Stable Flow Conditions Research Articles

Flow features of a horseshoe tunnel bend

Previous research on bend flow has mainly focused on rectangular channels or circular conduits with small bend radii. This study investigates the dynamics of bend flow in an unexplored geometry: the horseshoe cross-section with large bend radii, a typical configuration in hydraulic tunnels. We examine two critical flow features, energy losses and superelevation, employing theoretical equations and dimensional analysis based on experimental data collected on a physical model of a diversion tunnel. The findings reveal an exponential decrease in the bend loss coefficient with increasing Reynolds numbers and shockwaves within the bend for Froude numbers exceeding 1.945. These findings are relevant in a hydraulic tunnel design with similar features and offer insights to minimize energy losses and maintain stable flow conditions.

Effect of surfactant on dynamics and gas-liquid mass transfer for single carbon dioxide bubbles

In carbonation reaction, the impact of surfactants on the movement and mass transfer behavior of carbon dioxide bubbles were crucial for the production of high-quality silicon dioxide products. The study employed the Matlab image processing system to investigate the shapes, motion velocities, and rise path of single carbon dioxide bubbles within varying concentrations of cetyltrimethyl ammonium bromide (CTAB) solutions. This exploration aimed to elucidate the effect of CTAB on the movement and mass transfer coefficient (MTRC) of single carbon dioxide bubbles. Alterations in the CTAB solution concentration and bubble sizes significantly influenced the mass transfer and movement characteristics of single carbon dioxide bubbles. The conclusion was drawn through the computation of the MTRC of single carbon dioxide bubbles in deionized water and CTAB solutions: the addition of CTAB significantly reduced the mass transfer efficiency of carbon dioxide in deionized water, with the MTRC of CTAB solutions decreasing as the solution concentration increased. Utilizing the stagnant cap model, it can be concluded that CTAB's reduction of the MTRC of carbon dioxide was attributed to the high viscosity of the medium, low bubble velocity, stable flow conditions, and intensified adsorption degree of CTAB molecules at the gas-liquid interface. According to the significant periodic trajectories of single carbon dioxide bubbles in the stable range, the correlation between the trajectories of compressible bubbles in surfactant solution and mass transfer in liquid phase was established, and the previous method based on rigid sphere model was modified. The paper proposed the mechanism of CTAB's influence on single carbon dioxide bubbles, offering crucial theoretical insights into the industrial application of surfactants in the carbonation process for producing silicon dioxide.

Research on Micro-Turbine Operating State Characterization Based on Bearing Vibration Signals Analysis

An air flow-driven micro-turbine, widely used in air-condition control systems in aircraft cabins, train coaches, etc., exhibits complex vibration behaviors under stable or unstable inlet flow conditions, and especially has a certain correlation with speeds. In this paper, the vibration responses of the micro-turbine undergoing stable and unstable inlet flows measured on a test rig are analyzed and compared by using different signal processing methods, which include time and frequency domain methods, and statistical and nonlinear methods. First, the test rig system of the airflow-driven micro-turbine, the instrument system and four typical experimental cases are introduced. Then the measured vibration signals are analyzed and compared by time domain characteristic parameters (peak-to-peak value, RMS value and kurtosis value), statistical parameters (auto-correlation and BDS), and amplitude spectra in the frequency domain, statistic spectrum indicators (SSI) based on Welch's periodogram of power spectra, and the spectra of selected IMF components based on Hilbert-Huang Transform (HHT). In particular, some nonlinear feature analyzing methods, including Pseudo-Poincare mapping diagrams and Lempel-Ziv(LZ) complexity, are also used for analyzing measured vibration responses. The obtained results using the above multiple methods are compared and show that, when the inlet flow of the turbine fluctuates significantly, the nonlinear characteristics of the turbine bearings are significantly higher than those of the relatively stable inlet flow and speed conditions. Under these circumstances, commonly used time-frequency analysis methods cannot characterize the different speed operating state of the turbine, and LZ-Complexity and other nonlinear characterization methods should be used to better understand the characteristics of different speeds under unstable conditions.This study provides references for the aerodynamic stability monitoring of the micro-turbine and its design improvement.

