VOF simulation of marangoni flow of gas bubbles in 2D-axisymmetric column

AbstractThe migration of gas bubbles immersed in a liquid under the action of temperature gradient and surface tension (Marangoni flow) in zero gravity environment is numerically investigated for different Ma, Re, and Pr (Marangoni, Reynolds, and Prandtl numbers). The full Navier–Stokes equations as well as the energy equation for temperature gradient are solved by a volume of fluid (VOF) method/Finite Volume method, and the surface tension force is modeled by a continuum surface force (CSF) model. The behavior of bubble migrating toward the hotter side by the action of surface tension using the flow relations between two bubbles (leading and trailing bubble), and the trajectories and the velocities of the different bubbles diameters, in microgravity environment have been investigated numerically. It has been verified that the calculated results are in good agreement with available experimental and numerical results. It is also concluded that the VOF is able to simulate two-phase flow under zero gravity conditions

Thermal performance of the chilled water spirally coiled finned tube in cross flow for air conditioning applications

AbstractThe thermal performance of spirally coiled finned tube in cross flow was investigated experimentally. The effects of curvature ratio, flow direction, fin pitch and flow rate of chilled water and air on thermal characteristics of spirally coiled finned tube have been studied. Six test sections with curvature ratios of 0.027, 0.03, 0.04, tube pitches of 18, 20, 30mm, and fin pitches of 33, 22, 11mm were used. The experiments were done using a pilot wind tunnel with air Reynolds number range 35,500–245,000. Innermost and outermost flow directions of chilled water with Reynolds number range 5700–25,300 have been investigated. The innermost flow direction has significant enhancement effect on the Nusselt number compared with outermost flow direction. The decrease of fin pitch enhances the Nusselt number on expense of pressure drop. Decreasing the curvature ratio increases air side Nusselt number on expense of pressure drop. A set of empirical expressions for predicting the friction factor and the Nusselt number for air flow across the spiral coils have been regressed based on the obtained data in the present experiments