Non-uniform Particle Distribution Research Articles

Numerical investigation on effects of alkali metals release during combustion of char particle groups

Alkali metals, especially Na, are generally accepted as the primary cause of serious ash-related problems in the industrial applications of pulverized coal. This paper investigates the effects of different variables, including particle size, ambient temperature, O2 mass fraction, and atmospheres: O2/N2 and O2/CO2 at particle level. The fictitious domain method (FDM) provides a true direct numerical simulation (TDNS) for the investigation. Computational results show the correlation between alkali metals release and carbon consumption during char particle combustion. Here, high ambient temperature is more positive to alkali metals release than carbon consumption. In an oxygen-dominated atmosphere, a small amount of CO2 tends to form a higher temperature field than N2, which promotes a greater release of alkali metals. This paper also investigates the specific effects of volume fraction and non-uniform distribution of particles for the combustion of particle groups. The computational results show that both temperature field and alkali metals release are significantly affected by the volume fraction of particles. The effects of the non-uniform distribution of particles, e.g., uniform distribution, dense distribution on the windward side, dense distribution on the leeward side, and asymmetric distribution, on temperature field and alkali metals release vary with different volume fractions of particles. As such, the non-uniform distribution of particles plays a role in changing the mass transfer of the oxidant and the heat transfer.

CFD-DEM modeling of suffusion effect on undrained behavior of internally unstable soils

Abstract This paper investigates the effect of suffusion on the undrained behavior of an internally unstable soil using the coupled computational fluid dynamics and discrete element method (CFD-DEM). A series of eroded specimens are prepared by exerting an upward flow through the granular assembly under a range of hydraulic gradients and suffusion durations. Both the eroded and non-eroded specimens are then subjected to undrained triaxial compression (or equivalently constant volume tests). The results indicate that the erosion rate and volumetric response of the soil skeleton are closely related to the hydraulic conditions. The eroded specimens exhibit a non-uniform distribution of fine particles, higher coordination numbers, higher global void ratio, and lower equivalent intergranular void ratio. The undrained behavior of the specimen changes from a strain hardening behavior before suffusion to a softening behavior with limited flow deformation after suffusion. The undrained shear strength of eroded specimen is enhanced at small axial strain due to the enhanced connectivity of particles, but can increase or decrease at larger strain levels depending on the degree of erosion. It is also observed that both suffusion and shearing can induce some degree of fabric anisotropy by inspecting the directional distribution of contact unit normals and contact normal forces.

Green synthesis of calcium oxide nanoparticles at different calcination temperatures

PurposeThe purpose of this paper is to prepare calcium oxide (CaO) nanoparticles by green synthesis technique and study its structural, morphological and optical properties. The prepared samples were calcined at, 200°C, 300°C and 500°C, and the variation in the properties at different temperatures were investigated.Design/methodology/approachGreen approach has been used in the present work to synthesise the CaO nanoparticles using Murraya Koenigii leaf (curry leaves) extract as a capping agent. This technique involves the use of nontoxic reagents and natural products derived from various parts of plants.FindingsStudies reveal that CaO nanoparticles with good optical properties can be synthesized successfully by green approach. The optical absorbance spectra show a broad absorption peak around 400–500 nm. FTIR studies confirm the presence of different functional groups that help in the stabilization of CaO nanoparticles. PL emission spectra show a high intensity emission peak at around 231 nm in addition to peaks at 375 nm and 400 nm. XRD studies show planes of CaO cubic phase. SEM images show a nonuniform distribution of spherical particles along with some clusters. EDX spectra confirm the presence of calcium and oxygen.Practical implicationsCaO nanoparticles have wide applications in optical devices as well as in phototherapy. It is thus interesting to devise new and eco-friendly techniques to synthesise these nanoparticles to suit these applications.Originality/valueThis work would provide a new insight into the preparation of different metal oxide nanoparticles by a very simple and cost-effective green technique without the use of toxic reagents.

