Circular Flow Research Articles

Integrating drivers of pro-environmental behavior and physical activity to explore (in) compatibilities between an active and an environmentally sustainable lifestyle

IntroductionSport and outdoor activities have benefits on people’s health and well-being but may also increase the frequency of unsustainable behaviors. The present study explores drivers of travel mode choice and consumption of material (clothes and equipment) associated with physical activity to clarify the extent to which an active and sustainable lifestyle is compatible. The role of identity and varying levels of internalized motivation for pro-environmental behaviors (autonomous and controlled environmental motivation) and engagement in physical activity (autonomous and controlled activity motivation) was examined. In addition, socio-demographic, physical context, and life situation correlates of environmentally significant behaviors associated with physical activity were analyzed.MethodsA survey of a random sample of the general public in Sweden (n = 1013) was conducted.ResultsAfter controlling for hours of physical activity, the study showed that environmental self-identity was related to a lower likelihood of using the car alone via autonomous environmental motivation and to a higher likelihood of buying and selling used material via controlled environmental motivation. Physical activity drivers displayed diverse impacts on environmentally significant behaviors, e.g., athlete identity was associated with a higher likelihood of using the car alone and buying new material, but also selling used material. Being a member of a sport or outdoor organization was related to a higher likelihood of using the car alone and buying new material, but also using active travel modes as well as buying and selling used material.DiscussionWith a better understanding of the drivers of environmentally significant behaviors in this domain, strategies to encourage sustainable transport and circular flows of material in sports and outdoors can be outlined.

Iron enrichment and alumina recovery from bauxite residue through hydrogen reduction followed by alkaline leaching and CaO circulation

ABSTRACT The alumina industry faces a significant challenge in effectively utilising bauxite residue due to its hazardous nature. A potential solution involves recovering iron and alumina from the bauxite residue, leading to a substantial reduction in residue volume and also drawing some material value. This study involved the production of self-hardened calcite pellets from the bauxite residue, which were then subjected to hydrogen reduction and subsequently leached with a sodium carbonate solution for alumina extraction. In an effort to establish a circular material flow, the leaching residue, which contains most of calcium and metallic iron, was reintegrated into the process to produce self-hardened pellets. Analytical techniques such as X-ray diffraction, electron probe microanalysis, X-ray fluorescence, and inductively coupled plasma-mass spectroscopy were employed for comprehensive microstructural, chemical, and elemental evaluations of the samples. The integrated process yielded a final alumina recovery rate exceeding 62%, a substantial improvement compared to the process lacking calcium looping. The incorporation of leaching residue recycling played a crucial role in significantly reducing calcium consumption throughout the integrated process, reaching approximately 70%. This research signifies a promising approach to efficiently recover valuable components from bauxite residue while mitigating environmental concerns and optimising resource utilisation.

Taylor–Couette system in the narrow-gap limit, revisited, with a corrigendum to the paper by Nagata (2023, Philosophical Transaction A.)

We study transition from circular Couette flow to Taylor–Couette flow in the narrow-gap limit. We find that subcritical bifurcations of a nonlinear axisymmetric flow occur at the linear critical point when the angular velocity ratio for the cylinders, μ , is less than approximately −0.5. We also demonstrate that two nonlinear axisymmetric flow branches with the same wavenumber as that for the critical mode exist for μ = 0 . Introducing the modified Taylor number τ , analyses for any μ < 1 are made possible, so that this study supplements the recent analysis of Nagata M. 2023 Taylor-couette flow in the narrow-gap limit. Philos. Trans. R. Soc. A 381, 20220134. (doi: 10.1098/rsta.2022.0134 ), in which the case μ = − 1 was excluded, because the critical value of the conventional Taylor number T a used therein approaches zero as μ → − 1 . The present analysis takes into account all the contributions from the inertia term, including a component which was neglected in [1]. The effect of the inclusion of this previously neglected component is surveyed at the end.

