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Ventilative cooling of residential buildings in China:A simulation-based evaluation of lightweight modular integrated constructions considering climate change
No full textVentilative cooling technology is crucial for achieving low-carbon and resilient buildings, but there is a lack of systematical investigations on its energy performance in emerging lightweight modular integrated constructions (MIC). A residential building model was employed to examine the load demands of lightweight (LWC) and heavyweight constructions (HWC) under five climate zones of China. The impacts of envelope thermal transmittance and ventilative cooling on energy demand were evaluated, not only considering current climate conditions but also extending the assessment to the future weather conditions. The results emphasize the importance of thermal mass in nearly-zero energy building standards. Without implementing ventilative cooling, LWC that meets the same energy-efficiency standards as HWC exhibits lower annual load demand than HWC in all climate zones excluding the mild zone, and the energy-saving benefit can be further enhanced by climate change. There is a turning point of the airflow rate of ventilative cooling, where the cooling demand of LWC exceeds that of HWC, and the value of this turning point increases with climate change. The most economical airflow rate of mechanically ventilative cooling is lower in LWC than HWC excluding the mild zone, and this airflow rate is expected to increase with climate change and reduced energy efficiency of the mechanical cooling system. This study provides valuable insights into advancing MIC towards low-carbon goals
Microstructure evolution of Ni-yttria stabilized zirconia electrodes for solid oxide electrolysis cells:experimental characterization and phase field modeling
No full textThe growing global demand for energy necessitates the widespread adoption of renewable energy sources. To address the intermittent characteristics of renewable energy sources, such as wind and solar energy, numerous energy conversion devices have been developed. Solid oxide cells (SOCs) have generated interest worldwide in the last decades due to the advantages of high efficiency and gas flexibility. Another attractive feature is that the same cell can be operated as either a solid oxide fuel cell (SOFC) for electricity generation or a solid oxide electrolysis cell (SOEC) for fuel production. Despite the numerous advantages of SOCs, the durability during long-term operation has become a major limiting factor for their large-scale commercialization, especially in SOEC mode. The microstructure evolution in the fuel electrode of a single cell has been observed to play a primary role in cell performance degradation. Therefore, quantifying the microstructure evolution during long term operation and understanding the mechanism behind is crucial for the improvement of cell performance and durability. This thesis investigates microstructure evolution of the Ni/yttria stabilized zirconia (YSZ) electrode under different operating conditions through experimental characterizations and phase-field modeling.In order to clarify the mechanism of cell performance degradation, efforts are devoted to the following three aspects in this thesis:➢ Microstructure evolution of the Ni/YSZ electrode in CO2 electrolysis. Extensive studies on microstructure evolution of Ni/YSZ in steam electrolysis have been reported, whereas for CO2 electrolysis the information is rather limited. We characterized Ni/YSZ electrode microstructure before and after 1000 hours CO2 electrolysis. There Ni migrates also toward the support layer and the extent of Ni migration was found to be similar to the one in steam electrolysis. We conclude that the driving force for Ni migration is not necessarily the gradient in the partial pressure of Ni-containing gas species, but the gradient of Ni-YSZ interfacial energy as we and some other researchers speculated.➢ Ni/YSZ electrode microstructure after being exposed to different steam electrolysis conditions (gas composition, current density, and operation duration) and from different positions along the steam/hydrogen flow direction. We further simulated the distribution of local Ni/YSZ electrode overpotential and oxygen partial pressure at the Ni-YSZ interface using an in-house developed multi-physics model. The obtained microstructure characteristicscorrelate well with the electrode and cell electrochemical performance and also with the local and global operating conditions.