Advanced Topics in Heat, Momentum and Mass Transfer

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Advanced Topics in Heat, Momentum and Mass
Transfer

• Lecturer
• Payman Jalali, Docent
• Faculty of Technology
• Dept. Energy Environmental Technology
• Lappeenranta University of Technology

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Practical applications of CFD simulations
Electronic cooling The use of electronic chips
have been growing constantly. There are numerous
amount of switches in a tiny area of an
electronic chip such as the central processing
unit (CPU) in computers. New generation of
electronic chips contain larger number of
switches per unit area, thus the density of the
heat dissipation across the surface of the chip
is constantly growing. This requires suitable way
for the cooling of the chip. A chip is usually a
thin plate attached on a electronic board. A heat
sink is attached to the chip to conduct the
generated heat into the environment.
Assembly of electronic components simulated
thermally
CPU fan for forced cooling
Heat sinks
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The CPU dissipates heat, which is absorbed by the
heat sink and emitted to the ambient air (by
natural or forced convection).
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Consider the following model of an electronic
assembly subject to a forced air cooling. Build
the geometry in GAMBIT. Create the mesh. Export
it to FLUENT and solve it using laminar flow
model.
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The chip is in a box with the height of 3 cm.
The box
Split the box with the volume (sink)
Split the base with this face (the chip)
The base
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Mesh faces of sink
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Mesh faces of box
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Mesh volumes of sink and box
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wall
wall
Inlet
base
outlet
chip
wall
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After a successful export, open the msh file in
FLUENT. Make all initial steps prior to the
solution of the case Grid Check, Grid Scale (to
cm), and Grid Smooth/Swap. The model is steady
state, laminar flow. Set the residuals to some
lower values (10-5) and initialize the variables.
Fluid, Air
Wall, heat flux4000 W/m2
Solid, Aluminum
Velocity inlet, V0.1m/s, T300K
Pressure outlet
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Iterate and get a convergence
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The temperature of the sink is about 388K with
the given material and coolant air velocity.
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Changing the air velocity to 0.2 m/s brings the
temperature down to 379K.
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Changing the air velocity to 1.0 m/s brings the
temperature down to 340K.
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A bad conductor would raise the temperature
significantly. If we create a material with k0.1
W/mK the distribution of temperature would be as
follows at the same velocity of air, i.e. 1 m/s.