Volume Fraction Field Research Articles

Numerical Simulation of the Two-Phase Flow Dynamics in an Alkaline Water Electrolyzer Considering Difference in Bubble Diameter

For more efficient hydrogen production, predicting the characteristics of bubble flow inside a water electrolyzer is critical since bubbles affect ion transport, and electrode coverage by bubbles influence overpotentials and the entire electrolysis performance. Transport of bubble significantly depends on its size. In this study, a CFD model of an alkaline water electrolyzer which considers difference in sizes of generated bubbles was developed. The model treats bubbles of different sizes as different gas phases, which are independent of each other. The total bubble mass source for a given current density is divided into phases of each bubble size according to experimental visualizations. Drag, virtual mass, lift, wall lubrication, and turbulent dispersion forces are considered as interaction between gas and liquid phase.The following three sizes of bubbles were considered: diameters d = 36 μm (small), 75 μm (medium), and 208 μm (large). The entire calculation domain represents the anode side of a zero-gap monopolar alkaline water electrolyzer. Figure 1 shows the volume fraction fields of the three gas phases (i.e., bubble sizes) at a constant current density of 0.6 A/cm2. The bubbles are generated on the electrode surface at the z=0 plane. As the liquid phase forms a circulating flow inside the electrolyzer, small bubbles are transported along the circulating downstream flow due to smaller buoyancy force compared to their viscous drag. In contrast, large bubbles flow out directly to the upper outlet because buoyancy force dominates. This result points out the need to consider the difference in bubble diameter for designing flow field inside alkaline water electrolyzer.[Acknowledgements]This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).Fig. 1. Total gas phase volume fraction field obtained from the sum of the volume fraction field for each size bubble, and its experimental visualization. Figure 1

Maturity characterization of soot in laminar coflow diffusion flames of methane/anisole under different oxygen indices

Anisole fuel has gained increased attention, since it is considered a biofuel, and its addition to gasoline increases the octane number, improving the engine performance. This study focuses on the comprehensive characterization of soot maturity and sooting propensity of a well-controlled laminar coflow diffusion flame fueled with anisole and using methane as the carrier gas. Four laminar non-premixed flames were established below the smoke point. The oxidizer composition ranged from a molar fraction of oxygen (oxygen index, OI) of 21% to 35% (doped with pure oxygen), while keeping constant the total volumetric flow rate of oxidizer stream. Multi-wavelength line-of-sight attenuation experiments were performed from visible to infrared wavelengths, and the measurements of the extinction coefficient and flame temperature were used to retrieve two dimensional fields of soot temperature, volume fraction, radiative intensity and degree of soot maturity. In general, the sooting propensity and radiative behavior of the anisole flames follows a similar trend than typical hydrocarbon fuels when increasing the OI. However, the spatial distribution of soot volume fraction is enhanced, particularly near the flame centerline. In contrast, the soot production is promoted by the OI, near the flame wings. The same effect can be observed for the soot temperature. Indeed, temperature increases, promoting formation and oxidation processes, specially at the locations near the maximum soot volume fraction. In general, the maturity of soot particles is affected as the OI is changed. Also, it is observed that the degree of maturity is enhanced by flame temperature. In order to support these local observations, a statistical analysis was carried out. Finally, the results obtained yield a curated database for validating detailed soot production models of oxygenated fuels, and to gain further insights on the evolution of soot maturity and propensity of these particular fuels under different oxidizer conditions.

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.

Numerical and Experimental Reconstruction of Temperature Distribution and Soot Concentration Field for Thin-Slice Flames Using a Charge Coupled Device Camera

This work proposed a novel model to simultaneously reconstruct temperature distribution and soot volume fraction field for two-dimensional thin-slice flames using the knowledge of monochromatic radiation intensities at two wavelengths using a CCD camera. The deduction process and numerical analysis of the model were described. Effects of wavelength combinations and measurement errors on reconstruction accuracy were considered in detail. Numerical results have proven the model’s accuracy and showed that the temperature and soot volume fraction fields can be reconstructed well even with noisy input data from flame radiation. In addition, a series of experiments were conducted on a mesoscale combustor to obtain the real thin-slice flames for further experimental reconstruction via the model. The experimental results indicated that the proposed model can successfully reconstruct the flame temperature distribution and soot volume fraction field and the main features of thin-slice flames also can be reasonably reproduced.

