2A4_Lecture02_2008

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Unformatted text preview: tinuously Thought Experiments Thought Experiments 2. Fill two cups with hot water; one cup made of Styrofoam and one made of wax paper. Water is at 100°C and room temperature is at 20°C. Hold both 100°C cups and draw the temperature profiles cups T Ti To cup wall room r Thought Experiments Thought Experiments The temperature profile should look like Styrofoam cup Ti T Ti T Wax paper cup Close to 100 To cup wall outside To cup wall outside r r Importance of Heat Transfer Importance of Heat Transfer Used whenever we are concerned with the flow Used of heat — impacts on every engineering every discipline discipline Heat Exchanger Fuel Cell PCs Problem 1.31: Power dissipation from chips operating at a surface temperature of 85°C and in an enclosure whose walls and air are at 25°C for (a) free convection and (b) forced convection. Schematic: T A ir = 25 C h = 4 . 2 ( T s - )1 / 4 or W /m 2 -K o sur = 25oC q ra d S u b s tra te C h ip , P e le c o Ts = 85 C , ε = 0 .6 0 q conv L = 15 m m Assumptions: (1) Steady-state conditions, (2) Radiation exchange between a sma...
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This note was uploaded on 01/24/2010 for the course CHEM ENG 2A04 taught by Professor Toddhoare during the Winter '10 term at McMaster University.

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