Varying Volume Fractions Research Articles

Deformation Behavior of AZ31 Magnesium Alloy with Pre-Twins under Biaxial Tension.

In the present study, the mechanical response and deformation behavior of a Mg AZ31 plate with different types of pre-twins was systematically investigated under biaxial tension along the normal direction (ND) and transverse direction (TD) with different stress ratios. The results show that significant hardening was observed under biaxial tension. The yield values in the direction of larger stress values were higher than those under uniaxial loading conditions, and the solute atom segregation at twin boundaries generates more obvious strengthening effect. Noting that, for TRH (with cross compression along the rolling direction (RD) and TD and annealing at 180 °C for about 0.5 h) sample, the strength effect of the RD yield stress σRD:σND = 2:1 was higher than that of the ND yield stress under stress ratio σRD:σND = 1:2. There is a complex competition between twinning and detwinning under biaxal tension along the ND and TD of the pre-twinned samples with the variation in the stress ratio along the TD and RD. The variation in the twin volume fractions for all samples under biaxial firstly decreases and then increases with a higher stress ratio along the ND. As for the TDH sample (precompression along the TD and annealing), the changes of the twin volume fraction were lower than that of the TR sample (cross compression along the TD and RD). However, the amplitude of variation in twin volume fraction of the TRH sample is higher than that of the TR sample. This is because the relative activity of detwinning decreases and that of twinning increases, as the ND stress mainly leads to the growth of pre-twins and the TD stress often promotes detwinning of primary twins. With a higher stress ratio along the ND, the activity of twinning deformation increases and that of detwinning decreases.

Three-dimensional characteristic and evolution of creep cavity and microcrack of HR3C austenitic heat resistant steel after long-term creep at 650 °C

Three-dimensional characteristics of creep cavities and microcracks in HR3C austenitic steel after creep at 650 °C were investigated using high resolution X-ray computed tomography (CT) and three-dimensional atomic probe (3DAP). The variation of cavity volume fraction is related to the increasing fraction of cavities undergoing growth and coalescence. Irregular lamellar or “W” shaped microcrack along the grain boundary were observed by the CT and the number large sized microcracks decreased significantly with decreasing stress levels. 3DAP results show that the concentration of P elements was high at the M23C6/γ interface at the early stage of creep. With the increase of creep time, M23C6/γ interface have been found to not only contain high concentration of P element, but also be enriched with Si. The coarsening of the carbides at the grain boundary and the enrichment of P and Si elements at the interface creates the conditions for the nucleation of creep cavities and microcracks under stress. Thus, stress has an tremendous influence on the distribution of creep cavities and the propagation path of microcracks. Additionally, with the decrease of stress, the creep damage mode changes from intergranular/transgranular mixed cracks to creep cavity.

Evaluating mechanical and biological responses of bipolymeric drug-chitosan-hydroxyapatite scaffold for wounds: Fabrication, characterization, and finite element analysis

This study aims to explore the potential of a scaffold composed of drug-chitosan-hydroxyapatite (HA) in improving tissue treatment. The focus of the investigation lies in analyzing the physical and biological properties of the scaffold and evaluating its mechanical characteristics through finite-element analysis. To synthesize microcapsules containing dextran-diclofenac sodium, the electrospraying method was employed. The drug-chitosan-HA scaffold with varying volume fractions (VF) of the synthesized microcapsules (10, 15, and 20) was fabricated using the freeze-drying technique. Microscopic and scanning electron microscopy (SEM) images were utilized to evaluate the morphology, shape, and size of the microcapsules, as well as the porosity of the scaffolds for wound healing purposes. The mechanical properties of the synthesized microcapsules were determined via a nanoindentation test, while the mechanical behavior of the fabricated scaffolds was assessed through compression testing. Additionally, a multiscale finite-element model was developed to predict the mechanical properties of tissue scaffolds containing pharmaceutical microcapsules. The findings indicate that the incorporation of drug-chitosan-hydroxyapatite into the tissue significantly enhances both mechanical and biological responses. The mechanical evaluations demonstrate that the drug-chitosan-hydroxyapatite tissue exhibits excellent resistance to pressure, making it a suitable protective covering for skin wounds. Moreover, biological evaluations reveal that an increase in scaffold porosity leads to higher swelling behavior. The scaffold containing 20 % pharmaceutical microcapsules demonstrated the greatest swelling and desirable antibacterial properties, thereby indicating its potential as an effective wound dressing. Furthermore, a multiscale finite-element model was developed to predict the mechanical properties of tissue containing pharmaceutical microcapsules. The results indicated that the average size of the microcapsules was in the range of 170 to 180 µm, and the porosity of the prepared tissue was between 52 % and 61 %. The experimental compressive properties revealed that an increase in the volume fraction of the embedded microcapsules led to an increase in the maximum compressive stress and compressive modulus of the scaffolds by up to 54.95 % and 53.18 %, respectively, for the scaffold containing 20 % VF of pharmaceutical microcapsules compared to the specimen containing 10 % VF. In conclusion, the developed scaffold has the potential to serve as an effective wound dressing, with the ability to provide structural support, facilitate controlled drug release, and promote wound healing.

