Thermomagnetic Convection of Ferrofluid in an Enclosure Channel with an Internal Magnetic Field.

Lee Lee,Kim Kim

doi:10.3390/mi10090553

Abstract

Ferrofluid is a colloidal liquid in which magnetic nanoparticles such as Fe3O4 are dispersed in a nonconductive solution, and the average diameter of the nanoparticles is 10 nm. When a magnetic field is applied, the ferrofluid generates magnetization, which changes the physical properties of the fluid itself. In this study, characteristics of the thermomagnetic convection of ferrofluid (Fe3O4) by the permanent magnet in the enclosure channel were studied. To effectively mix the ferrofluid (Fe3O4) and disturb the boundary layer, the heat dissipation of the heat source depending on the strength of the magnetic field and the shape of the enclosure channel was numerically studied. In particular, four different enclosure channels were considered: Square, separated square, circle, and separated circle. The hot temperature was set at the center of the enclosure channel. The ferrofluid was affected by the permanent magnet in the center of the channel. The magnetic field strength in the region close to the permanent magnet was enhanced. The magnetophoretic (MAP) force increased with increasing magnetic field strength. The MAP force generated a vortex in the enclosure channel, disturbing the thermal boundary. The vortex occurs differently, depending on the shape of the enclosure channel and affects the thermomagnetic convection. The temperature and velocity fields for thermomagnetic convection were described and the convective heat flux was calculated and compared. Results show that when the magnetic field strength was 4000 kA/m and the shape of the enclosure channel was a circle, the maximum convective heat flux of 4.86 × 105 W/m2 was obtained.

Highlights

IntroductionElectronic devices are getting smaller and the amount of power used is increasing
With advances in technology, electronic devices are getting smaller and the amount of power used is increasing
The results showed that the magnetic field strength, Darcy number, and Rayleigh number affect the heat transfer in the square enclosure

Summary

Introduction

Electronic devices are getting smaller and the amount of power used is increasing. Ferrofluid has been highlighted with cooling technology It has higher thermal conductivity than conventional heat transfer fluid and has the advantage of controlling the fluid by using the magnetic field. The flow of ferrofluid can be controlled by magnetophoresis and the temperature gradient changes, depending on the relationship between the intensity of the applied magnetic field and the flow of the ferrofluid. For these reasons, many researchers of engineering fields proposed new design parameters to various applications using fluid element [3,4,5]. Many researchers studied the thermomagnetic convection characteristics of ferrofluid in a square enclosure when applied to an external magnetic field. Temperature and velocity distributions were graphically depicted with various geometrical configurations and operating conditions

Governing Equations

Numerical Analysis

Results & Discussion

Conclusions