Concentration Of Sand Particles Research Articles

A Study of the Relationship between Sand Movement and Flow Field Distribution and Wear Causes in a Multiphase Pump

The Rosin–Rammler function is used in this paper to model the diameter distribution of sand particles. It investigates the characteristics of sand distribution and identifies the primary factors contributing to wear on flow components in a blade-type multiphase pump, considering varying particle sizes. The result of research shows that the blade head of the impeller and the middle section of the flow passage in the diffuser domain represent primary areas prone to sand particle accumulation. The concentration of sand particles within the diffuser surpasses that within the impeller, yet wear severity and extent are more pronounced in the impeller domain compared to the diffuser domain. Meanwhile, the movement trajectory of sand particles is linked to both shear flow and vortex flow. The wear of the front section of the impeller blade is more severe than the second half. On the pressure surface of the blade, particle Reynolds number emerges as a primary factor influencing wear, while on the suction surface, sand particle concentration plays a dominant role in determining wear. The particle concentration in the diffuser domain is the primary factor influencing wear on both the suction and pressure surfaces. The wear rate in the impeller is primarily influenced by the sand particle Reynolds number, whereas the wear rate in the diffuser domain is affected by a combination of sand particle diameter, sand particle concentration, and sand particle Reynolds number. The research findings possess significant engineering value in terms of enhancing the operational lifespan of multiphase pumps.

Numerical simulation and theoretical study on the impact of wind-sand flow of high-speed trains in long tunnel space

When high-speed trains (HST) run in enclosed spaces such as long tunnels, the thermal accumulation of their suspension devices is continuous and cannot be effectively dissipated. In addition, previous experiments or simulations for the heat dissipation of HST in tunnel spaces did not consider the impact of sand. To clarify the impact of HWS-LT on the heat accumulation of HST equipment cabin, this study used the CFD method to numerically simulate the impact of different wind-sand flow concentrations or no-sand wind on the cooling of equipment in the long tunnel space. Firstly, the sand particles in the wind-sand flow gather at the tunnel entrance and enter the equipment cabin with the train as it enters the tunnel. This boundary condition is more in line with actual engineering situations. Secondly, both flows show asymmetric intrusion into the cabin due to the asymmetrical tunnel arrangement, but the sand particles in the wind-sand flow are affected by the vortices and tunnel walls, resulting in more asymmetric flow and some particles being trapped in the grids or filters, leading to outflow ρQ < inflow ρQ. Under the wind-sand flow condition, the temperature of some equipment surfaces shows more significant increases than under the no-sand wind. Finally, contrary to popular perception, the wind-sand flow carrying sand particles can dissipate heat more effectively than no-sand wind, and the higher the volume fraction φ within a certain concentration range, the better the heat dissipation effect. This is because the wind-sand flow has a higher specific heat capacity, which can remove some heat from the contact point between the sand particles and the equipment wall upon contact. The higher sand particle concentration increases the contact frequency and contact area between the sand particles and the equipment wall, and the heat transfer pathway and heat dissipation efficiency are improved.

Mid-Term Effects of Fire on Soil Properties of North-East Mediterranean Ecosystems

Fire is a fundamental ecological process with a long history on Earth, determining the distribution of vegetation formations across the globe. Fire, however, does not only affect the vegetation but also the soil on which vegetation grows, creating a post-fire environment that differs significantly in terms of soil chemical and physical properties from the pre-fire environment. The duration of these alterations remains largely unknown and depends both on the vegetation condition and the fire characteristics. In the current study, we investigate the effect of fire on some chemical and physical properties 11 years after the event in four plant communities. Two of them constitute typical Mediterranean fire-prone plant communities, dominated by sclerophyllous Mediterranean shrubs, such as Quercus coccifera and Q. ilex, while the other two are not considered fire prone and are dominated by deciduous broadleaved species such as Q. petraea and Castanea sativa, respectively. The results indicate that fire affects the soil properties of the various communities in a different manner. Burned sites in the Q. coccifera community have a significantly lower concentration of organic matter, total nitrogen, and available magnesium. At the same time, they have a significantly higher concentration of sand particles and a lower concentration of clay particles. The effect of fire on the soil properties of the other three communities is less dramatic, with differences only in total phosphorus, organic matter, and total nitrogen. The results are discussed in relation to the site conditions and the post-fire regeneration of plant communities.

