Statistical Tools for Ultrasonic Analysis of Dispersive Fluids

This thesis focuses on the possibility of using ultrasonic measurement techniques for energy gas characterization. The idea is to combine both on-line flow measurements with non-invasive fluid characterization in the same measurement setup using the same sensor(s). The long-term goal of the project is to develop measurement methods based on ultrasonic techniques that can measure; the flow rate, the energy content, detect impurities, and estimate the composition. In this thesis different problems concerning gas characterization and modeling are addressed. The information obtained from ultrasonic measurements are limited to spectral variations in the attenuation and phase velocity. Hence, part of the research is focused on estimating these quantities accurately with low uncertainty. Another area is parametric modeling and identification of the bulk modulus, where a new model structure for gas mixtures with complex dynamic behavior and/or unknown components is presented, capable of handling the combined effect of the absorption mechanisms. Finally, the problem of estimating the composition of a gas mixture is considered. The results show that it is possible to estimate the composition of processed and upgraded biogas, with high accuracy and precision, by combining the developed estimation techniques with multiple linear regression methods. The thesis consists of two parts. The first part includes an introduction to the research area together with a short summary of the contributions. The second part contains a collection of four papers describing the research.