Increasing Particle Volume Fraction Research Articles

Solid–Liquid Two-Phase Flowmeter Flow-Passage Wall Erosion Evolution Characteristics and Calibration of Measurement Accuracy

Solid–liquid two-phase flowmeters are widely used in critical sectors, such as petrochemicals, energy, manufacturing, the environment, and various other fields. They are indispensable devices for measuring flow. Currently, research has primarily focused on gas–liquid two-phase flow within the flowmeter, giving limited attention to the impact of solid phases. In practical applications, crude oil frequently contains solid particles and other impurities, leading to equipment deformation and a subsequent reduction in measuring accuracy. This paper investigates how particle dynamic parameters affect the erosion evolution characteristics of flowmeters operating in solid–liquid two-phase conditions, employing the dynamic boundary erosion prediction method. The results indicate that the erosion range and peak erosion position on the overcurrent wall of the solid–liquid two-phase flowmeter vary with different particle dynamic parameters. Erosion mainly occurs at the contraction section of the solid–liquid two-phase flowmeter. When the particle inflow velocity increases, the erosion range shows no significant change, but the peak erosion position shifts to the right, primarily due to the evolution of the erosion process. With an increase in particle diameter, the erosion range expands along the inlet direction due to turbulent diffusion, as particles with lower kinetic energy exhibit better followability. There is no significant change in the erosion range and peak erosion position with an increase in particle volume fraction and particle sphericity. With a particle inflow velocity of 8.4 m/s, the maximum erosion depth reaches 750 μm. In contrast, at a particle sphericity of 0.58, the minimum erosion depth is 251 μm. Furthermore, a particle volume fraction of 0.5 results in a maximum flow coefficient increase of 1.99 × 10−3.

Aerodynamic breakup of gel suspension droplets loaded with aluminum particles

The persistent and frequent space explorations are affected by the performance of propellants, among which the closely related gel propellants have been widely used due to their unique characteristics. Currently, research efforts primarily concentrate on the metallization and atomized combustion of gel propellants, emphasizing the combustion performance of metallized gel propellants. However, little attention has been given to the secondary breakup process that occurs just before combustion. By utilizing high-speed flow visualization technology, this study examines the key aerodynamic breakup process of gel suspension droplets loaded with micro aluminum particles, experimentally and theoretically investigating the droplet dynamics induced by particle volume fraction. The experimental confirmation of the three breakup behaviors exhibited by gel suspension droplets, namely oscillation mode, bag-stamen breakup, and hemline breakup, is presented along with the construction of a phase diagram. The impact of heterogeneous effects resulting from an increase in particle volume fraction on the critical breakup Weber number is revealed, with a concentration of 9% as the turning point. Within the range of moderate Weber numbers, the tail flick deformation of suspension droplets in airflow is observed and reported for the first time. At different particle concentrations, there keeps a linear correlation between the dimensionless tail length and Weber number. Spherical suspension droplets will deform into thin disks in the airflow, with a nearly constant deformation rate regardless of changes in particle concentration. Additionally, the relationships between characteristic times and droplet parameters are discussed through statistical analysis of the results. As Ohnesorge number and particle volume fraction increase, the characteristic times both show a monotonically increasing trend. Moreover, a model of unstable growth rate associated with the particle volume fraction is established through linear instability analysis, accurately predicting the variation in critical Weber number for gel suspension droplet breakup. The congruence between our theoretical framework and experimental findings not only enhances comprehension of the impact of micro aluminum particles on the secondary breakup of gel suspension droplets but also provides valuable guidance for the aerospace applications of metallized gel propellants.

CFD-DEM mixing of rod-like and spherical particles in fluidized beds

Understanding the behavior of particle mixing in fluidized beds is crucial for enhancing process design. This article focuses on investigating the effect of key parameters, such as volume fraction of spherical particles, length of rod-like particles, and aspect ratio of rod-like particles, on the mixing of binary mixtures containing spherical and rod-like particles. The study employs a computational approach which couples the computational fluid dynamics and discrete element method (CFD-DEM) to explore mixing behavior of particles. Non-spherical particles are modeled using the multi-sphere method. A combination of qualitative and quantitative approaches is employed to assess the mixing performance, including visual examination of the fluidized bed and calculation of the subdomain-based mixing index. It was shown that an increase in rod-like particle length, aspect ratio, and volume fraction of rod-like particles weaken the mixing. Furthermore, the quality of mixing is directly influenced by bubble size and particle granular temperature. This study offers valuable insights into the mixing behavior of rod-like and spherical particles, contributing to the design and optimization of binary fluidization processes.

