【作者】 姚骏；

【导师】 李斌；

【作者基本信息】 上海大学 ， 控制理论与控制工程， 2006， 博士

【摘要】 近年来，液固两相流特性分析及检测技术是国内外两相流研究领域高度关注的热点课题。作为一种常见的工业液固两相流体，在管道中流动的纸浆悬浮液质量浓度是造纸过程的基本工艺参数。另一方面，纸浆悬浮液的流量参数及温度参数也是生产中需要测量的重要参数。因为超声检测技术具有非侵入性、非接触性、穿透力强、响应快速、结构简单等突出优点，本论文考虑采用测量超声衰减的方法实现纸浆悬浮液质量浓度的在线检测。从多传感器集成化测量的角度出发，本论文将超声换能器和温度传感器集成到电磁流量计的测量管道中，实现了管道中纸浆悬浮液浓度、流量、温度三参数的一体化测量。无论在理论上还是在实践中，采用超声衰减检测技术来测量纸浆悬浮液浓度都是一个有待深入研究的课题。现有悬浮液超声衰减理论的研究大多只限于以球体离散相介质为散射元模型构成的悬浮液系统。对于以圆柱体离散相介质为散射元模型构成的悬浮液系统超声衰减理论至今还缺少系统地研究。本论文的理论研究工作从线性声学的基本原理出发，针对纸浆悬浮液中具有圆柱体外形的纸纤维介质，分别建立了基于无限长圆柱体散射和基于有限长圆柱体散射的超声衰减模型。作为研究基于无限长圆柱体散射和基于有限长圆柱体散射的超声衰减模型的出发点，论文首先推导了在粘滞导热流体和弹性圆柱体纸纤维中传播模式散射波、热模式散射波和剪切模式散射波的速度势方程表达式。为了完善现有的无限长圆柱体超声散射模型，根据矢量势的规范不变性，论文建立了速度、应力、温度和热流的连续边界条件线性方程组，并由此求解得到了斜入射到单个无限长圆柱体超声波散射模型。根据Epstein的单个球体能量损耗模型，论文推导了无限长圆柱体空间中超声能量损耗表达式。从稀释悬浮液的单次散射近似出发，论文提出了基于无限长圆柱体散射的纸浆悬浮液超声衰减理论模型。根据纸纤维的实际形状，考虑到基于无限长圆柱体散射的超声衰减模型存在的缺陷，论文首次提出了纸纤维的复合型有限长圆柱体模型，并从Kirchhoff标量衍射理论出发讨论了有限长的纸纤维尺寸与远场衍射的关系，推导得到了粘滞导热悬浮液中复合型有限长圆柱体远场前向散射波的速度势表达式。论文通过研究适用于分析纸浆悬浮液超声传播特性的迭代有效介质近似方法，得出了预测纸浆悬浮液超声衰减的基本方法。以上述纸浆悬浮液超声衰减模型为基础，论文采用符号计算软件Maple编写了数值计算软件包，实现了超声衰减模型的计算机描述。利用软件包的计算结果，分析了散射波速度势无穷级数谐波表达式收敛特性、纸浆悬浮液超声衰减与悬浮液浓度关系及超声衰减模型对纸浆悬浮液材料参数变化的敏感度等问题。数值计算结果与相关文献的理论结果和实验结果的对比，验证了本论文的理论分析和数值计算结果可靠性。论文从造纸工业现场多参数测量的实际需要出发，讨论了可实现纸浆悬浮液流量、浓度及温度等多参数在线测量的浓度流量测量装置总体方案及其实现技术，重点研究了用于测量纸浆悬浮液超声衰减的超声换能器设计，建立了基于虚拟仪器的浓度流量测量系统的信号测试平台。同时也对浓度流量测量系统的仪表化设计进行了探索性的研究。论文采用浓度流量测量装置及信号测试平台分别对非流动状态纸浆悬浮液超声衰减特性及在管道中流动纸浆悬浮液的浓度流量测量进行了一系列实验研究，取得实验结果与理论计算值相符合的研究结论。实验表明，基于无限长圆柱体散射的超声衰减模型和基于有限长圆柱体散射的超声衰减模型在实验所测量的纸浆悬浮液浓度内具有各自的浓度适用范围。论文最后提出了有待于进一步解决的问题。更多还原

