Principle of Operation
Each high power component is fitted with a heat riser (see top of first picture below). The thickness of the individual risers is set so their top surfaces are all at the same plane. A highly compliant and conductive thermal interface (TIM) is positioned on the top of the risers and a cold plate is brought into contact with the top of the TIM. Cooling liquid is circulated through the cold plate.
Generally water is the coolant selected for systems with moderate to high heat flux and refrigerant for high to extreme heat fluxes or in locations where water is undesirable.
In operation, the generated heat is spread and conducted through the riser and TIM. The heat is absorbed by a cooling liquid circulating through the cold plate. In the water based version, the water absorbs the heat and is itself slightly warmed. In the case of a refrigerant system, some of the refrigerant changes phase from liquid to gas. There is little temperature change (0F for refrigerant and 10F for water) and thus no significant “shadowing” of downstream components that would be subjected to higher temperatures as in an air based system.
Note that in the pumped refrigerant systems there is no compression cycle. The mixture of gas and liquid exiting the cold plate returns to a heat exchanger where it is re-condensed into a liquid and pumped back to the cold plate in one continuous cycle.
The Exablade (right) is shown with two half width servers. The blocks covering the CPUs can be clearly seen in the middle of the picture. Note that the DIMMs also have metal jackets which so that heat can be conducted through their tops to the cold plate.
The lower section shows a cold plate in position after the blade has been inserted into the chassis. On operation the blade slides under the blade’s lid as it is inserted. Operating a small crank on the face of the blade then brings down the lid as it is pulled forward thus pressing the cold plate hard against the heat risers.
Each position in the Hyperscale is equipped with a flexible cold plate and an associated insertion mechanism. To insert a server the sliders on each side are pulled out so that the server tray is dropped down. The server is inserted and the sliders pushed back in. This action presses the server against the cold plate.