Transient thermoelastic response analysis of porous composite structures ablated by the ultrashort pulse laser considering absorption mechanisms of plasma plume

The absorption mechanisms of plasma plume (such as inverse bremsstrahlung, photo-ionization and Mie absorption) to ultrashort pulse laser have significantly influence on efficiency and quality of laser machining. This motivates us to establish the spatial nonlocal generalized thermoelastic model with plasma absorption mechanisms. Based on the new model, the porous sandwich composite material with perfectly bonded interface is researched. The two outer layers are made of copper and two boundaries are heated by the picosecond pulse laser. The middle layer's material properties are proportionate to those of the outer layers. By using the Laplace transformation and inverse Laplace transform, the governing equations that incorporate spatial nonlocal parameter, strain and thermal relaxation factors are solved. The transient responses, such as temperature, volume fraction field, etc., with different laser parameters, material characteristic parameter and absorption mechanisms of plasma plume are obtained and illustrated graphically.

Film Boiling around a Finite Size Cylindrical Specimen—A Transient Conjugate Heat Transfer Approach

The DNS of film boiling requires strong computational resources that are difficult to obtain for daily CFD use by expert practitioners of industrial R&D. On the other hand, film boiling experiments are associated with the usage of expensive and highly sophisticated apparatus, and research to this end is relatively difficult due to high heat flow rates that are present in the process itself. When combined with transient heat conduction in a solid, the problem becomes significantly difficult. Therefore, a novel method in computation of conjugate heat transfer during film boiling in a quiescent liquid is proposed in this paper. The method relies on the solution of mass, momentum and energy conservation equations in a two-fluid framework, supplemented with the appropriate closures. Furthermore, turbulent flow was determined as an important parameter in obtaining an accurate solution to temperature field evolution in a solid specimen, via the proper modeling of the turbulent kinetic energy (TKE) value, that was imposed as a constant value, i.e., the frozen turbulence approach. It was found, in addition, that the appropriate TKE value can be obtained by use of Kelvin–Helmholtz instability theory in conjunction with boundary layer theory. The obtained results show excellent agreement with the experimental data within the first 15 s of the experiment, i.e., the first ca. 10% of the total duration of the film boiling mode of heat transfer. Furthermore, the heat transfer coefficient matched the error bands prescribed by the authors of this paper, which presented the correlations, whilst the averaged values are far beyond this band, i.e., are slightly more than 30% higher. Further inspection revealed a measure of similarity between the computational result of the volume fraction field distribution and the experiment, thus confirming the capability of the method to obtain realistic interface evolution in time. The method shows full capability for further pursuing industrial-scale film boiling problems that involve turbulent flow and the conjugate heat transfer approach.

Pullback exponential attractors in nonlocal Mindlin's strain gradient porous elasticity

ABSTRACT In this paper, we study the long-time dynamics of a pullback exponential attractors for non-autonomous one dimensional system in nonlocal Mindlin's strain gradient porous elastic theory recently developed by Aouadi [Well-posedness, lack of analyticity and exponential stability in nonlocal Mindlin's strain gradient porous elasticity. Z Angew Math Phys. 2022;73:111]. In this theory, the second gradient of deformation and the second gradient of volume fraction field are added to the set of independent constitutive variables by taking into account the nonlocal length scale parameters effect. By virtue of Galerkin method combined with the priori estimates, we prove the existence and uniqueness of global solution. Then we establish a Lipschitz stability result. We also prove the existence of pullback exponential attractors which as a consequence, implies the existence of a minimal pullback attractor with finite fractal dimension. Finally, we prove the upper-semicontinuity of minimal pullback attractors with respect to the perturbations parameter in natural energy space.

