Forced Convection of Fe3O4-Water Nanofluid in a Bifurcating Channel under the Effect of Variable Magnetic Field (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.
Thermal Science, 2022
This paper focuses on the convective heat transfer characteristics of Fe3O4-water magnetic nanofluids under laminar and turbulent conditions. After verifying the accuracy of the experimental apparatus, the effects of magnetic field strength, concentration, Reynolds number and temperature on the convective heat transfer coefficient have been studied. The convective heat transfer characteristics of nanofluids under laminar and turbulent flow conditions were studied in depth, and the influence of each factor on the heat transfer coefficient was analyzed by orthogonal experimental design method. Under the laminar flow conditions, the convective heat transfer of magnetic nanofluids performed best when the Reynolds number was 2000, the magnetic field strength was 600, the temperature was 30?C, and the concentration was 2%. The convective heat transfer coefficient, h, increased by 3.96% than the distilled water in the same conditions. In turbulent state, the convective heat transfer of mag...
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.
Strojniški vestnik – Journal of Mechanical Engineering, 2016
This paper presents research on the forced flow convective heat transfer of a ferrofluid (water and Fe 3 O 4) in a horizontal two-dimensional channel under the influence of a 2D non-uniform magnetic field, which is applied through a line dipole. The governing equations of this research include continuity, momentum, energy and entropy generation, which are solved with a finite volume technique. Moreover, a gridindependent test and the validation of numerical results are carried out. The effect of the Fe 3 O 4 volume fraction (1 vol % to 6 vol %) on the hydro-thermal characteristics of the ferrofluid flow and entropy generation is studied. Numerical results show that the flow pattern is highly changed, because the kelvin body force overcomes the viscous force by increasing the volume fraction under applied magnetic field. Furthermore, the average wall friction factor increases linearly. The average Nusselt number (Nu) increases with the increase of the Fe 3 O 4 volume fraction, so that Nu increases by 51.1 % in comparison to the base fluid at 6 vol %. It is observed that the Nusselt number ratio (NUR) at 6 vol % is enhanced by 10.4 % whereas the entropy generation ratio (NSR) is increased by only 6.2 % compared to 4 vol %. According to the results of the study, it is concluded that using volume fractions between 4 vol % to 6% would result in an observable improvement in convective heat transfer while enhanced entropy generation is relatively small, so it is thermodynamically affordable.
Symmetry
Heat transfer in a symmetrical cavity with two semi-cylinders was explored in this study. Several parameters, such as (103≤Ra≤106), (10−5≤Da≤10−2), (0.02≤ϕ≤0.08), (0.2≤ε≤0.8), and (0≤Ha≤100) were selected and evaluated in this research. The outcome of the magnetic field and the temperature gradient on the nanofluid flow is considered. The geometric model is therefore described using a symmetry technique. The flow issue for the governing equations has been solved using the Galerkin finite element method (G-FEM), and these solutions are presented in dimensionless form. The equations for energy, motion, and continuity were solved using the application of the COMSOL Multiphysics® software computer package. According to the results, there is a difference in the occurrence of the magnetic parameter and an increase in heat transmission when the right wall is recessed inward. The heat transmission is also significantly reduced when the right wall is exposed to the outside. The number of Nus...
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.
Journal of Thermal Analysis and Calorimetry, 2018
Forced convection heat transfer of multi-wall carbon nanotubes-iron oxide nanoparticles/water hybrid nanofluid (MWCNT-Fe 3 O 4 /water hybrid nanofluid) inside a partially heated s-shaped channel has been numerically investigated. The effect of magnetic field is taken into account. The governing equations are solved by the lattice Boltzmann method in the domain, and the results were compared with other numerical methods by an excellent agreement between them. The effects of parameters such as Hartmann number (0 B Ha B 60), volume fraction of nanoparticles (0 B / B 0.003) and different location of two heaters on the fluid flow and heat transfer are studied. The results indicate that for all cases, the average Nusselt number of each heater increases as the volume fraction of nanoparticles increases. The heat transfer characteristics were significantly affected by the arrangement of the two heaters. The heaters located on the left half of the top wall is convection-dominant mechanism, and the conduction heat transfer is the primary mechanism when the heater is on the right half of the top wall. The average Nusselt number increases as Ha increases for the heater of dominating convection mechanism but decreases for the heater of dominating conduction mechanism.
Journal of Magnetism and Magnetic Materials, 2011
In this paper, effects of applying a linear magnetic field on a ferrofluid (water and 4 vol% Fe 3 O 4 ) flow in horizontal straight and curved tubes have been investigated. The hydro-thermal behavior of the flow is investigated numerically using the two phase mixture model and control volume technique. The linear magnetic fields with various gradients in the perpendicular direction of the main flow have been examined. Based on the obtained results the heat transfer coefficient can be enhanced using the curved tube instead of straight tube, adding magnetic nanoparticles to the base fluid and applying external magnetic field. It is concluded that the heat transfer is enhanced due to the secondary flow augmentation (because of centrifugal force and Kelvin force) and thermal conductivity improvement (because of high thermal conductivity of magnetic nanoparticles relative to base fluid).
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 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.