A power transistor with three 0.8 mm diameter leads of a copper-silver alloy (k = 400 W/m-K) dissipates 3.5 Watts of power. The printed circuit board (PCB) on which the transistor is mounted is maintained at 30 C. The air temperature is 20 C and the heat transfer coefficient for the leads is 60 W/m² K. The length of the leads from the transistor to printed circuit board is 9.0 mm. (a) Determine the maximum lead temperature neglecting all convection effects. (b) Determine the maximum lead temperature if convection is present. T=20C h = 60 W/m²K Air Power Transistor Lead k = 400 W/m K TPCB = 30 C 9 mm

A power transistor with three 0.8 mm diameter leads of a copper-silver alloy (k = 400 W/m-K) dissipates 3.5 Watts of power. The printed circuit board (PCB) on which the transistor is mounted is maintained at 30 C. The air temperature is 20 C and the heat transfer coefficient for the leads is 60 W/m² K. The length of the leads from the transistor to printed circuit board is 9.0 mm. (a) Determine the maximum lead temperature neglecting all convection effects. (b) Determine the maximum lead temperature if convection is present. T=20C h = 60 W/m²K Air Power Transistor Lead k = 400 W/m K TPCB = 30 C 9 mm

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.10P: 1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss...

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1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4
2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.
1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1
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