One potential commercial application based on a current product line at ACT is pressure-controlled isothermal furnace liners. An isothermal furnace liner is an annular alkali metal heat pipe. Replacing the current heat pipe with a pressure controlled VCHP will allow much tighter temperature control. A second commercial application is alkali metal VCHPs in fuel cell reformers. In a fuel cell reformer, diesel fuel and air pass through a series of high temperature reactors to generate hydrogen. The operating temperature of the reactors must be closely controlled to maintain their chemical equilibrium. A typical system must maintain inlet and outlet temperatures within ¬±30o
C despite a turndown ratio of 5:1 in reactant flow rate. The current scheme uses a bypass valve, which has several drawbacks: it requires active control, requires power, and has a large pressure drop. ACT believes that alkali metal VCHP heat exchangers can replace the current heat exchanger and control system with a passive system that automatically maintains the output stream from the heat exchanger at a constant temperature. The immediate application for this proposal is thermal management for a long-lived Venus lander that is cooled with a Stirling system integrated with a large number of GPHS modules. The thermal management system will efficiently collect the heat from the GPHS modules and deliver it to the Stirling engine. In addition, the thermal management system will allow the Stirling convertors and cooling to be shut off during the transit to Venus, saving heater head life. More generally, the systems developed on this program are applicable to all NASA missions with high powered radioisotope systems that require a large number of GPHS modules. In particular, the system will allow the use of alternative isotopes with a shorter half-life than Pu-238. The excess heat is passively rejected. In addition, the heat collection system is useful for smaller systems that use the less efficient Am-241 based GPHS modules, because they require a larger number of modules than the systems with the standard GPHS modules. Backup cooling is also an important feature that is needed in almost all missions (and ground testing) that use GPHS modules. Beside the Venus mission applications, Beside the Venus mission applications, the developed system is applicable to deep space missions powered by alternate radioisotopes, as well as missions to other high temperature locations in the Solar System.