Phase Change Material Device for Spacecraft Thermal Control

On board a satellite, the experiments and subsystems have to be maintained within specified temperature limits. Phase Change Materials (PCM) offer the possibility to store thermal energy directly as latent heat of fusion. Usually, the melting PCM can easily be used in reversible, closed systems. Two advantages of a PCM device are the stability of temperature control and the absence of moving parts. The heat-storage requirement is mainly defined by the duty cycle along the orbital period. A trade-off is presented for typical missions, which takes into account the temperature range, the weight and thermal conductivity of the PCM device together with the specific design of the container. Candidates PCM for space applications are reviewed according to their main characteristics such as latent heat, phase transition temperature, conductivity, density but also corrosion potential, hysteresis and ageing. Potential weight and power gains are finally presented for selected missions

Phase Change Material Heat Accumulator for the HEXAFLY-INT Hypersonic glider

International audienceFrom the launchers to the spacecrafts, various on-board systems have to be maintained within specified temperature limits. Phase Change Materials (PCM) offer the possibility to store thermal energy directly as latent heat of fusion. Among the advantages of a PCM device are the stability of temperature control, the absence of moving parts and a reduced mass. The HEXAFLY-INTERNATIONAL project aims to flight test an experimental vehicle above Mach 7 to verify its potential for a high aerodynamic efficiency during a free-flight. European Major Resarch Centers and Industries are collaborating on this challenge. The presented activity focus on the use of a Phase Change Material device already developed under ESA projects up to TRL 6. Two efficient heat accumulators using PCM will allow avoiding overheating of electronic units such as telemetry & telecommand receivers, transmitters and data acquisition units for the hypersonic flight. The paper presents the complete cycle of design and environmental testing for the two PCM Heat Accumulators selected for the flight. The conclusions will show the benefit of adopting a Phase Change Material Heat Accumulator

SURFACE ENGINEERING FOR PARTS MADE BY ADDITIVE MANUFACTURING

peer reviewedthe surface preparation of metal parts made by additive manufacturing (AM). AM is a technology of choice for manufacturing of parts with complex shapes (heat exchangers, RF supports, optical parts…) and integrated functions such as conformal cooling channels, clips, hinges, etc. This opens the door for lightweight parts which are of prime importance for space applications. The potential of the AM technologies is however impeded by the quite rough surface finish that is observed on the as-manufactured parts. It is known that such a finish is likely to impact the performance of the parts. Several post-treatment techniques can be applied to improve the surface condition of the AM parts. However, so far, the influence of the successive post-processing steps on the final properties is not well established. Therefore, a better understanding of the impact of surface characteristics on the material behaviour is needed to expand the use of AM for high performance parts. The objective of this study, supported by ESA, is to propose and evaluate various surface finishing techniques for parts made by the AM technologies, in order to check their compatibility, evaluate their properties and derive guidelines for future applications. CRM is the prime proposer of this study and is in charge of the surface treatment and characterisations. Sirris additive manufacturing facilities are used to produce the parts. Thales Alenia Space and Walopt are included into the industrial team to provide concrete application cases. The study focuses on metals. Two metals under study are presented here: AlSi10Mg and Ti6Al4V. This paper is devoted to the early results of the first steps of surface preparation, namely material removal from the surface of the produced parts in order to improve their surface properties. As a first phase, tribo-finishing (TF) is tested on prototype parts to check its capabilities. Surface and volume parameters are analyzed, namely achieved roughness, material removal rate, location of removed material. The limitations in terms of geometry and applicability are discussed as well. These first observations should serve as guidelines for further application of AM for the design of parts used in space industry

Study of the effect of magnetic field on pearlite spheroidization and ferrite recrystallization

