Instrumentation development in two-phase flow

Abstract

Abstract 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.