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Film-wise vapour condensation on surfaces with different shapes and coatings

par Barakhovskaia, Ella
Président du jury Haut, Benoît
Promoteur Hendrick, Patrick ;Marchuk, Igor V
Publication Non publié, 2023-01-10

Thèse de doctorat

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Résumé :

This work is devoted to study the process of film-wise vapour condensation on surfaces with various shapes and coatings. A new experimental approach has been used to conduct condensation experiments on promising surfaces to intensify heat transfer under the influence of the selected factors: driving force or surface coating, under variable gravity conditions. A condensate retraction system, stabilising the condensate flow along a curvilinear surface, has been proposed. The introduction of the retraction system improved the condensate's stability during microgravity. However, the idea to ensure stability through special three-dimensional condenser shape arose. A one-parameter family of axisymmetric surfaces was numerically found for which the mean curvature gradient along the generatrix is constant. Such curves form surfaces that guarantee stable condensate flow under microgravity. Furthermore, it has been found that the condensate film is sufficiently thick on the proposed surface, which is an asset for experimental measurements with commonly used optical systems.To study the impact of coated surfaces on condensation process, high-quality graphene-based coatings were created by dip coating technique. Graphene caused an almost twofold increase in heat transfer intensification when the condensate thickness was comparable with the coating thickness. Therefore, the level of intensification depends on the parameters used to create the coatings. To verify the concept, the film thickness distribution on an uncoated reference condenser was compared with classical Nusselt's results. Concurrency with Nusselt's theory proves the correctness of the approach of gravity driving force only, and any deviations in film flow behaviour could be caused by the influence of the coating only.The research's results will allow the creation of effective two-phase systems for the thermal stabilisation of various heat-generating equipment, including those intended for operation in microgravity and variable gravity conditions on-board spacecrafts.This work has been done in the framework of the "Heat Transfer PRODEX" project with financial support from the Belgian Federal Science Policy Office. The microgravity experiments were conducted during the Parabolic Flight Campaigns of the European Space Agency (ESA). The research activities were realised thanks to the fruitful and long-term collaboration of the Centre for Research and Engineering in Space Technologies – CREST (formerly Microgravity Research Center), Novosibirsk State University and Kutateladze Institute of Thermophysics. Collaboration with industries, particularly with engineers from Redwire Space (formerly QinetiQ Space), made it possible to prepare the space breadboard setup for the ESA space project "Heat Transfer Host", which will be delivered on-board the International Space Station in 2024.