Kajian Rekayasa Lalu Lintas Simpang TNI AU Rembiga Akibat Rekayasa Sistem Satu Arah pada Jl. Dr. Wahidin

TNI AU Rembiga intersection is a three-way link between the central point of Mataram city, which is also connected to the Rembiga intersection and the Dakota intersection, Rembiga. Dr. Wahidin street is an economic pathway for education, offices, and trade. At certain times, the traffic flow is very congested because the road is also the direction to West Lombok district. Based on observations at the research location, it was found that the distance between the Rembiga intersection and the TNI AU intersection was 322.8 meters which caused the movement of traffic flow to be less than optimal between the intersection distances so that it would affect performance at TNI AU intersection. For this reason, the purpose of this study was to examine the performance of the unsignalized intersection at the TNI AU Rembiga intersection due to the continued flow from the Rembiga intersection which is a signalized intersection due to a one-way system engineering carried out on the Dr. Wahidin street and before the implementation of the one-way system on the Dr. Wahidin street. This research was conducted with reference to the MKJI 1997, in which researchers conducted field observations, then collected primary data and secondary data. There is traffic flow engineering on Dr. Wahidin street, by creating a one-way system, had an impact on changing the performance of the unsignalized intersection at the TNI AU intersection to a level of service F with obstructed flow conditions, low speed whereas, before the implementation of the one-way system the level of service was E with stable flow conditions, stalled vehicles.

Experimental investigation and analysis of two-phase flow instability of flow boiling in a mini-channel heat sink

High heat flux and good axial temperature uniformity of channel flow boiling demonstrate that it is ideally suited for next-generation cooling systems. Such systems, however, are hampered by undesirable flow fluctuations, making channel flow boiling ineffective due to the rapid bubble growth within the channels. Furthermore, especially in the mini-channel heat sink, the interactions between multiple parallel channels and inlet/outlet plenum induce complex hydraulic and thermal oscillations. Therefore, lots of consistent and detailed experimental data are still needed to design a reliable flow boiling system. However, only limited studies have examined the effects of channel interaction on flow boiling instability. Thus, to provide a better understanding of the flow boiling instabilities, a mini-channel heat sink was tested with near-saturated inlet conditions using FC-72 as the working fluid. The mini-channel heat sink consisted of a 150 mm long and 70.4 mm wide base area, having 22 identical rectangular channels measuring 1.6 × 4.8 mm2. The flow instabilities were analyzed by observing the vapor backflow and flow fluctuation in mini-channels with variations in the mass velocity, pressure, and heat fluxes. The analysis is based on the detailed flow visualization in the parallel channels and inlet plenum. It was found that the rapid bubble generation in individual channels promotes vapor backflow and hydraulic oscillations. Further observation of the high-speed camera images shows that the vapor crossing over between parallel channels through the inlet plenum led to the synchronization of vapor oscillations, which is responsible for the parallel channel flow instability. This visualization study revealed six dominant flow patterns showing multi-channel flow instability. Based on the classification of dominant flow patterns, a better understanding of the operating conditions for stable flow boiling was obtained.

Flow and plankton availability control young‐of‐the‐year fish diet in two floodplain nurseries

AbstractIn large river floodplains, the availability of trophic resources to the fish fauna is highly variable as a consequence of seasonal environmental change and habitat diversity. Young‐of‐the‐year fishes (YOY) must find suitable habitats to settle, feed and survive. However, very few in‐depth studies are available about the food preferences of the young fishes during their first growing season. Here, we investigated the composition of planktonic assemblages and the YOY diet of three generalist fish species Alburnus alburnus (Linnaeus, 1758), Squalius cephalus (Linnaeus, 1758) and Pseudorasbora parva (Temminck & Schlegel, 1846) from four floodplain sites of the French Upper Rhône River. More specifically, we studied their temporal and spatial variations in relation to five environmental variables: hydrology, dissolved oxygen, primary production, water temperature and conductivity. Stable flow conditions and the associated temperature and conductivity strongly structured the phytoplankton community in the floodplain channels, whereas water movements within channels and dissolved oxygen concentrations were significantly correlated to the zooplankton composition. A zooplankton density above ≈100 ind L−1 allowed the initiation of a YOY diet mainly based upon zooplankton for the three fish species. When zooplankton densities were insufficient, all three species used phytoplankton as their main food resource. Finally, the diet overlaps between species, differed significantly between sites. The study highlights the need to examine the diet of juvenile fishes and environmental variables in the floodplains.

