Numerical Study on Transportation of Cemented Paste Backfill Slurry in Bend Pipe

Wax deposition has always been an essential issue for flow assurance, especially in subsea pipelines. The coarse particles, which are usually measured in millimeters, will be carried out by oil flow during the deep-water oil fields production. However, due to insufficient understanding of the structure of wax deposits and the complexity of sandy crude oil deposition, the interaction between coarse particles and wax deposits in the pipeline have rarely been investigated. In this paper, the effect of coarse particles on the yield stress of wax deposits has been studied. The sample was mixed at reversible structure temperature so that the impact of shear history could be eliminated, and the rapid particle settlement at high temperature could be avoided. Experimental results have found that there is a critical fraction in coarse particle influences, below which a small number of coarse particles added will lead to a slight increase in bulk yield stress. On the contrary, a dramatic decrease in yield stress when exceeding the critical mass fraction and increasingly marked enhancement of yield stress as the fraction increases. This phenomenon has been explicated microscopically by the structural interaction between coarse particles and wax deposits. The interlock between wax crystals is the major contribution of the structure as the less particle fraction contains. Even though the silica sand is a typical non-colloidal particle, the asphaltene and resin could be absorbed on the surface of particles and forming a cluster of colloidal particles. As the fraction of particles slightly increased, the slip between colloidal particles and wax crystal interlock accelerates structural failure. Nevertheless, more particles involved the overall yield stress may depend on the friction and the adhesive force between solid particles. The subtle changes induced by coarse particles would have a harder deposit, which can hinder pig passing and affect pipeline pigging operations.

SUMMARYThis paper presents a method for designing the arm lengths of a screw drive in-pipe robot with a pathway selection mechanism to pass through bent pipes. The robot comprises a front-rotating unit (rotator), middle-steering unit, and rear-supporting unit (stator). Each unit has elastic arms, which can be elongated by springs and can be pushed against the inner wall of the pipe. The robot can travel and steer not only in straight pipes but also in bent pipes and T-branches. When the robot passes through such pipes, its mobility depends on whether the arms can touch the inner wall because the robot will lose the driving force if one of the arms cannot reach the inner wall. This is especially important in vertically positioned pipes, where the robot will fall down if it is unable to reach. In this paper, we focus on the cross-section of the bent pipes, arm length, spring stiffness, and mass of the robot to clarify the mobility of the robot in these types of pipes. A method for determining the initial arm length on the basis of simple quasi-statics is proposed and experimental verification is conducted.

Particulate erosion is a major concern in slurry handling unit of a thermal power plant. The pipe bends are the most erosion affected element of a pipeline unit thus, a cost-effective method to reduce pipeline erosion is highly desirable. This work aims to suggest the optimal pipe bend design to minimize the particulate erosion by analyzing the erosion wear in geometrically different pipe bends for bottom ash slurry flow by using Computational Fluid Dynamics code FLUENT. A Three-dimensional simulation study of erosion wear is carried out by implementing Euler-Lagrange modeling along with the standard k-ε turbulence model to solve the complex multi-phase flow. Pipe bends of different bending angle (30°, 45°, 60°, and 90°), diameter (50 to 250 mm) and bending ratio (r/D = 1 to 2.5) are evaluated at different flow condition. The wear location gets shifted to the upper section of the bend and its magnitude is significantly reduced with the increase in pipe diameter and bending angle. The dynamics of multiphase slurry through different bends is analyzed to understand the complex wear phenomenon. The simulation result shows good agreement with the published findings. Finally, a least erosion affected pipe bend profile is suggested for slurry transport unit.

Taguchi approach for optimization of pressure drop characteristics for fly ash with bottom ash addition in slurry pipeline

Investigation of abrasive wear in contact load-dominated slurry flows using a Toroid Wear Tester

Strength and Deformation Characteristics of Silty Sand improved by Gravel

Enhancement of cyclone solid particle separation performance based on geometrical modification: Numerical analysis

