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The slug frequency (SF), which refers to the number of liquid slugs passing through a pipe during a specific time, is an important parameter for characterizing the multiphase intermittent flows and monitoring some process involving this kind of flow. The simplicity of the definition of SF contrasts with the difficulty of correctly measuring it. This manuscript aims to review and discuss the various techniques and methods developed to determine the slug frequency experimentally. This review significantly reveals the absence of a universal measurement method applicable to a wide range of operating conditions. Thus, the recourse to recording videos with high-speed cameras, which can be used only at a laboratory scale, remains often necessary. From the summarized state-of-the-art, it appears that correctly defining the threshold values for detecting the liquid slugs/elongated bubbles interface from physical parameters time series, increasing the applicability of instrumentations at industrial scales, and properly estimating the uncertainties are the challenges that have to be faced to advance in the measurement of SF. [ABSTRACT FROM AUTHOR]

Due to their low mechanical strength, the limited applications of fused filament fabrication (FFF)-printed products eventually intrigued researchers to overcome this problem through several approaches. Powder addition reinforcement (PAR) has been recognized as the oldest among the proposed techniques. However, several studies have shown the drawbacks of this technique concerning the poor bond between the printed polymer matrix and powder filler, as well as the nozzle clogging that often occurs during the printing process. In this study, a novel powder addition method using equipment that enables powder delivery with a continuous and intermittent flow was conducted. A composite sample was prepared by printing polylactic acid (PLA) filament combined with iron oxide (Fe3O4) powder particles. The results showed that the printed PLA/Fe3O4 samples obtained from processing with intermittent particle flow had better quality compared to those processed by continuous particle flow. However, both the continuous and intermittent powder addition experienced a negative effect due to rapid cooling caused by air exposure during the printing process. Nonetheless, the novel technique proposed in this study could show the ability to avoid nozzle clogging that might occur during the printing of PLA/Fe3O4 composite samples. [ABSTRACT FROM AUTHOR]

Driven by the ever-growing heat load in industrial applications such as fast charging electrical vehicle batteries and high-performance processors, advanced cooling technologies for efficient thermal management are urgently needed. This numerical work demonstrates the great potential of flow intermittency in grooved channels for thermal performance improvement at laminar condition, and aims to reveal the underlying mechanism that governs the heat transfer enhancement. The open-source computational fluid dynamics code OpenFOAM is employed to resolve the intermittent channel flow with triangular surface grooves. The time-averaged Reynolds number Rem = 100 and the Strouhal number St = 0.2 are maintained, while the close time ratio γ ranges from 0.1 to 0.9. The thermal performance improvement is attributed to the "energy buffer" mechanism by cavity vortices, which induces strong near-wall reverse flow and promotes effective mainstream-boundary flow mixing. The results indicate that the averaged surface Nusselt number consistently increases with the close time ratio and at γ = 0.9 reaches 1.9 times of the steady-flow value. Particularly the heat transfer performance inside grooves is remarkably improved by a maximum of 175%. This novel concept of synergizing flow intermittency and surface structure achieves notable heat transfer enhancement under constant coolant consumption, and shows ample design space for further optimization. [ABSTRACT FROM AUTHOR]

The analysis of drop formation and the transition between separated and non-separated oil–water flows enables us to better regulate flow parameters and pipe inclination angle, which is of great significance for improving the efficiency of oil transportation. Previous studies mainly carried out qualitative analysis through experiments and studied the transition between separated flows, very few studies are conducted on the transition between separated flow and dual continuous flow or intermittent flow. In addition, the influence of pipe inclination angle was not considered in the study of drop formation, which results in inadequate force analysis of drop. This article presents the use of dimensionless numbers to predict the transition between separated flow and dual continuous flow or intermittent flow. The relation expression between dimensionless numbers is obtained by regression of experimental data. The critical values of flow parameters and pipe inclination angle can be calculated by the relation expression between dimensionless numbers and flow parameters. In addition, this article proposes a three-dimensional interfacial wave shear deformation mechanism by adding volume forces to the force analysis for the possible inclined pipe. The prediction equation is obtained and the critical value of flow parameters and pipe inclination angle for drop formation can be calculated, which are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Gas–liquid intermittent flow is a kind of flow pattern that distinguishes itself from the conventional flow by the apparent non-steady feature, which causes serious corrosion issues, including localized corrosion. Although it widely exists in wet gas pipelines, how the gas–liquid intermittent flow influences CO2 corrosion of pipeline steels remains a problem to be clarified. In this work, a testing device that enables good simulation of gas–liquid intermittent flow in wet gas pipelines under various conditions was developed and used to perform experimental studies, combining electrochemical tests and corrosion morphology observations. The result shows that flow velocity and gas–liquid ratio act together to affect the CO2 corrosion behavior of X70 steel in typical intermittent flow conditions. The flow velocity has a more profound effect on the corrosion rate, while the gas–liquid ratio is associated with the occurrence of localized corrosion. The effect of the gas–liquid ratio on corrosion behavior was discussed. [ABSTRACT FROM AUTHOR]