Precipitation mechanism of abrasive particles in magnetorheological polishing fluid and experimental verification

This study aims to address the issue of poor workpiece surface machining quality due to inadequate abrasive particle precipitation during the processing of magnetorheological polishing fluid. The paper employs magnetic dipole theory and molecular dynamics theory to establish a microdynamics model for magnetorheological polishing fluid and conducts kinematic and dynamic analyses of magnetic and abrasive particles. The chaining process of magnetic particles in magnetorheological polishing fluid was simulated under an external magnetic field, and the precipitation process of abrasive particles under the action of magnetic particles was simulated and analyzed. Furthermore, we established a microscopic observation experimental platform for magnetorheological polishing fluid and verified the precipitation law of abrasive particles under the action of dynamic magnetic field. The study findings indicate that the magnetic particles will form a chain structure, when the rotating magnetic field has an effect on the magnetorheological polishing fluid, and the abrasive particles will precipitate from the magnetorheological polishing fluid and adhere to the upper end of the magnetic chain. Moreover, the precipitation rate of abrasive particles is also affected by the magnetic field strength, the volume fraction of magnetic particles, and the rotating magnetic field speed, with the abrasive particles’ precipitation rate specifically increasing with higher magnetic field strength. At a magnetic field strength of 100 kA/m, the abrasive precipitation rate reaches 80 % in approximately 90 s, which increases to 80 % in only 60 s at a magnetic field strength of 200 kA/m. Additionally, with the increase of magnetic particle volume fraction, the precipitation rate of abrasive particles decreases. Within the first 40 s of the test, the magnetic particle volume fraction increases from 10 % to 30 %, and the precipitation rate of abrasive particles decreases by about 11 %. Similarly, the abrasive precipitation rate is affected differently by the rotating magnetic field speed. As the rotating magnetic field speed increases, the abrasive precipitation rate shows a trend of first increasing and then decreasing. When the rotating magnetic field speed increases from 20 r/min to 40 r/min, the abrasive precipitation rate of the first 40 s increases by about 25 %. When the speed continues to increase to 60 r/min, the precipitation rate of abrasive particles gradually decreases.

Measuring and Simulating the Transient Packing Density During Ultrasound Directed Self‐Assembly and Vat Polymerization Manufacturing of Engineered Materials

AbstractUltrasound‐directed self‐assembly (DSA) uses ultrasound waves to organize and orient particles dispersed in a fluid medium into specific patterns. Combining ultrasound DSA with vat photopolymerization (VP) enables manufacturing materials layer‐by‐layer, wherein each layer the organization and orientation of particles in the photopolymer is controlled, which enables tailoring the properties of the resulting composite materials. However, the particle packing density changes with time and location as particles organize into specific patterns. Hence, relating the ultrasound DSA process parameters to the transient local particle packing density is important to tailor the properties of the composite material, and to determine the maximum speed of the layer‐by‐layer VP process. This paper theoretically derives and experimentally validates a 3D ultrasound DSA model and evaluates the local particle packing density at locations where particles assemble as a function of time and ultrasound DSA process parameters. The particle packing density increases with increasing particle volume fraction, decreasing particle size, and decreasing fluid medium viscosity is determined. Increasing the particle size and decreasing the fluid medium viscosity decreases the time to reach steady‐state. This work contributes to using ultrasound DSA and VP as a materials manufacturing process.

