Magnetic Field Inclination Angle Research Articles

Origin and nature of the emissive sheath surrounding hot tungsten tokamak surfaces

The accurate description of the emitted current that escapes from hot tungsten surfaces is essential for reliable predictions of the macroscopic deformation due to melt motion induced by fast transient events. A comprehensive analytical electron emission model is developed and its implementation in the particle-in-cell 2D3V code SPICE2 is discussed. The properties of emissive sheaths of present tokamaks, where thermionic emission is strongly suppressed by space-charge effects and by prompt re-deposition, are reviewed for arbitrary magnetic field inclination angles. The unique characteristics of emissive sheaths that emerge during ITER ELMs, where weakly impeded thermionic emission is coupled with field emission and competes with electron-induced emission, are revealed. The first ITER simulations are reported for normal inclinations. • The properties of emissive sheaths relevant for present day tokamaks are reviewed. • A comprehensive electron emission model has been implemented in the SPICE2 PIC code. • Electron-induced electron emission is revealed to be important during ITER ELMs. • Thermionic emission is revealed to be coupled to field emission during ITER ELMs.

Magnetic field effect on double-diffusion with magnetic and non-magnetic nanofluids

Magnetic nanofluids also are known as ferrofluids behave differently under magnetic field effect in comparison to non-magnetic nanofluids. The inclusion of magnetic forces term into the governing equations of magnetic media gives rise to the magnetohydrodynamics of magnetic nanofluids, also named as ferrohydrodynamics. This ferrohydrodynaimcs claims promising applications Rosensweig (1985)[1] with the field of new phenomena Berkovsky and Bashtovoy (1996)[2]. In the present numerical study, 2D laminar steady governing equations for double-diffusive natural convection with inclined magnetic forces for magnetic nanofluid Fe3O4/H2O and non-magnetic nanofluid Cu/H2O inside an exponentially heated and concentrated enclosure have been solved via finite-difference based stream-vorticity approach. Further, a comparative study has been conducted to analyze the impact of the magnetic field upon magnetic nanofluid Fe3O4/H2O and non-magnetic nanofluid Cu/H2O. Influence of various parameters namely; Rayleigh number (Ra), Lewis number (Le), buoyancy ratio (N), Hartmann number (Ha), nanoparticle volume fraction (ϕ), and magnetic field inclination angle (γ) on heat and mass transfer has been studied in detail. Heat and mass lines visualization techniques have been used for better insight of heat and mass transfer. The present work validates against experimental and numerical benchmark results and found to be in satisfactory acceptance. Total heat and mass transfers strengthen with the rise in inclination angle (γ) of magnetic field. It concludes that the effect of the magnetic field at lower value of Rayleigh number on overall heat transfer utilizing magnetic nanofluid Fe3O4/H2O is more effective than non-magnetic nanofluid Cu/H2O. Whereas magnetic field effect on mass transfer is more effective at a higher value of Rayleigh number. Percentage reduction in mass transfer is 10% has been found for Fe3O4/H2O, which is less than 12% of Cu/H2O nanofluid at higher value of volume concentration of nanoparticle.

Magneto-thermal convection in lid-driven cavity

The fluid flow and convective heat transfer occurring in a lid-driven cavity which is filled with electricity conductive fluid and subjected to external magnetic field, is analyzed comprehensively. The variations in inclination angle of magnetic field and its strength are addressed during the investigation. The cavity is heated by a linearly varying heat source applied on the left wall. Different regimes of heat transfer are considered by varying pertinent flow-parameters namely Reynolds number (Re), Richardson number (Ri) and Hartmann number (Ha). The effects of magnetic field and the wall motion are studied extensively. The study is carried out using a well-validated in-house CFD code based on finite volume method and SIMPLE algorithm. The obtained results reveal strong influence of Ri and Ha on the heat transfer characterization.

