Volume Fraction Field Research Articles

Numerical simulations on effects of oxygen concentration on the structure and soot formation in a two-dimensional axisymmetric laminar C2H4/(O2–CO2) diffusion flame

In this paper, based on the oxy-fuel and dry product cycle combustion as an application background, using the CoFlame laminar flame procedures, we simulated numerically the effects of oxygen concentration on flame structure, temperature field, soot volume fraction field and soot formation process in a two-dimensional axisymmetric C2H4 diffusion flame for an oxygen concentration of O2–CO2 atmosphere of 21%, 30%, 40% and 50%, respectively. The results showed that the flame height was decreased and the peaks of flame temperature, polycyclic aromatic hydrocarbons (PAHs) concentration and soot nucleation rate proved a logarithmic growth trend with an increase in oxygen concentration of O2–CO2 oxidizing agent. For the soot volume fraction maximum (fVmax), soot surface growth rate and soot oxidation rate showed an exponential growth trend because the leading role was the enhancement of the PAHs concentration, the soot nucleation rate and the soot surface growth rate. While the soot oxidation rate was also enhanced obviously, it was smaller than the soot surface growth rate in the soot surface growth area.

Effects of nanoparticles volume fraction and magnetic field gradient on the mixed convection of a ferrofluid in the annulus between vertical concentric cylinders

In this paper, the thermomagnetic convection of magnetite-water ferrofluid is numerically investigated in the three-dimensional space between two vertical concentric cylinders under the influence of an external magnetic field. The main objective is to study the effect of volume fraction of the magnetic nanoparticles (0.01≤αp≤0.06) with the diameter of 10 nm and positive and negative gradients of the magnetic field (-5×105A/m2≤G≤5×105A/m2) on the hydrothermal behavior of the ferrofluid flow. For this purpose, the two-phase mixture model and the finite volume method are used to simulate the hydrodynamics and thermal behavior of the ferrofluid flow. The simulations are performed for a Reynolds number of 20, Grashof number of 10000, and outer to inner diameter ratio of 2.5. The numerical results indicate that the Kelvin force increases by increasing the volume fraction, decreasing the ferrofluid temperature and increasing the magnetic field gradient. In the presence of an external magnetic field with negative gradient, the skin friction coefficient on the inner wall is enhanced by increasing the volume fraction and the magnetic field gradient but on the outer wall, it decreases by increasing them. Besides, the Nusselt number increases with the increase in the volume fraction and the magnetic field gradient. In addition, positive gradient magnetic fields result in reducing the Nusselt number and friction coefficient on the inner wall, while they increase the friction coefficient on the outer wall.

Fundamental solution of the system of equations of pseudo oscillations in the theory of thermoelastic diffusion materials with double porosity

PurposeThe purpose of this paper to construct the fundamental solution of partial differential equations in the generalized theory of thermoelastic diffusion materials with double porosity.Design/methodology/approachThe paper deals with the study of pseudo oscillations in the generalized theory of thermoelastic diffusion materials with double porosity.FindingsThe paper finds the fundamental solution of partial differential equations in terms of elementary functions.Originality/valueAssuming the displacement vector, volume fraction fields, temperature change and chemical potential functions in terms of oscillation frequency in the governing equations, pseudo oscillations have been studied and finally the fundamental solution of partial differential equations in case of pseudo oscillations in terms of elementary functions has been constructed.

Probing the local radiative quenching during the transition from a non-smoking to a smoking laminar coflow ethylene/air non-premixed flame

