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This research focuses on the potential of greenhouse cultivation in circumpolar territories. It begins with a survey that encompasses most of the northern greenhouses in North America. This review emphasizes the need for appropriate data and for the right energy system design. Next, the paper focuses on a case study located in Nunavik, which is the northern Inuit territory of the province of Quebec. The Kuujjuaq cooperative greenhouse has been instrumented since June 2016 to collect data on temperature and relative humidity throughout the growing season. These measures have highlighted a major problem: a temperature difference between day and night that is too large, hindering crop development. To counteract this thermal behavior, a heat storage system was designed, built and installed in October 2018. It is the first time that a rock and air-based sensible thermal energy storage system, taking into account local materials and resources, has been designed and built in a northern greenhouse. This paper presents its main characteristics as well as records of temperature changes throughout the growing season. Moreover, an energy balance is presented for three days at the beginning of June 2019.

Modeling the thermal behavior of a plant or devices using Phase Change Materials (PCM) requires to know their thermophysical properties. The Differential Scanning Calorimetry (DSC) is a technic largely used to investigate them. However, under the pretext to experiment with small samples, some authors consider the DSC curves as directly representing the properties of the materials without realizing that this interpretation is very often incompatible with the thermodynamics laws: as an example, although a pure substance melts at a fixed temperature T F , it is proposed a melting through a temperature range higher than T F and depending on the experiments (heating rates, sample masses...), for solutions the suggested characteristic temperatures are incompatible with the phase diagram, and also a hysteresis phenomenon is invented... In this paper, we demonstrate by a model coupling thermodynamics and conduction heat transfers, that the DSC curves are exactly compatible with the thermodynamics of phase changes (melting at fixed temperature for pure substances, in conformity with phase diagrams for solutions...). The cases of pure substances, saline solutions, substances with impurities or solid solutions are detailed. We indicate which information can, however, be given by the curves. We also propose a more sophisticated method by inverse calculations to determine the specific enthalpy whose all the thermodynamical properties can be deduced. Finally, we give some indications to understand and use the results indicating supercooling.

The main challenge of working with thermoelectric generators lies in their low efficiency, so finding the optimal design to achieve the best thermoelectric generator (TEG) performance under the working conditions becomes a strong problematic. In this study, a numerical transient simulation tool was developed using different modelling techniques to achieve the performance improvement of a TEG. This TEG is composed of thermoelectric modules wrapped between two heat exchangers. A three-dimensional heat transfer transient model was first developed for the heat exchanger using the finite volume method and then coupled with a thermoelectric generation model. Materials properties vary as a function of temperature and the Thomson effect is taken into account to be able to get numerical results close to reality. Thermoelectric modules properties used in this model are those given by the manufacturer. The originality of this study is that it takes into account unsteady-state conditions, necessary for simulating a multitude of processes like the automobile (engine and exhaust systems), combustion processes, turbines working conditions and energy production. The use of this numerical tool can help maximize the TEG performance and possibly reduce material cost. In order to validate the model, the TEG has been built with the capacity of using different module quantities for different configurations. Experiments have been conducted at different inlet gas conditions (mass flow rate and inlet temperature). A comparison of experimental and predicted values of temperatures and output electrical power has been done in steady state regime. Using the three dimensional model for the heat exchanger, a good precision of the thermoelectric power generation model is obtained.

The use of phase change materials (PCMs) to increase solar domestic hot water (SDHW) system efficiency has been already studied by different ways. Some studies place the storage material in the water tank, others directly in the solar thermal collector. However both of them show that the effectiveness of such a use is not relevant. This paper is devoted to a new approach: the PCM is placed in the heat transfer fluid solar loop from the SDHW system. This configuration is studied under different weather conditions and system parameters. On the contrary to previous results, this parametric study highlights a significant increase of the system efficiency due to the PCM. Then, a genetic algorithm allows proposing an optimized system configuration.

Thermal energy storage is now a key parameter to overcome the delay between energy supply and demand in many applications. To address this issue, the use of phase change materials (PCM) tends to be more and more common. Given the attempted objectives of such applications, performances of the PCM are a cornerstone of the whole system. Therefore, a correct determination of their intrinsic properties is crucial. To perform this step, one may use a calorimetry experiment. Unfortunately, the interpretation of the thermogram is not straightforward and consequently, when not feasible at all, estimations may be wrong. As an example, pure substance as sometimes said to melt at a non-uniform temperature (their enthalpy being smeared over several degrees), and binary solutions are associated with liquidus temperature and latent heat that do not match the correct form of their enthalpy. The present work proposes a new method to avoid such issues. To summarize the novelty of our approach, the main idea is to use an inverse method to identify the thermodynamical parameters of the sample through a matching step between the experimental curves and theoretical ones. It means that contrary to many others methods, we do not directly extrapolate the thermodynamical properties ( e.g. the enthalpy) from the thermogram. Instead, we suppose an a priori formulation of the enthalpy, based on thermodynamical principles. Thus the thermodynamical parameters are inputs of which only values are computed from the experiments. Capabilities of the method are shown on pure substances and binary solutions examples.

This paper presents some results obtained by Differential Scanning Calorimetry (DSC) for characterizing the phase transition within an emulsion. The dispersed substances are either hexadecane, octadecane, water or binary solution. A non-equilibrium model taking into account the inter-phase heat transfer between the emulsifying medium and the dispersed droplet is proposed and explains the main experimental features.

International audience; The support of this study is a cement mortar containing a micro-encapsulated phase change material (PCM). The aim of this article is to identify by an inverse method the thermophysical properties of this composite material and all the parameters that are needed to build a physical model able to simulate the thermal behavior of a material containing PCM with accuracy. This approach consist in estimating different parameters that take place in the analytical relation of the enthalpy as a function of the temperature (h(T)) by comparing the response of the model with experimental results (here, heat flux measurement). A simplex algorithm allowed to minimize the quadratic criterion associated. The results obtained by inverse method are then analyzed and compared by experimental results obtained by direct method.

International audience; This article deals with the study of a mixture of a cement mortar with a phase change material. We performed together an experimental analysis and a theoretical modeling of the sample associated with transient simulation of its behavior when a heating or a cooling is imposed to this later one. A non pure enthalpy profile is supposed, which permits to better describe the measurements. Furthermore, the drawbacks no to use such a method in order to prefer a more classical one are pointed out.

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).

International audience; 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.

International audience; A two dimensional front-tracking method is developed in order to model dendritic growth during solidification processes of pure substances. The method uses a sequential set of moving marker points to describe and track the liquid-solid interface which evolves over a fixed background mesh describing the whole medium. The code behaviour is first checked by a simple stable case of solidification to provide homogeneous velocity at the interface. Then, test examples of unstable solidification cases considering different modes of anisotropy are performed. Finally, interface evolution, with primary and secondary branches, is described, showing the ability of the code to study realistic dendritic growth characteristics.

International audience; 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 N H 4 Cl. 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

We present in this paper a new method of determining the nucleation probability J(T) of a supercooled liquid dispersed within an emulsion, based on the analysis of the thermogram obtained during a regular cooling. The thermal behaviour of the sample during the cooling is modelled in order to calculate the thermogram and so to compare it with the experimental thermogram. A genetic algorithm (GA) is then used to identify the parameters of the J(T) function by minimizing a least squares objective function comparing calculated and measured thermograms. This identification procedure is used to determine the crystallization probability of two samples of same composition but of different manufacture. The results are compared with each other as well as with the results obtained through a traditional calorimetric method. These various tests show that GA associated with calorimetry is a useful and easy tool for the determination of the nucleation probability J(T).