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La rupture de la chaîne du froid est responsable de pertes alimentaires qui génèrent un coût économique et environnemental non négligeable. Cette rupture provoque une remontée en température des produits alimentaires et peut entraîner un risque sanitaire élevé pour le consommateur en particulier pour certains produits fragiles (viande hachée, poisson par exemple). Une solution pour ralentir le réchauffement consiste à utiliser des matériaux à changement de phase (MCP) dans des emballages ; ces matériaux lors de leur fusion deviennent une source de production de froid (de par sa chaleur latente de fusion) et permettent de maintenir pendant un certain temps le produit dans les bonnes conditions de conservation (température réglementaire). Toutefois, cette solution nécessite d'une part de trouver le(s) « bons » MCP avec les propriétés convenables à l'application « emballage » et d'autre part une mise en forme adéquate de ces matériaux permettant de supporter le changement de phase solide/liquide. En effet, le MCP doit à la fois apporter une inertie thermique dans la gamme de température de conservation (0-8 $^{\circ}$C, au voisinage du produit) et limiter le flux de chaleur entrant dans l'emballage (résistance thermique à la température ambiante). Si un seul MCP est utilisé, se pose alors la question du choix de sa température de fusion : doit - elle être inférieure à la température de conservation (au risque de congeler le produit), ou un peu plus élevée pour mieux résister au apports thermiques extérieurs. Concernant la mise en forme, certaines études récentes ont exploré la possibilité d'incorporer sous forme de microgouttes dans un film une fraction volumique importante de MCP. Cependant, une autre question se pose sur la quantité « optimale » du MCP à incorporer. Dans ce travail, un dispositif expérimental a été développé afin de tester 2 configurations d'emballages contenant des MCP: les films biosourcés (amidon) intégrant des MCP et un système dans lequel les MCP ont été déposés en son état naturel (bulk). Pour chaque configuration, plusieurs quantités de MCP et 2 MCPs (température de fusion à 5 $^{\circ}$C et à 18 $^{\circ}$C) ont été testés. En parallèle de ce travail expérimental, un modèle dynamique a été développé pour prédire l'évolution du même système étudié expérimentalement pendant un réchauffement (de 0 $^{\circ}$C à 30 $^{\circ}$C). Ce modèle a pris en compte plusieurs éléments du système (parois, MCP et produit test), différents modes de transfert thermique (conduction dans les parois, convection entre l'air et produit et entre l'air et les parois…) et le changement de phase du MCP. Il a été validé par des résultats expérimentaux de plusieurs configurations (films d'amidon avec/sans MCP, MCP en bulk…). Ce modèle a été également utilisé afin de prédire les caractéristiques optimales de la protection thermique pour des configurations différentes de celles testées expérimentalement, selon les critères thermiques attendus.

International audience

International audience

International audience

International audience

International audience; Electrical Energy Storage (EES) technologies have received considerable attention over the last decade because of the need to reduce greenhouse gas emission through the integration of renewable energy sources. Renewable sources have an intermittent power output to the electrical grid, thus EES represents a strategic solution in balancing electrical grids and enables the decarbonisation of the energy sector. Cryogenic Energy Storage (CES) is a novel method of EES falling within the thermo-mechanical category. It is based on storing liquid cryogenic fluids after their liquefaction from an initially gaseous state. A particular form of CES, Liquid Air Energy Storage (LAES), has gained growing attention respect to other cryogens. The current state of LAES is still at the development and demonstration stage since no commercial or pre-commercial plants have been built. This technology has been developed in different ways throughout its history (from 1977), and, to the best of our knowledge, no review paper has been published so far about the CES topic. Therefore, the present paper intends to provide a clear picture of the CES/LAES virtues in the literature as well as the challenges associated to the system to be commercially viable. For this purpose, this review includes: an investigation of the properties of cryogens and different CES processes as well as the main ways the system could be combined to other facilities to further enhance the energy efficiency, in particular the combination to a refrigerated warehouse with cold energy recovery from the cryogen evaporation.