➢ A modeling framework coupling the multi-physics electrochemical model and the phase field microstructure evolution model. The effect of overpotential on the microstructure evolution of Ni/YSZ electrodes under OCV, in SOFC and in SOEC was investigated first. The reliability of the model framework was validated by comparing simulations with the experimental results. Subsequently, semi-real-time coupling of electrochemical properties with microstructural evolution was also tried out. Only minor difference was found between time-constant and time-adjusted spatial distribution. Considering the reduction in computational efficiency, it was then concluded that real-time coupling is necessary only in long term scale where significant microstructure changes are expected after each simulation time step.This work demonstrates that a combination of experimental characterization and numerical modelling utilizing multi-physics and phase field provides important insights into the mechanisms of Ni redistribution in the Ni/YSZ electrode and the influencing parameters behind. Further development of the computational tool can hopefully lead to optimized Ni/YSZ electrode microstructure with enhanced performance and durability, thus promoting the commercialization of the SOEC technology in the long run
Acid gelation of high-concentrated casein micelles and pea proteins mixed systems
No full textThe increased demand for plant-based products brings a new challenge to the food industry. Especially, proteins from soy, chickpea, and pea are being highly demanded as food ingredients. However, they still present some drawbacks such as poor techno-functional properties and remarkable beany flavor that hamper their wider application. Contrarily, milk products such as yogurt and cheeses are highly consumed and accepted worldwide. Therefore, the association of plant proteins, such as pea with milk proteins is an interesting strategy to incorporate more plant-based proteins into people’s diet. However, this strategy can largely impact gel formation and final structure. This study aims to develop mixed casein micelles (CMs) and pea proteins gel at high concentrations in four protein ratios, 80:20, 60:40, 40:60, and 20:80 by acidification. The effect of a thermal treatment before gelation was also evaluated. The replacement of CMs for pea proteins disturbed the gel formation at the beginning of acidification, demand more time to increase the G*, being this effect more pronounced as more casein is replaced in the system. Despite of this effect, the final gel elasticity was higher in the presence of pea proteins for the ratios 80:20 and 60:40, probably due to the formation of pea network. It is hypothesized that pea proteins can form a network when surrounded by CMs, however, CMs restrict pea proteins aggregation. This study describes that the final characteristics of mixed gels can be tailored by changing protein ratios and applying thermal treatment before acidification, opening the possibility for the development of innovative food products
The secret of the Wilson equation
No full text60 years ago, Grant Wilson proposed the first successful activity coefficient model based on the local composition concept he introduced. The model has received wide acceptance and extensive applicability as it could represent accurately the vapor-liquid equilibria of complex mixtures. It could be readily extended to multicomponent systems without additional parameters and with good results. It has not dominated the chemical engineering practice compared to models proposed a few years after (NRTL and UNIQUAC) possibly due to one important shortcoming. The Wilson equation could never represent liquid-liquid equilibria no matter the values of the model's parameters. While this is well-established, the “physical” reasons behind this deficiency had not been fully explored. This work presents and explores the secret of the Wilson equation related to its ability to predict partial miscibility. It will be established that the capabilities of the Wilson model are possibly broader compared to what was originally thought. The presentation is also inspired by several discussions with professor Michael L. Michelsen over the years which are also cited in the manuscript
Autotrophic degradation of sulfamethoxazole using sulfate-reducing biocathode in microbial photo-electrolysis system
No full textSulfamethoxazole is a representative of sulfonamide antibiotic pollutants. This study aims to investigate the degradation pathways of sulfamethoxazole and the response of microbial communities using the autotrophic biocathode in microbial photo-electrolysis systems (MPESs). Sulfamethoxazole with an initial concentration of 2 mg L−1 was degraded into small molecule propanol within 6 h with the biocathode. Elemental sulfur (S0) was detected in the cathode chamber, accounting for 57 % of the removed sulfate. The conversion from sulfate to S0 indicated that autotrophic microorganisms might adopt a novel pathway for sulfamethoxazole removal in the MPES. In the abiotic cathode, sulfamethoxazole degradation rate was 0.09 mg L−1 h−1 with the electrochemistry process. However, sulfamethoxazole was converted to products that still contain benzene rings, including p-aminothiophenol, 3-amino-5-methylisoxazole, and sulfonamide. The microbial community analysis indicated that the synergistic interaction of Desulfovibrio and Acetobacterium promoted the autotrophic degradation of sulfamethoxazole. The results suggested that autotrophic microorganisms may play an important role in the environmental transformation of sulfamethoxazole.
