Chapter 11 FUNDAMENTALS OF THERMAL RADIATION
Chapter 11 FUNDAMENTALS OF THERMAL RADIATION
Chapter 11 FUNDAMENTALS OF THERMAL RADIATION
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<strong>Chapter</strong> <strong>11</strong> Fundamentals of Thermal Radiation<strong>11</strong>-48E A spherical ball emits radiation at a certain rate. The averageemissivity of the ball is to be determined at the given temperature.Analysis The surface area of the ball is2 2A D (5/ 12 ft ) 05454 . ft 2BallT=950 RD = 5 inThen the average emissivity of the ball at this temperature isdetermined to beE AT4E AT4(0.5454ft2)(0.171410120Btu/h-8Btu/h.ft2R4)(950R)4 0.158<strong>11</strong>-49 The variation of transmissivity of a glass is given. The average transmissivity of the pane at twotemperatures and the amount of solar radiation transmitted through the pane are to be determined.Analysis For T=5800 K:1T1 ( 03 . m)(5800 K) =1740 mK f 0035 .1 2T1 ( 3 m)(5800 K) =17,400 mK f 0977 .2The average transmissivity of this surface is ( T ) ( f f ) (0.9)(0.9770.035) 0.8481 210.92For T=300 K:1T2 ( 03 . m)(300 K) = 90 mK f 00 .2T2 ( 3 m)(300 K) = 900 mK f 00001685 .120.3 3, mThen, ( T ) ( f f ) (0.9)(0.00016850.0) 0.00015 01 21The amount of solar radiation transmitted through this glass isG 0.848(650 W/m ) 551tr G incident22W/m<strong>11</strong>-23
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