In the literature, many models can be found for a prediction of the frictional pressure drop in a slurry pipe. However, a vast majority of the models is proposed to predict slurry flows without ...deposits in pipes. In practice, some slurry pipelines operate with a stationary bed at the bottom of a pipe. Models covering this type of settling-slurry flow are lacking. In the article, a structure of a predictive model is proposed for the frictional pressure drop and the thickness of the stationary bed in a pipe flow of settling slurry at velocities that are too low to maintain all particles in motion. The governing equations of the model are described and the additional semi-empirical equations formulated. The proposed model is validated using experimental data from own laboratory tests and from the literature.
The flow of settling slurry above a stationary bed in a pressurized pipe is studied. The predictive model for the pressure drop and the thickness of the stationary deposit is proposed. The model is validated using experimental data from own laboratory tests and from the literature.
Display omitted
Sand-water slurry was investigated on an experimental pipe loop of inner diameter
= 100 mm with the horizontal, inclined, and vertical smooth pipe sections. A narrow particle size distribution silica ...sand of mean diameter 0.87 mm was used. The experimental investigation focused on the effects of pipe inclination, overall slurry concentration, and mean velocity on concentration distribution and deposition limit velocity. The measured concentration profiles showed different degrees of stratification for the positive and negative pipe inclinations. The degree of stratification depended on the pipe inclination and on overall slurry concentration and velocity. The ascending flow was less stratified than the corresponding descending flow, the difference increasing from horizontal flow up to an inclination angle of about +30°. The deposition limit velocity was sensitive to the pipe inclination, reaching higher values in the ascending than in the horizontal pipe. The maximum deposition limit value was reached for an inclination angle of about +25°, and the limit remained practically constant in value, about 1.25 times higher than that in the horizontal pipe. Conversely, in the descending pipe, the deposition limit decreased significantly with the negative slopes and tended to be zero for an inclination angle of about −30°, where no stationary bed was observed.
Selective and irreversible labeling of a cysteine present in artificial retro‐aldolase is achieved by employing modular tetrafluoroalkylation reagents based on hypervalent iodine. Unlike commonly ...used maleimide or iodoacetamide reagents, the fluoroalkyl‐transfer λ3‐iodanes leave the enzyme's active center, a nucleophilic lysine, intact. Many different functional moieties or dyes can be fused to the reagents in one step, making the method an attractive and robust approach for the derivatization of biomolecules. More information can be found in the Communication by P. Beier, D. Hilvert, A. Togni, et al. on page 6490 ff.
Slurry pipe transport has directed the efforts of researchers for decades, not only for the practical impact of this problem, but also for the challenges in understanding and modelling the complex ...phenomena involved. The increase in computer power and the diffusion of multipurpose codes based on Computational Fluid Dynamics (CFD) have opened up the opportunity to gather information on slurry pipe flows at the local level, in contrast with the traditional approaches of simplified theoretical modelling which are mainly based on a macroscopic description of the flow. This review paper discusses the potential of CFD for simulating slurry pipe flows. A comprehensive description of the modelling methods will be presented, followed by an overview of significant publications on the topic. However, the main focus will be the assessment of the potential and the challenges of the CFD approach, underlying the essential interplay between CFD simulations and experiments, discussing the main sources of uncertainty of CFD models, and evaluating existing models based on their interpretative or predictive capacity. This work aims at providing a solid ground for students, academics, and professional engineers dealing with slurry pipe transport, but it will also provide a methodological approach that goes beyond the specific application.
Pipe flow of sand-water slurry (settling slurry) is sensitive to pipe inclination. The effect of the angle to which the partially stratified flow is inclined from the horizontal has been subject to ...investigation in numerous studies. However, almost all of them focus on ascending flows, i.e. flows inclined to positive angles of inclination. It is well known that settling slurry flows inclined to negative slopes (descending flows) differ from those inclined to positive slopes, particularly at velocities near the deposition limit. The deposition limit velocity is the flow velocity at which stationary deposit starts to be formed at the bottom of the pipe. We investigate the effect of the negative slope on pipe flow near deposition limit velocity in the broad range of inclination angles. Besides the deposition limit, we focus on the distribution of solids across the pipe cross section. We combine experimental approach with mathematical modelling. Our new experiments with medium-to-coarse sand (mass-medium grain size 0.87 mm) in a 100-mm pipe inclined from 0 to -45 degree provide suitable data for a validation of predictions of our layered model for partially stratified flows in inclined pipes.
