Heat and fluid flow in a scraped-surface heat exchanger containing a fluid with temperature-dependent viscosity

Scraped-surface heat exchangers (SSHEs) are extensively used in a wide variety of industrial settings where the continuous processing of fluids and fluid-like materials is involved. The steady non-isothermal flow of a Newtonian fluid with temperature-dependent viscosity in a narrow-gap SSHE when a constant temperature difference is imposed across the gap between the rotor and the stator is investigated. The mathematical model is formulated and the exact analytical solutions for the heat and fluid flow of a fluid with a general dependence of viscosity on temperature for a general blade shape are obtained. These solutions are then presented for the specific case of an exponential dependence of viscosity on temperature. Asymptotic methods are employed to investigate the behaviour of the solutions in several special limiting geometries and in the limits of weak and strong thermoviscosity. In particular, in the limit of strong thermoviscosity (i.e., strong heating or cooling and/or strong dependence of viscosity on temperature) the transverse and axial velocities become uniform in the bulk of the flow with boundary layers forming either just below the blade and just below the stationary upper wall or just above the blade and just above the moving lower wall. Results are presented for the most realistic case of a linear blade which illustrate the effect of varying the thermoviscosity of the fluid and the geometry of the SSHE on the flow

Non-Newtonian flow behaviour in narrow annular gap reactors

In this paper local flow investigations under isothermal conditions have been established for a narrow annular gap reactor (NAGR, given by a rotor/stator system with a radius ratio of ri/ro=0.8) including two wall scraper blades of different geometry. Two-dimensional laminar flow fields are considered (with Reynolds numbers below Re \u3c 82.6), based on numerical flow simulations, where validations with experimental velocity measurements are in good agreement. Comparisons of the macroscopic flow structuring behaviour are shown for Newtonian and inelastic shear-thinning fluids based on velocity profiles, secondary flows, hydrodynamic pressure contours, shear stress and energy dissipation, by varying the rotor velocity (described in terms of a characteristic rotational Reynolds number Re), the scraper blade angle (β) and the non-Newtonian flow behaviour (power-law exponent n). © 2001 Elsevier Science Ltd. All rights reserved

Effects of flow incidence and secondary mass flow rate on flow structuring contributions in scraped surface heat exchangers

The effects of flow incidence and secondary mass flow rate on flow structuring contributions in scraped surface heat exchangers was discussed. Continuous mixing and dispersing process flows produced by scraped surface heat exchangers (SSHE) in food technology influences the microstructure of multiphase food systems. A scraped surface apparatus with special narrow annular gaps including two wall scraper blades was choosen as a model process