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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.
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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