Experimental Investigation of an Index-Mismatched Multiphase Flow Using Optical Techniques

An experimental investigation of multiphase flow involving a liquid (water) and a gas (air) is performed. The results for three different scenarios are presented: fixed bubble, ascending bubble, and dispersed-bubble turbulent pipe flow. This study involves a comparison of statistical data collected using two sensing systems, a wavefront sensor and a high-speed video camera. A signal analysis technique based on signal attenuation is developed for data collected using the wavefront sensor. The three experiments performed provide experimental evidence that the Shack-Hartmann wavefront sensor, operating on signal attenuation, is a viable method for the study of multiphase bubble flows. 1. Introduction Multiphase flow is defined as the simultaneous flow of several phases, with the simplest case being two-phase flow. The flow of two phases is found in many industrial processes including chemical and nuclear reactors, distillation towers, pipeline transport, injection of fluids for secondary recovery of oil and geothermal power plants. One form of two-phase flow is gas-liquid dispersed-bubble turbulent pipe flow. This flow is of significant importance in chemical and petroleum process industries where the interfacial area between phases needs to be large for improved process efficiency. Bubble size, velocity of bubbles, and their distribution along the pipe are all important parameters for optimizing the efficiency of processes that rely on dispersed-bubble turbulent pipe flow. Noninvasiveness is a desired attribute in any multiphase flow measurement technique given that the interference between the flow and the measurement device can affect the measured values. Many of the existing multiphase flow measurement techniques rely on the ability of the sensing apparatus to discriminate between certain physical properties that vary between phases, such as electromagnetic radiation attenuation or electrical impedance. A large number of investigations reported over the last fifteen years describe the application of nonintrusive flow sensing techniques applied to the measurement and the study of multiphase fluid flows [1]. Nonintrusive measurement techniques typically provide either integral or line-integrated information, with the most common consisting of capacitance [2], conductance [3], ultrasound [4], and gamma-radiation absorption [5] measurements. Both integral and line-integrated information collected from multiple sensors is often transformed into spatial information through the use of tomographic reconstruction algorithms. The long-term goal of a larger