Liquid cooling is necessary to cool components within electronic systems, and mitigate the risk of overheating. When cooling is applied correctly, components’ lifespan can increase, and the electronics can operate more efficiently. When it comes to electronic product design, there are four main electronics cooling techniques. These include natural convection, forced convection, fluid phase change, and finally—the most intricate—liquid cooling.
What are Liquid Cooled Electronics?
Liquid cooled electronics usually consist of high-powered components, meaning they use high voltage/currents, and require active liquid cooling to keep the internal system functioning. Applications most notably include consumer PCs and transistors such as IGBTs (insulated-gate bipolar transistor), along with standard sealed electronics, electric motors, and anything where forced air is no longer sufficient. The ‘liquid’ used to cool these devices can be glycol/water solutions, dielectric fluids such as fluorocarbons and PAO, but most commonly water and deionized water. Using computational fluid dynamics (CFD) within the SimScale platform, you can simulate your water cooled designs, and make modifications quickly and efficiently to solidify any necessary design improvements.
The Case: Water Cooling IGBTs
In this simulation project, 4 high-powered IGBT modules sitting in proximity are analyzed. These devices boast high efficiency as switching transistors and are useful in high load applications such as switched-mode power supplies, traction motor control, and induction heating.
The liquid cooling simulation allows for the evaluation of several key metrics including junction temperatures, consumed energy, removed energy, and heat path. Ultimately, the analysis aims to find how the heat travels from the sources, within the system, and around the components to the exit point with considerations to where resistance occurs and temperature gradients are heightened. Once identified, the objective is then to pinpoint these areas of resistance, modify the design, and improve the system’s efficiency; all through online simulation!
Simulation: Conjugate Heat Transfer Analysis of Electronics Cooling
The project uses conjugate heat transfer (CHT) analysis. This simulation type is a coupled thermal solver that is able to solve heat transfer problems that have both solid and fluid parts. CHT is the most common and effective for evaluating most electronics cooling problems.
CAD Model Including IGBT Modules
The CAD model used for the project contains a water cooling block, surrounding air, and an internal water channel. This design was directly imported onto the SimScale platform.
For the CAD model of the liquid cooled electronics, an automated mesh was created using an automatic hex-dominant algorithm with five inflated layers on no-slip surfaces and moderate refinement.
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The boundary conditions for the simulation featured a velocity inlet and a pressure outlet. The velocity inlet tells SimScale how much flow is coming into the water block. The inlet-outlet allowed for natural convection to take place within the system, and the pressure outlet represents the fluid exit where the temperature was defined. For more information about the boundary conditions, refer to the project specifications.
Heat Source and Thermal Properties
The project dictated each silicon IGBT dissipated 368W of energy, with a thermal interface, water block, and brass connectors. The heat generation was modelled as a volumetric heat source, and the materials were given standard values for thermal conductivity and specific heat capacities for each material, silicon, paste, aluminum, and brass.
Results: Evaluating the Liquid Cooled Electronic Design
The simulation found through the temperature distribution that the electronic design allowed for uneven cooling, large temperature gradients, and unacceptable temperatures in the component. The temperature gradient revealed that the biggest thermal resistances were due to conductivity within the thermal interface.
The IGBTs generated 1472W of heat altogether, and of that 92.6% of the heat removed was through water cooling, the other 7.4% through natural convection of the surrounding air. The maximum temperature of an IGBT should be around 90 degrees Fahrenheit to ensure that it will not be damaged through overheating, but to increase the component’s longevity, 70 degrees would be ideal. The first design revealed that the junction temperatures were too high.
Additionally, the conjugate heat transfer simulation found that the flow channel produced significant pressure losses due to the design’s sharp edges and contractions.
Optimization of the Liquid Cooled Electronic Design
The initial design created temperatures that were too high. This was because the heat flow faced too much resistance around the component due to the low conductivity of phase change material (PCM) in the interface. This revealed that a simple modification to improve this would be reducing the thickness or improving the grade of the PCM altogether. Along with this, in order to meditate pressure loss, increasing the size of the channels near the contractions coupled with reducing the number of sharp edges or adding fillets would improve the overall design.
These changes were subsequently made to the liquid cooled electronic design, and the simulation was repeated; this time with an improved outcome!
Conclusion: Liquid Cooling of Electronics
Using conjugate heat transfer from SimScale, analyzing complex thermal designs like water cooled electronic designs is not only possible but also allows for simplified design modification and quick design improvement. After the resistance areas were pinpointed and amended, the IGBTs’ internal temperatures were brought down to acceptable levels at the expense of PCM volume, and this could be further increased with a better understanding of heat transfer. Additionally, pressure loss was reduced and thus energy on pumping the water was decreased by approximately 50%.
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