Developing a three-dimensional laminar flow in the entrance region of rectangular microchannels has been investigated in this paper. When the hydrodynamic development length is the same magnitude as ...the microchannel length, entrance effects have to be taken into account, especially in relatively short ducts. Simultaneously, there are a variety of non-continuum or rarefaction effects, such as velocity slip and temperature jump. The available data in the literature appearing on this issue is quite limited, the available study is the semi-theoretical approximate model to predict pressure drop of developing slip flow in rectangular microchannels with different aspect ratios. In this paper, we apply the lattice Boltzmann equation method (LBE) to investigate the developing slip flow through a rectangular microchannel. The effects of the Reynolds number (1 <
< 1000), channel aspect ratio (0 <
< 1), and Knudsen number (0.001 <
0.1) on the dimensionless hydrodynamic entrance length, and the apparent friction factor, and Reynolds number product, are examined in detail. The numerical solution of LBM can recover excellent agreement with the available data in the literature, which proves its accuracy in capturing fundamental fluid characteristics in the slip-flow regime.
Coal hydropyrolysis (CHP) and coal hydrogasification (CHG) are two important processes during coal conversion in a hydrogen atmosphere. Much attention has been paid on this clean coal conversion ...technology because of its advantages. In this work, the CHP and CHG kinetic characteristics of a bituminous coal are studied in a pressurized thermogravimetric analyzer (P-TGA). The effects of the pressure on the CHP and CHG kinetics of the bituminous coal are detected with the non-isothermal thermogravimetric method. In addition, the kinetic compensation effect (KCE) and isokinetic points of the two processes are investigated. Besides, the kinetic triplets, including the pre-exponent factor, the activation energy and mechanism function are also calculated and defined for all of the cases during the CHP and CHG processes. Meaningful and interesting conclusions are finally obtained from this study. The initial pyrolysis temperature will increase with the reaction pressure when the pressure is within 3 MPa. The appearing time of the weight loss peak rate will be delayed when the pressure is lower than 2 MPa, and then it will become earlier gradually with the pressure increment. The weight loss peak rate will decrease sharply when the pressure is increased from 0.1 to 1 MPa, and then it will increase gradually with the reaction pressure increment. The KCE phenomenon during the CHP process is not detected, and the isokinetic point is not found. The KCE can be detected during the CHG process when the reaction pressure is within 3 MPa and the isokinetic point temperature is found as 1041.0 K.
We report a study comparing teaching written and spoken Chinese separately to adult learners without prior knowledge of Chinese in the traditional classroom setting and in the online format. The best ...way of introducing Chinese characters remains one of the major challenges in teaching Chinese as a foreign language: different methods have been used in practice and more empirical evidence is needed to identify their advantages and limitations. In a crossover design, we compared groups which received either four-week tuition in Chinese characters only (without teaching the sound or pinyin spelling) or the same period of tuition in spoken Chinese (without any writing, neither characters nor pinyin). After a two-week break, the groups were swapped, such that the writing class received tuition in spoken Chinese and vice versa. The first four-week block was delivered in the traditional classroom format, while the remaining tuition took place online, due to the Covid-19-related lockdown. The idea of teaching spoken and written Chinese entirely separately, although initially unfamiliar to teachers, proved to be feasible. The transition to online teaching worked well and brought not only challenges, but also new opportunities and advantages, particularly in the teaching of characters. Students’ experience of both parts of course (written and spoken) was overwhelmingly positive. However, while students who experienced classroom teaching first and then switched to online delivery perceived the online format as an unavoidable replacement, those who started the course online embraced it enthusiastically, accepting it as “the new normal” and focusing on its opportunities.
The interaction of microplastics (MPs) and nanoplastics (NPs) with natural organic matter (NOM) has opened new debate, defies and research prospects for the scientists owing to the development of ...‘eco-corona (EC)’ on plastic particles or ‘biogenic aggregates’ in the environment. MPs and NPs can intermingle with allochthonous NOM, autochthonous NOM, and anthropogenic NOM, and can form an EC film or aggregation that not only alters physicochemical characteristics but also the mobility, stability, bioreactivity, settling, and fate of MPs and NPs in the environment. Therefore, in this review, the up-to-date statue on the interaction of MPs and NPs with NOM in various environmental matrixes are critically debated to explore the modulations in the development of biogenic aggregates or EC in the environment. Importantly, the influence of various constituents on the interaction of MPs and NPs with NOM in different environmental matrixes is critically examined to better elucidate the myth and reality about the development of EC. The presence of NOM can increase or decrease the sorption of contaminants. Thus, the impact of NOM on the sorption behavior of anthropogenic contaminants on the surfaces of MPs and NPs has been critically interpreted to better understand the environmental fate of MPs/NPs and anthropogenic pollutants in the presence of NOM. Finally, this review also encapsulates current knowledge gaps and potential recommendations regarding the interaction of MPs and NPs with NOM to assist the scientific community in a battle against MPs and NPs pollution.
