Sand Volume Fraction Research Articles

Influence of Terrain on Windblown Sand Flow Field Characteristics around Railway Culverts

Aeolian sand hazards are often a threat to culverts, which are important channels and pieces of infrastructure of the desert railway. In addition to wind speed, wind direction, and culvert structure, terrain may also be an important reason for the formation of culvert sand hazards. However, there are few studies on the effect of terrain on the sediment accumulation characteristics of culverts. This paper established computational fluid dynamics (CFD) models of railway culverts (flat and concave culverts) based on Euler’s two-fluid theory. An analysis of the influence of terrain on the distribution law of the flow fields and sand accumulation around railway culverts was carried out. The results show that the horizontal wind speed curves changes in a “W” shape along the centre axis surface from the forecourt to the rearcourt within a range of 30 m~66.8 m. Low-speed backflow is formed at the inlet and outlet of the culvert, and the minimum wind speed reaches −3.6 m/s and −4.2 m/s, respectively, when the height from the bottom of the culvert is 1.0 m and 1.5 m, resulting in intensified sand sedimentation. In concave culverts, the lower the roadbed height, the easier it is for sand to accumulate at the culvert outlet, the rearcourt, and the track; the sand volume fraction is close to 0.63, affecting the normal operation of the trains. On the contrary, the higher the roadbed, the easier it is for sand to accumulate at the culvert inlet, hindering the passage of engineering vehicles and reducing the function of the culverts. These results reveal that terrain plays a pivotal role in the sand accumulation around culverts and that it should be one of the key considerations for the design of new railway culverts. This work can provide a theoretical basis for preventing and managing sand hazards in railway culverts.

Characterizing connectivity and tortuosity of pore network based on LF-NMR method to assess the water permeability of white cement mortar

To better understand the macro transport properties and durability of cementitious materials, their microstructure should be characterised more accurately. This study investigated white cement mortars with different water-cement ratios, sand volume fractions, and curing ages. The water permeability was measured using a self-manufactured facility. The low-field nuclear magnetic resonance (LF-NMR) technique combined with the displacement method was used to test the pore size distributions (PSD) of total pores and connected regions. Two-dimensional mortar and pore-based matrix models were established to obtain the tortuosity of the transport path. The results show that the pore connectivity of the mortar ranges from 32 % to 52 %, and the tortuosity ranges from 1.428 to 1.542. The pore connectivity was spatially sensitive, and small pores were densely connected, linking large pores to form a pore network. Although capillary pores dominate the permeability, the role of gel pores cannot be ignored. Considering gel pores can improve the accuracy of the predicted water permeability by 80 %. The relative error of the modified model is [-23.76 %, 37.19 %], which shows a significant improvement.

The Influence of Blade Wrap Angle on the Internal Flow Field and Hydraulic Performance of Double-Suction Pump for Yellow River Pumping

Abstract Analyzing the influence of blade wrap angle on the internal flow field and hydraulic performance of the pump, five different blade wrap angles were designed. Based on RNG k-ε and DPM were used to conduct a steady-state numerical simulation of impellers under the same conditions and different sand volume fractions, respectively. The results show that as the blade wrap angle increases, the flow separation and vortices in the impeller flow passage also decrease, and the flow is closer to the blade profile, but the friction loss in the impeller flow passage also increases. There is an optimal blade wrap angle to maximize the pump head and efficiency. By increasing the wrap angle of blade, the low-pressure zone at the blade inlet area increases, the high-pressure zone at the outlet decreases, and the low-speed zone within the impeller decreases, increasing the outlet velocity. When the sand volume fraction is less than 5%, the effect of sand volume fraction on the hydraulic performance of the pump is not obvious. When the sand volume fraction is more than 5%, the change of wrap angle of blade has a significant effect on the hydraulic performance of the pump.