Lattice Boltzmann Simulation of MHD Rayleigh–Bénard Convection in Porous Media

Lattice Boltzmann method is used to investigate the Rayleigh–Benard convection of magnetohydrodynamic fluid flow inside a rectangular cavity filled by porous media. The Brinkman–Forchheimer model is considered in the simulation to formulate a porous medium mathematically, and the multi-distribution function model is considered to include the magnetic field effect with different inclination angles. The water is considered as the working fluid, which is electrically conducting. A comprehensive analysis of the impact of governing dimensionless parameters is performed by varying Rayleigh (Ra), Hartmann (Ha), and Darcy (Da) numbers, porosity ( $$\epsilon $$ ), and inclination angles ( $$\phi $$ ) of the applied magnetic field. Numerical results are evaluated in the form of streamlines, isotherms, and the rate of heat transfer in terms of the local and average Nusselt number as well as the entropy generation due to the irreversibility of the fluid friction, temperature gradient, and magnetic field effects. The results imply that increasing Ha and decreasing Da reduce the rate of heat transfer. The average Bejan number $$\hbox {Be}_\mathrm{{avg}}$$ increases for increasing the Hartmann number. On the other hand, augmenting Ra and $$\epsilon $$ improves the heat transfer rate. It is also found that the change of the magnetic field inclination angle $$\phi $$ changes the rate of heat transfer and entropy generation.

Natural convective heat transfer in a nanofluid-filled square vessel having a wavy upper surface in the presence of a magnetic field

Copper oxide makes an excellent nanomaterial for various efficient heat transfer devices because of its high specific surface area,lightweight, high specific heat capacity, and high thermal conductivity. Heat transfer intensification using nanofluids has strong potential to improve innovative cost-efficient chilling technologies. The present study aims to analyze the heat transfer intensifications for various parameter settings in a practical application. In recognition of possible applications, the problem of natural convective heat transfer in a copper oxide nanofluid-filled square vessel having the wavy upper wall in the presence of a uniform magnetic field using a nonhomogeneous dynamic model is analyzed. The temperature of both the bottom and the near walls of the vessel are hot, while the upper wavy surface is cold. The remaining vertical wall is considered adiabatic. A Galerkin finite element method is applied to the governing equations, along with suitable boundary conditions. The effects of a wide range of control parameters, such as the Hartmann number, magnetic field inclination angle, gravity inclination angle, solid-volume fraction, nanoparticle diameter, and dimensionless time, on the flow and thermal fields, are studied. The results show that early steady-state heat transfer occurs and that the flow, thermal, and concentration fields become suitable for enhanced heat transfer with increases in the Rayleigh number, wall wavenumber, nanosolid volumetric ratio, and geometry inclination angle, and with decreases in the Hartmann number and the nanoparticle diameter. A 20% improvement in heat transfer can be achieved by increasing the number of waves on the upper surface of heat transfer devices.

Space-charge limited thermionic sheaths in magnetized fusion plasmas

A systematic particle-in-cell investigation is reported focusing on the sheaths surrounding hot planar surfaces that are embedded in fusion plasmas with an arbitrary magnetic field inclination angle. The transition to the space-charge limited regime and the subsequent strict limitation of the escaping thermionic current density are demonstrated to be global characteristics of strongly emitting sheaths also in the presence of inclined magnetic fields. A physically transparent semi-empirical expression has been identified for the limited thermionic current as a function of the plasma conditions and inclination angle that is accurate for both the inter–and intra-ELM plasmas of present-day tokamaks.

Natural convection of a hybrid nanofluid affected by an inclined periodic magnetic field within a porous medium

Heat transfer enhancement for various engineering systems can be achieved by the inclusion of metal nanoparticles inside the heat transfer liquid. Such an effect can be improved by considering the hybrid nanofluid when nanoparticles of different materials are added to the base fluid. The present study is devoted to computational analysis of thermal gravitational convection within a porous chamber under the impact of tilted periodic magnetic force. Governing equations formulated employing the single-phase nanoliquid approach, Brinkman-extended Darcy model for transport processes within the porous layer with the local thermal non-equilibrium approach, Boussinesq approximation for the description of the buoyancy force and magnetic field, have been resolved using the Galerkin finite element method. Impacts of the Darcy number, Hartmann number, Rayleigh number, periodicity of the magnetic field, magnetic field inclination angle, thermal conductivity ratio, and medium porosity on flow and thermal patterns have been examined. It has been found that parameters of the periodic magnetic field have the non-monotonic influence of the heat transfer performance.

