Increasing Volume Fraction Research Articles

Scouring erosion resistance of metallic materials with composite microstructures

Slurry erosion can cause severe damage and often constitutes a significant portion of the total production cost in many industries such as oil sands and mining. The most commonly used materials for such applications are metallic materials having a composite microstructure consisting of hard reinforcement phases in a more ductile metal matrix. Typical examples are high chromium white irons and tungsten carbide welding overlays. The main purpose of this work is to evaluate the scouring erosion resistance of such materials for applications in handling fine sand slurries and to introduce a wear model to help understand the correlation between erosion resistance and the characteristics of microstructures.Five high chromium white cast irons and four spray and fusion coatings composed of cast tungsten carbide particles and Ni–Cr–B–Si–Fe matrix have been studied using a Coriolis scouring erosion tester in a fine sand slurry. The relationship between the erosion resistance and different microstructure parameters was explored. For the chromium white cast irons, the erosion resistance increased with increase in carbide volume fraction but the spray and fusion coatings showed the opposite trend, i.e., their erosion resistance decreased with increase in the carbide volume fraction. No clear correlation was found between erosion resistance and free path for the spray and fusion coatings while for the chromium white cast irons, the erosion resistance was found to increase rather than decrease with increase in free path.To help explain the experimental results, a wear model has been proposed for the wear resistance of composite microstructures composed of a reinforcement phase (RP) and a metal matrix. In the model, the wear surface of the material is distinguished by four different features/regions, each having unique wear resistance. The rule of mixtures (ROM) for wear resistance is applied to formulate the wear resistance of the material with the above four wear surface features. It is shown that the results can be reasonably well explained based on the proposed model by using the total edge length, L, of the RP particles exposed on a unit area of the wear surface.

Characterization of microstructure, texture, grain structure, and thermal properties of Al/Ni/Al multilayered composites fabricated through cross-accumulative roll bonding

This research investigates microstructure, texture, and thermal properties of Al/Ni/Al composites fabricated by cross-accumulative roll bonding (CARB) process. According to the microstructural results, ultra-fine grain structure was observed in severely deformed layers. More grain refinement occurred when the content of Ni increased. In addition, shear texture components became stronger by increasing the CARB passes and Ni content even though the Copper-based texture components of {112}<111> existed in all deformed samples. Also, despite an improvement in thermal features of deformed aluminum and nickel layers versus temperature rise, the TD, and TC decreased as the number of passes increased. However, by increasing the rolling passes, the measured thermal capacity values modestly increased while the thermal expansion values first decreased and then increased. Regarding composites, all thermal features decreased with an increase in Ni volume fraction. Due to the restricting effect of harder reinforcement layers, the measured thermal expansion declined from 17.01 × 10−6 1/k in Al/0.2 Vf Ni to 15.4 × 10−6 1/k in Al/0.8 Vf Ni.

Computational micropolar model of hybrid nanofluid flow across a wedge

Non-Newtonian flow from wedges is a vital problem in coatings, polymer processing etc. Hence the main aim is to investigate the convective boundary layer flow of micropolar hybrid nanofluid (MHN)from a wedge. It is assumed that the wedge surface is isothermal. The Eringen model is employed to define micropolar fluid. Nanoscale Tiwari–Das formulations are used to study the specific effects of nanoparticles and volume fractions. The dimensionless boundary value problem arises by suitable coordinate transformations as a system of nonlinearly coupled ordinary differential equations. The so-called Falkner Skan flow case is resolved. Dimensionless, transformed, coupled momentum, microrotation, boundary layer equations are resolved using the numerical scheme MATLAB bvp4c. The parameteric investigations are performed on hybrid nanofluids using water as the basis liquid and varying volume fractions from 0 to 8%. Affirmation with previous work is done. The consequence of Eringen micropolar parameter, Hartree pressure gradient parameter, nanoparticle volume fraction, Eckert number, heat absorption (sink) parameter, on the flow and physical characteristics are visualized graphically and in tables. With rising material factor and volume fraction of nanoparticle, temperature is markedly enhanced. Increases in volume fraction dampen angular velocity close to the wedge surface, while farther from the wall, the opposite effect is seen. Temperature and thermal boundary layer thickness are both greatly enhanced by increasing Eckert number. With an increase in the volume proportion of nanoparticles, velocity decreases. Heat generation raises temperatures while a heat sink lowers them. The pressure gradient parameter increases skin friction while decreasing Nusselt number. Nusselt number for hybrid nanofluid is higher than for nanofluid.

