Horizontal Flow Research Articles

Inversion of VLF-R data using a non-linear rank order smoothing constraint and its implementation to image surface rupture of the North Anatolian Fault in Başiskele, Kocaeli, NW Turkey

Inversion of electromagnetic induction data is often realized using smoothing operators for regularizing the process. These operators are applied using derivative matrices, penalizing differences between neighboring mesh cells. The resulting smoothing effect is similar to that of low-pass Gaussian filters and may cause difficulties due to the smoothed boundaries between structures. To prevent such ambiguities, non-linear rank filters are applied widely in image processing applications to filter low frequency variations while keeping boundaries. Correspondingly, we have defined a non-linear rank order smoothing operator for regularization. The effects of the defined parameters are demonstrated on synthetic models and the operator is observed to be able to provide better defined boundaries. The implementation of the operator on field data is realized using single-frequency VLF-R data collected on profiles traversing the surface rupture of the North Anatolian Fault in Kocaeli, Turkey. In the study area, ERT data are also collected on a single profile, and its smooth inversions are realized individually and jointly with VLF-R data for comparisons. Inversions show that the recovered subsurface structure using the rank order smoothing is closer to that indicated by the ERT data and previous studies. According to the recovered models, the clayey fillings in the fault rupture are acting as a barrier affecting the horizontal fluid flow in the near-surface and the resulting water accumulations around the fault rupture may cause susceptibility for earthquake induced damages.

Nature based solutions applied to mature leachate treatment in the Latin American resource-poor environment

Some Latin American countries have implemented environmental policies which have enhanced a shift in domestic solid waste practices from open dumps to sanitary landfills, bringing about a serious challenge to the region in terms of leachate management both in the operation and the aftercare phases of landfills. This work looks at the viability of Nature based Solutions (NbS) in the Latin American resource-poor environment as a cost-efficient alternative for dealing with such a challenge. In particular, an experimental trial was carried out in order to evaluate the contaminants removal of four subsurface constructed wetlands at a pilot scale, for treating mature leachate with emphasis on nitrogen removal. The wetlands were set in two treatment lines: (1) a vertical flow wetland followed by a horizontal flow wetland and (2) two vertical flow wetlands in series. Each line was fed at a 173 L.d−1 rate of mature leachate. The wetlands were planted with a polyculture of the tropical plants Colocasia esculenta and Heliconia psittacorum in a random way and the support media used was composed of 3/8″ gravel and gross sand. Both treatment lines showed similar behaviours and it is important to highlight that ammoniacal nitrogen, that is the principal contaminant to treat, was significantly removed (40% approx.) considering the high loads the system was fed with (490 kg.d−1 TAN). It is considered that the removal mechanism of the ammoniacal nitrogen is a biological nitrification-denitrification process, due to the increase of nitrite and nitrate concentrations in the effluent, as well as the bicarbonate alkalinity consumption. These results suggest the system proposed as an NbS has promising potential for leachate treatment in Latin American countries.

Soaring migrants flexibly respond to sea-breeze in a migratory bottleneck: using first derivatives to identify behavioural adjustments over time