MHD mixed convection of Ag–MgO/water nanofluid in a triangular shape partitioned lid-driven square cavity involving a porous compound

In the current study, magnetohydrodynamics mixed convective flow of Ag–MgO/water hybrid nanofluid in a triangular shaped partitioned cavity involving a porous layer is numerically investigated by using the finite element method. In the numerical simulation, various effects of pertinent parameters such as Richardson number (between 0.01 and 100), Hartmann number (between 0 and 60), magnetic field inclination angle (between 0 and 90), Darcy number (between $$10^{-4}$$ and $$5 \times 10^{-2}$$ ), location of the vertex of triangular porous region (between 0.2 and 0.8 H) and hybrid nanoparticle solid volume fraction ( $$\phi _1$$ between 0 and 0.01, $$\phi _2$$ between 0 and 0.01) on the fluid flow and convective heat transfer features are examined. It was observed that a large vortex is established below the main vortex near the upper wall for the lowest value Ri number. At the highest magnetic field strength, multi-recirculation flow pattern is seen in the right bottom corner. The average heat transfer enhances with higher values of permeability of the porous medium, magnetic field inclination angle, distance of the porous layer vertex from the hot wall and solid nanoparticle volume fraction of each particles in the hybrid nanofluid. The impact is reverse for higher values of Richardson number and Hartmann number. In the current work, significant changes in the average Nusselt number are obtained by varying the location of the porous medium. The triangular shaped porous compound can be used as an excellent tool for convective heat transfer control.

EFFECT OF MAGNETIC FIELD ORIENTATION ON NANOFLUID FREE CONVECTION IN A POROUS CAVITY: A HEAT VISUALIZATION STUDY

Effect of magnetic field orientation on free convection of several water–based nanofluids in a square porous cavity is analyzed in this study. To this aim, the heatline visualization technique is implemented for the first time. Moreover, streamlines and isotherms are employed to present fluid flow and temperature distribution. The governing equations are transformed into a dimensionless form and then solved using the finite–volume method. Computations are undertaken for different orientations and magnitudes of the imposed magnetic field in circumstances with distinct Rayleigh numbers and the nanoparticles types and volume fractions. The corresponding results are presented in terms of dimensionless distributions of streamlines, isotherms, and heatlines as well as numerical values of the flow strength and the average Nusselt number. Inspection of the results demonstrates that increase in the magnetic field strength deteriorates the heat transfer rate. This effect, however, diminishes with rise in the magnetic field inclination angle.

Nanoliquid thermal convection in I-shaped multiple-pipe heat exchanger under magnetic field influence

The present work is investigated the heat management of thermogravitational convection inside a shell and tube heat exchanger filled with Fe3O4/water nanoliquid by lattice Boltzmann method (LBM). The seven internal pipes with hot or cold temperature insert in the I-shaped heat exchanger. The impacts of Rayleigh number (104-106), nanoparticles concentration (0–0.06), Hartmann number (0–60), magnetic field inclination angle (0-π/2) and the thermal arrangement of active pipes (Case 1–4) on the flow structure and energy transport characteristics are examined. The computational data are shown by streamlines, isothermal lines and the variations of the mean Nusselt number. It has been ascertained that the thermal arrangement of active pipes affects the velocity patterns and thermal transmission performance significantly. However, an increasing in the volume fraction of nano-size particles and Rayleigh number, the average Nusselt number raises regardless of the thermal arrangement. The rate of energy transport showed an opposite dependence with Hartmann number, but a direct relationship with the magnetic field inclination angle. The most suitable thermal arrangements for heat transfer rate of heated and cooled pipes are same at low magnitudes of the Rayleigh number, but different at high Rayleigh number.