Co-deposition characteristics of hydrates and sands in gas-salty water-sands flow system

The study of hydrate flow assurance is critical for the efficient and safe development of natural gas hydrates. The natural gas produced by the dissociation of hydrate may re-hydrate in the gathering pipeline, and even lead to the blockage of the gathering pipeline. However, the co-deposition mechanism of the Micron-sized Sand Particles(MSPs) produced in the exploitation, and natural gas hydrate particles during pipeline transportation is still unclear. Therefore, the hydrates and MSPs slurry flow law and co-deposition mechanism are studied by horizontal high-pressure flow loop experiments. A new method to calculate the thickness of the deposition layer for water-dominant systems is proposed. Then, based on the variation of deposition layer thickness, the solid deposition process and flow behaviors are discussed in the pure water system, the salt-containing system, the sand-containing system, and the salt-sand coexistence system, respectively. The results show that the hydrate-MSPs co-deposition process is divided into five stages in the salt-sand coexistence system: the initial deposition stage, hydrate formation and adhesion on the pipe wall stage, rapid deposition stage, deposition layer sloughing stage, and stable deposition stage. And the hydrate-MSPs co-deposits in various stages are characterized by the Hydrate Aggregates Deposition Rate, the Hydrate Aggregates Deposition Layer Thickness, and the particle Chord Length Distribution. The influence of sand particle concentration and initial flow velocity on the hydrate-MSPs co-deposition process in the salt-sand coexistence system is also explored. In addition, the interaction between particles in the deposition process is revealed by Particle Vision and Measurement. The findings of this work provide insights into the solid deposition process in the salt-sand coexistence system, which is beneficial for flow assurance in natural gas hydrate production.

Modeling the inhibition effect of straw checkerboard barriers on wind-blown sand

Abstract. Straw checkerboard barriers (SCBs) are usually laid to prevent or delay desertification caused by eolian sand erosion in arid and semiarid regions. Understanding the impact of SCBs and their laying length on eolian sand erosion is of great significance to reduce damage and laying costs. In this study, a three-dimensional wind-blown-sand model in the presence of SCBs was established by introducing the splash process and equivalent sand barriers into a large-eddy simulation airflow. From this model, the inhibition effect of SCBs on wind-blown sand was studied qualitatively, and the sensitivity of eolian sand erosion to the laying length was investigated. The results showed that the decrease in the wind speed in the SCB area oscillates along the flow direction. Moreover, the longer the laying lengths are, the lower the wind speed and the sand transport rate in the stable stage behind SCBs will be. We further found that the concentration of sand particles near the side of SCBs is higher than that in its central region, which is qualitatively consistent with previous research. Our results also indicated that whether the wind speed will decrease below the impact threshold or the fluid threshold is the key factor affecting whether sand particles can penetrate the SCBs and form stable wind-blown sand behind the SCBs under the same conditions. Although our model does not include the collision between sand particles and SCB walls, which makes the suppression of wind-blown sand by SCBs obtained from the current model conservative, our research still provides theoretical support for the minimum laying length of SCBs in anti-desertification projects.

The influences of boundary layer thickness on the characteristics of saltation sand flow – A large eddy simulation study

In this paper, Large Eddy Simulation (LES) of turbulence and Lagrangian model of sand particle motion are adopted to study the characteristics of wind-blown sand flow for different boundary layer thickness. The simulations are conducted within computational domain height (boundary layer thickness) of δ = 0.5 m, 1 m, 5 m and 12 m, respectively. It is found by comparing the computational results that the mass flux and sand transport rate increase with the increase of boundary layer thickness for the same frictional wind velocity, and the fluctuation of particle velocity and sand transport rate increase significantly too. The spatial scales of particle structure, defined by the correlation of sand particle concentration, significantly increase with δ, so does the time scale of statistical stability of sand transport rate. For two computational domains of δ = 1 m and 12 m, the statistical relative error of sand transport rate reduce to less than 5 % only when the average time goes higher than 45 δ/Ub, where Ub is the bulk fluid velocity. In the context of turbulence, it might take about 10 mins to obtain reliable sand statistics in the neutral atmospheric boundary layer whose boundary layer thickness is about 100–200 m.

Aleurite particle concentration profiles in the surface layer of the atmosphere on desertificated areas

The large particle mass flux profile measurement at heights from 0.125 to 16 m and parameters of the size distribution function received by O.E. Semenov on the desertificated areas in the Aral region were analyzed. The technique has been worked out for the large particle height profile characteristic retrieving. The aleurite particle number concentration profiles with sizes less than 50, 73 and 100 μm and sand particle concentration have been retrieved. Power-law approximations of the vertical aleurite and sand particles concentrations profiles are proposed.