Semi-analytical solution of MHD free convective flow of a nanofluid over an exponentially stretching porous sheet in the presence of heat source/sink

In this study, the magnetohydrodynamic flow and heat transfer of electrically conducting nanofluid over an exponentially stretching porous sheet is investigated. By introducing similarity variables, the non-linear set of partial differential governing equations, are transformed into a system of ordinary nonlinear differential equations. The equations are solved semi-analytically by the Optimal Collocation Method (OCM) which is a powerful method to solve equations containing infinite boundary conditions. The accuracy of the OCM results is examined by the Richardson method. The effects of the different physical parameters such as magnetic field strength, nanofluid volume fraction, suction strength, and the heat sink/source value are discussed on the flow and heat transfer characteristics of the problem. The obtained results show that the velocity and temperature of nanofluid increase with the increase in volume fraction. Also, when suction increases, the thickness of the boundary layers decreases. As the strength of the magnetic field (Hartmann) increases, the temperature slightly increases but the flow rate of the nanofluid decreases. The skin friction coefficient and Nusselt number increase when the values of suction parameters, volume fraction, magnetic field, and the field angle increase.

Multiple-relaxation-time lattice boltzmann simulation of natural convection of ethylene Glycol -Al[formula omitted]O[formula omitted] power-law Non-newtonian nanofluid in an open enclosure with adiabatic fins

The heat transfer by natural convection of a nanofluid, which is ethylene glycol−Al2O3 has been analyzed in an open cavity numerically using the multiple-relaxation-time - lattice Boltzmann method by the graphics processing unit high-performance parallel computing. The right side of the cavity is open, and different boundary conditions have been applied to all the walls. Besides, one adiabatic fin has been installed on each side of the enclosure’s top and bottom sides. Here, the Prandtl number is fixed at 16.6, and the Rayleigh number changes from 104−106 with the nanoparticle volume fraction from 0%−5% has been used for numerical simulations. Besides, in this work, the power-law index is an important parameter as well, and 0.7, 0.8, 1, 1.2, and 1.4 are the values of this parameter. Results are presented concerning both the average and local Nusselt numbers in the form of streamlines, isotherms, temperature distributions, velocity distributions, heat transfer rate, and entropy production. It is observed when increases, average Nusselt number increases 607.94%, and for this reason, the overall heat transfer rate rises because of buoyancy force. In addition, the average Nusselt number falls by 83.28% when the power-law index rises; as a result, the total heat transfer rate falls because fluid viscosity increases with the power-law index. It is also observed that for shear-thickening fluids, the temperature gradient is higher. On the contrary, the temperature started decreasing with the increase of the power-law index. Additionally, the local Nusselt number value rises as power-law index falls. Moreover, the heat transfer rate increases by 7.08% when volume fraction increases. The intensity of buoyancy force reduces with the increase of volume fraction. Besides, the overall entropy generation rises when the Rayleigh number and the volume fraction increase, but it decreases when the power-law index increases. So, when the Rayleigh number is 106, the power-law index is 0.7, and the volume fraction is 0.00 then the entropy generation is the highest. This current research has many applications for example heat exchangers, electronic cooling equipment, solar heating systems, aerospace applications, medical devices, and entropy generation-related systems.

