Sheet [6 Radiation Heat Transfer The total incident radiant energy upon a body whlch partially reflects, absorbs and transmits radiant energy is22O0W/m2. Of these amounts, 45OW/m2 is reflected and 900 W /mz is absorbed by the body. Find the.transmissivity of that body. For a blackbody maintained at 390 K, determine the total emissive power, the wavelength that which the maximum spectral emissive power occurs and the maximum spectral emissrve power. The emission of radiation from a surface can be approxrmated as a blackbody radiation at T=L000 K. a. What fraction of the total energy emitted is below A=5pm? b. What is the wavelength below which the emission is 10.0BBBo/o of the total emission at 1000 K? c. What is the wavelength at which the maximum spectral emission occurs at 1000 k? A glass plate 0.3 square is used to view radiation from a furnace. The transmissivity of the glass is 0.5 from 0.2 pm to 3,5 prm. The emissivity may be assumed to be 0.3 up to 3.5pm and 0.9 above that. The transmissivity of the glass is zero, except in the range from 0.2 FIn to ',1.5 pm.Assume thatthe furnace is a blackbodyat20000C, calculate the energy absorbed in the glass and the energy transmitted through it. Consider a large isothermal enclosure that is maintained at a uniform temperature of 2000 K. Calculate the emissive power of the radiation that emerges from a small aperture on the enclosure surface, a. What is the wavelength Ar helor.t, r,,,rhich lUoh of the emission is concentrated? b. What is the wavelength ),: above v"'iich 70oh of the emission is concentrated? c. Determine the maximum spe i--lral i missive power and the wavelength of which it occurs? d. What is the irradiation incident on a small object placed inside the enclosure? Enclosur.e s1 f=fO00 K
A small surface of A=5cm2 is subjected to irradiation of constant intensity I=1.8x104[W/m2.Sr) over the solid angie subtended by 0the radiation energy incident on the surface. Determine the solid angels subtended by the surface dAr and dAz, when they are viewed from the point 0 for the dimensions and geometric arrangement in the accompanying figure. dAz=10cm2 rz=B0cm dAr=4cm B. A smali surface of area Ar=3cmz emits radiation as a blackbody at temperature of Td000 K. Part of the radiation emitted byAr strikes another small surface of area Az=lcm?, oriented as shown in the accompany figure. Determine the solid angle subtended by Az when viewed from Ar and the rate at which radiation emitted by Ar that strikes Az. 9. Two small surfaces as illustrated in the dA1=Sgmz and dAz=12cm2 are separated figure. Caiculate the view factors between by r=60cm and oriented the surf,aces. dAz 0r=450 rr=50cm 0z=450 r=75cm Ar=3cm2, Tr=1000 k dAr r=60cm i" 10. Determine the following view factors for the geometries shown in the accompanying _ figures, a. From the bas&f the cube to each of its surfaces. b. From the base of circular cylinder of radius r and the height L to its top surface and the cylindrical surface for case r=L. c. Between the surfaces of two concentric spheres with Ar and Az being the surface of the inner and the outer sphere. tdl tD.J [c) 11' The energy flux associated with solar radiation incident on the outer surface of the 'darth's atmosphere has been accurately measured and known to be 13 53 W/mz. The diameter of the sun and the earth are 1.39x10e and 1.29xI07 m, respectiveiy, and the center distance between the earth and the sun is 1.5x1011 m, a. What is the emissive powe.r of the sun? b. Approximating the sun's surface as a blackbody, what is its temperature? c. At what wavelength is the spectral emissive power of the sun a maximum? d' Assuming the earth's surface to be black and the sun to may be only source of energy for the earth, estimale the earth's temperature. 12.Two square plates, each 1m by 1m are parallel and directly opposite to each other at a distance 1m, the hot plate
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