Magnetic Volume Fraction Research Articles

Newtonian heating effect in pulsating magnetohydrodynamic nanofluid flow through a constricted channel: A numerical study

This article investigates the pulsatile flow of viscous incompressible MHD nanofluid in a rectangular channel. At the upper and lower walls, the channel has symmetrical constrictions. The goal is to analyze the heat transfer features of the nanofluid flow under the effect of the magnetic field and thermal radiation. Five different nanofluids, formed with nanoparticles of copper (Cu), magnetite (Fe3O4), silver (Ag), titanium oxide (TiO2), and single wall carbon nanotube (SWCNT) in the base fluid of water, are considered in the study. The unsteady governing equations are transformed using the vorticity-stream function approach. The solution is obtained using the finite difference technique (FDM). The effect of various flow controlling parameters on velocity, temperature, Nusselt, and skin-friction profiles is inspected by using graphs. Across the channel, graphs of vorticity, streamlines, and temperature distribution are also displayed. The thickness of the thermal boundary layer upsurges with escalating values of the magnetic field, radiation parameters, and solid volume fraction, whereas it declines with escalating values of the Strouhal and Prandtl numbers. The profiles are usually found to have a more regular pattern upstream of the constriction than that downstream of the constriction. At the throat of the constriction, the carbon nanotube-based nanofluid attains higher temperatures than the other nanofluids downstream of the constriction. However, in the lee of the constriction, silver-based nanofluid attains higher temperatures than the other nanofluids downstream of the constriction. The behavior, in most cases, is opposite upstream of the constriction. The findings of the study can be utilized to cure stenosis in blood vessels, design biomechanical devices, and employ flow pulsation to control industrial operations.

MHD Boundary Layer Flow Past an Exponentially Stretching Sheet with Darcy-Forchheimer Flow of Nanofluids

Objectives: To investigate an exponentially stretched sheet with a magnetic force to explore the Darcy-Forchheimer flow of a two-dimensional blood-based nanofluid and the effect of different relevant parameters of the fluid flow assumption for velocity and temperature profiles. Methods: Nanoparticles such as Ag, TiO2 and Fe with base fluid blood are being investigated. The governing equations of the problem, such as continuity, motion, and energy, are derived and translated into ordinary differential equations by employing appropriate optimization techniques. The bvp4c technique is used to perform numerical computations. The impacts of non-dimensional governing factors like the prandtl number (Pr), magnetic field parameter (M), Forchheimer number (Fr), porosity parameter (b ) and nanofluid volume fraction (ϕ ) are determined numerically and displayed through graphs. Tables illustrate and explain the local Nusselt number and skin friction coefficient. Findings: Velocity profile of Ag-blood, TiO2-blood and Fe-blood decreases and temperature profile increases for increasing values of Pr, b , M and Fr. For rising values of M, b , and Fr, the skin friction coefficient increases and the Nusselt number decreases, but the accelerating trend of ϕ exhibits a reversible trend. Novelty: The Darcy-Forchheimer flow of a two-dimensional blood-based nanofluid with a magnetic field is novel in the model. The (Ag-Blood, TiO2-Blood, Fe-Blood) nanofluid flow past an exponentially stretching surface is considered in the present study, while no one has considered these nanofluids for the same model. Keywords: MHD; Bloodbased nanofluid; Nanoparticles; Exponentially stretching surface; Darcy Forchheimer flow; Blood based nanofluid

Study on the microscopic model of magnetorheological fluids of three magnetic particles with different diameters

In this article, a micromechanical model of three-diameter magnetorheological fluids is established by analyzing the particle size of magnetic particles, based on the theory of magnetic dipoles, using mechanical and mathematical statistics method. To simplify the analysis of the problem, this study makes assumptions including: (1) Assume that the magnetic particle size in each cell is large: medium: small is 1:8:1, and the large particles and small particles are located at both ends of the cell; (2) During the shearing process, the slope angle of each chain obeys normal distribution. The oil-based magneto-rheological fluids with different volume fractions were also prepared to test the mechanical properties of the magneto-rheological fluids. By comparing the model with the experimental data, it is found that the micromechanical models of magnetorheological fluids with three different particle sizes were more accurate compared with the mechanical models of magnetorheological fluids with single-particle size at the same magnetic particle volume fraction, shear rate, and magnetic field strength, with an average optimization accuracy of 13.46%. The model can be used to improve the performance and accuracy of magnetorheological devices.