The high temperature creep and fracture behavior of Inconel 718 produced by additive manufacturing

High-temperature creep tests of additively manufactured (AM) and wrought nickel alloy 718 (IN718) were conducted at 650 °C and 704 °C at stresses ranging from 316 to 819 MPa. The AM alloy had a greater creep strength than the wrought alloy at nearly all testing conditions due to increased volume fractions of γ” in the matrix and carbides at grain boundaries; however, the creep rupture ductility of the AM material was significantly reduced at all testing conditions. Secondary ion mass spectrometry (SIMS) revealed that sulfur segregation, resulting from a lack of Mg in the AM alloy, is the most plausible explanation for the observed ductility loss in AM IN718. Overall, this work focuses on understanding and defining the mechanism of embrittlement in AM IN718.

Simultaneously improving mechanical properties and electrical conductivity of Al-1.9Mn alloys with different Mg and Si addition

A simultaneous achievement of high strength and toughness, as well as high conductivity in traditional Al-1.9Mn cast aluminum alloy used in the manufacture of water-cooled radiator shells has proven to be challenging. The addition of Mg and Si elements was implemented in the cast aluminum alloy for a modified treatment to solve the problem. The results showed that the inclusion of Si facilitated the transformation of the plate-like Mn-rich phase (Al6Mn) in the initial Al-1.9Mn alloy into a Chinese-script phase (Al15Mn3Si2) in the new Al-1.9Mn alloy. A higher Si content resulted in an increased volume fraction of Al15Mn3Si2 and a decreased solid solution of Mn in the matrix. Furthermore, a high content of Mg (0.9 wt%) in the Si modified Al-1.9Mn alloy resulted in a notable property reduction, not only in its elongation, but also in its electrical conductivity. It can be attributed to the formation of Mg2Si and the increased solid solution of Mg in the matrix. Through the optimization of the Mg and Si contents, new Al-1.9Mn alloys with superior mechanical properties and excellent electrical conductivity were successfully developed. With the addition of 0.45 wt% magnesium and 0.75 wt% silicon, the new Al-1.9Mn alloy increased its tensile strength to 170 MPa and yield strength to 88 MPa while maintaining 10 % elongation. At the same time, its electrical conductivity increased by 10.7 % compared to the original Al-1.9Mn alloy. The addition of magnesium and silicon elements can achieve a simultaneous enhancement of both the strength and electrical conductivity of the Al-1.9Mn alloy. This holds the potential to meet the usage requirements for cast aluminum alloys used in water-cooled radiator shells.

Developing Zn-2Cu-xLi (x < 0.1 wt %) alloys with suitable mechanical properties, degradation behaviors and cytocompatibility for vascular stents

Biodegradable Zn alloys show great potential for vascular stents due to their moderate degradation rates and acceptable biocompatibility. However, the poor mechanical properties limit their applications. In this study, low alloyed Zn-2Cu-xLi (x = 0.004, 0.01, 0.07 wt %) alloys with favorable mechanical properties were developed. The microstructure consists of fine equiaxed η-Zn grains, micron, submicron-sized and coherent nano ε-CuZn4 phases. The introduced Li exists as a solute in the η-Zn matrix and ε-CuZn4 phase, and results in the increase of ε-CuZn4 volume fraction, the refinement of grains and more uniform distribution of grain sizes. As Li content increases, the strength of alloys is dramatically improved by grain boundary strengthening, precipitate strengthening of ε-CuZn4 and solid solution strengthening of Li. Zn-2Cu-0.07Li alloy has the optimal mechanical properties with a tensile yield strength of 321.8 MPa, ultimate tensile strength of 362.3 MPa and fracture elongation of 28.0 %, exceeding the benchmark of stents. It also has favorable mechanical property stability, weak tension compression yield asymmetry and strain rate sensitivity. It exhibits uniform degradation and a little improved degradation rate of 89.5 μm∙year−1, due to the improved electrochemical activity by increased ε-CuZn4 volume fraction, and generates Li2CO3 and LiOH. It shows favorable cytocompatibility without adverse influence on endothelial cell viability by trace Li+. The fabricated microtubes show favorable mechanical properties, and stents exhibit an average radial strength of 118 kPa. The present study indicates that Zn-2Cu-0.07Li alloy is a potential and promising candidate for vascular stent applications. Statement of significanceZn alloys are promising candidates for biodegradable vascular stents. However, improving their mechanical properties is challenging. Combining the advantages of Cu and trace Li, Zn-2Cu-xLi (x < 0.1 wt %) alloys were developed for stents. As Li increases, the strength of alloys is dramatically improved by refined grains, increased volume fraction of ε-CuZn4 and solid solution of Li. Zn-2Cu-0.07Li alloy exhibits a TYS exceeding 320 MPa, UTS exceeding 360 MPa and fracture EL of nearly 30 %. It shows favorable mechanical stability, degradation behaviors and cytocompatibility. The alloy was fabricated into microtubes and stents for mechanical property tests to verify application feasibility for the first time. This indicates that Zn-2Cu-0.07Li alloy has great potential for vascular stent applications.

