This is a dataset of ground truth annotations for benchmark data provided in A. Sielaff, D. Mangini, O. Kabov, M. Raza, A. Garivalis, M. Zupančič, S. Dehaeck, S. Evgenidis, C. Jacobs, D. Van Hoof, O. Oikonomidou, X. Zabulis, P. Karamaounas, A. Bender, F. Ronshin, M. Schinnerl, J. Sebilleau, C. Colin, P. Di Marco, T. Karapantsios, I. Golobič, A. Rednikov, P. Colinet, P. Stephan, L. Tadrist, The multiscale boiling investigation on-board the international space station: An overview, Applied Thermal Engineering 205 (2022) 117932. doi:10.1016/j.applthermaleng.2021.117932. The annotations regard the 15 image sequences provided in the benchmark data and denoted as D1-D15. The annotators were asked to localize the contact points and points on the bubble boundary so an adequate contour identification is provided, according to the judgement of the expert. The annotators were two multiphase dynamics experts (RO, SE) and one image processing expert (ICS). The annotators used custom-made software to pinpoint samples upon contour locations in the images carefully, using magnification, undo, and editing facilities. The experts annotated the contact points and multiple points on the contour of the bubble until they were satisfied with the result. The annotations were collected for the first bubble of each sequence. For each bubble, 20 frames were sampled in chronological order and in equidistant temporal steps and annotated. All experts annotated data sets D1-D15. The rest were annotated by ICS after learning annotation insights from the multiphase dynamics experts. The format of the dataset is as follows. A directory is dedicated to each bubble annotation. The directory name notes the number of the dataset and the annotator id. Each directory contains 20 text files and 20, corresponding, images. Each text file contains a list with the 2D coordinates of one bubble annotation. The first coordinate marks the left contact point and the last coordinate marks the right contact point. These coordinates refer to a corresponding image contained in the same directory. Text files and image files are corresponded through their file names, which contain the frame number. The frame number refers to the image sequence. Images are in lossless PNG format.

The present work has been carried out in the framework of the European Space Agency Research projects AO-2004-111: BOILING, AO-1999-110: EVAPORATION, AO-2004-096: CONDENSATION. We thank all the Multiscale Boiling Science Team Members of the different institutions for their contribution in making possible the implementation of the experiment on-board the International Space Station: Technical University of Darmstadt, Institute for Technical Thermodynamics; Aix-Marseille University, IUSTI; University of Pisa; Institute of Thermal-Fluid Dynamics, ENEA; Institut de Mécanique des Fluides de Toulouse; Aristotle University of Thessaloniki; Transfers Interfaces and Processes, Université Libre de Bruxelles; University of Ljubljana; Kutatteladze Institute of Thermo-physics, Novosibirsk. The authors would also like to gratefully thank ESA, and in particular Daniele Mangini, Olivier Minster, Anne Pacros, Balazs Toth, and Marco Braibanti for their interest and support of the activities linked to Multiscale Boiling, and for the fruitful discussions. They would also like to thank AIRBUS (with particular gratitude to the project manager, Olaf Schoele-Schulz), as well as B.USOC for the kind cooperation (and especially Carla Jacobs and Denis Van Hoof) during all the pre-flight, in-flight and post-flight operations. Co-authors from the Technical University of Darmstadt would like to thank the German Aerospace Center (DLR) for the financial support in the framework of the Vapor II project, grant no. 50WM2257.