NUMERICAL STUDY OF VISCOPLASTIC FLOW IN A T-BIFURCATION: IDENTIFICATION OF STAGNANT REGIONS

Gleison R Inácio,Paulo S B Zdanski,Júlio C Tomio,Miguel Vaz Jr

doi:10.1590/0104-6632.20190363s20180361

Abstract

Abstract Identification of stagnant regions of viscoplastic fluid flows in production lines and equipment is of paramount importance owing to potential material degradation and process contamination. The present work introduces an assessment strategy to identify, classify and quantify unyielded regions with the objective of optimizing the flow conditions with the purpose of minimizing stagnant regions. Flow of Carbopol® 980 in a T-bifurcation channel is adopted to illustrate the procedure. The rheological behavior of Carbopol® 980 was simulated using the Herschel-Bulkley viscoplastic model regularized by Papanastasiou’s exponential approach. The analysis shows that three distinct types of stagnant unyielded regions take place in the bifurcation channel depending upon the Reynolds condition. Furthermore, the rheological characteristics of the fluid indicate the existence of an ideal Reynolds condition which allows the smallest flow stagnant area at the bifurcation zone.

Highlights

Viscoplastic flows are found in distribution channels and equipment of a wide variety of production processes, such as in the cosmetic, pharmaceutical and food industries
The numerical solution of a viscoplastic fluid flow in a two-dimensional plane channel using ANSYS FLUENT® was compared against solutions (i) obtained using an in-house code developed by the authors based on finite differences (FDM) and (ii) reported by Boualit et al (2011) determined using the finite element method
The flow conditions, geometry and rheological parameters follow the analysis performed by Boualit et al (2011), who adopted the Bingham-Papanastasiou model to compute the apparent viscosity of the viscoplastic fluid

Summary

Introduction

Viscoplastic flows are found in distribution channels and equipment of a wide variety of production processes, such as in the cosmetic, pharmaceutical and food industries. The ideal viscoplastic models, such as Bingham plastic, Herschel-Bulkey and Casson, are discontinuous and numerical solutions for complex geometries require regularized models, such as the biviscosity equation (Tanner and Milthorpe, 1983) and models proposed by Bercovier and Engelman (1980) and Papanastasiou (1987). The latter was adopted in this study to investigate the hydrodynamic behavior of a Herschel-Bulkley fluid in a T-bifurcation. The Papanastasiou regularization uses an exponential modification widely applied in numerical studies involving viscoplastic materials (Mitsoulis, 2007)

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