Investigation on the thermoelastic response of a porous microplate in a modified fractional-order heat conduction model incorporating the nonlocal effect

In recent years, the application of porous materials in practical engineering has become increasingly common. Under extreme thermal conditions, how to accurately describe the heat conduction and structural response of porous materials is a key issue in the structural safety and functional design of porous materials. Among them, it is particularly important to consider the size-dependent and memory-dependent effects for small-sized structures or microdevices of porous materials. To address these issues of porous structures and to guide their applications as well as optimization, this paper first investigates the thermoelastic transient response of porous microplates subjected to thermal and stress shocks at the left boundary based on the Atangana-Baleanu (AB) fractional-order generalized thermoelastic theory by considering nonlocal effects and fractional-order strain, which is combined with the thermoelasticity theory of porous materials and the dual-phase-lag (DPL) heat conduction model. The governing equations are then established and solved using the Laplace transform and its numerical inversion. Finally, the effects of newly defined fractional order parameters, nonlocal parameters and the initial magnitude of the mechanical shock on the dimensionless temperature, volume fraction field, displacement and stress distribution are discussed and displayed graphically.

Thermo-hydro-mechanical nonlocal response on porous deep-sea sediments under vibration of mining vehicle

The excessive deformation of deep-sea sediments caused by the vibration of the mining machine will adversely affect the efficiency and safety of mining. This paper reports the study of coupled thermo-hydro-mechanical problem for saturated porous deep-sea sediments, subjected to the vibration of the mining vehicle. Based on nonlocal Moore–Gibson–Thompson thermoelastic theory and Darcy’s law, the model for thermo-hydro-mechanical dynamic response for saturated porous deep-sea sediments under the vibration of mining vehicle is established. Analytical solutions for vertical displacement, excess pore water pressure, vertical stress, temperature and the change in the volume fraction field have been obtained on implementing the normal mode analysis, and the numerical results have been depicted graphically. The result provides the direction on how the vibration frequency and the loading amplitude can affect the physical quantities of the foundation of the seabed. The influence of nonlocality and memory effect on the seabed is also reported.

On torsional wave in void type porous layers between viscoelastic and piezoelectric media with parabolic irregularity

The viscoelastic earth model is increasingly utilized by seismologists for studying surface seismic wave propagation through Earth’s porous crustal regions such as granular materials, including rock, soils, and synthetic porous bodies. The present study characterizes torsional wave propagation in an irregular void-type porous layer sandwiched between an initially stressed inhomogeneous viscoelastic layer and a piezoelectric substratum. Displacement fields for the layer and half spaces are obtained separately using a variable separable technique, whereas volume fraction and electric potential field are derived for layer and substratum, respectively using the matrix calculus approach. Dispersion relations have been derived for both electrically open and short circuit conditions and agree with standard results. Particular cases have been deduced to validate the finding of the study with literature results. Effects of change in relevant parameters such as initial stress, heterogeneities, attenuation coefficient, void parameters, piezoelectricity and dissipation factor have been analyzed on the phase velocity of the torsional wave through various plots and summarized in a tabular form for ready reference to researchers. Analysis of the present geophysical problem may be useful in characterizing torsional velocity in porous silicate rocks which are abundantly found in the transition zone between oceanic and continental crust called Conrad discontinuity. Highlights Torsional propagation in a void-type porous layer crammed between an initially stressed inhomogeneous viscoelastic layer and piezoelectric half-space has been investigated. Variable separable technique, the matrix calculus approach is used for computing the displacement fields of respective media. A comparative study has been carried out for both electrically open and short conditions. The impact of pertinent parameters including initial stress, heterogeneities, attenuation coefficient, void parameters, piezoelectricity, and dissipation factor on the phase velocity of the torsional wave has been examined.

In-silico investigation of intratumoural magnetic hyperthermia for breast cancer therapy using FePt or FeCrNbB magnetic nanoparticles