Tracing the Soil Water Flux in Variably Saturated Zones Using Temperature Data

AbstractThe coexistence of water, vapor, and solid phases and the spatiotemporal changes in thermal conductivities in response to variations in water content pose a challenge to the heat‐tracing method used to calculate water flux in variably saturated zones. In this study, a new approach, which adopted finite difference numerical schemes along with the limited‐memory Broyden–Fletcher–Goldfarb–Shanno bounded (L‐BFGS‐B) parameter optimization algorithm, was developed to inversely trace vertical soil water fluxes in variably saturated zones using temperature‐depth time‐series data. The newly developed method did not utilize hydraulic parameters, and only temperature time‐series data were used at the adjacent depths as boundary conditions. The soil water, vapor flux, and spatiotemporal variations in thermal conductivity at a given location were optimized by fitting the temperature time‐series at the target depth using the L‐BFGS‐B algorithm. Further, the method was verified through laboratory experiments under different saturated conditions that were conducted in two columns with saturated and free drainage bottom boundaries, and five sets of different flow rates with a relatively stable flow condition. The soil water flux calculated using the proposed method was consistent with the observed data, thus, verifying the reliability of the approach in applications with relatively stable flow rates. Furthermore, the new method was applied to a field site to estimate the time‐varying soil water flux using the measured temperature data. The trends of the calculated soil water flux at different depths were consistent with the field hydrologic conditions and observations. Thus, this study provides a novel computationally efficient and easy‐to‐implement tool to determine soil water flux using temperature measurements.

Experimental investigation of the development of surfactant stabilized oil-water pipe flow downstream of a choke valve

In wells and multiphase flowlines the presence of valves, pumps and other complex geometries will considerable contribute to dispersion of the phases. In combination with the droplet stabilizing effect of natural surfactants contained in the crude oil and other production chemicals, this may lead to a considerable development length of the flow. Such effects should be understood and considered by future simulation tools. In the presented work, the described scenario was experimentally tested under controlled conditions. The development of dispersed oil-water flow downstream of a valve was monitored. Surfactant was added to the mineral oil to obtain a suitable droplet stability. The near horizontal test section was 220 m long and had an inner diameter of 109 mm. The vertical phase fraction distributions were measured at six locations along the pipe with traversing gamma densitometers. The test section was further instrumented with nine pressure transducers, four optical sections, and three droplet sampling points to monitor flow development. The flow development showed a characteristic behavior of a rather sudden separation after a certain length with stable dispersed flow conditions. The degree of inlet mixing and thus initial droplet size governed by the pressure drop over the mixing valve was found to be crucial for the development length. Flow rate and initial water fraction were of minor importance. The separation behavior was coalescence controlled as it would be expected for a surfactant stabilized system. Still, even if static separation bench tests resulted in very long separation time scales, the in-flow separation happened much faster. This indicates the importance of dynamic flow conditions and associated effects such as shear and a certain mixing to be preferential for the separation. The measured pressure drop of the dispersed flow was more than 20% higher than separated flow with otherwise the same conditions. As the flow separates, the pressure drop decreases and, as expected, finally approaches the value for separated flow. The work presents a detailed data set as basis for model development.