International audience; Taking into consideration all the life cycle of a product is now an important step in the design of a product or a technology. Despite the improvement in refrigerant regulation, the environmental impacts of refrigeration systems remain important and need to be improved. In this paper, the environmental impacts of refrigeration systems in a typical hypermarket are compared using the LCA methodology under different conditions. The system is used to provide cold at two levels of temperature: medium and low temperature during a life period of 15 years. The most commonly used architectures of hypermarket cold production systems are investigated: centralized direct expansion systems and indirect systems using a secondary loop to transport the cold. The variation of power needed during seasonal changes and during the daily opening/closure periods of the hypermarket are considered. R134a as the primary refrigerant fluid and two types of secondary fluids are considered (liquid CO2 and ammonia). The composition of each system and the leakage rate of the refrigerant through its life cycle are taken from the literature and industrial data. Twelve scenarios are examined. They are based on the variation of three parameters, 1. location: France (Paris), Spain (Toledo) and Sweden (Stockholm), 2. different sources of electric consumption: photovoltaic panels and low voltage electric network and 3. architecture: direct and indirect refrigeration systems. SimaPro software was used to assess the environmental performances and different impact assessment methods were used; CML method is used to evaluate the midpoint environmental indicators and IMPACT 2002+ to assess endpoint indicators. This study highlights the most environmentally damaging parameter to be electric consumption compared to the impacts of refrigerant leakage supporting the conclusions of previous studies. The use of a secondary loop lowers the refrigerant amount in the primary loop and thus the climate change indicator is reduced. The cost estimation of CAPEX and OPEX shows that depending on the location the use of photovoltaic panels can be more expensive and does not bring any improvement in environmental impacts.

International audience; The preservation of perishable food via cold supply chain is essential to extend shelf life and ensure food safety. However, the use of refrigeration processes requires energy consumption with economic and environmental impact. Increasing the temperature set point in cold equipment could save energy, but the global cost may increase due to food waste or safety issues. The study of potentially conflicting objectives such as food safety, food waste, and energy consumption may be challenging because the comparison between the outcomes of those objectives (risk of illness, amount of food waste, energy consumption in kWh). Methodologies leading to overcome issues involving conflicting impacts and the knowledge of their limitations are essential to support decision makers. This study focuses on the modeling of the energy consumption of cold facilities, food temperature, food contamination and growth of Listeria monocytogenes and lactic acid bacteria in a puff pastry plant. An event based framework was used to model the main components of the production line (kneader, conveyor, cooling spiral and cold room). Own-checks (microbial and temperature) data from food industry premises were used to inform and parameterize the model. Different scenarios were tested to evaluate the impact of operating conditions (setting temperature and duration) on energy consumption, food waste and food safety. Results showed that the temperature setting of the cooling spiral had a low impact on energy consumption and a high impact on the microbial quality. The opposite phenomena were observed in the cold room with a moderate impact of the cold room temperature setting on the food microbial quality and a high impact on energy consumption. Finally, a multi-criteria decision analysis approach is proposed to identify the optimal operating conditions regarding the three criteria. Criteria weights were set by the operators of the food plant (quality manager, production manager, energy advisor and plant director). This methodology helps manufacturers in decision making to optimize operating conditions and reduce energy consumption with a limited impact on food waste and safety.

International audience; The preservation of perishable food via cold supply chain is essential to extend shelf life and ensure food safety. However, the use of refrigeration processes involves energy consumption with economic and environmental impact. Increasing the temperature set point in cold equipment could save energy, but the global cost may increase due to food waste or safety issues. This study focuses on the modeling of the energy consumption of cold facilities, food temperature and bacterial growth in a puff pastry plant. Main components of production line (kneader, cooling spiral and cold room) were considered. Different scenarios were tested to evaluate the impact of operating conditions (setting temperature and duration) on energy consumption, food waste and food safety. This methodology helps manufacturers in decision making to optimize operating conditions and reduce energy consumption with a limited impact on food waste and safety.

International audience

International audience

International audience; The preservation of perishable food via refrigeration in the supply chain is essential to extend shelf life and provide consumers with safe food. However, electricity consumed in refrigerationprocesses has an economical and an environmental impact. This study focuses on the cold chain of cooked ham, including transport, cold room in supermarket, display cabinet, transport by consumer, and domestic refrigerator, and aims to predict the risk for human health associated with Listeria monocytogenes, the amount of food wasted due to the growth of spoilage bacteria, and the electrical consumption to maintain product temperature through the cold chain. A set of eight intervention actions were tested to evaluate their impact on the three criteria. Results show that the modification of the thermostat of the domestic refrigerator has a high impact on food safety and food waste and a limited impact on the electrical consumption. Inversely, the modification of the airflow rate in the display cabinet has a high impact on electrical consumption and a limited impact on food safety and food waste.A cost-benefit analysis approach and two multicriteria decision analysis methods were used to rank the intervention actions. These three methodologies show that setting the thermostatof the domestic refrigerator to 4 °C presents the best compromise between the three criteria. The impact of decisionmaker preferences (criteria weight) and limitations of these three approaches are discussed. The approaches proposed by this study may be useful in decision making to evaluate global impact of intervention actions in issues involving conflictingoutputs.

