Forced convection heat transfer in a channel under the influence of various non-uniform transverse magnetic field arrangements (original) (raw)
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Magnetic Nanofluids for Heat Transfer Enhancement Inside Straight Channels
Journal of Advanced Research in Materials Science, 2020
A numerical study for investigating the fluid flow and heat transfer enhancement inside square, circular and triangular straight channels with hydraulic diameter of 0.01 m using magnetic nanofluid (Fe3O4 suspended in water) as a base fluid under constant heat flux subjected around the geometries walls has been presented to determine the effects of nanoparticle volume fraction and flow rate on the convective heat transfer and friction factor of nanofluid without the influence of magnetic field. The nanofluid consists of Fe3O4 magnetic nanoparticles with average diameter of 36 nm suspended in water with a different volume fraction which were 0.2, 0.4, and 0.6%. The study was conducted at steady state, turbulent forced convection with Reynolds number (5000 ≤ Re ≤ 20000), three-dimensional flow, and single-phase approach. Certain boundary conditions and assumptions to solve the governing equations have been implemented using finite volume method. CFD software involving GAMBIT and FLUENT were employed to perform the investigation numerically. The results revealed that as Reynolds number increased, the heat transfer rate was also increased for all the geometries but it is better in circular tube case. While in the case of using pure water as a coolant, the heat transfer rate is lower than that the case of using nanofluid with respect to the flow inside all the geometries. In addition, as Reynolds number increase, friction factor decreases for all cases and it is large in case of square duct. New correlations were proposed to predict Nusselt number and friction factor based on the dimension less numbers which are valid for the three geometries.
SN Applied Sciences, 2020
An attempt to examine the relevance of heat source/sink on magnetohydrodynamics free convection flow in a vertical channel with an induced magnetic field is achieved. The analytical solution to the set of the differential equation is obtained by perturbation method for small thermophoresis and Brownian diffusion parameters under the unified thermal boundary condition (isothermal and isoflux boundary condition) for the energy equation. Numerical solution to the flow equation is also obtained by incorporating RKF45 in Maple software. The influence of active parameters such as Hartman number (Ha), magnetic Prandtl number (Pm), heat source/sink parameter (± S), Buoyancy ratio (Br), Brownian motion (Nb) and thermophoretic parameter (Nt) on velocity, induced magnetic field, induced current density, nanoparticles concentration, temperature and skin friction are depicted and discussed in detail. Results reveal that the Brownian motion parameter (Nb) and Buoyancy ratio (Br) augment enhances the shear stress whereas the contrast is observed with Hartman number (Ha) and thermophoretic parameter (Nt). Results also reveal that Hartman number (Ha) and thermophoretic parameter (Nt) enhances the induced current density while the contrast is true for heat sink parameter (−S). Finally, the temperature of the nanofluid could be enhanced with increase in Brownian motion parameter (Nb) and heat source parameter (+ S). Keywords Nanofluid • Isothermal (iso-t) • Isoflux (iso-f) • Heat source/sink • Induced magnetic field Abbreviations B Induced magnetic field (Ampere (A)m −2) � ⃗ b Magnetic field vector (Tesla (T)) T Temperature of the nannofluid (Kelvin(K)) Temperature (dimensionless) Concentration (dimensionless) C Concentration (mol dm −3) U Vertical velocity (dimensionless) � ⃗ v Velocity vector (ms −1) h Distance between two vertical walls (m) Fluid density (kgm −3) g Acceleration due to gravity (ms −2) Nb Brownian motion parameter (dimensionless) Thermal expansion coefficient (K −1
Heat Transfer, 2019
In this paper, swirling flow boiling of a dilute nanofluid (water and 0.1 vol%Fe 3 O 4) in an annulus with a twisted fin on the outside of the inner wall in the presence of transverse magnetic gradient has been numerically investigated, using a two fluid model and a control volume technique. The results indicate that, in the boiling of swirling flow, the rate of the heat transfer increases. This phenomenon can be attributed to the effect of centrifugal force on the liquid phase flow and also reduction of the conductive sub-layer thickness that exists on the heated wall. The effects of improved surface wettability induced by nanoparticle deposition during the boiling process are accounted. The results demonstrate that the modified liquid property due to the existence of nanoparticles in the liquid has a negligible effect on the boiling heat transfer performance with dilute nanofluids while the improved surface wettability plays an important role and leads to reduction of the void fraction and consequently, an increase of critical heat flux. Applying a transverse magnetic field causes augmentation of the centrifugal force and results in increased flow turbulence. Furthermore, in the presence of the magnetic field due to magnetic force, the bubble departure diameter is reduced and bubble detachment occurs faster. Therefore, the critical heat flux will be increased. Swirling flow boiling in the presence of magnetic field is strongly suggested in devices requiring high heat transfer rates.
Physics of Fluids
The present numerical study investigates the effect of external magnetic field on a magnetic nanofluid flow in an inclined channel. A uniform magnetic field is used to generate vortex in the channel for heat transfer enhancement. Fe3O4–water nanofluid of 2 vol. % is flowing in an inclined two-dimensional channel with a heated bottom wall. Numerical simulations are carried out for different inclination angles varying from −90° < θ < 90° at low Reynolds numbers, in the presence of external magnetic field of intensities varying from 0–2000 G. The heat sink has dimensions of 40 × 4 mm2, with a magnet pair placed at 15 mm from the origin. Different thermo-hydraulic properties, like Nusselt number, friction factor, pressure drop and thermal enhancement factor (TEF), are calculated for all the cases. There is an average increase in the Nusselt number by 4.95% and 19.27% when a magnetic field of 1500 and 2000 G is applied, respectively. This heat transfer enhancement comes with a pena...
