Heat exchanger system

A system for transferring heat from a first (inner) surface through a second (outer) surface. The system includes at least two adjacent porous and thermally conductive layers between the first surface and the second surface. The innermost layer is characterized by a relatively high porosity and the outermost layer is characterized by a relatively low porosity. The innermost layer houses a fluid coolant. The pores of the innermost and outermost layers are coupled, permitting coolant flow therebetween. A vapor chamber is positioned between the outer surface and an outer member. A controller is adapted to control the vapor pressure in the vapor chamber whereby the coolant has a liquid vapor phase transition in the outermost layer.