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Bubble injection for heat transfer enhancement : from physics to applications
No full textThis article presents a comprehensive review of recent advancements in bubble-induced heat transfer enhancement, with a primary focus on understanding the fundamental underlying physics. Accordingly, this review first highlights recent novel concepts and techniques developed to enhance heat transfer through bubble injection, followed by explaining the essential physical aspects of this development. It attempts to clarify the impact of bubble injection on heat transfer by examining key mechanisms in two-phase bubbly flow. The factors that influence heat transfer and fluid flow, including mechanisms of bubble ascent, bubble breakage, and coalescence, as well as the impact of bubble size and shape, are examined. Furthermore, the review explores the use of bubble injection in different types of heat exchangers in addition to other applications, including solar collectors, hydrogen production, internal combustion engines, and energy storage systems. Furthermore, the article identifies current research gaps and existing challenges and suggests potential directions for future research in bubble-induced heat transfer enhancement
Federal transformation costs of e-mobility in Germany: Effectiveness and efficiency of EV incentives between 2015 and 2023
No full textThis study evaluates Germany's federal electric vehicle (EV) incentive package, analyzing its impact on the automotive market, consumer purchase decisions, and environmental outcomes. Utilizing data from the German Ministry of Finance, Federal Motor Transport Authority, and Federal Office of Economics and Export Control, the research assesses new EV registrations, as well as federal total, specific, and CO2 abatement costs from 2015 to 2023. Results show the environmental bonus significantly boosted EV adoption, with a 250% increase in subsidized vehicles between 2020 and 2021 and battery electric vehicles (BEV) comprising 18.3% of new registrations by 2023. Fiscal analysis uncovers combined costs of tax revenue shortfalls and subsidies at approximately EUR 17 billion, underscoring substantial financial commitments. Nonetheless, the incentives have significantly fostered EV adoption and environmental goals, achieving CO2 savings of 3 million tons, excluding production emissions compared to assumed average petrol cars. Conclusively, Germany's EV incentives have effectively promoted electric mobility despite fiscal and societal challenges. These findings inform policy design, advocating for a balanced approach to innovation and societal impacts on electric mobility's progression
How social entrepreneurs search for knowledge to solve complex social problems – an empirically based model and typology
No full textIn order to tackle today's grand challenges, we need to better understand how social entrepreneurs (SEs) search for knowledge to solve complex social problems. However, existing search models in social entrepreneurship lack an explicit focus on complexity. To address this gap, our explorative study adopts concepts from organizational search within open innovation as our theoretical lens to analyse 18 narrative interviews with SEs in Germany and Ethiopia. Our findings provide empirical accounts for a social entrepreneurial search model integrating different search mechanisms and search heuristics. We identify three distinct types of SEs who apply the different search types focused search, tentative search and hybrid search based on their different complexity perceptions in different search environments and two distinct normative theories that guide their search as cognitive heuristics. We contribute to both research on organizational search and social entrepreneurship and our findings have practical implications for politicians, social entrepreneurs and educators
Hybrid optimization methodologies for the design of chemical processes
No full textProcess synthesis and design problems in chemical engineering usually require a solution to complex nonlinear optimization problems with continuous and discrete decision variables. The resulting mixed-integer nonlinear programming problems are particularly hard to solve, and different strategies are frequently applied for their solution. Gradient-based optimization enables fast computations, exploiting local sensitivity information, but is usually limited to local optima for nonconvex problems, whereas derivative-free optimization methods can be linked to available simulation models, with little effort, but also without any guarantee of optimality. Metaheuristics, especially swarm intelligence and population-based algorithms, are frequently applied for simulation-based process optimization, overcoming the lack of gradient information, at the cost of a considerable number of simulations. Another strategy that is receiving increasing interest builds on surrogate models that are first generated based on an initial sampling of process simulations for systematically varied design variables. Tractable surrogate models do provide the necessary sensitivity information that enables efficient gradient-based optimization, while being only an approximation of the original problem. Each strategy has its advantages and limitations, and no single best option is generally favorable for all kinds of problems. Thoughtful combinations of different strategies have the potential to overcome or at least reduce the individual limitations, while simultaneously combining the strengths of the individual methods. The current chapter provides an introduction and overview of such hybrid optimization methodologies, together with some illustrations of their use for applications in chemical engineering. Several case studies, including utility and entrainer selection, illustrate the performance of hybrid optimization methods and indicate the ability to solve even more complex design problems
Key competencies for circular product development
No full textSustainable development goals and changing environmental policies lead the transformation of organizations to incorporate the circular economy principles and employ circular product development (CPD) practices. Consequently, this implies new competencies that need to be developed at organizational and individual level. There is lack of comprehensive understanding on the distinct competencies that are relevant for such transition, whereas the research on the competencies critical to CPD is scarce. Building on the two empirical studies involving experts and practitioners in the field of sustainability and circular economy, this chapter aims to integrate the findings for providing key competencies for CPD at the level of both an organization and an individual, and to inform on a holistic approach to competency development for CPD
