Loop Heat Pipe Testing and Analytical Model Verification at the U.S. Naval Research Laboratory
Heat transfer characteristics of a Loop Heat Pipe (LHP) is difficult to predict due to the complex nature of thermal interaction between the LHP itself and the environment it operates in. The overall thermal conductance varies not only with the power input, sink temperature and ambient temperature as expected, but also with the system initial condition and/or previous history of its operation. Hence, the analytical modeling of LHPs often yielded inaccurate results when compared with the actual data. The U.S. Naval Research Laboratory (NRL) recently completed the development of a transient LHP model. Accordingly, NRL carried out an extensive LHP test program, in part, to provide test data for the model verification. In this paper, description of the test program and results of the model verification will be presented.
Development of a Two‐Phase Capillary Pumped Heat Transport for Spacecraft Central Thermal Bus
Thermal requirements of future spacecraft and satellites will certainly outgrow the capability of conventional heat pipes in terms of heat transport, heat density, and temperature control. Emerging passive heat transport technologies such as Capillary Pumped Loop (CPL) and Loop Heat Pipe (LHP) have demonstrated in both ground testing and micro‐gravity flight experiments that they have the potential to replace heat pipes as primary heat transport devices in next generation thermal control technology. Like heat pipes, CPLs and LHPs are completely passive systems which have no mechanical moving part to wear out or to introduce unwanted vibration to the spacecraft. However, the heat transport capabilities of CPLs and LHPs are at least one order of magnitude higher than those of heat pipes. Despite sharing many operational characteristics. CPLs and LHPs do have differences. CPLs require a lengthy and tedious start‐up procedure to prime the wicks before heat is applied to the evaporator plate. Even with the sta...
Investigation of the Temperature Hysteresis Phenomenon of a Loop Heat Pipe
The temperature hysteresis phenomenon of a Loop Heat Pipe (LHP) was experimentally investigated. The temperature hysteresis was identified by the fact that the operating temperature depends upon not only the imposed power but also the previous history of the power variation. The temperature hysteresis could impose limitations on the LHP applications since the LHP may exhibit different steady-state operating temperatures at a given power input even when the condenser sink temperature remains unchanged. In order to obtain insight to this phenomenon, a LHP was tested at different elevations and tilts by using an elaborated power profile. A hypothesis was suggested to explain the temperature hysteresis. This hypothesis explains well the experimental observations. Results of this study provide a better understanding of the performance characteristics of the LHPS.