Class Problem _2_solution (2).pdf - EEN-E1020 Heat Transfer 2016 Class Work 2 Topic Convection Class Problem 1 To cool an electronic device six

Class Problem _2_solution (2).pdf - EEN-E1020 Heat Transfer...

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EEN-E1020 Heat Transfer 2016 Class Work # 2 Topic: Convection Class Problem 1 To cool an electronic device, six identical aluminum fins, as shown in the figure below are attached. Cooling air is available at a velocity of 5 m/s from a fan at 20°C. If the average temperature at the base of a fin is not to exceed 100°C, estimate the maximum permissible power dissipation for the device. Solution: GIVEN Aluminum fins with air flowing over them Air velocity ( U ) = 5 m/s Air temperature ( T ) = 20°C Maximum average temperature of the fin base ( T s ) = 100°C FIND The maximum permissible power dissipation q PROPERTIES AND CONSTANTS For dry air at the film temperature (60°C) Kinematic viscosity ° = 19.4 × 10 ±² ³ ´ µ¶· Thermal conductivity ( k ) = 0.0279 W/(m K) Prandtl number ( Pr ) = 0.071 For aluminum at 100°C Thermal conductivity ( k al ) = 239 W/(m K) SOLUTION: The Reynolds number at the trailing edge of the fins is ¸¹ º = » ¼ ½ ° = 5 × .06 19.4 × 10 ±² = 1.55 × 10 ¾ < 1 × 10 ¿ (ÀÁ !Á") The average transfer coefficient for a laminar boundary layer
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