The three-dimensional thermocapillary-driven melting of a phase change material (PCM) in a large-aspect-ratio cuboidal domain in microgravity is investigated numerically. The dynamics within the liquid phase is characterized by various mode transitions that can affect the heat transfer rate. Here we describe the types of melting dynamics that can occur with a selection of three different applied temperature differences Delta T and four different choices of container width W. A proper orthogonal decomposition (POD) method using Singular Value Decomposition (SVD) is applied to determine the dominant modes that describe the melting process, with particular attention to the transition to oscillatory flow. It is found that the oscillatory dynamics are typically associated with an interaction between oblique and longitudinal hydrothermal traveling waves, and that the latter have a slightly lower frequency. The leading-order oscillatory modes may be symmetric with respect to the lateral midplane or not, depending on the applied temperature and the spanwise aspect ratio. Mode (frequency) splitting is sometimes observed, as well as secondary harmonic modes satisfying a 1:2 spatiotemporal resonance condition. These results show that PCM melting is a complex dynamical process involving competition among various hydrothermal traveling waves with distinct orientation and that symmetry-breaking and spatiotemporal resonance play prominent roles in the mode selection problem.

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.

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.

Steady-state measurements in a thermogravitational microcolumn using optical digital interferometry are presented here for the first time in the literature in the case of ternary mixtures. These measurements enabled the subsequent obtaining of thermodiffusion coefficients of a ternary mixture once convection reaches the steady-state. The ternary mixture used was the benchmark one, tetrahydronaphthalene (THN) – isobutylbenzene (IBB) and n-dodecane (nC12) with mass fraction of 0.8-0.1-0.1 respectively. Contrast factors due to the change in the concentration field were measured and compared with the corresponding ones in the literature. Uncertainty in the results was found to be of similar order of magnitude as in the case of Selectable Optical Diagnostic Instrument (SODI), which means that the condition number of that contrast factor matrix is almost equal to the present one. Final values of thermodiffusion coefficients were compared with the results reported from other optical techniques, as well as with the results obtained by the traditional long opaque thermogravitational columns (TGC). Some proposals were then made in order to improve accuracy reducing the condition number of the contrast factor matrix.

The present work is focused on the 3D numerical analyses of the n-octadecane melting process, under microgravity conditions and Marangoni convection, by using the configuration of the liquid bridges (melting bridge). These analyses were conducted for various temperature differences (AT) between hot and cold plates ranging from 18 K up to 50 K. The temperature oscillations in one point of the bridge volume showed distinctive behavior in three different ranges of AT. These domains have been fully characterized in terms of frequency and wave patterns. Standing and travelling wave modes of different wave numbers have been observed and the instabilities produced within their transitions have been deeply analyzed. The results showed that the complexity of the flow increased with AT and oscillation frequencies decreased while the melted fraction increased. Moreover, Marangoni convection enhanced the heat rate efficiency by a factor of 1.7 approximately compared to a pure conductive process, which depended on temperature difference applied. (c) 2021 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.

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.

Experiments for measuring the thermodiffusion and diffusion coefficients in ternary liquid mixtures need to be performed in a gravity free environment to avoid convective flows. If convection can be neglected, the resulting concentration field can be used to fit the analytical solution and subsequently obtain the values of the two Soret coefficients. The so-callled Diffusion Coefficients Measurements in ternary mIXtures (DCMIX) experiments carried out onboard the International Space Station use a parallelepipedic cavity (10×10×5mm) called Soret cell, with two opposite heated walls at different temperatures to attain a linear concentration between them. When a reboosting (to keep, for instance, the station in the correct orbit) occurs, the acceleration level increases considerably and, thus, the induced convection can potentially distort the experimental results. In the present study numerical simulations have been carried out using five different reboosting scenarios (reboosting occurring at equally distributed times from beginning up to the end of the thermodiffusive step), and the experimental procedure for measuring the Soret coefficient has been reproduced. Three different mixtures have been considered, corresponding to the DCMIX1, DCMIX2 and DCMIX3 campaigns. It has been found that the thermal Grashof number determines the sensitivity of the system to the reboosting in these three cases. The reboosting maneuvers can strongly affect the concentration field, and therefore, the calculation of the Soret coefficients. The closer to the end of the thermodiffusive step the reboosting occurs, the larger the error is. The DCMIX2 is the most distorted mixture reaching an approximately 100% of error when reboosting acts at the end. But if the reboosting takes place at the beginning, the above-mentioned error is smaller than 1%. Also, the results depend on the method used to measure the concentration field. When the concentration difference averaged at the hot and cold walls method is used, the error is generally lower.

