Abstract: A heat exchanger for a turbine generator power plant includes a plurality of heat transfer tubes for transferring heat from a primary fluid cooling system to a secondary water cooling system subject to variations in inlet temperature and the presence of emulsified particles. Upon a reduction in flow rate in the secondary system, as when accommodating a reduced inlet temperature, a reusable plug assembly comprising compression-actuated cap and plug members is installed on the ends of a selected portion of the heat transfer tubes to increase flow through the remaining heat transfer tubes and thereby reduce the tendency toward sedimentation of the impurities in the tubes. An alternative construction of the plug assembly allows the assembly to be installed with access to only one end of the heat transfer tubes.