Investigation on flow structure and pressure fluctuation of gas-liquid two-phase flow in a mixed flow pump

Abstract Mixed flow pump is characterized by high-efficiency operation and wide range of flow rate conditions, while research on transporting gas-liquid two-phase flow is quite limited. The present work investigates the energy performance, two-phase flow pattern and pressure fluctuations of a mixed flow pump, on basis of the numerical method of inhomogeneous Eulerian-Eulerian multiphase flow model. Results show that the pump head and efficiency decline with the increase of gas volume fraction. In impeller, gas phase is mainly distributed at the tip clearance, the blade pressure side and suction side, and the hub outlet. The low pressure of tip leakage vortex core leads to the gas phase concentration and the formation of gas strip. Moreover, X-shaped gas strip appears at high gas volume fraction (GVF). In guide vane, gas phase is mainly distributed at the leading edge of blade pressure side, the blade suction side, and the middle of passage. As the inlet GVF increases, the spatial-temporal evolution of the gas phase shows obvious differences. The strong gas-liquid interaction causes broad low-frequency fluctuations, and the rotor-stator interference causes significant blade passing frequencies in the mixed flow pump.

The cyclic GTN model for ULCF fracture analysis of Q355 steel

The cyclic GTN (C-GTN) model, built upon the GTN model, considers the influence of cyclic loadings on the evolution of microvoids, enabling the prediction of ULCF fracture in materials. In this study, the C-GTN model was calibrated for Q355 steel based on tests on notched round bar specimens reported in the literature. Following existing four tests on single-edge notched plate (SENP) specimens subjected symmetric cyclic loadings, additional four ULCF tests were conducted on SENP specimens with asymmetric cyclic loadings. ULCF fracture was observed in these tests and ULCF lives of these SENP specimens were obtained. Mesh sensitivity was investigated for the ULCF fracture analysis of the SENP specimens with the C-GTN model. After balancing the computational accuracy and cost, the ULCF fracture analysis of the SENP specimens were conducted using finite element models with a mesh size of 0.2 mm at the notch tip. ULCF lives predicted by the C-GTN model agree very well with test results for all SENP specimens. The agreement validated the applicability of the C-GTN model for the ULCF fracture analysis of Q355 steel. The increase of the void volume fraction and the degradation of its critical value played dominant roles in the ULCF fracture of V-notched and U-notched SENP specimens respectively.

