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[en] Highlights: • The goal is to model the DSC thermograms of melting of binaries solid solutions. • The melting is modeled taking into account the heat conduction inside the DSC cell. • An enthalpic method is used considering the enthalpies of ideal solutions. • A parametric study, taking into account the sample heating rates and also the masses of the samples has been done. • Methods to determine the phase diagram (liquidus and solidus) and the energy of melting are explained. - Abstract: In this paper, a model is developed in order to determine the melting thermogram of a binary mixture, presenting a solid solution. Considering the case of an ideal solution, whose enthalpy function is analytically derived, we highlight the large differences existing between the thermogram and the derivative of the enthalpy function. The influence of the heating rates and the mass of the sample are analyzed for different concentrations. Finally, in the case of a thermodynamical equilibrium, we describe how to construct the phase diagram of the solution (liquidus and solidus temperatures, total latent heat)
[en] The aim of this paper is to present an inverse identification method to determine specific enthalpy of PCM from calorimetry experiments. We will focus on the cases of pure substances and ideal binary solutions including the eutectic equilibrium. The corresponding direct model, based on energy balance, is first presented. A classical enthalpy method is then used, which presents the advantage of easily decoupling the thermal transfers from the specific energetic behavior of the material (i.e. thermodynamical phenomenon). In the second part of the paper, we will present the used inverse method (genetic algorithms). The sensibilities of the different parameters for the identification are analyzed. Finally, we will present the identification from DSC experiments (1) at different rates of heating for pure substances and (2) at different concentrations of aqueous solutions of NHACl. In each case, we identify the thermodynamical parameters of the model and compare the corresponding thermograms with the experimental ones. A good agreement is obtained for both cases.
[en] Highlights: • Extension to binary solutions of a previous method developed for pure substances. • Thermal behavior of DSC sample can be obtained using a one-dimensional reduced model. • Thermodynamical parameters remain unchanged using this model. • In the perspective of future identification, this leads to a reduced computational time by 100 or even 1000. - Abstract: It is known that when studying the fusion of phase change materials (PCM) in differential scanning calorimetry (DSC) experiments, the geometry of the samples is not well known. Yet, some studies show that a numerical model, needing obviously to clearly define the shape of the sample, may reproduce the experimental DSC curve. In particular, such methods are currently applied to identification process based on inversion methods applied to the thermodynamical parameters governing the numerical model. Consequently, it means that if several numerical models are able to reproduce the thermal behavior of a PCM undergoing phase transition, the best one is the simplest one, that is to say the one which is the fastest to solve. Recently, we have thus shown that for pure substances PCM, a reduced model based on a spherical assumption for the shape of the sample leads to similar DSC curves that a more general model based on cylindrical shape. Clearly, if this result may be extended to other kinds of PCM, this will promote the capability of this method to be used in inversion process involved by identification process. The aim of the present paper is therefore to further study this method by considering non-pure materials, i.e. binary solution in the present case
[en] The thermal solar energy production is a promising and strongly growing sector. However, these technologies must be integrated to electric power systems, i.e. coupled with fossil-fired or biomass-fired plants, and the energy must be stored. This production can be either centralised or decentralised: this corresponds to different situations, different markets, different technologies and equipment (rows of mirrors to concentrate solar heat on a tube, linear Fresnel reflectors to concentrate solar heat on a tube, heliostats or mirrors which concentrate heat at the top of a tower, and parabolic disks which produce electricity with a Stirling gas engine at their focal point). This road-map focuses on electric power generation, and discusses key variables of the present market, proposes a vision for 2050, identifies objectives to be reached by 2015, and barriers to be removed, outlines the needs of demonstrators and their administrative framework.
[en] Highlights: • Impact of the thermodynamical modelling on PCM in building walls is studied. • A composite cement mortar with micro-encapsulated PCM is developed. • Experimental data are obtained with a home-made apparatus. • Three different models are compared with the experimental data. - Abstract: The objective of this study is to evaluate three different phase change models used to predict the energy behaviour of a PCM cement mortar sample. Reference data are measured on large samples of composite material using a special experimental set-up. The phase change models tested are: the apparent specific capacity method, the enthalpy method assuming a pure body and the enthalpy method assuming a binary mixture. Numerical results are compared to the reference data of heat flux and energy stored/released. The main conclusions of the study are: (1) the thermodynamically inconsistent apparent specific capacity method is not suitable, (2) the enthalpy method gives better results than the specific capacity method and (3) the enthalpy method gives better results with an appropriate guess of the enthalpy curve