Heat storage in alloy transformations

The feasibility of using metal alloys as thermal energy storage media was determined. The following major elements were studied: (1) identification of congruently transforming alloys and thermochemical property measurements; (2) development of a precise and convenient method for measuring volume change during phase transformation and thermal expansion coefficients; (3) development of a numerical modeling routine for calculating heat flow in cylindrical heat exchangers containing phase change materials; and (4) identification of materials that could be used to contain the metal alloys. Several eutectic alloys and ternary intermetallic phases were determined. A method employing X-ray absorption techniques was developed to determine the coefficients of thermal expansion of both the solid and liquid phases and the volume change during phase transformation from data obtained during one continuous experimental test. The method and apparatus are discussed and the experimental results are presented. The development of the numerical modeling method is presented and results are discussed for both salt and metal alloy phase change media

Development of new eutectic phase change materials and plate-based latent heat thermal energy storage systems for domestic cogeneration applications

327 p.La presente tesis doctoral tiene como objetivo el desarrollo de nuevos sistemas de almacenamiento térmico latente para aplicaciones de cogeneración en edificios, con el fin de contribuir al ahorro energético en los mismos. Para ello se han desarrollado las siguientes tareas de investigación: (i) investigar mezclas eutécticas binarias de materiales para desarrollar nuevos PCMs adecuados para almacenar calor en el rango de temperaturas correspondiente a sistemas de calefacción y agua caliente sanitaria (ACS); (ii) desarrollar un procedimiento genérico de diseño de sistemas de almacenamiento térmico latente para permitir el rápido dimensionamiento de dichos sistemas y su optimización, (iii) diseñar y construir un prototipo de almacenamiento térmico latente a escala real, incluyendo la definición de una ruta de fabricación adecuada y la evaluación del sistema y sus componentes en términos de integridad mecánica y (iv) evaluar el comportamiento térmico de dicho sistema en una planta piloto de cogeneración y realizar un estudio económico completo con el fin de proponer futuras mejoras del sistema

Experiments on a lab scale TES unit using eutectic metal alloy as PCM

The behavior of a magnesium and zinc eutectic metal alloy used as thermal energy storage (TES) material is tested in a laboratory scale TES unit. The TES unit consists of two concentric tubes with the central tube surrounded by 67 kg of the metal alloy and two caps at both ends of the tube through which the heat transfer fluid (HTF) flows. Charging (melting) and discharging (solidification) processes of the eutectic metal alloy are performed using synthetic oil as the HTF. The experimental results are used to test the validity of the model via simulations performed with a computational fluid dynamics tool. The results corroborate that phase change materials with high thermal conductivity, such as eutectic metal alloys, are ideal for the evaporation process of water in direct steam generation applications due to the quasi-constant melting and solidification temperatures and to its high heat transfer capacityThe authors would like to thank the Department of Industry, Innovation, Commerce and Tourism of the Basque Government for funding Etortek 2011 Energigune’11 grant (IE11-303). The authors would like to express their gratitude to Felix Mendia for his valuable and constructive suggestions and very much appreciate the collaboration of Julian Izaga from IK4-Azterlan and Rafael de Diego from Melfun in the synthesis of the eutectic allo

Pertinence of micro-gravity studies for solid/liquid phase change (Actes)

International audienc

Noncontact modulation calorimetry of metallic liquids in low Earth orbit

Noncontact modulation calorimetry using electromagnetic heating and radiative heat loss under ultrahigh-vacuum conditions has been applied to levitated solid, liquid, and metastable liquid samples. This experiment requires a reduced gravity environment over an extended period of time and allows the measurement of several thermophysical properties, such as the enthalpy of fusion and crystallization, specific heat, total hemispherical emissivity, and effective thermal conductivity with high precision as a function of temperature. From the results on eutectic glass forming Zr-based alloys thermodynamic functions are obtained which describe the glass-forming ability of these alloys

Investigation of microstructure and mechanical properties by direct metal deposition

Microstructure and properties of Direct Metal Deposition (DMD) parts are very crucial to meeting industrial requirements of parts quality. Prediction, and control of microstructure and mechanical properties have attracted much attention during conventional metal manufacturing process under different conditions. However, there is few investigations focused on microstructure simulation and mechanical properties control under different process parameters during DMD process. This dissertation is intended to develop a multiscale model to investigate Ti6Al4V grain structure development and explore Ti6Al4V based functionally graded material (FGM) deposit properties during DMD process. The first research topic is to investigate and develop a cellular automaton-finite element (CA-FE) coupled model to combine with thermal history and simulate nucleation sites, grain growth orientation and rate, epitaxial growth of new grains, remelting of preexisting grains, metal addition, and grain competitive growth. The second research topic is to develop grain growth algorithm, which is appropriate for highly non-uniform temperature field and high cooling rate, to control grain structure under real-time changing process parameters. The third research topic is to investigate the influence of process parameters on microstructure and properties of Ti6Al4V-based FGMs, which are fabricated with different TiC volume fraction from 0 to 30vol%. The microstructure, Vickers hardness, phase identification, tensile properties of FGM are measured to investigate the fabricated FGM qualities. The Digital Image Correlation (DIC) is developed to analyze Young\u27s modulus versus composition of FGM parts --Abstract, page iv

NUMERICAL SIMULATION OF TEMPERATURE DISTRIBUTION ON METAL CASTING IN VERTICAL SOLIDIFICATION

The metals and alloys solidification can be defined as a transient heat transfer process. A liquid/solid transformation is followed by thermal energy liberation, with a movable boundary separating two phases with different thermophysical properties. The solidification is of great interest to mechanical and chemical engineers. It is a non-linear transient phenomenon, where heat transfer between the casting and the mold plays a important role. This paper aims to propose a study of heat flow from the casting to the mold using a numerical technique to compute the temperature history of all points inside the casting. The cooling process consists of water-cooled mold with heat being extracted only from the bottom, resulting in unidirectional vertical solidification. The ANSYS software was used to obtain the temperature distribution in the casting. Good agreement was obtained when the simulation results were compared with the experimental data

Simulation of solidification grain structures with a multiple diffusion length scales model

International audienceA cellular automaton (CA) - finite element (FE) model is presented for the prediction of micro-and macrosegregation based on solute diffusion. On the one hand an open microsegregation model is implemented. It applies to each solidifying CA cell, i.e. a representative elementary volume of the mushy zone. Diffusion in the solid and in the extradendritic liquid are modeled with analytical expressions for two length scales based on the primary and secondary dendrite arm spacing and assuming cylindrical geometries representative of the dendritic network. On the other hand an unstructured and anisotropic FE mesh adaptation is used. The FE mesh is generated based on an error estimation method of the average composition field. Mesh refinement takes place in regions located ahead of the mushy zone growth front where diffusion layers are built up due to segregation. As a result, the diffusion length scale outside the envelopes of mushy zones (i.e., in the intergranular liquid that surrounds the envelopes of the grains) is directly captured. Numerical implementations of the coupling between the CA and FE methods being validated by comparison with the predictions of other models, simulations are compared with experimental results in Al-Cu alloys; thus demonstrating the capability of the model to predict segregation based on the coupling between several length scales