This study investigates the adiabatic boundary condition in experiments and numerical simulations involving the melting of phase change materials (PCMs), with n-octadecane (Pr = 52.5) as the model PCM. This material is selected for the MarPCM experiment aboard the ISS, which explores heat transfer enhancement through the Marangoni effect. The experimental setup features a parallelepiped cell with one hot and one cold vertical wall, and a free surface in contact with air, allowing heat transfer and Marangoni flow. A key focus of this study is the effectiveness of the adiabatic condition at the bottom wall. Two setups were developed progressively to minimize heat loss and optimize thermal efficiency. The modified setup demonstrated excellent performance, consistent with expected PCM melting dynamics. Numerical simulations conducted under similar conditions showed results in excellent agreement with experimental observations and confirmed the design improvements.

The melting of a phase change material (PCM) in a cuboidal domain under microgravity conditions is investigated numerically. The upper surface of the PCM is free (in contact with air, for example) and variations in its surface tension drive thermocapillary convection in the liquid phase, which significantly enhances heat transfer and accelerates melting. Furthermore, the change in liquid fraction during melting is associated with transitions among various modes of thermocapillary dynamics, including an oscillatory instability to hydrothermal waves. While the characteristics of PCM melting and thermocapillary dynamics have previously been investigated in this system using a two-dimensional model, the current work examines the important question of transverse dynamics and their effect on the melting process. Careful quantitative comparisons are made between the three- and two-dimensional models in terms of melting times, solid/liquid interface evolution, thermal fields, and spectrograms. The results show that transverse modes are often, but not always, reflection symmetric about the midplane and that their influence on melting and PCM performance is relatively minor in most cases. Thus, two-dimensional models may be used to reduce computational costs while still providing a reasonable approximation of the melting process for high Prandtl number materials, especially when compared to the midplane of the full cuboidal domain.

We present a comprehensive study on heat transfer in phase-change materials (PCMs), focusing on both melting and solidification phases, different temperature scenarios, an assessment of practical implementation aspects, and Marangoni convection. The research examines heat transfer rates during the melting-solidification cycle, with a focus on gallium (Ga) and n-eicosane (C20), the latter being a candidate for the MarPCM project aboard the ISS [1]. The paper explores different temperature scenarios using Ga to optimize PCM performance. N-eicosane requires extensive computational resources due to its significant thermal time, whereas gallium allows for more efficient simulations. The most effective scenario involves switching temperatures between cold and hot walls at a certain moment, which occurs earlier than the full melting time or reaching steady state. This specific moment corresponds to the beginning of a decrease in heat extraction efficiency. The success of this scenario relies on the symmetric thermal boundary conditions and multi-cyclic temperature inversion. We suggest that the implementation of this scenario is similar to rotating the PCM body within its package while maintaining the temperature of the external walls constant. Extending the strategy to n-eicosane yields promising results. This study also highlights the importance of Marangoni convection in heat transfer mechanisms.

The improvement of heat management based on Phase Change Materials (PCMs) is of increasing importance in space environments. In this context, a future ESA project called "Effect of Marangoni Convection on heat transfer in Phase Change Materials (MarPCM)" will evaluate the degree of improvement in heat transport using thermocapillarity as convective activator of the liquid phase generated during the melting. Since this type of project needs to be performed onboard International Space Station, ISS, it is of outmost importance to know if the accelerometric environment of the Station could affect the experiment results. To do so, various 2D simulations of the solid-liquid phase change were carried out using n-octadecane as PCM material, by considering a pre-selected acceleration signal coming from a real ISS reboosting maneuver (June 24, 2021). Different gravity scenarios have been considered by changing both the intensity and the orientation of the reboosting maneuver, parallel (x direction) and perpendicular (y direction) to the thermal gradients. The acceleration levels were enhanced up to 1000 times the intensity achieved during the real reboosting in order to predict the safety margins of the ISS experiment. The results showed alterations of the liquid-solid interface, during the melting process in the high g-level scenarios considered. In these cases, the oscillatory flow pattern became more complex detecting sudden changes in the main frequency which were maintained approximately 1000 s after the reboosting ended. Nevertheless, applying real boosting maneuver no significant influence in the melting process was detected.