Circular economy implementation: from selective measures to absolute environmental sustainability
No full textTightening environmental policies are forcing companies and society to transform and adopt more sustainable and circular economy (CE)-oriented practices. CE principles present an alternative approach to the dominant strategies of eco-efficiency or relative environmental sustainability, called eco-effectiveness or absolute environmental sustainability. The CE challenges the relative sustainability approach by introducing the goal of maximizing the benefit to ecological systems and increasing the positive environmental impacts (i.e., absolute environmental sustainability) rather than reducing the negative impacts and keeping the focus on eco-efficiency. Various CE definitions are commonly associated with a set of R principles, in scientific research frequently used to evaluate the CE implementation in firms. There is a growing evidence that only a selection of these principles as R strategies are implemented in firms, risking of minimizing the impacts rather than aiming for maximizing the benefits. The paper builds on the dataset of 145 circular firms and shows the selective implementation of CE principles in most cases. The eco-effectiveness of the analyzed circular firms is revealed by introducing a comprehensive circularity framework that weights-in the flow of resources, loop closure and additional generated benefits. The results reveal that current CE-related frameworks do not address the firms acting as CE enablers, i.e. providing services and products to the CE implementers
Effects of established carsharing services on carsharing acceptance, car ownership, and mobility behavior in urban residential neighborhoods
No full textIn recent years, business-to-consumer carsharing has evolved from a niche market to a relevant mobility option in the inner-city areas of major German cities. However, most previous research on the use and impact of carsharing has only addressed the initial stages of its diffusion, focusing mainly on early adopters of carsharing. It remains uncertain to what extent findings from these studies can be applied to more mature carsharing services and their users.
This dissertation, therefore, examines the acceptance and effects of carsharing in the inner city of Hamburg—a study area with comparatively well-established carsharing services and advanced diffusion of carsharing memberships among the population. Acceptance is defined as the current use of carsharing or the willingness to use it in the future. Regarding the effects of carsharing, the dissertation focuses on its impact on car ownership and mobility behavior. A survey of carsharing users and non-users in 16 inner-city neighborhoods in Hamburg, conducted in November and December 2019, serves as the empirical basis.
The results show that the attitudes and socio-demographic characteristics of current carsharing users in Hamburg remain different from those of non-users, despite the advanced diffusion of carsharing memberships. Carsharing users in Hamburg are significantly more likely to be young, male, highly educated, have a high income, and have a relatively positive attitude toward car use, although the differences between carsharing users and non-users are rather modest. However, non-users who are strongly interested in carsharing—and thus represent potential future carsharing users—differ from the typical profile of current users. Compared to existing users, these interested non-users are more heterogeneous in terms of socio-demographics and attach less importance to car use while valuing cycling and public transport more. This suggests that the further establishment of carsharing services is indeed leading to a diversification of the user base.
Regarding the effects of carsharing in Hamburg, the results show that carsharing reduces car ownership and the general level of car use, benefiting not only the carsharing services themselves but also (other) environmentally friendly means of transport. However, these effects are relatively small, mainly due to the different use and impact of station-based versus free-floating carsharing. Unlike station-based carsharing, free-floating carsharing does not appear to significantly reduce car ownership, yet it has seen the strongest growth in membership in recent years and is preferred by the vast majority of carsharing members in Hamburg.
The results of this dissertation suggest that (more comprehensive) transport planning and policy support for carsharing services is advisable. This includes measures to increase the adoption of carsharing among currently underrepresented demographic groups, as well as measures to amplify the effect of carsharing on car ownership of its users.In den letzten Jahren hat sich das Business-to-Consumer-Carsharing in den Innenstädten deutscher Metropolen von einer Nische zu einer bedeutenden Mobilitätsoption entwickelt. Der Großteil der bisherigen Forschung zur Carsharing-Nutzung und -Wirkung deckt jedoch nur die frühen Phasen der Carsharing-Diffusion ab, untersuchte also vor allem die frühzeitigen Nutzer („Early Adopters“) der Carsharing-Angebote. Es ist unklar, inwiefern sich Erkenntnisse, die durch die Beforschung von jungen und noch relativ wenig etablierten Carsharing-Diensten gewonnen wurden, auch auf reifere Carsharing-Dienste und deren Nutzer übertragen lassen.
Diese Dissertation richtet den Fokus daher auf die Carsharing-Akzeptanz und -Effekte in der Hamburger Innenstadt – einem Untersuchungsraum mit vergleichsweise stark etablierten Carsharing-Angeboten und weit fortgeschrittener Verbreitung von Carsharing-Mitgliedschaften in der Bevölkerung. Unter Carsharing-Akzeptanz wird in dieser Arbeit die bereits erfolgte Carsharing-Nutzung oder die Bereitschaft zur zukünftigen Nutzung verstanden. Bei den Carsharing-Effekten stehen die Auswirkungen der Carsharing-Nutzung auf den Pkw-Besitz und das Mobilitätsverhalten im Vordergrund. Als empirische Basis dient eine im November und Dezember 2019 durchgeführte Befragung von Carsharing-Nutzern und -Nichtnutzern in 16 Innenstadtquartieren Hamburgs.