Investigation on cutting deformation behavior of Al/SiCp composites considering particle feature distributions

Al/SiCp composite machining is considerably difficult owing to the presence of abrasive particles that results in weak synergetic deformation capacity during cutting. Therefore, to enhance the machinability of Al/SiCp composites, investigations on the cutting deformation behavior are imperative through finite element simulation. Aiming to address the limitations of conventional finite element models in accurately representing the actual microstructure of Al/SiCp composites, this study proposes a realistic microstructure-based finite element model to investigate the cutting deformation and damage behavior. The microstructural characteristics of the composites namely, particle feature distributions, including size distribution, aspect ratio distribution, and spatial aggregation of SiC particles, are analyzed and extracted based on the microstructure image of composite and the Gaussian stochastic model. Then, the particle feature distributions are incorporated into the microstructure-based model for the first time. Besides, all the failure mechanisms (i.e., the brittle fracture of SiC particles, the elastoplastic damage of Al matrix, as well as the particle-matrix decohesion) and the tool-chip contact behavior are comprehensively integrated into the modeling. The experimental results show that as the particle volume fraction and size increase, the chip radius and the number of chip curls decrease, the chips vary from little waviness to prominent saw-tooth type, and more particles are broken or debonded. According to the comparison with experimental results, the finite element model can effectively capture the deformation and failure process, as well as the characteristics of chip morphology, cutting force, and machined surface quality. In addition, the comparisons further demonstrate that SiC particles with large size, slender shape, and aggregation are prone to fracture and detachment in the cutting deformation. Finally, the influences of the particle feature distributions on the machinability of Al/SiCp composites are discussed in detail. It is found that decreasing the dispersion degree of particle size and aspect ratio distribution as well as minimizing the degree of particle clustering degree benefit the machinability of Al/SiCp composites.

Influence of side dilution jets on swirling and non-swirling pulverised biomass turbulent annular flows

The use of pulverised biomass in non-premixed combustion systems, featuring turbulent annular flows (swirling, non-swirling) with downstream air dilution jets, is of immense practical importance. The overall combustion performance and emissions heavily rely on the underlying flow dynamics, turbulence and dispersion behaviour of the pulverised biomass particles. Despite the practical significance of side dilution jets in aiding complete combustion and controlling pollutants, the fundamental understanding of side dilution jets influence on the biomass particle velocity field, turbulence, and dispersion characteristics is still lacking. However, the presence of a multi-phase (solid-gas) flow field, highly turbulent annular flows, swirl, and cross-wise turbulent dilution jets poses significant challenges to these investigations. This work employs a combination of two-dimensional planar Particle Image Velocimetry (PIV) experiments and three-dimensional multi-phase numerical modelling to resolve the influence of turbulent side dilution jets (Red = 18,000 and 27,000) on the particle flow and dispersion characteristics of turbulent annular jets equipped with a central pulverised biomass-laden jet. The numerical modelling uses Reynolds stress model (RSM) and discrete phase model (DPM) for the solution of gas and dispersed phases, respectively. Walnut flour based raw pulverised biomass is injected at a certain particle loading ratio (Φp=0.33 and 0.49) through a turbulent central jet (Rj = 4500) into non-swirling (S = 0) and swirling (S = 0.3) turbulent confined annular flows (Res = 35,500 and 17,800). Comprehensive Constant Temperature Anemometry (CTA) experiments are conducted to obtain well-defined boundary conditions for experiments as well as numerical simulations. Prior to numerical predictions, the models are duly validated against the experimental data.Results reveal that the characteristic flow feature of side dilution jets, i.e., peripheral recirculation zones (PRZ) significantly entrains pulverised biomass particles from the turbulent particle-laden (central jet) annular flows (both swirling and non-swirling) and alters the particle flow and turbulence characteristics. Under non-swirling conditions (S = 0), side dilution jets reduce mean particle axial velocity by 22.4% and increase turbulent fluctuating velocity by 52.6%. These figures elevate to 32.5% and 100% respectively for swirling conditions (S = 0.3), depicting enhanced turbulent mixing between solid particles and the gas phase. In terms of particle dispersion, side dilution jets significantly enhance lateral dispersion of biomass particles, particularly under swirling flow conditions. In the PRZ region, side dilution jets led to a 108% and 279% increase in normalised particle count for non-swirling and swirling cases, respectively. These findings suggest that swirl doubles the particle dispersion in the PRZ. Furthermore, a 50% increase in Red enables side dilution jets to entrain more biomass particles and disperse them into the PRZ. Conversely, a 50% increase in ṁp leads to a significant increase in particle volume fraction along the central axis of the nozzle.

