Transcript Chapter 3: Steady-State Heat Transfer

Steady-State Thermal Analysis of a
Transistor
A transistor is mounted on a
copper isolator which is in turn
mounted on an aluminum heat
sink. The transistor generates
heat, and the system also
receives heat radiated by other
nearby components. The system
is fan cooled.
Design Requirements:
•
The steady-state temperature of
the system must be less than
100°C.
Transistor
Copper
isolator
Aluminum heat sink
plane of symmetry
•
An ANSYS input file for this workshop is
provided in Appendix C
HEAT TRANSFER 5.7
Basic Problem Description:
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Steady-State Thermal Analysis of a
Transistor
Assumptions
• One plane of mirror symmetry.
• Use SI units. (kg, m, s, W, J)
• Radiation from surrounding
components is modeled as an
equivalent uniform heat flux.
• Neglect contact resistance at
component interfaces.
• Homogeneous transistor material.
• Uniform transistor heat generation.
• No heat transfer on front and back
surfaces; (i.e., no axial temp gradient).
• Convection modeled with uniform film
coefficient and constant bulk fluid
temperature.
• Depth is 0.025m
• All dimensions shown are in meters.
HEAT TRANSFER 5.7
Dimensions:
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Steady-State Thermal Analysis of a
Transistor
Thermal
Loads
Symmetry
Plane
20 W - high power
Equivalent heat flux
due to radiation from
other devices: q* =
1500 W/m2
Forced convection
from high speed
cooling fan on fin
surfaces:
HEAT TRANSFER 5.7
Transistor Power
Dissipation:
Workshop Supplement
h = 51 W/m2 °C
T = 50 °C
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