Determining the bulk viscosity in clay–sand mixtures: A combined investigation with slump tests and lattice Boltzmann simulations

Viscosity measurements for clay slurry and sand mixtures can be challenging for standard rheometers because of the sand particles. To solve this, we suggest combining slump test experiments with numerical simulations. Slump tests are performed on clay–sand mixtures, with the sand's volume fraction varying between 0≤ϕ≤0.32. The run-out distance of the slump is tracked over time using a high-speed camera. By comparing the results of lattice Boltzmann simulations with the experimental data, we can accurately estimate the mixture's overall viscosity. Our findings reveal that fluid consistency increases significantly with ϕ, consistent with predictions made by the Maron–Pierce formula.

Overview of Marginal Lands in Henan Province, China and Evaluation of Development Potential of Biomass-To-Liquid Fuels

Developing marginal lands to plant energy crops and then develop biomass-to-liquid fuels is an effective way to ease the energy crisis, promote greenhouse gas emission reduction, and protect the natural ecological environment. Taking Henan Province, China as a research object, the research obtained spatial distributions and areas of marginal lands in the province by processing remote-sensing data for land use using software ArcGIS. Marginal lands in Henan Province were classified into the first-class, second-class, and third-class ones by selecting key natural conditions including the soil thickness, slope, soil texture (sand volume fraction), accumulated temperature above 10 °C, organic matter content, and total annual precipitation as indices. The research showed that the total area of marginal lands in the province is 1.68×104 km2, including 0.62×104 km2 of first-class marginal lands, 0.83×104 km2 of second-class marginal lands, and 0.23×104 km2 of third-class marginal lands. Taking production of bioethanol with sugar grass as an example, 8.92×107 t of sugar grass can be harvested on the marginal lands in Henan Province, which can be converted into 5.80×106 t of bioethanol, equivalent to 6.96×106 t of standard coal. The research can provide reference for realizing energy structure optimization and consolidating energy security in Henan Province.

Experimental and numerical investigation on low‐velocity impact response of sandwich structure with functionally graded core

AbstractThe present research investigates optimizing the impact resistance of functionally graded sandwich structures using experimental and numerical approaches. The low‐velocity impact (LVI) responses of functionally graded sandwich composite (FGSC) with different configurations with skin material jute/rubber/jute (JRJ) and core material having epoxy and sea sand by volume fraction of sea sand at 0%, 10%, 20%, and 30%. Sandwich structures were impacted with LVI (5.89, 10.92, and 15.18 m/s), with the impactor dropped from heights of 0.5, 1, and 1.5 m with precompressed spring loads. FGSC samples are considered a deformable body, and the impactor is modeled as a rigid body using commercially accessible dynamic explicit software. The burn‐out test and weight method were used to test the core's gradience; both methods' results substantially matched, and the variance in gradation could be observed. The proposed sandwich structure characteristics are examined by energy absorption, peak force, energy loss percentage, and coefficient of restitution. Results showed that SC30S provides greater energy absorption and superior damage resistance when tested on LVI. To evaluate the accuracy of experimental findings in predicting the indentation behavior of the sandwich structure, the finite element analysis was used to compare with the experimental results. According to the examination of these proposed FGSC overall performance, they could potentially be employed as sacrificial materials for LVI applications like claddings to shield major structural components. The systematic approach used in this work serves as a standard for choosing and using FGSC effectively for LVI applications.Highlights Low‐velocity impact behavior of sandwich structures was investigated. Combining flexible skin and epoxy core enhances energy absorption. Based on impact energy levels, impact damage areas were determined. Examined sandwich structure advantages in structural and aerospace uses. In terms of time and cost, the numerical analysis method would be useful.

Effect of siliceous sand volume fraction on the properties of alkali-activated slag mortars

One of the critical factors affecting the performance of alkali-activated slag (AAS) is the nature and dose of alkali activator. The activator type can play a significant role during the transition from pastes to mortars or concretes. Therefore, three basic sodium activators (water glass, carbonate, and hydroxide) of the same molarity of 4M Na+ were used to prepare AAS-based mortars with different volume fractions of siliceous sand. These were compared by means of workability, mechanical strength, and long-term shrinkage under autogenous conditions. The results were compared to those obtained on pastes with similar workability. Increasing the content of the sand tended rather to decrease the mechanical properties, while greatly decreased autogenous shrinkage. Nevertheless, the most remarkable differences for different activators were observed when comparing the mortars with pastes. The transition from pastes to mortars resulted in the highest reduction in both compressive and flexural strength for sodium hydroxide. The flexural strength of the mortars with sodium water glass and sodium carbonate even increased considerably in presence of sand.