Appraisal of CFD Discrete-Phase Models to be employed for Modeling Coal Particle Feeding in a Staged, Pressurized Oxy-fuel Combustor (SPOC)

In the present computational study employing the ANSYS Fluent commercial software, two different discrete phase formulations, namely, the discrete phase model (DPM) and the dense discrete phase model (DDPM) are tested and compared. Specifically, the unsteady Reynolds averaged Navier-Stokes (RANS) simulations with the Lagrangian-Eulerian models are performed in both cases. The configuration employed is a cylindrical combustor with three inlet gas streams that feed the system with mixtures of different O2 and CO2 mole fractions under an operating condition of 15 bar, emulating the 100 kW lab-scale facility employed at Washington University in St. Louis (WUSTL). Specifically, the coal particles are fed into the system by the secondary gas stream through an annulus-axial convergent duct surrounding the primary inlet stream. Distributions of the DPM concentration (the ratio of the dispersed phase mass to the mesh cell volume; in kg/m3) of the coal particles along the axial direction within this secondary inlet agree for both the DPM and DDPM models even though these models mimic the coupling between the phases in a different manner. However, the particle grouping is observed not only axially, along the inlet duct, but also in the radial direction as there are zones experiencing non-uniform particle distribution. Overall, the impact of DPM concentration on the flame stability is shown to be minor since a continuous particle release prior to burning zone is successfully achieved for both models.

Safety assessment of polyolefin and nonwoven separators used in lithium-ion batteries

This paper features a comprehensive safety assessment of lithium nickel manganese cobalt oxide (NMC)/graphite pouch cells incorporating several different types of polyolefin and nonwoven separators, including polyethylene (PE), polypropylene (PP), tri-layer PP/PE/PP, Al2O3-coated polyethylene terephthalate (hereinafter called CPET) and Al2O3-filled polyethylene terephthalate (hereinafter called FPET). We investigate the cell safety by means of thermal ramp, overcharge, internal short circuit, and external short circuit tests; at the same time, we characterize the structure and properties of the separator materials used in the cell samples. The results disclose that thermal dimensional stability, melt or melt rupture temperature and shutdown function of the separators greatly impact the lithium-ion battery safety. The nonwoven separators demonstrate exceptional thermal resistance and dimensional stability and greatly enhance the safety of lithium cells under certain conditions of abuse; however, the non-uniform distribution of the ceramic particles filled in the nonwoven separators could cause uneven current-density distribution leading to cell failures.

Multifractal characteristics of soil particle distribution under different vegetation types in the Yellow River Delta chenier of China

Vegetation restoration on degenerated cheniers in the Yellow River Delta of China is important to maintain the ecosystem stability in the muddy coastal zone. This study mainly investigates the multifractal characteristics of the soil particle distributions under different vegetation types on a Yellow River Delta chenier, reveals the fractal mechanism of soil improvement by vegetation, and identifies the types of vegetation that provide the best remediation effects on the texture of degenerated chenier soils. Three vegetation types, including two shrub-grass communities, Ziziphus jujuba var. spinosa-Artemisia mongolica (ZA) and Periploca sepium Bunge-Messerschmidia sibirica (PM), and one mixed herbaceous community, Artemisia mongolica-Phragmites australis (AP) at the beach ridge of the Yellow River Delta were used as the study subjects, and bare land was used as the control (CK). The results showed that (1) the shell sand under the different vegetation types had the highest sand contents, with low silt and clay contents, and exhibited a nonuniform soil particle distribution with obvious heterogeneity. Restoration of shrub-grass communities can reduce the heterogeneity of the particle size distribution (PSD) of shell sand by increasing the range of the PSD and its degree of concentration in dense areas. (2) The shrub-grass communities can increase the clay and silt contents and decrease the sand content of shell sand. The shrub-grass communities were more effective than the mixed herbaceous community in refining the soil texture, and the ZA exhibited the strongest shell sand particle refinement capability. (3) The shell sand in the different soil layers under the different vegetation types had significantly different capacity dimensions (D0), information dimensions (D1), correlation dimensions (D2), and D1/D0 and D0-D1 ratios (P < 0.05). The multifractal parameters of the shell sand were correlated to the soil depth. With increasing soil depth, the correlations of D1, D2, and D1/D0 with the clay, silt, and sand contents weaken. (4) The coarseness and nonuniformity of the texture of the shell sand under the shrub-grass communities were significantly lower than those on bare land. Shrub-grass communities can control wind erosion of the soil surface, preventing the coarsening of topsoil and promoting the accumulation of fine particles. The shrub-grass communities were more effective than the mixed herbaceous community in improving the soil structure; furthermore, the ZA was better than the other communities in improving the soil structure. Additionally, the degree of soil improvement in the 10–30 cm layer was better than that in the 0–10 cm layer.

