Ultrasound Doppler Based In-Line Rheometry - Development, Validation and Application

Abstract: The trend within fluid industry is towards continuous production, leading to an increasing demand for new and improved methods that allow real-time monitoring of quality parameters and fast process control. The consistency and viscosity can be described by fluid rheology and are frequently used as quality control parameters. Rheological properties can be correlated with product microstructure, they govern the performance of unit operations and detailed knowledge is fundamental for the design of new process equipment and for predicting e.g. heat transfer. The determination of rheological properties in-line, in real time, thus has a great economical impact and is important from a quality perspective for the development of innovative and competitive products and a prerequisite for efficient process control. A method for in-line rheometry combining the Doppler-based Ultrasound Velocity Profiling (UVP) technique with Pressure Difference (PD) measurements, commonly known as UVP-PD, has recently been developed. It has a strong potential to be commercialized and the method allows measurements not possible with common rheometers such as radial velocity profiles and yield stress directly in-line. Furthermore, it has advantages over commercially available process rheometers and off-line instruments in being non-invasive, applicable to opaque and concentrated suspensions, having small sensors dimensions and relatively low cost. However, there exists even to this date no UVP-PD system in commercial production. This thesis describes an extended methodology and a complete UVP-PD system for in-line rheometry and flow visualization under realistic processing conditions. In contrast to systems described earlier, the present set-up allows direct access to demodulated echo amplitude (DMEA) or ?raw data? from the UVP instrument. DMEA provides new valuable information about the investigated fluid through spectral analysis and gives important information about the quality of acquired data. It further enables the implementation of a new fast Fourier transform (FFT) based algorithm for velocity estimation. New software based on MATLAB ® graphical user interface (GUI) and Active X library that allows synchronized data acquisition and provided powerful and rapid tools to process and visualize data was developed, a prerequisite for in-line real-time monitoring and process control. New flow adapter cells and methods for data enhancement, wall detection and in-line measurements of sound velocity and attenuation are introduced. This leads to greater measurement accuracy and provides a feasible tool for determining particle concentration and possibly also particle size distribution in-line. The UVP-PD system presented here was validated against conventional off-line rheometers, theoretical model predictions, laser Doppler anemometry (LDA) measurements and computational fluid dynamics (CFD) simulation, with good agreement. The UVP-PD system was then successfully applied to a range of model and industrial fluids and suspensions, including fluids containing large particles and fibers. Changes in rheology were monitored in real-time directly in the process line, with respect to changes in profile shape, in rheological parameters, as well as in terms of variations in the attenuation of transmitted ultrasound and changes in sound velocity. It was concluded that the UVP-PD methodology and system presented can be used to monitor changes in rheology in industrial unit operations such as rapid start-up or shutdown of the process, liquid displacements during rinsing or product change and in-line mixing. It may also be an interesting option for studying structure degradation and the position of macroscopic particles in the flow field, which would not have been possible without the present system.