Using fluid flow analysis (CFD), we will show you how to evaluate key metrics of water cooled electronic systems such as junction temperatures, energy consumption, energy removed and the path the heat takes out of the domain can be evaluated. Subscribe to our YouTube channel to watch our webinar recording for more details: https://youtu.be/s9QIyeD_qKM Find more on our website: https://www.simscale.com/

1. WATER-COOLED ELECTRONICS
WITH CFD
JON WILDE AND DARREN LYNCH

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6. CFD FOR WATER-COOLED ELECTRONICS
OVERVIEW
Electronic cooling is a vastly important topic,
as failure to sufficiently cool a component
within a system will lead to overheating,
reducing the component’s lifespan or in
severe cases damaging the component.
Water cooling is a great option for higher
power application, and this webinar will
demonstrate how CFD can be used to ensure
that there is sufficient cooling, and how to
ensure its efficiency within a system.

7. CFD FOR WATER-COOLED ELECTRONICS
SCENARIO
The application in which water cooling will
be applied and analysed is in the cooling of
multiple insulated gate bi-polar transistor
(IGBT) modules.
These devices are highly efficient fast
switching transistors, useful in high load
applications.
(Source:https://www.littelfuse.com/~/media/electronics/images/power_semiconductors/littelf
use_power_semiconductor_igbt_module_mg1275w_xn2mm_image.jpg.jpg:

8. CFD FOR WATER-COOLED ELECTRONICS
OVERVIEW
We can use CFD to analyse electronics
cooling for several key things:
● Junction Temperatures
● Energy Consumed
● Energy Removed
● Heat Path

9. OUR CASE: WATER COOLING IGBT’s
OBJECTIVES
● Model the cooling of an
electronic assembly consisting
of 4 IGBT devices.
● Ensure that the component
temperatures are kept
sufficiently low.
● Analyse the heat and water flow
for potential efficiency
improvements.

10. CAD IMPORT
Upload your CAD model
or import it from other cloud
services into SimScale.
SIMULATION SETUP
All steps to define and run
a simulation are done
within SimScale.
DESIGN DECISION
Use the simulation insights
to make better and faster
design decisions.
3

11. THE CONJUGATE HEAT TRANSFER ANALYSIS TYPE
Conjugate heat transfer (CHT)
analysis on the SimScale platform is a
coupled thermal solver which is
capable of solving heat transfer
problems involving both solid and
fluid parts. This is the most common
analysis type for electronic cooling
applications.

12. CASE SETUP

13. ● 4 x IGBT Devices
● Water Cooling block
● Reverse side of
IGBTs exposed to
atmosphere
Source: http://www.skyscrapercenter.com/building/central-park-tower/14269
OUR CASE: Water Cooling IGBT’s

14. THE CAD MODEL
A CAD model of the IGBTs, water
cooling block, surrounding air, and
internal water channel was created.
This model was imported directly into
SimScale.

15. THE MESH MODEL
Automated meshing was used with
the following settings:
● Automatic Hex-dominant
algorithm
● 5 inflated layers on no-slip
surfaces
● Moderate refinement

16. BOUNDARY CONDITIONS
The freestream velocity profile was
calculated following a logarithmic
law.
This atmospheric boundary layer
wind profile is typically used in
simulations of the lower portion of the
atmosphere.
Velocity Inlet
Inlet-Outlet
● Air inlet-outlet conditions
● Water 1m/s inlet
● Water 1 standard atmosphere
pressure outlet
● All other external boundaries as
adiabatic, no-slip walls
Pressure Outlet

17. HEAT SOURCES AND THERMAL PROPERTIES
● Each IGBT dissipating 368W of
energy.
● Heat generation modeled as a
volumetric heat source.
● Materials were given standard
values for thermal conductivity
and specific heat capacities.
IGBT - 368W -
Silicon
Water
Block -
Aluminium
Interface -
Thermal Paste
(PCM)
Connectors
- Brass

20. SIMULATION RUN: TEMPERATURE DISTRIBUTION THROUGH SOLIDS
● Temperature gradient
reveals the biggest thermal
resistances are due to
conductivity, which is in the
thermal interface.
● Temperature distribution
shows a lot about the
design including uneven
cooling, large temperature
gradients, and
unacceptable temperatures
in the component.

21. SIMULATION RUN: TEMPERATURE DISTRIBUTION THROUGH FLUID CHANNELS
● Because aluminium is a
good conductor, the
temperature difference
across the block is only
around 3 degrees.
● Since the temperature of
the water increases as it
passes through the channel,
the block shows a similar
trend.
● Hot spots are particularly
visible where the solid
regions are centre to where
the interfaces touch the
block.

