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Phase-change Material (phase-change + material)
Selected AbstractsThe Dependence of Crystal Structure of Te-Based Phase-Change Materials on the Number of Valence Electrons,ADVANCED MATERIALS, Issue 5 2004M. Luo A simple criterion to identify potential phase-change materials is developed using density functional theory. These compounds rely on the switching between an amorphous and a crystalline state. Here it is demonstrated that suitable alloys have an average valence electron number larger than 4.1 and show p-electron bonding leading to a six-fold coordination, while materials with a smaller number of valence electrons favor sp3 -bonding (see Figure). [source] Structure and properties of phase change materials based on HDPE, soft Fischer-Tropsch paraffin wax, and wood flourJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010M. E. Mngomezulu Abstract Phase-change materials based on high density polyethylene (HDPE), soft Fischer-Tropsch paraffin wax (M3), and alkali-treated wood flour (WF) were investigated. The blend and composite samples were prepared by melt mixing using a Brabender Plastograph, followed by melt pressing. They were characterized in terms of their morphology, as well as thermal, mechanical, thermo-mechanical, and water absorption properties. Although SEM micrographs showed some evidence of intimate contact between the WF particles and the HDPE matrix as a result of alkali treatment, poor filler dispersion, and interfacial adhesion were also observed. Partial immiscibility of the HDPE and the M3 wax was noticed, with the WF particles covered by wax. There was plasticization of the HDPE matrix by the wax, as well as partial cocrystallization, inhomogeneity and uneven wax dispersion in the polymer matrix. The HDPE/WF/M3 wax composites were more homogeneous than the blends. The presence of wax reduced the thermal stability of the blends and composites. Both the presence of M3 wax and WF influenced the viscoelastic behavior of HDPE. The HDPE/M3 wax blends showed an increase in the interfacial amorphous content as the wax content increases, which resulted in the appearance of a ,-relaxation peak. The presence of M3 wax in HDPE reduced the mechanical properties of the blends. For the composites these properties varied with WF content. An increase in wax content resulted to a decrease in water uptake by the composites, probably because the wax covered the WF particles and penetrated the pores in these particles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Enhanced heat transfer analysis of latent functionally thermal fluidHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2004Fengwu Bai Abstract A physical model has been developed to analyze the enhanced heat transfer process of the latent functionally thermal fluid with microencapsulated phase-change material. The problem is solved by the combination of the finite difference method and the moving heat source method. The calculated results reveal that putting the phase-change microcapsules into the fluids can enhance the heat transfer capabilities of the mixture. The effects of capsule radius and concentration of particles are numerically predicted. The numerical results provide the theoretical basis for the application and design of the latent functionally thermal fluid. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(6): 383,392, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20025 [source] Numerical simulation of high-temperature phase change heat storage systemHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2004Yu-Ming Xing Abstract In this paper, numerical results pertaining to cyclic melting and freezing of an encapsulated phase-change material (PCM) have been reported. The cyclic nature of the present problem is relevant to latent heat thermal energy storage system used to power solar Brayton engines in space. In particular, a physical and numerical model of the single-tube phase change heat storage system was developed. A high-temperature eutectic mixture of LiF-CaF2 was used as the PCM and dry air was used as the working fluid. Numerical results were compared with available experimental data. The trends were in close agreement. