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Modeling the cross-section of finned-tube heat exchangers for Latent Heat Thermal Energy Storage Systems used in Carnot Batteries
Get PDFCarnot Batteries are proposed as a solution for the dispatchability problem caused by the growth of fluctuating renewable energy sources. Here, Thermal Energy Storages are combined with thermal power cycles to store electrical energy. In Carnot Battery concepts based on steam power cycles, Latent Heat Thermal Energy Storages (LHTES) are essential components due to their ability to reach high energy densities in a narrow temperature gap thus, allowing nearly isothermal charge and discharge. In LHTES systems, usually storage materials with low thermal conductivities are applied, the identification of effective solutions to transfer heat between the storage material undergoing a phase change and the working fluid is a key challenge, therefore, the development of simulation tools for the analysis of LHTES on different scales is essential for their application in Carnot Batteries
This paper analyses the charge and discharge behavior of four different longitudinal finned-tube heat-exchanger geometries with common fin fraction, as an initial step for the development of a multi-scale simulation tool for the integration of LHTES in Rankine-based Carnot Batteries.
Each fin geometry is analyzed numerically using COMSOL Multiphysics on a two-dimensional model, to obtain their characteristic charge and discharge curves, specifically in terms of the Phase Change Material (PCM) liquid fraction and the heat flux over a given period. A high-melting-temperature PCM eutectic mixture of KNO3-NaNO3 with a melting temperature of 222 °C was selected.
Alternative geometric and thermal performance parameters were proposed as a framework to compare the finned-tube heat exchanger designs. To determine the effectiveness of the proposed parameters to describe each geometry, a correlation between the parameters and the phase change time was made. The average minimum distance (ADmin) between the fin and PCM presented a better correlation compared to the contact perimeter between fins and PCM. Profiles with lower ADmin exhibited higher heat fluxes and lower discharge times due to better material distribution.
The insights gained from this study will be applied to the development of an equivalent resistance model based on the characteristic curves of each fin geometry. This model will be experimentally validated using a currently under-construction test rig
Ionospheric and thermospheric responses to the high-latitude solar eclipse on 10 June 2021
No full textA solar eclipse provides a rare opportunity to study upper atmospheric dynamics, including electrodynamics and coupling processes in the modified ionosphere and thermosphere system, where reduced solar radiation forces changes in the concentration, temperature, and natural wind. We present a multi-instrumental observational study of the high-latitude solar eclipse on June 10, 2021, using simultaneous measurements from incoherent scatter radars, GNSS satellites, and the GRACE-Follow-On satellite. We observed eclipse-induced electron density depletion and recovery in GNSS TEC observations over the European high latitude. Interestingly, the largest TEC depletion displayed a delayed response to the maximum solar obscuration. We used height-resolved measurements of plasma parameters to investigate their altitude variation and relation to TEC. We show that the depletion and recovery profiles of the electron temperature were consistent with the eclipse path across a wide range of F-region altitudes, while the electron density at higher altitudes showed delayed responses and persistent depletion after the maximum solar obscuration, which may explain the delayed behavior of GNSS TEC. Additionally, we show a concurrent decrease in the thermospheric neutral mass density by a few tens of percent from GRACE-FO satellite measurements in the polar region during the eclipse. We discuss how the depleted neutral density may further prolong the TEC recovery time
Übungsserie EUROMED: Eine Großübung aus der Vogelperspektive
Get PDFDamit die Übungsleitung während der Durchführung der EUROMED stets den Überblick behalten konnte, kamen zur Unterstützung des Stabes verschiedene luftgestützte Führungsmittel zum Einsatz. Im Rahmen der EUROMED-Übungsserie stellen wir in diesem Artikel drei eingesetzte Systeme vor: den Zivilschutzhubschrauber, ein Kamerasystem für hochauflösende Luftbildaufnahmen (VABENE) und die Satellitenfernerkundung. Nach Abschluss der Übung wertete das Deutsche Zentrum für Luft- und Raumfahrt (DLR) zudem die erhobenen Daten umfassend aus. Die gesammelten Erfahrungen und Ergebnisse lassen sich hierbei nicht nur für die Verbesserung einer Übungssteuerung, sondern auch in der Ad-hoc-Anwendung bei realen Einsatzszenarien verwenden
The digital urban frontier: Disparities in social media activity between consolidated and newly urbanized areas in Africa