Unsteady flow of magnetohydrodynamic hybrid nanofluid over a stretching/shrinking sheet: Multiple solutions

The main goal of this article is to perform a heat transfer analysis of unsteady magnetohydrodynamic hybrid nanofluid flow over a stretching/shrinking sheet. The hybrid nanofluid is synthesized by adding two kinds of nano-sized particles. In this examination, TiO2 and Cu nano-sized particles are taken with water as a base fluid. Using an appropriate similarity transformation approach, a set of nonlinear equations is obtained from the governing equations of the current study. To solve the changed system, the Runge–Kutta–Fehlberg approach is applied combined with the shooting method. The obtained data is presented in graphs and tables. Here, dual solutions can be seen utilizing upper and lower division solutions particularly aimed at a specific domain of unsteadiness parameter. The skin friction coefficient parameter shows a considerable improvement. Whereas in the case of the shrinking sheet, larger values of the magnetic parameter and solid volume fraction results in a significant drop in the local heat transfer rate for the upper branch case, while the lower branch case shows a different pattern.

Numerical simulation of magnetorheological fluid with a combined DEM-IMB-LBM scheme

Magnetorheological fluid (MRF) is an intelligent multiphase fluid, and its property and morphology are affected by several internal and external forces. To investigate the microscopic behavior of MRF, a combined simulation scheme on the bases of the discrete element method (DEM), the immersed moving boundary (IMB) and the lattice Boltzmann method (LBM) is proposed, the magnetic forces between magnetic particles (MPs) are calculated by an inter-particle magnetic force model (IMFM). After verifying the simulation method by two benchmark tests, a series of MRF with different volume fractions are simulated by this combined method. The simulated results show that the microscopic variation of MPs in MRF can be obviously visualized. The randomly distributed MPs form chained-alignment structures consistent with the magnetic field direction. The results also reveal that the higher magnetic particle volume fraction is easier to form the chained-alignment structures.

Experimental Analysis on the Dependence of the Capacitance of Magnetorheological Fluids on Frequency

The capacitance characteristics of magnetorheological fluids (MRFs) were studied experimentally based on simulation analysis. The nonlinear relationship between the capacitance of MRFs and electric field frequency was measured by the self-made circuit device. The effects of magnetic induction intensity and particle volume fraction on the capacitance characteristics of MRFs were investigated. The results show that the nonlinear dependence of the capacitance of an MRF on frequency induced by the effect of tunnel current decreases with the increase in frequency. The capacitance of an MRF is directly related to the particle structures. The capacitance of the MRF with a chain particle structure is greater than that of the MRF with a random particle distribution. The smaller the clearance between the adjacent particles, the greater the capacitance of the MRF. The network particle structure and particle contact will reduce the capacitance of an MRF. The capacitance of an MRF increases with the increment of external magnetic field. The capacitance of an MRF with higher particle volume fraction is smaller than that of an MRF with lower particle volume fraction.