The steel industry is constantly looking for innovations and solutions to improve production processes as well as product properties. However, current technologies result from decades of development and thus have already reached maturity. Therefore, bright innovations have to arise from technological breakthroughs. The objective of those novelties is to induce drastic changes in terms of process or product. Magnetic heat treatment might be a solution to reach both objectives. Indeed, recent researches have shown that magnetic fields can significantly modify the transformation kinetics in steels. This can turn into very positive impacts on the metallurgical processes. However, researches on this topic are in the early stage and a lot of fields have not been studied yet. This work has been carried out in this challenging context. The main objective is to study the effect of magnetic fields on cementite spheroidization and ferrite recrystallization. So far, these two transformations involve long thermal treatments at high temperatures. Thus, a reduction of the processing time or an improvement of the mechanical properties of the steels by using magnetic field processing would be a significant improvement for this kind of thermal treatment. The transformations that are studied imply large microstructure modifications: lamellae breaks into spheroids while ferrite recrystallizes. As a consequence, the developments of dedicated microstructure characterization techniques are concomitant objectives. As it will be shown latter, we decided to develop and optimize image analysis tools. Practically, the completion of this work has required the pursuit of four objectives: Objective 1: develop an image analysis tool dedicated to pearlite spheroidization study, Objective 2: study the effect of magnetic field on cementite spheroidization, Objective 3: develop an image analysis tool dedicated to ferrite recrystallization study, Objective 4: study the effect of magnetic field on ferrite recrystallization. This work is divided in four parts described below. A general introduction constitutes the first part. It contains two chapters. Chapter I focuses on a literature review of the effect of magnetic fields on steels. The first section of this chapter deals with the basics of metallurgy and magnetism required to understand this work. Then, the reader will find a literature review about the effects of homogeneous magnetic fields on steel transformations. As it has been said before, the specificity of this work lies in the fact that the transformations studied were analysed and characterized using image analysis. The Chapter II is dedicated to this technique. The basics of image analysis are summarized in the first section of this chapter. Then, specific sections are dedicated to each step of image analysis: pre-treatment, image segmentation and characterizations. The limits of this technique, as well as its applications are described in the two last sections of this chapter. The second part of this work is divided in three chapters and deals with cementite spheroidization under magnetic field. Chapter III provides a detailed introduction to cementite spheroidization. The first section of this chapter introduces the pearlite as well as its microstructure. Using these concepts, the mechanisms and the kinetic of cementite spheroidization and cementite ripening will be introduced. Finally, the last section of this chapter will focus literature results which indicate that a potential effect of magnetic field on cementite spheroidization might be expected. After this detailed introduction, the tools used to study the cementite spheroidization under magnetic field will be described in Chapter IV. The first section deals with the characterization techniques used to study pearlite spheroidization. Then, the furnace and the heat treatments that have been performed will be described. With these tools, we will describe, in Chapter V, the results that have been achieved about cementite spheroidization under magnetic field. First, we will deeply analyse the effect of temperature and heat treatment duration on cementite spheroidization. This will be the opportunity to study in details the mechanism of cementite spheroidization and spheroids ripening. Microstructure evolutions induced by these two transformations will also be analysed. The effects of magnetic field on cementite spheroidization are described in the last section of this chapter. The analysis of the effect of magnetic field on ferrite recrystallization constitutes the third part of this work. It is divided in three chapters. Chapter VI provides a detailed introduction to ferrite recrystallization. The first section of this chapter deals with the crystalline structure defects induced by the steel forming. The detailed description of the mechanisms and the kinetics of defects elimination by the recovery, primary recrystallization and secondary recrystallization constitute the three next sections of this chapter. The last section of this chapter summarizes the results of different relevant studies on the effects of magnetic fields on these three processes. The chapter VI is followed by a detailed description of the characterization techniques as well as the heat treatment performed to study ferrite recrystallization (Chapter VII). Chapter VIII describes the results that have been obtained about ferrite recrystallization under magnetic field. We will study the effect of temperature and heat treatment duration on ferrite recrystallization. The involved transformations will be studied in detail. Finally, the effect of magnetic field on ferrite recrystallization will be discussed in the last section of this chapter. The general conclusions as well as the prospects of this work will be addressed in the fourth part of this work, respectively in Chapters IX and X.Les sidérurgistes, et le monde industriel en général, sont en perpétuelle recherche d'innovations et de moyens permettant d'améliorer leurs procédés et leurs produits. Actuellement, les procédés de production et de préparation des aciers se basent sur des technologies mûres, résultat de nombreuses années de recherche. Les innovations à apporter à ces procédés doivent donc résulter de sauts technologiques susceptibles d'induire des modifications considérables en termes de technique de production ou encore des propriétés des produits. Les traitements thermiques sous champ magnétique constituent une option pour atteindre ces deux objectifs. En effet, des études récentes ont démontré