CFD–DEM Simulation of Sand-Retention Mechanisms in Slurry Flow

The primary motivation of this paper is to investigate the sand-retention mechanisms that occur at the opening of sand filters. Various retention mechanisms under various conditions are explored that have a particulate flow with a low concentration of sand particles (called slurry flow) such as particle shape, size, and concentration. The computational fluid dynamic (CFD)–discrete element method (DEM) model is applied to predict the retention mechanisms under steady flow conditions of the well-bore. By using coupled CFD–DEM (CFD to model the fluid flow, and DEM to model the particle flow), the physics involved in the retention mechanisms is studied. The coarse grid unresolved and the smoothed unresolved (refined grid unresolved) coupling approaches implemented in STAR-CCM+ (SIEMENS PLM) are used to transfer data between the fluid and solid phases and calculate the forces. The filter slots under investigation have different geometries: straight, keystone, wire-wrapped screen (WWS) and seamed slot and the particles are considered with different shapes and different aspect ratios and size distributions. The flow regime is laminar in all simulations conducted. The CFD–DEM model is validated from the perspectives of particle–fluid, particle–particle, and particle–wall interactions. Verification of the CFD–DEM model is conducted by mesh sensitivity analysis to investigate the coupling resolution between the CFD and DEM. By simulation of numerous slurry flow scenarios, three retention mechanisms including surface deposition, size exclusion, and sequential arching of particles are observed. However, the concentration of particles is too diluted to result in multiparticle arch formation. In the simulations, various conditions are tested to give us an insight into the parameters and conditions that could affect the occurrence of the retention mechanisms. As an example, the importance of the gravity force and interaction forces on retention mechanisms are confirmed at the microscale in comparison with others forces involved in retention mechanisms such as the drag force, lift force, cohesive force, buoyancy force, and virtual mass force.

CFD Analysis on Francis Turbine to Analyse Erosion Wear Due to Sediment Flow

In present work Computational fluid dynamics analysis based erosion wear prediction is performed for Francis turbine components, especially the runner. For the geometrical parameters, Francis turbine model with steady state condition and viscous flow turbulence SST model using ANSYS Fluent. The erosion effect on all the three component such as spiral casing, runner &amp; draft tube has been studied for different concentration of sand particles from 1% - 6%. For each of those concentration the effect of variation in size has been studied for different sizes 10 ?m - 80 ?m. Further the effect of total erosion was also analyzed for different particle size. Erosion damage is found close to the upper and lower portions of the leading edge of the stay vane. some erosion spots at guide vane on the blade pressure side where suction side has minimum erosion. Maximum erosion damage observed on runner especially at the middle of the blade. The draft tube situated closer to runner having highest velocity due to high absolute velocity of water coming out from the runner does not produce any serious erosion effect. Results shows that erosion rate is maximum on runner at particle size 80 ?m for all sand concentration 1% to 6% and minimum at 30 ?m. Thus, 30 ?m is the optimum size of sand particles for the erosion.

IMPROVEMENT OF THE OPERATION PROCESS OF WATERED DEEP OIL PUMP WELLS BY APPLICATION OF POLYFUNCTIONAL MEASURES

The article shows the types of complications that occur mainly in the fields of the Absheron archipelago in Azerbaijan and in the oil fields of the Azerbaijani sector of the Caspian Sea; the most common and frequent of them are the watering of the production of sucker rod pumping wells and the intensity of sand manifestations. It is noted that methods that prevent complications or reduce their negative impact are more appropriate than methods for their elimination. It is proposed to isolate formation water in flooded sucker-rod pumping oil wells using a universal hydrodynamic method; In this method, a liquid barrier should be created in front of the water in the formation, and not a solid barrier, and high-viscosity dead (non-gaseous) oil should be taken as a separating fluid, the specific gravity of which should be equal to the specific gravity of the formation water. The article uses the following five functions of multifunctional measures when carrying out various well survey methods: I. Pouring clean fluid into the annulus to increase the amount of fluid in the wellbore and reduce the concentration of sand particles in it. II. Without stopping the operation of the pumping unit, adding clean oil to the annulus with the help of a unit, raise its static level several meters higher. III. Determination of values of Pk, Po and G in rod deep well pumping wells producing viscous-plastic oil without stopping the operation of the pumping unit. IV. To determine the reservoir pressure in the simplest way, all well production is drained with a hose into the annulus. V. When removing the first lower curve by the method of two-sided restoration of curves without stopping the operation of the pumping unit VI. When applying the extraction method without changing the indicator diagrams S and n of water-cut oil wells. Thus, the use of multifunctional measures improves the performance of the considered wells and provides great economic benefits. Keywords: polyfunctional measure, irrigated well, sand manifestation, corrosion, erosion, wear, complication, pipe space, sand concentration in liquid, recovery curve.

