Research On Theory Of Ultrasonic Attenuation In Pulp Suspension And Its Application In Concentration And Flow Measurement

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.