que les champs magnétiques permettent de modifier considérablement les cinétiques de transformations des aciers. Des retombées positives peuvent donc être attendues. Néanmoins, les recherches portant sur ce sujet en sont encore à leurs débuts, de nombreux phénomènes restent inexpliqués et de nombreuses voies n'ont pas encore été explorées. C'est dans ce contexte que ce travail se situe. L'objectif principal de celui-ci est d'étudier l'effet des champs magnétiques sur des transformations très utilisées dans l'industrie. Les deux transformations étudiées, à savoir la sphéroïdisation de la cémentite et la recristallisation de la ferrite, nécessitent des traitements thermiques plus ou moins longs et à haute température. Une réduction du temps de transformation ou encore une amélioration des propriétés des aciers traités sous champ magnétique, constituerait une évolution importante pour ce type de traitement thermique. Les transformations étudiées présentent la particularité d'induire des modifications importantes de microstructure : rupture des lamelles en globules et recristallisation de la ferrite. C'est pourquoi le développement de techniques de caractérisation adaptées à l'analyse de ces microstructures constitue un objectif concomitant de cette recherche. Comme nous le verrons dans la suite, notre choix s'est porté sur le développement et l'optimisation de techniques d'analyse d'images. Plus concrètement, l'aboutissement de ce travail a nécessité la poursuite de quatre objectifs : Objectif 1 : développer une technique d'analyse d'images adaptée à l'étude de la sphéroïdisation de la perlite, Objectif 2 : étudier l'effet d'un champ magnétique sur la sphéroïdisation de la cémentite, Objectif 3 : développer une technique d'analyse d'images adaptée à l'étude de la recristallisation de la ferrite, Objectif 4 : étudier l'effet d'un champ magnétique sur la recristallisation de la ferrite. Ce travail est scindé en quatre parties décrites ci-dessous. L'introduction générale constitue la première partie. Celle-ci est composée de deux chapitres. Le Chapitre I a pour thème une étude bibliographique de l'effet des champs magnétiques sur les aciers. La première section de ce chapitre traite des notions de base en métallurgie et en magnétisme nécessaires à la compréhension de ce travail. Fort de ce bagage, le lecteur trouvera ensuite une revue bibliographique des effets des champs magnétiques homogènes sur les transformations des aciers. Comme nous l'avons dit plus haut, la spécificité de ce travail réside dans le fait que les deux transformations étudiées ont été analysées et caractérisées par analyse d'images. Le Chapitre II est consacré à cette technique d'analyse. Les notions élémentaires concernant l'analyse d'images sont rappelées dans la première section de ce chapitre. Ensuite, une section spécifique est dédiée à chacune des étapes principales de l'analyse d'images : le prétraitement, la segmentation des images et les différentes caractérisations qui peuvent être réalisées sur les régions. Les limites de cette technique ainsi que ses domaines d'applications sont alors brièvement introduits dans les deux dernières sections de ce chapitre. La seconde partie de ce travail est scindée en trois chapitres et traite de la sphéroïdisation de la cémentite sous champ magnétique. Le Chapitre III propose une introduction détaillée de la sphéroïdisation de la cémentite. La première section de ce chapitre sera l'occasion d'introduire en détail la perlite ainsi que sa microstructure. A l'aide de ces notions, les mécanismes et la cinétique de la sphéroïdisation de la cémentite et du mûrissement des globules, seront présentés. Enfin, la dernière section portera sur les résultats identifiés dans la littérature indiquant une influence potentielle d'un champ magnétique sur la sphéroïdisation de la cémentite. Après cette introduction détaillée, les moyens utilisés pour étudier la sphéroïdisation de la cémentite sous champ magnétique seront décrites dans le Chapitre IV. La première section traitera des techniques de caractérisation utilisées pour étudier la sphéroïdisation de la perlite. Ensuite, les recuits réalisés ainsi que le four utilisé pour réaliser ceux-ci seront détaillés. A l'aide des moyens présentés au Chapitre IV, nous présenterons dans le Chapitre V les résultats obtenus concernant la sphéroïdisation de la cémentite sous champ magnétique. Dans un premier temps, nous détaillerons l'effet de la température et de la durée du recuit sur la sphéroïdisation de la cémentite. Nous aurons ainsi l'occasion d'étudier en détail le mécanisme de sphéroïdisation de la cémentite et du mûrissement des globules. Les évolutions de microstructure induites par ces deux transformations seront également décrites. La dernière section de ce chapitre sera l'occasion de présenter les résultats obtenus concernant l'effet d'un champ magnétique sur la sphéroïdisation de la cémentite. L'analyse de l'effet d'un champ magnétique sur la recristallisation de la ferrite constitue la troisième partie de ce travail. Elle est composé de trois chapitres. Le Chapitre VI constitue une introduction détaillée de la recristallisation de la ferrite. La première section de ce chapitre traite des défauts de structures cristallines induits par la mise en forme de l'acier. La description détaillée des mécanismes et de la cinétique d'élimination de ces défauts par les processus de restauration, de recristallisation primaire et secondaire constituent les trois sections suivantes de ce chapitre. La dernière section de ce chapitre regroupe les résultats bibliographiques pertinents de différentes études traitant des effets des champs magnétiques sur ces trois processus. Ce chapitre sera suivi par une description détaillée des techniques de caractérisation utilisées dans le cadre de ce travail ainsi que des recuits réalisés pour étudier la recristallisation de la ferrite (Chapitre VII). Les résultats obtenus concernant l'étude de la recristallisation de la ferrite sous champ magnétique seront alors présentés dans le Chapitre VIII. Ainsi, nous étudierons l'effet de la température et de la durée du recuit sur la recristallisation de la ferrite. Ces deux sections seront l'occasion d'étudier en détail les transformations impliquées. Enfin, l'effet de l'induction magnétique sur la recristallisation de la ferrite sera abordé dans la dernière section de ce chapitre. Les conclusions générales et perspectives liées au travail réalisé seront évoquées dans la quatrième partie de ce travail, respectivement dans les Chapitres IX et X

