Gas entrainment at the bottom of a Taylor bubble in vertical gas-liquid slug flows

Gas-liquid slug flow occurs under many circumstances. A classical unit-cell model is constructed with mass balances and momentum balances for each phase. However these balances contain more unknowns than there are equations, so it is necessary to construct submodels to be able to solve the system of equations. The void fraction within the liquid slug is a critical unknown in the closure problem which is still poorly understood. This dissertation describes both experimental and theoretical studies of gas entrainment in vertical slug flows.; Since the high propagation velocity of Taylor bubbles and random characteristics of slug flows make detailed measurements difficult, a fixed bubble method was developed to overcome these problems. The gas entrainment rate, film thickness and wall shear stress were measured at different bubble lengths and liquid flow rates. Based on an analysis of the relationships between the gas entrainment rate and film characteristics, the published gas entrainment mechanisms were evaluated and a new mechanism was proposed. A similarity analysis between a fixed bubble and a Taylor bubble leads to application of the gas entrainment mechanism to predict void fraction in liquid slugs at different mixture velocities.; An experimental investigation was performed to study void fraction, bubble size and velocity distributions in the liquid slug using a new double-wire conductivity probe. The void fraction is uniformly distributed in the core region and there is a thin layer on the wall in which no bubbles exist. The void fraction is very high in the mixing zone at the top of the slug and decreases almost linearly to a much lower value in the fully developed region near the bottom of the slug.; Three liquids with differing viscosity and surface tension were used in this work to study the influence of liquid properties on the gas entrainment process. Decreasing surface tension only slightly increases gas entrainment rate but can decrease average bubble size. Liquid viscosity has a significant influence on gas entrainment, even changing the entrainment mechanism. High viscosity dramatically decreases gas entrainment rate and bubble size.