Different types of criteria for dealing with anomalous noise events in urban environments under stable road traffic flow conditions

The management of anomalous noise events in the assessment of environmental noise of specific sources is an important issue for determining the actual exposure of the population to noise pollution. Of all the sources currently considered in the European Noise Directive, road traffic is the most important in cities, both in terms of its temporal and spatial presence, as it is generally maintained 24 h a day and affects almost all streets in urban environments. This paper proposes two types of criteria for dealing with these events in urban environments under stable vehicle flow conditions. The results show the convenience of using each type of the suggested criteria for the elimination of anomalous noise events depending on the objective of the research. Those exclusion criteria based on applying a threshold to the average sound level, may be considered the best among the proposed options to study the variation of the annual average LAeq,1h. However, to study the relation between road traffic noise and temperature, a novel proposal for anomalous event elimination criteria based on dividing the full temperature range into small intervals may be a relevant approach. Overall increases of 8 %, respectively, 14 %, in the explanation of variability were found for the criteria C6 (successive application of the thresholds ±10 dB, ±6 dB and ±3 dB at each temperature interval of 3 °C) with respect to the cases where anomalous sound events were not excluded, respectively, using criteria C1 from the scientific literature. The application of this type of criteria for the management of anomalous noise events could also be useful for the study of the relation between road traffic noise and other objective and subjective variables in cities, especially in those areas with a greater daily thermal oscillation.

Comparison of arterial storage conditions for delayed arterial ring testing

ObjectiveArterial ring testing is the gold standard for measuring arterial function. Increased arterial tone through arterial contraction and impaired endothelial relaxation (endothelial dysfunction) are key metrics of impaired arterial health in peripheral arterial disease (PAD). To allow for comparative testing of arteries during standard laboratory hours, storage buffers and conditions have been used to extend the functional life of arteries. Various storage conditions have been compared, but there has not been a robust comparison or validation in human arteries. The objective of this work is to optimize storage of arterial segments for endothelial cell (EC) testing in a murine model and to test EC function in human PAD arteries. We hypothesized that certain storage conditions would be superior to others. MethodsHealthy murine aortas were harvested from 10- to 14-week-old C57/Bl6J male and female mice and compared under different storage protocols (24 hours) to immediate arterial testing. The storage conditions tested were: Opti-MEM (37°C or 4°C), Krebs-HEPES with 1.8 mmol/L or 2.5 mmol/L calcium (4°C), or Wisconsin (WI) solution at 4°C. Vascular function was evaluated by isometric force testing. Endothelium-dependent and -independent relaxation were measured after precontraction with addition of methacholine or sodium nitroprusside, respectively. Arterial contraction was stimulated with potassium chloride or phenylephrine. Analysis of variance was used to determine significance compared with immediate testing with P < .05. Under institutional review board approval, 28 PAD arteries were collected at amputation and underwent vascular function testing as described. Disturbed flow conditions were determined by indirect (upstream occlusion) flow to the harvested tibial arteries. Stable flow arteries had in-line flow. Arterial calcification was quantified manually as present or not present. ResultsWe found that 4°C WI and 37°C Opti-MEM best preserved endothelium-dependent relaxation and performed similarly to immediately testing aortas (termed fresh for freshly tested) (P > .95). Other storage conditions were inferior to freshly tested aortas (P < .05). Vascular smooth muscle function was tested by endothelial-independent relaxation and contractility. All storage conditions preserved endothelial-independent relaxation and contractility similar to freshly tested arteries. However, 4°C WI and 37°C Opti-MEM storage conditions most closely approximated the maximum force of contraction of freshly tested arteries in response to potassium chloride (P > .39). For human arterial testing, 28 tibial arteries were tested for relaxation and contraction with 16 arteries with peripheral artery occlusive disease (PAD with disturbed flow) and 12 without peripheral artery occlusive disease (PAD with stable flow), of which 14 were calcified and 14 were noncalcified. Endothelial-dependent relaxation data was measurable in 9 arteries and arterial contraction data was measurable in 14 arteries. When comparing flow conditions, arteries exposed to disturbed flow (n = 4) had significantly less relaxation (2% vs 59%; P = .03) compared with stable flow conditions (n = 5). In contrast, presence the (n = 6) or absence of calcification (n = 3) did not impact arterial relaxation. Arterial contraction was not different between groups in either comparison by flow (n = 9 disturbed; n = 5 stable) or calcification (n = 6 present; n = 8 absent). ConclusionsIn healthy murine aortas, arterial storage for 24 hours in 4°C WI or 37°C Opti-MEM both preserved endothelium-dependent relaxation and maximum force of contraction. In human PAD arteries stored in 4° WI, flow conditions before arterial harvest, but not arterial calcification, led to differences in arterial relaxation in human PAD arteries. Arterial contractility was more robust (11/28 arteries) compared with arterial relaxation (7/28 arteries), but was not significantly different under flow or calcification parameters. This work defines ideal storage conditions for arterial ring testing and identifies that EC dysfunction from disturbed flow may persist in delayed ex vivo arterial testing.