MFIX–DEM simulation of gas-solid flow dynamics in a dual fluidized bed system

Abstract To overcome the operational difficulties associated with bubbling and circulating fluidized bed gasifiers, a new gasification technology termed dual fluidized bed gasification (DFBG) has evolved. To strengthen the understanding of the gasification and combustion processes in the DFBG system, a thorough analysis of bed hydrodynamics is of paramount importance. Furthermore, the complexity of the hydrodynamics escalates while incorporating diverse fuels like biomass and coal, along with bed materials fluidized in a single reactor due to its nonlinearity and transience. As a result, the study of hydrodynamics in such a system is indispensable. The present study focuses on the discrete element model (DEM) simulation of the bed hydrodynamic behaviour within the gasifier of a DFBG system. The simulation was conducted using Multiphase Flow with Interphase eXchanges (MFiX) software. The influence of superficial velocity on the number of particles in a gasifier was analyzed using the 2-D discrete element model (DEM). In this numerical investigation, transient variation of pressure drop, axial and radial solid volume fraction, and particle velocity was evaluated, and the data were analyzed using the ParaView software. The simulation results of the gasifier indicated an increase in the bed pressure drop with the rise in inlet air velocity. The effective height of solid volume fraction also increased with the surge in superficial velocity. The solid velocity profile and streamlines were also investigated to understand its variation pertaining to the location within the fluidized bed.

Enhanced thermal cycle stability and shape memory effect in NiTiHf shape memory alloys fabricated by laser powder bed fusion

We report on the fabrication of NiTiHf high temperature shape memory alloys (SMAs) via laser powder bed fusion (LPBF), which are almost free of micro-pores and display (Ti, Hf)2Ni nanoprecipitates with variable size and volume fraction. The effect of variable laser powers of 50 W, 60 W and 70 W on the martensite variant microstructures and mechanical properties of the LPBFed SMAs was investigated. Interestingly, all LPBFed NiTiHf samples display enhanced thermal cycle stability of transformation temperatures with a temperature eviation of −3°C, which is attributed to the lack of dislocation slip originated from the habit plane configuration characteristic with multidomain (001) martensite compound twins. Meanwhile, all LPBFed NiTiHf samples exhibit trained one-way and two-way shape memory effects due to the dislocation slip upon compression deformation at room temperature.

Experimental study on the effects of SS304 and Aluminium reinforcements on mechanical and vibration properties in jute‐epoxy composites

AbstractJute fiber has emerged as a promising reinforcement material in polymer composites, and researchers are actively exploring hybrid composite materials to overcome its individual mechanical property limitations and enhance overall performance. The paper introduces a unique hybridization of polymer composites that harnesses the advantages of stainless steel and aluminium offering a lightweight material for potential engineering applications. In this study, stainless steel 304 wire mesh (S), aluminium wire mesh (Al) and aluminium perforated sheet (Alp) are used as an additional reinforcement along with jute (J) and glass (G) fibers to fabricate hybrid polymer composites with varying volume fractions of SS304 and Al wire mesh. Seven laminates of hybrid composites namely J/J/J/S/J/J/J, J/J/S/J/J/S/J/J, J/J/J/Al/J/J/J, J/J/Al/J/J/Al/J/J, J/J/J/Alp/J/J/J, G/J/J/J/S/J/J/J/G, (J/J/S/J/J/S/J/J)450 along with virgin composite laminate J/J/J/J/J/J/J/J were fabricated and tested to obtain mechanical and vibration properties. Bonding between metal wire and matrix is investigated and reported through ILLS tests and SEM observations. Experimental findings indicate a notable 24% and 7% increase in tensile and ILSS strength, respectively, with SS304 reinforcement. Moreover, significant improvements in flexural and impact strength, approximately 48% and 33% for J/J/S/J/J/S/J/J, demonstrate the effectiveness of the hybrid approach. The J/J/S/J/J/S/J/J laminate excels in damping capacity under various boundary conditions. The study underscores the potential of metallic reinforcement to enhance the mechanical properties of jute fiber‐reinforced polymer composites, presenting opportunities for the development of lightweight, sustainable, and high‐performance materials in engineering applications.Highlights Developed jute fiber‐based hybrid polymer composites with metal wire reinforcement. Significant increase in strength and stiffness observed with addition of metal wires. Bonding between metal wire and matrix is investigated through ILLS tests and SEM observations. Vibration damping of all hybrid materials is reported. Study provides valuable data to develop sustainable, lightweight, and cost‐effective materials.

