Abstract: An apparatus and method is disclosed for regulating flow of working fluid through parallel condensation tubes requiring subcooling. The apparatus provides an elongated restriction element extending into the outlet of the respective condensation tubes to the approximate point of onset of subcooling. The elongated restriction element is braced externally to the condensation tube with a support that is used for positioning and maintaining the elongated restriction element in the correct position. The elongated restriction element has a pentagonal cross-section and is slightly undersize with respect to the working fluid passageways through the condensation tubes. The restriction member significantly restricts flow of partially vaporized working fluid but does not significantly affect the flow of fully liquid working fluid.