Schinnerl, Martin ; Sielaff, Axel ; Zabulis, Xenophon ; Evgenidis, Sotiris ; Oikonomidou, Ourania ; Stephan, Peter (2023)
Heat transfer in single bubble nucleate boiling within the multiscale boiling project onboard the International Space Station.
17th International Heat Transfer Conference. Cape Town, South Africa (14.08.2023-18.08.2023)
doi: 10.1615/ihtc17.490-40
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Kurzbeschreibung (Abstract)

Boiling is widespread in a variety of engineering applications. This ranges from power generation and environmental engineering across the food and chemical industries to space applications. Consequently, this process must be well understood for the design of appropriate technical equipment. However, the existing correlations have limited parameter ranges in which they can be applied with sufficient accuracy. This is primarily due to the large number of physical variables influencing local heat and mass transport. The investigation under weightlessness allows a deeper understanding as the processes are slowed down, and several effects can be observed, which are not accessible under normal gravitational conditions. To investigate heat and mass transfer from a solid heater to a single bubble and the bulk liquid for various pressures, bulk subcoolings, and input heat fluxes without and under the influence of external forces, the Multiscale Boiling Project was carried out on the International Space between 2019 and 2021. As part of the project, this work focuses on the heat transfer to the bubble via the solid-liquid interface and the bulk liquid without the influence of external forces. Therefore, a total number of 12 pool boiling runs has been selected for further data processing and analysis. The raw-data of the Multiscale Boiling Project include high-speed black & white images of the nucleating and growing bubbles as well as high-speed infrared images of the surface of the solid heater. Black & white image data are processed using elaborated techniques for bubble contour detection and refinement, bubble volume calculation, and total heat calculation. Infrared image data are used for numerical calculation of the local heat flux on the surface of the substrate heater at the solid-liquid interface. For this, the initial temperature of the substrate heater is estimated using numerical modeling and calculation. Subsequently, the local heat flux data are used for calculation of the heat transported from the solid heater via the solid-liquid interface into the bubble, more specifically, the three-phase contact line and the area in the center of the bubble. Results show that heat transported via the three-phase contact line is significantly higher than heat transported via the area in the center of the bubble in all analyzed runs. Heat transported via the bulk liquid is positive or negative and is accordingly dominated by evaporation or condensation phenomena in dependence of the experimental parameter values.

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