Comparison of Cooling Performance in a Cylindrical Battery with Single-Phase Direct Contact Cooling under Various Operating Conditions

This study compares the performance according to a working fluid, the number of battery cooling block ports, and header width required for cooling according to the application of the direct contact single-phase battery cooling method in a 1S16P battery module and examines the battery cooling performance according to the flow rate under the standard and summer conditions based on an optimized model. The analysis result verified that R134a showed low-pressure drop and high cooling performance as the working fluid of the direct contact single-phase cooling system in the 1S16P battery module, and R134a showed the best cooling and stability when applied with three ports and a 5 mm header. In addition, under 25 °C outdoor conditions, the maximum temperature of the battery and the temperature difference between the batteries at 3 and 5 lpm excluding 1 lpm are 30.5 °C, 4.91 °C, and 28.7 °C, 3.28 °C, indicating that the flow rate of refrigerant was appropriate for battery safety. In contrast, in the summer condition of 35 °C, the maximum temperature of the battery and temperature difference between the batteries were 38.8 °C and 3.27 °C at the R134a flow rate of 5 lpm or more, which was verified as a stable flow condition for battery safety.

Numerical Analysis of Gas Flow Instabilities in Simplified Vertical HVPE GaN Reactors

This paper investigates the gas flow and the mass transport in simplified axial-symmetric vertical HVPE reactors for the growth of GaN bulk crystals through numerical simulations. We evaluate the relative significance of different flow and transport phenomena in dependence on the direction of gravity. The performed simulations show that buoyancy effects due to density differences between neighboring gas lines are the main factor causing the deformation of laminar flow patterns and the formation of recirculation cells within the growth zone. Baroclinic instabilities have been identified as the source for these phenomena. In contrast, typical vertical temperature gradients show only a minor impact on the stability of the gas flow within the growth zone in the vicinity of the growing crystal. Based on these results, major differences of the species transport in vertical HVPE reactors, where the flow is parallel or anti-parallel to the direction of gravity, referred to as down-flow and up-flow, respectively, are summarized. The performed analysis of the interplay and relative significance of different flow effects in the HVPE environment allows a general recommendation for reactor design and scaling with respect to stable gas flow conditions within the growth zone.

Physical model setup and tests on cooling circulation water pumping intake system

Abstract The thermal power plant built by the Taiwan power company intends to use multiple cooling circulation water intake systems to introduce seawater from adjacent sea areas. The water in the front pool of the water inlet is introduced into the pump chamber through the large pump in the circulating water pump sump. The primary function of the pump chamber is to provide a stable and uniform flow condition before the large pump sucks in the seawater. When the hydro-dynamic conditions outside the pumping station are not ideal, and the inflow is relatively unstable, the pumping chamber can provide a buffer space for rectification. In addition, when the flow field near the suction intake of a large pump can maintain a certain degree of stability in space and time, it can reduce the frequency and intensity of the vortex or other harmful factors caused by the flow field. Moreover, a pump sump flow field can also maintain the pump's working efficiency, reducing vibration and maintenance costs. Although the relevant design standards such as the Hydraulic Institute (H.I.) standard in the United States or the British Hydromechanics Research Association (B.H.R.A.) standard in the United Kingdom can be consulted for different types of pumping room geometric layout planning and design recommendations. However, most design references are obtained from the boundary conditions of general cases. Therefore, these design criteria indicate that when the pump room geometry and flow conditions have special considerations or detail design, physical model tests should be conducted to verify it or correct the layout according to the model test results. Because the fluid mechanisms involved in the relevant research are complex, the current theoretical or numerical models are not enough to fully simulate flow fields. Therefore, it is necessary to conduct a physical model test based on the feasibility model scale. Based on the similarity theory to scale down prototype structures, the flow mechanism of preliminary design is reproduced, and the revised plan is also verified in the physical model to satisfy the project objectives. The qualitative flow field visualization method was used to observe the free surface vortex, subsurface vortices, and the swirl angle in the suction pipe under different layout schemes at each physical test case. The tested results show that the flow pattern and vortex strength are both acceptable with designed anti-vortex devices.

