# Effect of Magnetic Nanofluids on the Performance of a Fin-Tube Heat Exchanger
## 1 Introduction  
Heat dissipation is very important because it is directly related to the life and safety of electronic devices. Accordingly, various studies for managing heat in electronic devices are being conducted [1]. Among them, this study aimed to improve the heat transfer performance using ferrofluid. Ferrofluid is a colloidal suspension, containing magnetic nanoparticles with a diameter of 3 to 15 nm [2]. There are many kinds of particles, such as Fe\({}_{3}\)O\({}_{4}\), CoFeO\({}_{4}\), and FePt, which have ferromagnetic properties. Due to the magnetism of the particles, this fluid has the characteristic of reacting with a magnetic field. When a magnetic field is applied, the fluid has kinetic energy and forms a specific shape [3]. That is, there are the advantages that a flow can be created only by a magnetic force without direct contact with the fluid, and that control is possible with a relatively simple configuration. In addition, it was confirmed that nanofluids have superior thermal performance compared to general fluid, due to the properties of the particles [4, 5]. [PERSON] et al. [6] observed heat transfer by natural convection when a magnetic fluid is contained in a cavity. AR (aspect ratio) values, such as 1, 15, and 2 of the cavity, were set as variables. Ra\({}_{\rm m}\) (magnetic Rayleigh number), Ra (Rayleigh number), Ra\({}_{\rm c}\) (critical Rayleigh number) corresponding to each variable were observed. As AR increased, the Ra\({}_{\rm c}\) tended to decrease, and it was confirmed that many vortex fields appeared. In addition, when a magnetic field was applied, the improvement in heat transfer was confirmed. It is due to the occurrence of various vortex shapes and strong circulation. [PERSON] et al. [7] observed the flow phenomenon in a partially heated cavity. In their study, Ra, the location of the heat source and the strength and the location of the magnetic field were set as variables. Circulation was related to the strength of a magnet, and was caused by the partial change in susceptibility, according to the temperature gradient. It was concluded that the change in the circulation shape increases when the value of Ra also increases. [PERSON] et al. [8] analyzed the heat transfer performance, according to the strength, number, and position of magnets when high-temperature ferrofluid was injected. Five different magnetic field strengths were specified, and magnets were arranged in six places. When the magnetic field was stronger than a certain standard, the cooling performance was proportionally increased. The small circulation was combined to create a big vortex, which circulated the low-temperature ferrofluid to the relatively high-temperature wall. Finally, the position of magnets showed that the heat transfer performance was improved when all magnets were placed near the cold wall and closer to the inlet area. [PERSON] et al. [9] placed a permanent magnet in the toroidal loop. Thermomagnetic convection characteristics in which circulation occurs depending on the heat source were used. The magnitude of the heat flux from the heat source, the temperature of the heat sink, the position of the magnet, and the strength of the magnetic field were set as variables. It was shown that the ferrofluid in the loop can be cycled continuously without additional energy consumption. In addition, as the temperature difference between the heat source and the heat sink increased, the circulation speed in the loop increased, indicating that the heat transfer performance was improved. [PERSON] et al. [10] studied the heat transfer performance when two phases (water and Fe\({}_{3}\)O\({}_{4}\)) exist in a square channel. The density, particle size, and magnetic field strength of the nanofluid were set as variables. As a result, the heat transfer performance improved as the density and the particle size increased. In addition, it was concluded that the circulation of the fluid increases as the magnetic field strength increases. [PERSON] et al.