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.

A theoretical and experimental investigation of continuous oil–water gravity separation

In this study, we have developed a mathematical model for a three-phase separator. The model consists of two sections: the inlet section and the separation section, separated by a perforated calming baffle. In the inlet section, two dispersion layers undergo droplet size evolution due to turbulent breakage and coalescence, described by a spatially homogeneous PBE. In the separation section, the two dispersion layers flow alongside each other and interact at an interface. The volumetric flow and velocity profiles are influenced by interfacial coalescence, with considerations for plug and laminar flow assumptions. The model incorporates droplet gravity-driven transport using the Kumar and Hartland model, binary and interfacial coalescence employing a film drainage model, and an effective diffusion term to account for the formation of the dense packed layer which ensures a physical volume fraction range of 0–1. Steady-state and transient numerical solvers are developed to solve the resulting advection–diffusion equations. Additionally, a series of experiments were conducted using a lab-scale multi-parallel pipes separator to investigate the impact of varying volume fractions and flow rates on the separation efficiency of the equipment. The model results are compared with the experimental data which shows relatively good agreement.

Quantitative analysis of flame luminance and explosion pressure in liquefied petroleum gas explosion and inerting: Grey relation analysis and kinetic mechanisms

To evaluate the explosion intensity by flame luminance, a series of explosive and inerting tests on LPG in a 20-L spherical chamber were taken. A quantitative assessment of flame luminance was performed using the grey level theory, and the association between explosion pressure parameters and flame luminance parameters was examined through grey relation analysis. Furthermore, the intrinsic relationship and mechanism between these two variables were explored based on heat-chain reaction kinetics and energy conversion. The findings revealed a synchronous trend between flame luminance and explosion pressure during the LPG explosion process. Notably, a significant positive correlation between explosion pressure and flame luminance was established. Flame luminance emerged as a valuable indicator of explosion intensity, akin to explosion pressure. The grey relational grade between flame luminance and explosion pressure remained remarkably consistent under varying volume fractions of both LPG and CO2. The addition of CO2 exerted a comprehensive influence on factors such as reaction rate, heat release rate, and the concentration of key radicals. This collective impact resulted in reduced explosion pressure and flame luminance. This study offers a theoretical foundation for assessing explosion risks and enhancing energy safety management within the domains of chemical, petroleum, and natural gas industries.

Local strain heterogeneity and damage mechanisms in zirconia particle-reinforced TRIP steel MMCs: in situ tensile testing with digital image processing

In this work, the microstructural deformation and damage mechanisms of TRIP steel metal matrix composites (MMCs) reinforced with Magnesia Partially Stabilized Zirconia (Mg-PSZ) particles are investigated by employing in situ tensile testing within a scanning electron microscope chamber, complemented by digital image correlation and advanced image processing techniques. The study is carried out on samples with varied volume fractions (0%, 10%, and 20%) of zirconia particles and damage mechanisms in different samples under specified loading conditions. Through both qualitative and quantitative assessments of deformation, damage, and clustering, the investigation provides a comprehensive understanding of the distribution and damage initiation. The study findings reveal that, generally, the steel matrix exhibits high toughness, with minimal occurrences of microcracking at high strains that cause significant damage. In samples with increasing particle content, delamination at the matrix–particle interface and cracking of Mg-PSZ particles were found to be critical contributors to material failure and were quantitatively analyzed using computational analyses conducted with MATLAB. The work highlights the initiation and evolution of each damage mechanism in zirconia particle-reinforced TRIP steel MMCs to facilitate scientists and engineers in improving manufacturing and application decisions in industries such as automotive, aerospace, and heavy machinery, which demand materials with exceptional toughness and durability.Graphical

