Techniques of PIV in stratified two-phase headers
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The stratification of two fluid phases, namely gas and liquid, within flow distribution devices, such as headers, that have side or bottom oriented fluid pipe connections, or discharges, has shown relevance to loss-of-coolant accidents in nuclear power plants. Under critical conditions the gas phase could entrain into the predominantly liquid discharge flow causing the fluid quality to be dramatically affected. This condition is referred to as the onset of gas entrainment (OGE) phenomenon and it occurs at a specific critical liquid height which changes with the Froude number. The liquid velocity field at the OGE is of importance, for example, to theorists who may find a semi-empirical approach to model this phenomenon. Stereoscopic particle image velocimetry (PIV) technique is an excellent candidate for non-intrusively investigating the velocity field. The liquid-phase velocity field was investigated for three discharge Froude numbers at the OGE. It was found that the stereoscopic PIV could be used to extract the velocity field experimentally, yet a high degree of error was found in the region closest to the discharge. The relative error was determined through conservation of mass by comparing the flow rate obtained with the PIV data to that obtained using a flow meter. In summary it was found that the number of image planes used, the resolution of the image planes, and consequently the number of vectors used to calculate the flow rate, all contributed a great deal to the relative error. 2010 Elsevier Inc.
