## 1 Introduction
[11] performed a numerical study on the optimization of microchannel geometry for nanofluid flow using COMSOL Multiphysics software. The result showed that the rectangular shaped collector shows greater uniformity in the distribution of the hat transfer in microchannel. [PERSON] et al. [12; 13] investigated the convective heat transfer performance of nanofluids containing solid-liquid phase change materials. They investigated properties such as nanoparticle size and thermal conductivity, which affected the convective heat transfer, and reported that nanofluids with small nanoparticles were desirable for convective heat transfer applications. [PERSON] et al. [14] studied the characteristics of the forced convective heat transfer of Fe\({}_{3}\)O\({}_{4}\)-water nanofluids using the finite element method. [PERSON] et al. [15] experimentally studied the convective heat transfer characteristics of decane and micelle nanofluids in the turbulent region. The results indicated that the Nu number increased up to 15% at a high Re number. [PERSON] et al. [16] demonstrated that when a 0.6 vol% Fe\({}_{3}\)O\({}_{4}\) nanofluid was used, the heat transfer coefficient and friction factor increased by 31% and 10%, respectively, compared with the existing working fluid. [PERSON] et al. [17] comparatively studied the thermal conductivity of graphene nanoparticles/ethylene glycol nanofluid and ethylene glycol nanofluid in the temperature range of 25-79 \({}^{\circ}\)C. The result showed that the incorporation of nanoparticles increases the thermal conductivity. More addition of nanoparticles reduces the positive effect on thermal conductivity, and the increase in temperature strengthens the positive effect. Recently, studies on the forced convective heat transfer characteristics of hybrid nanofluids in which two or more materials are dispersed in a fluid to complement the shortcomings and develop more effective nanofluids have been actively conducted. Better convective heat transfer characteristics can be achieved using a hybrid nanofluid. [PERSON] et al. [18] prepared a nanofluid by adding three types of nanoparticles, namely Al\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), and carbon nanotubes (CNTs), to the existing fluid based on polyalphaolefin. The results confirmed that the thermal conductivity increased by 21% compared with that of the existing fluid. [PERSON] et al. [19] studied the thermal properties of TiO\({}_{2}\) and CNTs by dispersing them in a mixture of water and propylene glycol (50:50), and the results confirmed that the thermal conductivity of the nanofluid increased compared with that of the conventional fluid. [PERSON] et al. [20] prepared Ag-multiwall carbon nanotubes (MWCNT) nanofluids, which exhibited a higher thermal conductivity than single MWCNT nanofluids. [PERSON] et al. [21] studied the heat transfer and friction coefficient of an MWCNT-Fe\({}_{3}\)Ohybrid nanofluid. When the concentration was 0.3 vol%, the Nu number increased by approximately 32.7%. [PERSON] et al. [22] investigated the pressure drop and heat transfer characteristics of Al\({}_{2}\)O\({}_{3}\) and MWNCT hybrid nanofluids. The experimental results indicated that the heat transfer coefficient was higher than that of the Al\({}_{2}\)O\({}_{3}\) single nanofluid, with a lower pressure drop, confirming that it is suitable for heat transfer applications. [PERSON] et al. [23] executed an experimental study of forced convective heat transfer in a coiled flow inverter using TiO\({}_{2}\)-water nanofluid. The authors presented the determination of flow ranges for coil flow inverter and limitations on nanoparticle concentration with the aim of heat transfer enhancement. Among the various types of nanofluids, magnetic nanofluids can improve heat transfer performance through the effect of a magnetic field and have been studied for different applications. Generally, magnetic nanofluids can enhance the efficiency of heat exchange devices such as heat pipes, thermal siphons, and heat exchangers by applying an external magnetic field.