Numerical study of hydrodynamic and thermal behaviors of agitated yield-stress fluid

Computational Fluid Dynamic and Transfer Phenomena, Mechanical Engineering Department, National Engineering School of Sfax, Soukra, B.P. 1173-3038 Sfax, Tunisia

^a Corresponding author: HammamiMoez2003@yahoo.fr

Received: 24 April 2013
Accepted: 11 August 2013

Abstract

Heat transfer during agitation of Bingham viscoplastic fluid is studied in this paper. The fluid is agitated with an anchor impeller and the heating is made by a jacketed wall of the stirred vessel. Transfers in the agitated vessel, translating hydrodynamic and thermal phenomena, are numerically predicted by means of Computational Fluid Dynamics (CFD) in transient regime. The purpose of this numerical study is to identify the rigid zones and to optimize mixing and heating performances. The Navier-Stokes and energy equations are discretized using finite volume method, and a two-dimensional analysis of the hydrodynamic and transient thermal behaviours generated in the agitated vessel are performed. Fluid rheology is modeled by the Bingham approximation and Papanastasiou’s regularization model. Results show the presence of recirculation zones and permit to explain the unpredicted Nusselt number increasing when Oldroyd number increases. This study shows also the importance of the anchor position on the size and the shape of the rigid zones and on the heating performances.