tailieunhanh - Identificat ion of two phase flow regimes by void fraction measurements

This paper will present a method to identify flow patterns (bubble & slug flow) in vertical air-water two-phase flow by void fraction measurement (using an impedance probe) at Inst. of Mechanics Hanoi. | Vietnam Journal of Mechanics, VAST, Vol. 27, No. 1 (2005), pp . 59 - 65 IDENTIFICAT ION OF TWO PHASE FLOW REGIM ES BY VOID FRACTION MEASUREMENTS Bur DINH TRI Institute of Mechanics Abstract. This paper will present a method to identify flow patterns (bubble & slug flow) in vertical air-water two-phase flow by void fraction measurement (using an impedance probe) at Inst. of Mechanics Hanoi. 1. INTRODUCTION Identification of flow patterns is one of the most fundamental problems in investigating the basic phenomena of two-phase flow. At present, there are two available methods to identify two phases flow patterns: direct observation (including visualization, high speed photography, X-ray) and indirect determination (including measurement, the analytical tools such as probability density function (pdf) or power spectral density (psd), etc . ) However, this paper is only mentioned of an indirect determination method, which is generally preferable to direct observation at Inst. of Mechanics Hanoi. Void fract ion measurement of two-phase flow in the pipe is one of the indirect determination methods. There are many results of various authors which showed that the void fraction could be · used as a parameter to identify two-phase flow patterns, especially for gas-liquid two phase flow in the pipe. Y. Ma et al 1991 [1] and Wang et al 1991 [2] have proposed a simple and effective method (using the void fraction sensor) to identify the flow patterns. Costigan and Whalley 1997 [3] developed and used this method for slug flow regimes identification in vertical air-water flow. Recently, M. J. Watson and G. F . Hewitt 1999 [4] have carried out the investigation using the impedance probe to determine from the slug to churn flow pattern transition at various flow rate and pr,~ ssure in vertical upwards gas-liquid flow. In gerieral, most of previous investigations are based on a certain statistical analysis of fluctuating characteristics of the . In this paper, a method .