实验研究了不同体积分数Fe3O4/Water纳米流体在磁场作用下的水平小圆管内的湍流流动对流换热特性，测量了体积分数为3%的Fe3O4/Water纳米流体的沿程压力降并计算了其能量比率，探讨了在磁场作用下纳米流体强化对流换热的机制.实验结果表明：Fe3O4/Water纳米流体的对流换热系数随着体积分数的增加而升高，其平均值最大提高了4.3%；在与流动方向垂直的匀强磁场作用下，当磁场强度为 23.809和 39.682kA/m时，纳米流体的换热系数几乎没有提高，当磁场强度为 63.492A/m时，换热系数有所提高，其平均值最大提高了3%；Fe3O4/Water纳米流体的沿程压力降相对于基液去离子水增加了50%，外加磁场使其进一步增大，并随着磁场强度的增加而增大，当磁场强度为 63.492A/m时增加了 11.3%；Fe3O4/Water纳米流体相对于基液去离子水的能量比率计算值小于1，说明添加Fe3O4纳米粒子没有达到节能的效果.
The effect of magnetic field on the convective heat transfer of Fe3O4/Water nanofluids was experimentally studied. The Fe3O4/Water nanofluids flowed through a horizontal circular tube under the turbulent flow regime conditions. The pressure drop of Fe3O4/Water nanofluids was measured at volume fraction of 3%. The mechanism of the heat transfer of magnetic nanofluids under the magnetic field was discussed. The experimental results showed that the heat transfer coefficient increased with the increase of the Fe3O4/Water nanofluids concentration, and the maximum averaged enhancement was 4.3%. In the presence of the perpendicular uniform magnetic field, almost no obvious enhancement of the convective heat transfer coefficient of Fe3O4/Water nanofluids was observed in fields up to 23.809 and 39.682kA/m but it was observed in fields of intensity up to 63.492kA/m. The maximum averaged enhancement was 3%. Compared with the pressure drop of the distilled water, 50% enhancement was observed using Fe3O4/Water nanofluids at the volume fraction of 3%. Enhancement was also obtained under the applied magnetic field and the maximum averaged enhancement was 11.3%. The power ratio was less than 1, and thus the utilization of Fe3O4/Water nanofluids in heat transfer could not save energy.
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