It is a traditional practice to store many agricultural products after drying, ensuring that they are used all year round. Mixed counter flow air drying is one of the most common and traditional methods in the bulk drying process. In this application, the air flow produced by the air channels placed in the dryer bed is forced to flow through the grains in the opposite direction to the grain flow. The moisture contained in the grains is thrown out of the dryer through forced convection. However, it is expected that the air ducts installed in the dryers should not obstruct the flow of grain and provide the best possible drying performance. In this study, computational fluid dynamics (CFD) modeling for a counter-flow grain dryer was performed and the effect of the geometry of the drying channels on the process was investigated. Fluent 2020 R2 commercial software was used for 2-D flow modeling through the dryer. The airflow in the grain zone, modeled as porous media, was included in the calculation for three different geometries of the dryer air ducts (circular, angular, and straight). A constant temperature boundary condition (37°C) was applied for the air ducts in which the drying air circulated without mixing with the grain. As an output of the analysis, the dryer outlet temperature and differential pressure variation along the flow were calculated for 5 different inlet velocities (between 0.005-0.25) to determine the behavior of different air flow rates in the drying process. The increase in the inlet velocity increased the pressure difference and consequently the stability of the flow for all models. The outlet temperature decreased by about 2.5 °C with a 5-fold increase in velocity. The results showed that the sufficient outlet air for moisture removal depends on the structure of the porous medium and the flow geometry. For this analysis, the best flow was found to be for the circular cross-section model and the outlet temperature could be at acceptable levels.

Some recent epidemiologic studies suggest a stronger effect of fine particles (PM2.5) than of coarser particulate matter. To examine the support for such a differential effect, the authors conducted a daily time-series analysis of mortality in relation to measurements of PM2.5, PM10, and PM10-2.5 in southwestern Mexico City in the years 1992–1995. A generalized linear model based on Poisson regression was used to control for weather and periodic cycles, and the average concentration of the previous five days was the index of particle exposure. The mean concentrations of PM 2.5 and PM10 were 27.4 μg m−3 and 44.6 μg m-3, respectively, and the mean concentration of PM10-2.5 was 17.2 μg m-PM10 was highly correlated with both the fine and coarse fractions, but PM 2.5 and PM 10–2.5 were rather weakly correlated with each other (correlation coefficient 0.52). All three particle size fractions were associated individually with mortality: a 10-μg m3 increase in PM10 Supported by cooperative agreements CR-820076 and CR-821762 between the U.S. Environmental Protection Agency and the University of North Carolina and Harvard University Schools of Public Health and a grant from the Mexico-U.S. Commission for Educational and Cultural Exchange. We thank Bill McDonnell, Armando Retama, Daniel Varela, and Silvia Bierswinski for contributions to the research and comments on the manuscript. Address correspondence to Dr. Dana Loomis, Department of Epidemiology, CB-7400, School of Public Health, University of North Carolina, Chapel Hill, NC 27599–7400, USA. E-mail: dana.loomis@unc.edu was associated with a 1.83% increase in total mortality (95% CI −0.01-2.96), and an equal increment in PM2.5 was associated with a 1.48% increase in deaths (95% CI 0.98-2.68%). The largest effect was observed for a 10 μg m−3 increment in PM 10-2.5; mean daily mortality increased 4.07% for each 10 μg m−3 (95% CI 2.49-5.66%). The effect of coarse particles was stronger for respiratory diseases than for total mortality, cardiovascular diseases, or other noninjury causes of death. These patterns persisted after adjustment (or O3 and NO2. When both PM2.5 and PM 10-2.5 were included simultaneously in the regression model, the effect of PMW-2.5 remained about 4% per 10 μg m−3 (95% CI 1.96-6.02%), while the effect of PM2.5 was virtually eliminated (0.18% change). These associations may be attributable to specific combustion or biogenic materials within the coarse particle mass. Understanding these relationships will require analyses of the composition of coarse particles. The findings also suggest a need to that the relative effects of coarse and fine particles on mortality should be examined in more cities with a wider variety of climates, population characteristics, and air pollutants.

Cemented coal gangue-fly ash backfill (CGFB) slurry has commonly been used to control subsidence damage caused by underground coal mining. This paper discusses the characteristics of CGFB slurry fluidity in its pipe transportation. A general description about the components of the CGFB is provided involving the percentage of composition, particle size distribution (PSD) and rheological performance. The CGFB flow characteristics of the slurry pipeline were simulated in a straight pipe and 90° elbow pipe, respectively, combined with the pressure loss and conveying velocity distribution. With the help of the commercial computational fluid dynamic (CFD) code FLUENT, the modeling was conducted with various slurry feeding velocities. These results showed the local resistance loss in a bending pipe is significantly higher than the resistance in a straight pipe under the same conditions associated with CGFB transportation. The velocity distribution of the slurry solid particles in the slurry’s movement forward is more decentralized as the hydraulic inlet velocity increases. Based on these simulation data, a correlation was developed to predict the resistance loss of the CGFB slurry as a function of the hydraulic inlet velocity, pipe diameter and CGFB slurry rheological characteristics.