This paper experimentally documents the transition from the “closed-tip” flame configuration to the “open-tip” one that a laminar axisymmetric coflow ethylene/air non-premixed flame experiences with increasing the fuel flow rate at the smoke point in terms of soot temperature and volume fraction distributions. To this end, the two-dimensional soot temperature and volume fraction fields are measured by the two-color Modulated Absorption/Emission (2C-MAE) technique. The MAE setup has been specifically extended to a third spectral range centered at a lower wavelength (405 nm). With this new 3C-MAE technique, information on the level of scattering attributed to soot particles can be obtained. The experimental investigations are combined with radiative heat transfer computations to gain a comprehensive understanding of the radiative quenching of soot oxidation that happens at the flame tip responsible for soot release from the flame at the smoke point. In addition, the field of spectral scattering coefficient at 405 nm can be estimated, confirming that the non-scattering approximation is valid within the context of radiative models in this kind of flame. As a result, numerical simulations implementing radiative models without scattering should be able to decently capture the transition at the smoke point. Since the simulation of such a transition is crucial to the control of carbonaceous nanoparticles release process from flames, an original contribution of the present paper to this challenge is the supplemental material that contains the measured two-dimensional fields of both soot temperature and volume fraction.

Forced vibrations of a thermoelastic double porous microbeam subjected to a moving load

The present paper deals with forced vibrations of a homogeneous, isotropic thermoelastic double porous microbeam subjected to moving load, in context of Lord-Shulman theory of thermoelasticity with one relaxation time. The Laplace transform has been applied to obtain expressions for the axial displacement, lateral deflection, volume fraction field and temperature distribution. A numerical inversion technique has been used to recover the resulting quantities in the physical domain. Effects of velocity and time parameters are shown graphically by plotting axial displacement, lateral deflection, volume fraction field and temperature distribution against distance. Some particular cases are also deduced.

Fundamental solution of steady oscillations for porous materials with dual-phase-lag model in micropolar thermoelasticity

This article deals with the study of propagation of plane waves in an isotropic thermoelastic medium for porous materials with the linear theory of micropolar thermoelasticity. The problem is treated in the context of dual-phase-lag model of thermoelasticity. It is found that, for one-dimensional model, there exists three longitudinal waves, namely elastic (E-mode), thermal (T-mode), and volume fraction (V-mode) in addition to transverse waves which get decoupled from rest of the motion and not affected by thermal and volume fraction fields. In case of steady oscillations, the fundamental solution of the system of differential equations in terms of elementary functions has been constructed. The phase velocity and attenuation coefficient of these waves are computed numerically and presented graphically.

Effect of magnetic field on the hydrodynamic and heat transfer of magnetite ferrofluid flow in a porous fin heat sink

Abstract The present study numerically investigates the effects of a uniform external magnetic field and porous fins on convective heat transfer and pressure drop of magnetite ( F e 3 O 4 /water) nanofluid in a heat sink. Effects of volume fraction, porosity, Reynolds number, and magnetic field strength on the performance of the heat sink are studied. Results indicate that heat transfer increases at high volume fractions, fin porosities and magnetic field intensities and decreases with the Reynolds number. A 13% enhancement of heat transfer is obtained for the heat sink with solid fins by using ferrofluid compared to the pure water flow. This value grows up to 35% by using porous fins and imposing magnetic field to the heat sink. Moreover, using porous fins is shown to decrease the pressure drop while the magnetic field effect is not considerable. Therefore, it is concluded that the proposed methods result in a remarkable heat transfer enhancement while decreasing the pressure drop.

Fundamental solution of steady oscillations in thermoelastic medium with voids

ABSTRACT The article deals with the study of plane wave propagation in the thermoelastic medium in the presence of voids. The problem is considered in the context of three-phase-lag model of generalized thermoelasticity. There exists three longitudinal waves, namely elastic (E-mode), thermal (T-mode) and volume fraction (V-mode) in addition to transverse waves which get decoupled from the rest of motion and not affected by thermal and volume fraction fields. The fundamental solution of the system of differential equations in case of steady oscillations in terms of the elementary functions has been constructed. The phase velocity and attenuation coefficient of these waves are computed numerically and presented graphically.