Experimental study on the characteristics, rheological factors, and flowability of MK-GGBFS geopolymer slurry

In this study, we investigated the effects of concentration and modulus of alkaline activator, liquid–solid (L/S) ratio, and sand volume fraction on rheological properties and flowability of metakaolin (MK)–ground granulated blast furnace slag (GGBFS) geopolymer slurry (pastes and mortars). The rheological property of geopolymer slurry was consistent with the Bingham model. A decrease in the modulus and the L/S ratio, or an increase in the concentration increased the plastic viscosity of geopolymer paste. The geopolymer pastes with higher plastic viscosity exhibited a lower fluidity. The yield stress of geopolymer paste was negatively correlated with concentration, modulus, and L/S ratio. An increase in the sand volume fraction increased the plastic viscosity and yield stress of geopolymer mortar, and decreased the consistency and fluidity of that. Moreover, the correlation between rheological parameters of the geopolymer mortar and paste, and the relationship between the flowability parameters and rheological parameters of geopolymer slurry were constructed.

Sand Sedimentation Mechanism in and around the Railway Culvert and Its Structural Optimization of Sediment Reduction

A computational fluid dynamics (CFD) model of a railway culvert was established based on the two-phase flow theory to investigate wind-blown sand transport and sand sedimentation in and around a railway culvert. Then the flow field and the accumulation distribution of sand particles were analyzed through numerical simulation. The results show that the flow field around the culvert can be divided into deceleration, acceleration, and vortex areas. The curve of the horizontal wind speed along the central axis of the culvert had a W shape, indicating a significant increase in the wind speed inside the culvert. A large amount of sand accumulated at the culvert inlet because of the wing walls. The sand volume fraction in the culvert decreased with an increase in the inflow velocity, and there was almost no sand sedimentation when the inflow velocity was greater than 20 m/s. Three reasons for the sand accumulation in the culvert included the deflection by the wing walls, subgrade blocking, and a low inflow velocity. Based on the simulation results, straight and protruding culverts were designed to minimize sand accumulation. The straight culvert exhibited better performance than the protruding culvert and is recommended for use in railways. This work can provide theoretical support for designing railway culverts that minimize or prevent wind-blown sand accumulation.

Preparation and properties of green high ductility geopolymer composites incorporating recycled fine brick aggregate

Reusing of waste bricks, particularly as recycled aggregates to prepare concrete, plays an important role in reducing dependence on natural resources and solving the problem of waste accumulation. However, there is a lack of applied research on fine-grained size brick aggregates. In this study, recycled fine brick aggregate (RFBA) and industrial by-products are successfully used to develop green high ductility geopolymer composites (RFBA-HDGC) with appropriate composition tailoring. The effects of the volume fraction of river sand replaced by RFBA, slag content, and silicate modulus as the most important matrix parameters on the compressive strength, fracture properties, tensile properties, fiber/matrix interface and crack characteristics of the composite are evaluated. The experimental results show that increasing slag content and decreasing the silicate modulus can improve the fracture strength, compressive strength, and tensile strength. The utilization of recycled fine brick aggregates reduces the strength, but the close binding of high-roughness RFBA to the matrix promotes the interlocking effect between the fiber and the matrix, which increases the frictional bond during the fiber pull-out process and facilitates the development of fiber bridging capabilities. The maximum tensile strength and tensile ductility of the high ductility geopolymer composites prepared from the RFBA with 100% volume fraction can reach 4.41 MPa and 4.27%, respectively, with medium strength and medium-to-high ductility grades. This research shows the engineering application potential of RFBA-HDGC and can provide new solutions for the utilization of brick aggregates.