Non-breaking Wave Effects on Buoyant Particle Distributions

The dispersal of buoyant particles in the ocean mixed layer is influenced by a variety of physical factors including wind, waves, and turbulence. Microplastics observations are often made at the free surface, which is strongly forced by surface gravity waves. Many studies using numerical simulations to examine how turbulence and wave effects (e.g. breaking waves, Langmuir circulation) control buoyant particle dispersal at the ocean surface, however, are not wave phase-resolving. Therefore, the effects of an unsteady free surface due to surface gravity waves remain unknown in this context. Using numerical models and analytical techniques, we quantify the effects of a nonbreaking, monochromatic, progressive wave train on the equilibrium vertical and horizontal distributions of buoyant particles. We find that waves result in non-uniform horizontal distributions of particles with more particles under the wave crests than the troughs. We also find that the waves can stretch or compress the equilibrium vertical distribution. Finally, we consider the effects of waves on the sampling of microplastics with a towed net, and we show that waves have the ability to lower the measured concentrations relative to nets sampling without the influence of waves.

VOF-DEM study of solid distribution characteristics in slurry Taylor flow-based multiphase microreactors

Solid particle distribution determines the reactor internal phases placement and the contact mode between catalyst particles and the liquid phase, thus plays a key role in dictating the overall performance of slurry Taylor flow-based microreactors. This study numerically investigates the distribution characteristics of particles within liquid slugs (reactors) in a vertical capillary tube, with the aim to describe the corresponding underlying mechanisms.The Volume of Fluid (VOF) method was deployed to solve the evolution of transient gas-liquid interfaces, whilst the motion of individual particles was directly tracked using the Discrete Element Method (DEM). Various fluid forces were considered based on the fully resolved Taylor flow field. Different body-fixed frames of reference were introduced to aid the analysis of the results.The particle distribution was found strongly dependent on the liquid flow field and particle physical properties, described in this study using the slurry Reynolds number (Re') and particle Stokes number (Stp), respectively. As Re' increased, the liquid flow experienced three distinctly different circulation patterns. Accordingly, three different particle distribution patterns were observed: I, particles distributed in the slug central region when Re'≤47; II, particles were trapped inside the liquid circulations for Re'∈95,190; and III, particles distributed at the edges of the liquid circulations when Re'≥379. III was the predominant particle distribution pattern in slurry Taylor flow systems. The drag force was found to be the main force governing the vertical particle motion, whilst shear lift force and horizontal drag force were the main forces driving the lateral particle motion. Generally, as Re' or Stp increased, particles tended to migrate from the core to the edge of the liquid circulations, leading to a more nonuniform particle distribution. The solid volume fraction variance (σ2) of 0.0025 could be viewed as the threshold less than which the particle distribution in the liquid slugs was considered uniform. The relatively uniform particle distribution (with σ2≤0.0025) was achievable forRe'<550 and Stp<0.1.