• A S-PLIF system is designed to detect the interface structures of horizontal gas–liquid intermittent flow. • The effects of the interface fluctuations and detached bubbles on the S-PLIF70&90 results are investigated. • Hydrodynamic parameters are detected by paired parallel-wire conductance sensors and compared with previous correlations. • The interface structures and hydrodynamic parameters are uncovered as the flow condition changes. Horizontal gas–liquid two-phase flows widely exist in a variety of industrial fields such as the environment, chemical industry and energy. Intermittent flow, characterized by the quasi-periodic alternation motion of liquid slugs and large-scale Taylor bubbles, is the most prevalent flow pattern in horizontal gas–liquid two-phase flows. Comprehensive research on the hydrodynamic behavior of gas–liquid intermittent flow is essential for revealing the mass and heat transfer characteristics between phases, thereby establishing physical models of flow parameters. In this study, a structured planar laser-induced fluorescence (S-PLIF) system and paired parallel-wire conductance sensors (PWCSs) are designed to detect the gas–liquid interface structures and the hydrodynamic parameters. The S-PLIF system consists of a laser, a visualization box, a Ronchi ruling-plate and a pair of high-speed cameras. An optical linear prism forms a laser sheet in the transverse direction and the middle of the test section, and the cameras are positioned at 70 ° and 90 ° respectively to the plane of the laser sheet, referred to as S-PLIF70 and S-PLIF90. Under the laser excitation, bright and dark stripes generated by the Ronchi ruling-plate are deflected at the gas–liquid interface. The influence of total reflection can be effectively avoided by identifying the deflection position of the stripes, allowing for accurate detection of the gas–liquid interfacial structures. The effects of the interface fluctuations and detached bubbles on the S-PLIF70&90 results are investigated. Fluctuation and evolution characteristics of the gas–liquid interface are analyzed by probability density function (PDF) and power spectral density (PSD). Meanwhile, hydrodynamic parameters, i.e., Taylor bubble nose and tail velocity, Taylor bubble and slug length, and slug frequency, are detected by the PWCSs, and compared with previous correlations. The evolution characteristics of the interfacial structures and hydrodynamic parameters are uncovered as the flow condition changes. [ABSTRACT FROM AUTHOR]

Environmental change and growing anthropogenic pressure on water resources is increasing the duration and intensity of drying events in streams in many geographical locations. Favourable sediment characteristics (e.g. high porosity and low fine sediment load within the substrate matrix) may facilitate benthic macroinvertebrate use of subsurface sediments in response to drying. However, the influence of sedimentary characteristics on the use and subsequent recovery of macroinvertebrates from initial vertical migration into, survival during unfavourable conditions within, and subsequent re‐emergence from subsurface sediments have not been directly observed.Transparent mesocosm tanks were used to directly observe the vertical movement and subsequent re‐emergence of Gammarus pulex from subsurface sediments in response to increasing dry period (1, 7, or 21 days) and fine sediment load (0.5–1 mm particle diameter used for light and heavy sediment treatment) and following rehydration and resumption of flowing conditions.Increasing volumes of fine sediment addition limited the ability of G. pulex to access subsurface sediment in response to drying and re‐emerge following rehydration. The longest dry period (21 days) reduced the ability of G. pulex to re‐emerge from the subsurface sediments following rehydration and flow resumption.Increasing fine sediment load negatively affects taxa using subsurface sediments as a refuge. Increased fine sediment deposition has the potential to reduce both access to the sub‐surface and re‐emergence once surface flow resumes.As many rivers are beginning to dry out, or are showing prolonged drying due to global warming, it is increasingly important that river management reduces the input of fine sediment into rivers and increase sediment porosity of riverbeds to facilitate access into the subsurface refuge by benthic fauna. [ABSTRACT FROM AUTHOR]

Gas–liquid intermittent flow is a kind of flow pattern that distinguishes itself from the conventional flow by the apparent non-steady feature, which causes serious corrosion issues, including localized corrosion. Although it widely exists in wet gas pipelines, how the gas–liquid intermittent flow influences CO2 corrosion of pipeline steels remains a problem to be clarified. In this work, a testing device that enables good simulation of gas–liquid intermittent flow in wet gas pipelines under various conditions was developed and used to perform experimental studies, combining electrochemical tests and corrosion morphology observations. The result shows that flow velocity and gas–liquid ratio act together to affect the CO2 corrosion behavior of X70 steel in typical intermittent flow conditions. The flow velocity has a more profound effect on the corrosion rate, while the gas–liquid ratio is associated with the occurrence of localized corrosion. The effect of the gas–liquid ratio on corrosion behavior was discussed.

