Axial-grooved variable-conductance heat pipes - The Marangoni effect

The Marangoni Effect has been included in the performance analysis of partially shut gas-loaded, axial-grooved variable-conductance heat pipes. In addition to the direct surface tension effects, the temperature-induced surface tension gradients in the gas-blocked region of the condenser sets up a recirculating flow in the liquid contained in the grooves. This results in a reduction in the capillary pressure available to support the condensate return in the active region of the pipe. The magnitude of the Marangoni reduction depends upon both the active pipe temperature and the lowest temperature in the blocked region. The paper presents an approach to the analyses of a typical VCHP/radiator system. The transport requirement is compared to the transport capability of the axial groove, and ground test data is presented to support the analyses. Finally, a technique of overtesting the heat pipe to establish performance margins is discussed. It is concluded that the Marangoni Effect should not be a limiting parameter in an optimized axial-grooved VCHP/radiator system.