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The chicken or the egg dilemma is an often used metaphor to explain the problem where car manufacturers are not eager to produce hydrogen cars since there are no hydrogen fueling stations. Petrochemical companies on the other side, do not want to invest in hydrogen fueling stations for there are no cars to fuel. Many proposals have been made to overcome this predicament, for example starting the implementation of the hydrogen economy with early markets such as public busses that run on hydrogen, because they can use a centralized fueling infrastructure and thereby reduce initial costs. However, another way to address this stalemate is by avoiding the dependency on hydrogen fueling infrastructure. This can be achieved by using flex-fuel vehicles that can run on hydrogen as well as on gasoline and/or compressed natural gas.

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.

In the frame of an ESA technology programme, the development of a High Capacity Grooved Heat Pipe (HGP), based on the thermal requirements of the next generation of telecommunication satellites, was contracted to SABCA. After a trade-off and a design study, the selected concept was an aluminium extruded heat pipe (outer diameter of 25 mm) based on a multi re-entrant grooves design. This heat pipe was submitted to an acceptance test campaign: leak, proof, burst tests as well as thermal performance tests (maximum heat transport capacity, maximum tilt capability, start-up, priming, bending influence, ageing / gas plug, non-uniform heat input). The test results showed for the multi re-entrant groove heat pipe a good confidence in the design and the fulfilment of the required specifications on heat transport and on tilt capability (experimental maximum heat transport capability of 1500 Watt-metres for a vapour temperature of 20°C -with ammonia-).

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.

This paper presents the general objectives, the design concept and the potential performances of the two-phase capillary pumping loop (CPL) as a heat transportation system. In particular the actual design of the ESA funded development program “CPL”, designed and developped by SABCA and DORNIER will be shown as well as of its development status. Results obtained with the first breadboard CPL model are reported together with comparison of predicted against tested performances.