Vertical Profiles of the Saltating Particle Concentration on a Desertified Area

Vertical profiles of the total saltating particle concentration have been constructed for a range of wind speed changes in the surface layer of the atmosphere from 5.5 to 10.5 m/s, and the profiles of the concentration of aleurite (silt) and sandy particles according to measurements in a desertified area in the Astrakhan Region under conditions of quasi-continuous saltation have been found. In the saltation layer from 0 to 15 cm, the concentration of silty particles with a size of 47 μm decreases two times more slowly than the concentration of sand particles with a size of 156 μm. In the lower saltation layer about 9 cm thick, the logarithmic gradient of the total concentration does not depend on the wind speed, and in the upper saltation layer it changes from –0.40 to –0.21 cm–1 with an increase in the wind speed in the atmospheric surface layer from 5.5 to 10.5 m/s. It is shown that, in contrast to the lower saltation layer at heights of 11 and 15 cm, the dependences of the particle concentration on the wind speed turned out to be nonlinear. For the lower and upper layers of saltation, approximations of the concentration of saltation particles are obtained as a function of height, wind speed, and the threshold speed of saltation.

Experimental investigation of erosion-corrosion phenomena in a steel fitting due to plain and slurry seawater flow

The present work presents an experimental characterization of the erosion-corrosion phenomena caused by confined slurry seawater flow. A set of experiments were conducted under a carefully controlled environment to estimate the erosion-corrosion severity in a 90° pipe bend. Sand particle concentration ranged from 0 to 9 g/l. Accurate spectrometric measurements of eroded iron concentration in the drain flow were carried out in order to characterize the erosion-corrosion severity in the bend. Both the flow Reynolds number and sand particle concentration were directly correlated to the onset of erosion phenomena. Consequently, this study proposes empirical correlations to predict the erosion-corrosion rate as a function of sand concentration and Reynolds number with two sets of coefficients for both laminar and turbulent flow regimes.

Monitoring sand particle concentration in two-phase flow using acoustic emission

This technical note presents an experimental investigation using acoustic emission technology to monitor sand transportation in two-phase flow. The investigation consisted of a preliminary experiment where a single sand particle was dropped onto metal plates to provide a basis for monitoring particle impingement on metal pipes in two-phase or three-phase flow systems. Further investigations were undertaken on two-phase (air–sand) flow in a horizontal pipe where the superficial gas velocity ( VSG) was varied. The objective of this research programme was to explore the possibility of employing acoustic emission as a non-invasive technology for monitoring sand particle concentration levels in multi-phase flow conditions. The experimental findings clearly show that a correlation exists between acoustic emission energy levels, sand concentration and superficial gas velocity.

Investigation on Sand Particle Impingement on Steel Pipe in Two Phase Flow Using Acoustic Emission Technology

This paper presents an experimental investigation that employed the acoustic emission (AE) technology to monitor sand transportation in two-phase flow. This investigation was undertaken on two phase (air-sand) flow in a horizontal pipe for varying Superficial Gas Velocities (VSG). The objective of this research programme is to develop a simple, non-invasive technique for monitoring of sand particle concentration levels in multi-phase flow conditions. The experimental findings show that AE absolute energy can be correlated with the size of sand, number of sand particles and Superficial Gas Velocity (VSG).

Laboratory and field performance of a laser particle counter for measuring aeolian sand transport

