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In the scope of the COLUMBUS-preparatory support technology programme, funded and coordinated by the European Space Agency (ESA/ESTEC), critical components of a mechanically pumped two-phase heat transport system, i.e. evaporator cold plate, evaporative heat exchanger, vapour quality sensors, condenser, accumulator, gas trap and control system, have been identified and developed by a number of European companies under Dornier-subcontract. A comprehensive test programme, focussed on the investigation of critical components performance characteristics and limits, has generally demonstrated very satisfactory and partially even excellent results. However, experience gained during test performance as well as overall test evaluation have concluded in several recommendations for further analysis, improving modifications and a continuation of testing aimed at an enhancement of European two-phase technology know-how.

Under the COLUMBUS Preparatory Support Technology Programme, the European Space Agency has coordinated the development of critical components for a European pumped two-phase heat transport system. The critical components are Evaporator Cold Plate (Dornier GmbH), Evaporative Heat Exchanger (Aeritalia) being an interface component to an external loop, Heat Rejection Interfaces/Condensers (Fokker), active Accumulator/Control Reservoir (British Aerospace) and Vapour Quality Sensors (Dornier GmbH and NLR). They have been incorporated into a flexible and fully instrumented test bed at BAe. The test bed is designed to evaluate the performance of a complete representative loop with heat loads up to 15 kW and primary loop lengths up to 40 metres. It includes an implementation of algorithms developed at Fokker and NLR for the control of evaporator inlet temperature conditions, vapour temperature setpoint and vapour quality.

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.

In order to demonstrate two-phase heat transport system technology in orbit, the Dutch-Belgian Two-Phase eXperiment TPX was successfully flown as Get Away Special G557, aboard STS60, February 1994. Based on TPX conclusions and lessons learned, a reflight experiment TPX II is being developed in order to usefully fill the time gap between TPX and possible future full-scale Capillary Pumped Loop flights. The characteristics of TPX II, intended to fly early 1998, are discussed in detail: configuration and component changes, updates of objectives/scenario, current status, results of pre-launch (components) testing and outlook.

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.

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.

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. As two-phase flow and heat transfer in a low-gravity environment is expected to (considerably) differ from terrestrial behaviour, the technology of two-phase heat transport systems and their components has to be demonstrated in orbit. Therefore a Dutch-Belgian two-phase experiment (TPX) is being developed within the ESA In-Orbit Technology Demonstration Programme TDP1. TPX concerns a two-phase ammonia system in the (5ft3, gaseous nitrogen filled) Get Away Special canister G-557. The system is a downscaled capillary pumped two-phase loop. It includes downscaled versions of mechanically pumped two-phase loop components: multichannel condensers and vapour quality sensors (plus a controllable 3-way valve for control exercises). The Critical Design Review status of TPX is discussed.

Based on the thermal requirements of future large European platforms such as the Columbus Space Station, several developments in the field of two-phase flow systems were initiated over the last few years in Europe. This paper will give a general overview of the objectives, development status and test results of an ESA-funded ‘Two-phase heat transport system’ study and of two studies sponsored by the German Ministry of Research and Technology on two-phase heat transport. The ESA two-phase loop system resulting from the concept trade-off is driven by an electrically powered liquid pump and is provided with a capillary cold plate and an evaporative heat exchanger mounted in parallel. Under certain conditions, a simplified version of this type of system is able to work in a capillary-pumped mode. The system is designed for a heat load of 10-20 KW, a length of 20 m, a working temperature around 20°C and R114 as working fluid.