• A gas–liquid flow in a vertically oriented coiled tubing is computed. • A novel model of bubble breakup is incorporated into CFD code as a UDF. • Bubble – intermittent flow regime transition in a coiled tubing is simulated. • A novel breakup model provides better results than standard models. Simulations of gas–liquid turbulent flows in helically coiled tubes are conducted by a two-fluid hydrodynamic model coupled with the population balance equation. A model of bubble breakup in a turbulent flow, recently developed by the authors, is incorporated into the ANSYS Fluent CFD code employed as a computational tool. The population balance equation is solved by a discrete method. A realizable k-epsilon turbulence model is used for all computations. Numerous simulations of gas-liquid flows in vertically oriented coiled tubes are conducted. Three different coil diameters are employed for simulations. Computed bubble chord distributions are close to experimental data. Simulated dependencies of the superficial liquid velocity on the superficial gas velocity, corresponding the bubbly-intermittent flow regime transition, are in excelled agreement with measured ones. On the other hand, dependencies, obtained using standard bubble breakup models, significantly deviate from experimental results. Thus, it is demonstrated that employment of the novel bubble breakup model greatly enhances a computational accuracy of gas-liquid flows in helically coiled tubes. [ABSTRACT FROM AUTHOR]

A parallel combined sensible-latent heat storage unit with intermittent flow was developed. Heat transfer fluid (HTF) alternately flowed between two tubes for creating cyclic intermittency within a single tube to enhance the heat transfer performance. In this study, a two-dimensional transient model was established and validated with experimental data from the previous study. The effect of heat transfer fluid intermittency cycle length on the heat transfer performance was investigated and the change rule of the optimum intermittency length in different stages during the melting process was designed by a recursion method. It is demonstrated that the optimum intermittency cycle length in each stage plotted as a function of time or melting fraction has an initial non-linear regime followed by a linear regime. The critical point separating these two regimes is related to propagation of melting front. These correlations between heat transfer fluid intermittency and melting behavior provided guidance for enhancing heat transfer performance in the parallel combined sensible-latent heat storage unit. A multistage intermittent mode is recommended to further reduce full melting time by 8.73% compared with that under the continuous mode. This design can improve the charging/discharging power, thus providing better economical efficiency for concentrated solar power (CSP). [ABSTRACT FROM AUTHOR]

Highly variable flow has to be expected in decentralized greywater treatment and can lead to intermittent operation of the treatment system. However, few studies have addressed the influence of variable flow on the treatment performance of a biological activated carbon filter (BAC). In this study, we investigated the influence of intermittent flow using small-scale BAC columns, which treat greywater as a second treatment step following a membrane bioreactor (MBR). Three operating strategies to respond to variable flow were evaluated. The activated carbon was characterized before and after the experiments in terms of biological activity and sorption capacity. The performance of the BAC filters was assessed based on total organic carbon (TOC) removal, TOC fractions and growth potential. No significant differences were observed between constant flow compared to on-off operation with intermittent flow over the range of tested influent concentrations. Peaks with high TOC during 24 h periods were attenuated by sorption and biological degradation. Adsorbed TOC was released after switching back to normal concentrations for influent concentrations more than 5 times higher than usually observed, the BAC functioned as a temporary sink. In line with these results, the high influent TOC values led to increased biological activity in the filter but did not influence the sorption capacity. The experiments showed that intermittent flow does not negatively impact the performance of a BAC and that there is no need for additional equalization tanks to buffer the variable flow, for example in household-scale greywater treatment.

Macroinvertebrates are widely used as bio-indicators in streams and rivers, and it is usually assumed that their community composition is primarily controlled by local environmental conditions. We examined the distribution of macroinvertebrates within the Guadalupe River basin (3256 km2) in Central Texas across physiographic gradients. Spatial analysis with variables that considers flow direction, connectivity and distances between sites (asymmetric eigenvector maps, AEM) detected distinctive communities in the lower reaches of the mainstem, in spring-influenced reaches, and in a tributary with intermittent reaches. Variation partitioning with redundancy analysis showed that large-scale factors, i.e. riverine network patterns (large-scale AEM variables), climatic variation and ecoregion explained a significant proportion (28%) of the variation in community composition within a river basin. The riverine network patterns were the most important factor, explaining 12% alone. Local environmental factors were significant, but completely confounded within these spatial patterns. We propose that there are distinctive macroinvertebrate communities depending on the location in the river network and this may apply to other (subtropical) rivers, which should be tested by future studies. We recommend spatial analysis that considers distances and connectivity within a river network as a powerful tool to recognize multiscale riverine network patterns, which can help to identify priority areas for conservation and to develop sound monitoring programs.