In this work, we conduct a numerical study on magnetic nanoparticle hyperthermia for the treatment of a breast tumour. The geometry of the problem is comprised of a deformed ellipsoidal tumour region, a healthy glandular tissue region, a fat tissue layer and a skin tissue layer. An aqueous suspension of magnetic nanoparticles (FeCrNbB or FePt) is directly injected into the breast tumour using a syringe. The perfusion of blood through the tissue regions is modelled using the Darcy-Brinkman-Forchheimer equation, and the shear-thinning behaviour of blood is described by the Carreau–Yasuda model. The transport and deposition of nanoparticles within the tissues, the temperature distribution during therapy, and the survival rates of healthy cells and cancer cells are also considered. The governing equations with their associated initial and boundary conditions are solved using the finite element method, and the solution algorithm developed in FreeFEM++ was validated against results from the existing literature. Subsequently, the influence of the nanoparticle solid volume fraction, injection time, and magnetic field amplitude and oscillation frequency on the velocity, temperature, nanoparticle concentration distribution, duration required for effective hyperthermia, and thermal damage to healthy tissues was examined. The numerical results reveal that the cell damage is greater in skin tissue than the healthy gland and fat tissues. For small injection time (tinj=0.4), the healthy gland tissue damage is greater for FePt nanoparticles than FeCrNbB nanoparticles. However, this trend is reversed for larger injection times (tinj=0.5, 0.6). For small magnetic field frequency (ω=5×104, 105), the maximum tissue temperature is higher with FePt nanoparticles than FeCrNbB nanoparticles, but a reversal in trend occurs for larger values of ω (ω=2×105). The findings show that the time duration required for effective magnetic hyperthermia and thermal damage to the healthy tissue regions is reduced with increased injected nanoparticle volume fraction, duration of nanoparticle injection, and the amplitude and frequency of the alternating magnetic field. Moreover, the effective hyperthermia duration and the healthy tissue damage are less for FePt nanoparticles than FeCrNbB nanoparticles.

Novel Class of Additive Manufactured NiTi-Based Hierarchically Graded Chiral Structure with Low-force Compressive Actuation for Elastocaloric Heat Pumps

Elastocaloric refrigeration is the most promising green solid-state refrigeration technology to replace conventional vapor compression refrigeration. The development direction of the elastocaloric component that acts as a key part of the elastocaloric refrigeration system contains a large elastocaloric effect, low stress hysteresis, high heat exchange performance, and small driving loads. The first two indices can be realized by material modification; however, the last two are more dependent on a novel porous structure design. However, the conventional porous structure is confronted with some critical challenges, including inhomogeneous stress, a significant hysteresis area, and deformation instability under the alternating cyclic loading. In this study, a NiTi-based elastocaloric structure model with chirality feature and gradient design as innovative elements was presented, bio-inspired by the structure of the plant tendrils. A quantitative optimization for the NiTi-based elastocaloric structure was performed using the finite element analysis (FEA) method. Strain and martensite volume fraction (MVF) fields during the loading and unloading processes were predicted and evaluated. The simulated results indicated that increasing the thickness gradient g1 of the strip or decreasing the diameter gradient g2 of the structure was beneficial to achieving more homogeneous strain and martensite distribution, simultaneously with higher energy storage efficiency and specific surface area. In addition, these NiTi-based chiral structures with different structural parameters were fabricated by laser powder bed fusion (LPBF). At the optimized structure parameters of g1 = 2 and g2 = 1.11, the LPBF-fabricated NiTi-based chiral structure could achieve an adiabatic temperature change ΔTad of 2.3 K, driving force of as low as 149.11 N, and |ΔTad/F| of as high as 15.42 K/kN at a recoverable compressive strain of 10%.

An accurate and efficient multiphase solver based on THINC scheme and adaptive mesh refinement

This paper presents an accurate and efficient multiphase solver which is developed based on THINC/QQ (THINC method with quadratic surface representation and Gauss quadrature) scheme and AMR (adaptive mesh refinement) technique in the framework of OpenFOAM. In order to make consistent interpolation after the mesh refinement, a novel algorithm is proposed for the algebraic mapping of the volume fraction field in the child cells, which significantly improves the geometric faithfulness of mapped interface particularly for curved surface. Second-order schemes are used for the spatial and temporal discretization of momentum equations which further enhances the solution accuracy compared with interFoam. Using THINC/QQ scheme with AMR technique in the multiphase simulation, the so-called thincFoam delivers high fidelity solutions in the vicinity of interface while largely improving the computational efficiency. As verified by various benchmark tests in 2D and 3D, such as bubble rising, dam-break and propagation of solitary wave, it convinces that the numerical results predicted by thincFoam are in excellent agreement with experimental data and other reference solutions. Thus, the present solver possesses a promising prospect in capturing complicated interfaces undergoing large deformations and topological changes for the simulation of nonlinear interaction between multiphase flows with solid structures.

