Thin Film Flow Modelling of a Vertically Rotating Disk Using an Immersed Boundary Method

Abstract

Thin film flows on rotating disks can be found in various applications of chemical- and process engineering. Horizontal discs are often used for coating processes where a thin liquid layer must be distributed homogenously on the plate. Vertical discs are mainly used in plastics production for the devolatilization where thin films are advantageous to improve the transport of gaseous components. Therefore, the local distribution of the film height on the disks is essential for the determination of the required times for devolatilization. Normally, disks in industrial applications can have diameters of up to a few meters whereas film heights can be in the order of millimetres. Furthermore, the rotating discs can be perforated to provoke falling films which increase the complexity of modelling. In this study, an Immersed-Boundary Method (IBM) in combination with a Volume-of-Fluid (VoF) method to describe the two-phase flow is presented. The IBM, which is a new implementation in the open source CFD code OpenFOAM®, offers advantages to model the rotation of complex rotors compared to sliding mesh approaches. The new implementation of the Immersed Boundary Method is presented in detail showing the integration into OpenFOAM as a library and the handling of the movement of different parts which allow the modelling of real apparatuses consisting of several disks rotating with different speeds, etc. The model is validated with data from literature for a vertical rotating disk which is partially immersed in a liquid pool. The local distribution of the film height and coverage of the disk is compared to experimental data for different liquids with varying densities, viscosities and different rotational speeds of the disk. The experimental data and numerical results show a good agreement and will be discussed for the different cases of the experiment. A perspective on further applications of the IBM is given as well.