Abstract

The time-dependent rheological behavior of the thixotropic fluids is presented in various industrial fields (cosmetics, food, oil, etc.). Usually, a couple of equations define constitutive model for thixotropic substances: a constitutive equation based on linear viscoelastic models and a rate equation (an equation related to the micro-structural evolution of the substance). Many constitutive models do not take into account the micro-structural dependence of the shear modulus and viscosity in the dynamic principles from which are developed. The modified Jeffreys model (considering only one single micro-structure type) does not show this incoherence in its formulation. In this chapter, a constitutive model for thixotropic fluids, based on modified Jeffreys model, is presented with the addition of one more micro-structure type, besides of comments on some possible generalizations. The rheological coherence of this constitutive model and thermodynamic consistency are analyzed too. This model takes into account a simple isothermal laminar shear flows, and the micro-structures dynamics are relate to Brownian motion and de Gennes Reptation model via the Smoluchowski™s coagulation theory.

Highlights

  • The thixotropic substances are considered structured fluids and have a rheological behavior guided by their structural nature [1–5]

  • Aiming to extend the modified Jeffreys model for two distinguished microstructures, the constitutive model is formally presented in terms of equations, the analysis of its thermodynamics consistence is done, points related to the characterization of the transition region are discussed and some illustrative numerical simulations of rheological tests are presented as well

  • The main objective of this chapter is to investigate the constitutive model for thixotropic fluids based on [8] related to the existence of two different types of micro-structure, and their consistence in some rheological tests

Read more

Summary

Introduction

The thixotropic substances are considered structured fluids and have a rheological behavior (time-dependent) guided by their structural nature [1–5]. In large number of works [5, 18–21], Eq (1) is represented by a linear viscoelastic model/mechanism (Maxwell, Jeffreys, Kelvin-Voigt, etc.) or combinations of that (in parallel or in series) It exists a problem with these approaches, they do not consider, the time/micro-structural dependence of the shear modulus (G) and viscosity (ημ and ην) in physical principles from which the constitutive equation system is obtained. A new perspective in terms of constitutive approach for thixotropic substances, with apparent-yield-stress nature and based on the modified Jeffreys model [8], is presented in terms of two different types of micro-structure (i.e., two structural parameters), and some of their properties are investigated in a rheological and thermodynamic sense. Aiming to extend the modified Jeffreys model for two distinguished microstructures, the constitutive model is formally presented in terms of equations, the analysis of its thermodynamics consistence is done, points related to the characterization of the transition region are discussed and some illustrative numerical simulations of rheological tests are presented as well

Main ideas on two types of micro-structures approach
On the thermodynamic consistence
On the transition region
Numerical results
Constant shear rate test
Constant stress test
Concluding remarks
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.