Rhombus Energy Solutions: Cooling an IGBT Module

Figure 1. Modeling of Evaporator Thermal Performance

Rhombus Energy Solutions came to ACT looking to replace their liquid cooling system with a passive heat transfer solution.  The primary heat source in the system was a large IGBT module, which produces a maximum of 4kW of heat.  The goal was to design a solution that provides cooling to keep the IGBT module case temperatures below 85°C, while fitting inside Rhombus’s existing packaging.

To achieve the program goals, ACT developed a custom loop thermosyphon assembly comprised of a custom brazed aluminum evaporator, microchannel aluminum condenser, and fluid transport lines.

Figure 2. Angled Microchannel Condenser

The fluid in a loop thermosyphon is driven around the loop by gravity; this means that the pressure drop of the loop has to be lower than in a pumped system.  ACT iterated through multiple evaporator, condenser, and transport line designs to determine the best combination, taking into account the performance, cost, and packaging of each design.  Ultimately, the choice of an angled condenser was able to provide a large airflow area, while keeping the overall height of the assembly to a minimum. ACT designed-in flexible lines between the evaporator and condenser to improve the installation of the cooling system.  The final solution is predicted to keep the IGBT case temperature below 79°C, providing ample cooling to the customer.

The key benefits of ACT’s solution are an increase in both the reliability, and power consumption, of the cooling system.  This will drive up Rhombus’s efficiency rating, and improve the reliability and maintenance requirements for their system.

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