Magnetic Nanofluid Fe3O4 in Passive Cooling System Based on Thermo-Osmotic Effect

Due to the dependence of the magnetic susceptibility of nanofluid on temperature, magnetic nanofluid is able to move in a nonuniform temperature field and an external magnetic field. In a passive cooling system based on the thermomagnetic effect, the coolant can move without the use of a pump. Here we demonstrate the principle of operation of a brand-new passive cooling system, where the convective flow of a magnetic nanofluid is driven by the combined action of thermo-osmosis and magnetic force. Therein lies the fundamental difference between the passive cooling system proposed here and the previously known systems, where the movement of ferrofluid is due to the action of the thermomagnetic effect. Based on nonequilibrium thermodynamics, a phenomenological model is proposed to describe the motion of a magnetic nanofluid in a channel in nonuniform temperature and magnetic fields. In the experimental study, the motion of ferrofluid Fe3O4 in the micro-channel is analyzed with variations in temperature, temperature gradient, channel thickness, and nanoparticle concentration. It is shown that in a non-uniform temperature field water-based ferrofluid moves in the direction of increasing temperature, while tridecane-based ferrofluid moves in the direction of decreasing it. If the thickness of the micro-channel exceeds a certain critical value, then the movement of ferrofluid under the influence of thermo-osmosis degenerates. It has been established that with an increase in concentration of nanoparticles the velocity of ferrofluid motion decreases due to the opposite direction of nanoparticle motion under the action of thermophoresis and the motion of liquid under the action of thermo-osmosis.