On the Yield Stress of Magnetorheological Fluids

• Effect of magnetic field and particle volume fraction are investigated experimentally. • MRFs with different particle concentration are tested through steady stress sweep test. • A nonlinear model is proposed for the yield stress of MRFs. • Model includes two parameters, covers a wide field range and captures magnetic saturation. • A modified form of the magnetic dipole model is also proposed. Magnetorheological fluids (MRFs) are a category of functional materials that exhibit magneto-mechanical coupling. These materials exhibit a reversible and instantaneous change from a free-flowing Newtonian fluid to a semi-solid state upon application of a magnetic field. In contrast to ordinary fluids, MRFs can tolerate shear stresses up to a yield value in the presence of a magnetic field. The yield stress strongly depends on intensity of the applied magnetic field and volume fraction of magnetic particles. As the yield stress is the most important parameter of an MRF and must be considered in the design of MR devices, in this work, effects of magnetic field and volume fraction of particles are investigated both experimentally and theoretically. MRF samples with the same carrier fluid but different particle concentrations are analyzed, and an empirical model is proposed for the yield stress of MRFs that covers a wide field strength range and also captures magnetic saturation of the MR fluids. Though the model is mathematically simple, it also includes the effect of particle concentration such that once calibrated, it can be utilized for different particle concentrations as well. Moreover, a modified form of the magnetic dipole model is proposed to model the yield stress of MRFs where an exponential distribution function is utilized to describe the arrangement of particle chains in the presence of a magnetic field. It is shown that, though the model has a simple mathematical formulation, it leads to a reasonable distribution of chains compared to previous similar models.

Significance of adding titanium dioxide nanoparticles to an existing distilled water conveying aluminum oxide and zinc oxide nanoparticles: Scrutinization of chemical reactive ternary-hybrid nanofluid due to bioconvection on a convectively heated surface

Abstract With the emphasis on the properties of titanium dioxide nanoparticles and numerous applications of chemical reactive distilled water due to bioconvection in the industries, nothing is known about the significance of adding titanium dioxide nanoparticles to an existing distilled water conveying aluminum oxide and zinc oxide nanoparticles when viscous dissipation, heat source, and higher buoyancy forces and thermal radiation are substantial. The governing partial differential equations that model the motion of both transport phenomena mentioned earlier were transformed into ordinary differential equations using appropriate similarity transmutations and solved with bvp4c (MATLAB built-in function). Multiple linear regression (i.e., a statistical tool used to explain outcomes related to engineering parameters of interest) was adopted for a deep scrutinization and exploration. The outcome of the analysis suggests that the thermal radiation parameter can be used to control the heat transferred via convection in the fluid flow. It is detected that the magnetic field parameter and volume fraction of nanoparticle parameters are useful to reduce the shear stress near the surface. The heat source ameliorates the fluid temperature, and the concentration of the fluid decreases with the rise in the chemical reaction parameter. Worthy to conclude that the Peclet and Schmidt number escalates the density number of motile microorganisms.

Group method analysis for blood‐Mn‐ZnFe2O4 flow and heat transfer under ferrohydrodynamics through a stretched cylinder

In this paper, a steady, viscous, incompressible, and electrically non‐conducting laminar flow of biomagnetic fluid, namely, the flow of blood with magnetic particles over a stretched cylinder in the presence of magnetic dipole, is studied. Since magnetic particles with low cytotoxicity can carry away unwanted reactive oxygen species and provide safeguard for biomedical applications, this study has immense applications in medical and bio‐engineering sections like cancer treatment, drug delivery, and magnetic resonance imaging (MRI). The problem is first analyzed by applying group theoretical method, namely, one parameter group method. The invariance property of system of partial differential equations (PDEs) under one parameter group method transformations yields the weeny generators. By using the basic theorem of one parameter group method including invariance conditions, the set of PDEs is converted into ordinary differential equations (ODEs), and consequently, the number of independent variables is reduced into one variable. Afterwards, the resulting coupled nonlinear set of ODEs is numerically solved by introducing an efficient numerical technique that based upon common finite difference with central differencing, a tridiagonal matrix manipulation, and finally, an iterative procedure. A comparative graphical analysis of velocity, temperature profiles, skin friction coefficient and rate of heat transfer for blood‐Mn‐ZnFe2O4 magnetic fluid has been carried out for various physical parameters such as ferromagnetic interaction parameter and magnetic particles volume fraction etc. The important findings from the present investigation are that the temperature of blood is enhanced for larger values of magnetic particles volume fraction and more effectively than pure blood. It is also found that blood velocity is increased as the ferromagnetic number increases. The skin friction coefficient is enhanced 132.22%, and the rate of heat transfer is increased by 5.86% by the application of magnetic field; whereas for particles volume fraction, skin friction decreases about 0.61%, and rate of heat transfer declines about 4%. Additionally, this study also discloses that the application of group theoretical method is justified in biomagnetic fluid dynamics especially research on blood flow and heat transfer, where the blood flow significantly influenced by the ferromagnetic number. A comparison has been also performed, and the results are found in excellent agreement with previous published in literature. The present study could be considered for magnetic driving of biologically suitable magnetic particles filled with medicine.