A New Porous Nozzle for Aluminum Melts Purification—Preparation and Mathematical–Physical Model

Aluminum and its alloy castings are used more and more widely, and it is particularly important to remove impurities in the alloy. According to the principle of bubble floatation for degassing aluminum melt, a new porous nozzle with controllable pores was developed, and a hydraulic simulation experimental device was studied with the nozzle. The effects of the particle size ratio of the coarse sand to fine sand and volume fraction of fine sand on the porosity of the porous nozzle were studied by orthogonal experiment, and permeability and compressive strength of the porous nozzle were used as test indicators to determine the optimal parameters of preparation for the porous nozzle. The optimal parameters are fine sand of 100 mesh, and fine sand of 50 wt.%, binder of 17.5 wt.%, pore-forming agent of 6 wt.%, and pressure of making sample of 5 MPa. The nozzle with optimal parameters was prepared and tested, and the permeability is 112.2 × 10−12 m2 and the compressive strength is 2.3 MPa. In addition, a physical model of gas transmission in the porous nozzle was proposed. With the increase in the proportion of fine sand, the permeability of the porous nozzle decreases, the compressive strength increases, and the calculated porosity increases. The hydraulic simulation of melt injection was carried out, and the mathematical model for calculating the bubble diameter of bubble floatation was formulated. The model shows that the bubble diameter increases with the increase in gas flow rate. The experiment shows that the prepared porous nozzle has the merits of a simple preparation process and low-cost, which is expected to degas aluminum melts.

Seasonal Dynamics of Soil Enzymatic Activity under Different Land-Use Types in Rocky Mountainous Region of North China

To reveal the effects of different land-use types on soil enzyme activities, soil samples were collected from 0–10, 10–20 and 20–30 cm soil layers to compare and analyze soil β-glucosidase (BG), urease (URE), protease (PROT) and catalase (CAT) activities in farmland (FL), abandoned land (AL) and three plantation forests: Platycladus orientalis (L.) Franco (PO), Robinia pseudoacacia L. (RP) and Quercus variabilis Bl. (QV) in the rocky mountainous region of North China. The results showed that the soil enzyme activities varied significantly under different land-use types, and the interannual mean values of FL and PO were remarkably higher than those of other land uses in the 0–30 cm soil layer, in which the soil BG and URE activities of FL were 22% and 12% higher than those of AL, and 428% and 179% higher than those of QV, respectively; the soil PROT and CAT activities of PO were 66% and 23% higher than those of AL, and 479% and 113% higher than those of QV, respectively. Soil BG, URE and PROT activities were all higher in June and lower in December, while soil CAT activity was slightly lower in June. The soil enzymatic activities all showed a notable decrease with the depth of the soil layer. Soil BG, URE, PROT and CAT activities were remarkably (p < 0.01) or significantly (p < 0.05) positively correlated with available nitrogen, available phosphorus, available potassium, dissolved organic carbon (DOC), NO3−-N, soil organic carbon, water content, clay and silt volume fraction, and significantly negatively correlated with sand volume fraction. Soil DOC and pH were important factors influencing soil enzymatic activity, implying that changes in soil enzymatic activity under different land-use types may be the result of a combination of temperature, moisture and plant type. In conclusion, PO plantations are conducive to improving the physicochemical and biological properties of soil and enhance soil fertility, which is a reasonable land-use method to achieve sustainable development in the rocky mountainous region of North China.

