Heat Pipes for Power Control Case Study

The Design Challenge

A manufacturer of industrial appliances had a new power conditioningand control system with very limited heatsink space available. The newsystem had three high power IGBT’s in close proximity with a smallthermal window due to a 50°C max ambient temperature condition. Tocompound the complexity of the project, there was a transient conditionto the system that would double the power for 1 minute every 10minutes. Aavid, Thermal division of Boyd Corporation, had assistedmany other projects with similar form factors although not with this levelof power.

The cabinet that housed the heatsink had two fans for forced convectionbut the airflow was shared with another heatsink to cool an SCR.Although the heatsinks were fully ducted to force all of the available airthrough them, the top of the system was obstructed by baffling therestricted 65% of the airflow. The new heatsink design would need tomind the difficult balance of airflow vs pressure drop through the entirecabinet.

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The Aavid Solution

Similar applications in the past had been addressed by Aavid withextruded solutions but with this high power the fin density of anextrusion was not going to cut it. A bonded fin approach with higher findensity was adopted to increase the surface area for heat transfer. Thenext performance enhancement was to spread the power throughout asmuch of the base as possible to lower the temperature of the localizedhot spots. Using multiple heat pipes under each IGBT, the effectivefootprint of each device was increased. This made it easier for heat toget into the fins that were not directly over the IGBT’s.

The heat pipes embedded in the base helped to meet the thermalrequirements for the 9 minute steady state but the performance wasstill lacking for the double power 1 minutes transient state. To give theheatsink a performance bump, heat pipes were run from the top of thebase and then in through the middle of the fins. By transporting heat tothe middle of the fins, the fin tips furthest from the base became moreeffective.

Following extensive thermal CFD design work, prototypes were built andtested with passing results. This design is now in successful massproduction.

The end result was a very efficient heatsink that took up no morevolume than a typical extruded or plain bonded fin heatsink.