Die Ergebnisse zeigen, dass sich die Einstellungen und soziodemographischen Merkmale der gegenwärtigen Carsharing-Nutzer in Hamburg trotz fortgeschrittener Carsharing-Diffusion noch immer von denen der Nichtnutzer unterscheiden. Carsharing-Nutzer sind demnach signifikant häufiger jung, männlich, hochgebildet, gutverdienend sowie relativ affin für die Autonutzung, wobei das Ausmaß der Unterschiede zwischen Carsharing-Nutzern und -Nichtnutzern allerdings überschaubar ist. Nichtnutzer, die stark am Carsharing interessiert sind und somit potenziell zukünftige Carsharing-Nutzer repräsentieren, weichen hingegen vom Bild des typischen Carsharing-Nutzers ab. Im Vergleich zu den bisherigen Carsharing-Nutzern sind die am Carsharing interessierten Nichtnutzer in soziodemographischer Hinsicht heterogener und messen der Autonutzung eine geringere, der Nutzung des Fahrrads und öffentlicher Verkehrsmittel wiederum eine größere Bedeutung bei. Dies lässt darauf schließen, dass die fortschreitende Etablierung der Carsharing-Angebote tatsächlich zu einer Diversifizierung der Carsharing-Nutzerbasis führt.
Bei der Untersuchung der Carsharing-Effekte zeigte sich, dass die Hamburger Carsharing-Angebote den Pkw-Besitz und infolgedessen auch den generellen Umfang der Autonutzung reduzieren, wovon neben den Carsharing-Diensten selbst vor allem der Umweltverbund profitiert. Gleichwohl sind diese Effekte relativ schwach ausgeprägt, was hauptsächlich an der unterschiedlichen Nutzung und Wirkung der stationsbasierten und der stationslosen Carsharing-Variante liegt. Im Gegensatz zum stationsbasierten scheint das stationslose („free-floating“) Carsharing keine wesentliche Verringerung des Pkw-Besitzes zu bewirken, ist zugleich aber die Carsharing-Variante, die in den letzten Jahren hinsichtlich der Mitgliederzahlen am stärksten gewachsen ist und von der großen Mehrheit der Hamburger Carsharing-Mitglieder bevorzugt wird
Novel nanoparticle mixing approach for the production of solid-state battery hetero-agglomerates in vibrated fluidized beds
No full textA vibrated fluidized bed with microjet assistance is utilized to mix heterogeneous submicron-sized battery materials. This process aims to improve the homogeneity and electrochemical performance of a solid-state cathode composite consisting of LiFePO4 (LFP), Li3InCl6 (LIC) and carbon black (CB). A downwards directed microjet was employed to enhance fluidization and mixing quality. The research involved a parametric study, examining various vibration intensities, microjet nozzle sizes, and fluidization times to determine the optimal conditions for achieving a homogeneous composite on the microscale. Scanning electron microscope (SEM) and focused ion beam SEM (FIB-SEM) imaging were used to assess the mixing quality and confirm the formation of heteroagglomerates. Assisted fluidization alone produces composites with inferior mixing quality, whereas a microjet significantly improves mixing. Electrochemical testing reveals that a vibrated fluidized bed alone is inadequate for mixing submicron-sized particles for battery applications, whereas the microjet enables the mixing and ionically bound active material
Multi-contrast MPI matrix compression
No full textMulti-contrast magnetic particle imaging (MPI) reconstructs the signal from different tracer materials or environments, resulting in multi-channel images that enable temperature or viscosity quantification. Since the multi-contrast problem is ill-posed, it is addressed by regularization methods that are commonly solved using the Kaczmarz algorithm. Unlike the single-contrast MPI problem, the multi-contrast one requires a high number of iterations to converge. Matrix compression techniques were already successfully used in single-contrast reconstruction and matrix recovery applications as in compressed sensing. Our work proposes to use matrix compression to reduce the reconstruction time needed to achieve good reconstruction quality in multi-contrast MPI
Stereo hard X-ray ptychography
No full textHard X-ray ptychography has strongly developed during the last decade, enabling one to visualize structural properties of materials at high spatial resolution. By combining it with multi-slicing or tomographic techniques, optically thick samples can be investigated in 3D. Nevertheless, the depth resolution in multi-slicing is often limited to several micrometers by the ptychographic optical system and a full laminographic or tomographic investigation may be hindered by experimental constraints of limited space or acquisition time. Here, we introduce a stereoscopic imaging system using two inclined nanofocused X-ray beams to illuminate a sample at varying angles at the same time. Similar to human vision, adding these stereoscopic views results in considerably improved in-depth resolution beyond the current limits of pure 2D imaging systems. This is especially promising for experimental applications requiring bulky sample environments