An investigation on the flow structures of the intermittent flow in a helically coiled tube

In this work, a series of numerical investigations are carried out to explore the flow structures of intermittent flow in a helically coiled tube. The distributions of velocity magnitude and turbulence kinetic energy for several cross sections along the flow process of plug flow, slug flow, and slug-annular flow are compared to reveal the asymmetric characteristics of intermittent flow. For the elongated bubble zone of slug-annular flow, the maximum turbulence kinetic energy at the middle part of the pipe can reach nearly three times the maximum turbulence kinetic energy at the bottom part of the pipe. In addition, the tangent vectors are extracted to reflect the rotational flow of the fluids. The Dean vortex induced by centrifugal force is found in the liquid slug zone and as well as in the gas region of the body part of the elongated bubble zone. The directions of the tangent vectors with larger components would develop from gas to liquid at the nose part while develop from liquid to gas at the tail part due to the increased turbulence fluctuations of liquid phase at the tail part of the elongated bubble.