The main objective of the study is to propose a technical solution integrated into the pipeline for the transition of the flow regime from slug to bubbly two-phase flow. The object of research is isothermal two-phase gas–Newtonian-liquid flow in a horizontal circular pipeline. There is local resistance in the pipe in the form of a streamlined transverse mesh partition. The mesh partition ensures the transition of the flow from the slug regime to the bubbly regime. The purpose of the study is to propose a technical solution integrated into the pipeline for changing the flow regime of a two-phase flow from slug to bubbly flow. The method of research is a simulation using computational fluid dynamics (CFD) numerical simulation. The Navier–Stokes equations averaged by Reynolds describes the fluid motion. The k-ε models were used to close the Reynolds-averaged Navier–Stokes (RANS) equations. The computing cluster «Polytechnic—RSK Tornado» was used to solve the tasks. The results of simulation show that pressure drop on the grid did not exceed 10% of the pressure drop along the length of the pipeline. The mesh partition transits the flow regime from slug to layered one, which will help to increase the service life and operational safety of a real pipeline at insignificant energy costs to overcome the additional resistance integrated into the pipeline. [ABSTRACT FROM AUTHOR]

This article presents void fraction and pressure gradient data for sulfur hexafluoride(SF6) with gas densities of 28 and 45 kg/m3and oil (with viscosity 35 times that for water) in a 127 mm diameter pipe. The superficial velocities of gas ranged from 0.1 to 3 m/s and those for liquid from 0.1 to 1 m/s, respectively. Measurements of void fraction data were recorded using a capacitance wire mesh sensor (WMS) system,which permits the 3D visualization of the flow patterns. All the data were obtained with a data acquisition frequency of 1,000 Hz. A differential pressure transducer was used to measure the pressure drops along the length of the pipe. The WMS provide time and cross-sectionally resolved data on void fraction and from an analysis of its output, flow patterns were identified using the characteristic signatures of probability density function (PDF) plot of time series of void fraction. The PDF plots showed the single peak shapes associated with bubbly and churn flows but not the twin-peaked shape usually seen in slug flows. This confirms previous work in larger diameter pipes but with less viscous liquids. For the bubble and churn flows investigated, the pres-sure gradient was observed to decrease with an increase in gas superficial velocity.Nevertheless, there was an insignificant observed effect of pressure on void fraction below certain transitional flow rates, the effect however became significant beyond these values. In the present work, wisps appear to be smaller, which might be due to the different fluid properties of the working fluids employed. In addition, wisps are easily revealed as long as there is a transition between churn and annular flows regardless of the pressure. Experimental data on void fraction and pressure gradient are compared against existing data. Reasonably good agreements were observed from the results of the comparison. [ABSTRACT FROM AUTHOR]

Passive acoustic monitoring has revolutionized the characterization of industrial processes and the acoustic wavefield in various environments. However, cryospheric acoustic phenomena remain largely unknown, especially at medium and small scales. Furthermore, the englacial drainage system is poorly documented, even though it is fundamental for understanding water routing through the glacier body. Here I present the first‐of‐its‐kind in situ records of periodic or sustained acoustic signals generated by water drainage through crevasses at the calving front of a glacier, in this case a Greenlandic tidewater glacier. The generative mechanisms of gurgling and bubbling noise are explained as flow‐induced sounds that are excited by intermittent air‐water two‐phase flow and Helmholtz resonance, respectively. This paper demonstrates that there is the tremendous potential to study near‐surface glacier systems using acoustic methods and detect different flow patterns in englacial conduits from their acoustic signatures, both of which can significantly advance our understanding of glaciological processes. Plain Language Summary: The glacier surface is full of various audible sounds. While early polar explorers have documented this noisy glacier environment, these qualitative observations have never been supported by measurements. For example, Nansen (1897), wrote, "I can hear reports from the glacier... whenever it turns cold–it writhes horribly, and crevice after crevice appears in the huge body; there is a noise like the discharge of guns, and the sky and the earth tremble so that I can feel the ground that I am lying on quake" while wintering in Franz Josef Land, and Baldwin (1896) described his crossing of Bowdoin Glacier, which is the subject of this study, as follows: "...shrieking sounds frightful enough, came...to our ears, seeming to vibrate through...our very bodies, spitefully shouting in our ears: Why, presumptuous man, hast thou set disturbing foot upon my chaste bosom?" Here I analyze the first acoustic records that were directly acquired on a glacier, in Greenland, which reveal previously unknown repetitive or continuous sound sources. It appears that different patterns in air‐water interactions give rise to interesting acoustic phenomena, such as bubble resonance and unstable flow in cracks. Future glaciological investigations could consider using microphones to better understand englacial water drainage. Key Points: This is the first report of repeating and continuous acoustic radiators in a near‐surface englacial drainage systemWater‐air phase interactions in the drainage system hold the key to understanding self‐excited flow pulses and bubble burstsThere is tremendous potential in acquiring passive acoustic observations to characterize glaciological processes [ABSTRACT FROM AUTHOR]