Particle transport velocity correction for the finite volume particle method for multi-resolution particle distributions and exact geometric boundaries

The finite volume particle method (FVPM) is a meshless computational fluid dynamics (CFD) method, where the fluid domain is represented by a set of overlapping particles, and boundaries are defined as exact geometries. Particle-based CFD methods, such as smoothed particle hydrodynamics (SPH) and FVPM, are susceptible to non-uniform particle distributions, which result in errors. Particle regularisation techniques, based on displacement or particle transport velocity, improve particle distributions. Here, improvements are made to the previous particle regularisation methods in SPH and FVPM. The method presented here takes advantage of the arbitrary Lagrangian-Eulerian nature of FVPM and applies a small correction to the particle transport velocity. It incorporates a novel symmetric formulation to maintain specified spatially varying resolution. Difficulties associated with the FVPM definition of the geometric boundaries are overcome, in that the correction method automatically adjusts to varying geometry segment size, without requiring fictitious boundary particles, as in SPH. The method is evaluated in a static multi-resolution test, cylinder in flow, and dambreak flow. Results show that the method yields improved particle distribution with few voids, with improved wall pressure results in the dambreak. The method maintains multi-resolution and adaptive particle distributions and is insensitive to the resolution of boundary geometry.

Development of Biodegradable Films from Marine Ingredients Incorporated with Natural Antimicrobial Agents for Food Packaging

The fish gelatin obtained from processed fish waste was used in the development of biodegradable film. The film was obtained by dissolving the fish gelatin with distilled water as a solvent and glycerol as a plasticizer. The developed film was stable and exhibited good tensile strength. Irish moss-I-Carrageenan and laminarin were added to improve the properties of the developed film. The films were also incorporated with micro- and nano-forms of curcumin to have antimicrobial properties. The developed films were characterised following the standard protocols. The developed films with incorporated curcumin extract exhibited enhanced mechanical properties. It was observed that there was 71.4% increase in Nano-curcumin Fish Gelatin Film (NCFGF) film compared to Fish Gelatin Film (FGF). Marginal decrease in the water vapour transmission rate (WVTR) of the film was observed. The scanning electron microscopic (SEM) images of the curcumin incorporated film showed the non-uniform distribution of the curcumin particles, while, in the nano-curcumin film, there was a uniform distribution with tubular pattern formation. FTIR studies showed that the some of the peaks were shifted to higher or lower wave numbers with the incorporation of curcumin and nano-curcumin. The incorporation of curcumin and nano-curcumin slightly transformed the molecular structure and intermolecular interactions in the film. There was increase in glass transition temperature as compared to the pure gelatin film, indicating that fish gelatin film and fish gelatin films added with curcumin and nano-curcumin particles have good miscibility. Shelf life studies of pangasius fish fillet packaged in the developed films showed less change in colour in curcumin incorporated film compared to the control. The microbial analysis showed decrease in total plate count (TPC) of FGF, CFGF, and NCFGF films. Yeast and molds count showed trends similar to TPC. The shelf life of pangasius fish fillets was of 8 days in the control, 10 days in FGF, 12 days in CFGF, and 15 days in NCFGF. Hence, NCFGF film can be used to pack food products like pangasius fish fillet to increase the shelf life.

Phase-field simulation of abnormal grain growth during carburization in Nb-added steel

Abnormal grain growth of austenite phase often takes place during carburization of steels, originating from carbon concentration dependence of pinning pressure of fine precipitates, the size of which is typically a few orders of magnitude smaller than the austenite grain size. In this study, the phase-field model for simulating the abnormal grain growth during carburization in steels is developed based on a mean field approximation in which the curvature-driven growth with the pinning pressure due to fine particles is reproduced by explicitly introducing the pinning pressure into the time evolution equations of order parameters. This model is applied to simulations of the austenite grain growth during carburization in Nb-added steels. Simulations are carried out to understand the occurrence of abnormal grain growth at different carburization temperatures for different steel compositions. In addition, an effect of non-uniform distribution of fine particles, which often appears as a consequence of microsegregation, on abnormal grain growth is investigated.

