Thermodynamics HW Solutions 3

# Thermodynamics HW Solutions 3 - Chapter 1 Basics of Heat...

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Chapter 1 Basics of Heat Transfer 1-13E A logic chip in a computer dissipates 3 W of power. The amount heat dissipated in 8 h and the heat flux on the surface of the chip are to be determined. Assumptions Heat transfer from the surface is uniform. Analysis ( a ) The amount of heat the chip dissipates during an 8-hour period is Logic chip W 3 = Q & QQ t == = = & () ( ) Δ 38 2 4 W h W h 0.024 kWh ( b ) The heat flux on the surface of the chip is 2 W/in 37.5 = = = 2 in 08 . 0 W 3 s s A Q q & & 1-14 The filament of a 150 W incandescent lamp is 5 cm long and has a diameter of 0.5 mm. The heat flux on the surface of the filament, the heat flux on the surface of the glass bulb, and the annual electricity cost of the bulb are to be determined. Assumptions Heat transfer from the surface of the filament and the bulb of the lamp is uniform . Analysis ( a ) The heat transfer surface area and the heat flux on the surface of the filament are 2 cm 785 . 0 ) cm 5 )( cm 05 . 0 ( = = = ππ DL A s 2 6 W/m 10 1.91 × = = = = 2 2 W/cm 191 cm 785 . 0 W 150 s s A Q q & & ( b ) The heat flux on the surface of glass bulb is 2 2 2 cm 1 . 201 cm) 8 ( = = = D A s 2 W/m 7500 = = = = 2 2 W/cm 75 . 0 cm 1 . 201 W 150 s s A Q q & & ( c
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