A pipeline slurry friction loss model consisting of three regimes was initially proposed by Wilson then extended to four components consisting of fluid, pseudo‐homogeneous, heterogeneous, and fully ...stratified regimes. The weighting technique using up to four regime‐related components often works well for friction loss estimations based on simple input data and model parameters. This also holds for the Hydraulic Institute's pump performance derating procedure for settling slurries. The comparisons and discussion focus on coarse particle slurries and some cases where the modelling estimations for pipeline and pump performance were not particularly accurate.
For the safe and economical design and operation of freight pipelines it is necessary to know slurry flow behaviour in inclined pipe sections, which often form significant part of pipelines ...transporting solids. Fine-grained settling slurry was investigated on an experimental pipe loop of inner diameter D = 100 mm with the horizontal and inclined pipe sections for pipe slopes ranging from −45° to +45°. The slurry consisted of water and glass beads with a narrow particle size distribution and mean diameter d50 = 180 µm. The effect of pipe inclination, mean transport volumetric concentration, and slurry velocity on flow behaviour, pressure drops, deposition limit velocity, and concentration distribution was studied. The study revealed a stratified flow pattern of the studied slurry in inclined pipe sections. Frictional pressure drops in the ascending pipe were higher than that in the descending pipe, the difference decreased with increasing velocity and inclination. For inclination less than about 25° the effect of pipe inclinations on deposition limit velocity and local concentration distribution was not significant. For descending pipe section with inclinations over −25° no bed deposit was observed.
Did they leave or not? Dreslerová, Dagmar; Venclová, Natalie; Demján, Peter ...
Archeologické rozhledy (Praha),
01/2022, Letnik:
74, Številka:
4
Journal Article
Recenzirano
Odprti dostop
One of the key unresolved questions regarding the archaeology of La Tène Europe concerns the continuity of settlement around 400 BC. Archaeological evidence of settlement in the countries north of ...the Alps, including the Czech Republic, declines during this period – a decline which for decades has generally been attributed to population migration. Demographic growth, climate deterioration, land depletion, disease, and social crisis have all been put forward as reasons for this migration. Our contribution critically reflects on all these alternatives and asks whether there was indeed any significant migration out of Bohemia. We suggest that a reduction in archaeological visibility – the possibility of detecting archaeological traces of human activity – is behind most of the decrease in the number of recorded settlement sites during the transition from LT A to LT B. Some form of social ‘revolution’ is considered the main cause of the changes recorded in this period.
Paths to this and the next world Venclová, Natalie; Dreslerová, Dagmar; Kyselý, René ...
Archeologické rozhledy (Praha),
05/2024, Letnik:
75, Številka:
4
Journal Article
Recenzirano
The article presents the assemblage of finds from a sunken hut in Nižbor opposite the Stradonice oppidum on the other bank of the Berounka River. The inventory from the sunken hut, which testifies to ...its contemporaneity with one of the phases of settlement at the oppidum in the Late La Tène period, was composed of common settlement finds of pottery and animal bones but also the skeletal remains of an older male. As such, it is a source for the study of excarnation, or the handling of the body of the deceased in the central European Late La Tène period following the end of burials at the so-called flat cemeteries. Radiocarbon dating of human and animal bones is important for establishing the chronology of the accompanying find assemblage, especially painted pottery in Bohemia. The location of the site near a probable ford over the Berounka River is the starting point for the reconstruction of the roads in the broader vicinity of the oppidum.
Trifluoromethylated and fluoroalkylated cyclic λ3‐iodanes and their acyclic salts were used for visible light‐driven fluoroalkylation of tryptophan and tryptophan‐containing peptides in aqueous ...media. In comparison to previously reported fluoroalkylation using similar reagents and sodium ascorbate as reductant, the photochemical process did not require any additive or catalyst and was more selective for Trp versus other aromatic amino acids due to the gradual production of fluoroalkyl radicals over the whole irradiation period. However, in the presence of Cys residues, both methods were not selective and cysteine sulfhydryl groups were fluoroalkylated in side reactions. Spectroscopic and photochemical investigations as well as quantum chemical calculations provided insight into the reaction mechanism. The process was found to be photoinduced involving the formation of fluoroalkyl radical from the excited state of λ3‐iodane.
Additive‐free: A photochemical process is used for fluoroalkylation of indoles, tryptophan and Trp‐containing peptides starting from fluoroalkylated cyclic λ3‐iodanes or their acyclic salt forms. The process is biocompatible, selective to Trp and does not require the use any photocatalyst or additive.
PDF