Reuse of building materials—the perspective of Swedish clients

In the context of the circular economy, there is an urgent need for transformation into circular material flows by avoiding waste, reducing extraction of virgin raw materials, and extending product life cycles. Within the construction and real estate industry, the reuse of building materials stands out as a critical strategy for value retention. The objective of this paper is to localise the forefront of the practical implementation of reused materials within the Swedish construction and real estate industry. To achieve this, the current state of reuse practices through the perspective of property companies as clients in decision-making positions was conducted through semi-structured interviews to identify key barriers and enablers associated with reuse. The three most significant barriers that emerged were a lack of measurable economic incentives, the absence of a professional reuse market, and obsolete project management. Conversely, the three most significant enablers were new and improved project management methods, enhancing competence and learning within and beyond organisations, and introduce reuse at an early stage. The results emphasise the need for project management to develop and adopt circular economy principles. This is further understood due to responders highlighting the industry's linear approach as a major obstacle to circularity together with uncertainties related to product performance, responsibilities and economics characterising reuse efforts. However, an industry in transition is witnessed, e.g. by the emergence of new roles which suggests a continued need for focused research in organisational matters.

Combustion of Pelletized Coffee Residues for Bioenergy Valorization Within a Circular Economy Vision

Combustion of Pelletized Coffee Residues for Bioenergy Valorization Within a Circular Economy Vision

A numerical approach for inlet-outlet boundary conditions with least-square moving particle explicit (LSMPE) method on GPU

ABSTRACT In severe accidents of nuclear reactors, studying the pressure drop of debris beds is of great significance for delaying the progression of the accident. However, traditional MPS often exhibits significant pressure oscillation issues when dealing with the inlet-outlet boundary. The study introduces a method for managing inlet and outlet boundary conditions using the Least-Square moving particle explicit method (LSMPE). A high-precision least squares discrete method was applied to the moving particle explicit method (MPE) based on predictive-corrected pressure. The code was accelerated using OpenACC for parallelization. Special boundary treatments were applied to minimize errors induced by boundaries, including particle number density correction for inlet particles, addressing slip or nonslip boundaries, and introducing concept particles at the outlet. The stability and accuracy of this method were validated through three cases. Simulation results for Poiseuille flow and circular flow demonstrated the method’s good precision, exhibiting stable pressure fields. Results from single-phase flow simulations through a porous medium bed agreed well with predictions from the Ergun equation, highlighting the method’s potential for practical engineering applications.

How can manufacturers identify the conditions for financially viable product-as-a-service?

IntroductionWith the much-needed transformation from linear to more circular resource flows, it is imperative for enterprises to understand their financial prospects. Transforming towards Product-as-a-Service (PaaS) with circular elements introduces new considerations that must be addressed to ensure profitability and sustainability. However, there is a lack of comprehensive financial assessments based on empirical cases to guide companies in assessing the lucrativeness of their transformations. This paper addresses this gap by proposing a simple-to-use and flexible financial assessment model for PaaS, helping practitioners identify the conditions necessary for financial viability from both provider and user perspectives.MethodsGrounded in transdisciplinary research, this study focuses on a construction machine manufacturer's transformation from a traditional one-off sales business model to PaaS. The transformation is analysed through the development of a life cycle costing financial assessment model that addresses relevant cost drivers.ResultsUsing discounting methods, the model can help practitioners generate scenarios to identify feasible solutions for profitable PaaS setups. Additionally, the paper presents an analytical procedure to identify conditions for a financially viable PaaS. The procedure includes scenario-based analysis that accounts for systemic changes often necessary for successfully realising PaaS.DiscussionBy following the proposed procedure, along with the financial assessment model, manufacturers can streamline their financial assessments to identify necessary changes. For the analysed case company, the modelling results indicate that it must redesign its products for PaaS to outperform its previous business model.

