磁流体中Helmholtz和Kelvin力的界定

磁流体磁彻体力的两种简化形式Helmholtz力和Kelvin力具有一定的适用范围.在推导磁流体中的磁彻体力表达式基础上，分析Helmholtz力和Kelvin力在磁流体中的起源，得出两种形式的成立条件.计算结果表明:当磁流体磁导率与外磁场强度无关时，磁流体磁彻体力可由Helmholtz力表示；当磁流体中磁性颗粒的平均磁矩与磁流体比体积无关时，Kelvin力为磁彻体力的简化形式；在磁流体磁化系数与其密度成正比情况下，Helmholtz力可转换为Kelvin力.关键词：磁流体磁彻体力Helmholtz力Kelvin力

Definition of Helmholtz and Kelvin forces in magnetic fluids

The Helmholtz and Kelvin forces for volume force density in magnetic fluids are valid only in some situations. Based on calculation of the volume force density in magnetic fluids, the origin for the Helmholtz and Kelvin forces in magnetic fluids is suggested, and the range of validity of them is analyzed in this paper. The calculation results show that the volume force density can be expressed in the form of Helmholtz force when the permeability of magnetic fluid is independent of the applied magnetic field, while the Kelvin force is valid when the average magnetic moment of magnetic particles in the magnetic fluid is independent of the specific volume of magnetic fluid. When the susceptibility is proportional to the density of magnetic fluid, the Helmholtz force is reduced to the Kelvin force.