Volume Ratio Of Particles Research Articles

Dielectric constant enhancement of BaTiO3/SU-8 for low-voltage droplet actuation

Digital microfluidics (DMF) technology, which called lab-on-a-chip will bring technological innovations to the field of biochemistry. Electro-wetting-on-dielectric (EWOD) is one of the forms of DMF which actuate independent droplets through electric field enabling more accurate and efficient actuation. Nowadays, the high driving voltage required for droplet actuation remains a major obstacle to the practical application of this technology. Dielectric layer is the main factor affecting the driving voltage. In this study, we fabricate a dielectric layer film that can reduce the driving voltage by doping BaTiO3 nanoparticles with high dielectric constant in SU-8 at room temperature. The volume ratio of dopant particles and spin coating speed are studied to determine the optimal processing conditions for low-voltage droplet actuation. As the volume ratio of the dopant particles increased, the dielectric layer dielectric constant firstly increases and then decreases. When the volume ratio of BaTiO3:SU-8 is 1:10, the maximum dielectric constant is achieved. The dielectric wetting properties follow the same trend as the change in dielectric layer dielectric constant. Thus, the parameters of a volume ratio of 1:10 and spin coating speed of 7500 rad/min are finally selected for the preparation of the dielectric layer. These measures resulted in lower threshold voltages for droplet actuation, which contributes to advancing the application and widespread adoption of DMF technology.

Research on enhancement of screening performance of a novel drum screen based on the Discrete Element Method simulation

Screening is one of the most basic technologies for size classification of granular materials. Based on discrete element method simulations, a new built-in component was developed to address the problems of particle piling and poor segregation in drum screening process, and the particle dynamics and spatial distribution were carefully investigated. The results showed that, increasing the blade length will enhance the particle spreading, and a gap between the rotating blade end and the screen wall can lead to proper size segregation; Built-in slits can act as a ‘secondary screen’ by changing the volume ratio of large and small particles, and the curved-end blades can not only push the particles forward but also exert pressure on the ones underneath them; The screening efficiency changes non-linearly with the change in baffles' height; Contrastively, the screening efficiency of the optimized built-in component drum screen is significantly increased up to 82.34%.

Mean field homogenization schemes using averages of stress, strain and strain energy density and applications

The average of stress (AS) and average of strain (AN) were often used in the development of conventional mean-field homogenization (MFH) schemes, but their correlation with the average of strain energy density (AE) has rarely been discussed. In this work, we examined the correlations of AE with AS and AN, and found that AE can be reduced to the product of AS or AN under uniform boundary stress or linear surface displacement associated with a uniform strain field. By introducing a reference matrix and using any two among AE, AS and AN, three MFH schemes were developed: NS (using AN and AS); NE (using AN and AE); and SE (using AS and AE). Following the concept of the Mori-Tanaka's (MT) method, three MFH schemes obtained above were reduced to MT-NS, MT-NE and MT-SE, respectively. Effective elastic properties of composites consisting of isotropic elastic matrices and spherical isotropic elastic inclusions were predicted using these schemes and compared with experimental results. The comparison revealed that MT-SE and MT-NS can reasonably replicate the experimental results in the case of moderate particle volume fractions and ratios between the Young's moduli of matrix and the reinforcement particles, demonstrating the validity of the MFH schemes. This work is significant because it not only clarifies the correlation of AE with AN and AS, but also provides more options for the development of MFH schemes, which can enrich the theory and methods for the analysis of the effective properties of composites.

Investigation on Thermal Conductivity Silver-coated Copper/GaInSn Composite Thermal Interface Materials

To enhance the heat transfer performance of GaInSn liquid metal, a new type of composite thermal interface material with GaInSn as thermal conductive matrix and silver-coated copper particles as thermal conductive fillers was prepared in this article. The morphology of the composites were characterized by scanning electron microscopy. The thermal conductivity of silver-coated copper/GaInSn composites with different silver-coated copper particle contents were measured by laser flash method. The interfacial bonding of the composites were investigated by X-ray diffraction. The results show that when the volume ratio of silver-coated copper particles is 15%, thermal conductivity of the silver-coated copper/GaInSn composite reaches the largest value of 25.01 W·m−1·K−1. The silver-coated copper/GaInSn composite material and commercially available thermal grease were put into the chip and copper plate to simulate the actual application scenarios for comparison. The heat dissipation capacity of silver-coated copper/GaInSn composite material is obviously better than that of the two commercially available thermal grease, and the chip temperature can be reduced by about 5°C.