Ni–supported palm oil fuel ash catalyst (Ni–POFA) from in situ glycine-nitrate combustion for methane cracking

Metal-supported catalysts synthesized using a conventional impregnation method are usually suffered from non-uniform distribution and agglomeration of catalyst particles. In this work, in situ glycine-nitrate combustion method has been explored to synthesize Ni catalyst supported on palm oil fuel ash (Ni–POFA). The properties and performance of the catalyst were compared with one produced using impregnation method. Effects of pre-treatment and catalyst preparation method have been investigated and characterizations of POFA and Ni–POFA catalysts were performed using XRF, XRD, BET surface area, FESEM and TGA. Catalytic activity of the catalysts was evaluated for methane cracking at 550 °C. Results showed that pre-treatment has improved the composition of SiO2 in POFA from 42.4 to 72.0%. Ni–POFA catalyst synthesized using in situ glycine-nitrate combustion method exhibited a good catalytic performance during the methane cracking with an initial H2 yield of 6.4%. This was attributed to high Ni metal dispersion on POFA support. Nevertheless, the degradation of CH4 conversion for this particular catalyst was more significant than one produced using impregnation method. Catalyst prepared using in situ glycine-nitrate combustion was active towards carbon formation, thus led to an obvious formation of carbon on the catalyst surface. Additionally, catalyst preparation method influenced the type of carbon formed on the spent Ni–POFA catalysts.

Enhanced oil recovery mechanism and recovery performance of micro‐gel particle suspensions by microfluidic experiments

AbstractMicro‐gel particle suspensions (MGPS) have been proposed for enhanced oil recovery (EOR) in reservoirs with harsh conditions in recent years, yet the mechanisms are still not clear because of the complex property of MGPS and the complex geometry of rocks. In this paper, the micro‐gel particle‐based flooding has been studied by our microfluidic experiments on both bi‐permeability micromodels and reservoir‐on‐a‐chip. A method for reservoir‐on‐a‐chip design has been proposed based on QSGS (quartet structure generation set) to ensure that the flow geometry on chip owns the most important statistical features of real rock microstructures. In the micromodel experiments with heterogeneous microstructures, even if the MGPS has the same macroscopic rheology as the hydrolyzed polyacrylamides (HPAM) solution for flooding, MGPS may lead to significant fluctuations of pressure field caused by the nonuniform concentration distribution of particles. In the reservoir‐on‐a‐chip experiments, clustered oil trapped in the swept pores can be recovered by MGPS because of pressure fluctuation, which hardly happens in the HPAM flooding. Compared with the water flooding, the HPAM solution flooding leads to approximately 17% incremental oil recovery, while the MGPS results in approximately 49.8% incremental oil recovery in the laboratory.

Investigation on distribution of particles in inlet region of an FCC external catalyst cooler with different inlet structures

An external catalyst cooler has been widely used in fluid catalytic cracking, its stability and heat transfer performance are affected by non-uniform distribution of particles in inlet region. Therefore, particles distribution of inlet region is investigated. Most particles flow rapidly to the opposite region to the inlet in the parabolic form in the original structure. Two new inlet structures are designed, which are made of a decelerator and a rectifier plate. For inlet structure 1, particles velocity is decreased obviously by the decelerator and they are divided into two parabolic streams. For inlet structure 2, particles flow into the bed in the form of three parabolic streams due to the groove above the rectifier plate. Particles distributions are improved at Gs = 120–750 kg/(m2·s) in two new inlet structures, while the structure 2 has superior effect. The empirical correlations predicting the uniformity of particles distribution in three inlet structures are obtained.