Present as well as future challenges of space exploration point to the need for improved thermal control systems. The “Effect of Marangoni Convection on Heat Transfer in Phase Change Materials” experiment, which is approved by ESA for execution on board the International Space Station, aims to contribute directly to current knowledge and basic understanding of heat and mass transport in phase change materials (PCMs) that incorporate a free surface in reduced gravity. The experiment will apply fixed temperatures to opposite ends of PCM samples held in cuboidal and cylindrical containers in order to drive controlled melting and solidification cycles that will be observed by means of optical cameras. The recorded images will be complemented by thermal measurements at key positions along the samples, which will allow different thermocapillary flow regimes to be distinguished according to their temporal dynamics. It is anticipated that thermal Marangoni (thermocapillary) convection will increase the heat transfer rate in these PCM devices by a significant factor (on the order of two or more) compared to melting governed by thermal diffusion (conduction). If the PCM designs prove robust, the experiment results can be expected to lead to substantial improvements in future designs for passive PCM applications in space missions.

Phase change materials (PCM) are commonly used for energy storage in a variety of terrestrial applications and offer promise for future space exploration. We present a three-dimensional numerical investigation of the thermocapillary (Marangoni) flows in liquid and melting bridges in microgravity. The focus is placed not only on the role of the melting process in changing flow regimes, but also on emphasizing comparative nonlinear dynamics in these bridges. The hydrothermal instability in a melting bridge (MB) with a unit aspect ratio is compared to the liquid bridges with an aspect ratio between 0.7 and 1, in order to match the liquid fraction during the melting process with the liquid content in the liquid bridge. Since the characteristic size affects the Marangoni number, the temperature difference between the disks ( AT ) is selected as the control parameter, and calculations are carried out for AT = 25, 30, 40 K. At the end of the melting process, an oscillatory traveling wave regime is established in both systems at high AT , albeit with different frequencies. At low AT , this similarity disappears. The processing of temperature time-series, such as the density power spectrum (PSD), the spectral entropy (SEN) and the embedded dimension, was used to describe and compare flow patterns in liquid and melting bridges. (c) 2022 Elsevier Ltd. All rights reserved.

This work presents the preliminary characterization of the vibrational environment of the DCMIX4 thermodiffusion experiment conducted onboard the ISS from December 2018 to March 2019. Given the long duration of each one of the 58 runs of the campaign and to ensure a correct interpretation of the results, an accurate analysis of acceleration levels all along the experiment is advisable. Digital signals coming from the nearest sensor, es09006, located in the Microgravity Science Glovebox (Destiny module) were downloaded from the PIMS NASA website. The techniques used to identify the main disturbances during the experiments were defined both in time and frequency domains. It is expected that the results obtained can help the experimentalist to have an overview of the possible sources of disturbances that may affect their experiments. To visualize the possible impact of the accelerometric environment on the experiment a numerical simulation has been performed. Four signals have been chosen, one considering the ideal case g = 0, one coming from the OSS raw sensor (outside the Microgravity Science Glovebox) and the other two, coming from the es09006 sensor that needed to be mathematical manipulated for considering only the low frequency range. Independent of the location of the sensor, numerical simulations do not detect, in any case, appreciable flow disturbances if quiescent periods are considered. Therefore, in case the reference sensor is not available one can use other sensors placed in the same module.

A growing number of companies in the aerospace industry are already leading projects to deploy Augmented Reality (AR) to improve their workplace performance, knowledge transfer, as well as workforce productivity. In parallel, national and international agencies in aerospace, such as the European Space Agency (ESA), are running studies to evaluate the application of AR to enhance the quality and cost effectiveness of space missions. We hereby present the results of a study performed by ESA to assess the maturity and potential business value of AR for application to space product assurance and safety activities. For this purpose, we conduct an on-line survey and interviews with product assurance and safety professionals. Moreover, we provide a detailed review of space industry use case requirements and readiness levels of potentially involved technology components. Findings indicate that maturity of many components enabling AR may not fully satisfy the space industry's requirements, while, at the same time, there is great potential for impact and long-term benefits from AR introduction.

The influence of different body forces on the frequencies of the oscillatory regime in liquid bridges of molten silicone is studied. To do so, three different gravity levels are applied: the first related with Earth gravitational acceleration, the second with International Space Station reboosting maneuvers and the third with zero gravitational acceleration. In addition, different Marangoni numbers are considered in order to compare the influence of bulk body forces on them. Finally, a short study of the possible impact of the relationship between length and diameter of a liquid bridge on the number of instability modes is presented.

