153 research outputs found

    Transient climate change scenario simulation of the Mediterranean Sea for the 21st century using a high-resolution ocean circulation model

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    International audienceA scenario of the Mediterranean Sea is performed for the 21st century based on an ocean modelling approach. A climate change IPCC-A2 scenario run with an atmosphere regional climate model is used to force a Mediterranean Sea high resolution ocean model over the 1960-2099 period. For comparison, a control simulation as long as the scenario has also been carried out under present climate fluxes. This control run shows air-sea fluxes in agreement with observations, stable temperature and salinity characteristics and a realistic thermohaline circulation simulating the different intermediate and deep water masses described in the literature. During the scenario, warming and saltening are simulated for the surface (+3.1°C and +0.48 psu for the Mediterranean Sea at the end of the 21st century) and for the deeper layers (+1.5°C and +0.23 psu on average). These simulated trends are in agreement with observed trends for the Mediterranean Sea over the last decades. In addition, the Mediterranean thermohaline circulation (MTHC) is strongly weakened at the end of the 21st century. This behaviour is mainly due to the decrease in surface density and so the decrease in winter deep water formation. At the end of the 21st century, the MTHC weakening can be evaluated as -40% for the intermediate waters and -80% for the deep circulation with respect to present-climate conditions. The characteristics of the Mediterranean Outflow Waters flowing into the Atlantic Ocean are also strongly influenced during the scenario

    Validation of a Modelica numerical model for pillow plate heat exchangers using phase change material

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    Refrigeration systems are often installed in industrial facilities where the difference between the peak and average thermal loads can be considerable due to the throughput of products and changes in the ambient conditions throughout the year. Cold Thermal Energy Storage (CTES) technologies can be introduced to increase the flexibility of such installations by decoupling the supply and demand of refrigeration. CTES systems based on the latent heat storage principle using Phase Change Materials (PCM) are preferred over sensible heat storage due to higher compactness, operation over a narrow temperature range and ability to tailor the storage temperature to each specific application. The current study presents a numerical model of a CTES unit using PCM as the storage medium and CO2 as refrigerant. The heat exchanger in the CTES unit consists of a stack of pillow plates immersed into a stainless-steel container filled with PCM. The charging and discharging processes of the PCM-CTES unit are carried out through evaporation and condensation of the CO2 circulating inside the plates, respectively. The dynamic model of the PCM-CTES unit is developed in the object-oriented programming language Modelica using the component library TIL-Suite. The model of the PCM-CTES unit is validated by using previously published experimental data from a test facility with an identical setup. Various heat exchanger configurations, storage medium and refrigerant parameters are tested, and the model demonstrates good agreement with the experimental data.Validation of a Modelica numerical model for pillow plate heat exchangers using phase change materialacceptedVersio

    Cold storage using phase change material in refrigerated display cabinets: experimental investigation

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    Refrigerated display cabinets are the main energy consumers in supermarkets. Cold thermal energy storage (CTES) using phase change materials (PCM) can significantly reduce temperature variations in a display cabinet during loading of warm items, defrost cycles or power outages. This contributes to reduced loss in product quality and less food being wasted. With an increasing share of intermittent renewables in the power grid, PCM-enhanced systems benefit from low-cost electricity during periods with low demand. Stored excess cooling can be later used during periods with high demand. A CTES prototype was developed using water as PCM integrated in an evaporator. This system was experimentally compared to a reference case not using the PCM capabilities. The results show the potential for PCM-CTES to consistently keep the cabinet air temperature low, thus prolonging shelf life and product quality. Charged PCM-CTES systems provide cooling for several hours after the main evaporator is deactivated. Keywords: Refrigerated Display Cabinet, Thermal Energy Storage, Cold Storage, Phase Change Material, Supermarket Refrigeration, Defrost Cycle.acceptedVersio

    Impact of the ocean-atmosphere coupling on high-resolution future projections for the Mediterranean sea and surrounding climate from the Med-CORDEX ensemble

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    Med-CORDEX is an international initiative that aims at developing fully coupled high resolution Regional Climate System Models (RCSMs) for the Mediterranean basin. After 11 years of work an ensemble of more than 25 multi-model and multi–scenario climatic simulations is now available (Darmaraki et al., 2019; Soto-Navarro et al., 2020). In this study, we analyze the impact of the high-resolution representation of the Mediterranean Sea and of the interaction between ocean and atmosphere, explicitly resolved in the Med-CORDEX simulations, in the projected evolution of the most relevant climatic variables for the Mediterranean basin and the adjacent regions during the 21st century. The final goal is to quantify up to what extent including the explicit and high-resolution representation of the ocean-atmosphere coupling is relevant for regional climate projections. The preliminary results show that, in general, higher resolution coupled simulations project a lower increase in the Sea Surface Temperature (SST) than lower resolution runs. This translates in a smaller input of heat and humidity to the atmosphere that, in turn, affect the cloud cover and precipitation over the basin and the adjacent continental areas. These changes are the result of a better representation of the Mediterranean Sea functioning in the Med-CORDEX RCSMs. In particular, they resolve better the mesoscale processes of the basin, which are partly responsible of the heat transport from the surface to deeper layers, and the ocean-atmosphere feedback that regulates the heat exchange

    The MED-CORDEX ensemble future climate projections for the Mediterranean Sea: impacts of the high resolution and ocean-atmosphere coupling

