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As two-phase flow and heat transfer is expected to strongly depend on the gravity level, a Two-Phase eXperiment has been developed for ESA to demonstrate two-phase heat transport system technology in orbit. TPX, a reduced-scale capillary pumped two-phase ammonia loop with a flat and a cylindrical capillary evaporator and an actively controlled reservoir for loop temperature setpoint control, included downscaled components of mechanically pumped loops: multichannel condensers, vapour quality sensors, and a controllable 3-way valve for vapour quality control exercises. The presented detailed evaluation of the experiment results obtained during the TPX flight on STS60, clearly proves the viability of two-phase technology for space.

With the successful retrieval of EURECA, the EUROPEAN RETRIEVABLE CARRIER, again a long term orbit satellite (11 month in space) is available for the space material community to investigate the influence of low earth orbit environment on materials which stayed in orbit for a prolonged time. EURECA, designed, manufactured and launched to carry out numerous experiments in the fields of fluid- and solar physics, materials science, biology and astronomy under orbital conditions, in parallel presents a huge material expositon experiment in itself, providing detailed insight into the possible orbital degradation mechanisms due to the synergistic effects of atomic oxygen, UV radiation, thermal cycling, high vacuum and micrometeorite/debris impacts. In order to exploit the valuable information, an integrated ESTEC/ERNO team has been established to perform a detailed investigation of the EURECA surface and - as far as accessible -internal structural parts and experiments.

Mechanically pumped two-phase heat transport systems are currently developed to meet the high power and long transport distance requirements of thermal management systems for future large spacecraft. Capillary pumped systems are being developed for applications with special requirements concerning microgravity disturbance level, temperature stability and controllability. As two-phase flow and heat transfer in a low-gravity environment is expected to differ from terrestrial behaviour, two-phase heat transport system technology has to be demonstrated in orbit. Therefore the Dutch-Belgian Two-Phase eXperiment TPX has been developed within the ESA In-Orbit Technology Demonstration Programme. TPX is a two-phase ammonia system, flown in the 5ft3 gaseous nitrogen filled Get Away Special canister G557, aboard STS-60.

Mechanically and capillary pumped two-phase heat transport systems are currently developed to meet the high power and long transport distance requirements of thermal management systems for future spacecraft. Compared to existing single-phase systems, two-phase loops offer important advantages: reduced overall mass and pumping power consumption, virtually isothermal behaviour, adjustable working temperature, insensitivity to variations in heat load and sink temperature, and high flexibility with respect to the location of heat sources within the loop. As two-phase flow and heat transfer in low-gravity environment is expected to (considerably) differ from terrestrial behaviour, the technology of two-phase heat transport systems and their components is to be demonstrated in orbit. Therefore a Dutch-Belgian Two-Phase experiment has been developed within the ESA In-Orbit Technology Demonstration Programme.