The transition from natural convection to thermomagnetic convection of a magnetic fluid in a non-uniform magnetic field

As electrical devices become smaller, it is essential to maintain operating temperature for safety and durability. Therefore, there are efforts to improve heat transfer performance under various conditions, such as using extended surfaces and nanofluids. Among them, cooling methods using ferrofluid are drawing the attention of many researchers. This fluid can control the movement of the fluid in magnetic fields. In this study, the heat transfer performance of a fin-tube heat exchanger, using ferrofluid as a coolant, was analyzed when external magnetic fields were applied. Permanent magnets were placed outside the heat exchanger. When the magnetic fields were applied, a change in the thermal boundary layer was observed. It also formed vortexes, which affected the formation of flow patterns. The vortex causes energy exchanges in the flow field, activating thermal diffusion and improving heat transfer. A numerical analysis was used to observe the cooling performance of heat exchangers, as the strength and number of the external magnetic fields were varying. VGs (vortex generators) were also installed to create vortex fields. A convective heat transfer coefficient was calculated to determine the heat transfer rate. In addition, the comparative analysis was performed with graphical results using contours of temperature and velocity.

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“…Magnetic flux density, B, and magnetic field strength, H, related to Maxwell's equation, are defined as below [15]:…”

Section: Governing Equationsmentioning

confidence: 99%

Effect of Magnetic Nanofluids on the Performance of a Fin-Tube Heat Exchanger

Choi

Kim

2021

Applied Sciences

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“…They found that increasing Lorentz force increases heat transfer rate while buoyancy force produces the opposite effect. Szabo and Früh [11] investigated the transition from natural convection to thermomagnetic convection numerical of a magnetic fluid subjected to a non-uniform magnetic field. Yamaguchi et al [12] analyzed flow and heat transfer characteristics of magnetic fluid natural convection inside a two-dimensional cavity.…”

Section: Introductionmentioning

confidence: 99%

Effect of a Magnetic Field on Mixed Convection in a Rectangular Cavity Filled with Ferrofluid

Harfi¹,

Kaddiri²,

Lamsaadi³

et al. 2021

IJHT

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The present work analyzes both numerically and analytically mixed convection heat transfer in shallow rectangular enclosure files confining ferrofluid, and exposed to temperature conditions of Neuman type with uniform heat flux applied to the short vertical sides, while the top wall is moving with a uniform velocity in the same direction as the applied heat flux. The finite volume method and the SIMPLER algorithm were used to numerically solve the governing equations, while the analytical solution is based on the parallel flow approximation. Simulations are conducted a wide range of controlling parameters, namely, the Reynolds, Hartmann and Richardson numbers and the solid volume fraction of ferroparticles. Effects of mentioned parameters, on the flow structure, temperature fields, and heat transfer rate, were studied and discussed.

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“…Results show that the convective flow and heat transfer rise, increasing with the strengthening of the magnetic field in the absence of a gravity field. Szabo and Früh [17] numerically studied the transition from natural convection to thermomagnetic convection of a magnetic fluid in a non-uniform magnetic field. Their results show that the transition from a single buoyancy-driven convection cell to a single thermomagnetically driven cell is via a two-cell structure, and that the local effect on the flow field leads to a global effect on the heat transfer with a minimum of the Nusselt number in the transition region.…”

Section: Introductionmentioning

confidence: 99%

Thermomagnetic Convection of Paramagnetic Gas in an Enclosure under No Gravity Condition

Song

Tagawa

et al. 2019

Fluids

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The thermomagnetic convection of paramagnetic gaseous oxygen in an enclosure under a magnetic field was numerically studied to simulate the thermomagnetic convection in a space environment with no gravity. The magnetic field in the enclosure was non-uniform and was generated by a permanent magnet which had a high magnetic energy product. The magnet was placed at different locations along one of the adiabatic walls with magnetic poles perpendicular to the hot and cold walls of the enclosure. The heat transfer performance, flow field, and temperature field were studied with each location of the magnet. The results show that the thermomagnetic convection in the enclosure was obviously affected by the location of the magnet. There was an optimum magnet location in terms of the best heat transfer performance in the enclosure. The optimum magnet location changed slightly and moved toward the hot wall as the magnetic flux density increased. The value of the Nusselt number, defined as the ratio of convection to conduction, reached up to 2.54 in the studied range of parameters. By optimizing the magnet location, the convection was enhanced by up to 77% at the optimum magnet location.

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The transition from natural convection to thermomagnetic convection of a magnetic fluid in a non-uniform magnetic field

Cited by 70 publications

References 21 publications

Effect of Magnetic Nanofluids on the Performance of a Fin-Tube Heat Exchanger

Effect of Magnetic Nanofluids on the Performance of a Fin-Tube Heat Exchanger

Effect of a Magnetic Field on Mixed Convection in a Rectangular Cavity Filled with Ferrofluid

Thermomagnetic Convection of Paramagnetic Gas in an Enclosure under No Gravity Condition

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