Dynamics of colloidal particles in microchannels under combined pressure and electric potential gradients

Dynamics of charged sub-micron or colloidal particles in a microfluidic device through cross-stream migration under combined pressure gradients and electric potential gradients was demonstrated using confocal microscopy. The microfluidic device was a rectangular cross-section poly(dimethylsiloxane) or PDMS microchannel sealed with a borosilicate glass lid to form a hybrid PDMS-glass device. We postulate that the reported particle migration may arise in response to electrophoretic particle slip, i.e., the difference between the particle and fluid velocities, due to the applied electric potential gradient across the microchannel. Colloidal particle migration was observed either towards or away from the microchannel walls depending on the relative directions for the applied potential and pressure gradients. When pressure gradient driving the fluid flow and potential gradient were applied in the same direction, colloidal particles migrate away from the microchannel walls. In the case of opposite directions for the pressure and potential gradients, colloidal particles migrate towards the microchannel walls and subsequently assemble into distinct bands next to both the bottom glass and top PDMS walls. The results reported here demonstrate that the particle dynamics due to electrophoresis in Poiseuille flow within a microchannel result in non-uniform spatial distributions of colloidal particles via cross-stream migration, with the ability to assemble particles into distinct band structures at channel walls. Such manipulation, once fully realized, could lead to several microfluidics applications in material synthesis, particle separation, and biosensing.

Effect of curing temperature and particle size distribution on unconfined compressive strength of raw and treated fly ash-lime modified phosphogypsum waste

The Voluminous quantity of phosphogypsum waste is generated by phosphoric acid manufacturing industry and end up being landfilled, resulting into environmental pollution. This study was done to determine applications for raw and treated waste phosphogypsum in building and construction, to determine the best conditions to produce the final product. Two readily available wastes namely phosphogypsum and fly ash were used and blended with hydrated lime. Best strengths was obtained from a mixture of phosphogypsum-lime-fly ash specimens were at elevated temperatures. The strengths obtained at the temperature of 80°C were above the 3.5 MPa permissible strength for building masonry with unconfined compressive strength up to 4.8 MPa. At lower temperature of 40°C the optimum strength obtained was at the minimal phosphogypsum content of 30%. The optimum strength was achieved at the PG content of 50% for raw PG and 60% for treated phosphogypsum. The strengths obtained for the treated phosphogypsum were lower than the minimum permissible load bearing strength due to the non-uniform particles distribution and the presence of impurities and forces of adhesion between citric acid and phosphogypsum. Increasing the curing temperature also reduced the radionuclides initially present in the raw PG without any prior treatment.

Experimental investigation of hydrodynamics and mass transfer in a slurry multistage internal airlift loop reactor

Hydrodynamics and mass transfer of gas-liquid-solid slurry flow in a simple pilot multistage internal airlift loop reactor with a classic stage clearance are investigated experimentally. The presence of a critical superficial gas velocity to keep the multistage internal airlift loop reactor operating normally without particle deposit was first observed at a certain solid concentration and a fixed height of stage clearance, and an empirical model related to solid concentrations for a constant stage gap is also put forward here to predict the minimum critical superficial gas velocity in the slurry multistage internal airlift loop reactor. The results showed that compared to hydrodynamics and mass transfer in the gas-liquid two-phase flow at the same conditions, the solid concentration and the superficial gas velocity have some distinct effects. The increment of superficial gas velocity can increase the gas holdup, circulating liquid velocity, and volumetric mass transfer coefficient and at the same time decrease the mixing time, while the addition of solid particles would get the opposite effects. Additionally, compared to the two-phase flow, reverse tendencies of the gas holdup and circulating liquid velocity in different stages in the three-phase slurry multistage internal airlift loop reactor are first observed due to axial non-uniform distribution of solid particles. Therefore, solid particles can change the nature of multiphase flow in the multistage internal airlift loop reactor, and some critical information for designing this type of reactor was provided in this work.