The accelerometric environment of IVIDIL and DCMIX experiments were successively monitored not only to identify the main disturbances that could affect the experiments but as well to ensure the correct interpretation of the experimental results. To do so, the conventional techniques used by NASA have been complemented by new tools developed and adapted to help the surveillance of the runs. A summary of these main new techniques is presented further. To show the potentiality of all these techniques, moderate and strong disturbance episodes such as berthings, dockings and reboostings were analyzed by using acceleration signals that came from three different sensors located in the Destiny, Columbus and JEM/Kibo modules, respectively. The first technique proposed is based on the Shannon entropy concept in both time (TEN) and frequency (SEN) domains. It has been found, that SEN technique is a fast and easy tool to detect the different disturbances registered throughout the experiments. The second technique suggested by the authors is based on the one-third octave frequency band RMS values and is called RMS warning map. It is a visual tool which was demonstrated to be very efficient in detecting the range of the frequencies that surpasses the ISS limits requirements, especially when a sudden disturbance occurs. Finally, in order to identify nonlinearities in the frequency domain within a signal, bispectrum and trispectrum functions have been applied. Quadratic and cubic phase couplings have been detected with these techniques only between high frequencies and especially for the signals coming from JEM/Kibo module.

In the present work, by using a paralelepipedic thermogravitational microcolumn, the temperature gradient influence on the stability of the flow was or has been examined, emphasizing mixtures with negative Soret coefficients. Experiments and numerical analysis were conducted for DCMIX2 Toulene-Methanol binary subsystem. This binary subsystem has a broad range of negative Soret values for low concentrations of Methanol which was analysed. Two different concentrations have been studied in order to confirm existence of temporal stability windows of those mixtures. Experiments were compared with numerical simulations conducted in open source software OpenFOAM, for both cases.

A comparative analysis of the vibratory environment of the DCMIX2/3 thermodiffusion experiments is presented here by using acceleration signals coming from different sensors placed in the Destiny, Columbus and Kibo modules. The es03 sensor nearest to the experimental device and located inside the Glovebox (Destiny module) has been defined as reference. Data were downloaded from the NASA PIMS website paying special attention to the runs coinciding with disturbances such as dockings or extravehicular activities (EVAs) as they could particularly affect the International Space Station (ISS) microgravity levels. The analyses have been made minute by minute for the three acceleration components by using the Frequency Factor Index (FFI), Spectral Entropy (SEN) and Root Mean Square (RMS) values evaluated over one-third-octave frequency bands. Spearman’s rank correlation coefficient and the coherence function have been used to investigate the degree of linear correlation between the reference signal and the other ones. SEN evolution showed different patterns compared to the reference. Also, RMS values surpassing the ISS microgravity limits were detected in all sensors, mainly at low frequency bands (< 10 Hz) and prevailing on z A direction. However the sensors located in the Destiny module better accomplished the ISS vibratory limits requirements. Finally, some degree of linear correlation at structural frequencies (< 3 Hz) has also been detected. Overall, the sensors placed in the Destiny, Columbus and Kibo modules presented different vibratory characteristics and, despite they offer valuable information of the whole environment, may not be sufficient to properly characterize DCMIX2/3 experiments.

The present work aims to investigate the degree of correlation existing between the information contained in the ISS reduced quasi-steady accelerometric data and different external mechanical disturbances (reboostings, dockings/undockings, berthings/deberthings and Extra Vehicular Activities), compiled for the period 2009 to 2016. The eight hour mean (Mean8h) and the eight hour root mean square (RMS8h) acceleration values, considered as reduced data, have been extracted from the quasi-steady records provided by NASA Principal Investigator Microgravity Services website. The advantage of applying the present strategy is to drastically reduce the amount of information to be processed all along these eight years. The Mean8h values have been used for the evaluation of trends as function of time while the RMS8h ones were used to define the level (weak, medium and strong) of the different kind of external mechanical disturbances considered. These criteria has been applied for approximately four hundred selected disturbances, compiled in the Appendix. Results indicate that reboosting is always detected as a strong disturbance, while dockings/undockings, as weak ones, having lower, though detectable level, depending on the type of spacecraft considered. Extra Vehicular Activities are undetectable by the use of this reduced quasi-steady approach. The inverse problem, in other words, knowing the value of the RMS8h one could try to predict the kind of disturbance responsible of it, is thus feasible except for berthing/deberthings and Extra Vehicular Activities.