Multiple linear regression on bioconvective MHD hybrid nanofluid flow past an exponential stretching sheet with radiation and dissipation effects

The flow past a stretching sheet has been explored by many scientists for its application in metal spinning, drawing of plastic films, glass blowing, crystal growing, and cooling of filaments. In addition, the presence of microorganisms enhances the stability of the fluid that plays a significant role in biotechnology, bio-microsystems, and bio-nano coolant systems. Therefore, the dynamics of bioconvective MHD hybrid nanofluid (TiO2 and Ag in water) flow over an exponentially stretching permeable surface considering thermal radiation, heat generation, chemical reaction, porosity, and dissipative effects has been investigated. Apposite similarity variables are applied in transforming the modeled PDEs into a system of nonlinear ODEs and are then solved utilizing the finite-difference based bvp5c algorithm. It is observed that an increase in the porosity parameter ascends the temperature and descends the velocity. It is also noted that the temperature profile is proportional to augmentations in radiation parameter, magnetic field parameter, Eckert number, and volume fraction of TiO2 and Ag nanoparticles. The mass transfer rate and the motile density number increase with mounting values of chemical reaction parameter. Further, multiple linear regression has been utilized to statistically scrutinize the effect of pertinent parameters on drag coefficient and heat transfer rate.

Machine Learning Approach for Evaluation of Nanodefects and Magnetic Anisotropy in FePt Granular Films

This paper reports a machine learning approach for evaluating micromagnetic and microstructural parameters from demagnetization curves of FePt granular films for heat-assisted magnetic recording (HAMR) media. We developed a neural network to predict parameters of magnetic anisotropy and volume fractions of defects such as [200] misoriented grains, {111} twined variants, and disordered grains. The neural network was trained on a synthetic dataset of out-of-plane demagnetization curves that were simulated using the micromagnetic model constructed from actual nanostructure of a FePt-X HAMR medium. Predicted nanodefects agreed well with those estimated by synchrotron X-ray diffraction, and the demagnetization curve simulated with the predicted parameters accurately reproduced the experimental one. This work paves the way for a high-throughput magnetometry-based characterization of FePt granular media for its structural optimization toward higher areal density of HAMR.

An Experimental Validation Study on Ferrofluid Evaporation

The current research on the evaporation of ferrofluids mainly focuses on the characterization of ultra-low vapor pressure ferrofluids in vacuum and the theoretical analysis of the evaporation process. Few studies have focused on the experimental validation of the proposed evaporation rate equations and on the comparison of the differences in ferrofluid evaporation. In this study, based on the Bolotov’s model, an evaporation rate equation is deduced from the experimental model. The experimental study included a comparison of the evaporation, magnetic particle volume fraction, temperature, height of the fluid surface from the outlet, and magnetic field of a kerosene-based ferrofluid and its base carrier liquid. The prepared sample was evaporated in a test tube, and the evaporation rate was calculated by measuring the weight loss of the sample. The experimental results show that the evaporation rate of the base carrier liquid is higher than that of the ferrofluid. The smaller the volume fraction of the magnetic particles, the greater the evaporation rate. The magnetic particles play a key role in preventing evaporation of the base liquid. The higher the temperature, the smaller the deviation of the evaporation rate from the predicted value. The evaporation rates obtained by the two control groups at the height of the fluid surface from the outlet were lower than the predict value. The magnetic field had a certain promotional effect on the evaporation of the ferrofluid. The experimental results were consistent with the results obtained using Bolotov’s model. This research validates Bolotov’s model and shows that the model is somewhat biased but still responds well to different variables.