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•Interaction of MPs and NPs with natural organic matter is critically assessed.•Influence of various constituents on the interaction are critically examined.•Elucidated the myth and reality about the development of eco-corona.•Discussed the impact of NOM on the sorption behavior of anthropogenic contaminants.•Knowledge gaps and future recommendations have been emphasized.
•Developments of promising adsorbents for MPs/NPs removal are critically assessed.•Pertinent factors can inhibit adsorptive performance of MPs/ NPs.•Practical application of the developed adsorbents ...is emphasized.•Briefly highlighted the barriers in market penetrations of adsorption-based technologies.•Knowledge gaps and future recommendations have been emphasized.
Microplastics and nanoplastics are being assumed as emerging toxic pollutants owing to their unique persistent physicochemical attributes, chemical stability, and nonbiodegradable nature. Owing to their possible toxicological impacts (not only on aquatic biota but also on humans), scientific communities are developing innovative technologies to remove microplastics and nanoplastics from polluted waters. Various technologies, including adsorption, coagulation, photocatalysis, bioremediation, and filtration, have been developed and employed to eliminate microplastics and nanoplastics. Recently, adsorption technology has been getting great interest in capturing microplastics and nanoplastics and achieving excellent removal performance. Therefore, this review is designed to discuss recent innovations in developing promising adsorbents for the remediation of microplastics and nanoplastics from wastewater and natural water. The developed adsorbents have been classified into four main classes: sponge/aerogel-based, metal-based, biochar-based, and other developed adsorbents, and their performance efficiencies have been critically examined. Further, the influence of various pertinent factors, including adsorbents' characteristics, microplastics/nanoplastics’ characteristics, solution pH, reaction temperature, natural organic matter, and co-existing/interfering ions on the removal performance of advanced adsorbents, have been critically assessed. Importantly, the particle application of the developed adsorbents in removing microplastics and nanoplastics from natural water has been elucidated. In addition, barriers to market penetration of the developed adsorbents are briefly discussed to help experts transfer adsorption-based technology from laboratory-scale to commercial applications. Finally, the current knowledge gaps and future recommendations are highlighted to assist scientific communal for improving adsorption-based technologies to battle against microplastics and nanoplastics pollution.
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A representative steady-state heat conduction problem in rectangular solids with uniformly distributed heat generation has been investigated analytically. An analytical solution is provided by ...solving a non-homogeneous PDE. A simple and accurate model is proposed to predict the dimensionless shape factor parameter for the first time. The dimensionless shape factor is obtained in the light of the solution of Poisson equation with constant wall temperature boundary conditions. The area-mean temperature is found by integration on the rectangular cross-section. The model is very concise and nice for quick real world approximations, and it provides acceptable accuracy for engineering practice.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Sphere Drag and Heat Transfer Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
Scientific reports,
07/2015, Letnik:
5, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed ...to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.
The transition flow regime is the most complicated domain for modeling since the transition regime is a varying mixture of different transport mechanisms. Modeling the Navier-Stokes equations with ...the appropriate second order slip boundary condition at high Knudsen numbers is further explored in this paper. The general models proposed by one of the authors are validated against extensive numerical and experimental data in the literature. It is noteworthy that the geometry and the partial momentum accommodation are taken into account by the models. The present work provides a markedly simple way to compute quantities of engineering interest in microchannels and nanochannels of various cross sections over the full transition flow regime that is estimated to be accurate to 10%, with most data within 5%. As in the transition regime no data exist for most various geometries, this proposed engineering model fills this void. This paper further explores and validates working engineering macro models that can be easily implemented in applications.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Colony formation is a crucial trait that enhances the ability of
Microcystis
to withstand the complex and ever-changing aquatic environment. However, the cellular response within a colony has not ...been extensively investigated. This research gap can be attributed to the difficulty of isolating individual cells within the colony. In this study, we employed a colonial strain of
Microcystis
and devised a preliminary method framework known as the ‘onion peeling method’ to analyze the cell characteristics within different regions of the colony. The method demonstrated high efficiency by successfully isolating 34.8% of cells from the colony while causing minimal damage. Additionally, we conducted an application study using this method to examine the influence of external nutrient availability. The findings indicate that the peripheral
Microcystis
cells located near the colony’s surface were more vulnerable to a decrease in external nutrient availability, resulting in a reduced frequency of cell division (from 0.27 to 0.11 – 0.12). On the other hand, the internal cells showed more stability, which could be attributed to the presence of the intra-colony phycosphere. The findings of the application study indicate the significant role of colony formation in minimizing the impact of adverse environmental conditions on internal cells. This could be one of the factors contributing to the prolonged occurrence of
Microcystis
blooms. Furthermore, our method framework study suggests a broader application potential, as comparing the cellular characteristics of
Microcystis
from different intra-colony regions may help uncover biological or ecological strategies.
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