Effective Geometric Algorithms for Immersed Boundary Method Using Signed Distance Field

We present three algorithms for robust and efficient geometric calculations in the context of immersed boundary method (IBM), including classification of mesh cells as inside/outside of a closed surface, projection of points onto a surface, and accurate calculation of the solid volume fraction field created by a closed surface overlapping with a background Cartesian mesh. The algorithms use the signed distance field (SDF) to represent the surface and remove the intersection tests, which are usually required by other algorithms developed before, no matter the surface is described in analytic or discrete form. The errors of the algorithms are analyzed. We also develop an approximate method on efficient SDF field calculation for complex geometries. We demonstrate how the algorithms can be implemented within the framework of IBM with a volume-average discrete-forcing scheme and applied to simulate fluid–structure interaction problems.

Response of Thermoelastic Interactions in Micropolar Porous Circular Plate with Three Phase Lag Model

Abstract The present study deals with a homogeneous and isotopic micropolar porous thermoelastic circular plate by employing eigenvalue approach in the three phase lag theory of thermoelasticity due to thermomechanical sources. The expressions of components of displacements, microrotation, volume fraction field, temperature distribution, normal stress, shear stress and couple shear stress are obtained in the transformed domain by employing the Laplace and Hankel transforms. The resulting quantities are obtained in the physical domain by employing the numerical inversion technique. Numerical computations of the resulting quantities are made and presented graphically to show the effects of void, phase lags, relaxation time, with and without energy dissipation.

A Two Dimensional Axisymmetric Thermoelastic Diffusion Problem of Micropolar Porous Circular Plate with Dual Phase Lag Model

Abstract In the present work, we consider a two dimensional axisymmetric problem of micropolar porous circular plate with thermal and chemical potential sources in the context of the theory of dual phase lag generalized thermoelastic diffusion. The potential functions are used to analyze the problem. The Laplace and Hankel transforms techniques are used to find the expressions of displacements, microrotation, volume fraction field, temperature distribution, concentration and stresses in the transformed domain. The inversion of transforms based on Fourier expansion techniques is applied to obtain the results in the physical domain. The numerical results for resulting quantities are obtained and depicted graphically. Effect of porosity, LS theory and phase lag are presented on the resulting quantities. Some particular cases are also deduced.

Improved dielectric constant and energy density of P(VDF-HFP) composites using NBT-xST (x=0, 0.10, 0.26) whiskers

The high-performance energy-storage dielectric capacitors are increasingly important due to their wide applications in high power electronics. Here, we fabricated a novel P(VDF-HFP)-based capacitor with surface-modified NBT-[Formula: see text]ST ([Formula: see text], 0.10, 0.26) whiskers, denoted as Dop@NBT-[Formula: see text]ST/P(VDF-HFP). The influences of ST content, fillers’ volume fraction and electric field on the dielectric properties and energy-storage performance of the composites were investigated systematically. The results show that the dielectric constant monotonously increased with the increase of ST content and fillers’ volume fraction. The composite containing 10.0 vol% NBT-0.26ST whiskers possessed a dielectric constant of 39 at 1[Formula: see text]kHz, which was 5.6 times higher than that of pure P(VDF-HFP). It was noticed that the D-E loops of the composites became thinner and thinner with the increase of ST content. Due to the reduced remnant polarization, the composite with 5.0 vol% NBT-0.26ST whiskers achieved a high energy density of 6.18[Formula: see text]J/cm3 and energy efficiency of approximately 57% at a relatively low electric field of 200[Formula: see text]kV/mm. This work indicated that NBT-0.26ST whisker is a kind of potential ceramic filler in fabricating the dielectric capacitor with high discharged energy density and energy efficiency.

Exploration of activation energy and binary chemical reaction effects on nano Casson fluid flow with thermal and exponential space-based heat source

