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Engineering and Tech / Introduction to Heat Transfer 6 / Chapter 1 / Problem 1.63

Introduction to Heat Transfer | 6th Edition | ISBN: 9780470501962 | Authors: Theodore L. Bergman

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A 50 mm 45 mm 20 mm cell phone charger has a surface

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QUESTION:

A 50 mm 45 mm 20 mm cell phone charger has a surface temperature of Ts 33 C when plugged into an electrical wall outlet but not in use. The surface of the charger is of emissivity 0.92 and is subject to a free convection heat transfer coefficient of h 4.5 W/m2 K. The room air and wall temperatures are T 22 C and Tsur 20 C, respectively. If electricity costs C $0.18/kW h, determine the daily cost of leaving the charger plugged in when not in use.

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QUESTION:

A 50 mm 45 mm 20 mm cell phone charger has a surface temperature of Ts 33 C when plugged into an electrical wall outlet but not in use. The surface of the charger is of emissivity 0.92 and is subject to a free convection heat transfer coefficient of h 4.5 W/m2 K. The room air and wall temperatures are T 22 C and Tsur 20 C, respectively. If electricity costs C $0.18/kW h, determine the daily cost of leaving the charger plugged in when not in use.

ANSWER:

The power dissipated by the charger is given by:

P = h*A*(Ts - Trm)

where h is the free convection heat transfer coefficient, A is the surface area of the charger, and Ts and Trm are the surface temperature of the charger and room air temperature,

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