Performance assessment of a sample nanorefrigerant cooling process as a function of flow Reynolds number, evaporator and ambient temperatures

In this paper available experimental data of nanorefrigerant, NRF cooling process are processed using MATLAB to determine the coefficient of performance COP as a function of Reynolds number, Re of NRF, evaporator and ambient temperatures, Te and Ta as a novelty. The cooling process performance assessment of NRF is provided in comparison with a pure refrigerant, R through relative COP term, COPr. The used data ranges with 20–70 nm of Al2O3 in R134a are at varying volume fraction, φ of 0.075–0.303% and volumetric flow rate, Q of 6.5–11 L/h for Ta in 294–306 K and Te in 288–309 K. Re calculations are based on the thermophysical parameters evaluated at Te not only in the cited experimental ranges of Q, φ but also extrapolated for the extended range of Q of 15–25 L/h for a generalization purpose. Since data processing is under the interactive influence of the parameters the functional relationships of COP, Re, φ, Te are expressed as 3D graphical plots which are the start of a trial-error procedure. The experimental data are expressed in terms of fitted equations for functional relationships between various non-dimensional parameters as Re, COP, (COP*φ), (COP*Te/Ta*φ), (Re*Te/Ta*φ), (Re*Te/Ta), and COPr to provide a practical assistance for whom designing and using NRF cooling. A functional relationship of Re*(Te/Ta) with COPr at varying φ is found as the most critical output of the study due to the practice of the appeared parameters in cooling performance assessment. COPr>1 corresponds to φ>0.151% for the processed data ranges.

Investigation of ballistic performance on metal-coir fiber composite laminate with variation of fiber volume fraction: Experimental and simulation

Investigation of ballistic performance on metal-coir fiber composite laminate with variation of fiber volume fraction: Experimental and simulation

Study on the fatigue life and toughness of recycled aggregate concrete based on basalt fiber

This paper studies the influence of basalt fibers on the mechanical properties, fatigue life, and toughness of Mechanically Recycled Aggregate Concrete (MRAC). Basalt fibers of varying volume fractions and lengths, along with quantified amounts of mineral powder and fly ash, are incorporated into MRAC to prepare Basalt Fiber Mechanically Recycled Aggregate Concrete (BFMRAC). The results of basic mechanical tests and fatigue tests showed that mineral powder and fly ash reduce cement consumption, achieve the effect of green construction, and basalt fibers improve the mechanical properties and toughness of concrete. The results of the response surface method (RSM) model indicate that the volume fraction of basalt fibers has a greater influence on the mechanical properties of BFMRAC compared to fiber length. The fatigue test results indicate that under different fiber volume fractions and lengths, the uniaxial compressive fatigue life (N) of specimens for each mix proportion is consistently improved. When the length of basalt fibers is 12 mm and the volume fraction is 0.3 %, the uniaxial compressive fatigue life of BFMRAC reaches its maximum (231638), which is twice that of MRAC. When the survival rate (P) is set to 0.5, with a basalt fibers volume content of 0.3 % and a length of 12 mm, the fatigue limit strength (Se) attains its maximum (0.8648 fc). When stress levels (S) reach 0.75 and the basalt fibers length is 12 mm, the relative CI Intensifying Coefficient achieves its maximum (1.133), resulting in optimal fatigue toughness. When the basalt fibers length is 6–12 mm, Se generally increases with the increase of fiber length, and the enhancement effect is best at 12 mm.

Impact of Different Protrusions in Energy Transfer and Fluid Flow Characteristics Using Al₂O₃ Nanofluid in Pipe Flow

The study investigates how the protruded surface (the part sticking out of an otherwise flat surface) over the small channel affects flow characteristics and heat transfer within a circular flow regime, utilizing computational methods. This investigation uses an alumina nanofluid to compare and analyze the thermo-physical parameters of protruding pipes such as boxes, cylinders, dimples, and pyramids in pipe flow. Alumina nanofluid with varying volume fractions was evaluated as a thermo-fluid under laminar flow conditions, exploring its ability to enhance energy transmission (heat) over the protruded channels. The protruded surface induces turbulence around the protruded region, altering the coolant's physical characteristics. Since heat transfer predominantly occurs on surfaces, the alteration in surface geometry due to the protruded shape increases detectable heat transfer and the Nusselt number. With an increase in the volume percentage of nanofluids, there's a tendency for pressure loss to rise along the flow direction's centerline. The dimpled channel exhibits the highest Nusselt number among all protruding channels, indicating that increasing the Reynolds number also increases the surface heat transfer coefficient for all protrusions. When compared to the base fluid, cylindrical protrusions show the greatest pressure drop. Additionally, comparing a protruded channel with base fluid to one with a 4% volume of alumina nanofluid, it can be observed that the latter significantly improves heat transfer, followed by volume fractions of 1% to 3%.

