A cooling technique involves: reducing a pressure of a cooling fluid to a subambient pressure at which the cooling fluid has a boiling temperature less than a temperature of a heat-generating structure; bringing the cooling fluid at the subambient pressure into thermal communication with the heat-generating structure, so that the coolant absorbs heat, boils and vaporizes; thereafter removing heat from the coolant so as to condense substantially all of the coolant to a liquid; and thereafter extracting a selected portion of the cooling fluid that has been cooled, the selected portion being a vapor that includes a non-condensable gas.