【Abstract】 Recently techniques for characterization of liquid-solid two phase flow have aroused great attention in domestic and foreign two phase flow research area. Pulp suspension is a kind of typical liquid-solid two phase flow in industry. Mass concentration of pulp suspension flowing in pipe is a fundamental technical parameter. Flow and temperature of pulp suspension are two other important parameters to be measured in production process. Due to the prominent advantages of ultrasonic technique, such as non-destructiveness, non-intrusiveness, good penetrability, rapid response, and simple structure, on-line measurement of mass concentration of pulp suspension was carried out by means of ultrasonic attenuation in this paper. Based on the point of view of multi-sensor integration, ultrasonic transducers and a temperature senor were mounted in the measuring pipe of electromagnitic flowmeter to measure concentration, flow and temperature in pulp suspension integratively.Employing ultrasonic attenuation technique to determine mass concentration in pulp suspension is a problem to be studied thoroughly either in theory or in application. Most theoretical studies on ultrasonic attenuation in suspension were limited to the suspension system in which the scatterer model is composed of spheral solid particles in disperse phase. However, the ultrasonic attenuation theory of the suspension system in which the scatterer model is composed of cylindrical solid particles in disperse phase has not been studied systematically yet. According to fundamental principles of linear acoustics, aiming at cylindrical paper fiber in pulp suspension, ultrasonic attenuation models based on infinite cylinder scattering and the model based on finite cylinder scattering were established in the paper.As the starting point of theoretical study, the velocity potential equations of compressional scattered wave, thermal scattered wave and shear scattered wave in viscous, heat conduction liquid and elastic cylindrical fiber were deduced respectively. In order to complete the existing ultrasonic scattering model of infinite cylinder, system of linear equations at continuous boundary conditions of velocity, stress, temperature and heat flux, was established based on gauge invariance and then the oblique incidence ultrasonic scattering model of single infinite cylinder was gained. According to Epstein’s energy dissipation model of single sphere, the ultrasonic energy dissipation expression in infinite cylindrical space was deduced. From single scattering approximation in diluted suspension, ultrasonic attenuation model based on infinite cylindrical scattering in pulp suspension was built in the paper.According to the actual shape of paper fiber, compound finite cylinder model of paper fiber was put forward for the first time due to the disadvantages of ultrasonic attenuation model based on infinite cylindrical. From Kirchhoff’s diffraction theory, the relation between finite fiber size and far field scattering amplitude was discussed in the paper. The velocity potential expression of far field forward-scattering wave from compound finite cylinder in viscous, heat conduction suspension was deduced. The iterative effective medium approximation for ultrasonic attenuation analysis in pulp suspension was established and the essential method to predict ultrasonic attenuation in pulp suspension was acquired. Based on above ultrasonic attenuation model in pulp suspension, a numerical computation software package was programmed with symbol computing software Maple to implement the computer description of ultrasonic attenuation model. Several problems were analyzed from the results of numerical computation, including the convergence criteria for infinite series partial expressions of scattering wave velocity potential, the relationship between ultrasonic attenuation in pulp suspension and concentration of suspension, ultrasonic attenuation model’s sensitivity to suspension material properties. The result of the comparison between the numerical computation data and theoretical or experiment data in correlative literatures validated the reliability of theoretical analysis and numerical computation in this paperThe overall design scheme and techniques of concentration-flow measurement device were put forward in the paper, which can measure concentration, flow and temperature in pulp suspension. Emphasis was placed on the design of ultrasonic transducer which can be applied in the measurement of ultrasonic attenuation in pulp suspension. The signal testing platform based on virtual instrument for concentration flow measurement system was designed. Meanwhile the instrumented device design techniques for the concentration-flow measurement system were researched initially.Employing the concentration-flow measurement device and signal testing platform, several experiments were carried out to test the ultrasonic attenuation characteristic of pulp suspension in static state and measure concentration-flow value of the pulp suspension flowing in pipe. Experimental results agreed with the theoretical results quit well. Experimental results showed that within the whole concentration range in the experiments, there existed different applicable range of suspension concentration in the ultrasonic attenuation model based on finite cylinder and the ultrasonic attenuation model based on infinite cylinder.Some questions needed to research firth were discussed in the end of the paper.更多还原