T T H RESEARCH INC — National Aeronautics and Space Administration SBIR Phase I: S3

Description

Vital to the LHP operation is the evaporator/reservoir assembly where waste heat from a heat-dissipating source is absorbed through the metal casing to vaporize the liquid on the outer surface of the primary wick.nbsp; To compel the vapor to vent into the vapor line to be transported to the condenser for heat rejection and not to percolate into the wick core, a liquid-vapor (LV) ldquo;sealrdquo; is established.nbsp; A knife-edge seal is formed by using a hydraulic press to ldquo;incisionrdquo; join anbsp;tube with sharp edges into the primary wick.nbsp; It requires tedious manufacturing steps driving up the hardware cost.nbsp; The knife edge introduces hidden micro-cracks in the primary wick, which cannot be detected if the cracks do not propagate all the way through the wick.nbsp; The wick may produce a satisfactory pressure head initially but, when exposed to an excessive shock/vibration environment or recurring thermal cycling, the micro-cracks become larger and progressively advance all the way to the core.nbsp; To make matters worse, the cost of LHP manufacturing has risen significantly,nbsp;mainly because of the intricate design and ldquo;hand-maderdquo; fabrication/assembly process of the wick structure inside the evaporator/reservoir.nbsp; The wick sintering, machining, insertion into the metal casing, and forming the knife-edge seal require expensive specialized tooling with tight tolerances and highly-skilled technicians many hours to carry out, contributing to the overall LHP price tag.nbsp; However, the consistency/reproducibilitynbsp;of identical design LHPs in terms of performance have always been at issue with the users.nbsp; TTH Research proposes to modify the existing LHP design and manufacturing process to (i) do away with the knife-edge L-V seal, (ii) simplify/modify the evaporator design to reduce the amount of tight-tolerance machining of the wicks and casing, and (iii) automate the wick fabrication and insertion methods for consistent quality assurance.