Computer-Aided Formulation of Magnetic Pastes for Composition Improvement for Power Magnetics

The size of magnetic components can be reduced with novel designs, but the intricate structures are difficult to make due to the limited sets of conventional magnetic core geometries and materials. Magnetic pastes have the flexibility of forming complicated structures with a pressure-less and low-temperature molding process, and are ideal for making the novel magnetic designs. The conventional approach of developing magnetic pastes involves time-consuming experimental iterations to determine the optimal composition parameters. Instead of relying on the trial-and-error efforts, we explored a computer-aided approach to guiding the magnetic paste development by creating material’s microstructure by discrete element method (DEM) and studying the property by finite element method (FEM). From a starting formula with two different-sized spherical powders, we improved the composition guided by DEM and FEM, and studied the magnetic permeability versus two variables: powder mixing ratio and magnetic volume fraction. The simulated permeability agreed well with the experimental data with an average error of only 10%. With the computer-aided formulation methodology demonstrated in this work, one can develop magnetic pastes with minimum experimental efforts and explore different compositions to meet various magnetic design needs.

Lattice Boltzmann-based numerical analysis of nanofluid natural convection in an inclined cavity subject to multiphysics fields

This research conducts a study of natural convection heat transfer (NCHT) in a nanofluid under a magnetic field (MF). The nanofluid is in a cavity inclined at an angle of 45°. The MF can take different angles between 0° and 90°. Radiative heat transfer is present in the cavity in volumetric form. There are two hot semicircles, similar to two half-pipes, on the bottom wall. The top wall is kept cold. The side walls and parts of the bottom wall, except the pipes, have been insulated. The lattice Boltzmann method has been used for the simulation. The studied parameters are the Rayleigh number (in the range 103–106), magnetic field angle, radiation parameter (in the range 0–2), and nanoparticle volume fraction (in the range 0–5%). The generated entropy has been studied as the NCHT. The results indicate that adding nanoparticles improves heat transfer rate (HTR). Moreover, the addition of volumetric radiation to the cavity enhances the Nusselt number by 54% and the generated entropy by 12.5%. With an augmentation in the MF angle from 0° to 90°, HTR decreases and this decrease is observed mostly at higher Rayleigh numbers. An augmentation in the Ra increases NCHT and entropy generation. Indeed, a rise in the Ra from 103 to 106 increases HTR by almost sixfold.

Investigation on magnetic force and buoyancy force on flow and heat transfer of Al2O3-water nanofluid at various temperature-dependent thermophysical models by a novel PLBM

A novel preconditioned lattice Boltzmann method (PLBM) is applied to investigate the thermo-hydrodynamic characteristics of Al2O3-water nanofluid with various temperature-dependent thermophysical properties and slip boundary conditions in a microchannel. Also, the effects of a magnetic field force, buoyancy force, and volume fraction of nanoparticles are analyzed, respectively. The theoretical level confirms that the convergence performance of the PLBM is greatly improved at large Reynolds numbers compared to the original LBM. Numerical results show that the Koo & Kleinstreuer model has the largest average shear stress and average Nusselt number. Among all the physical models considered, these two values are approximately 1.05 times and 1.2 times of the values by the Maxwell & Brinkmann model, respectively. Once the magnetic field is considered, the average shear stress is increased twice and the average Nusselt number increases by about 10% and further by about 20% at higher buoyancy forces. The growth of these two values gradually slows down when the volume fraction of nanoparticles exceeds 2%. The heat transfer process makes the largest contribution to entropy generation when the magnetic field force is not considered. Accordingly, it will dominate the irreversible loss due to the strong shear stress once the magnetic field force is involved in the heat transfer process.

Steady Squeezing Flow of Magnetohydrodynamics Hybrid Nanofluid Flow Comprising Carbon Nanotube-Ferrous Oxide/Water with Suction/Injection Effect.

