1,631 research outputs found

    Droplet impact on doubly re-entrant structures

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    Doubly re-entrant pillars have been demonstrated to possess superior static and dynamic liquid repellency against highly wettable liquids compared to straight or re-entrant pillars. Nevertheless, there has been little insight into how the key structural parameters of doubly re-entrant pillars influence the hydrodynamics of impacting droplets. In this work, we carried out numerical simulations and experimental studies to portray the fundamental physical phenomena that can explain the alteration of the surface wettability from adjusting the design parameters of the doubly re-entrant pillars. On the one hand, three-dimensional multiphase flow simulations of droplet impact were conducted to probe the predominance of the overhang structure in dynamic liquid repellency. On the other hand, the numerical results of droplet impact behaviours are agreed by the experimental results for different pitch sizes and contact angles. Furthermore, the dimensions of the doubly re-entrant pillars, including the height, diameter, overhang length and overhang thickness, were altered to establish their effect on droplet repellency. These findings present the opportunity for manipulations of droplet behaviours by means of improving the critical dimensional parameters of doubly re-entrant structures

    Laser induced forward transfer: Propelling liquids with light

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    Laser‐induced forward transfer (LIFT) constitutes an interesting alternative to conventional printing techniques in microfabrication applications. Originally developed to print inorganic materials from solid films, it was later proved that LIFT was feasible for printing liquids as well, which substantially broadened the range of printable materials. Any material which can be suspended or dissolved in an ink can be in principle printed through LIFT. The principle of operation of LIFT relies on the localized absorption of a focused laser pulse in a thin film of the ink containing the material to print (donor). This results in the generation of a cavitation bubble which expansion displaces a fraction of the liquid around it, leading to the formation of a jet which propagates away the donor and towards the receiving substrate, placed at a short distance from the liquid free surface. The contact of the jet with this receiving substrate results in the deposition of a sessile droplet. Thus, each droplet results from a single laser pulse, and the generation of micropatterns is achieved through the printing of successive droplets. A similar ejection and deposition process is produced by generating a cavitation bubble below the surface of a liquid contained in a reservoir in the film-free laser printing configuration. In this work we review our main achievements on the laser printing of inks, paying special attention to the analysis of the liquid transfer dynamics and its correlation with the printing outcomes

    Laser-induced forward transfer based laser bioprinting in biomedical applications

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    Bioprinting is an emerging field that utilizes 3D printing technology to fabricate intricate biological structures, including tissues and organs. Among the various promising bioprinting techniques, laser-induced forward transfer (LIFT) stands out by employing a laser to precisely transfer cells or bioinks onto a substrate, enabling the creation of complex 3D architectures with characteristics of high printing precision, enhanced cell viability, and excellent technical adaptability. This technology has found extensive applications in the production of biomolecular microarrays and biological structures, demonstrating significant potential in tissue engineering. This review briefly introduces the experimental setup, bioink ejection mechanisms, and parameters relevant to LIFT bioprinting. Furthermore, it presents a detailed summary of both conventional and cutting-edge applications of LIFT in fabricating biomolecule microarrays and various tissues, such as skin, blood vessels and bone. Additionally, the review addresses the existing challenges in this field and provides corresponding suggestions. By contributing to the ongoing development of this field, this review aims to inspire further research on the utilization of LIFT-based bioprinting in biomedical applications

    Charakterisierung von FlĂŒssigkeitsfilmen mittels Laserabsorptionsspektroskopie in der Abgasnachbehandlung