Computational damage analysis of metal matrix composites to identify optimum particle characteristics in indentation process

This paper presents an integrated numerical model that investigates the effects of Al2O3 particle volume fraction, distribution, size, shape, and clustering on the deformation, damage, and failure behaviors of particle-reinforced metal matrix composites. Additionally, the effects of the cohesive strength of the matrix-particle interface and the initial void volume fraction on these behaviors are investigated. In this study, random microstructure-based finite element modeling approach is used. The Gurson-Tvergaard-Needleman model is used to capture the plastic deformation and ductile cracking of the matrix, whereas the Johnson–Holmquist II model is used to model particle fracture. The matrix-particle interface decohesion is modeled using the surface-based cohesive zone method. A two-dimensional nonlinear finite element model augmented with Python-generated code is developed in ABAQUS/Explicit to analyze the damage mechanisms in AA6061-T6/Al2O3 particle-reinforced metal matrix composites. The results show that Al2O3 particle enhance the ability of particle-reinforced metal matrix composites to resist deformation. However, this enhancement is dependent on the indentation location, particulate characteristics, and the applied load. An increase in the particle volume fraction increases the risk of particle fracture, particularly when particles are close to the material surface. Circular particles are the optimal choice for the reinforcement of particle-reinforced metal matrix composites. The predictions are in good agreement with the experimental data, particularly in terms of Rockwell hardness and deformation characteristics.

Strategies to improve the thermal performance of solar collectors

Abstract The paper evaluates a passive method for heat transfer improvement in heat exchangers, which implies the use of nanofluids. All calculations were carried out with a constant volumetric flow rate. The study examines three fluids with 0–4 % volume concentrations of CuO, MgO, and Al2O3 particles. The results indicate an increase in the heat transfer coefficient with increasing temperature. An Al2O3 nanofluid (4 % concentration) contributed to the best thermal performance. The incorporation of a 4 % content of MgO yielded an augmentation in heat transfer ranging from 15 % to 22 %, whereas an analogous concentration of CuO led to a more substantial enhancement of 25 %. Notably, the introduction of nanoparticles of Al2O3 produces a remarkable augmentation in heat transfer performance, with potential improvements of up to 36 %. The Nusselt number increases with increasing particle volume fraction and Reynolds number, according to results obtained for several nanoparticles (Al2O3, CuO, SiO2, and ZnO) with volume percentages in the range of 1–4 % and nanoparticle diameters of 25–70 nm. For all nanofluids, the time-averaged Nusselt number rises with a solid phase volume fraction increase of less than 5 %.

Strategies to improve the thermal performance of solar collectors

Abstract The paper evaluates a passive method for heat transfer improvement in heat exchangers, which implies the use of nanofluids. All calculations were carried out with a constant volumetric flow rate. The study examines three fluids with 0–4 % volume concentrations of CuO, MgO, and Al2O3 particles. The results indicate an increase in the heat transfer coefficient with increasing temperature. An Al2O3 nanofluid (4 % concentration) contributed to the best thermal performance. The incorporation of a 4 % content of MgO yielded an augmentation in heat transfer ranging from 15 % to 22 %, whereas an analogous concentration of CuO led to a more substantial enhancement of 25 %. Notably, the introduction of nanoparticles of Al2O3 produces a remarkable augmentation in heat transfer performance, with potential improvements of up to 36 %. The Nusselt number increases with increasing particle volume fraction and Reynolds number, according to results obtained for several nanoparticles (Al2O3, CuO, SiO2, and ZnO) with volume percentages in the range of 1–4 % and nanoparticle diameters of 25–70 nm. For all nanofluids, the time-averaged Nusselt number rises with a solid phase volume fraction increase of less than 5 %.

