Loop Heat Pipes
ACT LHPs – high thermal transfer for extreme conditions.
ACT manufactures LHP products under its AS9100:2009 certified quality system. Many of the LHP manufacturing processes and equipment are similar to the CCHPs and VCHPs. However, there are a number of processes and equipment that are unique to the LHP manufacturing.
ACT manufactures its own Loop Heat Pipe Primary Wicks in-house. Primary wick forms are sintered and machined to meet exact performance specifications.
Throughout the LHP manufacturing process, LHP parts are continually checked to verify that they meet the performance requirements. For example, the LHP primary wick is characterized to determine its porosity, pore radius, permeability and thermal conductivity.
The LHP secondary wick performs the critical function of hydraulically linking the primary wick and the reservoir. ACT has the facilities and processes to fully characterize the performances of LHP secondary wicks at various power and body force conditions. ACT also has a LHP evaporator/reservoir characterization apparatus for quick and accurate assessment of the performance of a LHP evaporator/reservoir assembly, prior to installing it into the overall transport line and condenser assembly.
Once the LHP assembly is completed, it is tested to verify its performances. These tests typically include start-up, transient power, high power, shut-down and un-balanced condenser heat removal (in case of multiple condensers).
It is sometimes desirable for the LHP to stop transferring heat to maintain the temperature of the payload and minimize the magnitude of the temperature swing through an orbit. The figure below demonstrates the ability to shutdown a LHP almost immediately and with a very small heater power. With a small heat input of approximately 10 Watts to the reservoir, the condenser temperature dropped quickly to match the environment, while the evaporator stays nearly constant in temperature.