This paper describes the development and testing of a compact heat-pipe heat exchanger that is designed to transfer thermal energy from hot combustion gases to the heater tubes of a 25-kWe Stirling engine. In this system, sodium evaporates from a surface that is heated by a stream of hot gases and the liquid metal then condenses on the heater tubes of a Stirling engine where energy is transferred to the engine's helium working fluid. Recent tests on a prototype unit illustrated that a compact (8 cm x 13 cm x 16 cm) sodium evaporator can routinely transfer 15-kWt of energy at an operating vapor temperature of 760°C. Four of these prototype units will eventually be used to power a 25-kWe Stirling engine system. Design details and test results from the prototype unit are presented in this paper.