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(1): 32,41, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10132 [source] Synthesis and Characteristics of a Phase-Change Magnetic Material,ADVANCED MATERIALS, Issue 12 2008Wen-Dong Song A phase-change magnetic material is synthesized by doping the known GeSbTe phase-change material with Fe, and its properties are compared with the parent chalcogenide material (see figure). Besides different optical (reflectivity) and electrical properties in the amorphous and crystalline states, its magnetic properties are different in the two states; a fact that can be used to realize the fast control of ferromagnetism by phase change. [source] A study on latent heat storage exchangers with the high-temperature phase-change materialINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2001Qiao He Abstract This paper presents a theoretical analysis and an experimental test on a shell-and-tube latent heat storage exchanger. The heat exchanger is used to recover high-temperature waste heat from industrial furnaces and off-peak electricity. It can also be integrated into a renewable energy system as an energy storage component. A mathematical model describing the unsteady freezing problem coupled with forced convection is solved numerically to predict the performance of the heat exchanger. It provides the basis for an optimum design of the heat exchanger. The experimental study on the heat exchanger is carried out under various operating conditions. Effects of various parameters, such as the inlet temperature, the mass flow rate, the thickness of the phase-change material and the length of the pipes, on the heat transfer performance of the unit are discussed combined with theoretical prediction. The criterion for analyzing and evaluating the performance of heat exchanger is also proposed. Copyright © 2001 John Wiley & Sons, Ltd. [source] The Dependence of Crystal Structure of Te-Based Phase-Change Materials on the Number of Valence Electrons,ADVANCED MATERIALS, Issue 5 2004M. Luo A simple criterion to identify potential phase-change materials is developed using density functional theory. These compounds rely on the switching between an amorphous and a crystalline state. Here it is demonstrated that suitable alloys have an average valence electron number larger than 4.1 and show p-electron bonding leading to a six-fold coordination, while materials with a smaller number of valence electrons favor sp3 -bonding (see Figure). [source] The study of structural changes of amorphous Ge2Sb2Te5 films after annealing by optical absorption spectroscopyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010Tamihiro Gotoh Abstract Optical absorption spectra of post-annealed Ge2Sb2Te5 films were measured in the photon energy range from 0.5 to 3.5,eV. Optical absorption edge and Urbach slope parameter changed slightly with increase in annealing temperature and then abrupt changes occurred at around crystallization temperature. The band gaps of amorphous and cubic Ge2Sb2Te5 are 0.74 and 0.54,eV, respectively. The spectroscopic method is demonstrated to be suitable for evaluation of structural disorder and crystalline composition in phase-change materials. [source] Thermoaktive Bauteilsysteme mit integrierten Phasenwechselmaterialien , eine SimulationsstudieBAUPHYSIK, Issue 1 2007Doreen Kalz Dipl.-Ing. Gegenstand der vorliegenden Arbeit ist die Analyse und Evaluierung von thermoaktiven Bauteilsystemen (TABS) und einem Nachtlüftungskonzept hinsichtlich des thermischen Raumkomforts auf Grundlage einer modellbasierten Simulationsstudie. Das Gebäude- und Anlagenmodell wurde in der Simulationsumgebung ESP-r mit Meßdaten aus Experimenten in einem Niedrigenergie-Bürogebäude validiert. Die Untersuchung umfaßt: Betonkerntemperierung (BKT), Kapillarrohrmatten ohne und mit 20% mikroverkapselten latenten Wärmespeichermaterialien (PCM) im Deckenputz. Zentrale Ergebnisse sind: Die Konditionierung mit Kapillarrohrmatten ermöglicht ein zufrieden stellendes Raumklima vergleichbar mit BKT, die Verwendung von PCM trägt entscheidend zur Reduzierung der Raumtemperaturen bei und der optimale Schmelzbereich des PCM-Speichers liegt in dieser Untersuchung bei 19 bis 22 °C. Thermo-active building systems using phase-change materials , a simulation study. The objective of this study aims at analyzing and evaluating thermo-active building systems as well as a night ventilation concept with respect to thermal interior comfort by means of a simulation study. Preliminary experiments in a low-energy office building facilitate the calibration of the simulation model in ESP-r. In particular, the analysis was carried out for (i) concrete core conditioning, (ii) grid conditioning without and (iii) with 20% of micro-encapsulated latent heat storage materials (PCM) applied to the ceiling. The central conclusions of this study are: (1) Grid conditioning provides a satisfactory room condition comparable with concrete core conditioning, (2) the application of PCM contributes to a reduced operative room temperature, and (3) in this study PCM with a melting range of 19 to 22 °C is most favorable. [source] | |||||||||||||