热磁对流氧浓度传感器感应机理的实验
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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%.
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 the heating and the temperature measurement are separated, which is favorable for study of the thermal magnetic type oxygen sensor. The permanent magnets used in the experiment have the remanence of 1.32 T. The ambient temperature around the sensitive element is measured by the thermocouple. The experimental device, which includes the sensitive element and some appropriately insulating elements, is placed in a rectangular cavity, and the size of the square cavity is much larger than the sensitive element. By comparing temperature difference of the tube wall, the increment of the convective heat transfer coefficient and the increment of velocity under conditions with and without the magnetic field to illustrate the relationship of the thermal magnetic convection phenomenon and heating power, oxygen concentration and other parameters. It is found that when magnetic field is pesent, the surface temperature of the tube wall is significantly lower than that of the case without magnetic field, and with the increase of heat flux, the surface temperature of tube wall decreases significantly. The relationship between the heat flux density and the change of the wall temperature is nearly liner.With the increase of heat flux density, the increasments of average velocity and convective heat transfer coefficient caused by the thermal magnetic convection phenomenon increase. When oxygen content increases by 10%, the temperature of the tube wall decreases by 0.12°C. The resolution of the studied oxygen concentration senser is about 0.08%.
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 the heating and the temperature measurement are separated, which is favorable for study of the thermal magnetic type oxygen sensor. The permanent magnets used in the experiment have the remanence of 1.32 T. The ambient temperature around the sensitive element is measured by the thermocouple. The experimental device, which includes the sensitive element and some appropriately insulating elements, is placed in a rectangular cavity, and the size of the square cavity is much larger than the sensitive element. By comparing temperature difference of the tube wall, the increment of the convective heat transfer coefficient and the increment of velocity under conditions with and without the magnetic field to illustrate the relationship of the thermal magnetic convection phenomenon and heating power, oxygen concentration and other parameters. It is found that when magnetic field is pesent, the surface temperature of the tube wall is significantly lower than that of the case without magnetic field, and with the increase of heat flux, the surface temperature of tube wall decreases significantly. The relationship between the heat flux density and the change of the wall temperature is nearly liner.With the increase of heat flux density, the increasments of average velocity and convective heat transfer coefficient caused by the thermal magnetic convection phenomenon increase. When oxygen content increases by 10%, the temperature of the tube wall decreases by 0.12°C. The resolution of the studied oxygen concentration senser is about 0.08%.
引文
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2 Wakayama N I.Effect of a decreasing magnetic field on the flow of nitrogen gas.Chem Phys Lett,1991,185:449-451
3 Wakayama N I,Ito H,Kuroda Y,et al.Magnetic support of combustion in diffusion flames under microgravity.Combust Flame,1996,107:187-192
4 Wakayama N I.Behavior of gas flow under gradient magnetic fields.J Appl Phys,1991,69:2734-2736
5 Wakayama N I.Magnetic promotion of combustion in diffusion flames.Combust Flame,1993,93:207-214
6 Wakayama N I.Magnetic buoyancy force acting on bubbles in non-conducting and diamagnetic fluids under microgravity.J Appl Phys,1997,81:2980-2984
7 Wakayama N I,Ataka M,Abe H.Effect of a magnetic field gradient on the crystallization of hen lysozyme.J Cryst Growth,1997,178:653-656