Instabilities in Fixed Bed Reactors with Downwards Directed Flow for the Oligomerization of 1‐Butene

AbstractIn this work instabilities in fixed bed reactors with downwards directed flows for the oligomerization of 1‐butene were investigated. For very long residence times or very low velocities in combination with strong exothermic reactions, the buoyancy force can exceed the inertia force and the downwards directed liquid flow in the fixed bed becomes instable. These flow conditions might result in hotspots, the shift of the conversion towards unwanted by‐products or even in a runaway of the reactor. Therefore, the detailed understanding of the transition between stable and instable flow conditions in fixed bed reactors is essential for a safe and reliable operation of the reactor. Various simulation methods and correlations were applied to predict instable conditions that were observed in an experimental setup. 3D CFD simulations could be used to predict instable flow conditions in fixed bed reactors.

Experimental investigation on stable/unstable flow behaviors of parallel boiling channels under forced vertical vibrations

• Stable/unstable boiling flows in parallel channels were tested under vibrations. • A non-dimensional void difference was introduced to identify system stability. • Stable flow behaviors can be clearly affected by forced vertical vibrations. • Unstable flow oscillation frequency can be validated with 1-D drift flux model. • An empirical correlation for predicting oscillation frequency was proposed. Experimental tests were carried out to investigate the dynamic behaviors of parallel boiling channels under stable and unstable flow conditions with/without forced vertical vibrations. The parallel channels with a length of 1.91 m and diameter of 11.9 mm were attached to a vertical vibration platform. The inlet flow was controlled with average velocity of 0.142–0.277 m/s and subcooling of 6.0–12.6 °C, and the parallel channels were loaded with heat flux of 12.5–36.9 kW/m 2 . Overall 35 flow conditions were tested along with three static and vibration subset conditions ( f = 0, 1.06 and 1.62 Hz), which covered the stable and unstable flow conditions in the parallel channels, and the dynamic variations of void fraction, pressure difference and temperature were recorded and analyzed. A non-dimensional void difference was proposed to identify the system stability of parallel channels, and fast Fourier transform (FFT) was utilized to extract the dominant frequencies of flow behaviors. While system is stable under vibrations, the dominant frequencies of flow properties were identical to the vibration frequencies; whereas if the system is unstable, the extracted frequencies were dominated by unstable flow oscillations, which are much lower than the vibration frequencies. In addition, the unstable flow oscillation frequencies can increase with increasing inlet velocity and heat flux, and an empirical correlation was proposed for estimating the oscillation frequencies, which can predict the present database with an averaged accuracy of 8.85%.

In Situ Detection of Interfacial Flow Instabilities in Polymer Co-Extrusion Using Optical Coherence Tomography and Ultrasonic Techniques.

