Heat pipe with dual working fluids

Claim 1

A heat pipe structure, comprising: a. means forming a first heat pipe wall area of given longitudinal extent; b. means forming a second heat pipe wall area joining said first heat pipe wall area substantially along their entire longitudinal extent; c. first capillary means covering said first heat pipe wall area; d. second capillary means covering said second heat pipe wall area; e. said first and second capillary means being in thermal exchange relationship with each other and with said first and second heat pipe wall areas along their entire longitudinal extent; f. a first working fluid arranged for transport through said first capillary means but not through said second capillary means; g. a second working fluid arranged for transport through said second capillary means; h. said first working fluid having a freezing point above the lowest expected operating temperature of said heat pipe structure; and i. said second working fluid having a freezing point below the lowest expected operating temperature of said heat pipe structure whereby, during periods when said heat pipe structure is subjected to said lowest operating temperature to cause solidification of said first working fluid with consequent interruption therein of thermal transport action, said second working fluid will remain sufficiently fluid to continue functioning as a thermal transport medium.