Evaluating heat in vehicles' instrument panels

Being able to combine the existing ECAD data with thermal representations of components in the CFD simulation enables creating the thermal analysis model quickly, saving time in the design process.

Comparing experimental data and numerical results
An experimental setup of the cluster board without the housing was created to correlate the numerical results. Figure 5 demonstrates how the PCB was mounted standing vertically above a table in a room at 24°C. The PCB was operating with the backlight running at nominal brightness. IR camera images of the cluster were generated during the test.

Figure 5: Experimental and numerical setup of the PCB assembly. Images courtesy of Visteon.

A first comparison between the experimental data and the numerical results was done to validate which PCB modelling technique was the most appropriate for this model. The second technique gives a component temperature that is within 5% of the measured temperature while the first modelling technique shows a difference of 14% (table 1).

Table 1: Comparison of experimental and simulation results by the numbers.

Therefore, the second modelling technique was chosen as a reference for this particular model. Looking deeper, figure 6 demonstrates that both the measured IR camera images and the simulated images compare well, with heated areas being highlighted consistently between the two. A comparison component-by-component shows a maximum discrepancy of 5% with the experimental data, confirming the validity of the thermal analysis model.

Figure 6: Comparison of experimental and simulation thermal image results. Images courtesy of Visteon.

Once the model is validated, the PCB assembly can then be placed in the cluster full assembly to determine its performance in worse-case conditions at an air ambient temperature of 85°C.

Modelling the housing
The housing design contains features such as screw holes and pointers: these could potentially increase the thermal analysis solution time with no gain in the level of accuracy (figure 7).

Other features, such as the back cover holes, were important to keep because they allow some airflow movement inside the cluster. The mesh settings were defined so that the 2-mm hole opening would be captured appropriately by a minimum gap-size setting applied to a local mesh region.

The remainder of the mesh was set up automatically and was able to capture all the relevant details such as the PCB, its components, and the housing as well as the critical heat-transfer paths between the PCB and the housing.

Figure 6: Original CAD model of the housing assembly (top) and the simplified model in the CFD simulation (bottom). Images courtesy of Visteon.

Figure 8: Simulation results showing the original venting pattern (top) and the modified wider venting pattern (bottom). Images courtesy of Visteon.

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