MHD Stagnation Point of Blasius Flow for Micropolar Hybrid Nanofluid toward a Vertical Surface with Stability Analysis

This study investigates the magnetohydrodynamics of a micropolar fluid consisting of a hybrid nanofluid with mixed convection effects. By using the dimensionless set of variables, the resulting equations of ordinary differential equations are solved numerically using the bvp4c solver in MATLAB. In the present work, the water-based alumina–copper hybrid nanofluid is analytically modeled with modified thermophysical properties. The study reveals that the highest critical value of opposing flow is the hybrid nanofluid (ϕ1 = ϕ2 = 2%). By comparing the hybrid nanofluid with Cu–water nanofluid (ϕ1= 0%, ϕ2= 1%) as well as water (ϕ1= 0%, ϕ2= 0%), hybrid nanoparticle volume fraction enhances the dynamic viscosity performance and surface shear stress. In addition, the augmentation of the nanoparticle volume fraction and magnetic field parameter will increase the physical quantities Rex1/2 Cf, Rex Mx, and Rex−1/2 Nux. The result from the stability inquiry discloses that the first solution is more physically stable and trustworthy. It is proven that magnetohydrodynamics could contribute to controlling the fluid flow in a system, i.e., engineering operations and the medical field. In addition, this theoretical research can be a benchmark for experimental research.

Deep learning of interfacial curvature: A symmetry-preserving approach for the volume of fluid method

Estimation of interface curvature in surface-tension dominated flows is a remaining challenge in Volume of Fluid (VOF) methods. Data-driven methods are recently emerging as a promising alternative in this domain. They outperform conventional methods on coarser grids but diverge with grid refinement. Furthermore, unlike conventional methods, data-driven methods are sensitive to coordinate system and sign conventions, thus often fail to capture basic symmetry patterns in interfaces. The present work proposes a new data-driven strategy which conserves the symmetries in a cost-effective way and delivers consistent results over a wide range of grids. The method is based on artificial neural networks with deep multilayer perceptron (MLP) architecture which read volume fraction fields on regular grids. The anti-symmetries are preserved with no additional cost by employing a neural network model with input normalization, odd-symmetric activation functions and bias-free neurons. The symmetries are further conserved by height-function inspired rotations and averaging over several different orientations. The new symmetry-preserving MLP model is implemented into a flow solver (OpenFOAM) and tested against conventional schemes in the literature. It shows superior performance compared to its standard counterpart and has similar accuracy and convergence properties with the state-of-the-art conventional method despite using smaller stencil.

Sooting propensity and maturity of gasoline/anisole blends in a laminar coflow diffusion flame

Liquid oxygenated biofuels such as anisole have been used as additives, since they increase the octane number and improve spark-ignition engines’ performance. In this study, the sooting propensity of a gasoline surrogate, anisole, and gasoline/anisole mixture is quantified by measuring bidimensional fields of soot volume fraction, temperature and radiative heat flux in a coflow laminar flame using well-established non-intrusive optical diagnostics. The maturity of soot particles is also measured using innovative multiwavelength line-of-sight attenuation and emission measurements. Experimental measurements shows that increasing anisole content in fuel mixture results in a greatly enhanced soot volume fraction, while overall temperature is slightly decreased. In addition, maps of soot maturity index are reported based on the spectral dependence of soot optical properties with the amount of immature soot. Mature soot is found near the outer edge of the flame for the three flames, and mature soot content was found to decrease with increased anisole addition to the fuel mixture. In addition, high temperature zones were found to correlate with the presence of more graphitic compounds within the soot particles for the investigated fuels. The comprehensive dataset reported in this study provides rich information for a better understanding of soot formation processes, and for the development and validation of soot models in coflow laminar diffusion flames using complex fuels of interest for practical applications.

