Numerical investigation of energy potential and performance of a residential building-integrated solar micro-CHP system

International audienceThe studied micro-CHP unit converts concentrated solar energy into electricity and heat by coupling a 46.5 m² parabolic trough collector with an oil-free single-cylinder steam engine operating according to the Hirn cycle. Originalities of this system are two axis solar tracking and direct steam generation. The exhaust heat of the cycle is recovered to cover building's heat needs, while the electricity is either self-consumed or fed back into the electricity grid. Experimental studies have shown that it is impossible to achieve continuous operation of the facility without an additional heat source. Thus, we are studying solutions for integrating a backup heating system from dynamic thermal simulations performed with TRNSYS© software One of them consists in adding a 30 kW boiler to the primary circuit in order to ensure daily electricity production. However, this is restricted by the considered storage tank. A parametric study on the volume of the storage tank makes it possible to propose an optimal solution for heat recovery. The results indicate that a storage volume of 3 m 3 meets the needs of the building and limits the heat losses due to heat storage. In order to optimize the use of such a micro-CHP unit, a heat sharing between several buildings equipped with 3 m 3 storage seems therefore to be a coherent solution

Modelling heat and mass transfer in bread baking with mechanical deformation

International audienceIn this paper, the thermo-hydric behaviour of bread during baking is studied. A numerical model has been developed with Comsol Multiphysics© software. The model takes into account the heat and mass transfers in the bread and the phenomenon of swelling. This model predicts the evolution of temperature, moisture, gas pressure and deformation in French “baguette” during baking. Local deformation is included in equations using solid phase conservation and, global deformation is calculated using a viscous mechanic model. Boundary conditions are specified with the sole temperature model and vapour pressure estimation of the oven during baking. The model results are compared with experimental data for a classic baking. Then, the model is analysed according to physical properties of bread and solicitations for a better understanding of the interactions between different mechanisms within the porous matrix

Resilient cooling strategies – A critical review and qualitative assessment

The global effects of climate change will increase the frequency and intensity of extreme events such as heatwaves and power outages, which have consequences for buildings and their cooling systems. Buildings and their cooling systems should be designed and operated to be resilient under such events to protect occupants from potentially dangerous indoor thermal conditions. This study performed a critical review on the state-of-the-art of cooling strategies, with special attention to their performance under heatwaves and power outages. We proposed a definition of resilient cooling and described four criteria for resilience—absorptive capacity, adaptive capacity, restorative capacity, and recovery speed —and used them to qualitatively evaluate the resilience of each strategy. The literature review and qualitative analyses show that to attain resilient cooling, the four resilience criteria should be considered in the design phase of a building or during the planning of retrofits. The building and relevant cooling system characteristics should be considered simultaneously to withstand extreme events. A combination of strategies with different resilience capacities, such as a passive envelope strategy coupled with a low-energy space-cooling solution, may be needed to obtain resilient cooling. Finally, a further direction for a quantitative assessment approach has been pointed out

Optimal Operating Conditions of Microwave−Convective Drying of a Porous Medium

International audienc

Modélisation multiphysique des transferts de masse et de chaleur dans un milieu poreux déformable non saturé (application à la cuisson du pain)

