Experimental study of two-phase flow structure and pressure drop across a sudden contraction in horizontal pipe

摘要

Two-phase flow, particularly; gas-liquid flow is widely encountered in industrial applications like boilers, condensers, evaporators and reactors. These systems often exhibit complex geometry consisting on singularities such as expansions, contractions, orifices, bends etc. The presence of geometrical singularities in pipes may affect significantly the behavior of two-phase flow and subsequently the resulting pressure drop. Therefore, it is an important subject of investigation in particular when the application concerns design, safety and economical operations. This study investigates the pressure change and flow pattern subject to the influence of a sudden contraction. The pressures through sudden contraction in horizontal circular pipes have been measured with a capacitive differential pressure transducer, using air and water as the working fluids. The pressure drop is determined by extrapolating the pressure profiles upstream and downstream of the contraction. The larger and smaller tube diameters are 40 mm and 30 mm, respectively, with an area contraction ratio >u1d70e= 0.567 . The ranges of the gas and liquid superficial velocity were 0.54 to 5.5 m/s and 0.011 up to 0.24 m/s respectively. It is noted that the sudden change in cross-section have a significant influence on the downstream phase distribution of the air-water flow. In addition, close to the sudden contraction, a significant pressure drop occurs for single phase flow (water). While, for two-phase flow cases, a local pressure minimum was not detectable, the vena contracta phenomenon may not occur at all especially at low flow rates.