Thermal-Flow Characteristics of Ferrofluids in a Rotating Eccentric Cylinder under External Magnetic Force
Abstract
:1. Introduction
2. Methodology
3. Results and Discussion
3.1. Magnetophoretic Force
3.2. Velocity Distribution
3.3. Nusselt Number
4. Conclusions
- When a magnetic field is applied to a ferrofluid through the permanent magnet, magnetization distribution appears due to magnetic flux density distribution. It was confirmed that the MAP force was concentrated in the portion where the magnetic flux density gradient was large. It has also been confirmed that various velocity changes and vortex fields are generated by the MAP force.
- Since the center of the inner cylinder moves away from the center of the outer cylinder, it has a higher Nusselt number because it forms a sufficient flow. However, it has been confirmed that the effect of heat transfer is reduced by direct contact when it is too close to the outer wall. Therefore, the highest Nusselt number was confirmed in Case 4 (e = 0.3), which is considered to be the most appropriate location.
- The eccentricity of the inner cylinder was found to influence the vortex field under the magnetic field. It is considered that a highly efficient heat dissipation system can be constructed by using the characteristic that a change in efficiency is caused by a small eccentricity change. However, a comparative study of the results obtained from the experiment should be performed to confirm the accuracy of numerical studies.
- The characteristics of the heat transfer according to the eccentricity of the ferrofluids can be applied to various rotating devices such as electric motors and generators.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Cases | Eccentricity, e |
---|---|
Case 1 (ref.) | 0 |
Case 2 | 0.1 |
Case 3 | 0.2 |
Case 4 | 0.3 |
Case 5 | 0.4 |
Case 6 | 0.5 |
Case 7 | 0.6 |
Properties | Value |
---|---|
1221 (kg/m3) | |
2.552 | |
2.208 | |
1.552 | |
0.00727 (Pa∙s) | |
k | 0.19 (W/m∙K) |
1840 (J/kg∙K) | |
8.6 × 10−4 (1/K) |
H | 10 (kA/mm) |
308.15 (K) | |
298.15 (K) | |
Wall condition | No-slip |
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Kim, J.-H.; Seo, H.-S.; Kim, Y.-J. Thermal-Flow Characteristics of Ferrofluids in a Rotating Eccentric Cylinder under External Magnetic Force. Micromachines 2018, 9, 457. https://doi.org/10.3390/mi9090457
Kim J-H, Seo H-S, Kim Y-J. Thermal-Flow Characteristics of Ferrofluids in a Rotating Eccentric Cylinder under External Magnetic Force. Micromachines. 2018; 9(9):457. https://doi.org/10.3390/mi9090457
Chicago/Turabian StyleKim, Jae-Hee, Hyeon-Seok Seo, and Youn-Jea Kim. 2018. "Thermal-Flow Characteristics of Ferrofluids in a Rotating Eccentric Cylinder under External Magnetic Force" Micromachines 9, no. 9: 457. https://doi.org/10.3390/mi9090457