Analysis of heat and momentum transfer in screw-drive heat transfer systems

Screw drive systems might be used in various thermal food processing operations where the food product within the liquid (e.g. water) is moved with rotational effect of screw. The externally given inertial force creates a mixing within the system, and heat transfer rate increases. However, this mixing effect might lead to certain residence time problems for the processed particles. In the literature, there are studies focusing on determining heat and momentum transfer to optimize rotational systems like axial, end-over-end and reciprocal agitation retort systems, and they conclude a possible optimum condition based on a force analysis for gravitational, inertial, Coriolis and viscous forces. Therefore, the objective of this study was first to develop a numerical model for screw-drive system for a process including a processing liquid. For this purpose, a freesurface (liquid - air) fluid dynamics problem was considered. Two - phase volume of fluid (VOF) method was utilized to monitor headspace and solve fluid - thermal energy interactions. A compressive interface capturing scheme for arbitrary meshes was applied to track the interface adopting a moving mesh approach for hydrodynamic and shear forces with 3-rotational and translational degrees of freedom. This approach was used to determine how the rotation rate would affect the fluid movement inside the system. The results of this study are expected to be used for optimization in continuous systems to process the particulate food products in the hot liquid. © Copyright 2017, AIDIC Servizi S.r.l.