When polyethylene terephthalate microplastics meet Perfluorooctane sulfonate in thermophilic biogas upgrading system:Their effect on methanogenesis
No full textMicroplastics (MPs) and Perfluorooctane sulfonate (PFOS) are two hard-biodegradable pollutants widely existing in the waste streams treated by anaerobic digestion. However, their synergistic effect on methanogenic metabolism is still unknown. This study investigated the impact of polyethylene terephthalate (PET) MPs alone and co-existing with PFOS on CO2 conversion to CH4 in a thermophilic biogas upgrading system. The results showed that either PET MPs addition alone or coexisting with PFOS improved the ultimate CH4 percentage and increased CO2 utilization rate. When Fe0 was added into the reactors with PET to enhance the interspecies electron transfer, a potential defluorination was observed with a defluorination rate of 15.88 ± 1.53%. Exposure of the reactor to PFOS of 300 μg/L could change the methanogenic pathway, resulting in a newly emerged Methanomassiliicoccus with dominance of 16%. Furthermore, under the exposure of PFOS, the number of predicted genes regulating enzymes in methanogenic steps from CO2 increased. These results suggest that the co-existence of PET MPs and PFOS will not inhibit the activity of hydrotrophic methanogenes, and a portion of PFOS may be biodegraded during the methanogenesis under Fe0 regulation
Tools for quantification of the duration and impact of pesticides in groundwater resources
No full textThe widespread occurrences of pesticides and their metabolites in Danish groundwater resources pose a challenge to water utilities and regional authorities. In recent years, several “new” pesticide metabolites have been discovered in Danish groundwater with an alarming detection frequency. These metabolites can typically be classified as persistent and mobile organic compounds (PMOCs), a group which also encompasses other micropollutants such as short-chained per- and polyfluorinated alkyl substances (PFAS), pharmaceuticals and biocide metabolites.The fungicide metabolite N,N-dimethylsulfamide (DMS) was the most frequently detected pesticide compound in Danish drinking water wells in 2021 and findings are also many across the EU. The ubiquity of DMS in groundwater has created a need for mapping the sources and origin of contamination to determine whether remedial measures can address the sources. Furthermore, tools for estimating the duration of DMS in groundwater systems are required by water utilities to support their management of well fields and planning of long-term investments.The aim of this PhD thesis was to improve the understanding of the sources of DMS in groundwater systems and to provide tools for estimation of its duration at drinking water well fields. Knowing possible origins of DMS is the foundation for tracking its sources in groundwater systems.Three parent compounds for DMS were identified. Tolylfluanid and dichlofluanid were formerly in use as both pesticides (horticultural crops, such as strawberries and pome fruits) and biocides (outdoor paint/wood protection), while cyazofamid is currently in use for potato cultivation. Due to these diverse applications, sources of DMS can be found in both rural and urban areas. Both types of sources can adversely affect downgradient drinking water well fields and cause concentrations above the groundwater quality criterion (0.1 μg/L).Several field investigation methods were tested in the context of tracking DMS sources or estimating its duration at well fields in agricultural areas. Review of site history, sales statistics, aerial photographs, and screening of topsoil was key in identifying possible sources and building source functions for modelling, while porewater sampling from clayey till proved useful in estimating source strength. Based on depth-discrete groundwater samples obtained from several investigation transects, contaminant mass discharge (CMD in g/yr) was estimated, and vertical concentration profiles were applied for tracking diffuse- and point sources of DMS.At catchment scale, several concurrent water samples from a gaining stream obtained in combination with flow measurements helped identify stretches of the stream which were subject to DMS discharge. This could be a tool to narrow down the locations of contaminant sources within a catchment.To estimate the duration of DMS contamination at a drinking water well field, several methods were applied in combination: CMD estimations based on comprehensive field data, numerical modelling, and groundwater dating. Simulated CMD was compared with estimations based on field observations, and simulated travel time was supported by retention time from dating of groundwater samples. On