BackgroundMillions of birds travel every year between Europe and Africa detouring ecological barriers and funnelling through migratory corridors where they face variable weather conditions. Little is known regarding the response of migrating birds to mesoscale meteorological processes during flight. Specifically, sea-breeze has a daily cycle that may directly influence the flight of diurnal migrants.MethodsWe collected radar tracks of soaring migrants using modified weather radar in Latrun, central Israel, in 7 autumns between 2005 and 2016. We investigated how migrating soaring birds adjusted their flight speed and direction under the effects of daily sea-breeze circulation. We analysed the effects of wind on bird groundspeed, airspeed and the lateral component of the airspeed as a function of time of day using Generalized Additive Mixed Models. To identify when birds adjusted their response to the wind over time, we estimated first derivatives.ResultsUsing data collected during a total of 148 days, we characterised the diel dynamics of horizontal wind flow relative to the migration goal, finding a consistent rotational movement of the wind blowing towards the East (morning) and to the South-East (late afternoon), with highest crosswind speed around mid-day and increasing tailwinds towards late afternoon. Airspeed of radar detected birds decreased consistently with increasing tailwind and decreasing crosswinds from early afternoon, resulting in rather stable groundspeed of 16–17 m/s. In addition, birds fully compensated for lateral drift when crosswinds were at their maximum and slightly drifted with the wind when crosswinds decreased and tailwinds became more intense.ConclusionsUsing a simple and broadly applicable statistical method, we studied how wind influences bird flight through speed adjustments over time, providing new insights regarding the flexible behavioural responses of soaring birds to wind conditions. These adjustments allowed the birds to compensate for lateral drift under crosswind and reduced their airspeed under tailwind. Our work enhances our understanding of how migrating birds respond to changing wind conditions during their long-distance journeys through migratory corridors.

Meandering Flow Filter for Phosphorus Removal as a Component of Small Wastewater Treatment Plants—A Case Study

Chemical phosphorus removal in wastewater treatment plants can be carried out by precipitation with iron or aluminum salts or by filtering wastewater through a bed of active sorptive material. This work aimed to investigate whether using a meander flow filter filled with the sorption material Rockfos® would improve phosphorus removal efficiency in a selected wastewater treatment plant. Tests were performed under laboratory conditions using a model of a meander flow filter and a similar filter under field conditions at full technical scale. This filter was the final element of a hybrid constructed wetland located in the village of Białka in the municipality of Dębowa Kłoda in southeastern Poland. A laboratory model of a phosphorus removal filter with vertical incomplete baffles forcing a meandering water flow was constructed to determine the hydraulic conditions of the flow. After one year of operation, the filter with horizontal wastewater flow operating at its full technical scale (without meanders) was modified by inserting appropriate baffles that were analogous to those in the laboratory model. The analysis of the hydraulic conditions in the laboratory model showed that, under the assumed conditions, wastewater flows through the filter layer in a laminar motion, so such filters can be modeled using the Kozeny–Carman formula. It was shown that, after approximately a year of operation in a filter operating at full technical scale, before modification, dead spaces formed, thus causing the channel and primarily surface flow of wastewater. The phosphorus removal efficiency during this test period averaged 9.4%. After introducing baffles and forcing meander flow in the filter chamber, the efficiency increased to 40.6%. The results indicate that meander flow filters can improve phosphorus removal efficiency in small wastewater treatment plants.

Experimental study of liquid/dense-gas pipe flow

The pre-salt reservoirs play a significant role in the current Brazilian ultradeep water offshore scenario. Their importance is expected to increase soon. The fluids are transported through horizontal, inclined, and vertical wells of several kilometers, and due to the environmental conditions at the reservoir, dense-gas/liquid flow occurs in the pipelines. However, the literature lacks experimental data for gas-liquid flow with densities of the same order of magnitude, which affects the mechanistic model's accuracy for flow patterns, pressure gradients, and holdup predictions. To improve the understanding of that specific two-phase flow, an experimental apparatus was built, and an experimental study was carried out using sulfur hexafluoride (100 kg/m3) and mineral oil (850 kg/m3) at medium pressures. A density ratio lower than 10 was obtained for steady-state horizontal flow in a 50.8-mm-i.d. stainless-steel pipe, and flow patterns, pressure gradient, and holdup were measured. The experimental results show the effect of the low-density ratio on the stratified to non-stratified flow-pattern transition and the occurrence of the dual-continuous flow pattern at high mixture superficial velocity. Moreover, the pressure gradient and holdup data were compared with the results of a commercial multiphase flow simulator, showing good agreement.

