磁场强化磁性液体自然对流传热的机理

在重力场中流体密度变化产生自然对流，在磁力场中磁性液体的表观密度随外加磁场强度的变化而明显变化，磁场可以改变磁性液体的自然对流.通过对磁场中的磁性液体的静力学计算和分析，建立一个由均匀磁场和均匀梯度磁场同轴叠加的合成磁场，合成磁场使磁场引起的磁性液体密度变化各处均等，各处的自然对流传热均等，从而使磁性液体的表观密度和自然对流传热系数得以准确测量，由此建立起磁性液体的磁场强度、表观密度、Grashof数之间的关联式.磁场强度的增大使磁性液体表观密度增大，使磁性液体处于超重状态，是磁场强化磁性液体自然对流传热的机理.

Mechanism of natural convection heat transfer of magnetic fluid enhanced by magnetic field

In a gravity field, the changes of fluid density caus e natural convection, while in a magnetic field, the apparent density of magnetic fluid changes markedly with the change of the intensity of external magnetic fie ld.Therefore,magnetic field can influence the natural convection of the magnetic fluid.Through static calculation and analysis,a synthesized magnetic field can be established resulting from the coaxial superposition of a uniform magnetic fi eld and a uniform gradient magnetic field.The change of the density of magnetic fluid caused by the synthesized magnetic field is equal everywhere in the fluid, and natural convection heat transfer is also equal everywhere.Thus the apparent density and the coefficient of natural convection heat transfer can be accurate ly measured and a correlation equation can be established between magnetic field intensity,apparent density and the Grashof criterion of the magnetic fluid.Acco rdingly, the increase of magnetic field intensity causes an increase of apparent density of magnetic fluid, which is magnetic fluid in a state of overweight.Tha t is the mechanism of natural convection heat transfer of magnetic fluid enhance d by magnetic field.