Synergetic softening-strengthening behaviors of gradient nano-grained CoCrFeMnNi high-entropy alloys located in the inverse Hall-Petch range revealed by atomistic simulations

Gradient-structured CoCrFeMnNi high-entropy alloy (HEA) with all grain sizes lying in the inverse Hall-Petch range exhibits a significant synergistic softening behavior, with the yield strength even lower than the rule of mixtures (ROM) under uniaxial tensile loading. The softening of grain boundaries (GB) is very pronounced in hard domains due to the extremely small grain size. Moreover, the coordinated deformation of heterostructure promotes grain rotation in soft domains with large grain sizes. However, the extra strength generated by hetero-deformation induced (HDI) strengthening increases with increasing volume fraction of hard domain, contributing to a gradual decrease in the gap between yield strength and ROM. Here, we identify multiple deformation mechanisms promoted by mechanical incompatibility through molecular dynamics (MD) simulations. On the one hand, the higher volume fraction of the hard domain encourages the adaptation of dislocation-mediated activities to plastic strains, thus reducing the possibility of GB sliding or intergranular brittle cracking. More importantly, soft domains are more susceptible to detwinning under additional compressive stress, which induces grain refinement in localized regions and contributes extra strength. Observation of the strain distribution reveals that the banded shear bands (SBs) are spread throughout the soft domains, which effectively improves strain gradient strengthening. It has been verified that the gradient structure has the highest extra strength at the hard domain volume fraction of 40–50%. The findings provide insights into the engineering applications of gradient-structured HEA.

The Lattice Boltzmann Simulation of Free Convection Heat Transfer of a Carbon-Nanotube Nanofluid in a Triangular Cavity with a Solar Heater

In this paper, the flow and free convection heat transfer of a multi-walled carbon nanotube/water nanofluid in a triangular cavity with a solar heater is studied using the lattice Boltzmann method. The side walls of the cavity are cold and the bottom wall is partially heated by a solar heater, which have a non-uniform temperature distribution. It is assumed that the heating energy is provided by an absorber that is directly exposed to sunlight. Because of the limited variations of density, the Boussinesq approximation is used, which causes the coupling of hydrodynamic and thermal fields. For velocity and temperature distribution functions, a lattice Boltzmann model with two dimensions and nine directions is adopted. The effect of parameters, such as the Rayleigh number, the volume fraction of nanoparticles, and the position of solar heater, on the flow and heat fields is studied. The results show that, for all Rayleigh numbers studied, the Nusselt number increases as nanoparticles volume fraction increases. The addition of 4% nanoparticles causes the average Nusselt number to increase about 11% at low (Ra = 103) and moderate (Ra = 104) Rayleigh numbers and 217% at the high Rayleigh number (Ra = 105). Furthermore, it is shown that for a fixed Rayleigh number, heat transfer can be optimized by adjusting solar heater’s position. This study can provide a useful insight for utilizing solar heaters with non-uniform temperature distribution in triangular cavities.

Simultaneously promoting strength and ductility by regulating TRIP effect in TiZrCuBeO bulk metallic glass composite

In this study, a novel series of Ti-based bulk metallic glass composites has been developed, exhibiting high specific strength and significant ductility (fracture strain exceeding 11 %). The TRIP effect of these composites was promoted by oxygen microalloying, ensuring uniform deformation under tensile loading. The outstanding mechanical properties could be attributed to the well-controlled metastability of the β phase, as well as the increased volume fraction and variants of martensite, effectively coordinating the micro-strain. It demonstrates that well-designed composition could significantly enhance the TRIP effect and ductility of bulk metallic glass composites, and prevent premature failure while preserving strength.

Study on the Flow Characteristics of Heavy Oil-Water Two-Phase Flow in the Horizontal Pipeline.