Unsteady Aligned MHD Boundary Layer Flow and Heat Transfer of a Magnetic Nanofluids Past an Inclined Plate

A theoretical study has been done on the unsteady aligned MHD boundary layer flow as well as magnetic nanofluid's heat transfer through an inclined plate with leading edge accretion. For conventional base fluid, water and kerosene were used as they contain magnetite (Fe3O4) nanoparticles. Magnetic (Fe3O4) and non-magnetic (Al2O3) nanoparticles are compared as well. The governing partial differential equations are reduced into nonlinear ordinary differential equations through a suitable similarity transformation, where the Keller box method is used to solve numerically. Graphical and tabular results are discussed quantitatively in terms of the impact of pertinent parameters like magnetic parameter, M magnetic field inclination angle, α , angle of plate inclination, γnanoparticles volume fraction, o and free convection parameter, Grx,on the dimensionless velocity, skin friction coefficient, temperature and heat transfer rate. The outcomes indicate that the leading-edge accretion can significantly alter the fluid motion and the heat transfer attributes.

Hydromagnetic natural convection from a horizontal porous annulus with heat generation or absorption

The problem of unsteady laminar, two-dimensional hydromagnetic natural convection heat transfer in a concentric horizontal cylindrical annulus filled with a fluid-saturated porous medium in the presence of a transverse magnetic field and fluid heal generation effects is studied numerically. It is assumed that the inner and outer walls of the cylindrical annulus are maintained at uniform and constant temperatures Ti and To respectively. The model consists of the heat equation and the equations of motion under the Darcy law. The derived problem with the stream function-temperature formulation is solved numerically using the alternating direction implicit method. This investigation concerns the effect of magnetic field inclination angle, Hartmann number and heat generation on the heat transfer and the flow pattern. The obtained numerical results are presented graphically in terms of streamlines and isotherms. It was found that the heat transfer mechanisms and the flow characteristics depend strongly on the magnetic field inclination angle, Hartmann number and heat generation..

Effects of Dufour and Soret mechanisms on MHD mixed convective-radiative non-Newtonian liquid flow and heat transfer over a porous sheet

The mixed convection heat transfer combined with thermal radiation of a viscoelastic liquid circulation driven by a porous accelerating sheet under the inclined uniform magnetic field impact is studied. The considered phenomenon is modeled by the set of nonlinear differential equations affected by the boundary conditions. These equations are reduced into coupled nonlinear ordinary differential equations with the proper choice of similarity transformations. Further, the analytical solution is determined for transformed system. Also, the governing equations and the solutions are obtained for all considered functions. The temperature distribution impacted by the thermal radiation is very important in industrial fields as in accelerating sheet where cooling of the liquid plays a vital role in obtaining the desired outcome. In engineering applications like extrusion processes, metal spinning, dye casting of metals and polymer production this type of flow problem exists and where the maximum temperature and difference prediction should be controlled. Analysis has been performed for a wide range of radiation number (0 ≤ Nr ≤ 1), Richardson number (0.5 ≤ Λ ≤ 6), and magnetic field inclination angle (0 ≤ τ ≤ π/2).

Effect of heat and mass transfer on the peristaltic flow of a Jeffrey nanofluid in a tapered flexible channel in the presence of aligned magnetic field

In this paper, we have studied the influence of wall properties and aligned magnetic field on the peristaltic transport and heat and mass transfer of a Jeffrey/Newtonian nanofluid in a tapered channel. The analytical solutions are obtained for the stream function, the temperature and the concentration. Further, we obtained the Nusselt and Sherwood numbers at the wall. The effects of all important parameters on the physical quantities of the flow for both Jeffrey and Newtonian fluids are investigated through graphs and deliberated in detail. The velocity and temperatures are high for Newtonian fluid than Jeffrey fluid and the opposite situation is observed for concentration field. The large values of the magnetic parameter suppress the velocity and temperature fields but the reverse situation is seen in the case of concentration field. Also observed that the inclination angle of magnetic field and wall parameters have shown a significant effect on this investigation.

