Abstract
In the design and operation of two-phase flow systems, it is essential to know the two phase flow pattern, on which the hydro- and thermo-dynamic data such as pressure drop, void fraction and quality are dependent. It is therefore important to develop a technique to evaluate the invisible flow pattern in a pipe or duct.
Pressure signals generated by flowing are easily accesible to measurement and also they may contain sufficient information on peculiar features of the flow pattern and flow condition for the two-phase mixture. In this study we propose a technique of estimating the representative flow pattern of gas-liquid two-phase flow in a vertical tube, based on the processing of measurement data on four static pressure signals. Differential pressures are measured in order to eliminate the influence of pressure fluctuations occurring outside of the measurement section. Differential pressure signals at both small and large intervals are examined at the same time. Two small intervals are chosen to be respectively equal to the inside radius of pipe in order to discriminate a bubble (i. e. a spherical bubble) with a length half of the inside diameter of pipe. The large one is chosen to be about ten times the inside diameter in order to evaluate a fully developed gas slug.
Experimental results with vertical pipe flows of nitrogen gas-water mixtures show that in a regular flow pattern the differential pressures exhibit a characteristic statistical property different from that of another flow pattern. Therefore it is possible to estimate the flow pattern from the configuration of probability density function, the presence of periodicities, the order of variance and the average value of differential pressures. The slug-length, rise velocity and characteristic frequency in slug-like flows are also obtainable.
