Local gas and liquid parameter measurements in air–water two-phase flows

Local measurements of flow parameters for the gas and liquid phases are conducted in an air–water two-phase flow loop. The test section is a vertical circular pipe with an inner diameter of 50 mm and a height of 3.2 m. The local measurements are performed at two elevations, namely 10 and 32 pipe diameters downstream from the test section inlet. The gas-phase measurements are carried out using four-sensor conductivity probes. The data taken from the probes at different radial locations are processed using a signal-processing program to yield radial profiles of the void fraction, bubble velocity, bubble number frequency, and interfacial area concentration. The measurements of the liquid-phase velocity are made using a particle image velocimetry (PIV) system with an optical phase separation method, namely, planar laser-induced fluorescence (PLIF). Raw PIV images are acquired by a CCD camera using fluorescent particles and an optical filter. An image pre-processing scheme is developed and applied to the raw PIV images to minimize the residual signals due to the presence of bubble surfaces. A systematic uncertainty introduced by multiple refractions on the circular test section wall and a square viewing box is discussed and the measurement accuracy can then be improved by compensating for this uncertainty source. A statistical cross-correlation algorithm provided by LaVision Inc. is adopted to determine the liquid-phase velocity and its fluctuations. The local liquid-phase velocity is compared with data available in the literature. This relatively high spatial resolution data set for both the gas and liquid phases can be used for two-phase computational fluid dynamic (CFD) model development and benchmarking.