International audience; A heat and mass transfer model was developed to predict, during the drying of a food processing plant, the evolution of the water mass, wet surface, air temperature and relative humidity. The model was previously validated by comparing the predictions with the experimental results obtained in a food processing plant. Then, this model was coupled with a microbiological model to predict the fate of Listeria monocytogenes (growth or inactivation) at different locations in the plant (floor, wall and equipment). Simulations were carried out for blown air at 50%, 68% and 85% relative humidity in order to study the influence of air dehumidification in the plant on the drying rate and on the evolution of the microbial load. It was found that bacteria are more likely to develop on equipment when the drying time is longer. A technical solution involving heating of the equipment was proposed and the impact on the wet surface and the evolution of the microbial load was presented.

La réfrigération secondaire permet de réduire drastiquement la quantité de frigorigène (à fort potentiel de réchauffement global), et donc les fuites. Les coulis d’hydrate transportent de la chaleur latente délivrée à une température qui peut être adaptée à l’utilisation. Cette étude évalue l’influence de la cinétique du changement de phase sur les performances énergétiques du procédé, et analyse les couplages et les paramètres pilotant cette influence. Les calculs comparent les coulis de glace et d'hydrates de tetra-n-butylphosphonium bromide et expliquent leurs différences de comportement.

International audience; Two-phase fluids are considered as high-performance fluids for secondary refrigeration thanks to high energy density of phase change material (PCM). Nevertheless, one limitation in such system is thermal energy storage dynamic, in particular PCM charging/discharging rate, which depends generally on fluid temperature and flow rate. In the present work, the influence of pressure on the charging/discharging processes of gas hydrates has been studied experimentally using a stirred tank reactor. A model of stirred tank reactor was also developed and validated. The results showed that pressure can be used to adjust gas-hydrate phase-change temperature and consequently to improve charging/discharging time. For the same working conditions (temperature, flow rate, charging time…), the amount of stored energy using gas hydrates at 3 MPa is two times higher than that using water. The model was used to compare gas hydrates slurries to other slurries at ambient pressure.

International audience; Two-phase fluids are considered as high-performance fluids for secondary refrigeration thanks to high energy density of phase change material (PCM). Nevertheless, one limitation in such system is thermal energy storage dynamic, in particular PCM charging/discharging rate, which depends generally on fluid temperature and flow rate. In the present work, the influence of pressure on the charging/discharging processes of gas hydrates has been studied experimentally using a stirred tank reactor. A model of stirred tank reactor was also developed and validated. The results showed that pressure can be used to adjust gas-hydrate phase-change temperature and consequently to improve charging/discharging time. For the same working conditions (temperature, flow rate, charging time…), the amount of stored energy using gas hydrates at 3 MPa is two times higher than that using water. The model was used to compare gas hydrates slurries to other slurries at ambient pressure.

International audience; Secondary refrigeration is an often used solution to reduce the amount of refrigerant leakage and the impact of refrigerants on global warming. The use of two-phase fluids in refrigeration systems is known to increase the quantity of stored energy. In this work, the impact of gas hydrates on the energy release of a heat exchanger is quantified thanks to the dynamic modelling of a secondary refrigeration system. The system is composed of a chiller, a stirred tank reactor (hydrate formation), a loop and a heat exchanger (hydrate dissociation). The model validated by experimental data can be used to simulate various operating conditions in transient and permanent regimes (various slurry mass flow rate, various thermodynamic conditions) and to compare their energy performances. The numerical and experimental results showed better heat exchanger efficiency with hydrate slurry than with water alone.

International audience; 50% of the energy consumed in food cold chain is for chilling, freezing and storage steps. For cold storage facilities, refrigeration is the main source of energy consumption with an average of 50 kWh/m3/year. A possible strategy to reduce their energy consumption is to take advantage of the variation of performance of the refrigeration systems during a day due to external and internal temperature variations. Electricity cost can also widely change during a day, depending on the local production. This strategy can be based on additional storage capacities to delay the refrigeration running period, but also on the use of the thermal inertia provided by the storage warehouse itself and the products stored. Using coupled models of the building, products and refrigeration system, potential energy savings of additional thermal storage units in a frozen products warehouse are evaluated.

International audience; Display cabinet is the most widely used equipment to keep food at the required temperature in supermarket. Despite a good design and good control of operating conditions in stores, the heterogeneity of the temperature inside the display cabinet has been observed in several studies. This temperature difference is mainly due to thermal losses through walls, the infiltration of outside air and the heterogeneity of the evaporator temperature. The aim of this work is to develop a transient heat transfer model to study the temperature evolution of loaded products and air inside a display cabinet. The developed model is validated by experimental data obtained with different operating conditions. This model is combined with a model describing the melting and freezing process of a PCM unit located inside the display cabinet. The global model can be used to study the effects of PCM addition on air and food temperatures.

International audience