Variable Conductance Heat Pipes

Heat pipes – two-phase heat transfer devices – in their basic form exhibit a constant conductance (heat transfer capability) that is demanded by the duty, for example cooling a chip in a computer.  The main aim is to transfer as much heat as possible from the chip to a heat sink where it can be safely rejected to, for example, cooling air.

Where there is a need to control or modulate the heat transferred by the heat pipe (or even to cut off heat transfer completely), a Variable Conductance Heat Pipe (VCHP) is employed.

The VCHP can operate in a number of ways.  In the figure below a passive control method relies on an inert gas buffer to block part of the condenser section, this restricting heat removal from the heat source (which would be at the LHS of the pipes shown below).

As the ambient temperature rises and more cooling is needed) the vapour in the heat pipe compresses the gas, allowing more area for heat rejection.  This has the interesting effect of keeping the LHS of the heat pipe (or devices mounted there) at a near-constant temperature.

The passive VCHP is capable of limited temperature control. For more precise control an active feedback-controlled VCHP can be used. The research will identify current VCHP technologies and build on this to develop, starting from the basic VCHP, a solid-state active feedback-controlled VCHP for process/thermal control uses.

For more information please contact Prof David Reay or Prof Adam Harvey.