Wall-mounted circular cylinder flows

The flow over wall-mounted circular cylinders is influenced by variations in aspect ratio, Reynolds number, and boundary layer thickness, all of which affect the vortical structures in the wake. In this study, we conducted direct numerical simulations and data-driven techniques, including proper orthogonal decomposition (POD) and dynamic mode decomposition, to examine vortical flows behind wall-mounted circular cylinders with aspect ratios of 4, 8, and 12 at Reynolds numbers ranging from 60 to 800, based on cylinder diameter. The incoming boundary layer thickness varied from 0.05 to 0.25. Our findings reveal that a thicker boundary layer promotes the development of low-frequency symmetric vortical structures along the wall surface, suppressing antisymmetric wake shedding. Consequently, the induced upwashing motion of the flow behind the cylinder pushes the wake shedding region closer to the free-end side, facilitating quadrupole mean streamwise vortices. The wake shedding frequency is significantly altered as the symmetric low-frequency mode intensifies along the boundary. POD analysis demonstrates the coexistence of symmetric and antisymmetric vortical structures in the wake region. The presence of either antisymmetric or symmetric wake shedding is determined by the dominant frequency in the instantaneous flow. These findings substantiate previous conjectures about the simultaneous presence of symmetric and antisymmetric wake shedding modes and enhance our understanding of vortical flows around wall-mounted circular cylinders.

A deep learning framework for solving the prediction and reconstruction problem of Bingham fluid flow field

As a typical non-Newtonian fluid, Bingham fluid is employed in a multitude of fields, including petroleum, construction, and the chemical industry. However, due to the intricate intrinsic properties of Bingham fluids and the necessity for precision and efficacy in specific engineering applications, the rapid and precise prediction and reconstruction of its flow field information has become a challenge and a focal point of contemporary research. In this paper, we introduce a novel deep-learning approach to address the two-dimensional laminar motion of Bingham fluids. The proposed Papanastasiou Regularization Physics-Informed Neural Network (PR-PINN) framework effectively predicts and reconstructs the flow field of Bingham fluids. Initially, the framework applies Papanastasiou regularization to the governing equations of Bingham fluids, enhancing the network's adaptability to solving the flow field problem by incorporating boundary conditions and an adaptive weight assignment strategy. We consider two scenarios: equal-diameter circular pipe flow and conical pipe flow. The PR-PINN network is utilized for flow field prediction and reconstruction. Our results show that PR-PINN achieves high accuracy in flow field prediction and can reconstruct velocity and pressure fields using limited measurement data. Based on these findings, we explore the impact of boundary constraints, the effect of large intrinsic parameters on prediction accuracy, and the influence of measurement points and boundary constraints on flow field reconstruction. In summary, the PR-PINN network exhibits satisfactory performance and significant potential for predicting and reconstructing Bingham fluid flow fields.

Electrocatalytic Hydrogenation of Pyridines and Other Nitrogen-Containing Aromatic Compounds.

The production of cyclic amines, which are vital to the pharmaceutical industry, relies on energy-intensive thermochemical hydrogenation. Herein, we demonstrate the electrocatalytic hydrogenation of nitrogen-containing aromatic compounds, specifically pyridine, at ambient temperature and pressure via a membrane electrode assembly with an anion-exchange membrane. We synthesized piperidine using a carbon-supported rhodium catalyst, achieving a current density of 25 mA cm-2 and a current efficiency of 99% under a circular flow until 5 F mol-1. Quantitative conversion of pyridine into piperidine with 98% yield was observed after passing 9 F mol-1, corresponding to 65% of current efficiency. The reduction of Rh oxides on the catalyst surface was crucial for catalysis. The Rh(0) surface interacts moderately with piperidine, decreasing the energy required for the rate-determining desorption step. The proposed process is applicable to other nitrogen-containing aromatic compounds and could be efficiently scaled up. This method presents clear advantages over traditional high-temperature and high-pressure thermochemical catalytic processes.

