An apparatus comprising a heat exchanger which includes: a conduit having spaced first and second portions and a thermally conductive portion disposed therebetween, said second portion being vertically lower than said first portion; a supply section configured to supply to said first portion of said conduit a fluid coolant, at least a portion of the coolant being in a vapor state, and said conduit configured to allow at least a portion of the coolant to flow from said first portion of said conduit through said thermally conductive portion thereof to said second portion thereof; a thermally conductive structure having a portion which is thermally coupled to said thermally conductive portion of said conduit configured to receive heat from the coolant in said thermally conductive portion of said conduit, said thermally conductive structure configured to cool the coolant from the vapor state to a liquid state; first and second valves (56, 58) which each have an inlet and an outlet, said inlets of said valves (56, 58) being physically spaced from each other in a predetermined direction; a discharge section configured to communicate with said outlets of said valves (56, 58); and first and second fluid communication structures (46, 86, 48, 88) each configured to provide fluid communication between said inlet of said first or second valve (56, 58) and said second portion of said conduit, wherein said fluid communication structures are in communication with the conduit at angularly spaced locations; and a valve control structure configured, responsive to a presence of coolant in the liquid state at the inlet to either of said valves (56, 58), to open that valve (56, 58). a conduit having spaced first and second portions and a thermally conductive portion disposed therebetween, said second portion being vertically lower than said first portion; a supply section configured to supply to said first portion of said conduit a fluid coolant, at least a portion of the coolant being in a vapor state, and said conduit configured to allow at least a portion of the coolant to flow from said first portion of said conduit through said thermally conductive portion thereof to said second portion thereof; a thermally conductive structure having a portion which is thermally coupled to said thermally conductive portion of said conduit configured to receive heat from the coolant in said thermally conductive portion of said conduit, said thermally conductive structure configured to cool the coolant from the vapor state to a liquid state; first and second valves (56, 58) which each have an inlet and an outlet, said inlets of said valves (56, 58) being physically spaced from each other in a predetermined direction; a discharge section configured to communicate with said outlets of said valves (56, 58); and first and second fluid communication structures (46, 86, 48, 88) each configured to provide fluid communication between said inlet of said first or second valve (56, 58) and said second portion of said conduit, wherein said fluid communication structures are in communication with the conduit at angularly spaced locations; and a valve control structure configured, responsive to a presence of coolant in the liquid state at the inlet to either of said valves (56, 58), to open that valve (56, 58).