An experimental and numerical investigation of two-phase slug flow in a vertical tube

The multi-dimensional liquid velocity field and interfacial configuration of Taylor bubbles rising in stagnant kerosene in a vertical 25.6 mm I.D. pipe was investigated experimentally with a non-intrusive flow visualization technique based on photochromic dye activation, and numerically using a computer program for incompressible flows with free surfaces.; The experimental results show that a change in flow direction of the liquid occurred at the nose of the Taylor bubble. From the nose, the liquid film accelerated downwards as the velocity profile became characteristic of developing falling film flow. At the tail, the liquid film penetrated into the wake creating vortices of different sizes. The film penetration distance in the wake region was not proportional to the film velocity, and therefore the bubble length. Within 1 to 1.5 tube diameters (26-38 mm) below the tail of the Taylor bubble, the vortices rapidly decayed and the liquid near the wall returned to essentially a stagnant state. However, small vortices in the bulk fluid remained visible up to 100 mm behind the Taylor bubble.; An analysis of the flow revealed the liquid film surrounding the neatly cylindrical portion of the Taylor bubble to be approximately one-dimensional, whereas near the nose and in the wake it was highly two-dimensional. Furthermore, the velocity in the wake region was determined to be qualitatively similar for different runs. A simple predictive procedure for estimating the radially averaged streamwise film velocity and Taylor bubble shape concluded that the boundary-layer development at the pipe wall only influenced the falling film velocity.; The numerical simulation of the Taylor bubble flow was conducted using the volume-of-fluid approach. However, the range of physical property values that yielded stable numerical results for the inertia-controlled rise of the bubble was severely limited, due to significant stability problems. The Taylor bubble shape was well predicted and velocity profiles in the liquid surrounding the Taylor bubble were computed with partial success for the first time in comparison with measured results. The flow in the wake was only qualitatively similar to the experimental data.