A new pressure gradient model of slurry shield pipeline system coupling with rheological properties and wall slip behaviour under sandy stratum

Pipeline transport is of uttermost importance during slurry shield tunneling, and the precise calculation of the pressure gradient of the pipeline system is the premise for the optimal design of industrial slurry pipeline system. This paper proposed a new muck slurry pressure gradient model of slurry shield pipeline system coupling with the wall slip behaviour based on the Herschel-Bulkley rheological model (H-B model) to estimate the pressure gradient of the muck slurry under sandy stratum. Effects of the sands volume fraction and average particle size on the rheological properties of the muck slurry in pipeline system were investigated to construct the H-B rheological parameters prediction models, which were coupled into the proposed pressure gradient model. Besides, the accuracy and dependability of the proposed model were validated through the engineering field tests and model tests, and the prediction results of the proposed pressure gradient model has an average error of 10.6% and 8.2% with engineering field test data and model test data respectively. The results indicated that the muck slurry is a typical thixotropic fluid. The sand volume fraction and particle size both significantly affect the rheological properties of the muck slurry, the yield stress and plastic viscosity of H-B rheological parameters increase exponentially with the sand volume fraction increasing and increase linearly with the average particle size increasing, the power law index of H-B rheological parameters increases linearly as average particle size and sands volume fraction increase. Ultimately, the research results can provide reasonable suggestions and references for the designing of pipeline system and efficient tunneling of slurry shield.

Effect of Spiral Inlet Geometric Parameters on the Performance of Hydrocyclones Used for In Situ Desanding and Natural Gas Hydrate Recovery in the Subsea.

The inlet structure of hydrocyclones has great impact on performance. In this paper, the effects of spiral inlet geometric parameters on the flow field characteristics and separation performance were investigated by CFD. Numerical results show that the pitch has the largest influence, followed by the heads, the turns, and the steady flow cone. With the increase of the steady flow cone angle, the turbulence intensity increases. The efficiency, pressure drop, tangential velocity, sand volume fraction at the spigot, and natural gas hydrate (NGH) volume fraction at the vortex finder decrease, when the pitch increases. With the increase of the number of heads and turns, the efficiency, pressure drop, tangential velocity, the NGH volume fraction at the vortex finder, and the sand volume fraction at the spigot increase. The efficiency and pressure drop of hydrocyclones with the optimal parameters are 90% and 0.05 MPa, respectively. Therefore, the performance of the NGH hydrocyclone can be improved by increasing the inlet pitch and the number of spiral heads and inlet spiral turns. The results provide theoretical guidance for the engineering design of NGH in situ separators.

Natural fibers as an alternative to synthetic fibers in the reinforcement of phosphate sludge-based geopolymer mortar

Geopolymers are a kind of material of great technological and ecological interest thanks to their high mechanical properties and their ability to be produced from industrial by-products. However, like all cementitious matrices, geopolymers have a fragile character and suffer from low ductility. To overcome this challenge while staying environmentally conscious, the present research focuses on the efficiency of using natural fibers instead of synthetic fibers in the reinforcement of geopolymer mortars based on phosphate industry by-products. Geopolymer mortar composites were prepared by incorporating high contents of pine cone fibers (NF) and glass fibers (GF) into a geopolymer mortar matrix based on treated phosphate sludge, metakaolin, and sand. Pine cone fibers reinforced composites were assessed and compared to glass fibers reinforced composites and control mortar in terms of structural, physical, and mechanical properties. The structural analysis revealed that the prepared mortars consist of a continuous three-dimensional network characteristic of a geopolymer matrix without undesirable interactions between the used fibers and the mortar matrix. Density, porosity, and water absorption studies indicate that pine cone fibers created fewer defects in the geopolymer mortar matrix than glass fibers, and that NF-reinforced composites are more resistant to moisture than GF-reinforced ones by about 2%. The results of the mechanical properties showed that the addition of fibers, whether natural or synthetic, decreases the compressive strength and significantly increases the flexural strength. However, Although the flexural strength rises with the fiber content in the matrix, the fiber content of 50 wt% sand volume fraction was the limit, since beyond this content, the workability and flowability of the composites notably decrease. Overall, when both mechanical properties are considered, as well as the ecological and economic impacts, it can be stated that pine cone fibers could potentially replace synthetic fibers in the reinforcement of phosphate sludge-based-geopolymer mortars.