22. SIMULATION RUN: PRESSURE DISTRIBUTION THROUGH FLUID CHANNELS
● Low pressure regions are
visible in the channel
restrictions and at sharp
edges.
● Low pressure regions lead
to a higher pressure drop
across the system, leading
to a less efficient flow.

23. SIMULATION RUN: TEMPERATURE DISTRIBUTION THROUGH FLUID CHANNELS
● Uneven velocities across
the channels at each
hotspot lead to uneven
cooling, where the transfer
coefficient will likely be
lower in lower velocity
channels.
● Separation is also visible by
low velocities and streak
line divergence.

24. SIMULATION RUN: TEMPERATURE DISTRIBUTION THROUGH FLUID CHANNELS
● The IGBTs generate
1472W of heat altogether,
of that 92.6% of the heat
removed is through water
cooling, the other 7.4% is
through natural convection
of the surrounding air.
-109W through
natural
convection
-1363W
through water
cooling
1472W from
IGBT’s

25. SIMULATION RUN: TEMPERATURE DISTRIBUTION THROUGH FLUID CHANNELS
● The maximum temperature
of the IGBT should be
around 90 degrees to
ensure that it will not be
damaged through
overheating.
● Although 90 degrees is the
maximum, to prolong the
components’ life a lower
temperature (i.e. 70
degrees) would be ideal.
● Currently, the junction
temperatures are
significantly too high.

26. PROBLEM 1
Problem:
Junction temperatures are too high
Cause:
Heat is not being transferred out of the component fast
enough due to high resistances from the phase change
material (PCM).
Solution:
● Improve the grade of the PCM
● Reduce the thickness of the PCM

27. PROBLEM 2
Problem:
Flow channel produces significant pressure losses
Cause:
Sharp edges and contractions
Solution:
● Increase the size of the channels near the contractions
● Reduce the number of sharp edges, adding fillets or
shape modification

28. DESIGN IMPROVEMENT 1
Design improvement 1 was focused
around reducing the temperatures of
the IGBT components, through
reducing the resistance between the
block and the IGBTs.
● The volume of PCM was
reduced, which may impact the
transient performance.
● A heat spreader with extrusions
was sunk into the PCM to
reduce the distance between
the conductor and the block.

29. SIMULATION RUN: IMPROVED DESIGN TEMPERATURES
● The junction temperatures
are much lower and
significantly lower than the
ideal temperature.
● The volume of the phase
change material could be
re-increased with the new
design to ensure it
performs the same
transiently.

30. SIMULATION RUN: TEMPERATURE DISTRIBUTION THROUGH SOLIDS
● The gradients of
temperature reflect the
observation, showing a
lower temperature
gradient in the majority of
the PCM, this leads to less
Thermal resistance.
● The design improvement
shows how the large
temperature gradient is
held off until after the tips
of the PCM heat sink.

31. DESIGN 2: TEMPERATURE DISTRIBUTION THROUGH FLUID CHANNELS
● Cooling block
temperatures are much
higher since there is less
resistance between the
IGBTs and the block.

32. DESIGN IMPROVEMENT 2
Design Improvement 2 improved on
the cooling channel of the water. The
following geometric changes were
made:
● Larger radii at in the channels
that turn back on themselves.
● Channels were replaced by pins
to reduce sharp edges.
● Channel connections were
wider to reduces the effect of
the contractions on the
pressure loss.

33. SIMULATION RUN: PRESSURE DISTRIBUTION THROUGH FLUID CHANNELS
● The pressure at the inlet is
much lower, approximately
half of the previous channel
design.
● Flow is not restricted in a
single direction causing
separation at sharp edges.
● Larger joining channels
reduces the pressure
changes before, after and
at contraction.

34. SIMULATION RUN: PRESSURE DROP IMPROVEMENT
● The pressure drop across
the cooling channel was
reduced by approximately a
half.
● That translates to to a
saving of about 0.45W of
Power saved, which in
comparison to the energy
removed in heat is very
insignificant, however, over
a lifetime, may save some
money.

35. SUMMARY
● We can use a CHT analysis to understand
complex thermal designs consisting of
fluid and solid components.
● Heat transfer through the air of a water
cooled device is small, and could be
neglected or modelled.
● IGBTs’ internal temperatures were
brought down to acceptable levels at the
expense of PCM volume, and this could be
increased with better understanding of
heat transfer.
● Pressure loss was reduced and thus
energy on pumping the water was reduced
by approximately 50%.