Measurement of the thermal conductivity of erasable phase-change optical recording media

We describe a method to estimate the thermal conductivity of the substrate, the dielectric layer, the phase-change (PC) layer, and the reflective layer of PC optical recording media. The method relies on the amorphous-to-crystalline phase transition that occurs in the PC layer and takes advantage of the difference in the thermal diffusion behavior under different-sized focused spots. All the results obtained here are reliable with better than ?5% accuracy, which is within the margin of our experimental error.     

Polarization dependence of thermal behavior in rewritable phase-change optical recording media

Thermal behavior in land-groove phase-change optical recording has been examined for different polarizations of the incident beam. Three-dimensional temperature distribution in the grooved medium is evaluated by the numerical solution of Maxwell's equations and the heat transfer equation with the finite-difference method. Both experiments and calculations have shown that the thermal behavior in the medium is dependent on the state of polarization and the nature of the track. The calculated mark shapes in a quadrilayer stack are in good agreement with experimental observations.     

Finite-element model for phase-change recording

The finite-element method is applied to model phase-change recording in a grooved recording stack. A rigorous model for the scattering of a three-dimensional focused spot by a one-dimensional periodic grating is used to determine the absorbed light in a three-dimensional region inside the phase-change layer. The optical model is combined with a three-dimensional thermal model to compute the temperature distribution. Land and groove recording and polarization dependence are studied, and the model is applied to the Blu-ray Disc.     

Study on Heat Transfer Characteristics of Phase-Change Energy Storage Unit for Thermal Management

The objective of the study was to investigate the heat transfer characteristics of a phase-change energy storage unit for thermal management. Considering the conduction in the solid and natural convection in the liquid, a physical and mathematical model for heat transfer was formulated. The governing conservation equations were solved using the finite-volume method on fixed grids. An enthalpy-porosity method was used for modeling the melting phenomenon of a phase-change energy storage unit. The time and space movement of the phase front, the temperature distribution, and the heat dissipation rate have been analyzed based on the model. The influence of the unit geometry, heat source location, and types of phase-change materials on the thermal performance of the energy storage unit were investigated. The model and numerical method were evaluated by comparing the numerical predictions with the experimental results. There was found to be excellent agreement between the calculation and experiment, indicating that the numerical method for heat transfer simulation of a phase-change energy storage unit is accurate. The results from the analysis elucidate the thermal performance of the phase-change energy storage unit and will provide the basis for the design and optimization of thermal management systems.     

空气源热泵机组冬季除霜热量补偿新方法

空气源热泵机组在冬季运行时,由于机组需要不断除霜,将导致机组供热能力不足、室内吹冷风、房间热舒适性下降等问题出现。为此,提出了一种利用相变蓄热技术解决空气源热泵机组冬季除霜问题的新途径。其基本原理是,将笔者研制的填充了DX40相变材料板的新型蓄热装置与空气源热泵机组相连接,当热泵机组在制热工况运行时,热泵机组向空调系统供热的同时也向相变蓄热装置蓄热;当热泵机组转换至除霜工况运行时,相变蓄热装置向空调房间放热,在提高房间热舒适性的同时,缩短热泵机组除霜时间,提高机组工作效率。试验结果表明,该相变蓄热装置应用于空气源热泵机组冬季除霜性能的优良性。     

Measurement of the thermal coefficients of nonreversible phase-change optical recording films

We have developed a procedure to obtain the critical temperature for the amorphous-to-crystalline phase transition as well as the thermal conductivity and the specific heat of the phase-change media of optical recording. The procedure involves estimating the thermal conductivity from the data obtained by measuring the threshold cw laser power required for inducing phase transition. Then, from the data obtained in short-pulse measurements, we estimate the specific heat. In principle this method can yield the thermal parameters of any number of layers, so long as one of the layers is made of a phase-change material having a well-defined transition temperature.     

Simulation study on heat conduction of a nanoscale phase-change random access memory cell

We have investigated heat transfer characteristics of a nano-scale phase-change random access memory (PRAM) cell using finite element method (FEM) simulation. Our PRAM cell is based on ternary chalcogenide alloy, Ge2Sb2Te5 (GST), which is used as a recording layer. For contact area of 100 x 100 nm2, simulations of crystallization and amorphization processes were carried out. Physical quantities such as electric conductivity, thermal conductivity, and specific heat were treated as temperature-dependent parameters. Through many simulations, it is concluded that one can reduce set current by decreasing both electric conductivities of amorphous GST and crystalline GST, and in addition to these conditions by decreasing electric conductivity of molten GST one can also reduce reset current significantly.     