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    Die Auswirkungen des Klimawandels fĂŒhren zu einer zunehmenden Sensibilisierung fĂŒr den Schutz von Umwelt und Gesundheit. Ein wesentlicher Aspekt betrifft dabei die Reduktion der Stickoxide aus Dieselmotoren auf Grundlage der selektiven katalytischen Reduktion (SCR). In SCR-Systemen reagieren Stickoxide katalytisch mit Ammoniak zu molekularem Stickstoff und Wasser. Aus SicherheitsgrĂŒnden wird Ammoniak jedoch nicht als reine FlĂŒssigkeit in Fahrzeugen mitgefĂŒhrt, sondern eine Harnstoff-Wasser-Lösung (32,5 %m Harnstoff, HWL) verwendet, die in den heißen Abgasstrom vor dem SCR-Katalysator eingespritzt wird. Durch thermische Zersetzung und anschließende Hydrolyse des Zwischenprodukts IsocyansĂ€ure wird die Lösung zu Ammoniak und Kohlendioxid umgesetzt. Obwohl dieses De-NOx-SCR-Verfahren in der Serienapplikation von Dieselfahrzeugen bereits seit LĂ€ngerem Anwendung findet, weist es noch immer erhebliche MĂ€ngel auf. Insbesondere die Benetzung der WĂ€nde des Abgassystems wĂ€hrend der Einspritzung ist ein unerwĂŒnschter und effektivitĂ€tsmindernder Prozess. Um die Robustheit und Regelbarkeit von SCR-Systemen zu optimieren, wird daher ein besseres VerstĂ€ndnis der physikalischen Prozesse benötigt, die der Entstehung von FlĂŒssigkeitsfilmen zugrunde liegen. Dazu wurde im Rahmen dieser Arbeit ein absorptionsbasierter Filmdickensensor entwickelt und validiert. Mit diesem Sensor ist es möglich, Filme berĂŒhrungslos und zeitlich hochdynamisch zu vermessen. Die robuste Auslegung des Sensors ermöglicht es dabei, in SCR Umgebungen mit hohen Temperaturen und begrenztem optischen Zugang zu messen. Um nachfolgend mit dem validierten Sensor Filme in einer SCR-Umgebung wohldefiniert untersuchen zu können, wurde ein generischer PrĂŒfstand mit kontrollierbaren und reproduzierbaren Randbedingungen konzipiert. In diesem können variabel Temperaturen und Massenströme in einem fĂŒr SCR-Anwendungen typischen Bereich eingestellt werden. Anschließend erfolgte die Messung von Filmdicken an diesem PrĂŒfstand unter systematischer Variation der Parameter Temperatur, Geschwindigkeit und EindĂŒsungsmenge. Dabei konnte festgestellt werden, dass sich grundsĂ€tzlich die Filmbildung nicht vermeiden lĂ€sst. Der im Film gebundene Harnstoff kann dem Prozess nur mit zeitlicher Verzögerung zur VerfĂŒgung gestellt werden. Dies hat zur Folge, dass die Stickoxidkonversion reduziert und damit die EffektivitĂ€t von SCR-Systemen gemindert wird. Deshalb sind neben der Filmbildung auch die grundsĂ€tzlichen Prozesse der Verdampfung einer HWL von Interesse. Im Rahmen dieser Arbeit konnte eine neue Messtechnik entwickelt werden, die in der Lage ist, alle drei Filmparameter von dynamischen HWL-Filmen auf technischen OberflĂ€chen simultan zu messen. Durch eine zusĂ€tzliche Messung der Gasphase ĂŒber dem Film konnte dabei zudem gezeigt werden, dass sich bereits in der Anfangsphase der Filmverdunstung Ammoniak bildet. Dies ist von großer Bedeutung fĂŒr weitere grundlegende Untersuchungen, die dem VerstĂ€ndnis der Verdunstungsprozesse dienen

    Towards value from waste: Bioreactor selection for the reduction of nutrient load and production of Poly-y-glutamic acid