Implementation of the moving particle semi-implicit method for free-surface flows on GPU clusters

The moving particle semi-implicit (MPS) method performs well in simulating incompressible flows with free surfaces. Despite its applicability, the MPS method suffers from the fundamental instability problem and high computational cost in its practical application. Substantial research has been conducted on improving the stability and accuracy of the MPS method. Moreover, graphics processing units (GPUs), which are multi-processors that execute many three-dimensional geometric processes at high speed, provide unprecedented capability for scientific computations. However, the usage of a single GPU card is not sufficient for engineering applications that require several million particles that predict the desired physical processes, because the available memory space is insufficient. In this work, the dynamic stability (DS) algorithm and particle shifting (PS) algorithm have been used to overcome the instability and inaccuracies caused by tensile instability and non-uniform particle distribution, respectively. Based on the stable MPS method, a GPU-based MPS code that uses the compute unified device architecture (CUDA) language has been developed. An efficient neighborhood particle search is performed using an indirect method, and the matrix for the pressure Poisson equation (PPE) is assembled in parallel. Based on the single-GPU version, a multi-GPU MPS code has been developed. The approach uses a non-geometric dynamic domain decomposition method that provides homogeneous load balancing whereby different portions (subdomains) of the physical system under study are assigned to different GPUs. Communication between devices is achieved with the use of a message passing interface (MPI). Based on the neighborhood particle search, the techniques for building and updating the “halo” are described in detail. The speed-up of the single-GPU version is analyzed for different numbers of particles, and the scalability of the multi-GPU version is analyzed for different numbers of particles and different numbers of GPUs. Last, an application with more than 107 particles is presented to show the capability of the code in handling large-scale simulations.

Four-way coupling of particle-wall and colloidal particle-particle interactions in direct absorption solar collectors

A novel model based on the Eulerian-Lagrangian approach was introduced in order to capture the physics of particle-fluid, particle-wall, and colloidal particle-particle interactions through four-way coupling in low-flux nanofluid-based direct absorption solar collectors (DASCs). This was accomplished by means of a computationally efficient particle-particle-interaction detection algorithm implemented within the frame of an in-house fluid-particle coupling algorithm that allowed for the simultaneous evolution of the carrier and particulate phases. The optical, thermal, and dispersion effects of particle-wall and colloidal particle-particle interactions were investigated over a range of particle volume fractions ϕp and flow Reynolds numbers (Re). It was found that the outcome of a particle-wall collision is either particle deposition or rebound, depending on the balance between kinetic energy of the incoming particle and particle-wall van der Waals potential energy. Brownian motion was established to be the main deposition mechanism for nanoparticles in the boundary layer. As Re decreased, Brownian motion of nanoparticles dominated over convection, which led to higher deposition rates. Deposited particles were found to cause greater attenuation of solar radiation near the collector upper surface, especially in the visible region of the solar spectrum. Whereas in the infrared region, radiation attenuation became less sensitive to particle deposition. The drop in collector efficiency when particles are allowed to deposit relative to the case when particles are not allowed to deposit was highest for low Re and ϕp. Yet, regardless of Re, an increase in particle surface potential led to a better dispersion of nanoparticles. Furthermore, colloidal interparticle interactions were found to have a negligible effect on collector performance. The results highlight the important effects of particle deposition and non-uniform particle distribution on the performance of DASC systems, which cannot be captured using conventional single-phase models.

Dual tree traversal on integrated GPUs for astrophysical N-body simulations

In astrophysical N-body simulations, O( N) fast multipole methods (FMMs) with dual tree traversal (DTT) on multi-core CPUs are faster than O( N log N) CPU tree-codes but can still be outperformed by GPU ones. In this article, we aim at combining the best algorithm, namely FMM with DTT, with the most powerful hardware currently available, namely GPUs. In the astrophysical context requiring low accuracies and non-uniform particle distributions, we show that such combination can be achieved thanks to a hybrid CPU-GPU algorithm on integrated GPUs: while the DTT is performed on the CPU cores, the far- and near-field computations are all performed on the GPU cores. We show how to efficiently expose the interactions resulting from the DTT to the GPU cores, how to deploy both the far- and near-field computations on GPU, and how to overlap the parallel DTT on CPU with GPU computations. Based on the falcON code and using OpenCL on AMD Accelerated Processing Units and on Intel integrated GPUs, this first heterogeneous deployment of DTT for FMM outperforms standard multi-core CPUs and matches GPU and high-end CPU performance, being hence more cost- and power-efficient.