Numerical study of hydrodynamic and thermal behaviors in a scraped surface heat exchanger with helical ribbons

Abstract

This study deals with numerical simulations of the hydrodynamic and thermal behaviors in scraped surface heat exchanger (SSHE) which includes helical ribbon instead of scraper blades. A three-dimensional resolution of the conservation equations of continuity, momentum and energy was conducted using a specific CFD code based on the finite volume method. Laminar, steady-state and non-isothermal flow of Bingham fluids, characterized by high viscosity, were investigated. The conjugated effect of rotational and axial Reynolds numbers on the hydrodynamic and thermal behaviors is studied. Increasing the ratio of rotational Reynolds to axial Reynolds numbers improves scraping surface frequency and consequently, the tube-side heat transfer coefficients are enhanced. Simultaneously, the back-mixing phenomenon becomes more important and reduces the temperature driving force for heat transfer. Moreover, the influence of Oldroyd number on the velocity and temperature fields, the apparent viscosity and rigid zones is established. The numerical results have shown that increasing the Oldroyd number reduces recirculation zones and improves slightly the heat transfer. In this work, the determination of correlation is presented using a dimensionless analysis method in order to predict the heat transfer coefficient within SSHE in the case where the ratio of rotational to axial Reynolds numbers is inferior to 1.