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    Humanity is reaching a critical point in history where the re-use of resources previously classified as waste is becoming a necessary strategy to long term sustainability, through concepts such as circular economies. The re-use and reimagination of wastewater through the concept of a wastewater biorefinery (WWBR) is one such potential opportunity. It is the merging of integrated wastewater processing with bioproduction of valuable products from a waste stream, whilst still achieving clean water as an equally important and valuable product. These value-add products need to have sufficient value, and fulfil a market need to ensure that the WWBR is economically viable. South Africa's wastewater treatment plants, whilst faced with the challenges of rapidly growing populations, limited financial investment in infrastructure, maintenance and skilled operators, have the potential to achieve the goals of the bioeconomy and wastewater treatment through the implementation of the wastewater biorefinery concept. One of the main challenges facing the implementation of WWBR is the dilute and non-sterile nature of the wastewater. In traditional bioprocessing, this does not favour product formation due to the high flowrate and dilute streams. However, through optimisation of bioreactor design and careful selection against a set of design and operational criteria, a suitable reactor technology can be chosen that will facilitate bioproduction from these dilute streams and overcome the tensions. This project investigated the current wastewater treatment technologies used in a South African context and selected a reactor technology that meets the bioreactor selection criteria to address the challenges of bioproduction. To test its concept, the study focuses on an example product and microorganism from wastewater. One such product that has high potential for application in a WWBR is poly-ɣ-glutamic acid (ɣ-PGA.) It is a naturally occurring biopolymer with potential for application in medical, food, agricultural, wastewater treatment and cosmetic industries. A known ɣ-PGA-producing Bacillus subtilis strain was isolated (referred to as Isolate 1) from a wastewater treatment facility in Mitchells Plain, South Africa by Madonsela (2013). The kinetics of Isolate 1 were studied in stirred tank reactors (STRs) with a dilute minimal media under ideal temperature conditions (37°C) as well as uncontrolled room temperature to mimic environmental fluctuations that could be seen in a WWBR. The biomass productivity and maximum specific growth rates were estimated. Fed-batch room temperature cultivation was used to investigate if the biomass and PGA productivities could be maintained over extended time by feeding at the maximum glucoseutilisation rate seen during the batch cultivations. The maximum specific growth rates determined were used to inform the critical dilution rate expected in the continuous experiments. A detailed review of the existing reactor technologies used in South Africa's wastewater treatment plants was contrasted against the criteria for WWBR reactor selection, and through further literature review and refinement of the criteria, a SWOT analysis was done. The Moving Bed Biofilm Reactor or MBBR fulfilled the key criteria of a WWBR. With its reputation as a simple, yet robust technology with the ability to be retrofitted into existing wastewater treatment plant infrastructure (Odegaard, 2006; Wang et al., 2006; van Haandel & van der Lubbe, 2012), it was identified as the most promising reactor technology to investigate the aims of this research. A lab-scale MBBR was designed and constructed to demonstrate the continuous production of ɣ-PGA and the impact of biomass retention on productivities and nutrient removal, under continuous and nonsterile conditions. The dilution rate was increased beyond the calculated critical dilution rate to confirm that biomass retention would allow operation at higher dilution rates, whilst still maintaining or improving biomass and ɣ-PGA yields. The results from the STR batch cultivations compared the growth and productivity of Isolate 1 (Bacillus subtillis) at room temperature (RT) and 37 °C. The overall and maximum biomass productivities in the room temperature batch cultivations were an average of 0.071 ± 0.007 g/L/h and 0.425 ± 0.108 g/L/h respectively. These increased to 0.174 g/L/h and 1.246 g/L/h at 37 °C. The maximum specific growth rates under the RT conditions achieved average values of 0.150 ± 0.049 h -1 and 0.376 h -1 at 37 °C. Based on the maximum specific growth rates, a range of critical dilution rates were calculated to guide the process design and operating parameters in the continuous cultivation studies. Duplicate fed-batch experiments were conducted with the feed-rate set to the maximum glucose utilisation rate calculated from the batch experiments to achieve a final glucose loading of 2.86 g/L/h. Overall biomass productivities were increased from batch to fed batch phase from 0.092 ± 0.004 g/L/h to 0.189 ± 0.008 g/L/h. The average overall yield and productivities of ɣ-PGA (YP/S) in the fed-batch cultivations were calculated to be 0.681 ± 0.066 gP/gS and 0.667 ± 0.801 g/L/h. Following the design and construction of the MBBR, optimal operating parameters such as the loading of carrier and aeration rate needed to be found. Mass transfer studies using the static gassing in-out method were conducted to determine the preferred biofilm carrier loading (percentage of carrier volume in the reactor working volume) allowing the highest oxygen mass transfer. It was found that the optimal filling percentage was 40% and aeration rates of 3 to 5 L/min with volumetric mass transfer coefficient range of 17.23 to 35.64 h -1 . Hydrodynamic studies conducted at three different retention times (24h, 12 and 6 hours) and fixed aeration rate of 4 L/min. An increase in the liquid flowrate through the reactor resulted in shortened mixing times. No dead zones were observed. The mixing times of 40.5 ± 5.2 minutes (24 h), 24.5 ± 3.8 minutes (12 h) and 12.5 ± 2.7 minutes (6 h) found to be significantly smaller than the retention times, and thus the system was well-mixed with no visible dead zones or poor mixing. Biofilm attachment of Isolate 1 was demonstrated on the K3 Annox Kaldnes9Ÿ carriers. After a 4-week acclimation period, SEM imaging confirmed a thin and robust biofilm layer consisting of rod-shaped Bacillus-looking cells on the carriers. The MBBR continuous studies were commenced at a 24 h retention time (0.042 h-1 dilution rate) to ensure adequate biofilm retention and attachment onto the carriers. SEM imaging of the carriers again confirmed the presence of attached biofilm and dominance of rod-shaped bacteria as expected from Bacillus subitilis. The dilution rate was gradually increased until it reached the critical dilution rates calculated from the RT batch experiments. To test the robustness of the system the dilution rates were doubled twice thereafter until a decrease in substrate utilisation was observed at dilution rate 3-fold higher than the critical dilution rate. The retention times tested were 24, 21, 15, 10, 6.6, 4 and 2 hours (corresponding dilution rates of 0.042, 0.048, 0.037, 0.100, 0.152, 0.250 and 0.500 h-1 ). The steady-state results showed an increase in biomass and ɣ-PGA productivities with an increase in dilution rate. The biomass productivity increased from 0.156 g/L/h at 24 h (0.042 h-1 ) to 0.839 g/L/h at 2 h (0.500 h -1 ). The substrate utilisation (total carbon fed) decreased from 100% at a retention time of 0.042 to 95% at a retention time of 0.500 h-1 , while ɣ-PGA productivity increased from 0.367 g/L/h to 7.519 g/L/h. At dilution rates > 0.152 h-1 , the OD600 of the planktonic cell started to decrease. This is a significant result as, in a suspension culture, it would signify that cell washout was occurring and there would be a decrease in productivity. This is, however, not the case with productivity increasing; this demonstrates that significant biomass retention and biofilm development within in the MBBR and the uncoupling of hydraulic and biomass retention times drive productivity up, with decreasing dilution rates. One of the key objectives of this research was to demonstrate the proof of concept of the MBBR following its selection against key criteria required for the WWBR bioreactor and prove that bioproduction is possible. The MBBR was able to achieve increasing productivities of biomass and ɣPGA and high substrate utilisation at dilution rates higher than the critical dilution rate. This result demonstrates that WWBR using existing wastewater reactor technologies have great potential. Alongside this, the MBBR is easily retrofitted into existing activated sludge infrastructure that is widely used across South Africa. It is recommended that further study at a larger scale and conditions closer mimicking those of a WWTP be investigated to further test the potential of a WWBR in a South African context in fulfilling the sustainable future we all hope to achieve

