3 dimensional computational fluid dynamic analysis of heat transfer in a scraped surface heat exchanger for bingham fluids

Abstract

This study is focused on numerical analysis of the thermal behavior within a scraped surface heat exchanger (SSHE) for threshold fluids (Bingham fluids). An innovative SSHE is considered which includes helical ribbon, instead of using scrapers. Heat transfer simulations were carried out by means of specific CFD code to solve the three dimensional form of continuity, momentum and energy equations. In this work, the influence of dimensionless numbers (rotational Reynolds, axial Reynolds and Oldroyd numbers) on thermal behavior is studied. Numerical results show that for low axial Reynolds numbers compared to rotational Reynolds number (Reax/Rer <1), there is opposition between the axial components of velocity coming from the flow (ascending components) and axial components at the helical ribbon due to the mixing effect (descending components). However, for high axial Reynolds numbers (Reax/Rer >1), a parabolic-like flow is generated, indicating low degree of back mixing. Numerical results show also that an important heated zone was observed near the blades due to high blades rotating speed. The highest temperatures are found at the thermal boundary layer periodically disturbed by the helical ribbon. It appears that increasing the Oldroyd number produces a slight rise in the temperature field.