PurposeThe purpose of this paper is to explore the effects of binary chemical reaction and activation energy on nano Casson liquid flow past a stretched plate with non-linear radiative heat, and also, the effect of a novel exponential space-dependent heat source (ESHS) aspect along with thermal-dependent heat source (THS) effect in the analysis of heat transfer in nanofluid. Comparative analysis is carried out between the flows with linear radiative heat process and non-linear radiative heat process.Design/methodology/approachA similarity transformation technique is utilised to access the ODEs from the governed PDEs. The manipulation of subsequent non-linear equations is carried out by a well-known numerical approach called Runge–Kutta–Fehlberg scheme. Obtained solutions are briefly discussed with the help of graphical and tabular illustrations.FindingsThe effects of various physical parameters on temperature, nanoparticles volume fraction and velocity fields within the boundary layer are discussed for two different flow situations, namely, flow with linear radiative heat and flow with non-linear radiative heat. It is found that an irregular heat source/sink (ESHS and THS) and non-linear solar radiation play a vital role in the enhancement of the temperature distributions.Originality/valueThe problem is relatively original to study the effects of activation energy and binary chemical reaction along with a novel exponential space-based heat source on laminar boundary flow past a stretched plate in the presence of non-linear Rosseland radiative heat.

Effect of liquid bridging on bubbles injected into a fluidized bed: A magnetic resonance imaging study

Rapid magnetic resonance imaging was used to take snapshots of solids volume fraction and particle velocity fields in an incipiently fluidized bed with single bubbles injected under both dry and wet conditions. Under wet conditions, cohesive liquid bridges formed between particles, altering the flow such that bubbles became flatter as compared to dry cases, and in some cases, the bubbles split or disintegrated entirely. The alteration in bubble behavior can be attributed to liquid bridging causing an increased heterogeneity in the roof of the bubble, which decreases the drag force on particles in the roof such that the gas flow through the roof can no longer support the weight of the particles in the roof. Quantification of the change in bubble behavior shows that increasing liquid loading has a much stronger effect on bubble behavior than increasing liquid viscosity, and liquid bridging affects small bubbles more than large bubbles.

Variable viscosity effects on third-grade liquid flow in post-treatment analysis of wire coating in the presence of nanoparticles

PurposeThe features of coated wire product are measured by the flow and heat transport occurring in the interior of dies. Therefore, an understanding of characteristics of polymers momentum, heat mass transfer and wall shear stress is of great interest. Enhancement of heat transfer rate is fundamental need of wire coating process. Therefore, this study aims to investigate the effect of suspended nanoparticles in heat and mass transport phenomena of third-grade liquid in post-treatment of wire coating process. Buongiorno model for nanofluid is adopted. Two cases of temperature dependent viscosity are considered.Design/methodology/approachThe governing equations are modelled with the help of steady-state conservation equations of mass, momentum, energy and nanoparticle concentration. Some appropriate dimensionless variables are introduced. Numerical solutions for the nonlinear problem are developed through Runge–Kutta–Fehlberg technique. The outcome of sundry variables for dimensionless flow, thermal and nanoparticle volume fraction fields are scrutinised through graphical illustrations.FindingsThe study’s numerical results disclose that the force on the total wire surface and shear stress at the surface in case of Reynolds Model dominate Vogel’s Model case. Impact of nanoparticles is constructive for force on the total wire surface and shear stress at the surface. The velocity of the coating material can be enhanced by the non-Newtonian property.Practical implicationsThis study may provide useful information to improve the wire coating technology.Originality/valueEffect of nanoparticles in wire coating analysis by using Brownian motion and thermophoresis slip mechanisms is investigated for the first time. Two different models for variable viscosity are used.

Effect of initial stress and Hall current on a magneto-thermoelastic porous medium with microtemperatures

In this paper, the effect of initial stress on a thermoelastic porous medium with microtemperatures in the presence of magnetic field taking Hall current into account is investigated. The medium is permeated by a strong transverse magnetic field imposed perpendicularly on the displacement plane so the induced electric field is neglected. The normal mode analysis is used to obtain the exact expressions for displacement components, normal conduction current density field, transverse conduction current density field, microtemperature components, heat flux moments, stress components, temperature distribution and change in the volume fraction field. The variations of the considered variables with the horizontal distance are illustrated graphically. The results of comparisons we obtained were with and without initial stress and Hall current effect. Some particular cases of special interest have been deduced from the present investigation.