[1] This paper reports the results of laboratory and field tests that evaluate the performance of a new laser particle counter for measuring aeolian sand transport. The Wenglor® model YH03PCT8 (“Wenglor”) consists of a laser (655 nm), photo sensor, and switching circuit. When a particle passes through the 0.6 mm diameter, 30 mm long laser beam, the sensor outputs a digital signal. Laboratory tests with medium sand and a vertical gravity flume show that the Wenglor count rate scales approximately linearly with mass flux up to the saturation point of the sensor, after which the count rate decreases despite increasing mass flux. Saturation depends on the diameter and concentration of particles in the airstream and may occur during extreme events in the field. Below saturation sensor performance is relatively consistent; the mean difference between average count rate response was between 50 and 100 counts. Field tests provide a complimentary frame of reference for evaluating the performance of the Wenglor under varying environmental conditions and to gauge its performance with respect to a collocated piezoelectric impact sensor (Sensit H11-B). During 136.5 h of deployment on an active sand dune the relative proportion of time sand transport recorded by two Wenglors was 0.09% and 0.79%, compared to 4.68% by the Sensit H11-B. The weak performance of the Wenglors is attributed to persistent lens contamination from adhesion of sand grains on the sensors after rainfall. However, during dry and windy conditions the Wenglor performance improved substantially; sensors measured a concentration of sand particles in the airstream more than seven times greater than that measured by the Sensit. Between the two Wenglors, the mean absolute count rate difference was 6.16 counts per second, with a standard deviation of 8.53 counts per second. For short-term measurement campaigns in dry conditions, therefore, the Wenglor is relatively consistent and can outperform the Sensit in detecting particles in the airstream. The Sensit, however, is more reliable in detecting particle transport during longer unattended deployments. Two additional field tests show that the sensor is well-suited to the measurement of snow drifting but could be ineffective in dusty settings because of lens contamination. Overall, the main advantages of the Wenglor include (1) insensitivity to particle momentum; (2) low measurement variability; (3) low cost ($210 USD); and perhaps most important of all, (4) a consistent design that will improve comparison of results between investigations. At present, no other particle detector used in aeolian research can claim all these characteristics.

Sand slurry erosive wear of thermal sprayed coating of stellite

The present paper describes the sand slurry erosive wear behaviour of the flame sprayed stellite (Co–Cr–W–Ni–C) coating. The wear behaviour was evaluated with the help of a slurry pot tester by using two sand slurry concentrations (20 and 40% sand particles) at different rotational speeds (600–1000 rev min−1). It was observed that the weight loss of the coating material and rotational speed relationship is governed by the concentration of sand particles in slurry. Slurry erosive wear of the coating showed that in case of 20% silica sand slurry, weight loss increases with increase in rotational speed from 600 to 1000 rev min−1 while in case of 40% silica sand slurry weight loss first increases with increase in rotational speed from 600 to 800 rev min−1 followed by marginal decrease in weight loss with further increase in rotational speed from 800 to 1000 rev min−1. Improvement in wear resistance of mild steel due to development of the thermal sprayed coating was calculated as wear ratio which is a ratio of weight loss of mild steel and that of coating. Wear ratio was found in range of 4·2–7·5 under different test conditions. The microstructure study showed polyhedral shaped Cr dominated carbide particles in eutectic matrix. The average microhardness of the coating was 680 HV. Wear behaviour of coating has been discussed in light of microstructure and microhardness of coating. Scanning electron microscopy study of wear surface showed that loss of material from the coating takes place by indentation, crater formation and lip formation and its fracture.

Study of sand transport in the ocean

The sand transport that causes the movement and deformation of a sand hill in a periodically oscillating flow is investigated in the laboratory. An experimental technique is developed to assess the variation of the state of concentration of sand particles in the process of the interaction of the particles with the fluid in motion around the sand hill as well as with the particles themselves. The method of measuring the concentration of sand particles is based on the digital image processing. It is confirmed that under the well-controlled experimental conditions of homogeneous distribution of sand particles, the decrease in brightness of the digital images of an area is determined by the concentration of the particles in the area. Taking a space average on the images with an appropriate scale to the size of sand particles to fade out the unfavorable effect of each particle makes it possible to predict inhomogeneous and continuous distribution of the concentration of sand particles from the brightness of the digital images with the limited resolution.We make a visualization experiment of the two-dimensional flow field around a sand hill on sand bed in a flow sinusoidally oscillating in a straight channel with square section. The digital images of the unsteady flow field with suspended sand particles around the sand hill is analysed to estimate the concentration of sand particles. The results show that in the periodically oscillating flow the sand particles repeat a basic motion every half period such as sand particles running up the slope of the hill by accelerating flow, running off the hill by flow separation at the top of the hill, running down the hill as suspended in a turbidity current, and running into the roll by the rotational motion of shed vortices. It is found that these periodic motions of sand particles have particular distinguishing features of the change in the state of concentration in the process of fluidization, movement, transport, sedimentation, and accumulation.