Nanojet impingement cooling of an isothermal surface in a partially porous medium under the impact of an inclined magnetic field

In this study, jet impingement heat transfer characteristics for a layered nanofluid and porous domains under the effects of inclined uniform magnetic field are examined by using Galerkin weighted residual finite element method. Effects of various pertinent parameters such as Reynolds number (between 100 and 500), Hartmann number (between 0 and 6), magnetic inclination angle (between 0 and 90), Darcy number (between $$10^{-4}$$ and $$10^{-2}$$ ) and height of porous layer (between 0.25 H and 4 H) on the fluid flow and heat transfer are analyzed. It was observed that local and average heat transfer rate enhance when the value of Reynolds number, magnetic field inclination angle and permeability of the porous layer increase, while the impact is reversed for magnetic field strength. Magnetic field inclination angle has more influence on the convective heat transfer features as compared to strength, and for a horizontally aligned magnetic field heat transfer process is inefficient. When cases in the absence and presence of magnetic field (at Hartmann number of 6) are compared, $$28\%$$ of reduction in the average heat transfer is obtained. An optimum value of porous layer height is observed where the highest heat transfer rates are achieved.

MHD free convection flow in an inclined square cavity filled with both nanofluids and gyrotactic microorganisms

Purpose This paper aims to study the magnetohydrodynamic (MHD)-free convection flow in an inclined square cavity filled with both nanofluids and gyrotactic microorganism. Design/methodology/approach The benefits of adding motile microorganisms to the suspension include enhanced mass transfer, microscale mixing and anticipated improved stability of the nanofluid. The model includes equations expressing conservation of total mass, momentum, thermal energy, nanoparticles, microorganisms and oxygen. Physical mechanisms responsible for the slip velocity between the nanoparticles and the base fluid, such as Brownian motion and thermophoresis, are accounted for in the model. Findings It has been found that the Hartmann number suppresses the heat and mass transfer, while the cavity and magnetic field inclination angles characterize a non-monotonic behavior of the all considered parameters. A rise of the Hartmann number leads to a reduction of the influence rate of the magnetic field inclination angle. Originality/value The present results are original and new for the study of MHD-free convection flow in an inclined square cavity filled with both nanofluids and gyrotactic microorganisms.

Numerical Investigation on the Robson Drift of a Single Cathode Spot of Vacuum Arc

The Robson drift phenomenon is a macroscopic reflection of the movement of a cathode spot (CS) in oblique magnetic field (OMF). Although it was discovered many years ago, its physical mechanism remains unclear. In this paper, the influence of OMF on the Robson drift of CS motion is simulated. A 2-D stepwise model of the movement of a single CS in OMF is established. It is assumed that the probability of generating a new spot in directions of Amperian force, anti-Amperian force, and directions perpendicular to Amperian force, is proportional to the magnetic pressure around the old spot. The drift angle and velocity of the CS in OMF are simulated. The simulation results show that the drift angle of the CS in OMF has liner relationship with the inclination angle of magnetic field, and it has no obvious relationship with the strength of the applied magnetic field and the amplitude of the arc current, which are in a good agreement with the experimental results. Besides, under the same angle of magnetic field, the velocity of spot motion increases linearly with the strength of OMF. Moreover, the simulation results show that the transverse magnetic field component has a much more predominant influence on the CS velocity than the axial magnetic field component, which are also in agreement with the experimental results.