Assessment methods and digital tools to support circular building strategies

Abstract The aim of the paper is to highlight how digital technology can be a vector for maintaining information of buildings products, promoting supply chain transparency and traceability of materials and environmental data, contributing to activate a sustainable circular economy. Indeed, the current lack of knowledge of product characteristics often hinders the activation of reverse logistic and the assessment of the environmental benefits of circular material flows. This means, on one hand, the need to trace and collect product characteristics and product environmental information throughout the entire life cycle, and, on the other hand, the to identify ways of communicating and sharing information. This paper outlines current digital tools to support transparency and traceability of materials. Next, the paper verticalises the method and indicators used to declare the circular and sustainable profile of products, emphasising the importance of applying Life Cycle Assessment (LCA). Finally, the prefiguration of a possible integration between traceability tools and the LCA methodology is discussed, identifying possible drivers (e.g. legislative, trainings) and possible key-operators for the widespread of the “LCA-integrated traceability tools”.

Concentric circular flow field to improve mass transport in large-scale proton exchange membrane water electrolysis cells

Uniform reactant supply is challenging for high-performance proton exchange membrane water electrolysis (PEMWE) in renewable energy storage. The anode flow-field pattern, anode flow-field orientation, and stoichiometric ratio influence mass transport. In this study, the performances of two flow-field patterns were compared for a single PEMWE cell with an active area of 100 cm2. Straight serpentine was used as the reference model and a concentric circle with an arc shape was designed. In addition, the optimal anode flow field orientation and stoichiometric ratio were determined. The results indicate that the optimal anode flow-field pattern differs depending on the stoichiometric ratio. At low flow rates, mass transfer via diffusion was dominant; therefore, a straight serpentine flow was preferred. In contrast, a concentric circle, which induces a significant differential pressure between adjacent channels, is preferable at a high flow rate. This is because convection is dominant in mass transfer. Maintaining a stoichiometric ratio of 10 or more is recommended during the operation. At a ratio of less than 10, the reactant was depleted at a high current density, and the mass transfer resistance increased. In addition, water is better distributed by gravity and buoyancy when the electrolyte membrane is parallel to the ground, and the anode flow path is above the porous medium. This leads to high PEMWE cell performance.

Fabrication Information Modeling for Closed-Loop Design and Quality Improvement in Additive Manufacturing for construction

Additive Manufacturing (AM) has emerged as a disruptive technology with the potential to revolutionize the construction industry by integrating digital design with automated manufacturing. This paper presents and extends Fabrication Information Modeling (FIM), a comprehensive framework tailored for automated manufacturing in construction. FIM facilitates the seamless integration of digital design concepts with automated manufacturing processes, enabling precise control over fabrication information and enhancing construction efficiency and quality. This paper demonstrates its potential to optimize construction processes through a detailed exploration of FIM’s capabilities, including data preparation, path planning, simulation integration, robot control, and data feedback. By enabling a circular data flow between digital modeling and manufacturing, FIM is able to bridge the gap between digital design and physical construction, revolutionizing how construction projects are conceived, planned, and executed. The paper concludes by highlighting the challenges and future research directions in advancing FIM-based construction systems, emphasizing its transformative potential in driving innovation and sustainability in the construction industry.

Remittance Inflow, Investment, and Economic Growth in Africa amidst COVID-19 Pandemic

Africa has fared well in the aspect of remittance receipts in recent years; however, the region recorded a decline in remittances amid the COVID-19 pandemic which constrained the circular flow of income significantly and ultimately economic growth. In view of this, this study investigates the economic effects of remittance inflows and investment on economic growth in Africa amid COVID-19 pandemic using a panel of 48 economies and estimated with pooled OLS and two-step system GMM. The study employed two distinct approaches for estimation; pre-COVID-19 (2010–2019) and amid COVID-19 (2010–2023). The results indicate that the behavior of remittances, investment and economic growth in Africa is not significantly different between pre-COVID-19 and amid COVID-19. That is, remittances remain a significant economic growth catalyst in Africa whereas investment is not (though with growth effect potential). Overall, the study concludes that African economic policy stakeholders and other relevant policy authorities should sustain the current remittance and labor policy frameworks with possible fine-tuning where applicable while doubling their investment efforts especially in productive sectors of the economy.