The main purpose of the current article is to scrutinize the flow of hybrid nanoliquid (ferrous oxide water and carbon nanotubes) (CNTs + FeO/HO) in two parallel plates under variable magnetic fields with wall suction/injection. The flow is assumed to be laminar and steady. Under a changeable magnetic field, the flow of a hybrid nanofluid containing nanoparticles FeO and carbon nanotubes are investigated for mass and heat transmission enhancements. The governing equations of the proposed hybrid nanoliquid model are formulated through highly nonlinear partial differential equations (PDEs) including momentum equation, energy equation, and the magnetic field equation. The proposed model was further reduced to nonlinear ordinary differential equations (ODEs) through similarity transformation. A rigorous numerical scheme in MATLAB known as the parametric continuation method (PCM) has been used for the solution of the reduced form of the proposed method. The numerical outcomes obtained from the solution of the model such as velocity profile, temperature profile, and variable magnetic field are displayed quantitatively by various graphs and tables. In addition, the impact of various emerging parameters of the hybrid nanofluid flow is analyzed regarding flow properties such as variable magnetic field, velocity profile, temperature profile, and nanomaterials volume fraction. The influence of skin friction and Nusselt number are also observed for the flow properties. These types of hybrid nanofluids (CNTs + FeO/HO) are frequently used in various medical applications. For the validity of the numerical scheme, the proposed model has been solved by another numerical scheme (BVP4C) in MATLAB.

Spin order and fluctuations in the EuAl4 and EuGa4 topological antiferromagnets: A μSR study

We report on systematic muon-spin rotation and relaxation ($\mu$SR) studies of the magnetic properties of EuAl$_4$ and EuGa$_4$ single crystals at a microscopic level. Transverse-field $\mu$SR measurements, spanning a wide temperature range (from 1.5 to 50 K), show clear bulk AFM transitions, with an almost 100% magnetic volume fraction in both cases. Zero-field $\mu$SR measurements, covering both the AFM and the paramagnetic (PM) states, reveal internal magnetic fields $B_\mathrm{int}(0) = 0.33$ T and 0.89 T in EuAl$_4$ and EuGa$_4$, respectively. The transverse muon-spin relaxation rate $\lambda_\mathrm{T}$, a measure of the internal field distribution at the muon-stopping site, shows a contrasting behavior. In EuGa$_4$, it decreases with lowering the temperature, reaching its minimum at zero temperature, $\lambda_\mathrm{T}(0) = 0.71$ $\mu$s$^{-1}$. In EuAl$_4$, it increases significantly below $T_\mathrm{N}$, to reach 58 $\mu$s$^{-1}$ at 1.5 K, most likely reflecting the complex magnetic structure and the competing interactions in the AFM state of EuAl$_4$. In both compounds, the temperature-dependent longitudinal muon-spin relaxation $\lambda_\mathrm{L}(T)$, an indication of the rate of spin fluctuations, diverges near the onset of AFM order, followed by a significant drop at $T < T_\mathrm{N}$. In the AFM state, spin fluctuations are much stronger in EuAl$_4$ than in EuGa$_4$, while being comparable in the PM state. The evidence of robust spin fluctuations against the external magnetic fields provided by $\mu$SR may offer new insights into the origin of the topological Hall effect and the possible magnetic skyrmions in the EuAl$_4$ and EuGa$_4$ compounds.

Acoustic scattering properties of multilayer membrane structured magnetic microbubbles

Normal ultrasound contrast agents (UCAs) loaded with magnetic nanoparticles are called magnetic microbubbles (MMBs), which can be used in multimodal imaging, thrombolytic therapy, and targeted drug delivery. The MMBs are often studied by &lt;i&gt;in situ&lt;/i&gt; measurement techniques, however scattering model is the basis of inversion techniques. Therefore, we develop a scattering model of multilayer structured MMBs with magnetic fluid inner layer and phospholipid outer layer, in which outer layer’s viscoelasticity and the effect of nanoparticles on inner layer’s density are considered, while scattered sound fields in each region are obtained by solving normal series. The MMB model is compared with other bubbles, and its acoustic scattering characteristics are analyzed numarically, including the effects of radius, magnetic nanoparticle volume fraction, inner layer thickness and outer layer characteristics parameters. The results show that when the volume fraction &lt;i&gt;α&lt;/i&gt; of magnetic nanoparticles in the inner layer does not exceed 0.1, magnetic nanoparticles have a two-sided effect on resonant scattering of MMBs, depending mainly on its radius, and the bubble has a critical radius value. If the radius of MMBs exceeds this critical value, the particles will enhance scattering, on the contrary, if the radius of MMBs is smaller than this critical value, the particles will reduce scattering; for a given microbubble radius, when &lt;i&gt;α&lt;/i&gt; is not more than 0.1, the larger the &lt;i&gt;α&lt;/i&gt; value&lt;i&gt;,&lt;/i&gt; the stronger the resonant scattering of MMBs will be; the smaller the thickness of the inner film layer and outer film layer or the Larmé constant, the stronger the scattering will be. This study provides a theoretical guidance for the optimal structural design of MMBs and its &lt;i&gt;in situ&lt;/i&gt; monitoring and therapeutic applications.

