Postcards from Space: Taking Heat Transfer Research to a New Level
Ingmar Lafaille – Project Manager
QinetiQ’s latest experiment facility for space is the European Space Agency’s Heat Transfer Host 2 – a programme that has now reached a significant development milestone.
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The design and specification of highly sophisticated and complex experiment facilities for deployment in space demands painstaking attention to detail as well as exhaustive test and evaluation procedures. QinetiQ’s latest system is the Heat Transfer Host 2 for the European Space Agency that will provide unprecedented insight into evaporation and condensation processes. Among many other benefits, this new scientific data will help to optimise the performance and efficiency of thermal management devices and various industrial processes. Once the development and integration phases are completed, Heat Transfer Host 2 will be operated in the European Drawer Rack 2 in the Columbus laboratory on-board the International Space Station.
The development of Heat Transfer Host 2 has now reached an important milestone, with the design of the three experiments to be hosted in the facility now completed and all instrumentation and hardware, at large, successfully tested to build confidence on the attainable scientific performance. Test campaigns were held in partnership with the relevant science teams - comprising leading experts in the field of gas-liquid phase change thermodynamics - to reflect on the critical specifications and target performance of each experiment.
Precision optical diagnostics, developed or adopted by Lambda-X, will be used in each of the three experiments to observe in detail the physical phenomena relating to drop evaporation, thermocapillary convection in evaporating liquid films and film condensation on external surfaces - all within a weightless environment.
Having obtained reassuring indications on the prospective operational performance of the different experiments and optical systems, the focus of our Heat Transfer Host 2 team is now moving onto the next phase of production – the engineering modelling phase.
The European Space Agency’s Heat Transfer Host 2 facility comprises three experiments:
- Condensation on Fins aims to reveal the link between the thickness of the condensed liquid film on an axisymmetric condenser finger and the heat transfer characteristics. In weightlessness, a relatively large condenser can be studied as a model of ground-based capillary driven devices. It enables detailed instrumentation and accurate characterisation of the condensate thickness distribution that, together with the heat transfer characteristics, is necessary for the validation of theoretical models. The improved understanding from such experiments is expected to support the development of more efficient and/or more compact condensers - contributing to the conservation of resources, both on ground and for future space missions.
- Drop Evaporation will investigate instabilities that form in evaporating liquid droplets sitting on a substrate and the spreading of the vapour away from the droplet, with a range of gas-phase characteristics. It also aims to study the effect of an electric field on the evaporation process. Dropwise evaporation occurs in a wide spectrum of circumstances in nature as well as in technical processes, ranging from printing technologies, nano-coatings, to DNA mapping. If the space experiment allows an accurate characterisation and subsequent modelling of all underlying mechanisms (that gravity will mask during on-ground experiments), it will enable knowledge-based optimisation of existing processes and the establishment of new technologies such as surface functionalisation.
- Marangoni in Films pursues a better understanding of the formation of instabilities and the transfer of heat to the surface of an evaporating liquid film that covers a heated substrate with a structured surface. For its success, the detailed and accurate mapping of the liquid film thickness distribution, the thermal stability of the evaporating region as well as the characterisation of the vapour concentration distribution are all key. The fundamental experiment is expected to advance and validate numerical models which can then be applied in the future design of film-wise evaporators. This will help to improve the efficiency of terrestrial thermal control devices and/or enable the realisation of compact evaporators for space applications.