Calculation of particle volume fraction in computational fluid dynamics-discrete element method simulation of particulate flows with coarse particles

Computational fluid dynamics-discrete element method is frequently used for modeling particulate flows due to its high efficiency and satisfactory accuracy. The particle volume fraction is a crucial parameter that significantly affects the computation accuracy. It may be extremely large when the particulate flows contain coarse particles because it is determined by the ratio of particle volume to cell volume. In this paper, the performance of different methods, such as the divided particle volume method (DPVM), the big particle method, and the diffusion-based method, for computing the particle volume fraction is thoroughly reviewed, implemented, and investigated. It turns out that the DPVM must not be used when the particle size is larger than cell size due to significant fluctuation of the particle volume fraction field. The big particle method is optimized for simulation accuracy and code implementation. The optimized big particle method is similar to the diffusion-based method by diffusing the particle effects to the surrounding cells. It demonstrates greater consistency with experimental observations compared to the diffusion-based method, primarily attributed to its incorporation of polydisperse effects.

Investigation of the Fabrication of Diamond/SiC Composites Using α-Si3N4/Si Infiltration.

Diamond/SiC (Dia/SiC) composites possess excellent properties, such as high thermal conductivity and low thermal expansion coefficient. In addition, they are suitable as electronic packaging materials. This study mainly optimized the diamond particle size packing and liquid-phase silicon infiltration processes and investigated a method to prevent the adhesion of the product to molten silicon. Based on the Dinger-Funk particle stacking theory, a multiscale diamond ratio optimization model was established, and the volume ratio of diamond particles with sizes of D20, D50, and D90 was optimized as 1:3:6. The method of pressureless silicon infiltration and the formulas of the composites were investigated. The influences of bedding powder on phase composition and microstructure were studied using X-ray diffraction and scanning electron microscopy, and the optimal parameters were obtained. The porosity of the preform was controlled by regulating the feeding amount through constant volume molding. Dia/SiC-8 exhibited the highest density of 2.73 g/cm3 and the lowest porosity of 0.6%. To avoid adhesion between the sample and buried powder with the bedding silicon powder, a mixed powder of α-Si3N4 and silicon was used as the buried powder and the related mechanisms of action were discussed.

Studies on Evaluation of the Thermal Conductivity of Alumina Titania Hybrid Suspension Nanofluids for Enhanced Heat Transfer Applications.

Extensive investigations were made and empirical relations were proposed for the thermal conductivity of mono-nanofluids. The effect of concentration, diameter, and thermal properties of participating nanoparticles is missing in the majority of existing thermal conductivity models. An attempt is made to propose a model that considers the influence of such missing parameters on the thermal conductivity of hybrid nanofluids. Al2O3-TiO2 hybrid nanofluids have a 0.1% particle volume concentration prepared with distinct particle volume ratios (k - 1:6 - k, k = 1 to 6) in DI water. The samples were characterized, and the size and shape of the nanoparticles were verified. Also, the influence of varying particle volume ratios and the fluid temperature (varying from 283 to 308 K) were examined. 2.4 and 2.1% enhancements were observed in the thermal conductivity of alumina (5:0) and titania (0:5) nanofluids (having 0.1% volume concentration), respectively. Due to the low thermal conductivity of titania nanoparticles, the conductivity of the hybrid solution is above that of titania and below that of alumina nanofluids. An empirical relation for the thermal conductivity of hybrid nanofluids is established and validated considering the individual particle size, volume ratio, and thermal conductivity of particles.

Thermal Performance Evaluation of Plate-Type Heat Exchanger with Alumina–Titania Hybrid Suspensions

This paper aims to develop models for the thermal conductivity and viscosity of hybrid nanofluids of aluminium oxide and titanium dioxide (Al2O3-TiO2). The study investigates the impact of fluid temperature (283 K–298 K) on the performance of a plate heat exchanger using Al2O3-TiO2 hybrid nanofluids with different particle volume ratios (0:5, 1:4, 2:3, 3:2, 4:1, and 5:0) prepared with a 0.1% concentration in deionised water. Experimental evaluations were conducted to assess the heat transfer rate, Nusselt number, heat transfer coefficient, Prandtl number, pressure drop, and performance index. Due to the lower thermal conductivity of TiO2 nanoparticles compared to Al2O3, a rise in the TiO2 ratio decreased the heat transfer coefficient, Nusselt number, and heat transfer rate. Inlet temperature was found to decrease pressure drop and performance index. The Al2O3 (5:0) nanofluid demonstrated the maximum enhancement of around 16.9%, 16.9%, 3.44%, and 3.41% for the heat transfer coefficient, Nusselt number, heat transfer rate, and performance index, respectively. Additionally, the TiO2 (0:5) hybrid nanofluid exhibited enhancements of 0.61% and 2.3% for pressure drop and Prandtl number, respectively. The developed hybrid nanofluids enhanced the performance of the heat exchanger when used as a cold fluid.