Aiming at the problem of transportation for heavy oil during the middle-later development stages of the Lvda oilfield, based on the self-developed design of a visual circulating flow experimental apparatus for heavy oil-water two-phase flow-the flow regime characteristics and corresponding drag properties of the two-phase flow of Lvda viscous oil, which is simulated by 500# industrial white oil and water in a horizontal pipeline are investigated experimentally. According to the Kelvin-Helmholtz instability theory, the flow pattern transition criteria from stratified flow to annular flow (AF) are proposed. The effects of 0.11-0.90 m/s oil superficial velocities, 0.06-1.49 m/s water superficial velocities, and 0.09-0.93 input water cuts on the drag reduction effect of different flow regimes are analyzed. The experimental results indicated that with the increase of mixing velocity and water volume fraction, stratified flow, AF, oil plug flow, and dispersed oil lump flow are successively observed in the horizontal heavy oil-water two-phase flow, in which AF is the main flow pattern. As the Froude number increases to 4.0, the input water volume fraction does not change any more and remains at about 10% of the total flow rate in the process of converting from stratified flow to AF. The four delivery approaches can archive the reduction of transportation resistance for heavy oil at different degrees, in which the transportation of heavy oil surrounded by a water ring has the best effect of drag reduction. At the optimal working conditions of 0.61 m/s oil superficial velocity, 0.07 m/s water superficial velocity, and 0.10 input water cut, the pressure drop of water annulus conveying for heavy oil is only 1/62.54 of that of separate transport for pure heavy oil under the same oil flow rate.

MHD Casson ternary hybrid nanofluid flow through a vertical porous plate with thermal radiation: A finite difference approach

AbstractThis entire study aims to investigate the impacts of linear thermal radiation and MHD Casson ternary hybrid nanofluid flows over a vertical porous plate for comparison of nanofluid, hybrid, and tri‐hybrid nanofluids with Newtonian and non‐Newtonian fluids. We used a ternary hybrid nanofluid, Blood contains three types of oxides and metals: spherical ferric oxide (Fe3O4), platelet‐shaped zinc (Zn), and cylindrically‐shaped gold (Au) nanoparticles. The coupled nonlinear dual partial differential equations (PDEs) are turned into PDEs using nondimensional quantities. The Finite Difference Method (FDM) and the Perturbation Method are then used to solve the PDEs. The impacts of different parameters on temperature, velocity, Nusselt number, and Skin friction profiles have been discussed. The increase in viscosity occurs because an increase in Gr also causes an increase in the velocity field for nanofluid, hybrid, and tri‐hybrid nanofluids. A tri‐hybrid nanofluids performs better among the three, such as nanofluid, hybrids and tri‐hybrid nanofluids. As the volume fractions (Fe3O4) increase, the temperature increase for both Newtonian and non‐Newtonian fluids. The increase in temperature is due to the thermal conductivity of nanoparticles, which is enhanced by growth estimates of the nanoparticle volume fraction. The high temperature of the fluid is observed for large estimates of nanoparticle volume fraction. An increase gold (Au) also increases the temperature for shapes (cylinder, platelet, and spherical). A spherical shape performs better among the three, such as cylinder, platelet, and spherical. In this model, biomedical applications such as antiviral and therapeutic, treatment of the COVID‐19 virus, cancer treatment, and anticancer medication delivery systems.

Heat Transfer and Entropy Generation for Mixed Convection of Al2O3–Water Nanofluid in a Lid-Driven Square Cavity with a Concentric Square Blockage

The present numerical investigation is focused on analyzing the characteristics of steady laminar mixed convection flow in a lid-driven square cavity, specifically considering the utilization of Al2O3–water nanofluid. The Al2O3–water nanofluid is assumed to be Newtonian and incompressible. Within the cavity, a square blockage is positioned at its center, which is subjected to isothermal heating. The blockage ratio of the square is B = 1/4, and the Grashof number is Gr = 100. The walls of the cavity are maintained at a constant temperature, Tc, while the square blockage remains at a constant temperature, Th. The primary objective of this study is to investigate the flow and heat transfer mechanisms, as well as the entropy generation within the cavity. This investigation is conducted for a range of Richardson numbers (0.01 ≤ Ri ≤ 100) and volume fractions of the nanofluid (0 ≤ ϕ ≤ 0.05). Several parameters are obtained and analyzed, including streamlines, isotherms, velocity variations on the vertical and horizontal midplanes, local Nusselt number variations on the surfaces of the square blockage, the average Nusselt number on the square blockage, and the total dimensionless entropy generation of the system. The results of the investigation revealed that both the average Nusselt number on the square blockage and the total dimensionless entropy generation of the system exhibit an increasing trend with an increasing volume fraction of the nanofluid and a decreasing Richardson number. Furthermore, correlations for the average Nusselt number and the total dimensionless entropy generation with the Richardson number, and the nanofluid volume fraction are derived.