Sand Deposition Inside a Horizontal Well-A Simulation Approach

Abstract Horizontal wells have been shown to be successful in improving oil recovery for marginal heavy oil reservoirs in Saskatchewan and Alberta. One commonly encountered problem in recovery operations for these poorly consolidated reservoirs is the production of sand and fines into the horizontal wellbore, where they settle and accumulate. This paper reports the numerical modeling of gravitational deposition of sand in a horizontal well in such heavy oil reservoirs. The numerical model described in this work examines the transport process mechanistically, based on the conservation equations for the fluid phase (heavy oil) and the solid phase (sand particles). The interaction between these phases is described by empirical correlations. The equations are solved numerically to determine the concentration of sand particles and oil, and their respective pressure and velocity distributions inside the horizontal well. According to the simulation results, oil viscosity and particle size play important roles in the transport process, including controlling the gravitational settling tendency of solid particles inside the horizontal wellbore. The results provide insight into the roles different mechanisms affect the transport of sand particles; as such, they provide guidelines for production operations involving horizontal wells in poorly consolidated and unconsolidated reservoirs. Introduction The use of horizontal wells, in Saskatchewan and Alberta heavy oil reservoirs underlain with bottom-water, has been found to improve primary recovery performance prior to water coning-recovering up to 15%, in some cases, of the initial oil in place, compared with only 5% for a vertical well(1). Horizontal wells have also been successfully used for increasing steamflood recovery(2,3). Due to the unconsolidated or poorly consolidated nature of these reservoirs, solid (sand and fines) production is quite prevalent. The produced solids lead to several production problems, including sand filling up the wellbore, preventing the operation of downhole pumps and surface equipment, etc.(4) In horizontal well cases, sand production potentially poses a serious problem, as the sand could settle and accumulate inside the horizontal wellbore. This settlement and accumulation of sand particles could give rise to reduced cross-sectional areas of the wellbore open to flow. The study reported in this paper examines, using numerical simulation, the gravitational deposition of sand particles inside a horizontal wellbore. A brief survey of the relevant literature is given in the following. Solid-liquid multiphase flows are usually very complex, due to the large number of variables involved in the transport processes, and typically poorly understood interaction between the variables. There have been many experimental investigations of these (and other) flow processes, particularly focused on the deposition of the solid particles. Many of the earliest investigations of solid liquid flows focused on the settling tendency of solid particles. Richardson and Zaki(5) experimentally determined that the falling velocity of a suspension relative to a horizontal plane was equal to the upward velocity of the fluid required to maintain a suspension at the same concentration. For different flow regimes (i.e., Reynolds numbers), separate correlations were developed (from experimental data) for the exponent which corresponds to the slope of log-log plot straight lines between suspension falling velocities and suspension porosities.

Effects of alumina particle dispersion on the erosive–corrosive wear response of a zinc-based alloy under changing slurry conditions and distance

This investigation analyses the influence of dispersed alumina particles on the wear behaviour of a zinc-based alloy in a slurry, comprising suspended sand particles. The influence of the sand content (in the slurry) and travel distance on the wear characteristics of the samples was also studied. Wear rate increased initially with distance, attained a peak, decreased thereafter, and finally, attained a steady-state value at longer distances. These stages were more defined when tests were conducted in the liquid (electrolyte) medium without sand. Addition of sand particles in the electrolyte reduced the wear rate of the specimens. It was also observed that when tests were conducted in the electrolyte plus sand (i.e., slurry with sand), wear rate first increased with the sand content (of the electrolyte), attained a maximum at an intermediate sand concentration, and then finally, decreased as the concentration of sand particles was increased further. The composite showed better wear resistance than the matrix alloy in general. The observations have further been substantiated through the examination of wear surfaces and subsurface regions of the samples. Wear response of the samples has been explained on the basis of (i) predominance of the operating mechanisms of material removal such as corrosive, erosive and abrasive wear under a given test condition, and (ii) the nature and properties like corrosive nature, hardness and interfacial characteristics of the various microconstituents of the samples. The study suggests that the predominance of one or more of the mentioned (material/experimental) parameters basically controls the wear behaviour of the specimens, and that the nature of their contribution is further governed by the specific test conditions.

The theory of similarity and the profile of vertical distribution of concentration of sand particles

In this article, we treat the problem of two-dimensional uniform steady channel flow of turbid water with theory of similarity. Under the condition of similarity of turbulent fluctuation velocity and fluctuation of concentration of sand particles, we obtain the profile of the vertical distribution of concentration of sand particles. This profile of vertical distribution of concentration of sand particles is slightly different from that obtained by diffusion theory, and departs from that obtained by gravitational theory.