Preparation and energy absorption of flexible polyurethane foam with hollow glass microsphere

This paper presents the preparation of a partially open-cell and partially closed-cell flexible polyurethane foam material (flex-PUF), which exhibits improved cushioning performance compared to conventional protective materials. Hollow Glass Microspheres (HGM) were used as a filling material to enhance the compressibility of the material. In order to investigate the effects of HGM on the multi-impact protection and vibration damping performance of flex-PUF with different thicknesses, flex-PUF samples filled with varying volume fractions of HGM were subjected to multi-impact testing and dynamic viscoelasticity experiments. The destructive mechanism of HGM under impact was observed using scanning electron microscopy (SEM). The experimental results revealed that, under the same impact energy conditions, filling flex-PUF with HGM reduced the maximum impact displacement while enhancing energy absorption, although at the expense of cushioning performance. As the number of impact increases, the stiffness of flex-PUF decreased. In the vibration experiments, as the frequency increased, the proportion of flex-PUF’s viscous damping energy dissipation decreases.

Assessment of flexural response of RC beams and unrestrained shrinkage of fiber-reinforced high-volume fly ash-based no-aggregate concrete and self-compacting concrete

The use of industrial byproducts as a substitute for cement in concrete production to improve its properties is becoming a widespread practice in producing sustainable concrete. Although research around the world emphasizes higher substitution levels of fly ash (FA) to accrue the benefits from the microstructure refinement, no attempt has been made to study the deflection behavior and drying shrinkage of concrete that is devoid of aggregates while supplementing 80% of cement with class F fly ash (F-FA). Two types of concrete are used to cast full-scale reinforced concrete (RC) beams of size 150×300×2200 mm. The first type is a novel no aggregate concrete (NAC) made up of 80% F-FA and 20% ordinary Portland cement (OPC). The second type is high-volume fly ash self-compacting concrete (HVFASCC), which has 60% F-FA as a cement supplement and is equivalent in compressive strength to NAC. The NAC is reinforced with polypropylene fibers (PF) in three varying volume fractions: 0.6%, 0.8%, and 1.0%. All the beams are tested under a simply supported four-point loading condition. The drying shrinkage strain and mass loss are measured for prisms of size 75×75×300 mm up to 220 days exposed at 20% relative humidity (RH) and 50 ºC temperature in a humidity oven for all the mixes. The mechanical properties are also assessed along with the water absorption (sorptivity). The results indicate that adding PF to the beams with NAC delays the formation of the first crack and improves the peak load, the ultimate load, and the ductility of the NAC beam. Additionally, the beams with PF exhibit lower mid-span deflection and ductile failure mode, improving the overall structural performance. Regarding drying shrinkage, the HVFASCC prisms record the lowest shrinkage strains of all mixes. Adding PF to NAC increases the initial and ultimate drying shrinkage strains. However, adding PF to NAC inhibits the rate of shrinkage strain over the test duration. This research enhances understanding of how PF affects no-aggregate concrete behavior, paving the way for more comprehensive construction materials.

Enhancement in thermo-hydraulic performance of ceramic-based disk heat sink with fractal micro-channels via double layering, hybrid nanofluids, and cross-sectional convergence

The focus of this paper is to further improve the thermo-hydraulic performance of a disk heat sink with fractal-like microchannels by introducing four distinct modifications: incorporating convergent cross-sections in microchannels, implementing double layering, utilizing a high-conductivity material (AlN ceramic) for the heat sink, and integrating hybrid nanofluids. Hybrid nanofluids, encompassing Aluminum Oxide-Graphene, Aluminum Oxide-Copper, and Copper-Graphene, each with varying volume fractions and an overall volume fraction of 2 % and 4 %, were systematically evaluated. The cumulative impact of these modifications on the four levels fractal-like microchannel heat sink's thermo-hydraulic performance was rigorously assessed through numerical simulations. The flow rate ranges from 300 to 600 ml/min, corresponding to an inlet Reynolds number in the range of 3014 to 6018.The findings reveal that the increase around 10 % in Nusselt number can be achieved through implementing converging cross-sections at levels 3 and 4. Substituting silicon with AlN ceramic leads to a reduction in maximum temperature from 1.85 to 2.58 ℃, depending on the flow rate. Under a heat flux of 40 W/cm2, double layering can reduce thermal resistance by 0.2. Most effective configuration involves a double-layered fractal microchannel with convergent cross-sections at levels 3 and 4, employing AlN ceramic as the material, and utilizing a hybrid water-based nanofluid with a volume fraction of Cu 3 %-Al2O3 1 %. This configuration achieves a notable reduction in maximum temperature by 11.1 °C and 17.97 °C under heat fluxes of 40 and 80 W/cm2, respectively, at a volumetric flow rate of 300 ml/min.

