As seen in the attached figure, a 5-mm-diameter spherical ball (k = 15 W/m·K, Cp=480 J/kg·K) at 50°C is exposed to a medium at 15°C, with a combined convection and radiation heat transfer coefficient of 20 W/m2·K (to be used for option a and b) a) If the ball is covered by a 1-mm-thick plastic insulation (k = 0.13 W/m·K), determine whether the plastic insulation on the ball will help or hurt heat transfer from the ball. b) Assume that the ball is initially at uniform temperature of 50 °C. Determine how long it will take for the center of the ball to drop to 20 °C.

Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
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As seen in the attached figure, a 5-mm-diameter spherical ball (k = 15 W/m·K, Cp=480 J/kg·K) at 50°C is exposed to a medium at 15°C, with a combined convection and radiation heat transfer coefficient of 20 W/m2·K (to be used for option a and b)

a) If the ball is covered by a 1-mm-thick plastic insulation (k = 0.13 W/m·K), determine whether the plastic insulation on the ball will help or hurt heat transfer from the ball.

b) Assume that the ball is initially at uniform temperature of 50 °C. Determine how long it will take for the center of the ball to drop to 20 °C.

As seen in the figure, a 5-mm-diameter spherieal ball (k = 15 W/m-K, p
= 8055 kg/m', Cp=480 J/kg-K) at 50°C is exposed to a medium at 15°C,
with a combined convection and radiation heat transfer coefficient of 20
W/m2-K
Plastic
insulation
5 mm
mm
Transcribed Image Text:As seen in the figure, a 5-mm-diameter spherieal ball (k = 15 W/m-K, p = 8055 kg/m', Cp=480 J/kg-K) at 50°C is exposed to a medium at 15°C, with a combined convection and radiation heat transfer coefficient of 20 W/m2-K Plastic insulation 5 mm mm
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