Experimental investigation of induced vibrations in horizontal Gas-Liquid flow

One of the governing contributors to offshore structures' (e.g., pipelines and deep-water risers) accumulative long-term fatigue damage is the internal flow-induced vibrations caused by slug flow. Due to the complexity of the numerical modeling of the internal flow and fluid–structure interaction, experimental campaigns are often performed to predict the asset response and provide a benchmark for numerical model validation. In this study, an experimental campaign was conducted which included a unique computer vision data acquisition system and a large-scale facility designed to mimic industry field conditions. This study aims to relate flow parameters to structural response and explain the mechanisms that govern the relationship between both domains.The presented results reveal that the gravitational forces of the fluid dominate the transverse deflections of the pipe and, therefore, the slug liquid holdup, film liquid holdup, and slug length showed strong correlations to pipe deflections. However, centrifugal forces were observed to have significant contributions to pipe deflection for high translational velocity slugs. Additionally, it was found that for most of the test conditions, the primary pipe excitation frequency correlates to the slug frequency. It was discovered that no-slip liquid holdup has a positive correlation to both the magnitude and range of pipe deflection and that increases in superficial gas and liquid velocities led to decreases and increases in pipe deflection, respectively. Furthermore, it was observed that the measured frequency responses of the structure tended to increase with increasing gas velocity until the flow pattern in the pipe began to transition to annular flow.

A survey on constructed wetland publications in the past three decades.

Decentralised wastewater treatment systems, such as constructed wetlands, are becoming increasingly popular these days because they are more economical and cost-effective than conventional plants. The primary objective of this review paper is to determine the number of studies that have been conducted on constructed wetlands, specifically 'free water surface flow constructed wetlands', 'horizontal subsurface flow constructed wetlands', 'vertical subsurface flow constructed wetlands', and 'hybrid constructed wetlands'. In addition, the paper examines the status of research publications on constructed wetlands by country, author, and journal. Based on the review, it has been found that although constructed wetland technology is economical and cost-effective, it is still not among the top 10 effluent treatment methods. Compared to other constructed wetland systems, 'hybrid constructed wetlands' have received minimal attention. Based on the search results, 4639 documents published between 1989 and 2021 have been extracted from the online edition of SCI-EXPANDED, Web of Science. The documents associated with constructed wetlands are divided into eight main document types. Articles and proceedings papers are the most common document type, accounting for 93% of all publications, followed by reviews (4%), meeting abstracts (1.3%), corrections (0.56%), editorial materials (0.38%), news items (0.2%), letters (0.04%), and book reviews (0.02%).

Thirty years of constructed wetlands for municipal wastewater treatment in the Czech Republic

Constructed wetlands (CWs) for wastewater treatment have been used in the Czech Republic since 1991. Nowadays, there are about 200 full-scale constructed wetlands for treatment of municipal sewage. Most CWS have been designed with horizontal subsurface flow, in the late 2010s and early 2020s, combination of vertical and horizontal flow or two-stage vertical flow CWs have been used. The average number of designed PE is 235 and the average surface area of the Czech CWs is 1132 m2. The average treatment efficiencies are 87.5% for BOD5, 78.5% for COD, 85.7% for TSS, 41.8% for N-NH4 and 41% for TP. The respective average outflow concentrations are (in mg l−1): 12.5, 48.5, 11.2, 16.6 and 3.35. The results from the oldest CWS in the Czech Republic revealed very consistent performance over the period of 30+ years with no refurbishment. The paper also provides information about two CWs which were refurbished after about twenty years of operation from horizontal subsurface flow to hybrid systems. In both CWs, the refurbishment was successful and the treatment efficiency increased.

Constructed Wetlands as Nature-Based Solutions for Wastewater Treatment in the Hospitality Industry: A Review

