(a) A small body with temperature T and emissivity e is placed in a large evacuated cavity with interior walls kept at temperature Tw. When Tw – T is small, show that the rate of heat transfer by radiation is 4TΑεσ(Τw - T) . dt (b) If the body remains at constant pressure, show that the time for the temperature of the body to change from T¡ to T2 is given by Cp Тw - Ti In 4Ty Aeơ Tw – T2 (c) Two small blackened spheres of identical size, one of copper and the other of aluminum, are suspended by silk threads within a large hole in a block of melting ice. It is found that it takes 10 min for the temperature of the aluminum to drop from 276 to 274 K, and 14.2 min for the copper to drop the same interval of temperature. What is the ratio of specific heats of aluminum and copper? (The densities of Al and Cu are 2.70 × 10³ kg/m³ and 8.96 × 10³ kg/m³ at 25°C, respectively.)

(a) A small body with temperature T and emissivity e is placed in a large evacuated cavity with interior walls kept at temperature Tw. When Tw – T is small, show that the rate of heat transfer by radiation is 4TΑεσ(Τw - T) . dt (b) If the body remains at constant pressure, show that the time for the temperature of the body to change from T¡ to T2 is given by Cp Тw - Ti In 4Ty Aeơ Tw – T2 (c) Two small blackened spheres of identical size, one of copper and the other of aluminum, are suspended by silk threads within a large hole in a block of melting ice. It is found that it takes 10 min for the temperature of the aluminum to drop from 276 to 274 K, and 14.2 min for the copper to drop the same interval of temperature. What is the ratio of specific heats of aluminum and copper? (The densities of Al and Cu are 2.70 × 10³ kg/m³ and 8.96 × 10³ kg/m³ at 25°C, respectively.)

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter11: Heat Transfer By Radiation

Section: Chapter Questions

Problem 11.56P

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