Use of PCM Boards for Solar Cell Cooling

This contribution explains the use of fractal theory to describe thermal properties of materials. The basic idea is rooted in the theory of fractal fields defined in E-dimensional Euclidian space. Generic equations describing heat distribution are then specialized to describe the changes in heat transfer as a response to step-wise increases in the amount of heat added to the system. This model was then applied to the study of properties of a systems consisting of solar cells attached on a phase-change material (PCM) back sheet board. The aim of this study is to evaluate the ability of PCM boards to decrease the working temperature of solar cells and thus to increase the efficiency of the cells. Regression of experimental data was used to obtain model parameters. The parameters obtained this way were the thermal diffusivity, thermal conductivity, and specific heat, as well as parameters of the heat source and parameters related to the heat losses of the system. The method was then verified against parameters of the system based on poly-methyl-methacrylate and then applied to a PCM with a phase-change temperature of 25 °C. The values of the thermal parameters were determined at temperatures where both components of the PCM composite (Micronal^® and gypsum wall) were solid and below the phase-change temperature and then again at temperatures where one of the components (gypsum) was still solid, while the other one was already liquid (wax). The attempt to determine the parameters during the phase change was not made due the physicochemical processes taking place which would alter the measured data.     

Optical characterization of multilayer stacks used as phase-change media of optical disk data storage

We report results of measurements of the optical constants of the dielectric layer (ZnS-SiO2), reflecting layer (aluminum-chromium alloy), and phase-change layer (GeSbTe, AgInSbTe) used as the media of phase-change optical recording. The refractive index n and the absorption coefficient k of these materials vary to some extent with the film thickness and with the film deposition environment. We report the observed variations of optical constants among samples of differing structure and among samples fabricated in different laboratories.     

定形相变蓄热单元周期性释热实验分析

针对相变蓄热材料实际应用中的周期性释热情况,本文采用响应面法设计实验方案,对一种基于圆环形赤藻糖醇/膨胀石墨复合相变材料的间接式蓄热器进行周期性释热实验.利用蓄热材料的释热量、释热动力、有效能利用率对蓄热单元的释热性能进行分析.结果表明:当间歇时间为20 min,材料累计释热时间为40 min,总释热功率、斯蒂芬数、火...     

Parametric study of solidification of PCM around a cylinder for ice-bank applications

This paper presents the results of a numerical parametric study of the solidification of a phase change material (PCM) around a cylinder carrying a heat-transfer fluid (HTF) inside. A pure conduction model is used for the PCM and tube wall, the finite volume method is used together with the interface immobilization technique for treating the phase-change process. The convection problem inside the tube is solved by an energy balance with a Nusselt number value, obtained from the steady-state values for constant wall heat-flux conditions. The effects of the HTF entry temperature, the initial PCM temperature and the thermal conductivity of the tube material on the evolution of the solidification front are studied. Results for the temperature distribution during the process, phase-change interface velocity and thermal energy stored in the system are also presented.     

相变储能材料应用于建筑围护结构中的研究

探讨了相变储能材料的种类、性能和发展历史,并对其进行了优劣评价.根据材料的相变温度选择宜于在建筑围护结构中使用的相变储能材料,研究了相变材料与现有建筑材料结合的方法,分析了墙体中加入相变材料的房间在夏季的热性能和节能效果,提出了几个近期需要解决的问题.     

Ultra-high-density phase-change storage and memory

Phase-change storage is widely used in optical information technologies (DVD, CD-ROM and so on), and recently it has also been considered for non-volatile memory applications. This work reports advances in thermal data recording of phase-change materials. Specifically, we show erasable thermal phase-change recording at a storage density of 3.3 Tb inch(-2), which is three orders of magnitude denser than that currently achievable with commercial optical storage technologies. We demonstrate the concept of a thin-film nanoheater to realize ultra-small heat spots with dimensions of less than 50 nm. Finally, we show in a proof-of-concept demonstration that an individual thin-film heater can write, erase and read the phase of these storage materials at competitive speeds. This work provides important stepping stones for a very-high-density storage or memory technology based on phase-change materials.     

Preparation and Thermodynamic Properties of Camphene/Stearic Acid Composites as Phase-Change Materials in Buildings

In this study, a series of shape-stabilized phase-change materials (PCMs) of camphene/stearic acid (CS) were prepared and their thermal properties were measured by differential scanning calorimetry. The results indicated that the mixture consisting of 60 mass% camphene and 40 mass% stearic acid is the most favorable as a PCM, in terms of the phase-change temperature and latent heat. Thereafter, the CS was absorbed in fly ash, pyroclastic, barite, and marble powder, which acts as a supporting material, to prepare four kinds of composite-based PCMs. DSC, FT-IR, and scanning electron microscopy measurements were made to investigate the structures and properties of the PCMs. DSC results showed that the latent heats of melting and freezing of the composite PCMs were sharply decreased. Morphology and structural characterization revealed that, in form-stable PCMs, the dispersion of the supporting materials in the camphene/stearic acid matrix is homogeneous and there is no chemical interaction between the CS and composites. The composite PCMs showed excellent thermal stabilities and reliabilities, when their phase-change temperatures were concerned. These indicate that the prepared composite-based PCMs are suitable for thermal energy storage because of their applicable temperature range, thermal reliability, and chemical stability.     