A quasi-physical method for random packing of spherical particles

In this work, a quasi-physical method for the random packing of spherical particles based on the equivalent spring structure and the principle of force equilibrium is proposed. The model is inspired by a meshing method “Distmesh”. For the purpose of generating a feasible packing, the proposed model calculates the displacements of each particle based on physical principles and disregards forces that may not help with convergence, thus offering a natural and possibly fast route towards the final packing configuration. The packing densities predicted by the proposed method are in good agreement with those predicted by other methods and the experimental results. Finally, the topological properties of the packing of particles with log-normal size distributions, binary mixtures and ternary mixtures are evaluated by radical tessellation. The results show that the particle size differences and the proportions of each kind of particles have significant effect on the packing properties of the mixture. • Proposing a new quasi-physical model for the random packing of particles. • The model is inspired by a meshing method, which can more easily form force grids. • The model offers a natural and possibly fast route towards the final packing. • The particle size and volume ratio have significant effect on the packing properties.

Numerical simulation of radiative heat transfer in a binary-size granular bed

The radiative heat transfer in a high temperature granular bed of binary-size mixture was explored in this paper. The effective view factor between particles decreases exponentially with the increase in particle interval, increases with the increase in the size of the absorption particle but is hardly affected by the volume ratio of the mixture. The effective thermal conductivity of granular bed was further deduced basing on the characteristic of the effective view factor. It is indicated that the thermal conductivity is proportional to the particle size and temperature cubed, and increases with the increase in the particle size ratio and volume ratio. Finally, modified calculation correlations of the effective view factor and effective thermal conductivity were developed for binary-size bed based on the simulation results, and good accuracy of less than 0.01 and 10% had been achieved, respectively.

COMBINED FREE AND FORCED CONVECTION OF NANOFLUIDS IN MINICHANNELS WITH DIFFERENT DIAMETERS

In this study, mixed convection heat transfer properties of nanofluids in minichannels were investigated by dispersing SiO2 nanopaticles into pure water. In the study, nanofluids prepared in three different volumetric ratios of 0.25%, 0.75%, and 1.25% were investigated experimentally under laminar conditions in circular horizontal minichannels with diameters of 1.21 mm, 1.5 mm, and 1.9 mm. For the minichannels with the diameters of 1.21 mm, 1.5 mm, and 1.9 mm, increasing the particle volume ratio from 0.25% to 1.25% provided a heat transfer enhancement compared to water by about 11-31%, 7-29%, and 9-27%, respectively. Increasing the minichannel diameter from 1.21 mm to 1.5 mm and from 1.5 mm to 1.9 mm caused an enhancement of the Nusselt number in the range of 6.9-13.9% and 3.39.3%, respectively. Summarizing the results, the natural convection/forced convection ratio and natural convection effect on total heat transfer increased at a constant Grashof number value when the volumetric ratio of nanoparticles increased. In contrast to the particle volumetric ratio, an increase in the minichannel diameter was found to reduce the natural convection/forced convection ratio and the natural convection effects on total heat transfer at a constant Grashof number value.

Development of a new CO2 liquefaction system using the Linde–Hampson process, Kalina power generation unit, and flat plate solar collectors with Al2O3/H2O nanofluid

AbstractGreenhouse gas emissions into the atmosphere have had devastating environmental effects, including ozone depletion and global warming. Carbon dioxide (CO2) is widely used in oil and gas plants, the food industry, and as a working fluid in the power industry. Carbon dioxide is liquefied for long‐term storage, to be transported to remote areas, and is used for peak shaving in the power plants. Solar flat plate collectors and wasted heat from the CO2 liquefaction system can be used in power plant systems. Also, the use of nanoparticles in the collectors improves the thermal properties of the working fluid and increases the efficiency of solar collectors. This study has developed a new hybrid system for CO2 liquefaction using Linde–Hampson system, Kalina power generation unit, and flat plate solar collectors. The Linde–Hampson system's dissipated heat and solar collectors are used to supplying part of the power of the CO2 liquefaction system. The combined system produces 9416 kmol/h of liquid CO2 by absorbing 35.97 MW of power. The Kalina power generation unit provides 9.546 MW of power by absorbing 76.98 MW of the CO2 liquefaction cycle's dissipated heat and 91.18 MW from flat plate collectors. Based on the output of exergy assessment, exergy efficiency and exergy degradation of the developed integrated structure are 44.16% and 118.3 MW, respectively. Moreover, significant portions of exergy destruction in the combined process belong to solar collectors (74.68%), heat exchangers (12.47%), and compressors (7.157%), respectively. The use of Al2O3 nanoparticles in pure water has been investigated for heat transfer in flat panel solar collectors. According to the sensitivity analysis results, as the volume ratio of particles in nanofluid increases to 6%, the production capacity of the Kalina cycle and exergy efficiency improves to 9.56 MW and 9.522%, respectively. Also, as the pressure of the pumped fluid in the Kalina cycle increases from 800 to 1600 kPa, the exergy yield of the Kalina cycle and the exergy yield of the whole combined system increase to 36.34% and 44.26%, respectively.