IMPACT OF TWISTED DUCTS WITH DIFFERENT TWIST RATIOS ON HEAT TRANSFER AND FLUID CHARACTERISTICS OF NiO/WATER NANOFLUID FLOW UNDER MAGNETIC FIELD EFFECT

Laminar forced convection of NiO/water nanofluid in a twisted square duct has been investigated numerically under the effect of an external magnetic field (B = 0 G, 450 G, and 550 G) in the Reynolds number range of 500 ≤ Re ≤ 2000. Four different twist ratios (D/L = 0.0, 1.0, 1.5, and 2.0) of the square duct have also been examined. The nanoparticle volume fractions (NPVF) of NiO/water nanofluid have been selected between 0.6 vol.% and 2.5 vol.%. The effects of the magnitude of the magnetic field (MF), twist ratio, Reynolds number, and nanoparticle volume fraction on thermohydraulic performance have been examined by using the homogeneous model in the numerical analyses. The results of the numerical computations have been reported with average Nusselt number Nu, pressure loss, average Darcy friction factor f, and performance evaluation criterion (PEC). The highest heat transfer increment by 20% has been achieved at D/L = 2.0 with the highest nanoparticle volume fraction, namely, 2.5 vol.% NiO/water nanofluid, compared to the case of distilled water (DW) flowing in a plain duct (PD). In addition, it was determined that the magnetic field effect increases the convective heat transfer in the twisted duct with D/L = 2.0 up to 35% compared to the cases in the absence of a magnetic field at D/L = 2.0. Among all cases, the highest PEC has been obtained with 2.5 vol.% NiO/water nanofluid flowing in the twisted duct with the twist ratio D/L = 2.0.

Combined Effects of Sequential Velocity and Variable Magnetic Field on the Phase Change Process in a 3D Cylinder Having a Conic-Shaped PCM-Packed Bed System

Effects of sequential velocity and variable magnetic field on the phase change during hybrid nanofluid convection through a 3D cylinder containing a phase-change material packed bed (PCM-PB) system is analyzed with the finite element method. As the heat transfer fluid, 40% ethylene glycol with hybrid TiO2-Al2O3 nanoparticles is considered. Impacts of the sequential velocity parameter (K, between 0.5 and 1.5), geometric factor of the conic-shaped PCM-PB (M, between 0.2 and 0.9), magnetic field strength (Ha number between 0 and 50) and solid volume fraction of hybrid nanoparticles (vol.% between 0.02% and 0.1%) on the phase change dynamics are explored. Effects of both constant and varying magnetic fields on the phase change process were considered. Due to the increased fluid velocity at the walls, the phase change becomes higher with higher values of the sequential velocity parameter (K). There is a 21.6% reduction in phase transition time (tF) between the smallest and highest values of K both in the absence and presence of a constant magnetic field. The value of tF is reduced with higher magnetic field strength and the amount of reduction depends upon the sequential velocity parameter. At K = 1.5, the reduction amount with the highest Ha number is 14.7%, while it is 26% at K = 0.5. When nanoparticle is loaded in the base fluid, the value of tF is further reduced. In the absence of a magnetic field, the amount of phase-transition time reduction is 6.9%, while at Ha = 50, it is 11.7%. The phase change process can be controlled with varying magnetic field parameters as well. As the wave number and amplitude of the varying magnetic field are considered, significant changes in the tF are observed.