Co-extrusion is a widely used processing technique for combining various polymers with different properties into a tailored multilayer product. Individual melt streams are combined in a die to form the desired shape. Under certain conditions, interfacial flow instabilities are observed; however, fundamental knowledge about their onset and about critical conditions in science and industry is scarce. Since reliable identification of interfacial co-extrusion flow instabilities is essential for successful operation, this work presents in situ measurement approaches using a novel co-extrusion demonstrator die, which is fed by two separate melt streams that form a well-controlled two-layer co-extrusion polymer melt flow. An interchangeable cover allows installation of an optical coherence tomography (OCT) sensor and of an ultrasonic (US) measurement system, where the former requires an optical window and the latter good direct coupling with the cover for assessment of the flow situation. The feasibility of both approaches was proven for a material combination that is typically found in multilayer packaging applications. Based on the measurement signals, various parameters are proposed for distinguishing reliably between stable and unstable flow conditions in both measurement systems. The approaches presented are well suited to monitoring for and systematically investigating co-extrusion flow instabilities and, thus, contribute to improving the fundamental knowledge about instability onset and critical conditions.

Deposition of Smoke Particles in Human Airways with Realistic Waveform

Exposure to toxic particles from smoke generated either from bush fire, stable burning, or direct smoking is very harmful to our health. The tiny particles easily penetrate deep into the lungs after exposure and damage the airways. Tobacco smoking causes the direct emission of 2.6 million tons of CO2 and 5.2 million tons of methane annually into the atmosphere. Nevertheless, it is one of the significant contributors to various respiratory diseases leading to lung cancer. These particles’ deposition in the human airway is computed in the present article for refining our understanding of the adverse health effects due to smoke particle inhalation, especially cigarette smoke. Until recently, little work has been reported to account for the transient flow pattern of cigarette smoking. Consideration of transient flow may change the deposition pattern of the particle. A high-resolution CT scan image of the respiratory tract model consisting of the oral cavity, throat, trachea, and first to sixth generations of the lungs helps predict cigarette smoke particle (CSP) deposition. With the same scan, a realistic geometric model of the human airways of an adult subject is used to simulate the transport of air and particle. The CSP deposition is determined at different locations from the oral cavity to the sixth generation of the bronchi. In addition, an unsteady breathing curve indicative of realistic smoking behavior is utilized to represent the breathing conditions accurately. The discrete phase model (DPM) technique is used to determine smoke particle deposition in the human airways. It is found that the deposition increases with the size of the smoke particle. Particles tend to deposit in the oral cavity around the bifurcation junction of the airways. The deposition fraction of CSP with the realistic waveform of smoking is found to be smaller compared to that during the stable flow condition. It is also observed that the fine particles (0.1–1.0 micron) escape to lower generations, leading to higher deposition of fine particles in the deeper airways. The outcome of the study is helpful for understanding smoke-related pulmonary complications.

Identification and quantification of microplastic particles in drinking water treatment sludge as an integrative approach to determine microplastic abundance in a freshwater river

Microplastic (MP) has been detected ubiquitously in freshwater systems. Until now MP sampling, however, is predominantly based on short-term net or pumping and filtration systems which can only provide snapshots of MP abundance; especially in flowing water bodies. To improve representativeness in the determination of MP occurrences in these aquatic compartments, an integrative approach that covers larger water volumes for a longer period of time is required. In this regard, surface water supplied drinking water treatment plants (DWTPs) represent an opportunity. In DWTPs, suspended solids from thousands of cubic metres of raw water are continuously removed over several hours and enriched in coagulation/flocculation and filtration processes. Our hypothesis was that MP is also removed to a full extent, like suspended solids, and that an integrative approach for identification and quantification in raw water can be derived from the analysis of MP in the treatment sludge. To prove this hypothesis, treatment sludge from a riverside DWTP (Warnow river, North-Eastern Germany) was analysed for MP > 50 μm. A sample purification protocol overcoming potential matrix effects caused by coagulants and flocculants was developed and validated. MP was analysed using micro-Raman spectroscopy. MP occurrence determined for the Warnow river was compared with in situ reference sampling using an established pumping and filtration system at relatively stable flow conditions. As result, the number of MP particles derived from treatment sludge was extrapolated to 196 ± 42 m−3 for the Warnow river and is statistically insignificantly different from 233 ± 36 m−3 identified by conventional water sampling. In addition, the polymer distribution and particles shape indicated the validity of the integrative concept. Consequently, the determination of MP abundance for freshwater systems based on DWTP treatment sludge represents an adequate method to estimate MP concentrations in flowing waters in an integrative way.