The invertebrate fauna of five ephemeral forest streams on Hauturu-o-Toi/Little Barrier Island in northern New Zealand was assessed in January 2014. Low summer flows restricted benthic sampling largely to pools that would, during periods of 'normal' flow, be main-channel riffle/run habitat. Additionally, adult stages of aquatic insects were sampled by light trapping. Fifty-three aquatic species/morphospecies were recorded during the study, including 25 new records, bringing total island species richness to 65. The fauna was dominated by Ephemeroptera and Trichoptera; species richness of Plecoptera and Diptera was low, and only single species of Mollusca and Crustacea were recorded. Species found were either common with broad New Zealand distributions, or species restricted to the North Island. No species was endemic to the island. Faunal comparisons with adjacent mainland streams indicated the island had similar assemblages of core taxa, but generally lower species richness, likely resulting from physiographic differences found there. [ABSTRACT FROM AUTHOR]

This paper examined the wax deposition of gas-liquid intermittent flow in a flow-loop apparatus. In the study, increases in gas superficial velocity have been observed to result in decreases in the deposit mass. While the increases in liquid superficial velocity have been observed to result in increases first, then decreases. The deposit distributes along the pipe circumference, at first, the top is thinner and bottom is thicker, then deposit distributes uniform as the gas/liquid superficial velocity increases. In addition, the deposit thickness will first increase and then decrease with oil temperature increases, but decrease with the coolant temperature increases. [ABSTRACT FROM AUTHOR]

A mechanistic model has been developed for scale-up of batch fluid bed (top spray) granulation, leading to a design space which was verified against experimental data at pilot-plant and commercial scales. Current published models fail to give reliable scale-up. The process is very sensitive to operating conditions, and intermittent spray and air flow during filter bag shaking is shown to substantially affect moisture content and the final granule properties. Three parameters (inlet air temperature, flow rate and humidity) are consolidated into a composite parameter Q air which, in combination with solution spray rate m sol , gives a two-dimensional design space which is typically trapezoidal. Peak moisture content influences final granule attributes and depends on the ratio Q air /m sol. Scale-up and product transfer between different equipment are predicted. The model has been applied to an actual pharmaceutical product, achieving robust product quality at commercial scale, and incorporated into a successful regulatory filing submission. Unlabelled Image • Design space is based on a composite parameter, net heat input, and is trapezoidal • The ratio Q/m (heat input/spray rate) is directly linked to peak moisture content • Previous models are extended by considering intermittent air and spray flows • The model gave successful scale-up where previous published methods had failed • A smaller rectangular operating space within the design space gives easy control [ABSTRACT FROM AUTHOR]

This research aims at analyzing the frequency and duration distribution of extreme floods, including flash, in the Wala catchment - Central Jordan. The observed daily flows series, October 2002 to August 2016, was short to characterize extreme events like the 10th of November 2018 deadly flash flood. Therefore, a very long series of intermittent daily flows was synthesized assuming that the daily flow-nonflow process is stationary two-state simple Markov and the daily flow magnitude is Gamma distributed. The synthesized flows have succeeded to copy the characteristics of the observed flows. The analysis of the Wala observed, simulated daily flows and results from the theoretical model showed that floods of duration 2 days or less were dominant events (64%); the single day type was more often (40%) compared to the 2 days flood (24%). Regarding the 10th of November 2018 deadly flash flood of 10.368MCM/day, the inspection of the synthesized daily flows showed that it was an uncommon incident of 78 years recurrence time. Afforestation the upper regions in the Wala catchment and construction of counter terracing are possible measures to mitigate the impact of future flash floods. [ABSTRACT FROM AUTHOR]

Macroinvertebrates are widely used as bio-indicators in streams and rivers, and it is usually assumed that their community composition is primarily controlled by local environmental conditions. We examined the distribution of macroinvertebrates within the Guadalupe River basin (3256 km2) in Central Texas across physiographic gradients. Spatial analysis with variables that considers flow direction, connectivity and distances between sites (asymmetric eigenvector maps, AEM) detected distinctive communities in the lower reaches of the mainstem, in spring-influenced reaches, and in a tributary with intermittent reaches. Variation partitioning with redundancy analysis showed that large-scale factors, i.e. riverine network patterns (large-scale AEM variables), climatic variation and ecoregion explained a significant proportion (28%) of the variation in community composition within a river basin. The riverine network patterns were the most important factor, explaining 12% alone. Local environmental factors were significant, but completely confounded within these spatial patterns. We propose that there are distinctive macroinvertebrate communities depending on the location in the river network and this may apply to other (subtropical) rivers, which should be tested by future studies. We recommend spatial analysis that considers distances and connectivity within a river network as a powerful tool to recognize multiscale riverine network patterns, which can help to identify priority areas for conservation and to develop sound monitoring programs. [ABSTRACT FROM AUTHOR]

