Multiple Evaporator Loop Heat Pipe

Loop Heat Pipe (LHP) technology has advanced to the point that LHPs are baselined for thermal control systems in many spacecraft applications. These applications typically utilize a loop heat pipe with a single evaporator. However, many emerging applications involve heat sources with large thermal footprints, or multiple heat sources that would be better served by LHPs with multiple evaporators. Dual evaporator LHPs with separate reservoirs for each evaporator have been successfully developed, but the volume and weight of such systems become impractical as the number of the evaporators increase to more than three or four. Other investigators have proposed systems containing several evaporators that are coupled to a common reservoir with a conduit to contain a capillary link (secondary wick). This approach places several restrictions on the relative location of the evaporators due to the limitation of the capillary link. This paper describes an advanced LHP design architecture that contains a single reservoir and multiple evaporators that do not require a capillary link connection between the evaporator and the reservoir. Thereby removing restrictions on the location of the evaporators and enhancing the system's applicability to spatially separated heat sources or payloads with large thermal interfaces.

To demonstrate the feasibility of the advanced multi-evaporator system architecture, a multiple evaporator Loop Heat Pipe consisting of three evaporators and a single reservoir was fabricated and tested. Tests were performed over a wide range of conditions typical of potential spacecraft applications, including start-up and operation with equal and non-uniform evaporator heat loads, and transient response to power and sink temperature cycles. This paper presents the results of the test program and summarizes the system's attributes and limitations.