The hospitality industry is increasing its awareness of how the integration of nature-based solutions can decrease its environmental impact while maintaining or increasing the service level of the sector. Constructed wetlands (CWs) constitute a promising sustainable solution for proper in situ domestic wastewater treatment. This literature review elucidates the status of CWs implementation in the hospitality industry to help foster the exchange of experiences in the field and deliver examples of approaches in different contexts to support future applications of this technology. Most of the studies reported in the literature were conducted in Europe, but studies emanating from Asia and South America are also available. The design of CWs, the horizontal and vertical subsurface flow CWs (HSFCW, VSFCW), and hybrid systems have been reported. The average removal efficiencies of the systems ranged from 83 to 95% for biochemical oxygen demand, 74 to 94% for chemical oxygen demand, 78 to 96% for total suspended solids, 75 to 85% for ammonium, 44 to 85% for ammonia, 50 to 73% for nitrate, 57 to 88% for total Kjeldahl nitrogen, 51 to 58% total nitrogen, and 66 to 99% for total phosphorus. The majority of the systems were implemented as decentralized treatment solutions using HSFCWs, with the second most common design being the hybrid CW systems in order to reduce area requirements, increase treatment efficiency, and prevent clogging. Overall, CWs are a promising sustainable solution which may support access to adequate sanitation worldwide as well as safe wastewater recycling and reuse, leading to more sustainable tourist destinations.

Fluidic Diode AICD Characteristic Curve Testing and Mathematical Modeling

In order to investigate an efficient water control method suitable for the bottom water occurring during the production process of horizontal wells in bottom water reservoirs, the characteristic curves of a Fluidic Diode AICD (Automatic Inflow Control Device) were tested, and a mathematical modeling method is proposed. First, the working principle of a Fluidic Diode AICD was analyzed; subsequently, a Fluidic Diode AICD test platform was designed and built independently, and pressure test experiments of the Fluidic Diode AICD under different flow conditions were carried out to obtain characteristic curves of the Fluidic Diode AICD. Finally, a mathematical model of the flow–pressure drop characteristic curves of the Fluidic Diode AICD was developed and applied to the simulation of water control production in horizontal wells in bottom water reservoirs. The results of the study showed that the Fluidic Diode AICD produces a more significant pressure drop under high water content conditions, and has a better oil and water stabilization function in production. In this study, the reservoir flow, annulus flow, AICD flow, and horizontal wellbore flow are considered, and an integrated coupling model for horizontal wells in bottom water reservoirs is established. This study provides a basis for using Fluidic Diode AICDs in horizontal wells in bottom water reservoirs.

Evaluation of heat transfer correlations based on input parameters in a solar parabolic trough collector using supercritical carbon dioxide

Concentrating Solar Power (CSP) technologies have emerged as leaders in generating renewable power. Parabolic trough collector (PTC) is the most widely used CSP technology for various applications of solar thermal heat at commercial level. Altering the heat transfer fluid (HTF) to supercritical CO2 (s-CO2) holds promise in improving the efficiency and operations of solar PTC. The present study discusses heat transfer correlations from literature for the horizontal flow in smooth tubes. The correlations have been evaluated for their suitability to predict the average Nusselt numbers by s-CO2 as the HTF in a solar PTC. Nusselt Numbers computed using these correlations have been compared with the validated numerical simulation. Utilizing a previously validated non-uniform solar heat flux as input for the three-dimensional finite volume method, the numerical thermal simulations were performed These correlations have been compared for the operating boundary range of the solar PTC. The impact of each thermophysical input parameter of HTF is outlined in the study. Additionally, a novel correlation is proposed based on the multiple regression of thermophysical input properties of the s-CO2 as HTF in the solar PTC. The proposed correlation based on input parameters has very high prediction accuracy. It can simplify the design analysis of the solar PTC field for the s-CO2.

A research on a GA-BP neural network based model for predicting patterns of oil-water two-phase flow in horizontal wells