We report on thermodiffusion experiments conducted on the International Space Station ISS during fall 2016. These experiments are part of the DCMIX (Diffusion and thermodiffusion Coefficients Measurements in ternary Mixtures) project, which aims at establishing a reliable data base of non-isothermal transport coefficients for selected ternary liquid mixtures. The third campaign, DCMIX3, focuses on aqueous systems with water/ethanol/triethylene glycol as an example, where sign changes of the Soret coefficient have already been reported for certain binary subsystems. Investigations have been carried out with the SODI (Selectable Optical Diagnostics Instrument) instrument, a Mach-Zehnder interferometer set up inside the Microgravity Science Glovebox in the Destiny Module of the ISS. Concentration changes within the liquids have been monitored in response to an external temperature gradient using phase-stepping interferometry. The complete data set has been made available in spring 2017. Due to additionally available measurement time, it was possible to collect a complete data set at 30∘C and an almost complete data set at 25∘C, which significantly exceeds the originally envisaged measurements at a single temperature only. All samples could be measured successfully. The SODI instrument and the DCMIX experiments have proven reliable and robust, allowing to extract meaningful data even in case of unforeseen laser instabilities. First assessments of the data quality have revealed six out of 31 runs with some problems in image contrast and/or phase step stability that will require more sophisticated algorithms. This publication documents all relevant parameters of the conducted experiments and also events that might have an influence on the final results. The compiled information is intended to serve as a starting point for all following data evaluations.

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.

In the present study, the effects of reboosting maneuvers on the diffusion process during the thermodiffusion experiments known as Diffusion and thermodiffusion Coefficients Measurements in ternary liquid mIXtures (DCMIX) are analyzed. These experiments have systematically conducted in the International Space Station (ISS). Six different compositions of a 1,2,3,4-TetraHydroNaphtalene (THN), IsoButylBenzene (IBB) and n-Dodecane (nC12) mixture have been studied by means of numerical simulations. Real acceleration levels have been used to compute the unsteady buoyancy term in the momentum equation. Different gravity scenarios have been considered by changing both the intensity and the duration of the reboosting as well as its orientation, parallel or perpendicular to the concentration gradients. In these thermodiffusion experiments, the different components of the mixture separate in a parallelepipedic Soret cell, with a constant externally imposed temperature gradient between two opposite walls. When the temperature and concentration distributions reach the steady state, and consequently linear concentration profiles between hot and cold walls are achieved, the temperature difference is switched off and the components of the mixture diffuse until uniform concentration distributions are obtained. The present simulations only reproduce this last pure diffusive part of the thermodiffusion experiment. Results show that when a reboosting occurs, errors in the obtaining of the diffusion coefficients arise because of the convection generated. The lower values of the diffusion coefficient show a larger error since they are more sensitive to disturbances. The maximum error is obtained when the acceleration is acting perpendicular to the concentration gradient, which is the most harmful orientation.

The present work attempts to characterize the accelerometric environment of the DSC-DCMIX1 thermodiffusion experiment carried out in the International Space Station, from November 7th 2011 until January 16th 2012. Quasi-steady and vibrational/transient data coming from MAMS and SAMS2 sensors have been downloaded from the database of the PIMS NASA website. To be as exhaustive as possible, simultaneous digital signals coming from different SAMS2 sensors located in the Destiny and Columbus modules have also been considered. In order to detect orbital adjustments, dockings, undockings, as well as, quiescent periods, when the experiment runs were active, we have used the quasi-steady eight hours averaged (XA, YA and ZA) acceleration functions as well as the eight hours RMS ones. To determine the spectral contents of the different signals the Thomson multitaper and Welch methods have been used. On the other hand, to suppress the high levels of noise always existing in the raw SAMS2 signals, denoising techniques have been preferred for comparative reboostings considerations. Finally, the RMS values for specific 1/3 octave frequency bands showed that the International Space Station vibratory limit requirements have not been totally accomplished during both quiescent periods and strong disturbances, specially in the low frequency range.