The relationship between parameters measured using intravoxel incoherent motion and dynamic contrast-enhanced MRI in patients with breast cancer undergoing neoadjuvant chemotherapy: a longitudinal cohort study.

The primary aim of this study was to explore whether intravoxel incoherent motion (IVIM) can offer a contrast-agent-free alternative to dynamic contrast-enhanced (DCE)-MRI for measuring breast tumor perfusion. The secondary aim was to investigate the relationship between tissue diffusion measures from DWI and DCE-MRI measures of the tissue interstitial and extracellular volume fractions. A total of 108 paired DWI and DCE-MRI scans were acquired at 1.5 T from 40 patients with primary breast cancer (median age: 44.5 years) before and during neoadjuvant chemotherapy (NACT). DWI parameters included apparent diffusion coefficient (ADC), tissue diffusion (Dt), pseudo-diffusion coefficient (Dp), perfused fraction (f), and the product f×Dp (microvascular blood flow). DCE-MRI parameters included blood flow (Fb), blood volume fraction (vb), interstitial volume fraction (ve) and extracellular volume fraction (vd). All were extracted from three tumor regions of interest (whole-tumor, ADC cold-spot, and DCE-MRI hot-spot) at three MRI visits: pre-treatment, after one, and three cycles of NACT. Spearman's rank correlation was used for assessing between-subject correlations (r), while repeated measures correlation was employed to assess within-subject correlations (rrm) across visits between DWI and DCE-MRI parameters in each region. No statistically significant between-subject or within-subject correlation was found between the perfusion parameters estimated by IVIM and DCE-MRI (f versus vb and f×Dp versus Fb; P=0.07-0.81). Significant moderate positive between-subject and within-subject correlations were observed between ADC and ve (r=0.461, rrm=0.597) and between Dt and ve (r=0.405, rrm=0.514) as well as moderate positive within-subject correlations between ADC and vd and between Dt and vd (rrm=0.619 and 0.564, respectively) in the whole-tumor region. No correlations were observed between the perfusion parameters estimated by IVIM and DCE-MRI. This may be attributed to imprecise estimates of fxDp and vb, or an underlying difference in what IVIM and DCE-MRI measure. Care should be taken when interpreting the IVIM parameters (f and f×Dp) as surrogates for those measured using DCE-MRI. However, the moderate positive correlations found between ADC and Dt and the DCE-MRI parameters ve and vd confirms the expectation that as the interstitial and extracellular volume fractions increase, water diffusion increases.

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.

A simple method for the preparation of cordierite ceramics with high strength and low thermal expansion coefficient

AbstractCordierite ceramics have great application prospects due to their very low coefficient of thermal expansion. However, the low purity of ceramics leads to their unsatisfactory fracture strength, which has always been a research focus. Herein, by applying external pressure to the green body of mixed raw materials and optimizing the synthesis temperature, high‐purity cordierite powder was prepared, and then it was used as the starting material for the fabrication of high‐strength cordierite ceramics. The optimal sample exhibited a flexural strength of 146 MPa, which is about 1.4 times that of the cordierite ceramics reported in the literature. This is attributed to applied external pressure increasing the contact area of raw materials, leading to a more thorough reaction, and the content of the α‐cordierite phase is 98.4 wt% in the sample synthesized at 1275°C. Concurrently, the samples possessed a thermal expansion coefficient of only 1.9 × 10−6°C−1 (room temperature to 800°C). In addition, the increase in columnar crystal volume fraction is also one of the reasons for the high strength and low thermal expansion coefficient of cordierite ceramics.

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.