One of the most vulnerable parts in high-pressure and temperature pipeline networks in steam turbine power plant installations is pipe bends, due to intense fluctuation of velocity and pressure of the superheated steam flowing through the piping bend. On the other hand, because of unique chemical and physical properties, the transportation of superheated steam can adversely effect on the integrity of the pipe bends in the piping network. Therefore, the potential risk of pipeline failure becomes more probable at bends. Therefore, to ensure the survivability of the piping network, thorough investigations of the superheated steam flowing through pipe bends are of great significance in better understanding its flow behavior. However, to predict flow behavior at piping bend, intensive research by direct experiment at high temperature and pressure might not be possible to some extent. In that case, computer codes and models can help us analyze flow behavior of superheated steam at pipe bends. The current work is a computational fluid dynamics investigation, where numerical examination is carried out by commercial code ansys fluent for thermal hydraulic analysis of flow behavior of superheated steam through multiple configurations of 3D angular piping bend: 90 deg, 120 deg, and 135 deg. Validation of credibility of the computational approach is done against Sudo et al.'s experiment. With relatively good agreement between the experiment and numerical result using air flowing through 90 deg elbow, single-phase turbulent flow of superheated steam is examined by the application of realizable turbulence model (k–ɛ). The final assessment of the computed results has been done using qualitative and quantitative analyses. The study reveals that unlike the pressure profiles, the radial velocity profiles at the bend exit are noticeably different from those at the bend inlet, since they exhibit more rounded peaks and gentler velocity gradients. The study also shows that the radial pressure and velocity profiles do not display any sign of the existence of a pair of vortices.

Modeling of solid-liquid flow inside conical diverging sections using computational fluid dynamics approach

The launch site security issues have been became the focus of the world’s research for several decades. Aiming at the filling system, the pipe vibration caused by the liquid hydrogen which flowed through the bend pipe was studied. And based on the computational fluid dynamics, the flow field was simulated according to the numerical simulation method. Then, the changes of flow parameters i.e. pressure and velocity at the bend were observed. The simulation results showed that: (1) the speed and the pressure of the liquid hydrogen would have a sudden change which was caused by flow direction and it would create a vortex which could erode the pipe and lead to the pipe vibration in the region. As a result, the pipe would deteriorate caused by the vortex. (2) the flow field analysis using the numerical simulation method was feasible. And the method provided a flow field distribution directly and design basis for filling system pipes.

Pressure drop is one of the problems that can occur due to bend components in the piping system. To minimize the pressure drop, modification of the bend pipe component was made at the bend outlet of the main steam line. In this study, an analysis of the effect of the bend angle on the pressure drop was carried out on the pressure and velocity steam distribution. The angle variations used are 30°, 45°, and 60° with the Computational Fluid Dynamics (CFD) method simulated by CFD software. The simulation results show that the lower the angle of curvature of the pipe, the lower the pressure drop and the lowest pressure drop is obtained in the 30° bend domain of 26.2 kPa. The pressure distribution pattern shows that the pressure value will increase from the inner wall to the outer wall. The greater the bend pipe angle, the greater the possibility of flow separation and pressure drop value. The velocity distribution pattern shows that the flow velocity becomes non-uniform after passing through the bend pipe. The greater the bend angle, the sharper the flow direction so that the time taken is longer. In addition, the greater the bend pipe angle, the greater the flow stagnation.

The volume distribution of atmospheric dust particles (microparticles) of 1–30 μm diameter in Muztagata, Dunde, Dasuopu and Everest ice cores from the Tibetan Plateau was measured and fitted as a log-normal function in order to characterize their basic size properties. Our results reveal that whether the volume distribution fits the log-normal function or not largely depends on the dust concentration and the specific dust-storm event but is independent of physiographical location and season. Our results show only high-concentration samples obey the log-normal distribution in volume, with mode sizes ranging from 3 to 161 μm. The log-normal distribution was largely attributed to the mid-sized particles between 3 and 15 μm, which contribute most (>70%) of the total volume. The volume size distribution characteristics for mineral dust particles from ice cores reveal that the coarse particles might be common in the upper-level troposphere over the Tibetan Plateau. These dust size features are useful to advance our understanding of dust effects on climate, and provide clues to better characterize atmospheric dynamics over the Tibetan Plateau that will help to improve the current models.