Numerical investigation of particle effect on wear characteristic of centrifugal slurry pump based on CFD-DEM coupling

PurposeIn the process of conveying the solid–liquid two-phase medium of the centrifugal slurry pump, the wear of the flow-passing parts is an important problem affecting its life and safe operation. Therefore, a numerical investigation on the wear characteristics of the centrifugal slurry pump under different particle conditions was conducted.Design/methodology/approachA solid-liquid two-phase model based on CFD-DEM coupling is established and used to analyze the flow field and the wear characteristics of the flow-passing parts with different particle densities, volume fractions and sizes.FindingsParticle conditions will affect the pump flow field. To analyze the pump wear characteristics, the wear distribution, wear value and cumulative force laws of flow-passing parts under different particle conditions are obtained. In each flow-passing part, with the increase of particle density, volume fraction and size, the wear area is concentrated and the wear depth increases. Under different particle conditions, the wear is mainly on the volute chamber and the blade pressure surface, and the tangential cumulative force of flow-passing parts is much larger than the normal cumulative force.Originality/valueAn accurate model and a coupled simulation method for predicting the wear of the slurry pump are obtained, and the wear characteristic law can provide a reference for the design of the slurry pump to reduce friction.

Microscopic modeling of magnetorheological fluids containing spherical and ellipsoidal ferromagnetic particles

Based on the magnetic dipole theory, the study of the single-chain structure of ferromagnetic particles in magnetorheological fluids(MRFs), and the analysis of the scanning electron microscope(SEM) image processing of ferromagnetic particles, a micromechanical model of MRFs containing spherical and ellipsoidal ferromagnetic particles was established. MRFs with different particle volume fractions were prepared, the shear properties of MRFs under different magnetic induction strengths were tested, and theoretical and experimental data were compared. Varying the volume fraction of the ferromagnetic particles and magnetic induction strength in MRFs at constant temperature and shear rate, the shear stress increases with increasing particle volume fraction and magnetic induction intensity. The MRF micromechanical model containing spherical and ellipsoidal ferromagnetic particles is more accurate than the model with only single-size spherical ferromagnetic particles, and the accuracy is improved by 16.85%.

Numerical analysis for the normal force of magnetorheological fluids

As one of the most important mechanical parameters of magnetorheological fluids (MRF), the normal force has been studied by a large number of researchers using various experimental equipment and methods. However, it is difficult to reveal the effects of particle microstructure characteristics on the normal force of MRF by experimental methods, especially for such factor as the particle size distribution. To advance this research area, a numerical method for calculating the normal force of MRF is proposed in this study. The accuracy of the simulation model is verified with the experimental results measured by a plate-plate magnetorheometer. The results show that the simulated values agree well with the experimental data, which indicates the feasibility of calculating the normal force of MRF using numerical methods and provides a new research idea for a more intuitive and comprehensive analysis of the normal force characteristics of MRF. Besides, the simulated data show that the increase in magnetic field intensity and particle volume fraction will sufficiently enhance the normal force of MRF and improve the response time of MRF. For the MRF with the same particle volume fraction, a decline in the average particle diameter will increase the normal force. Moreover, increasing the dispersion of particle size of MRF particles can also improve its normal force.

CFD-DEM coupled calculation of wall wear characteristics during particles flow impacting the wall process

The continuous impact of the particles flow on the wall during industrial bulk material transport can lead to wall wear. In this paper, a physical model of the particle flow impacting the wall at different angles is established, and the wear condition of the particles flow impacting on the wall is studied by using the coupling method of CFD-DEM. Firstly, the accuracy of the erosion model is verified by the existing experimental data. Secondly, the effects of particle incidence angle, particle velocity and particle volume fraction on wall wear are analyzed by numerical calculation. The results show that the mass loss and erosion ratio of the target plate are the largest when the particle incidence angle is between 15° and 30°. When the particle incidence angle is near 45°, the maximum wear depth will appear on the wall surface. The increase of particle impact velocity led to an exponential increase in the mass loss, erosion ratio and wear depth of the target plate, but did not change the wall wear morphology. The particle volume fraction is positively correlated with the mass loss of the target plate. With the increase of particle volume fraction, the change of erosion ratio is more obvious at 90° impact, but has little effect at 45° impact. The change of particle volume fraction has an important effect on the wall wear morphology.