No full textAfrica’s cities can be seen as the sites of the world’s current urban frontier, where potentials for urban growth and digital transformation are high. This study compares older and newer urban areas in Africa to investigate whether there is a digital divide in social media activity between them. Across 135 sites in Africa’s fastest-expanding cities, we identify age of built-up areas using remote sensing data and relate it to social media activity, measured by the density of geotagged tweets. We quantify disparities in tweet density and use permutation tests, descriptive statistics, and linear regressions to relate them to geographic regions, degrees of urban plannedness, and spatial structure of settlements. Findings show clear evidence of disparities. In most sites, more recently built areas featured significantly lower tweet densities than older ones, while the inverse case was not observed. These disparities were more frequent in Western Africa than in Northern and Southern Africa and decreased with increased plannedness and compactness of the settlement structure. We conclude that in many African cities, the digital urban frontier is lagging behind the physical one, creating a hitherto undocumented form of digital divide that should be considered in plans for the transformation of Africa’s cities
Identification of the potential for roof greening using remote sensing and deep learning
No full textUnder the mounting pressure from global warming, green roofs emerge as a valuable source for climate adaptation, particularly in compact metropolises where green space is limited. Consequently, there is a need to quantitatively evaluate the potential for roof greening where it is most needed and suitable. Despite the increasing importance of this issue, there have been limited studies on the effectiveness of remote sensing and deep learning in identifying the potential for roof greening in many cities. To address this, we have created a GreenRoof dataset, comprising approximately 6400 pairs of remote sensing images and corresponding masks of roofs with high greening potential in four European cities. Afterward, we exploit the capabilities of deep learning methods to identify roofs that are suitable for greening from remote sensing images. Using 15 German cities as a case study for future urban rooftop planning, we estimate the spatial potential for retrofitting green roofs.
Structural parameters for prioritizing green roof implementation include vegetation coverage, thermal environment, and building density. Results indicate that the total area suitable for green roof retrofitting exceeds 20
% of the roof area in the 15 German cities examined. The spatial analysis effectively reflects variation in demand and suitability for green roof retrofitting across different cities. In conclusion, this study provides a versatile screening approach utilizing remote sensing, deep learning, and spatial analysis, which can be readily adapted to inform municipal policies in other cities aiming to promote green roofs and enhance sustainable urban development
Remote Operation in Teleoperated Railways: Impact of a Supplementary Task, Attention-Guiding Take-Over Requests and Work Experience on Situational Awareness and Workload
No full textBackground: Remote railway operations can improve efficiency and reduce costs, but operators must still intervene when onboard systems reach their limits, requiring high levels of situational awareness (SA). Passive monitoring can affect SA, especially under low workload conditions. This study on SA and workload in remote train operation explores the effects of a supplementary task (ST) intended to maintain engagement, potentially at the cost of SA. It also examines whether attention-guiding takeover requests (AGTORs) and train-driving experience can mitigate these effects.
Methods: A mixed design online study was conducted with 160 participants, including 28 active train drivers. Participants completed two blocks, one with an ST and one without, and were randomly assigned to receive either AGTORs or simple warning tone takeover requests. Each block featured four eight-second video scenarios in which participants had to identify the reaons for the takeover and assess additional information from a dynamic remote environment. SA was measured using takeover reason recognition and SAGAT questionnaires. Additionally, workload after each block and a number of additional variables were assessed. Data were analyzed using mixed linear and logistic regression models.
Results: Engagement in the ST reduced recognition of takeover reasons but increased SAGAT scores. The ST condition also led to higher workload scores, though levels were above optimal across both conditions. AGTORs significantly improved recognition performance regardless of the ST condition. No significant performance differences were found between train drivers and non-train drivers. Additionally, age was negatively associated with SA, and participants evaluated the remote environment favourably.
