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Automatic Purging of Non-Condensable Gases from 2-Phase Immersion Cooling Systems
Keywords: power electronics, thermosyphon, immersion cooling
Passive, 2-Phase Immersion cooling has been used for decades to cool GTO thyristor devices in traction inverters. These systems are typically sealed pressure vessels partially filled with a volatile Chlorofluorocarbon (CFC) or Perfluorocarbon (PFC) liquid in which the thyristors are immersed. Fluid boils on those devices and condenses on the finned walls in the interior of the pressure vessel. Heat is ultimately removed by passing air across the finned exterior of the housing. During manufacturing and servicing, extreme measures are taken to ensure that the system is fully evacuated, that fluid added to these systems is degassed and that the system will not leak over time. Leakage concerns are related not to fluid loss during operation but to the infiltration of air which can enter the system when it is idle and under vacuum. Even small amounts of air will have a dramatic effect on condensation heat transfer and resulting system performance. Degassing, leak checking and repairing very small leaks are costly procedures that discourage use of immersion cooling despite it performance potential and packaging advantages for cooling modern IGBT type devices. Inexpensive DC solenoid valves can be mounted at a high point in such systems. Actuated using a very simple algorithm based on the evaporator and condenser saturation temperatures, such valves easily purge the gas present in a system under startup and any gas that may enter a system over time. Fluid losses from this procedure are easily quantified and shown to be an insignificant over the life of a typical system.
Phil Tuma, Advanced Application Development Specialist
3M Company
St. Paul, MN

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