    Polymer-based 3-D printing of G-band metal-pipe rectangular waveguide components

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    The objective of this thesis is to investigate the use of low-cost polymer-based 3-D printing for G-band (140 to 220 GHz) metal-pipe rectangular waveguide (MPRWG) components. First, various preliminary designs are investigated. Then, a successful ‘trough-and-lid’ assembly is demonstrated, which mitigates against the main design challenges for split-block waveguide construction at upper-millimeter-wave frequencies (ca. 100 GHz to 300 GHz), and can be realized using low-cost 3-D printing and conventional metal plating techniques. With this assembly, inexpensive masked stereolithographic apparatus (MSLA) 3-D printers and a standard commercial copper electroplating service are used. The trough-and-lid assembly is expected to provide a standard solution for the low-cost and low loss realization of most MPRWG implementations above 100 GHz; previously, this was infeasible without the use of high-cost, state-of-the-art 3-D printing and/or custom-developed metal plating techniques. Three different component types are successfully demonstrated: (i) straight thru lines; (ii) 90° twists; and (iii) bandpass filters (BPFs). Along with frequency-domain S-parameter measurements, a detailed time-domain reflectometry analysis is also included. For the more accurate characterization of these components, the additional insertion loss due to conductor surface roughness is investigated. Finally, the integration of an MPRWG component into a millimeter-wave subsystem, which is based on the design of a radiometer front-end, is presented.Open Acces

    Optimization of Lime Injection in EAF Systems by Using Pneumatic Sidewall Injectors

