Minimal-Temperature-Differential, Omni-Directional-Reflux, Heat Exchanger

An apparatus comprising:

• a substrate formed to have a first surface extending in at least first and second directions, and a second surface spaced therefrom in a third direction;
• a working fluid in contact with the second surface and selected to operate in two phases within the apparatus, converting at least a portion of a liquid phase thereof into a vapor phase in proximate a heat source and converting at least a portion of the vapor phase thereof into the liquid phase proximate a heat sink;
• the substrate formed to have first channels each having a corresponding first width, a first depth, and a first length extending in the first direction, the first channels extending substantially parallel to one another substantially continuously in a first direction along the second surface;
• the substrate formed to have second channels each having a second width, a second depth, and a second length extending substantially parallel to one another substantially continuously in the second direction along the second surface to intersect the first channels;
• and
• the first and second widths and first and second depths selected to provide flow of the working fluid through the first and second channels substantially isotropically with respect to the first and second directions.