Evaporation of liquid metals from capillary porous bodies
Abstract
Based on a simplified theory of gases some expressions were obtained for additional pressure drops arising at evaporation and condensation which should be taken into account when determining the maximum heat transfer of heat pipes. Superheating required for boiling has been shown to be constituted of superheating due to the heat flow passing through the wick (superheating due to heat conduction), superheating due to stretching of liquid at distortion of the liquid-vapor surface (capillary superheating), and superheating due to evaporation (phase superheating). An important condition for the high power heat pipe operation was noted. If the vapor nucleation site sizes be comparable with or larger than those of the wick pores, the capillary limit of power transferred by a heat pipe will not be reached and the crisis will take place because of boiling. Experimental data obtained at sodium evaporation reveal that crisis phenomena caused by pressure at the phase interface are characteristic of fine-porosity screens and that boiling within the wick is likely to take place at lower liquid-metal superheatings than under conditions of natural convection and smooth wall. It has been shown by experiments that at alkali metals evaporation from wicks an extremely intensive heat removal can be achieved. Substantial heat fluxes of 910 W/sq cm reached in the tests were not critical and can be further increased.
- Publication:
-
Heat Pipes
- Pub Date:
- 1976
- Bibcode:
- 1976hepi.rept..403S
- Keywords:
-
- Evaporation;
- Heat Transfer;
- Liquid Metals;
- Wicks;
- Capillary Flow;
- Evaporative Cooling;
- Experiment Design;
- Heat Pipes;
- Liquid Sodium;
- Metal Vapors;
- Nucleate Boiling;
- Performance Tests;
- Porous Materials;
- Superheating;
- Fluid Mechanics and Heat Transfer