Mechanism Of The Thermomagnetic Convection And Heat Transport Features Of Magnetic Fluid

A temperature-sensitive magnetic fluid means that its magnetization remarkably decreases with the increase in temperature, so that strong thermomagnetic convection can be seen to take place in the fluid:When this type of magnetic fluid experiences a temperature variation in the presence of an external magnetic field, a magnetic force will arise to drive the magnetic fluid flow. This field-induced flow may be controlled by the synergy function between the external magnetic field and the temperature difference in the fluid. If the thermomagnetic convection takes place in a loop shape channel, a continuous circulation flow can be maintained inside the loop, transferring heat from heat source to the heat sink. Since no mechanical moving part is needed in the whole device, it has application potentials in the field of thermal engineering and is worthy of deep research. However, the research efforts to the thermomagnetic convection loop are relatively sparse, and there were still some problems to be resolved. This paper is focused on the following aspects:(1) Visualization of the fluid inside the thermomagnetic convection loop and measurements of the flow velocityThe flow measurement of the magnetic fluid inside a thermomagnetic convection loop is still a challenge, which is important for deep research of the flow and heat transfer feature of the loop. In this paper, a particle image velocimetry (PIV) system has been put up, and due to the small transparency of the fluid to light a non- conventional light path was introduced to realize the visualization of the magnetic fluid inside the loop. The flow patterns of the magnetic fluid in the loop were observed and the velocity of fully-developed flow under main factors was measured. The measurement of velocity is helpful to further research of the operation characteristics of the thermomagnetic convection loop.(2) Experimental investigation on operational characteristics of the thermomagnetic convection loop using temperature-sensitive magnetic fluidA small thermomagnetic convection loop using a temperature-sensitive magnetic fluid was made. A permanent NdFeB magnet was used in the device to produce magnetic field. Heat sources and a heat sink were arranged at different parts of the loop, resulting in temperature difference in the fluid. It can be concluded that a circulation flow is formed inside the loop due to the thermomagnetic effect. The influences of heat source position, position of magnet, power of heat source and temperature of heat sink on the flow and heat transfer feature of the loop were discussed, in order to get insight into the mechanism of the operation characteristics of the loop and find out fine synergy between the magnetic field and thermal field.(3) Design method of automatic energy transport device using temperature-sensitive magnetic fluidBased on the knowledge of fluid dynamics, heat transfer, electromagnetics and the feature of magnetic fluid, a model for describing thermomagnetic convection of a temperature-sensitive magnetic fluid is established, which includes the coupling of the three fundamental phenomena, i.e., magnetic, thermal, and fluid dynamic features. The flow and heat transfer features of the fluid in the thermomagnetic convection loop were numerically simulated by using the CFD software. The design method for the temperature-sensitive automatic energy transport device is proven to be credible by the approving coincidence between the numerical values and experimental data.(4) Investigation on the operation features of thermomagnetic convection loop containing series-wound and shunt-wound multi thermomagnetic pumpsWhen the thermomagnetic convection of a temperature-sensitive magnetic fluid takes place in a loop, a continuous circulation of the fluid may be maintained due to the magnetic force resulting from the synergy of external magnetic field and the temperature gradient in the fluid, which plays as a thermomagnetic "pump". Researches on such thermomagnetic convection cooling loop have been limited to the "single-pump" situation. In this paper, mathematical models of series-wound and shunt-wound "multi-pump" thermomagnetic convection loops were established based on the above-mentioned mathematical model. The operation feature of these "multi-pump" systems were numerically investigated, which were then compared with those in the conventional "single-pump" loop, in order to find out the flow and heat transport features of these "multi-pump" systems and the influence between these thermomagnetic "pumps"(5) To explore the application potentials of the thermomagnetic convection loop in the field of thermal engineeringSmall heat transport devices are created based on the thermomagnetic effect. The magnetic field was shielded to minimize the field intensity in the surrounding area. The cooling performances of the devices with different strctures were investigated, and their application potentials were discussed by considering the cooling capacity and the configuration.