8 Qi J W,Wakayama N I,Yabe A.Magnetic control of thermal convection in electrically non-conducting or low-conducting paramagnetic fluids.Int J Heat Mass Tran,2001,44:3043-3052
9 Jovanovic G N,Sornchamni T,Atwater J E,et al.Magnetically assisted liquid-solid fluidization in normal and microgravity conditions:Experiment and theory.Powder Technol,2004,148:80-91
10 Ueno S,Iwasaka M,Eguchi H,et al.Dynamic behavior of gas flow in gradient magnetic fields.IEEE Trans Magn,1993,29:3264-3266
11 Wrobel W,Fornalik-Wajs E,Szmyd J S.Experimental and numerical analysis of thermo-magnetic convection in a vertical annular enclosure.Int J Heat Fluid Fl,2010,31:1019-1031
12 Wrobel W,Fornalik-Wajs E,Szmyd J S.Analysis of the influence of a strong magnetic field gradient on convection process of paramagnetic fluid in the annulus between horizontal concentric cylinders.J Phys Conf Ser,2012,395:12124-12131
13 Huang J,Edwards B F,Gray D D.Magnetic control of convection in non-conducting paramagnetic fluids.Phys Rev E,1998,57:R29-R31
14 Huang J,Gray D D,Edwards B F.Thermo-convective instability of paramagnetic fluids in a non-uniform magnetic field.Phys Rev E,1998,57:5564-5571
15 Huang J,Gray D D,Edwards B F.Magnetic control of convection in non-conducting diamagnetic fluids.Phys Rev E,1998,58:5164-5167
16 Wang L B,Wakayama N I.Control of natural convection in non-and low-conducting diamagnetic fluids in a cubical enclosure using inhomogeneous magnetic fields with different directions.Chem Eng Sci,2002,57:1867-1876
17 Lyubimova T,Mailfert A.Thermal convection in a closed cavity in zero-gravity space conditions with stationary magnetic forces.J Phys Conf Ser,2013,416:12027-12032
18 Kenjere?S,Wrobel W,Pyrda L,et al.Transients and turbulence pockets in thermal convection of paramagnetic fluid subjected to strong magnetic field gradients.J Phys Conf Ser,2011,318:072028
19 Kaneda M,Tsuji A,Ooka H,et al.Heat transfer enhancement by external magnetic field for paramagnetic laminar pipe flow.Int J Heat Mass Tran,2015,90:388-395
20 Lee S H,Hyun J M.Transient buoyant convection of air in an enclosure under strong magnetic effect.Int J Heat Mass Tran,2005,48:3097-3106
21 Jiang C W,Feng W,Zhong H,et al.Magnetic and gravitational convection of air in a porous cubic enclosure with a coil inclined around the y axis.Transport Porous Med,2014,102:167-183
22 Jiang C W,Li H S,Chen D L,et al.Influences of coil inclined around Y axis on thermomagnetic convection of air in a cubic enclosure(in Chinese).Proc CSEE,2011,31:76-83[姜昌伟,李贺松,陈冬林,等.线圈绕Y轴倾斜对方腔内空气热磁对流的影响.中国电机工程学报,2011,31:76-83]
23 Bednarz T P,Lin W,Patterson J C,et al.Scaling for unsteady thermo-magnetic convection boundary layer of paramagnetic fluids of Pr>1 in micro-gravity conditions.Int J Heat Fluid Fl,2009,30:1157-1170
24 Yang F,Ren J X,Yang K L,et al.Coordination analysis of magnetothermal convection in horizontal tube(in Chinese).J Eng Thermophys,2006,27(Suppl):89-92[杨帆,任建勋,杨昆仑,等.通道内空气热磁对流的协同分析.工程热物理学报,2006,27(增刊):89-92]
25 Yang L J,Du X Z,Yang Y P.Influences of permanent gradient magnetic field configurations on air natural convection heat transfer(in Chinese).J Chem Ind Eng,2007,58:2980-2985[杨立军,杜小泽,杨勇平.永磁梯度磁场布置方式对空气自然对流换热的影响.化工学报,2007,58:2980-2985]
26 Yang L J,Ren J X,Du X Z,et al.Influences of different magnetically induced longitudinal vortices on air convection heat transfer(in Chinese).J Eng Thermophys,2006,27:283-285[杨立军,任建勋,杜小泽,等.不同磁致纵向涡形式对空气对流换热的影响.工程热物理学报,2006,27:283-285]
27 Zhang X Y.The magneto-hydrodynamic characteristics of the thermal magnetic type oxygen sensor(in Chinese).Dissertation for Master Degree.Lanzhou:Lanzhou Jiaotong University,2014[张晓燕.热磁气式氧浓度传感器的磁流体动力学特性研究.硕士学位论文.兰州:兰州交通大学,2014]
2 Wakayama N I.Effect of a decreasing magnetic field on the flow of nitrogen gas.Chem Phys Lett,1991,185:449-451
3 Wakayama N I,Ito H,Kuroda Y,et al.Magnetic support of combustion in diffusion flames under microgravity.Combust Flame,1996,107:187-192
4 Wakayama N I.Behavior of gas flow under gradient magnetic fields.J Appl Phys,1991,69:2734-2736