• Void fraction distribution profile rotated a deviation angle due to centrifugal force. • Elongated bubbles and slugs shortened, and slug frequency increased due to dean Vortex. • A dimensionless parameter representing the ratio of the centrifugal force to the gravity was presented. • Correlations of void fraction deviation angle, drift flux model, elongated bubble length and slug frequency were presented. This paper experimentally investigated the air-water intermittent flow in four helically coiled tubes with inner diameter of 0.016 m, coil diameters of 0.24, 0.43 and 0.80 m, and inclination angles of 5° and 15°. A double conductivity probe was used to measure the hydrodynamic parameters at 48 points in the outlet cross section. The results showed that centrifugal force and Dean Vortices were the major mechanisms that influenced the void fraction distribution, elongated bubble length, slug length and slug frequency. Because of centrifugal force, the void fraction profile rotated an angle which approached to 90° as liquid superficial velocity increased and coil diameter decreased. Due to the Dean Vortices, the elongated bubble length and slug length decreased as the coil diameter decreased, leading to an increase of slug frequency. A dimensionless parameter Z representing the ratio of the centrifugal force to the gravity was presented, which provides a quantitative criterion to evaluate the influence of centrifugal force. In terms of Z , correlations predicting the deviation angle, elongated bubble length and slug frequency were built, which met the experimental data well when the coil diameter is between 0.24 and 0.80 m and the inclination angle between 5° and 15°. Moreover, a drift flux model for HCTs was presented. [ABSTRACT FROM AUTHOR]

• Quality images for intermittent flow presented. • El Hajal-Thome map modified in low vapor quality region. • Intermittent flow divided to four subdivisions: Bubble, Transition, Slug with and without vapor entrainment. • Best heat transfer prediction by Thome correlation (MAE = 13%) in intermittent region. • A new correlation has proposed for intermittant flow with MAE = 10.4% This study investigates condensation of R141b in an 8 mm ID horizontal smooth tube. Condensation of R141b is conducted at an average saturation temperature of 40 ° C with mass fluxes ranging from 40 to 400 kg m−2 s−1. The plant runs with low vapor quality of refrigerant where intermittent flow is expected to be the dominant flow regime. Visualization images presented for intermittent flow regime. Observation results compared with four types of flow regime map and a modified version of El Hajal-Thome map is presented. Condensation heat transfer coefficient in intermittent zone is evaluated. Comparison between the available experimental data and the values predicted by the most popular and current correlations for condensation heat transfer in horizontal tubes are reported. Finally, a new correlation is proposed to predict condensation heat transfer coefficient within intermittent region. [ABSTRACT FROM AUTHOR]

The goal of this study was to evaluate the effects of freezing–thawing and wetting–drying on heavy metals leaching from biosolids. Biosolid samples were irrigated with water at two flow rates and three flow stop events in 24 hr intervals. During the period of flow stop, biosolids were subjected to different temperatures, water contents, or freezing–thawing. Leachates were analyzed for heavy metals. The concentrations of metals in biosolids ranged from lower than detection limits (for Pb) to 1,039 mg/kg (for Zn). The leaching percentage of metals ranged from 0% (Pb, Ag, Cs) to 25% (Ni). Lower flow rate with longer residence time induced more metal leaching compared with higher flow rate with shorter residence time. At each flow rate, flow stop caused enhanced metal leaching. Higher drying temperature enhanced metal leaching. Water content or freezing–thawing had no significant effects on metal leaching. We expect that intermittent irrigation or rainfall would enhance the risk of metals leaching from biosolids after land application. However, freezing of biosolids during winter will likely not cause an enhanced leaching of metals in spring when biosolids and soils thaw. Application of biosolids in fall should therefore not cause enhanced leaching of metals out of land‐applied biosolids. Practitioner points: Lower flow rate with longer residence time induced more metal leaching compared with higher flow rate with shorter residence time.Flow stop or higher drying temperature enhanced metal leaching from biosolids.Water content or freezing‐thawing had no significant effects on metal leaching. [ABSTRACT FROM AUTHOR]