this basis, a prognosis for DMS load at the well field was developed: the DMS load was apparently still increasing, and a peak could be expected around year 2040. The well field may be affected by DMS until the end of the 21st century.The predicted duration in this groundwater system was surprisingly long, considering that DMS is highly mobile, and that the parent compounds have probably not been in use at the main source area for about 25 years. Simulations indicated that part of the explanation could be prolonged leaching caused by fracture-matrix interactions governed by diffusion during vertical transport in clayey till. This mechanism affects even highly mobile compounds, such as DMS, which is practically not retained by sorption.In conclusion, this PhD project has elucidated the origin and sources of the fungicide metabolite DMS and a comprehensive set of methods and tools was presented for estimation of its duration in groundwater systems
How do the BRICS approach sustainable concerns? A systematic literature review
No full textBrazil, Russia, India, China, and South Africa (BRICS) are recognized for their global impacts and representation across economic, social, and environmental aspects, as well as for comprising countries that strive to lead sustainable agendas in their respective regions. With a combined economy of $25.54 trillion and 42% of the world’s population, these nations are responsible for significant sustainable impacts on a global scale, eliciting interest in the practices they undertake to promote sustainability. Thus, the aim of this manuscript is to identify the primary approaches employed in those countries to address sustainability. For this purpose, a systematic literature review was conducted using the ROSES reporting standards and PRISMA Statement methodology, encompassing a sample of 93 case studies from the BRICS countries spanning the period from 2010 to 2022. The findings reveal (i) a rise in publications from 2016 to 2021, notably in China and Brazil, with a focus on the agricultural and urban sectors, and (ii) five sustainability tools emerge prominently, each with more than two applications in existing studies: Life Cycle Assessment, Multicriteria Decision Making, Cleaner Production, Material Flow Cost Accounting, and Water Footprint Assessment. These findings underscore five primary policy implications: (a) the discrepancy between scientific efforts and data regarding the sustainability impacts of the countries; (b) the need for the use of more tools to enable regional sustainable development of the countries; (c) dissemination of effective practices; (d) trends in sustainability management focusing on water management and supply, environmental protection in urban areas, decision-making for sustainable development, and environmental and waste management, and (e) the need for better-developed public policies related to environmental impact that are not currently well-represented in scientific research, aiming to promote sustainability in various critical areas
Recent Trends in Demand-Side Flexibility
No full textRenewable energy generation is inherently stochastic, and it rarely aligns with the periods of peak demand. Consequently, and despite continuous developments in storage technology, there is still a significant potential in using demand-side flexibility to balance generation and demand. The flexibility arises in many contexts, e.g., in the heating of buildings, and by shifting the demand, we can substantially reduce the need for infrastructure investments. However, it is not trivial to utilize the flexibility in a scalable manner. Energy customers are highly diverse (residential, commercial, industrial, etc.), and in most cases, their energy demand cannot be controlled directly. Furthermore, flexibility is both a dynamic and stochastic quantity. When the flexibility is used, it cannot be used at a later point in time as well. In this paper, we describe the Smart Energy Operating System, which is a framework for scalable exploitation of demand-side flexibility. It combines hierarchical forecasting with hierarchies of controllers and models. A key part of this framework is the Flexibility Function. It describes the energy demand of a flexible asset in response to a price signal, and it is continuously updated based on the actual demand. An aggregator can use it to predict the energy demand of the underlying flexible assets and participate in flexibility markets on their behalf. In other words, the Flexibility Function serves as a minimum interoperability mechanism (MIM). An important prerequisite is that markets must account for the dynamic and stochastic nature of flexibility, and we discuss current limitations and opportunities.</p