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A capillary pumped two-phase ammonia heat transport loop, developed at Lavochkin Assoc., Moscow, was tested under laboratory conditions at ERNO, Bremen. The tubular capillary pump evaporator contains a sintered Nickel powder body with a small pore size of 1. 5 μm. The line diameter of the vapour and the liquid line is only 6 mm and 4 mm, respectively, allowing an easy accomodation to any architecture in the filled state. The objective of the test was to determine the heat transport performance of the loop under different orientations w.r.t. gravity under steady state and transient, in particular priming load conditions. The tests have demonstrated a large heat transport performance of more than 1100 W in a vertical orientation, where the evaporator was located 2 m (!) above the condenser. The priming ability appears to depend on the load timeline as well as on the orientation.

Thermal Control System based on different types of Heat Pipes (HP), including Loop Heat Pipes (LHP) has been designed, manufactured and tested. The goal to design and to launch the Thermal Control System with LHP was established and achieved.

The paper presents the results of analysis, development and tests of an ammonia miniature loop heat pipe (MLHP) with a flat evaporator, which has an active-zone diameter of 30mm. The length and the diameter of the vapor and the liquid lines are 1m and 2/1.2mm. The device serviceability has been demonstrated at a horizontal and a vertical orientation in 1-g conditions. The maximum heat load achieved on trials was equal, respectively, to 160W and 120W, which corresponds to a heat flow in the evaporation zone of 23 W/cm2 and 17 W/cm2. The minimum thermal resistance at nominal heat loads from 40 to 80 W varied in the range from 0.42 W/m2K to 0.59 W/m2K. A comparison has been made with a model MLHP with a cylindrical evaporator equipped with a copper and aluminum “saddle”.

Loop heat pipes are one of the most promising modifications of two-phase heat-transfer devices with capillary pumping. Owing to their versatility these devices have filled a wide niche between ordinary heat pipes and CPLs. The paper presents the results of development and investigations of loop heat pipes carried out at the Institute of Thermophysics in the last five years.