Ground Testing and Thermodynamic Behavior of a Capillary Pumping Two-Phase Loop Roger R. Riehl , Eduardo G. Reimbrecht, Heitor V. R. Camargo, and Edson Bazzo Laboratory of Combustion and Thermal Systems Engineering Mechanical Engineering Department – Federal University of Santa Catarina Florianópolis, SC 88040-900 – Brazil, ++(55) 48 331-9390, rriehl@cet.ufsc.br Abstract Focusing on the extensive use of capillary pumping two-phase loops on satellites thermal control, an experimental investigation of a capillary pumped loop (CPL), a thermodynamic study and its integration on a scientific microsatellite has been performed. The process of manufacturing and characterization of porous structures is also presented. Results have been gathered in ground testing for different operation conditions, which show the reliability of the porous structure manufacturing and capillary evaporators construction. Experimental results showed that the proposed CPL has reliable startups and very short transients for different heat loads. From what has been observed on the experimental tests, a thermodynamic approach of the capillary evaporator behavior is presented considering the same working conditions. This investigation has shown the particularities of a CPL behavior on a reduced scale. Keywords: porous structure, capillary pumped loop, thermal control and satellite integration. 1. INTRODUCTION Investigations on the use of capillary pumped loop (CPL), applied to satellites and electronics thermal control have been extensively performed in the past. From what has been investigated, a CPL is considered a reliable thermal management device, as temperature control can be performed passively and heat can be transported over long distances. As the main component of a CPL is the capillary evaporator, which is the responsible for the generation of capillary forces that drive the working fluid via a porous structure, several studies have been done [1] regarding the manufacturing of different porous structures. Porous structures sinterization process of different materials have been investigated and used in capillary evaporators, which has lead to the increase of capillary pumping power and the use of CPL on different levels of temperature and heat fluxes. Several studies have also been performed on the behavior of CPL in ground and micro- gravity conditions [2, 3], in order to investigate its capability on the heat transport and temperature control. Different configurations of the capillary evaporator and the CPL itself have been attempted and many experimental results have been generated. Towards the use of a CPL on satellites thermal control, investigations have been performed considering particular working conditions on a controlled environment. Focusing on the development of a small-scale CPL to be integrated on a microsatellite, this paper has the objective of presenting several aspects related to this matter. The efforts regarding the fabrication of the porous wick by sinterization towards its use on a capillary evaporator, experimental tests of a proposed small scale CPL related to the conditions to be faced in space and its integration on a microsatellite are presented. A thermodynamic approach of the CPL behavior is also presented to better explain the experimental results. This work is also intended on showing the achievement of different technologies in order to use them on satellite and electronics thermal control. 2. THE MICROSATELLITE PROPOSAL The CPL experiment is part of a scientific project involving France and Brazil towards the development of space technology. Other experiments will be part of the microsatellite payload, which is scheduled to be launch in early 2004 by a four-stage SLV (Satellite Launching Vehicle) from the Alcantara Launching Base, in Brazil. The integration of all experiments will be done part in France at CNES and part in Brazil at the Brazilian Institute for Space Research (INPE). Figure 1 shows a scheme of all experiments and parts of the microsatellite [7]. 3. POROUS WICK DEVELOPMENT For the development of wick structures to be used in CPL, a nickel powder carbonyl with a particle size in the range of 3 to 7 µm (specific surface area: 0.3 – 0.4 m 2 /g) was used as raw material and a tap powder sintering technique was employed to manufacture the porous samples.