MATHEMATICAL-MODELING OF PARTICULATE 2-PHASE FLOW IN A HELICAL PIPE

The design of helical tubes for continuous sterilization of low-acid foods (pH > 4.6) containing large discrete particles depends on the knowledge of the flow behavior of the suspended particles. The flow behavior of a carrier fluid with suspended solid spherical particles in a helical tube was numerically simulated through an iterative solution of the Navier-Stokes equations and the particle dynamic equations in three dimensions. The Lagrangian approach was used to predict the individual particle velocities and trajectories under solid-liquid two-phase flow situation. The results indicate that the residence time distribution of the particles in helical tube flow was narrower than in a conventional holding tube (consisting of two straight tubes connected with a 180 degrees bend), Also, the average velocity of the particles was closer to the average velocity of the carrier fluid in the helical tubes. The secondary flow induced by the tube curvature greatly reduced the axial dispersion of the particles. There was a substantial particle influence on the fluid flow field. The pressure drop in helical tube was 18% higher for single-phase flow and 51% higher for two-phase flow than in conventional holding tube of equal length.