Heat Transfer Characteristics of the Two-Phase Closed Thermosyphon (Wickless Heat Pipe) Including Direct Flow Observation

摘要

In Part I a visual study of an annular two-phase closed thermosyphon (wickless heat pipe) is reported. The heat transfer surface was stainless steel. Working fluids were Freon-113, ethanol, and water. Photographs of pertinent phenomena are included. The visual observations were used to interpret the measured heat transfer characteristics. For small and intermediate liquid fill quantities four flow regimes were observed in the evaporation section, in addition to nucleate boiling in the liquid pool: (1) a smooth continuous film with surface evaporation; (2) breakdown of the film into stable rivulets; (3) a wavy film with unstable rivulets; and (4) a wavy film with bubble nucleation in the unstable rivulets. Three different types of 'dry-out' conditions (heat transfer limits) were also observed and are reported in detail. In Part II results obtained for a stainless steel tubular opaque device with Freon-113 as a working fluid are reported. This device was designed to permit a larger range of geometric configurations (heated length, adiabatic length, cooled length, and angle of inclination). Both steady state heat transfer characteristics and heat transfer limits are reported in detail. In Part III, results from the visual and opaque devices are compared and discussed. The present results are compared with those of other investigations, and conclusions and recommendations are drawn.