO2 and 15 per cent H2O by volume, flow through a 

 black wall cylindrical chamber 15 inches in diameter at a total pressure 

 of 5 atm. In the region where the gas temperature drops from 2700 to 

 2000°F and the wall temperature is substantially constant at 1200°F, 

 estimate the average heat transfer rate due to radiation from CO 2 and 

 H2O. 



The arithmetic mean gas and surface temperatures are (2700 + 2000)/ 



2 + 460 = 2810°R, and 1660°E,; 2810^ - 1660^ = 0.548 X lO^^. From 

 Fig. I,3g, (Tg — T'^/Tg = 0.016. The mean radiating gas temperature is 

 then 2810(1 — 0.016) = 2765°R. Mean gas and surface temperatures 

 differ sufficiently little to justify use of Eq. 3-5. 



T,, = (2765 + 1660)/2 = 2212°R (3-8) 



PeL = 0.10 X 5 ( ^ ) X 0.8 = 0.50 (3-9) 



(S) 

 (S) 



p^L = 0.15 X 5 ( ^ ) X 0.8 = 0.75 (3-10) = 



From Fig. 1, 3a and 1, 3b, 



ee (at T = 2212°R, p,L = 0.5) = 0.119 X 1.15 = 0.137 (3-11) 

 From Fig. 1, 3c and 1, 3d, 



€, (at T = 2212°R, p^L = 0.75) = 0.167 X 1.6(?) = 0.267 (3-12)^ 



0.404 

 From Fig. I,3e, the superimposed radiation correction^ = 0.057 



Total gas emissivity, eg = 0.347 



From Fig. I,3f, a and h for CO2 = +0.35 and -0.40; for H2O, 4-0.52 

 and -0.85. For the mixture, a = 0.46, h = -0.7, c = 0.52. Then, from 

 Eq. 3-5, 



(i\ ^ -,^-, r.^o.^ 4 + 0.46 - 0.7 - 0.52' 



^ =0.171 



0.347 



(27.65^ - 16.60 



24,500 BTU/ft2 hr 



- A smaller factor is used than for an infinite cylinder; the length of the system has 

 not been specified. 



' The pressure correction for H2O is far beyond the end of the plot; the extrapolation 

 is based on the assumption that the pressure effect levels off above a few atmospheres 

 pressure. 



^ In the absence of a recommendation, in the literature, as to the effect of total 

 pressure on the correction Ae, it may be assumed to be increased by the average of 

 Co and Cw The effect is negligible in the present example. 



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