The influence of magnetic field on heat transfer of magnetic nanofluid in a double pipe heat exchanger proposed in a small-scale CAES system

Globally, the integration of renewable energy (which has an intermittent nature) into the power system requires the system operators to improve the system performance to be able to effectively handle the variations of the power production in order to balance the supply and demand. This problem is seen as a major obstacle to the expansion of renewable energy if it is not handled in a suitable way. Efficient electricity storage technology is one of the feasible solutions. The current study proposes Fe3O4/water nanofluid under magnetic field as the secondary fluid in the proposed double pipe heat exchanger before the cavern. The heat of compressed air is absorbed by the secondary fluid and it is stored in an isolation tank. This stored fluid is used to warm up the air that leaves the cavern for expanding in the turbine. The results demonstrated that increasing the mass flow rate of secondary fluid decreases the cavern temperature. Also, the value of convective heat transfer of ferrofluid increases when the volume fraction of nanoparticle as well as magnetic field increases. Furthermore, increasing the volume fraction and magnetic field increases the pressure drop and friction factor of ferrofluid.

Research on the Effect of Soot Self-Absorption on Flame Multispectral Radiation Reconstruction

In this paper, an iterative multiwavelength method is proposed for the reconstruction of soot temperature and volume fraction fields in an axisymmetric flame with absorbing, emitting participating media. The Tikhonov regularized method is employed to solve the ill-posed matrix, by which the local radiative source term of two-dimensional space elements are obtained. The effects of the absorption term and the quantity of wavelength selected on the accuracy of reconstruction were evaluated quantitatively. When comparing with the two-color method, the present inversion results show that the accuracy of the multiwavelength method is better and the inversion range is larger than, even with external noise.

Laminar ferrofluid heat transfer in presence of non-uniform magnetic field in a channel with sinusoidal wall: A numerical study

This research is allocated to numerical study of two dimensional laminar forced convective heat transfer of ferrofluid (water and Fe3O4) in the presence of a non-uniform magnetic field in a channel with a sinusoidal corrugated wall. The hydrodynamic and thermal behavior of the ferrofluid is examined using the mixture model and the finite volume method. The effects of an increase in wavy channel amplitude, volume fraction, Reynolds number, and negative magnetic field gradient on the hydrodynamic and thermal behaviors are investigated and discussed. Nusselt number is found to increase as wave amplitude, volume fraction of nanoparticles, Reynolds number, or negative magnetic field gradient increase. The negative magnetic field gradient increases the pump work with a greater effect at lower Reynolds numbers. The results of this research can be utilized to enhance heat transfer in heat exchangers and to increase their efficiency.

Broadband modulated absorption/emission technique to probe sooting flames: Implementation, validation, and limitations

A new optical setup and its associated post-processing have been designed in an effort to map soot related quantities in an axisymmetric flame spreading over solid samples in microgravity environment where setup compactness constraints are stringent. Extending the well-established spectral modulated absorption/emission (S-MAE) technique that uses lasers as light sources together with a sophisticated optical arrangement, LEDs have been associated with broadband optics to enable the broadband modulated absorption/emission (B-MAE) technique. The design and the cautious assessment of the original B-MAE setup are reported in the present paper. Algorithms that need to be reformulated for broadband integration are first validated retrieving both two-dimensional soot temperature and volume fraction fields produced by numerical simulations. Then, these fields are measured with both B-MAE and S-MAE techniques in a largely documented steady laminar non-premixed coflow ethylene/air flame established at normal gravity. Thus, outputs delivered by the B-MAE technique can be compared with those obtained with the S-MAE setup. Both soot temperature and volume fraction are shown to be decently measured by the B-MAE technique. As the spread of the non-buoyant flames to be investigated in the near future is especially driven by radiative heat transfer, the discrepancies between both techniques outputs are commented in the light of the fields of local radiative loss computed from the fields measured by both techniques. As a result, the fields delivered by the B-MAE technique are expected to provide ground-breaking insights into the control of flame spread in the absence of buoyancy, therefore manned spacecraft fire safety.