5 Wakayama N I.Magnetic promotion of combustion in diffusion flames.Combust Flame,1993,93:207-214
6 Wakayama N I.Magnetic buoyancy force acting on bubbles in non-conducting and diamagnetic fluids under microgravity.J Appl Phys,1997,81:2980-2984
7 Wakayama N I,Ataka M,Abe H.Effect of a magnetic field gradient on the crystallization of hen lysozyme.J Cryst Growth,1997,178:653-656
8 Qi J W,Wakayama N I,Yabe A.Magnetic control of thermal convection in electrically non-conducting or low-conducting paramagnetic fluids.Int J Heat Mass Tran,2001,44:3043-3052
9 Jovanovic G N,Sornchamni T,Atwater J E,et al.Magnetically assisted liquid-solid fluidization in normal and microgravity conditions:Experiment and theory.Powder Technol,2004,148:80-91
10 Ueno S,Iwasaka M,Eguchi H,et al.Dynamic behavior of gas flow in gradient magnetic fields.IEEE Trans Magn,1993,29:3264-3266
11 Wrobel W,Fornalik-Wajs E,Szmyd J S.Experimental and numerical analysis of thermo-magnetic convection in a vertical annular enclosure.Int J Heat Fluid Fl,2010,31:1019-1031
12 Wrobel W,Fornalik-Wajs E,Szmyd J S.Analysis of the influence of a strong magnetic field gradient on convection process of paramagnetic fluid in the annulus between horizontal concentric cylinders.J Phys Conf Ser,2012,395:12124-12131
13 Huang J,Edwards B F,Gray D D.Magnetic control of convection in non-conducting paramagnetic fluids.Phys Rev E,1998,57:R29-R31
14 Huang J,Gray D D,Edwards B F.Thermo-convective instability of paramagnetic fluids in a non-uniform magnetic field.Phys Rev E,1998,57:5564-5571
15 Huang J,Gray D D,Edwards B F.Magnetic control of convection in non-conducting diamagnetic fluids.Phys Rev E,1998,58:5164-5167
16 Wang L B,Wakayama N I.Control of natural convection in non-and low-conducting diamagnetic fluids in a cubical enclosure using inhomogeneous magnetic fields with different directions.Chem Eng Sci,2002,57:1867-1876
17 Lyubimova T,Mailfert A.Thermal convection in a closed cavity in zero-gravity space conditions with stationary magnetic forces.J Phys Conf Ser,2013,416:12027-12032
18 Kenjere?S,Wrobel W,Pyrda L,et al.Transients and turbulence pockets in thermal convection of paramagnetic fluid subjected to strong magnetic field gradients.J Phys Conf Ser,2011,318:072028
19 Kaneda M,Tsuji A,Ooka H,et al.Heat transfer enhancement by external magnetic field for paramagnetic laminar pipe flow.Int J Heat Mass Tran,2015,90:388-395
20 Lee S H,Hyun J M.Transient buoyant convection of air in an enclosure under strong magnetic effect.Int J Heat Mass Tran,2005,48:3097-3106
21 Jiang C W,Feng W,Zhong H,et al.Magnetic and gravitational convection of air in a porous cubic enclosure with a coil inclined around the y axis.Transport Porous Med,2014,102:167-183
22 Jiang C W,Li H S,Chen D L,et al.Influences of coil inclined around Y axis on thermomagnetic convection of air in a cubic enclosure(in Chinese).Proc CSEE,2011,31:76-83[姜昌伟,李贺松,陈冬林,等.线圈绕Y轴倾斜对方腔内空气热磁对流的影响.中国电机工程学报,2011,31:76-83]
23 Bednarz T P,Lin W,Patterson J C,et al.Scaling for unsteady thermo-magnetic convection boundary layer of paramagnetic fluids of Pr>1 in micro-gravity conditions.Int J Heat Fluid Fl,2009,30:1157-1170
24 Yang F,Ren J X,Yang K L,et al.Coordination analysis of magnetothermal convection in horizontal tube(in Chinese).J Eng Thermophys,2006,27(Suppl):89-92[杨帆,任建勋,杨昆仑,等.通道内空气热磁对流的协同分析.工程热物理学报,2006,27(增刊):89-92]
25 Yang L J,Du X Z,Yang Y P.Influences of permanent gradient magnetic field configurations on air natural convection heat transfer(in Chinese).J Chem Ind Eng,2007,58:2980-2985[杨立军,杜小泽,杨勇平.永磁梯度磁场布置方式对空气自然对流换热的影响.化工学报,2007,58:2980-2985]
26 Yang L J,Ren J X,Du X Z,et al.Influences of different magnetically induced longitudinal vortices on air convection heat transfer(in Chinese).J Eng Thermophys,2006,27:283-285[杨立军,任建勋,杜小泽,等.不同磁致纵向涡形式对空气对流换热的影响.工程热物理学报,2006,27:283-285]
27 Zhang X Y.The magneto-hydrodynamic characteristics of the thermal magnetic type oxygen sensor(in Chinese).Dissertation for Master Degree.Lanzhou:Lanzhou Jiaotong University,2014[张晓燕.热磁气式氧浓度传感器的磁流体动力学特性研究.硕士学位论文.兰州:兰州交通大学,2014]