Influence of inhomogeneous magnetic field source location on the intensity of thermomagnetic convection in a closed loop

Purpose. Obtaining information on the influence of the location of the inhomogeneous magnetic field source relative to the heated section of a vertical hydrodynamic loop filled with magnetic fluid on the intensity of convective heat transfer along the loop.

Methods. Experiments were carried out using a hydrodynamic loop made of a thin tube of circular cross-section and placed in a vertical plane. Heat source was carried out by a heater on a short vertical section of the loop, and heat removal was implement out by blowing the entire surface of the tube with thermostated air. The source of the magnetic field was the flat pole tips of the ferrite magnetic core, in the gap between which the heater was located. The position of the pole tips relative to the heater varied vertically in the experiments. In the control experiments, the source of the magnetic field was deleted. The circuit was filled with medium concentrated magnetic liquid of the type "magnetite - kerosene - oleic acid". The intensity of steady-state convective heat flow along the tube was calculated from the results of measuring the tube surface temperature by copper-constantane thermocouples. The measurement results were presented in dimensionless form - the relationship between the Nusselt number and Rayleigh number.

Results. The unfluctuating mixed, thermomagnetic and gravitational, convection of the magnetic fluid in the loop was observed at any location of the pole tips of the magnetic core relative to the heater. At location of pole tips above the heater, competition of gravitational and thermomagnetic convection was observed, and the heat flux was weak. When the pole tips were placed below the heater, the Nusselt number was 2 - 4 times higher than in the control tests (only gravitational convection) with equal Rayleigh numbers. The highest Nusselt numbers were obtained when the field source was placed in center of the heater.

Conclusion. Information on the influence of the relative location of the magnetic field source and the heater on convective heat transfer by magnetic fluid in a hydrodynamic loop is obtained experimentally. The optimal concerning of heat transfer intensity position of the field source was found.

1. Berkovsky B.M., Medvedev V.F., Krakov M.S. Magnetic fluids: Engineering applications. Oxford: Oxford University Press; 1985. 243 p.

2. Lienhard IV J.H., Lienhard V J.H. А heat transfer textbook. Cambridge, MA: Phlogiston Press; 2019. 784 p.

3. Finlayson B.A. Convective instability of ferromagnetic fluids. Journal of Fluid Mechanics. 1970;40(4):753–767. https://doi.org/10.1017/S0022112070000423

4. Rosensweig R.E. Ferrohydrodynamics. Cambridge: Cambridge University Press; 1985. 344 p.

5. Matsuki H., Yamasava K. Experimental considerations on a new automatic cooling device using temperature-sensitive magnetic fluid. IEEE Transactions on Magnetics. 1977;13(5):926–940. https://doi.org/10.1109/TMAG.1977.1059679

6. Belyaev A.V., Smorodin B.L. The stability of ferrofluid flow in a vertical layer subject to lateral heating and horizontal magnetic field. Journal of Magnetism and Magnetic Materials. 2010;322: 2596–2606. https://doi.org/10.1016/j.jmmm.2010.03.028

7. Krakov M.S., Nikiforov I.V. Influence of the meridional flow and thermomagnetic convection on characteristics of magnetic fluid seal. Technical Physics. 2011;56(12):1745–1753. https://doi.org/10.1134/S1063784211120103

8. Fumoto K., Yamagishi H., Ikegava M. A mini heat transport device based on thermo-sensitive magnetic fluid. Nanoscale and Microscale Thermophysical Engineering. 2007;11:201–210. https://doi.org/10.1080/15567260701333869

9. Pattanaik M.S., Varma V.B., Cheekati S.K., Chaudhary V., Ramanujan R.V. Optimal ferrofluids for magnetic cooling devices. Scientific Reports. 2021;11(24167). https://doi.org/10.1038/s41598021-03514-2

10. Polunin V.M., Ryapolov P.A., Platonov V.B., Kuzko A.E. Free oscillations of magnetic fluid in strong magnetic field. Acoustical Physics. 2016;62(3):313–318. (In Russ.) https://doi.org/10.1134/S1063771016030131

11. Koskov M.A., Pshenichnikov A.F. Thermomanetic convection of a ferrofluid in a vertical hydrodynamic loop: intensification of heat exchange in magnetic field. Journal of Experimental and Theoretical Physics. 2022;135(6):884–896. https://doi.org/10.1134/S1063776122120044

12. Lian W., Xuan Y., Li Q. Design method of automatic energy transport devices based on the thermomagnetic effect of magnetic fluids. International Journal of Heat and Mass Transfer. 2009;52:5451–5458. https://doi.org/10.1016/j.ijheatmasstransfer.2009.06.031

13. Vargaftic N.B., Vinogradov Y.K., Yargin V.S. Handbook of physical properties of liquids and gases. 3rd. augm. and rev. ed. New York: Begel House, Inc.; 1996. 1358 p.

14. Koskov M.A., Lebedev A.V., Ivanov A.S. About the differential sweep method for measuring of ferrocolloids magnetization curves. Izvestiya Yugo-Zapadnogo gosudarstvennogo universiteta. Seriya: Tekhnika i tekhnologii = Proceedings of the Southwest State University. Series: Engineering and Technologie. 2023;13(3):89–104. (In Russ.) https://doi.org/10.21869/2223-1528-2023-13-3-89-104

15. Pshenichnikov A.F., Mekhonoshin V.V., Lebedev A.V. Magneto-granulometric analysis of concentrated ferrocolloids. Journal of Magnetism and Magnetic Materials. 1996;161:94–102. https://doi.org/10.1016/S0304-8853(96)00067-4

16. Koskov M.A. Ferrofluid convection in a hydrodynamic loop: analysis of temperature field. Izvestiya Yugo-Zapadnogo gosudarstvennogo universiteta. Seriya: Tekhnika i tekhnologii = Proceedings of the Southwest State University. Series: Engineering and Technologie. 2022; 12(2):166–182. (In Russ.) https://doi.org/10.21869/2223-1528-2022-12-2-166-182

17. Xyan Y., Lian W. Electronic cooling using an automatic energy transport device based on thermomagnetic effect. Applied Thermal Engineering. 2011;31(8/9):1487–1494. https://doi.org/10.1016/j.appthermaleng.2011.01.033

18. Pattanaik M.S., Cheekati S.K., Varma V.B., Ramanujan R.V. A novel magnetic cooling device for long distance heat transfer. Applied Thermal Engineering. 2022;201(1):117777. https://doi.org/10.1016/j.applthermaleng.2021.117777.

19. Varma V.B., Cheekati S.K., Pattanaik M.S., Ramanujan R.V. A magnetic nanofluid device for excellent passive cooling of light emitting diodes. Energy Reports. 2022;8:7401–7419. https://doi.org/10.1016/j.egyr.2022.05.237