Instrumentation development in two-phase flow

A multi-faceted instrumentation approach is described which has played a significant role in obtaining fundamental data for two-phase flow model development. This experimental work supports the development of a three-dimensional, two-fluid, four field computational analysis capability. The goal of computational analysis is to utilize mechanistic models and a fundamental understanding rather than rely on empirical correlations to describe the interactions in two-phase flows. In order to verify the fidelity of these models, local measurements of the flow variables are needed. Both invasive and non-invasive measurement techniques and their strengths and limitations are discussed in this paper. Measurement uncertainty is also discussed. A critical aspect of this instrumentation development has been the use of a low pressure/temperature modeling fluid (R-134a) in a vertical duct which permits full optical access to visualize the flow fields in all two-phase flow regimes. The modeling fluid accurately simulates boiling steam-water systems. A gamma densitometer is used to obtain line-averaged and cross-sectional averaged void fractions. Hot-film anemometer probes provide data on local void fraction, interfacial frequency, bubble and droplet size? as well as information on the behavior of the liquid-vapor interface in annular flows. A laser Doppler velocimeter is used to measure the local velocity of liquid-vapor interfaces in bubbly, slug and annular flows. Flow visualization techniques are also used to obtain a qualitative understanding of the two-phase flow structure, and to obtain supporting quantitative data on bubble size. Examples of data obtained with these various measurement methods are shown. (C) 1999 Elsevier Science Inc. All rights reserved.