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    This master’s thesis work is a project for Nordkalk corporation as a part of a Business Finland co-funded project on Fossil-Free Steelmaking (FFS). The experiments of this study were performed in the Laboratory of Process and Systems Engineering at Åbo Akademi University. The metal and steel industry play a key role in Finland’s pursuit of carbon neutrality by 2035. The transition to a low-carbon society offers Finland significant business potential but requires investment in research. In the FFS project, industrial and research partners are studying different solutions and options for producing fossil-free steel. The project investigates productive solutions for using green energy, such as hydrogen, biochar and biogas, in the steel industry. In addition, the project studies the production of fossil-free lime and new solutions for utilizing the by-products of steelmaking processes [1]. In this master’s thesis work, cold model experiments on lime particle injection systems were performed to find an optimum particle size and operational conditions for the lime injection systems in an Electric Arc Furnace (EAF). The aims of the study include gaining key knowledge on the injection process, minimizing the dust formation through optimal particle size, investigating the dust formation patterns in comparison to particle size, understanding the multiple phase behaviors, including solid, liquid, and gas interactions, in the injection process. The experiments performed in the study were divided into two different parts. In a first set of experiments, the behavior of a 3-phase system containing solid, gas, and liquids was investigated. The use of paraffin oil on top of water to simulate the slag and molten iron, respectively, in the EAF was a very useful tool for studying the effect of the slag on the possible interactions between particles and slag in the systems. In this set of experiments, by using a cold model observed by a high-speed camera, calcium oxide (CaO) particles with different size ranges were injected into the liquids. Operational conditions, such as the air flow rate and the nozzle size, were changed to study their influence on the injection process. The particle velocity and the penetration depth of the particles and jet were measured. In addition, gas-particle behavior, particle rebounding, dust formation patterns, and liquid phase behavior were observed and studied. The second part of the experiments was performed by the same rig. In this series of experiments, the main objective was to measure the amount of dust produced during the injection process in order to find the particle size that resulted in a minimum amount of dust. Moreover, the influence of operational conditions on the dust formation, such as the air flow rate and the nozzle size, were investigated. Due to the importance of the effect of the conveying on the solid particles behavior and flowability of the solids, the methods for conveying solids as well as the design of a conveying system were also reviewed and discussed, and related equations were presented. In conclusion, based on the results of the experiments the penetration depth was found to increase with the decrease in particle size and nozzle size, and increase with the air flow rate. The distribution of particles through the liquid phase in which all particles distribute in different depths and widths of the liquid occurs with particle sizes in the range of 710-1000 ”m and the air flow rate equal to 30 l/min. Moreover, by increasing the particle size and air flow rate the dust formation and particle rebounding decreased. These findings can be used for designing proper operational conditions in the true process by using relations derived based on dimensionless numbers

    Impact phenomena in multiphase flows

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    Extracting innovation: an integrated material and experimental analysis of early distillation technology and its characterisation in South-Central Asia

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    In considering the position of technology within contemporary society, the concept of ‘innovation’ is integral in the creation of national, regional, and global narratives. This thesis addresses how early distillation - the selective evaporation and condensation of mixed substances - has been identified from archaeological evidence in South-Central Asia and associated with dialogues on the ‘Hellenistic East’ that are tied to traditional views on the influence of ancient Greek cultural and scientific innovations. The emergence of distillation marks a changing understanding of material properties, encompassing ideas on extraction, purification, and essences, and historically connected to proto-chemical explorations of matter. Yet primarily, distillation has been researched through a distinctly technically-led framework of explanation and empiricism. This thesis, therefore, challenges the widespread reconstruction of the ‘Gandhāra still’ as a key component within global chartings of distillation technology, used intermittently to both indicate processes of Hellenisation in South-Central Asia, but also reject ancient Greek origins for early distillation. First noted as 4th c. BCE – 4th c. CE ceramic remains from modern-day Pakistan, Afghanistan, and northern India, the characterisation of the ‘Gandhāra still and tradition’ is comprehensively evaluated in this thesis following recent reappraisals through a systematic material survey and targeted exploratory experimental studies. Results demonstrate how the ‘Gandhāra tradition’ and its constituent components are unlikely interpretations, both archaeologically and functionally, exemplifying how cultural concepts underpinning a limited view of ‘innovation’ have influenced interpretations of regional change, material classifications, and site function. Instead, through a holistic approach to technology, the body of analysis developed in this thesis reconsiders the technical practices and processes of innovation in early distillation by utilising insights gained from the experimental work. In doing so, an alternative view on the original ‘Gandhāra still’ archaeological evidence in South-Central Asia is presented that is distanced from its entrenched connection with distillation
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