EXPERIMENTAL METHODS IN MULTIPHASE FLOWS

The research in the field of multiphase flows has been advanced as a result of the availability of optical diagnostics that allow the simultaneous measurement of the particle size and velocity of the dispersed phase. This capability also allows the measurement of the continuous phase turbulence parameters in the presence of the dispersed phase. The phase Doppler method has been a key method in providing this information. As an extension of the well-known laser Doppler velocimeter (LDV), it represents a major step in allowing the LDV instrument to be applied to the experimentation in multiphase flows. The phase Doppler method is described and the measurement characteristics are discussed along with the limitations of the method. Strategies for addressing these limitations which include the problems with high number densities and particle deformations are also presented. Evaluations of the measurement capability provide a credible measure of the instrument performance. The phase Doppler method is limited to the measurement of spherical particles, droplets or bubbles. In order to address the measurement of non-spherical particles, a new method based on near-forward light scatter detection is presented. This method utilizes the light scattering intensity to establish the particle size. The ambiguity that occurs as a result of random trajectories through the Gaussian beam intensity distribution is resolved with a confocal beam optical configuration along with a solution of the light scattering equations to obtain the particle trajectory through the beams. Because of the contemporary interest in the imaging methods, a brief discussion on the methods including particle imaging velocimetry (PIV) is provided. Although this method has not been extended to simultaneous particle size and velocity measurement, efforts are being made to reach this goal. The work concludes with some representative examples of the measurements in two-phase turbulent flows that are now possible. These measurements have been used to verify the drag coefficient and evaluate the particle response in turbulent flows. The particle interaction with large scale turbulent eddies has also been studied and some examples of these data are provided.