The typical geometry used for the case is as follows:
Figure 1. Main dimensions of the quarter model of the heat sink, with shown gap of 10 mm.
It represents a heat sink of dimensions 100 x 100 \(mm\) with 25 LEDs attached through Thermal Interface Material (TIM) patches of dimensions 7 x 7 x 0.1 \(mm\). Only one-quarter of the geometry is modeled to leverage the symmetry. Gaps of 10, 5, and 1 \(mm\) between LEDs were tested, with each model shown below for comparison:
Figure 2. Models with gaps between LEDs of 10, 5, and 1 mm (left to right).
The meshes were computed using the Tet-dominant algorithm with manual mesh sizing and local refinements for the TIM regions. The goal was to keep 2 elements across the thickness of the thin-walled parts, like the heat sink fins and TIM patches.
Figure 3. Typical tetrahedral mesh for 5 \(mm\) gap model.
Figure 4. Typical mesh refinement showing local details of the tetrahedral elements on a TIM body.
The thermal conductivity of the TIM was computed to achieve a total resistance of 9 \(K/W\), according to [INFINEON]\(^2\) with the relation:
$$ \kappa = \frac{t}{RA} $$
Where:
\(\kappa\) is the conductivity, \( W/(mK) \)
\(t\) is the thickness of the body, 0.1e-3 \(m\)
\(R\) is the thermal resistance, 9 \(K/W\)
\(A\) is the cross-sectional area, 4.9e-5 \(m^2\)
Boundary Conditions:
Heat Flux Load:
Surface heat fluxes of 1, 3, and 5 \(W\) per LED applied to the top surfaces of TIM bodies.
Convective Heat Flux:
Convective heat fluxes with heat transfer coefficients of 10, 25, 50, 75, and 100 \(W/(m^2K)\) with reference temperature of 300.15 \(K\) on all heat sink faces except the contact patches with TIM bodies and symmetry planes.
The following table relates the simulation runs for each case and the combinations of applied boundary conditions:
Run
Load 1 \([W]\)
Load 3 \([W]\)
Load 5 \([W]\)
Convective flux 10 \([\frac{W}{m^2K}]\)
Convective flux 25 \([\frac{W}{m^2K}]\)
Convective flux 50 \([\frac{W}{m^2K}]\)
Convective flux 75 \([\frac{W}{m^2K}]\)
Convective flux 100 \([\frac{W}{m^2K}]\)
1
X
X
2
X
X
3
X
X
4
X
X
5
X
X
6
X
X
7
X
X
8
X
X
9
X
X
10
X
X
11
X
X
12
X
X
13
X
X
14
X
X
Table 2. Simulation runs and their respective boundary conditions matrix.
Reference Solution
The reference solution is of the analytical type, as presented in [ADAM]\(^1\). It is given in terms of the temperature at the center point as a function of the thermal load and convection coefficients.
Result Comparison: High Power LED Packaging
Comparison of temperature at the mid point is shown for each case:
Figure 5. Results comparison for Case A.
Figure 6. Results comparison for Case B
Figure 7. Results comparison for Case C
The deviation of the results with respect to [ADAM]\(^1\) in the cases of gap 5 mm and 1 mm can be attributed to a non-uniform temperature distribution at the base of the fins:
Figure 8. Temperature contour plot for Case C, Run 12: 1 mm gap, 5 W/LED load and Convection coefficient of 50.
Christensen, Adam, and Samuel Graham. “Thermal effects in packaging high power light emitting diode arrays.” Applied Thermal Engineering 29.2 (2009): 364-371.
“Thermal Resistance Theory and Practice – Infineon” http://www.infineon.com/dgdl/smdpack.pdf?fileId=db3a304330f6860601311905ea1d4599
Note
If you still encounter problems validating you simulation, then please post the issue on our forum or contact us.
Last updated: December 20th, 2020
Did this article solve your issue?
How can we do better?
We appreciate and value your feedback.
Contents
Cookie Policy
SimScale uses cookies to improve your user experience. By using this website you consent to our cookie policy.
This website uses cookies so that we can provide you with the best user experience possible. Cookie information is stored in your browser and performs functions such as recognising you when you return to our website and helping our team to understand which sections of the website you find most interesting and useful.
Strictly Necessary Cookies
Strictly Necessary Cookie should be enabled at all times so that we can save your preferences for cookie settings.
If you disable this cookie, we will not be able to save your preferences. This means that every time you visit this website you will need to enable or disable cookies again.