Trajectory and spreading of falling circular dense jets in shallow stagnant ambient water

This study investigates the trajectory and spreading of a horizontal circular dense jet flow discharged above the water surface, the flow of which falls into shallow stagnant ambient water. For this purpose, 27 experiments were performed using three diameters, flow rates, and falling heights to investigate jet trajectory. In addition, nine experiments with constant falling height were conducted to study jet spreading. The densimetric Froude number of the jet flow at the nozzle outlet and water surface of the present study ranged from 0.72 to 4.22 and 36.96 to 86.10, respectively. The data pertaining to this study were extracted and analyzed through image processing. The results of the experiments showed that by increasing both the momentum and falling height, the trajectory of the jet flow reached a farther distance from the discharge nozzle. The spreading of the outer boundaries of the dense circular falling jet flow tended to extend downstream of the impact point and had an elliptical motion on the bed. The relationship between radial distance from the impingement point to the outer boundary of flow and time was determined to have a power of 0.67 for flow along the flume and 0.59 for flow along the flume's width.

Testing Algorithms for Controlling the Distributed Power Supply System of a Railway Signal Box

Trends in the use of renewable energy sources to power buildings do not bypass objects for which maintaining a power supply is critical. This also applies to railway signal boxes. The aim of the research work was to test the multisource power supply system for a railway signal box with power electronic converter systems and a DC bus, built as part of the research project. The assumption for powering the railway signal box building was to use renewable sources, energy storage devices, and a 3 kV DC traction network as the second required power supply grid. Both power grids were connected by power electronic converters, and the power values of the converters were set based on the calculated power balance values using the values measured at the system nodes and the set constraints. The tests primarily tested the response of the power supply system to changes in load power and power generated by the photovoltaic source, as well as the charge level of the energy storage devices. The correctness of the control algorithm’s operation was assessed based on the recorded power values in the power supply system nodes. The tests were carried out for 60 scenarios that covered all normal and emergency operating conditions. During the tests, delays in response to changes in the power supplied to the converters and the values of circular power flow between the power grid connections were recorded. The recorded delays ranged from 2 to about 50 s and the circular power flows did not exceed 1500 W. Based on the results of the tests, it was found necessary to improve the power measurement system in the power supply system nodes and to improve the quality of communication and the transmission time of measurement data transmission time.

Maximally efficient exchange in thin flow cells using density gradients.

Flow cells are ubiquitous in laboratories and automated instrumentation, and are crucial for ease of sample preparation, analyte addition and buffer exchange. The assumption that the fluids have exchanged completely in a flow cell is often critical to data interpretation. This article describes the buoyancy effects on the exchange of fluids with differing densities or viscosities in thin, circular flow cells. Depending on the flow direction, fluid exchange varies from highly efficient to drastically incomplete, even after a large excess of exchange volume. Numerical solutions to the Navier-Stokes and Cahn-Hilliard equations match well with experimental observations. This leads to quantitative predictions of the conditions where buoyancy forces in thin flow cells are significant. A novel method is introduced for exchanging fluid cells by accounting for and utilizing buoyancy effects that can be essential to obtain accurate results from measurements performed within closed-volume fluid environments.

A novel compartmental approach for modeling stomach motility and gastric emptying