Assessments of the heat transfer performance of a novel continuous oscillatory baffled crystallizer via two-fluid model

An Eulerian-Eulerian two-fluid model which incorporates the kinetic theory of granular flow, the energy balance equations, was firstly applied to investigate the heat transfer performance of solid–liquid two-phase flow in continuous oscillatory baffled crystallizers (COBC). The results show that the novel COBC (#6) has both excellent heat transfer and particle suspension performance, as compared with other COBCs, indicating that importance of optimizing the chamber connection structure of COBCs. Then, the COBC #6 was further selected to study the effects of operating conditions and particle physical properties on its heat transfer performance. With increase of oscillation Reynolds number (Reo), the radial mixing of fluid gradually reaches the peak, resulting in the increasing rate of Nusselt number (Nu) gradually decreases. Compared with single-phase flow, the existence of solid particles can produce shear stress on the wall surface, reducing the thickness of heat transfer boundary layer and thermal resistance, thereby increasing the heat flux. With increase of particle size or volume fraction, such effect becomes more obvious, which significantly enhances heat transfer. The novel designed COBC can be operated in the optimized Reo to achieve good heat transfer performance and low power consumption.

Heat transportation performance and entropy generation analysis of Iron (II, III) oxide microparticles on Taylor Couette flow over a slit wall

Despite the significance of Taylor Couette flow over a slit wall in industries, little is known about the impact of Iron (II, III) oxide (Fe3O4) microparticle on the dynamics and heat transfer properties of Taylor-Couette flow. This study aims to investigate the effect of solid particles on heat transfer performance of Taylor-Couette flow over a slit wall. The trajectory of particles in the flow field is described utilizing Eulerian-Lagrangian method in this report. The Fe3O4-water suspension with particle size dp = 1μm, 5μm and particle volume fraction φ = 0.5 % , 1.0 % , 1.5% are considered. Results reveal that the heat transfer performance of Taylor vortex is remarkable enhanced by adding the solid particles inside the annular gap compared to pure water. Solid particles in the annular gap show the movement of migration from inner to outer cylinders due to the interaction with fluid, which causes more disordered flow field around the inner cylinder. The addition of particles could significantly thin the velocity and temperature boundary layers. Frictional and thermal entropy generation display a reverse tendency with increasing particle volume fraction and size. Thermal entropy generation appears obviously higher than frictional entropy generation. Suspension with φ = 1.5% and dp = 1μm makes optimal performance of Taylor vortex because of the minimum entropy generation and boundary layers.

Dependent Scattering in Thick and Concentrated Colloidal Suspensions

This study demonstrates numerically and experimentally that dependent scattering occurs in colloidal suspensions and can, counterintuitively, cause their transmittance to increase with increasing particle volume fraction. Radiation transfer through colloidal suspensions has been modeled with the radiative transfer equation (RTE) assuming independent scattering. Then, the effective absorption and scattering coefficients of the disperse medium are predicted as the sum of the cross sections of all particles divided by the volume of suspension. However, this approach is not valid when the average interparticle distance is on the same order of magnitude as the wavelength, corresponding to large particle concentrations. The latter situation is referred to as dependent scattering. Rigorously accounting for dependent scattering requires solving Maxwell’s equations, but is limited to relatively thin suspensions. Here, we extend the Radiative Transfer with Reciprocal Transactions (R2T2) method to predict the normal-hemispherical transmittance of thick and concentrated plane-parallel slabs of nonabsorbing nanoparticle suspensions and to rigorously account for dependent scattering effects. The radiation characteristics of a large number of particle ensembles were estimated using the superposition T-matrix method and the RTE was solved using Monte Carlo method combined with strategies for sampling the previously computed radiation characteristics. A wide range of particle size parameter, volume fraction, and optical properties as well as colloidal suspension thickness were investigated. Dependent scattering effects were found to prevail for particle volume fractions as low as 1% depending on the particle size and refractive index. Evidences of dependent scattering were also observed experimentally in the visible normal-hemispherical transmittance of 10 mm thick colloidal suspensions of silica nanoparticles with diameter between 16 and 30 nm and particle volume fraction ranging from 2% to 15%. Moreover, good agreement was found between experimental measurements and numerical predictions from the R2T2 method. By contrast, assuming independent scattering underestimated systematically the normal-hemispherical transmittance, especially for large particle volume fraction. As such, this paper presents, for the first time, experimental validation of the R2T2 method and its ability to account for dependent scattering.

