Development of High-Performance Heat Transport Device Using Magnetic Fluid and Intermittent Magnetic Field

本文提出了一种利用磁流体和间歇磁场相互作用增强传热的独特技术。已知在外加磁场作用下，磁流体呈现出尖状界面。磁场的加减作用会交替产生尖状界面和扁平界面，使磁流体产生大体积流体运动，从而使传热显著增强。本文对上述方法的强化传热速率进行了定量研究。为此，磁性流体被放置在一个浅容器中。容器由加热的底壁和冷却的顶壁组成，磁场上方存在空气层。通过改变施加磁场的强度和频率，系统地测量了冷热壁之间的换热率。结果表明，间歇磁场作用下的换热速率比无磁场作用下提高了3 ~ 6倍。其中，以空气层代替水对磁流体的增强效果最好。讨论了最佳磁场强度、磁场频率、磁流体深度对传热的影响。本技术将用于电子设备的冷却。

A unique technique for the heat transfer enhancement that utilizes the interaction of a magnetic fluid and an intermittent magnetic field was proposed in the present study. It is known that the magnetic fluid shows spiky interface when the magnetic filed is imposed. The spiky interface and a flat interface will be generated alternately by putting on and off the magnetic field, and this will cause a bulk fluid motion of magnetic fluid, and thus, will result in the marked enhancement of the heat transfer. The rate of the heat transfer enhancement by the above method was investigated quantitatively in the present study. For the sake of this, the magnetic fluid was placed in a shallow container. The container was consisted with heated bottom wall and cooled top wall and air layer existed over the magnetic field. The heat transfer rates between the hot to cold walls were measured by varying the strength and frequencies of imposed magnetic field systematically. The results showed that the heat transfer rates under the intermittent magnetic field are increased by 3 to 6 times larger than those without magnetic field. In particular, the highest enhancement ratio was obtained when the water was replaced with air layer over the magnetic fluid. The optimum strength and the frequencies of the magnetic filed, the depth of the magnetic fluid on heat transfer were also discussed. The present technique will be utilized for the cooling of electronic equipment.