A computational framework for natural convective hydromagnetic flow via inclined cavity: An analysis subjected to entropy generation

One of the most interested and essential subjective in mechanical science is natural convection analysis in a cavity. Thus, natural convective flow and entropy generation are scrutinized numerically subjected to magnetic field effect in a semi-annulus enclosure which known as the effect of magneto-hydrodynamic (MHD). Firstly, the governing expressions are rewritten in non-dimensional form utilizing the definition of dimensionless parameters, stream function, and vorticity. Secondly, the entropy generation equation is expressed in non-dimensional form. Then governing non-dimensional expressions are computed by control finite element method (CVFEM). Furthermore, the governing expressions are computed employing finite volume method (FVM) utilizing ANSYS Fluent CFD code. A novel criterion for determination of thermal characteristics of cavity based on thermodynamics second relation is introduced that is called ecological coefficient of performance (ECOP). Flow and heat transport features in addition to entropy generation number are examined for distinct values of the Rayleigh number (Ra = 103,104,105), the orientation of the magnetic field (β = 0°,15°,30°,45°,60°,75°,90°), and Hartmann number (Ha = 0,5,10,15,20). For validation, the entropy generation number and average Nusselt number are compared with those available in literature and excellent agreement is observed. Isotherms and streamlines are calculated using CVFEM and FVM. Some correlations for entropy generation number are proposed. The results show that for constant Rayleigh number, the entropy generation number decays with increasing Hartmann number. Also, for each Hartmann number, there is an optimum inclination angle of magnetic field that gives a minimum for entropy generation number and a maximum for ECOP at each Rayleigh number.

Nanofluids flow over a permeable unsteady stretching surface with non-uniform heat source/sink in the presence of inclined magnetic field

This work analyzes the unsteady two-dimensional nanofluid flow over a vertical stretching permeable surface in the presence of an inclined magnetic field and non-uniform heat source/sink. Four different types of nanoparticles, namely silver Ag, copper Cu, alumina Al2O3, and titania TiO2, are considered by using water as a base fluid with the Prandtl number Pr = 6.785. The governing partial differential equations are transformed to coupled non-linear ordinary differential equations by appropriate similarity transformation. Furthermore, the similarity equations are solved numerically by using the fourth-order Runge-Kutta integration scheme with Newton Raphson shooting method. A comparison of obtained numerical results is made with previously published results in some special cases, and excellent agreement is noted. Numerical results for velocity and temperature profiles as well as skin friction coefficient and local Nusselt number are discussed for various values of physical parameters. It tends to be discovered that, the magnetic field inclination angle γ has the capability to strengthens the magnetic field and reduce the velocity profile of the flow. Also, it can be found that, by using various types of nanofluids, velocity and temperature distributions change, which means that the nanofluids are important in the cooling and heating processes. The thermal boundary layer thickness is related to the increased thermal conductivity of different types of nanofluids, i.e., the minimum (maximum) value of the temperature is obtained by adding titanium oxide (silver) to the fluid as the nanoparticles.

Electrical conductivity effect on MHD mixed convection of nanofluid flow over a backward-facing step

In this study, magneto-hydrodynamics (MHD) mixed convection effects of Al2O3-water nanofluid flow over a backward-facing step were investigated numerically for various electrical conductivity models of nanofluids. A uniform external magnetic field was applied to the flow and strength of magnetic field was varied with different values of dimensionless parameter Hartmann number (Ha=0, 10, 20, 30, 40). Three different electrical conductivity models were used to see the effects of MHD nanofluid flow. Besides, five different inclination angles between 0o~90o is used for the external magnetic field. The problem geometry is a backward-facing step which is used in many engineering applications where flow separation and reattachment phenomenon occurs. Mixed type convective heat transfer of backward-facing step was examined with various values of Richardson number (Ri=0.01, 0.1, 1, 10) and four different nanoparticle volume fractions (o=0.01, 0.015, 0.020, 0.025) considering different electrical conductivity models. Finite element method via commercial code COMSOL was used for computations. Results indicate that the addition of nanoparticles enhanced heat transfer significantly. Also increasing magnetic field strength and inclination angle increased heat transfer rate. Effects of different electrical conductivity models were also investigated and it was observed that they have significant effects on the fluid flow and heat transfer characteristics in the presence of magnetic field.