Ces études concernent l amélioration de l efficacité énergétique des fours de boulangerie utilisés pour la cuisson de baguette traditionnelle . Au cours de la cuisson, la pâte fermentée se transforme en mie avec des modifications importantes du milieu. Les apports de chaleur induisent différentes réactions physico-chimiques au sein de la pâte (production de C02, gélatinisation) qui se traduisent par une évolution de la structure alvéolaire et des mécanismes physiques. Puis on assiste en périphérie à la formation de croute. Les travaux ont porté sur le développement et la validation d un modèle macroscopique multiphysique capable de prédire le comportement transitoire du produit de l état de pâte à celui de mie et de croûte. On s est en particulier intéressé à la cuisson sur sole de baguettes. Le produit est alors soumis à des apports de chaleur par conduction directe, convection et rayonnement infrarouge. Une injection de vapeur est en plus réalisée à l enfournement de la pâte. Les variables d état retenues sont la température, la teneur en eau, la pression de gaz, la fraction de gaz et le déplacement. Les propriétés utilisées sont dépendantes des variables d états et de la structure du produit. Ces études numériques sont confortées par l exploitation de mesures expérimentales réalisées sur un four instrumenté. L analyse des évolutions des variables d état montre la nécessité de disposer d une bonne base de données sur les propriétés macroscopiques du produit lors de sa transformation. Dans la dernière partie de cette étude, le modèle numérique est utilisé afin d étudier différentes approches possibles d amélioration de l efficacité énergétique: diminution des températures du four, exploitation de nouveaux modes de chauffage.These studies relate to improving the energy efficiency of bakery ovens used for baking bread. During baking, the dough becomes crumb with significant changes in the media. Heat transfer induce different physico-chemical reactions in the dough which result in a change of the cellular structure and physical mechanisms. Then crust is created in the external part. The work focused on the development and validation of a multiphysic macroscopic model capable of predicting the transient behavior of the product. We were particularly interested in the baking bread on sole. The product is then subjected to heat transfer by conduction, convection and infrared irradiation. Steam injection is performed at the dough introduction in the oven. The state variables used are the temperature, the water content, the gas pressure, the gas fraction and the displacement. The properties used are dependent with the state variables and product structure. The numerical model is solved by a finit element method (Comsol Multiphysics ®). These numerical studies are supported by the use of experimental measurements performed on instrumented oven. The analysis of the evolution of state variables shows the need to have a good database on the macroscopic properties of the product during processing. In the last part of this study, the numerical model is used to study different approaches for improving energy efficiency: lower oven temperatures, use of new modes of heating.LORIENT-BU (561212106) / SudocSudocFranceF

Étude du comportement thermohydrique de matériaux "chanvre-chaux" lors de la phase de séchage (estimation par technique inverse des propriétés hydriques)

Les travaux développés dans cette thèse ont porté sur l étude des mécanismes de transfert de chaleur et de masse au sein de matériaux chanvre-chaux . L objectif était d élaborer et de valider un modèle prédictif du comportement thermohydrique de ces matériaux au jeune âge (phase de séchage) en ayant recours aux techniques inverses pour l estimation de propriétés difficilement mesurables. Des études expérimentales ont été effectuées afin de déterminer les propriétés thermo-physiques des matériaux nécessaires à la simulation. Les cinétiques de séchage ont été établies dans le cas du séchage convectif sur une face. L enregistrement automatique des mesures a permis de disposer des évolutions au cours du temps de la masse, des températures et des conditions réelles subies par les échantillons. En parallèle à ces études expérimentales, un modèle permettant de décrire le comportement de ces produits lors du séchage convectif a été développé. Les coefficients de transfert hydrique ont été estimés à partir de cinétiques de séchage convectif obtenues expérimentalement. La méthode inverse utilisée est basée sur l'algorithme SQP (Programmation Quadratique Successive), elle a permis d'identifier les propriétés hydriques des liant et des mélanges chanvre/chaux dans différentes conditions et de mettre en évidence les améliorations à apporterThe works developed in this thesis are focused on the mechanisms of heat and mass transfer in "hemp-lime" materials. The objective was to develop and validate a predictive model of thermo-hydrous behaviour of these materials at early age (drying phase) and use inverse techniques for estimating properties which are difficult to measure. Experimental studies were conducted to determine the thermo-physical properties of materials required for the simulation. The drying kinetics were also established in the case of one side convective drying. The automatic registration of the measurements has allowed obtaining the evolution with time of the mass, temperature and the conditions experienced by the samples. In parallel to these experimental studies, a mathematical model to describe the behaviour of these products during convective drying has been developed and moisture transfer coefficients were estimated by inverse method from convective drying kinetics obtained experimentally. This inverse method based on the SQP algorithm (successive quadratic programming), is allowed to identify the hydrous properties of binder and "hemp-lime" mixture under different conditions and highlight areas for improvement.LORIENT-BU (561212106) / SudocSudocFranceF

Study of the Drying Behavior of Poly(vinyl alcohol) Aqueous Solution

International audienc

Optimal operating conditions of microwave-convective drying of a porous medium

International audienc