中文摘要：

氧浓度分析仪被广泛地用于各行各业中,热磁对流氧浓度传感器具有使用寿命长、测量准确度高等优点.它巧妙地利用热磁对流现象引起传感器壁面温度的变化来感知氧气浓度的变化.但是由于热磁对流现象较为复杂,其感应机理尚不明确,为了进一步提高热磁对流氧浓度传感器的测量精度,有必要对其感应机理深入研究.本文通过实验的方法研究了两块方形磁铁构成的非均匀磁场作用下薄壁圆管中顺磁性气体在其中的传热特性.实验结果表明：圆管壁面温度在磁场的作用下较无磁场时有明显的降低,且随着热流密度的增大,管壁温度降低得越明显,管壁温度与热流密度成线性关系;随着热流密度的增大,热磁对流现象引起的平均速度及对流换热系数均增大;氧气浓度每增加10%,管壁温差降低0.12℃,即氧气浓度越高热磁对流现象越明显;所研究系统对于氧气浓度的分辨率约可达0.08%.

英文摘要：

The oxygen sensor is widely used in daily life. Thermal magnetic type oxygen sensor has some advantages such as long service life and high accuracy of measurement. It skillfully uses the change of the wall temperature that caused by the thermal magnetic convection phenomenon to sense the change of oxygen concentration. For a paramagnetic gas, the thermal megnetic convection is caused by the interaction between the temperature field and the magnetic field as the gradient of the magnet field and the temperature gradient both existing at the same time. The intensity of thermal megnetic convection is determined by the magnetic susceptibility of a gas and the gradient of H2（where H is the induced magnet field）. Oxygen is a common paramagnetic gas, the magnetic susceptibility of oxygen has a much higher than other gas, thus, the oxygen concentration of a gas can be detected by the thermal magnetic convection phenomenon. However, the thermal magnetic convection phenomenon is complicated, The sensing mechanism of this type sensor is not clear. Therefore, it is necessary to study the sensing mechanism in-depth to improve the accuracy and efficencey of thermal magnetic type oxygen sensor. This paper, by means of experiments, studies the wall temperature change characteristics of the thin-wall circular tube in a non-uniform magnetic field generated by two pieces of rectangular permanent magnets. In the experiment, a quartz glass tube with a thin wall thickness was used as the channel through which the measured gas flows. Two permanent magnets are arranged outside the quartz tube, which are used to provide the magnetic field required for the thermal magnetic convection. A kind of the sensitive element with double helically wounded resistance wires is designed. In which two resistance wires with different temperature coefficient are helically wounded on the wall of outside the quartz tube, one is the Manganin resistance wire for heating, and one is the platinum wire for measuring the temperature of tube wall. The loops of