Experimental Study on Thermal Conductivity of Hybrid Magnetic Fluids Under External Magnetic Field

In the paper, a hybrid magnetic fluid is prepared by adding carbon nanotubes to pure ferrofluid to improve its thermal conductivity. Furthermore, an electromagnet is used as magnetic source equipment, and the magnetic field strength in the air gap of the electromagnet is analyzed in theory, simulations, and experiments. A thermal conductivity measurement apparatus for magnetic fluid is established according to the transient hot-wire method. The effects of weight fraction and the length of carbon nanotubes, the external magnetic field strength, and the magnetic field duration time on the thermal conductivity of hybrid magnetic fluid are experimentally investigated. The results show that the thermal conductivity of the hybrid magnetic fluid is significantly improved by adding long carbon nanotubes (10–30 μm), and the thermal conductivity could be enhanced by 23.39% when its weight fraction is 1%. The magnetic field strength (41, 81, 122, 162 mT) and magnetic field duration time have little influence on the thermal conductivity of the hybrid magnetic fluid. The thermal conductivity of the hybrid magnetic fluid has good stability.