Mechanical properties of alkali-activated concrete containing crumb rubber particles

Substituting fine aggregate in alkali-activated concrete (AAC) with recycled rubber particles from waste tires helps reduce the excessive consumption of natural resources and the adverse environmental impacts of solid waste. This study investigates the feasibility of developing rubberized fly ash-slag-based AAC in the construction industry. Recycled rubber particles were used to partially replace fine aggregate in five volume ratios, ranging from 0% to 20%, to prepare AAC at ambient temperature, and their mechanical properties were measured through a set of experimental tests. The results show that the addition of rubber particles reduced the compressive strength, splitting tensile strength, and flexural strength of AAC by 5.2–34.5%, 7.2–46.1%, and 12.8–63.7%, respectively, while substantially improving its energy absorption capability by 31.5–53.3%. To balance the reduction in the strength of AAC with the improvement in its ductility, the recommended optimal volume ratio of rubber particles in it is 10–15%. A constitutive model of AAC containing crumb rubber is also proposed based on the experimental data. The findings of this study provide a reference for the use of crumb rubber in AAC, and can contribute to a circular economy in the construction industry.

Analysis of Mechanochemical Reaction in Dual Shot Peening

Abstract Using a combination of solid mechanics and reaction kinetics models, this work simulates a mechanochemical reaction in dual shot peening with a mixture of Al2O3 and Cu2S particles used to form a tribologically beneficial iron sulfide layer on treated surfaces. The model predicts that the dissociation of the Fe–Fe and Cu–S bonds needed for the formation of Fe–S bonds accelerates monotonically with an increase in the shot peening particle speed, whereas its rate reaches a local maximum at the impact angle of about 75 deg. The latter finding is validated by treating the rake faces of high-speed steel cutting tools and performing orthogonal cutting experiments in which the tools peened at the impact angle of 75 deg exhibit lower cutting and thrust forces than those peened at 40 deg. Additional peening parameters, namely, the particle volume ratio and the stage speed, are found to be much less statistically significant under the conditions tested. The developed approach may be instrumental in guiding process optimization to improve the tribological performance of mechanochemically treated surfaces.

Comparison of the effects of microwave and spark plasma sintering on the electrical, thermal, and mechanical properties of Cu-LaB6 nanocomposites

The effects of lanthanum hexaboride (LaB6) nano-particles on the electrical, thermal, and mechanical properties of copper-based nanocomposites (Cu-LaB6) produced using microwave sintering (MS) and spark plasma sintering (SPS) processes were investigated in this study. Nano LaB6 particles reduced the electrical conductivity of Cu matrix nanocomposites produced via MS and SPS by 20% and 13%, respectively. Cu-LaB6 nanocomposites had lower thermal conductivity than unreinforced Cu. The electrical and thermal conductivities of the Cu-LaB6 nanocomposite produced by the SPS process were higher than those of the Cu-LaB6 nanocomposite produced by the MS process. An equation that takes particle volume ratio and porosity into account was developed to predict the thermal conductivity of nanocomposites from their electrical conductivity. The calculated thermal conductivity values for Cu-LaB6 nanocomposites were very close to the experimental results. Cu-LaB6 nanocomposites had much higher hardness and compressive strength by 49% and 38%, respectively, compared to those of unreinforced Cu. The hardness and compressive strength of the Cu-LaB6 nanocomposite produced by SPS were higher than those of the Cu-LaB6 nanocomposite manufactured via MS. Although nano LaB6 reinforcement particles reduced the electrical and thermal conductivities of Cu, Cu-LaB6 nanocomposite having high hardness and compressive strength were produced by combining the positive influences of nano LaB6 reinforcement particles and the SPS process.

