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3. A small cylindrical filament is heated in a large combination convection-radiation oven. The filament has a diameter D= 50

3. A small cylindrical filament is heated in a large combination convection-radiation oven. The filament has a diameter D= 50 mm and length L= 1 m. During the process, the oven wall temperature is fixed at Tsur=800 K, and the hot air is blowing with a temperature T.= 500 K and an average heat transfer coefficient h=50 W/m²K. Assuming the filament surface is opaque and diffuse, and it has a spectral emissivity as shown below: (25 pts) 


The oven walls behave like a black surface, and the filament end effects are negligible. If initially the surface temperature of the filament is Ts=300 K, 

(a)Determine the total, hemispherical emissivity & and absorptivity a of the surface of filament. 

(b)Use energy balance on the filament and determine the net rate of heat transfer to the filament.

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Answer #2


0 Ts = 300k (6) UX 300 1200 mm From table 4 - Black body raclication functions Fo- XT = 0.002134 E=0.80.002134 +0:2[1-0.00213 AES.J = AESOT = TTX50x10 x0.2x5.67 x 108 x 3004 14.42w Qnet ti Eout - Ein [14.42-1570.7 -1422-7 ] -2978.a w

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Answer #1

si El End + of Eucht E for (T) + Este (T) E (T) = Eto, & Eg (1-t.) dit = 4x 300 = 1200 Klem fch-0-00234 E(T) = 0.8x8.00 2134

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