磁性液体在均匀磁场中的瞬态双热线导热系数的测试

Measurement of Thermal Conductivity of Magnetic Fluids under External Uniform Magnetic Field Using Transient Hot-wire Method

将封有聚α-烯烃合成油基磁性液体的两玻璃管放置于磁场中，为消除磁场力、重力所引起的磁性液体自然对流的影响，消除端部效应，研制了磁性液体在均匀磁场中瞬态双热线导热系数的实验测量系统，经与蒸馏水、乙醇标准样品的导热系数测量比较，实验装置有较高的测量精度。实验测量了不同方向的均匀磁场对不同体积浓度的磁性液体导热系数的影响。结果显示，当磁场方向与热通量方向一致时，磁场显著强化磁性液体的导热系数，其导热系数随磁场强度的增加而近似线性增加，且体积浓度越大增加量越大；当磁场方向与热通量方向垂直时，磁性液体的导热系数随磁场强度的变化不明显。

Polymeric α-olefin based magnetic fluids sealed in two glass tubes were placed in external magnetic field. To eliminate the end effect and the natural convection induced by magnetic field force and gravity force, the transient hotwire （THW） instrument was developed for accurate measurements of the thermal conductivity of magnetic fluids. The hot- wire apparatus was calibrated utilizing distilled water and anhydrous alcohol as reference fluids, which showed that the experimental system has a high accuracy. Effects of the direction of external magnetic field to the magnetic fluids with different volume fraction of suspended magnetic particles were measured. Results indicated that： when the direction of external magnetic field was parallel to the heat flow （the temperature gradient）, the thermal conductivity of the magnetic fluid increased greatly. The conductivity increased almost linearly with the strength of the magnetic field, the higher the particle concentration, the more increment was. On the other hand, when the magnetic field was perpendicular to the heat flow, little change in the thermal conductivity was found.