Prototyping of a Phase Change Material Heat Storage Device

peer reviewedA new concept of Phase Change Materials (PCM) device has recently been developed to improve the thermal control of spacecraft. Two Phase Change Material candidates have been selected after extensive testing of a set of available materials. Special attention has been paid to the hysteresis and ageing. In the design of the container, the thermal expansion of the PCM is a critical parameter that has been taken into consideration by two competing technologies. These designs have been tested: a prototype of PCM heat storage device has been effectively manufactured and tested under vacuum environment. 1D and 2D mathematical models have been developed. Conclusions are drawn to promote the use of PCM Heat Storage device in various space missions

Advanced Thermal Control of Launcher Equipment Bay using Phase Change Material

In the frame of ESA’s Future Launchers Preparatory Programme (FLPP), attention has been paid to the use of Phase Change Materials (PCM) for thermal control of Launchers. Among various possible applications, the avionics equipment bay of Ariane 5LV has been chosen to assess the performance of a Phase Change Material Heat Storage Device. Generally, the thermal control of the electronic units is passive and simply defined by their thermal inertia. In some specific case, an extra thermal inertia is added by using a spreader (thick Al plate) and the coupling with the platform is optimized. The price to pay is an extra mass for the launcher. A new concept of Phase Change Material device, using organic PCM, has recently been developed to improve the thermal control of spacecraft. This concept has been extended to the specific environment of a Launcher and to inorganic salt hydrates. The main results of this study are presented in this paper

Low Cost Concentrator Solar Array

Since the 70's, various researches have been undertaken to concentrate the solar flux on solar panels. In the 90's, concentrators with low concentration ratio appeared (C < 2.5), easily adapted to classical panels. From early 2000, the first commercial spacecrafts with such a technology were launched. Nevertheless, a gradual loss of power appeared and deep investigations concluded that this was due to various causes. From this incident, attention was paid to the contamination of the reflectors and more particularly to their operational temperature. Recently, in 2005, JAXA launched its small REIMEI scientific spacecraft, with two solar arrays equipped with a single lateral reflector. The good results achieved have triggered a new initiative in Europe to study a new concept of lightweight concentrator. The first results of this study including contamination and thermo-mechanical issues are presented

Image analysis of pearlite spheroidization based on the morphological characterization of cementite particles

Pearlite spheroidization is a metallurgical process in steels by which cementite lamellaer decompose into spheroids, a process accompanied by a decrease of the Vickers hardness of the samples. In thi study, different methods are compared for measuring cementite particles length and width from scanning electron micrographs. Based on a test-image, a so-called ribbon-like method is proposed for measuring particles length and width, and for discriminating lamellae from spheroids. Differently heat-treated samples are prepared and characterized. The results of analysis are used to rationalize the evolution of the microstructure of the samples. Compared to teh calssical DeHoff shape factor, it is shown that new insight into the spheroidization process is gained by analysing the lamellar length and widh distributions

Phase Change Material Heat Accumulator for the HEXAFLY Hypersonic Glider

From the launchers to the spacecrafts, various on-board systems have to be maintained within specified temperature limits. Phase Change Materials (PCM) offer the possibility to store thermal energy directly as latent heat of fusion. Among the advantages of a PCM device are the stability of temperature control, the absence of moving parts and a reduced mass. The HEXAFLY-INTERNATIONAL project aims to flight test an experimental vehicle above Mach 7 to verify its potential for a high aerodynamic efficiency during a free-flight. European Major Resarch Centers and Industries are collaborating on this challenge. The presented activity focus on the use of a Phase Change Material device already developed under ESA projects up to TRL 6. Two efficient heat accumulators using PCM will allow avoiding overheating of electronic units such as telemetry & telecommand receivers, transmitters and data acquisition units for the hypersonic flight. The paper presents the complete cycle of design and environmental testing for the two PCM Heat Accumulators selected for the flight. The conclusions will show the benefit of adopting a Phase Change Material Heat Accumulator

Texturation of YBa2Cu3O7-delta thick films by electrophoretic deposition under magnetic field

YBa2Cu3O7-delta coatings were deposited by electrophoretic deposition (EPD) onto Ni substrates. Particles of different sizes and shapes were used in order to study the influence of the powder microstructure on the film density. Texturation of the thick films was induced by application of a magnetic field during the electrophoretic deposition. X-ray diffraction analysis has clearly shown preferred c-axis alignment of the YBa2Cu3O7-delta films along the direction normal to the substrate surface. Scanning electron microscopy and optical polarised light microscopy were used to characterise the microstructure of the coatings, revealing a nonrandom platelets organisation