Miniature ammonia loop heat pipe for terrestrial applications: Experiments and modeling

Thermal management is always an exigent topic in various applications like electronic equipment cooling, aerospace, and avionics, defence electronics, etc. Loop Heat Pipes (LHPs) are highly efficient, robust, two-phase, passive heat-transfer devices, increasingly becoming popular for thermal management of terrestrial and avionics applications. Miniaturization of the device and its ability to perform well in different orientations with respect to the gravitational vector are essential for its employment in terrestrial applications. In the present study, complete thermal characterization of the developed ammonia miniature loop heat pipe (mLHP) in different orientations, keeping into view possible terrestrial applications, has been carried out utilizing infrared thermography coupled with conventional thermometry. The maximum capacity obtained is about 225 W (for maximum evaporator temperature of 70 °C) and the thermal resistance was better than 0.5 K/W in all experimental trials irrespective of the orientations. The effect of orientation on the operation of mLHP is insignificant because of its small dimensions and the device can be safely considered to be orientation-free. From the results of the study, mLHP can regard as a quite promising thermal management technology for terrestrial applications. A mathematical model is developed to predict the steady-state evaporator temperature of the mLHP for a given heat load, sink temperature and surrounding temperature. The model has been validated with the experimental results and a good match is obtained.