This paper investigates numerically the hydro-thermal characteristics of a ferrofluid (water and 4 vol% Fe 3 O 4) in a vertical rectangular duct which is exposed to a non-uniform transverse magnetic field generated by an electric current going through a wire located parallelly under the duct. The two phase mixture model and the control volume technique have been used to study the flow. The results show that applying the aforementioned magnetic field increases the Nusselt number and friction factor and also creates a pair of vortices that enhances heat transfer and prevents sedimentation of nano-particles. Furthermore, unlike the axial non-uniform magnetic field, the increase of the Nusselt number for the transverse magnetic field is considerable in all length along the duct and it is also concluded that with increasing the Reynolds number, the effect of the transverse non-uniform magnetic field on the Nusselt number is more than that of the axial non-uniform magnetic field.
Experimental Thermal and Fluid Science, 2013
This research study presents an experimental investigation on forced convection heat transfer of an aqueous ferrofluid flow passing through a circular copper tube in the presence of an alternating magnetic field. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated convection regimes caused by interactions between magnetic nanoparticles under various conditions were studied. The process of heat transfer was examined with different volume concentrations and under different frequencies of the applied magnetic field in detail. The convective heat transfer coefficient for distilled water and ferrofluid was measured and compared under various conditions. The results showed that applying an alternating magnetic field can enhance the convective heat transfer rate. The effects of magnetic field, volume concentration and Reynolds number on the convective heat transfer coefficient were widely investigated, and the Optimum conditions were obtained. Increasing the alternating magnetic field frequency and the volume fraction led to better heat transfer enhancement. The effect of the magnetic field in low Reynolds numbers was higher, and a maximum of 27.6% enhancement in the convection heat transfer was observed.
Journal of Magnetism and Magnetic Materials
Laminar forced convection heat transfer of water based Fe3O4 ferrofluid in a mini channel in the presence of constant and alternating magnetic fields is studied numerically. The hot ferrofluid flows into the 20 mm (l)×2 mm (h) mini channel with isothermal top and bottom cold surfaces and is subjected to a transverse non-uniform magnetic field produced by current carrying wires. Two-phase mixture model is implemented and the governing equations are solved using the finite volume approach. Primarily, the effects of the constant magnetic field location and intensity on the convective heat transfer are investigated. Simulation results show that the heat transfer is enhanced due to the disruption of the thermal boundary layer. However, this effect is more pronounced when the magnetic field source is placed in the fully developed region. In the next section, an alternating magnetic field with frequencies ranging from 0 to 10 Hz is imposed to the ferrofluid at different Reynolds numbers of...
Experimental investigation for enhanced ferrofluid heat transfer under magnetic field effect
Journal of Magnetism and Magnetic Materials, 2010
This paper reports an experimental work on the convective heat transfer of ferrofluid flowing through a heated copper tube in the laminar regime in the presence of magnetic field. Significant enhancement on the heat transfer of ferrofluid by applying various orders of magnetic field is observed in this experiment. Also in this experiment, the effect of magnetic nanoparticles concentrations and magnet position have been investigated. The main reason for the enhancement of heat transfer coefficient could be caused due to remarkable changes in thermophysical properties of ferrofluid under the influence of applied magnetic field.
Numerical study of magnetic field effect on nano-fluid forced convection in a channel
In this study heat transfer and fluid flow analysis in a straight channel utilizing nano-fluid is numerically studied, while flow field is under magnetic field. Usage of nano-particles in base fluid and also applying magnetic field transverse to fluid velocity are two ways recommended in this paper to enhance heat exchange in straight duct. The fluid temperature at the channel inlet (T in) is taken less than that of the walls (T w). With assuming thermal equilibrium state of both the fluid phase and nano-particles and ignoring the slip velocity between the phases, single phase approach is used for modeling of nano-fluid. The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. Numerical studies are performed over a range of Reynolds number, nano-fluid volume fraction and Hartmann number. The influence of these parameters is investigated on the local and average Nusselt numbers. Computations show excellent agreement with the literature. From this study, it is concluded that heat transfer in channels can enhance up to 75% due to the presence of nano-particles and magnetic field in channels. In industrial applications for cooling or heating purposes, the recommended ways in this paper, can provide helpful guidelines to the manufacturers to enhance efficiencies without heat exchanger area increase.
Energies
In this study, forced convection of Fe 3 O 4 –water nanofluid in a bifurcating channel was numerically studied under the influence of variable magnetic. Galerkin residual finite element method was used for numerical simulations. Effects of various values of Reynolds number (between 100 and 500), Hartmann number (between 0 and 3), and solid nanoparticle volume fraction (between 0% and 4%) on the convective heat transfer characteristics were analyzed. It was observed that location and size of the re-circulation zones established in the walls of the bifurcating channel strongly influenced by the variable magnetic field and Reynolds number. Average Nusselt number versus Hartmann number showed different characteristics for hot walls of the vertical and horizontal branching channels. The average Nusselt number enhancements were in the range of 12–15% and 9–12% for hot walls of the branching channel in the absence and presence of magnetic field (at Hartmann number of 3).