At present, unconventional oil reservoirs are usually exploited by means of horizontal wells. However, due to the influence of multiple factors such as well deviation, oil flowrate and water flowrate, the distribution (flow pattern) of oil and water in a wellbore is complex. In addition, an accuracy of flow pattern identification is also vital for accurately interpreting the oil-water two-phase production profile of a horizontal well. Therefore, the research on flow pattern prediction of wellbores is of great application significance. Firstly, at normal pressure and temperature, based on the multiphase flow simulation experiment device, a transparent glass wellbore with a diameter similar to the actual downhole well was used to carry out oil-water two-phase simulation experiments with different well deviations, different flowrates and different water cuts, while visual observation and whole-process HD video recording of oil-water flow states were performed. Secondly, with reference to the typical horizontal well oil-water two-phase theoretical flow pattern, the flow patterns under different experimental conditions were identified, and the distribution diagram of flow patterns at four well deviation angles was drawn. Then, the GA-BP neural network was used for learning and prediction of experimental flow pattern data, and a model for predicting four experimental flow patterns was established to realize the flow pattern prediction under different well deviations and different flowrates in horizontal well. Finally, the above prediction model was verified based on 24 data points of two sample wells. After comparison with logging data, it was found that the accuracy of identifying flow patterns through the prediction model was high, and the overall coincidence rate reached up to 87.25%, indicating that the prediction model met the requirements for interpretation of actual logging data.

Mechanism of pin thread and flat features affecting material thermal flow behaviors and mixing in Al-Cu dissimilar friction stir welding

Three different features of pin models in Al-Cu dissimilar friction stir welding processes are established to analyse the effects of threads and flats on the two-phase material thermal flow behaviors. Based on computational fluid dynamics (CFD), a simulation methodology that calculates pins with complex morphologies through an adaptive force boundary is proposed. The pin characteristics are gradually optimized from “conical contour” to “conical-thread” and then to “thread-flats”. For dissimilar Al-Cu materials, the physical properties are weighted by the volume fractions of two-phase materials in the mixing zone. To build a dynamic adaptive contact model that varies with the material flow state, the interfacial friction shear stress is calculated by using the relative slip between the tool and material. The linkage effects between the “thread + flats” on the dissimilar Al/Cu welding mechanisms are systematically analysed. The enhancing mechanisms of the thread and flats on the material flow are different. The thread mainly reinforces the longitudinal migration of the Al/Cu materials, which is perpendicular to the horizontal plane. The flats effectively expand the plastic flow range and material mixing zone on the horizontal plane. These flow expanding effects are observed on the Z = 1 mm plane since the radial range of material flow enlarges from 2 mm to 3 mm under the action of the flats, while the horizontal flow range undergoes little change with the thread. The coupled mechanism of the “thread + flats” shows 0.06 s periodic strengthening, and the fluctuation threshold of the material flow velocity is wider, significantly improving the upwards stirring of the bottom material. The enhanced horizontal flow and vertical migration are beneficial to the uniform dispersion of the second-phase material (Cu) and local material softening for the formation of Al-Cu heterogeneous joints. Moreover, the accuracy of the model is verified by comparing the simulated and experimental TMAZ boundaries.

What is the best design approach for estimating effluent concentrations from horizontal flow treatment wetlands: the use of volumetric (kV) or areal (kA) removal rate coefficients?

Effluent concentrations from horizontal flow (HF) treatment wetlands can be estimated by using the Tanks-In-Series model for describing hydraulics and first-order removal rate coefficients for describing pollutant removal. In the design of conventional wastewater treatment plants, volumetric removal rate coefficients (kV) are traditionally used in conjunction with the theoretical hydraulic retention time. Areal removal rate coefficients (kA) coupled with the applied areal hydraulic loading rate are widely used in the literature. Despite this, supporting evidence of its appropriateness is scarce in the literature. The objective of this study is to investigate the adequacy of both approaches by analyzing the influence of liquid depth on kV and kA. Data from 74 HF wetlands were collected, covering biochemical oxygen demand and chemical oxygen demand, and diverse types of influents (raw sewage and primary, secondary and tertiary effluents). For these conditions, kV decreased with depth of the wetland system. Regression analyses between depth and removal rate coefficients were performed, and the equations indicated that kV was approximately related to the inverse of depth, while kA was almost independent of depth. These findings endorse the utilization of the areal-based approach for design purposes. The volumetric-based approach can also be used, but the value of kV must be provided together with the depth being considered.