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    Med-CORDEX is an international initiative that aims at developing fully coupled high resolution Regional Climate System Models (RCSMs) for the Mediterranean basin. After 11 years of work an ensemble of more than 25 multi-model and multi–scenario climatic simulations is now available. In this study, we analyze the impact of the high-resolution representation of the Mediterranean Sea and of the interaction between ocean and atmosphere, explicitly resolved in the Med-CORDEX simulations, in the projected evolution of the most relevant climatic variables for the Mediterranean basin and the adjacent regions during the 21st century. The final goal is to quantify up to what extent including the explicit and high-resolution representation of the ocean-atmosphere coupling is relevant for regional climate projections. The preliminary results show that, in general, higher resolution coupled simulations project a lower increase in the Sea Surface Temperature (SST) than lower resolution runs. This translates in a smaller input of heat and humidity to the atmosphere that, in turn, affect the cloud cover and precipitation over the basin and the adjacent continental areas. These changes are the result of a better representation of the Mediterranean Sea functioning in the Med-CORDEX RCSMs. In particular, they resolve better the mesoscale processes of the basin, which are partly responsible of the heat transport from the surface to deeper layers, and the ocean-atmosphere feedback that regulates the heat exchange.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

    Representation of spatial and temporal variability of daily wind speed and of intense wind events over the Mediterranean Sea using dynamical downscaling: impact of the regional climate model configuration

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    Atmospheric datasets coming from long term reanalyzes of low spatial resolution are used for different purposes. Wind over the sea is, for example, a major ingredient of oceanic simulations. However, the shortcomings of those datasets prevent them from being used without an adequate corrective preliminary treatment. Using a regional climate model (RCM) to perform a dynamical downscaling of those large scale reanalyzes is one of the methods used in order to produce fields that realistically reproduce atmospheric chronology and where those shortcomings are corrected. Here we assess the influence of the configuration of the RCM used in this framework on the representation of wind speed spatial and temporal variability and intense wind events on a daily timescale. Our RCM is ALADIN-Climate, the reanalysis is ERA-40, and the studied area is the Mediterranean Sea. <br><br> First, the dynamical downscaling significantly reduces the underestimation of daily wind speed, in average by 9 % over the whole Mediterranean. This underestimation has been corrected both globally and locally, and for the whole wind speed spectrum. The correction is the strongest for periods and regions of strong winds. The representation of spatial variability has also been significantly improved. On the other hand, the temporal correlation between the downscaled field and the observations decreases all the more that one moves eastwards, i.e. further from the atmospheric flux entry. Nonetheless, it remains ~0.7, the downscaled dataset reproduces therefore satisfactorily the real chronology. <br><br> Second, the influence of the choice of the RCM configuration has an influence one order of magnitude smaller than the improvement induced by the initial downscaling. The use of spectral nudging or of a smaller domain helps to improve the realism of the temporal chronology. Increasing the resolution very locally (both spatially and temporally) improves the representation of spatial variability, in particular in regions strongly influenced by the complex surrounding orography. The impact of the interactive air-sea coupling is negligible for the temporal scales examined here. Using two different forcing datasets induces differences on the downscaled fields that are directly related to the differences between those datasets. Our results also show that improving the physics of our RCM is still necessary to increase the realism of our simulations. Finally, the choice of the optimal configuration depends on the scientific objectives of the study for which those wind datasets are used

    Cold thermal energy storage in solid-liquid transition of carbon dioxide: Investigating the possibility

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    Industrial freezing is an energy-intensive process which is growing due to the increasing demand. This is exerting stress on electrical grids, especially at peak hours. To tackle this issue, thermal energy storage has received attention; however, there is a gap in terms of suitable materials for thermal energy storage with temperatures below -40 °C commonly needed in these applications. In this paper, the solid-liquid phase change of carbon dioxide has been conceptually considered for thermal energy storage in a special type of heat exchangers known as pillow plate heat exchangers. Characteristically, these heat exchangers can withstand very high pressures which is a technical requirement for carbon dioxide thermal energy storage. This paper discusses the potential system layout and challenges ahead of this technology, along with the proposal for further investigation to verify the concept.Cold thermal energy storage in solid-liquid transition of carbon dioxide: Investigating the possibilityacceptedVersio

    Fourteen months operation of a 200 kWh latent heat storage pilot

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    A latent heat storage was in 2021 installed in an office building in Trondheim, Norway. The unit contains 3 tons of CrodaTherm 37, which is a bio-based wax phase-change material with a melting temperature of 37 degrees Celsius. The thermal energy storage can be charged from heat pumps or district heating and can be discharged to domestic hot water, radiators, ventilation, or heat pumps. This unit has been collecting data on operations for over 14 months. The total thermal energy capacity was measured to be 226 kWh, and the average discharge rate over 12.2 hours of 10.51 kW and average charge rate over 11 hours of 13.7 kW was measured. An average temperature reduction of 47.3 to 38 Celsius over 234 hours during storage was measured. The average heat loss was measured to be 64 W, or 0.68% of the total capacity per day.Fourteen months operation of a 200 kWh latent heat storage pilotacceptedVersio

    Factors affecting emission measurements from residential wood combustion

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    Simultaneous gravimetric filter sampling of particulate matter in flue gas from chimney and diluted flue gas from dilution tunnel, on hot filter (≥ 70 ˚C) and on ambient filter (≤ 35 ˚C) respectively, to determine to which extent variables inherent to EN 13240 DIN+ and NS3058-59 affect the amount of measured particulate matterpublishedVersio

    Effect of maintenance on particulate emissions from residential woodstoves

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    -Literature review and test results from particulate matter measurements based on Norwegian Standard NS 3058-59 coupled with EC and OC analyses on an artificially aged woodstove
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