Assessment of scale-adaptive turbulence modeling in coupled CFD-PBM 3D flow simulations of disperse liquid-liquid flow in a baffled stirred tank with particular emphasis on the dissipation rate

The effect of scale-adaptive simulations (SAS) on the droplet size distribution (DSD) is assessed in a baffled stirred tank and compared with a classical statistical turbulence model in terms of the widely used shear-stress transport (SST) eddy-viscosity model. DSD predictions are obtained by 3D multiphase flow simulations coupled with a population balance model. Inclusion of a turbulent dispersion model in the SST model simulations leads to a more homogeneous volume fraction field but has no visible effect on the DSD. On the one hand, enhanced mixing by the SAS shows a broader and more homogeneous DSD throughout the tank than predicted by the SST model, corresponding to experimental trends. On the other hand, turbulence energy dissipation rate ε is considerably underestimated by the SAS, leading to less breakup activity, while coalescence is essentially unaffected. It is suggested that SAS should be improved with regard to a sounder ε prediction in future studies.

MFIX-Exa: CFD-DEM simulations of thermodynamics and chemical reactions in multiphase flows

MFIX-Exa is a CFD-DEM code for the numerical solution of chemically reacting multiphase flows (fluid and solids phases), specifically targeted for flows in complex reactor geometries. The fluid is modeled using a low Mach number formulation with a multicomponent ideal gas equation of state, which is imposed as a constraint of the velocity field. The fluid equations are discretized using an embedded boundary (EB) aware Godunov scheme with an approximate projection. The particles (that constitute the solids phase) are represented by a soft-sphere spring-dashpot model and evolved using a forward Euler method with subcycling. The fluid and particles models are coupled through a volume fraction field in addition to interphase mass, momentum, and energy transfer. The mathematical model and numerical approach are benchmarked against three different verification tests and validated with two separate tests. Also, a scaling analysis is provided. This manuscript represents the current state-of-the-art of MFIX-Exa and describes the major extensions to the previous work presented in Musser et al. (2021), including the Godunov time integration algorithm for the fluid phase and the inclusion of thermodynamics and chemistry modeling to both the fluid and solids phases.

Heat transfer characteristics of nanofluid under the action of magnetic field based on molecular dynamics and flow states

Theoretical analysis, numerical simulations, and experimental studies are used to comprehensively investigate the changes in the heat transfer characteristics of Fe3O4–water magnetic nanofluid under different types of magnetic fields and the heat transfer mechanism, providing new ideas for its practical application. By combining the fundamental conservation theorem and the Boussinesq approximation, dimensionless control equations have been established. The analysis of the variation pattern of the calculated values of the source terms under different boundary conditions, as well as the order of magnitude analysis, concludes that: the enhanced trend of Brownian motion and thermophoretic motion is the main reason for the enhanced heat transfer capability of the magnetic nanofluid; where the thermophoretic motion contributes slightly more to the heat transfer; the increase in Joule heat is the reason for the further enhancement of the heat transfer capability by the magnetic field. Volume fraction, temperature, and magnetic field strength are positively correlated with the average convective heat transfer coefficient. The reason for magnetic fields to enhance heat transfer is revealed by the deflection of the magnetic nanofluid by the magnetic body flow under local magnetic fields to form localized reflux. The alternating magnetic field further enhances the ability of magnetic fields to enhance heat transfer in magnetic nanofluids. Overall, the effect of the applied magnetic field on the motion of the magnetic nanoparticles causes the disruption of the thermal boundary layer, which is responsible for the enhanced heat transfer capacity of magnetic nanofluids.

Microscale experimental results and their implications for mesoscale modeling of damage initiation in cross-ply fiber reinforced composites

The results from a combined experimental and computational study to evaluate local in-plane variations of elastic properties (at the microscale fiber/matrix level) in mesoscale progressive failure analysis models of composites due to local fiber volume fraction variations are reported. A rectangular cross-ply specimen subjected to tensile loading is used as a case study in this investigation. Experimental results in support of understanding the correlation between local fiber volume fraction and in-plane strain field variations, by using specimens with small length scales is reported. A micromechanics computational model is used to understand and explain the experimental findings. The microscale finite element results suggest that the strain variations on the surface of the outer 90 plies prior to damage initiation are caused by local geometrical changes caused by the fibers non-uniformly packed and lying closest to the surface and not by the through-ply thickness local fiber volume fraction variations. Implications of this finding for homogenized mesoscale models for damage and failure are discussed.