How to Couple Fluid Flow and Steady-State Heat Transfer for Forced Convection
The ability to predict how flow will affect temperature distribution in fluid and solid
components is
useful when analyzing systems that require cooling from fans or water,
such as a fan-cooled printed circuit board or a water-cooled heat exchanger, and those that operate at extremely high temperatures for
functions like transporting molten metal or liquefied plastic. Engineers can determine what fluid flow velocity is necessary to
produce the desired temperature distribution and prevent parts of a system from failing.
In such systems, the fluid flow cools the solid components via forced convection.
You can model forced convection as follows:
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First, create and mesh an assembly containing both the solid and fluid parts making sure that
the meshes are matched at the interfaces of the parts. It is recommended that you create a fine mesh near the edges of the fluid
where it will interact with the solid. For illustration, consider a water-cooled heat sink for a CPU
chip as shown in Figure 1.
- The green part is a block of aluminum, which has 30 Watts from the chip
applied to its bottom surface.
- The red part is an aluminum pipe in which water (at 70ºF) is inlet
at one end and outlet at the other.
- The blue part represents the water flowing through the pipe (inlet at 20 in./sec).
- The ambient air surrounding the top and side surfaces is 80ºF.
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Figure 1: A water-cooled heat sink is heated on its bottom surface
by a CPU chip.
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Next, save the model as a new filename and delete the solid parts. (Note:
Alternatively, you could use only one model and deactivate the solid
parts for the fluid flow analysis.) Perform a steady or unsteady fluid flow analysis
on the fluid model. As shown in Figure 2, a velocity profile is obtained.
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Figure 2: A steady fluid flow analysis produced the velocity magnitude results
shown in this display. The elements were
sliced to show the centerline flow profile.
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Go back to the original model and set up a steady-state heat transfer analysis.
The geometry of the part that was analyzed as a fluid flow model must be identical in the heat transfer model.
The processor will consider velocity results using the exact coordinates of
the nodes.
The parts that represent the solids require only thermal conductivity to be defined as a material property.
The part that represents the fluid requires thermal conductivity, mass density and specific heat values (see Figure 3).
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Figure 3: On the "Element Material Specification" screen, mass density, thermal conductivity and
specific heat values are specified for the fluid. |
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As shown in Figure 4, on the "Analysis Parameters" screen for a steady-state heat transfer analysis, access the "Multi-Physics" tab
and click on the checkbox to include fluid convection effects. Specify the location of the fluid velocity data (a .sfv file
for steady flow or a .ufv file for unsteady flow). The velocity values from the last load case of the fluid flow analysis
will be used.
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Figure 4: On the "Analysis Parameters" screen for steady-state heat transfer analysis, specify that fluid convection effects
will be included based on velocity results from the fluid flow analysis. |
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Run the steady-state heat transfer analysis to determine the temperature profile for both the fluid and solid components of the model.
As shown in Figure 5, forced convection was considered to determine the temperatures based on the cooling fluid velocity profile obtained from
the fluid flow analysis.
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Figure 5: The temperature distribution for both the fluid and solid parts of the model. |
For more information about the forced convection capability,
see the ALGOR User's Guide.
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