Climate change projections predict the increase of no-rain periods and storm intensity resulting in high hydrologic alteration of the Mediterranean rivers. Intermittent flow Rivers and Ephemeral Streams (IRES) are particularly vulnerable to spatiotemporal variation of climate variables, land use changes and other anthropogenic factors. In this work, the impact of climate change on the aquatic state of IRES is assessed by the combination of the hydrological model Soil and Water Assessment Tool (SWAT) and the Temporary Rivers Ecological and Hydrological Status (TREHS) tool under two different Representative Concentration Pathways (RCP 4.5 and RCP 8.5) using CORDEX model simulations. A significant decrease of 20–40% of the annual flow of the examined river (Tsiknias River, Greece) is predicted during the next 100 years with an increase in the frequency of extreme flood events as captured with almost all Regional Climate Models (RCMs) simulations. The occurrence patterns of hyporheic and edaphic aquatic states show a temporal extension of these states through the whole year due to the elongation of the dry period. A shift to the Intermittent-Pools regime type shows dominance according to numerous climate change scenarios, harming, as a consequence, both the ecological system and the social-economic one.

We study a high-viscosity two-phase flow through an analysis of the corresponding pressure signals. In particular, we investigate the flow of a glycerin–air mixture moving through a horizontal pipeline with a U-section installed midway along the pipe. Different combinations of liquid and air mass flow rates are experimentally tested. Then, we examine the moments of the statistical distributions obtained from the resulting pressure time series, in order to highlight the significant dynamical traits of the flow. Finally, we propose a novel correlation with two dimensionless parameters: the Euler number and a mass-flow-rate ratio to predict the pressure gradient in high-viscosity two-phase flow. Distinctive variations of the pressure gradients are observed in each section of the pipeline, which suggest that the local flow dynamics must not be disregarded in favor of global considerations.

Accurate water consumption measurement of customers is a crucial component of water utility sustainability. During the last decade, sophisticated measuring technologies without moving components, known as solid-state water meters or static meters, have emerged. Solid-state water meters promise an improved accuracy with more processing and transmission capabilities in comparison with traditional mechanical meters. A compromise needs to be reached between energy consumption and battery life as all these new features are extremely demanding on electric energy. The usual approach adopted by the manufacturer is to reduce the frequency with which static meters take measurements of the circulating flow. This reduction in signal sampling frequency can have a significant effect on the accuracy of the instruments when measuring water consumption events of 30 s or less, these events being common in residential customers. The research presented analyses of the metrological performance of 28 commercially available solid-state water meters from six different manufacturers in the presence of intermittent flows of various durations. The results show that the magnitude and dispersion of the error under intermittent flows is significantly larger in comparison to steady state flow conditions. The ultrasonic meters examined were more influenced by the intermittency than the electromagnetic meters.

Abstract Pseudo-slug flow is a subset of intermittent flow which has not been properly understood and modeled. However, this flow pattern is widely encountered in oil and gas production and transportation, driving the needs for proper modeling efforts. A new pseudo-slug unit cell model is proposed in this paper. The proposed model modifies the existing slug unit cell model by accounting the continuous gas passage, slippage, and interfacial momentum exchange in the pseudo-slug body. Pseudo-slug characteristics (length, velocity, and body holdup) reported in literature are incorporated through ad-hoc closure relationships. These closures remain to be improved in the future. Overall, the proposed model produces more accurate pressure gradient and film holdup (H LF) predictions compared to two state-of-the-art models which generally treat pseudo-slug as slug flow (TUFFP Unified model and OLGAS 7.3.5®). Highlights • A new model is proposed for gas-liquid pseudo-slug flow in pipes. • Slippage and interfacial momentum exchange in pseudo-slug body is accounted in the model. • The proposed model overall shows better performance than state-of-art slug flow models. [ABSTRACT FROM AUTHOR]

River channel drying caused by intermittent stream flow is a widely-recognized factor shaping stream ecosystems. There is a strong need to quantify the distribution of intermittent streams across catchments to inform management. However, observational gauge networks provide only point estimates of streamflow variation. Increasingly, this limitation is being overcome through the use of spatially contiguous estimates of the terrestrial water-balance, which can also assist in estimating runoff and streamflow at large-spatial scales. Here we proposed an approach to quantifying spatial and temporal variation in monthly flow intermittency throughout river networks in eastern Australia. We aggregated gridded (5 × 5 km) monthly water-balance data with a hierarchically nested catchment dataset to simulate catchment runoff accumulation throughout river networks from 1900 to 2016. We also predicted zero flow duration for the entire river network by developing a robust predictive model relating measured zero flow duration (% months) to environmental predictor variables (based on 43 stream gauges). We then combined these datasets by using the predicted zero flow duration from the regression model to determine appropriate ‘zero’ flow thresholds for the modelled discharge data, which varied spatially across the catchments examined. Finally, based on modelled discharge data and identified actual zero flow thresholds, we derived summary metrics describing flow intermittency across the catchment (mean flow duration and coefficient-of-variation in flow permanence from 1900 to 2016). We also classified the relative degree of flow intermittency annually to characterise temporal variation in flow intermittency. Results showed that the degree of flow intermittency varied substantially across streams in eastern Australia, ranging from perennial streams flowing permanently (11–12 months) to strongly intermittent streams flowing 4 months or less of year. Results also showed that the temporal extent of flow intermittency varied dramatically inter-annually from 1900 to 2016, with the proportion of intermittent (weakly and strongly intermittent) streams ranging in length from 3% to nearly 100% of the river network, but there was no evidence of an increasing trend towards flow intermittency over this period. Our approach to generating spatially explicit and catchment-wide estimates of streamflow intermittency can facilitate improved ecological understanding and management of intermittent streams in Australia and around the world. [ABSTRACT FROM AUTHOR]