The challenges confronting health care especially in today’s ageing societies of the industrialised countries demand a paradigm change in the medical sector. Among experts, it is generally expected that medicine and health care will focus on three tasks in the future:–health maintenance in healthy people,–individualised health care, and–challenging the traditional relation between physician and patient by providing the doctor’s advice irrespective of the location of the patients (telecare).At the same time, life sciences as a whole, i.e. biology and medicine, is seeing a fundamental reorientation at the beginning of the 21st century: The focus is no longer on analysing specific genes or proteins in an organism but on understanding living systems in their entirety – a concept successfully used in systems biology. This should determine also our approach to human beings, who should be considered as integrative systems and as individuals. This rethink is indispensable if we are to meet the global challenges of the 21st century. In Germany, the Federal Government follows that logic in its so-called “High-Tech Strategy Paper” dated 2010. Therein, the subjects of health and nutrition are defined as one of five global challenges it intends to confront by future work in the area of individualised medicine, nutritional science, and research on ageing Federal Ministry of Education and Research (BMBF). Within the recently released “New High-Tech Strategy Paper – Innovations for Germany “dated 2014, the topics of individualised health care and medicine are stressed even more and will be worked on with dedicated actions. The subjects of nutrition and prevention will be given special attention in programs that will take care of health and living quality of the individual in a life-course perspective Federal Ministry of Education and Research (BMBF). In annual “World Health Summits” countries around the world are discussing similar strategies www.worldhealthsummit.org [3].Now, what is all that to do with space medicine? First of all, medical research and health care in space have always been and still are focusing, in an integrative approach, on the healthy astronaut as an individual. Secondly, in terms of substance, space medicine essentially consists of ageing research: After all, the physiological changes that astronauts experience during their flights in space resemble the ageing processes of people on the ground. In space, these processes happen in quick motion, in a manner of speaking, and – luckily for the astronauts – most of the changes are fully or at least to a great extent reversible.From these considerations it is obvious, that – in particular for people living in an ageing but nevertheless active society – space medicine is of inestimable importance, witnessed by the numerous scientific findings and innovative non-invasive diagnostic devices developed in the recent past. In the years to come, space medicine, because of its special methodology, is likely to become an even more powerful driver of change in terrestrial medicine. The contributions which space medicine is expected to make in each research area of physiology within the next decade or so will be summarised in this review. It will hopefully become evident that all mankind will eventually benefit from what could succinctly be summarised as astronaut-style healthcare. It goes without saying, of course, that this benefit is enabled by the joint efforts of all space-faring countries.

The accurate determination of mass diffusion coefficients is a technologically relevant problem that has implications on the modelling and control of material processes such as crystal growth and casting. It is also important in the validation of different theories of atomic diffusion. The experimental determination of these coefficients, when there is a liquid phase, is difficult due to the unavoidable presence of buoyancy driven convection currents that enhance mass transport and disturb diffusion measurements. To minimize as much as possible these problems, long capillaries are used in order to confine the fluid and reduce the intensity of the convective motions. These measurements have also been done in reduced gravity environments, but the residual gravity may still be able to induce buoyancy driven convection motions. The aim of our work is to analyze the impact of low solutal Rayleigh number environments on the accuracy of the interdiffusion coefficient measurements using long capillaries. In the present study we deal with two liquid systems; photovoltaic silicon and Al-based liquid binary alloys at high temperature. We have numerically simulated two different experimental techniques used to determine the diffusion coefficients; the shear cell and the long capillary techniques. We also consider the effect of rotating the cylindrical cell along their axis as a mechanism to reduce axial convective transport even in Earth laboratories. Finally, we use typical accelerometric signals from the International Space Station (ISS) in the quasi-steady range of frequencies. The signals concentrate on typical station reboosts because the accelerometric level of the rest of potentially dangerous disturbances - dockings, undockings and Extra Vehicular Activities, EVAs - is considerably lower. (C) 2015 Elsevier Ltd. All rights reserved.

The present work aims to study mechanical nonlinearities detected in the accelerometric records during a thermodiffusion experiment performed at the International Space Station, ISS. In that experiment the test cell was subjected to harmonic vibrations of different frequencies and amplitudes. Accelerometric data associated to the runs were downloaded from NASA PIMS website. Second order spectral analysis shows that the shaker modifies the normality of the data and introduces nonlinearities in the distribution of energy. High Order Spectral Analysis, HOSA, based on the bispectrum, bicoherence, trispectrum and tricoherence functions enabled us to study the kind of these nonlinearities. Additionally, a new method using the biphase and triphase histograms helps us to assess if quadratic and/or cubic phase coupling mechanisms are responsible for the anomalous nonlinear energy transfer detected. Finally, the RMS acceleration values are investigated to check if the vibratory limit requirements of the ISS are exceeded. This methodology is important not only in generic research of aerospace engineering but also in space sciences in order to help space researchers to characterize more globally their experiments. It is mentioned finally that HOSA techniques are not new, but never have been used in the analysis of accelerometric data coming from the ISS.

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