Discussion: The study highlights the benefits and challenges of STs in remote train operations. Working on an ST led to higher SAGAT scores, suggesting a benefit for maintaining perception-level SA. However, it also resulted in fewer recognized takeover reasons, potentially reflecting task-switching costs and reduced comprehension-level SA. A promising design direction to tackle this might be AGTORs, that, in this study, improved takeover reason detection without affecting overall SA. Previous experience did not show beneficial effects, but this might be due to the small train driver sample size. Future research might investigate the effects of experience, using a larger sample and more complex scenarios. Overall, this study provides a valuable insight into the challenges associated with remote train operation and offers solutions in the form of maintaining engagement through STs and compensating switching costs with AGTORs to support operators in takeover situations
Flame-retardant impregnation of flexible hybrid-silica marshmallow aerogels for lightweight transportation
No full textOne of the main drawbacks for hybrid-silica aerogels is their flammability, an inherent property of the organic groups which severely limits their potential. This research is an important step to produce viable aerogels and take advantage of their low thermal conductivity and very low density, for example as lightweight insulation material used in aircraft cabins or other vehicles. Within this work, three different flexible hybrid-silica aerogel systems with different shapes and densities were investigated towards their burn behavior before and after soaking with the flame-retardant triphenyl phosphate (TPP). For this, different concentrations and evaporation temperatures were used before ultimately burning the samples while tracking the duration of the different fire stages. This data was used to calculate their flammability and overall performance for lightweight application in airplanes. In addition to this, other pre- and postburn analysis like IR, TGA or melting behavior were performed. In the end, we were able to produce promising samples with good flame-retardancy at only minimal increase in density, an overall key combination useful for many different applications
Tree species from space: a new product for Germany based on Sentinel-1 and -2 time series
No full textGerman forests are increasingly threatened by climate change, highlighting the need to understand tree species composition to preserve biodiversity, ecosystem resilience and climate regulation. Assessing tree species distribution is essential for effective forest management and adaptation to changing environmental conditions. The current remote-sensing-based dominant tree species products for Germany are based on reference data from the National Forest Inventory (NFI). The NFI data for Germany is not accessible to the general public, due to considerations pertaining to the safeguarding of individual privacy and the avoidance of unintended disruption to the dataset. Information on specific tree species can also be obtained from alternative sources. We collected a total of over 80 000 samples on dominant tree species across Germany by utilizing a range of databases, including city tree registers, Google Earth Pro, Google Street View, and our own on-site observations in order to generate a reference database. Spatio-temporal composites derived from Sentinel-2 (S2) and Sentinel-1 (S1) satellites, combined with a digital elevation model (DEM), were utilized to generate products showcasing the distribution of 10 specific tree species groups across Germany in 2022. This approach enabled continuous mapping of dominant tree species at a 10-m resolution. The accuracy of different machine learning algorithms was assessed using various data combinations. The combination of S2, S1, and DEM yielded the highest overall F1-Score of 0.89. S2 alone achieved results that were nearly as accurate with an F1-Score of 0.86. The optimal model (S2-S1-DEM) demonstrated an F1-Score range of 0.76 to 0.98 for the four primary tree species (pine, spruce, beech, and oak). For other common tree species, including birch, alder, larch, Douglas fir, and fir, the F1-Score ranges from 0.88 to 0.96. Here, we present a cost-effective and reproducible method for monitoring tree species in response to the rapid changes occurring in German forests
Signatures of Polar Vortex Weakening in the MLTI: A Review
No full textThis paper is a collaborative effort that originated at the International Space Science Institute Workshop on “Physical links between Weather and Climate in Space and the Lower Atmosphere” held 22–26 January 2024. Many scientists attended that workshop and contributed their expertise related to polar vortex impacts on upper atmosphere variability. This paper summarizes well-known and newly reported signatures of polar vortex weakening on mesosphere–lower-thermosphere (MLT) temperature, winds, composition, planetary waves, gravity waves, tides, and ionospheric foF2. A variety of observational and modeling results are shown and are consistent with previously published variations in the dynamical and chemical state of the MLT and ionosphere during weak vortex events. We present Superposed Epoch Analysis (SEA) of upper atmosphere diagnostics and phenomena where day 0 is the onset of major SSWs. We also present SEAs where day 0 is the onset of stratopause warmings followed by elevated stratopause events. Our goal in performing two SEAs is to test the sensitivity of 10 hPa versus 1 hPa winds to predict upper atmosphere variability. Results suggest that zonal winds and the semidiurnal migrating solar tide (SW2) in the MLT are more sensitive to zonal wind reversals at 1 hPa rather than 10 hPa. Alternatively, the non-migrating DW2 tide in the equatorial upper mesosphere is best predicted by planetary wave-1 amplitudes in the winter high-latitude upper stratosphere rather than zonal wind reversals. A notable aspect of both SEAs is extremely large event-to-event variability in all diagnostics. Thus, conclusions drawn based on any one event are less robust than those based on many events