The stomach, a central organ in the Gastrointestinal (GI) tract, regulates the processing of ingested food through gastric motility and emptying. Understanding the stomach function is crucial for treating gastric disorders. Experimental studies in this field often face difficulties due to limitations and invasiveness of available techniques and ethical concerns. To counter this, researchers resort to computational and numerical methods. However, existing computational studies often isolate one aspect of the stomach function while neglecting the rest and employ computationally expensive methods. This paper proposes a novel cost-efficient multi-compartmental model, offering a comprehensive insight into gastric function at an organ level, thus presenting a promising alternative.The proposed approach divides the spatial geometry of the stomach into four compartments: Proximal/Middle/Terminal antrum and Pyloric sphincter. Each compartment is characterized by a set of ordinary differential equations (ODEs) with respect to time to characterize the stomach function. Electrophysiology is represented by simplified equations reflecting the “slow wave behavior” of Interstitial Cells of Cajal (ICC) and Smooth Muscle Cells (SMC) in the stomach wall. An electro-mechanical coupling model translates SMC “slow waves” into smooth muscle contractions. Muscle contractions induce peristalsis, affecting gastric fluid flow velocity and subsequent emptying when the pyloric sphincter is open. Contraction of the pyloric sphincter initiates a retrograde flow jet at the terminal antrum, modeled by a circular liquid jet flow equation.The results from the proposed model for a healthy human stomach were compared with experimental and computational studies on electrophysiology, muscle tissue mechanics, and fluid behavior during gastric emptying. These findings revealed that each “ICC” slow wave corresponded to a muscle contraction due to electro-mechanical coupling behavior. The rate of gastric emptying and mixing efficiency decreased with increasing viscosity of gastric liquid but remained relatively unchanged with gastric liquid density variations. Utilizing different ODE solvers in MATLAB, the model was solved, with ode15s demonstrating the fastest computation time, simulating 180 s of real-time stomach response in just 2.7 s. This multi-compartmental model signifies a promising advancement in understanding gastric function, providing a cost-effective and comprehensive approach to study complex interactions within the stomach and test innovative therapies like neuromodulation for treating gastric disorders.

Co-learning approaches to talking and thinking about “peecycling”: Perspectives on communication, education, and practice

Narratives of linearity and control have driven conventional wastewater management and modern agriculture, resulting in widespread contamination and ecological damage. In response, a growing movement to reclaim the nutrient cycle emphasizes circularity and the entanglements between our bodies, the “shadow places” where our “waste” travels, and the ecosystems that sustain us. Parallel linear narratives of diffusionist knowledge dissemination have resulted in distrust between communities and scientists, but some researchers and practitioners are rebuilding trust through connections that emphasize accessibility, accountability, active learning and co-creation spanning rural and urban, campus, and civic contexts. From study sites in Vermont and Michigan, we explore urine recycling (or peecycling as some call it) as an example of both technological and pedagogical connections re-made, arguing that active learning methods can undergird engaged research. Urine recycling has the potential to foster curiosity about ecological interconnections and imaginative thinking about alternate infrastructural futures. Our evidence comes from interviews and focus groups, as well as participant observation at site-based interventions and in experiential learning contexts. We show that the advent of more circular economies, implemented with co-learning, advances both theory and practices of postmodern, and post–postmodern infrastructures. That is, rather than reinforcing a one-way flow of information that mirrors the linearity of conventional wastewater management, co-learning approaches—where scientists and practitioners are partners in generating knowledge and solutions—address the environmental, equity, and ethical aspects of reclaiming circular nutrient flows, transforming relationships between our bodies, waterways, and foodsheds.

Freecycling Markets as Sustainable Materialist Movements?

This paper seeks to redress the over-emphasis on state-driven circular policies in public and academic discourses by attending to two physical community-based freecycling markets at the emerging frontiers of circular waste/resource management in Singapore. Freecycling markets that close short reuse loops are a counterpoint to policies that close long recycling loops. Drawing primarily on empirical data from ethnographic fieldwork, we argue that freecycling markets exemplify a sustainable materialist movement concerned about the sustainability of material resources vis-à-vis the closing/shortening of material circularity loops. This is achieved through the reconfiguration of (a) material flows and (b) material relations. The redirection of unwanted but reusable household objects away from the incinerator and towards potential reusers animates a shift from a linear to circular material flow. We contend that this redirection of material resources for reuse is augmented by rescue and recirculation, which are relatively neglected within the scholarship on circular R-behaviours. Additionally, freecycling markets seek to transform material relations by encouraging care and stewardship, instead of use and disposal. Crucially, we highlight how freecycling markets may be plagued with material constraints that render them not-so-sustainable-and-scalable, thereby shedding light on the practical limits of sustainable materialist action. Taken together, this paper extends the scholarship on circular economies by bringing work on sustainable materialism into a productive dialogue with that on circular activisms and R-behaviours.