AM3F-FlowNet: Attention-Based Multi-Scale Multi-Branch Flow Network.

Micro-expressions are the small, brief facial expression changes that humans momentarily show during emotional experiences, and their data annotation is complicated, which leads to the scarcity of micro-expression data. To extract salient and distinguishing features from a limited dataset, we propose an attention-based multi-scale, multi-modal, multi-branch flow network to thoroughly learn the motion information of micro-expressions by exploiting the attention mechanism and the complementary properties between different optical flow information. First, we extract optical flow information (horizontal optical flow, vertical optical flow, and optical strain) based on the onset and apex frames of micro-expression videos, and each branch learns one kind of optical flow information separately. Second, we propose a multi-scale fusion module to extract more prosperous and more stable feature expressions using spatial attention to focus on locally important information at each scale. Then, we design a multi-optical flow feature reweighting module to adaptively select features for each optical flow separately by channel attention. Finally, to better integrate the information of the three branches and to alleviate the problem of uneven distribution of micro-expression samples, we introduce a logarithmically adjusted prior knowledge weighting loss. This loss function weights the prediction scores of samples from different categories to mitigate the negative impact of category imbalance during the classification process. The effectiveness of the proposed model is demonstrated through extensive experiments and feature visualization on three benchmark datasets (CASMEII, SAMM, and SMIC), and its performance is comparable to that of state-of-the-art methods.

Proposal of a new approach to perform advanced flow modeling for subsurface flow treatment wetlands.

This study describes a new approach to model treatment wetlands (TW) by using computational fluid dynamics (CFD) coupled with the discrete element method (DEM). This methodology is based on the adoption of open-source software to perform advanced hydraulic simulations that enable a detailed representation of water flow through CFD as well as solid phase consideration by using DEM. The main features of this approach are highlighted and details on how to perform CFD-DEM modeling of a horizontal flow treatment wetland (HFTW) are described. Validation of the CFD-DEM model was performed on two TW case studies. The results were compared to the Darcy-Forchheimer porous media model. Statistical and hydraulic performance indexes were used to evaluate the efficacy of models. Provided that no calibration was done, the results indicated that for these case studies the CFD-DEM approach outperformed the Darcy-Forchheimer model based on the aforementioned metrics and considering the similarity with experimental results. The application of CFD-DEM coupling for TW proved to be an interesting approach as it enables more complex analysis of the hydrodynamics of TWs, becoming a valuable tool for future research and system optimization.

Chromium and Zinc removal from synthetic industrial wastewater in pilot-scale constructed wetlands planted with Cyperus odoratus L

Introduction: Constructed wetlands (CWs) are a recognized technology to treat industrial wastewater. Objective: A pilot system of two horizontal subsurface flow CWs was used to remove Cr and Zn from industrial synthetic wastewater. Method: The study was carried out at Universidad del Atlántico in Barranquilla, Colombia. Two containers of 0.375 m2 were filled with a gravel bed (~10 mm and 40% of porosity) and a 0.3 m water column. One container was planted with Cyperus odoratus L. and another without plants was used as a control. Results: The removal efficiency of Cr and Zn was 93% and 96% in the CW planted, respectively and 67% and 98% removal were obtained in the unplanted system with statistical differences (P<0,05). The observed difference in biomass production (0.1 and 0.6 kg/m2) could be related to seasonal weather that could have favored the growth of the plant. C. odoratus reached a Translocation Factor greater than 1.5 for Cr and Zn, which is greater than that, reported by others for Cyperus species. However, a Bioconcentration Factor > 13.6 for Zn and < 7.7 for Cr indicated that C. odoratus is an accumulator species for Cr and Zn. Sorption metal processes in gravel can be occurring due to the high removal efficiency of Zn in unplanted systems Conclusions: These results show that C. odoratus could be recommended for use in constructed wetlands technology due to fast-growing and absorption and translocation heavy metals capacity.