Enhancing electrode wettability in lithium-ion battery via particle-size ratio control

Enhancing the electrolyte wetting has been claimed to be a great challenge in developing high-energy density and large-scale lithium-ion batteries (LIBs). Superb wettability ensures high-quality LIBs, but poor wettability incurs unstable capacity, shortened cycle life, and additional manufacturing cost. However, wettability issue has been understated so far, and associated breakthrough technology is not yet available. Here, we report the enhancement of electrode wettability by controlling the volume ratio of different-sized particles. We demonstrate the electrolyte transport behavior in a straightforward way, and investigate the effect of particle-size ratio on the cathode wettability in two aspects: with porosity preserved and by adding small particles. Results show that particle-size ratio and porosity greatly influence the electrode wettability. Electrolyte distribution and correlated pore-throat size distribution not only affect the wetting behavior but also pose crucial factors that determine the wetting speed. This study provides novel mechanistic insight into the electrolyte wetting process, and the results are one of the few published ones that give important information toward wettability enhancement.

Studying Corrosion Resistance of Weld Joints of Ultrafine-Grained Titanium Alloys

Ultrafine-grained (UFG) samples of PT-3V near-α titanium alloy were subjected to diffusion welding using the Spark Plasma Sintering system. It has been shown that the destruction of welded UFG samples under hot salt corrosion (HSC) is two-staged – first, intercrystalline corrosion is manifested, which then graduates to pitting corrosion. It has been established that the corrosion resistance of weld joints is determined by vanadium concentration at the grain boundaries, the size and volume ratio of β-phase particles and the presence of pores in the weld joints. It has been shown that welded UFG samples possess higher hardness and corrosion resistance than coarse-grained samples.

Ensemble effects in Cu/Au ultrasmall nanoparticles control the branching point for C1 selectivity during CO2 electroreduction.

Bimetallic catalysts provide opportunities to overcome scaling laws governing selectivity of CO2 reduction (CO2R). Cu/Au nanoparticles show promise for CO2R, but Au surface segregation on particles with sizes ≥7 nm prevent investigation of surface atom ensembles. Here we employ ultrasmall (2 nm) Cu/Au nanoparticles as catalysts for CO2R. The high surface to volume ratio of ultrasmall particles inhibits formation of a Au shell, enabling the study of ensemble effects in Cu/Au nanoparticles with controllable composition and uniform size and shape. Electrokinetics show a nonmonotonic dependence of C1 selectivity between CO and HCOOH, with the 3Au:1Cu composition showing the highest HCOOH selectivity. Density functional theory identifies Cu2/Au(211) ensembles as unique in their ability to synthesize HCOOH by stabilizing CHOO* while preventing H2 evolution, making C1 product selectivity a sensitive function of Cu/Au surface ensemble distribution, consistent with experimental findings. These results yield important insights into C1 branching pathways and demonstrate how ultrasmall nanoparticles can circumvent traditional scaling laws to improve the selectivity of CO2R.

Capillary performance analysis of copper powder-fiber composite wick for ultra-thin heat pipe

Excellent ultra-thin heat pipes (UTHP) require a wick with high capillary force (ΔPc) and a good permeability performance (K). In this work, a copper powder-fiber composite wick was fabricated by sintering of the copper powder and fiber mixture. Effects of the copper powder particle size, copper powder volume ratio, as well as the super-hydrophilic treatment were investigated, and the results indicate that the copper powder volume ratio is the most significant factor by orthogonal experiments. Moreover, sensitivity analysis shows that super-hydrophilic treatment contributes the lower capillary force and higher permeability, except when copper powder particle size is high to 80 mesh and powder ratio is low to 20%. Interestingly, the overall capillary performance (ΔPc·K) of the super-hydrophilic treated wicks is significantly improved. Besides, for the super-hydrophilic treated wicks, both the smaller copper powder particle size and volume ratio contribute the higher permeability and better comprehensive performance, even though a worse capillary force.

Study on the factors of large-scale space wave absorption of MWCNTs/Fe3O4 nanocomposite particles

With the application of nanoparticles in the field of microwave absorption more and more widely, so it is of great practical value to apply them in large-scale space, and the research on the influencing factors of nanoparticles in large-scale space becomes the key. Considering the diversity of nanocomposites, MWCNTs and Fe3O4, which are easy to prepare, are selected to composite. First, MWCNTs/Fe3O4 nanocomposites are prepared by ball milling and characterized by XRD, TEM and network vector analyzer. Then, the electromagnetic parameters are equivalent by using the strong disturbance equivalent theory, and the absorption loss in the frequency range of 2–18 GHz is calculated by numerical simulation. Finally, the influence of the volume ratio of particles (fs), background medium (eb) and thickness of absorbing layer (d) on electromagnetic wave absorption loss in space is analyzed by orthogonal experiment, and the absorbing mechanism is analyzed.