Investigation of the influence of morphology on thermal conductivity in hexagonal honeycomb structures and computational models with varied volume fraction and conductivity ratio

The effective thermal conductivity (ETC) is a critical parameter for simulating macroscopic heat transfer processes in composite materials, which estimation is particularly critical where the thermal conductivity of the composite phases is completely different. The huge difference in thermal conductivity of the composite phases makes their volume fraction modulation a classical way to reach the desired thermal conductivity. Nevertheless, the typical manufacturing process of honeycomb cellular structures allows various degrees of stretching of the structure, leading to various honeycomb geometries. In these ‘real’ structures some of the honeycomb wall sides are twice as thick as other parts, modifying the symmetry of the system with respect to honeycomb with uniform wall side thickness. A noticeable example of these composites is that of a hexagonal metallic honeycomb structure filled with phase change material (PCM) which is a widely utilized material in the field of thermal storage and thermal management by exploiting the heat absorbed/released by the PCM phase during its melting/solidification. While the thermal response of a PCM composite during a thermal cycle is not only defined by thermal conductivity (but also by cell size), this represents the basis for the with the optimization of a system based on a composite PCM.For this reason, in this study, steady-state simulations of heat transfer in unit honeycomb cells in different directions perpendicular to the cell axis are conducted to quantify the impact of morphology on the thermal property of the different wall types within honeycomb structures. The results demonstrate that in both SHS and DHS, the porosity exhibiting maximum anisotropy of ETC decreases as the thermal conductivity ratio increases. Moreover, simple predictive models for calculating the ETC in all directions are proposed for each type of honeycomb, considering a wide range of porosity and thermal conductivity ratio, with a relative error limited to 2 %.

Experimental study on the disturbance of microbubble liquid jets

The presence of microbubble significantly influences the rheological properties of a jet, thereby considerably increasing the complexity of the jet instability problem. However, the instability of microbubble jets has been rarely studied, and their breakup mechanism remains obscure. The present study was focused on conducting a comprehensive analysis of bubble jet flows. A high-precision experimental system was constructed to extract the time-series signals of each cross-sectional profile along the axial direction of a jet. Glycerol solutions with three different bubble volume fractions were prepared, and the standard deviation, spectral relationship, and nonlinear dynamical behavior (i.e., autocorrelation, phase space trajectory, Poincaré section, and Lyapunov exponent) were studied. The detailed development process of small surface disturbances in space was assessed, and the influence of variations in the bubble volume fraction on the nonlinear dynamics of the jet was examined. The results demonstrate that microbubbles can significantly change the energy transfer relationship between various sections of a jet and enhance the periodicity of the signal.

Debris-induced consequences on turbulence and vorticity in solar photovoltaic module-generated array wakes

Particle-laden flows in solar photovoltaic (PV) systems are inevitable, where wind-swept debris in open environments are carried by high winds and turbulence, coating panel surfaces or damaging structures. Particle deposition, or soiling, is a well-known issue for large-scale plants which rely on uninhibited solar rays for optimal production. But understanding the mechanisms leading to soiling requires a physical and fluid dynamics-centered focus, since turbulence dominates PV panel wakes and is also known to alter particle concentration and trajectories. This study presents an experimental campaign toward consequences of particle-laden flow between two model PV panels using time-resolved particle image velocimetry. The model array was subjected to varied particle volume fractions, including a tracer particle case and a water droplet case. Characterization of mean velocity, turbulence statistics, and mean kinetic energy within the single phase and, separately, particle phase flows showed modified features due to particle inertia. Images captured at a frequency of 1 kHz in the near wake of the upstream panel allow for a first experimental look at vorticity and convective velocity of vortex structures for single-phase and particle-phase flows which are crucial to debris transport and soiling in PV environments.