A fixed-grid numerical modelling of transient liquid phase bonding and other diffusion-controlled phase changes

A transient liquid phase (TLP), in which a liquid layer is formed and subsequently solidifies, and other diffusion-controlled phase changes are generally associated with moving phase-change interfaces. Both fixed and variable grid discretization models have been formulated to investigate these diffusion-controlled problems. However, all numerical efforts to date have employed one of the approaches explicitly to track the moving interfaces across which there exist step changes in concentrations. In this article, the fixed-grid source-based method originally developed to simulate the temperature fields for melting-solidification phase change processes has been adopted to simulate diffusion-controlled dissolution and solidification. This method solves a unique diffusion equation for the different phases and the moving interfaces using implicit time integration. Compared with previously developed models, it is not only simpler in numerical formulation and procedure, but also more convenient to extend to many phases and high-dimensional problems. We report here the detailed formulation of the relevant equations, and compare and validate the model using experimental data and previous modelling predictions for several systems available from the existing literature.     

Synthesis and infrared property of polyaniline/phase-change nanocapsule composite

A composite of polyaniline (PANI) and nanoencapsulated phase-change material (PCM) with polystyrene (PS) as the shell and n-octadecane as the core was synthesized using the ultrasonic technique assisted by in situ polymerization. The composite's morphology, structure, and thermal properties were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results showed that the surface of the PCM nanocapsules was covered with PANI. The phase-change temperature of the nanocapsules of PCM and the composite was slightly lower than that of n-octadecane. Their latent heat was less than the calculated value based on the mass ratio of n-octadecane measured by TGA. The infrared emission properties of PANI, the phase-change nanocapsule, and the composite were studied using an IR-II infrared emissivity instrument and an infrared camera. It was found that the infrared emissivity of the composite was appreciably higher than that of PANI. However, the composite showed lower temperature than the PANI when observed by infrared camera with the increasing ambient temperature around the n-octadecane phase-change temperature. This occurred because the phase-change material in the composite absorbs so much heat that infrared emissions were obviously decreased when the ambient temperature rose.     

Thermal Effects on the Crystallization Kinetics,and Interfacial Adhesion of Single-Crystal Phase-Change Gallium

Although substrates play an important role upon crystallization of supercooled liquids, the influences of surface temperature and thermal property have remained elusive. Here, the crystallization of supercooled phase-change gallium (Ga) on substrates with different thermal conductivity is studied. The effect of interfacial temperature on the crystallization kinetics, which dictates thermo-mechanical stresses between the substrate and the crystallized Ga, is investigated. At an elevated surface temperature, close to the melting point of Ga, an extended single-crystal growth of Ga on dielectric substrates due to layering effect and annealing is realized without the application of external fields. Adhesive strength at the interfaces depends on the thermal conductivity and initial surface temperature of the substrates. This insight can be applicable to other liquid metals for industrial applications, and sheds more light on phase-change memory crystallization.     

蓄冷箱在疫苗冷链中的研究进展

每年疫苗产品损耗的主要因素之一是冷链运输的失效,在运输过程中使用最为普遍的设备是蓄冷箱。影响蓄冷箱保温性能的因素主要包括保温箱体的绝热性能、蓄冷材料的蓄冷能力及保温包装方式的设计。本文综述了蓄冷箱在疫苗冷链中的研究进展,分析了疫苗蓄冷箱常用保温材料及相变蓄冷材料的选择和应用,并讨论了箱体热阻的计算及蓄冷箱温度的监控。在此基础上指出整体包装和开发相变蓄冷材料的研究方向。     

Thermal properties and crystallization dynamics of a phase-change alloy for write-once optical data storage

Using a two-laser static tester, we measured the crystallization temperature and the thermal conductivity of a phase-change alloy thin film used in write-once-read-many media of optical data storage. The experimental technique, in general, and the calibration procedures, in particular, are described. The measurement results are used as entry points into numerical calculations that ultimately yield estimates of the material parameters. Valuable information about the dynamics of mark formation (i.e., localized crystallization) in amorphous phase-change alloy films is obtained from the observed variations of the sample reflectance under short-pulse and long-pulse recording conditions. The dependence of these reflectance variations on the laser pulse power has also been investigated.     

The influence of a phase change on the thermal history of a sample undergoing laser irradiation

This paper presents a comparison of the shapes of the thermal history curves for the rear surface of a sample undergoing laser irradiation. The curves are obtained experimentally and also calculated using the quasi-implicit technique of finite differences. The position and the size of the plateau observed on the theoretical and experimental curves has a significant impact on the accuracy of the determination of the thermal diffusivity obtained using the axial laser flash method. The experimental measurements were performed on phase-change composite materials and also on moist porous material samples (a gypsum slurry). This revised version was published online in November 2006 with corrections to the Cover Date.