Effect of Volume Fraction of Fine Sand on Magnetorheological Response and Blocking Mechanisms of Cementitious Mixtures Containing Fe3O4 Nanoparticles

Active rheology control (ARC) or active stiffening control (ASC) is a concept with which the conflicting rheological requirements during different stages of concrete casting can be reconciled. For instance, formwork leakage could be reduced by actively controlling structuration at the formwork joints, without having the negative impact of increased structuration during pumping and form filling. Using the concepts of magnetorheology, an active control methodology was thus recently developed by the authors to study the control of formwork leakages under pressure. This was performed using a small-scale laboratory test setup, using cementitious pastes containing magnetisable particles. To upscale from paste to mortar, the effect of volume fraction of sand on the magnetorheological (MR) response and blocking mechanisms of mixtures containing Fe3O4 nanoparticles is thus investigated in the current study. The MR response is determined using storage modulus tests, and the impact of ASC for leakage reduction is investigated by measuring the flow rate. Experimental results show that increasing the sand volume beyond a threshold causes a reduction in mobility of the magnetic particles, and thus lowers the MR effect. Despite this reduction in the MR effect at high sand volume, the increased particle interactions induce clogging and filtration effects, drastically lowering the flow rate. Applying the ASC method refines the voids in the clog, thereby eliminating the filtration effect. It is concluded that ASC can be used on mortar, with the expectation that there would be a reduction in the magnetorheological effect with increasing volume of fine aggregates.

Measurement and simulation of electrical resistivity of cement-based materials by using embedded four-probe method

The electrical resistivity of cement-based materials is an important index that can be used for designing durable, multifunctional, and smart concrete structures. However, the measurement and prediction of electrical resistivity are far from being well addressed for cement-based materials. In this study, a modified four-probe test using embedded fine copper rods as electrodes was developed to measure the electrical resistivity of cement-based materials. A coupled thermal-electrical analysis was conducted to verify the feasibility of the modified four-probe method. The simulated results show that a linear relation between the electrical resistivity and the apparent electrical resistance. The contact resistance of the interface between the specimen and the electrodes has little effect on the electrical resistivity. The applied voltage ranging from 4 V to 28 V has a minor influence on the measured electrical resistivity. The electrical resistivity of the specimens cured under standard condition is greater than that under sealed condition. The electrical resistivity of cement-based materials cured under both sealed and standard conditions increases with increasing curing age. A higher volume fraction of sand contributes significantly to a higher electrical resistivity of cement-based materials. Moreover, the homogenization results indicate that the differential scheme predictions coincide quite well with the measured electrical resistivity of cement-based materials with a wide range of sand volume fractions (0%∼60%). The Voigt scheme, the self-consistent scheme, and the Mori-Tanaka scheme can predict well the electrical resistivity of cement-based materials with a low volume fraction of sand (<20%), but fail to give a good prediction at a higher sand content.

Quantification of soil textural and hydraulic properties in a complex conductivity imaging framework: Results from the Wolfsegg slope

We present an approach that permits to predict hydraulic conductivity from extensive, multi-methodical geophysical data collected on a hillslope affected by landslides in Austria. The objective of the investigation is the spatial characterization of a slope affected by mass movements to derive hydrogeological structures and preferential flow paths. The geophysical data sets presented in this study consists of 24 densely distributed complex conductivity (CC) imaging profiles, collocated to these profiles we also collected 517 transient electromagnetic (TEM) soundings and 10 refraction seismic tomography (RST) profiles. Additionally, we also present well-logging data (namely electrical resistivity, natural gamma logs) collected in five boreholes. Cores recovered during the drilling of the boreholes are used to aid in the interpretation of the geophysical units, while analysis of the sediments was conducted to obtain grain size distributions, cation exchange capacity and mineralogy of the subsurface materials. While all geophysical data was processed initially independently, the final complex conductivity imaging results are based on the incorporation of structural constraints about the electrical units obtained from the TEM soundings. The interpretation of the resolved CC units is then sustained by the RST images and the lithological information from the boreholes. We estimate then the hydraulic conductivity of the subsurface derived from the CC images using a two-step approach. In a first step, we investigated the link between the complex conductivity and the different soil volume fractions of gravel, sand, silt and clay. In a second step, we applied a pedo-transfer function, namely the well-known Rosetta model, that permits to predict the hydraulic conductivity from the estimated grain size volumes. This approach allowed a quantitative interpretation of the geophysical data and thus a 3-dimensional (3D) representation of the grain size distribution and hydraulic conductivity in the investigated slope section. Thereby, we observed well-determined site-specific relationships (R2 &amp;gt; 0.7) from the comparison of the complex resistivity images and grain size analysis. The obtained hydrogeophysical 3D model permits to delineate the geometry of an aquiclude, and, thus, the analysis of preferential water-flow paths. In particular, we can identify a spatial correlation between the aquiclude interface and morphological features.