The supercritical question for pyroclastic dune bedforms: An overview

AbstractSedimentary structures deposited from dilute pyroclastic currents are largely dominated by the products of metre‐scale dune bedforms containing backset lamination. Since the first seminal works in the 1970s, the vast majority of the literature called these structures antidunes and chutes‐and‐pools. This consensus led to a loose terminology, either as descriptive terms for structures containing backset beds or as an interpretation of hydrodynamic conditions related to Froude‐supercritical flows. Here, the main characteristics of pyroclastic dune bedforms are summarized and classified under four categories. The literature is examined and a discussion is provided regarding a possible interpretation in terms of supercritical‐flow bedforms, including antidunes, chutes‐and‐pools and cyclic steps. The interpretation of pyroclastic dune bedforms as related to supercritical conditions is a possibility among others, yet open questions remain, and under the present state of knowledge alternative interpretations are equally valid. There is consensus that an interpretation of pyroclastic dune bedforms as related to supercritical flows implies deposition from a basal underflow supporting an internal free‐surface formed at a density interface within the overall current structure. Antidunes are likely to be limited to low‐angle, incipient bedforms. Chutes‐and‐pools may occur in the form of series of steep truncations formed by an erosive supercritical ‘chute’, with a depositional signature occurring exclusively in the subcritical ‘pool’ of a Froude jump. Rare examples of cyclic steps may be found as large‐scale undulations with superimposed metre‐scale bedforms, or for short‐scale, fully‐aggrading structures in periodic trains. Additionally, some pyroclastic bedforms may be formed by granular flows passing granular Froude jumps or as frozen granular stationary waves. The dominance of chute‐and‐pool structures over bedforms characterized by relatively more stable morphodynamics (antidunes and cyclic steps) could be the likely result of pulsating flow conditions and abrupt high‐rate deposition, impeding stable flow conditions. In a majority of cases, the growth of pyroclastic bedforms appears triggered by the influence of an inherited bed topography and by bed‐flow feedback effects. Apart from a possible interpretation as supercritical bedforms, other specific dynamics of dilute pyroclastic currents may well explain the characteristics of pyroclastic dune bedform structures. In particular, the inherent turbulence fluctuations, internal organization and highly depositional dynamics may be key to the formation of pyroclastic dune bedforms. In this respect, rather than solely focusing on the Froude dimensionless number of the formative current, theoretical considerations accounting for the Reynolds, Richardson and Rouse dimensionless parameters may be also implemented for the understanding of pyroclastic bedforms.

The influence of estuary eutrophication on the benthic diatom community: a molecular approach

The occurrence of harmful algal blooms (HABs) is increasing in frequency and intensity in South African estuaries because of eutrophication. This study used DNA metabarcoding to identify the benthic diatom community structure in the eutrophic Sundays Estuary. The recurrent HAB phytoplankton species Heterosigma akashiwo was recorded at bloom concentrations (∼100 µg Chl a l−1) in the brackish, vertically stratified middle reaches of the estuary. In contrast, microphytobenthos biomass increased towards the upper reaches in response to elevated availability of total oxidised nitrogen (NOx) and increased sediment stability. A total of 76 diatom species were identified using the molecular technique. Seven known nutrient-tolerant diatom species indicate a preference for either ammonium or NOx enrichment. Benthic diatom community diversity (H′ < 1) and evenness (J′ < 0.25) were low in the brackish middle reaches of the estuary, where the HABs decreased available light. Heterosigma akashiwo has been found in previous studies to suppress the growth of co-occurring taxa. Future research efforts should focus on verifying this relationship over seasonal timescales given the dominance of H. akashiwo in spring/summer. As the persistently nutrient-enriched state and stable flow conditions of the Sundays Estuary is the key driver of change, management efforts should be geared towards re-establishing the estuary’s natural flow variations and to measures that can mitigate nutrient pollution.