Abstract:
A heat pipe capable of operation at temperatures above 900* C. is described characterized by an alkali metal working fluid contained within a conduit having a crystal face orientation only in selected planes to maximize the wetting between the sidewall and the working fluid. Preferably the conduit containing the working fluid is provided with a plurality of circumferentially disposed inwardly extending teeth overlayed with a thin wire mesh screen to define a plurality of capillary passages for liquid transport and the surface of the capillary passages contains the metal only in planes having work functions below a fixed value, e.g. 4.8 ev. for a sodium working fluid with the desired orientation of the capillary passage surface being formed by a hydrogen reduction of a metal fluoride. The zero contact angle between the working fluid and the conduit permit the initiation of operation of the heat pipe without prior warmup and eliminates localized ''''hotspots'''' destructive to the sidewall structure.