Impacts of Fracture Roughness and Near-Wellbore Tortuosity on Proppant Transport within Hydraulic Fractures

For unconventional reservoir hydraulic fracturing design, a greater fracture length is a prime factor to optimize. However, the core observation results from the Hydraulic Fracturing Test Site (HFTS) show that the propped fractures are far less or shorter than expected, which suggests that the roughness and tortuosity of hydraulic fractures are crucial to sand transport. In this study, a transport model of sands is first built based on experimental measurements on the height and transport velocity of the sand bank in fractures with predetermined width and roughness. The fracture roughness is quantified by using the surface height integral. Then, three-dimensional simulations are conducted with this modified model to further investigate the impact of tortuous fractures on sand transport, from which a regression model is established to estimate the propped length of hydraulic fractures at a certain pumping condition. The experiment results show that the height of the sand bank in rough fractures is 20–50% higher than that in smooth fractures. The height of the sand bank decreases with the reduction in slurry velocity and increases with the increase in sand diameter. Sand sizes do little effect on the transport velocity of the sand bank, but the increase in slurry velocity and sand volume fraction can dramatically enhance the migration velocity of the sand bank. The appearance of tortuous fractures decreases the horizontal velocity of suspended particles and results in a higher sand bank compared with that in straight fractures. When the sand bank reaches equilibrium at the tortuous position, it is easy to produce vortices. So, there is a significant height of sand bank change at the tortuous position. Moreover, sand plugging can occur at the entrance of the fractures, making it difficult for the sand to transport deep into fractures. This study explains why the propped length of fractures in HFTS is short and provides a regression model that can be easily embedded in the fracturing simulation to quickly calculate dimensions of the propped fractures network to predict the length and height of propped fractures during fracturing.

Erosion prediction of bypass crossover sub in eccentric operating positions in horizontal wells

Erosion wear is a serious problem in the fracturing process. The erosion of the bypass crossover sub, particularly in eccentric position, during fracturing in high flow rate and high proppant concentration can make a big difference in erosion results. CFD technology with Euler–Lagrangian approach is employed to solve the continuous phase and the discrete phase. In the fluid phase, realizable k−ϵ model was used to calculate the turbulent flows, and the Lagrangian method was applied to track the particle motion in the solid phase. In order to validate the accuracy of numerical simulation, scale model testing is used to obtain velocity of flow field in bypass crossover sub. The velocity profile is measured by a laser Doppler Anemonmetry (LDA). CFD simulation results are in a good agreement with experiment data. In this study, the particle trajectories and volume fraction in central and eccentric positions were obtained by simulation. This work aimed to conduct a detailed study on the flow phenomena of bypass crossover sub and analyze the difference in the bypass crossover sub between central and eccentric positions in terms of the magnitude of erosion rates and severe erosion locations and find out which erosion model is the most applicable to predict erosion. The numerical results show that the erosion contours predicted by the three erosion models have huge differences. Oka et al. erosion model is in a good agreement with practical observations by analyzing erosion patterns of the three erosion equations at specified locations and comparing them with actual image. The simulation of different flow rates and sand volume fraction were carried out. This research can help predict the erosion of bypass crossover sub more accurately and provide references for erosion prediction, as well as experiences for designing and improving the bypass crossover sub of horizontal wells in engineering.