Multiphase flow metering is an open research field, with challenges encompassing sensor development and thermofluid models, for instance. Sparse regression is a modern system identification strategy able to provide simple models with Physical interpretation. This papers applies sparse identification for the assessment of gas velocity, gas fraction and superficial velocities of liquid and gas in experimental air–water horizontal slug flow across a Venturi tube and a twin-plane capacitive sensor. We show that this technique can improve measurement accuracies, as deviations for superficial velocities fall below 2.8% for liquid and 8.7% for gas. More importantly, the analysis of three data sets discusses practical concerns when applying sparse regression methods in metering, including the choice of basis functions, the degree of sparsity and overfitting. Overall, sparse identification is perceived as an adequate method to simultaneously generate a measurement model and correction of measurement biases in a specific measurement setup. • Sparse identification of flow features in MPFM for air–water horizontal slug flow. • The simple models obtained correct for systematic errors and comply with Physics. • Deviations below 3% are reached for liquid superficial velocities. • Recommendations for broad usage of such algorithms in measurement setups. [Display omitted] [ABSTRACT FROM AUTHOR]

The influence of sub-regimes of intermittent flow on the pressure drop has been investigated. Two-phase, air-water, flow experiments were conducted on 30 mm ID pipe. The superficial velocities of the working fluids were chosen to cover three sub-regimes: Plug flow, Less Aerated Slug flow (LAS flow) and Highly Aerated Slug flow (HAS flow). The analysis of the experimental data, including the data drawn from the literature showed that the pressure drop depends on the flow sub-regime. A new empirical correlation, based on the Lockhart-Martinelli approach, taking into account the nature of sub-regime was proposed. The present correlations, in comparison with the existing correlations, give the best results. [ABSTRACT FROM AUTHOR]

The interrelationships amongst water and sediment physicochemistry, catchment hydrology, and allochthonous inputs are not well established for intermittent streams, especially in tropical climates. This remains a major concern in water resources management, and understanding these streams is vital in forming targeted frameworks for protection. A two-year comprehensive study showed spatially independent water quality variations, where similar temporal patterns were observed in different streams in close catchments for many variables (such as for electrical conductivity, pH, nitrogen species, and dissolved oxygen). This was not the case for sediment quality variables; in addition, in-stream variation was high. This gave an indication of the regulatory potential of intermittent stream sediment. Redundancy analysis models showed that stream water quality was significantly correlated to, and could be explained by discharge, rainfall parameters, litter, and sediment quality. Sediment quality was not influenced by litter inputs but by discharge and rainfall-related parameters. The study reported new insights into the unique physicochemistry of intermittent streams and proposes the fact that sediment quality needs comprehensive monitoring and management both spatially and temporally. [ABSTRACT FROM AUTHOR]

Abstract: Intermittent flow is a hydrological phenomenon observed at all latitudes. This phenomenon is characterized by a complete or partial interruption of flow in time and/or space in channels. In Quebec, even though the climate is humid, intermittent flow occurs downstream from headwater reservoirs. These reservoirs store water during spring and summer (from April to September) and release it in winter to supply hydroelectric power plants located downstream. During the water storage period, intermittent flow is common (discharges falling to <1 L/s/km2). The goal of the study is to analyse the characteristics (magnitude, frequency, and duration) of this flow downstream from 3 reservoirs built in the Saint‐Maurice River watershed, during the period from 1930 to 2010. Downstream, the contribution (magnitude) of intermittent flow to total altered flow is less than 2%. Intermittent flow frequency ranges from 24 to 65 days per year downstream from the 3 reservoirs. As far as duration is concerned, intermittent flow persists on average from 40 to 128 consecutive days. Canonical correlation analysis revealed that the frequency of intermittent flow is correlated with the North Atlantic Oscillation and its magnitude and negatively correlated with the Southern Oscillation. [ABSTRACT FROM AUTHOR]