Experimental study and correlation development of droplet sizes created by nozzle injection of oil into a horizontal water flow

The droplet of oil-in-water plays a crucial role in the performance of chemical process equipment. Accordingly, the present work is organized to develop a semi-empirical correlation to determine the Sauter mean diameter of oil droplets in the dilute oil-water flow field. In this regard, Experimental studies have been performed at three different average oil injection velocities (0.6, 0.9, and 1.2 cm/s) and three different average water velocities (0.438, 0.657, and 0.877 m/s) at turbulent conditions. The study is carried out in a horizontal pipeline with a diameter of 44 mm and 70D long. A 0.5 mm diameter needle is also utilized to inject oil at the center of the pipe's cross-section located 50D from the inlet. Image processing was applied to measure the diameter distribution of the oil droplet accurately. The linear, nonlinear regression techniques and Buckingham Pi theorem are used to derive a semi-empirical correlation for estimating the droplets' Sauter mean diameter in accordance with dimensionless parameters of the flow field. The results reveal that the PDF of the oil droplets' diameter presents a Gaussian distribution. The extension correlation is a function of oil and water Reynolds numbers that could predict the Sauter mean diameter with less than 6% errors in the turbulent flow field.

Prediction of pressure gradient and hold-up in horizontal liquid-liquid pipe flow

This paper aims to propose correlations to predict pressure gradient, friction factor and fluid phase hold-up in liquid-liquid horizontal pipe flow. To develop the correlations, experiments are conducted using high viscous oils (202 and 630 mPa⋅s) in a steel pipe of length 11.25 m and length-to-diameter ratio of 708. In addition, the experimental data from the literature comprising wide range of flow and fluid properties is analyzed. For the analysis, the liquid-liquid pipe flow data is categorized into two as: stratified and dispersed. The existing friction factor correlations are modified to incorporate the effects of viscosity of the oil phase, interfacial curvature (contact/wetting angle-in lieu of material of the pipe) and fluid phase fraction. In the two-fluid model of stratified flow, the wall stress and interfacial stress correlations are substituted with superficial velocities of fluids and superficial Reynolds numbers of fluid phases replacing fluid phase velocities and fluid Reynolds numbers. Similarly, for dispersed flow, an effective Reynolds number is described as the sum of superficial Reynolds number of oil and water phases. Substituting the generally employed mean or mixture Reynolds number with the effective Reynolds number into the existing single-phase turbulent flow friction factor correlation, an effective friction factor for oil-water flow is proposed. Employing the proposed correlations, the pressure gradient across the oil-water flow and hold-up volume fraction are predicted with significant reduction in error compared with that of conventionally employed correlations. The average error and standard deviation values of −7.06%, 20.72% and 0.31%, 18.79% are found for stratified flow and dispersed flow respectively.

Influence of vortical flow induced by a wall-mounted short cylinder with a streamlined front side on a horizontal air–solid two-phase flow

To induce large oscillations of air flow and suspend particles easily near the particle supply point in a low air velocity region of horizontal air-solid two-phase flow, a short cylinder model with a streamlined front side (refer to streamlined model) is proposed and is fixed on the bottom or top of the pipe in front of the particle feed. The streamlined front side of the model is designed to reduce the flow resistance, and the rectangular rear section of the model generates wake vortical flow so as to induce large airflow oscillation. The test tube consists of a horizontal pipe having an inner diameter of 80 mm and a length of 5 m. Spherical polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m3 were used as the test solid particles. Average air velocities and particle mass flow rates ranged from 9 to 16 m/s and 0.11 to 0.51 kg/s, respectively. Compared with the non-model air-solid two-phase flow, the streamlined model has reduced the pressure drop, critical and minimum conveying air velocities, power consumption, and additional pressure drop. This model achieved the highest reduction rate with a minimum air velocity of approximately 6% and an additional pressure loss of approximately 37.5%. According to particle image velocimetry measurement of air-solid two-phase flow, the time-averaged particle velocity and fluctuating particle velocity generated by the streamlined model are larger than those in the non-model flow, so even low air velocities can easily convey particles.