Effective Thermal Conductivity of Nanofluids Containing Silicon Dioxide or Zirconium Dioxide Nanoparticles Dispersed in a Mixture of Water and Glycerol

The present study investigates the effective thermal conductivity of nanofluids containing crystalline or amorphous silicon dioxide (SiO2), or zirconium dioxide (ZrO2) nanoparticles dispersed in a mixture of water and glycerol with a mass ratio of 60:40. Such fluids are relevant as potential cutting fluids in tribology and feature a broad distribution of irregularly shaped non-spherical particles of dimensions on the order of (100 to 200) nm that were produced by comminution of larger particles or particle aggregates. A new steady-state guarded parallel-plate instrument was applied for the absolute measurement of the effective thermal conductivity of the nanofluids with an expanded uncertainty (coverage factor k = 2) of 3% for temperatures from (293 to 353) K and particle volume fractions up to 0.1. For a constant volume fraction of 0.03 for the three particle types, the measured thermal-conductivity ratios, i.e. the effective thermal conductivity of the nanofluids relative to the thermal conductivity of the base fluid, are less than 1.05 and not affected by temperature. In the case of the nanofluids with crystalline SiO2, with increasing particle volume fraction from 0.03 to 0.10 the thermal-conductivity ratios increase up to values of about 1.18 for all temperatures. A comparison of the measurement results with the Hamilton-Crosser model and an analytical resistance model for the effective thermal conductivity of nanofluids shows that the former one allows for better predictions for the present nanofluids with a relatively large viscosity. In this context, it could be shown that detailed knowledge about the sphericity and thermal conductivity of the dispersed nanoparticles is required for the modeling approaches.

Evaluation of entropy generation characteristics of boehmite-alumina nanofluid with different shapes of nanoparticles in a helical heat sink

Entropy generation characteristics of different nanoparticle shapes are explored considering a nanofluid-cooled helical heat sink system for both laminar and turbulent flow regimes. For each flow regime, four different Reynolds numbers are considered, ranging from Re=500 to 20,000. Five different particle shapes (spherical, bricks, blades, cylindrical and platelets) are included for this comparative study, and their thermal, frictional, and total entropy generation characteristics are evaluated for four different nanoparticle volume concentrations (ϕ=0.5, 1.0, 1.5, and 2.0%), and the outcomes are compared to the base fluid case (ϕ=0%) as well as a comparison is considered among the investigated nanoparticles. Obtained results revealed that in the turbulent flow regime, the thermal entropy generation tends to decrease with increasing particle volume fraction, and the highest decrements are obtained for platelet shape (43%). The frictional entropy generation shows an opposite trend, and the platelet nanoparticles yield the highest increment, around 6.32 folds in both laminar and turbulent flow. In both flow regimes, the spherical particles have the smallest impact on the entropy generation among the examined ones. In addition to that, increment in Re results in a decrement in the thermal entropy generation, while it causes a remarkable increase in the frictional entropy generation.

Parameter optimization of particle-reinforced adhesive bonded joints based on the response surface method

We investigated the effects of process parameters on the quality of alumina-reinforced adhesive bonded joints. Single-lap joints of 1.5-mm-thick aluminum alloy 5182 sheets were prepared by adhesive bonding with particulate composite adhesive. The multivariate regression models between process parameters (particle size, adhesive layer thickness, and mass fraction) and response values (failure load, energy absorption value) were established, and the models were verified by experiments. The adhesive layer was modeled using the ABAQUS CPS4R mesh element. The representative volume element (RVE) model was then established to simulate the failure of adhesively bonded joints during tensile tests. The findings indicate that particle size has the biggest impact on the failure load of the joints, and particle mass fraction has the highest influence on the energy absorption value of the joints. The optimum process parameters ranges are: particle size of 0.046 mm, adhesive layer thickness of 0.6 mm, and mass fraction of 5%. As per finite element analysis, the failure load and tensile modulus of the adhesive layer decrease as particle size and particle volume fraction increase.