Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
Effect of Thixotropy in Complex Flows
Submission Author:
Carlos Eduardo Sanchez Perez , RJ
Co-Authors:
Carlos Eduardo Sanchez Perez, Danmer Maza, Marcio CARVALHO
Presenter: Carlos Eduardo Sanchez Perez
doi://10.26678/ABCM.ENCIT2022.CIT22-0112
Abstract
Several liquids, in important applications in industry and everyday life, present non-linear behavior and time dependency. These behaviors are associated with microscopic structures that are formed and destroyed during flow. Despite recent developments on time-dependent models, which are able to describe the mechanical behavior of thixotropic fluids, most steady-state complex flow analyses do not take these effects into account. Flow simulations of inelastic, shear-thinning liquids are generally developed by using generalized Newtonian models (GNM). In this case, the viscosity of the liquid is solely a function of the local shear rate, i.e., using the liquid steady-state flow curve. From a material point of view, the deformation rate changes as liquid particles pass through the flow field. Assuming that the viscosity at each point is the steady-state viscosity may lead to inaccurate results. Especially, if the characteristic time of the build-up or the time associated with the destruction of the material structure is in the same order of magnitude of the residence flow time. In this work, we study the flow of a thixotropic liquid through a constricted capillary and near the downstream meniscus of slot coating process. The rheological behavior is governed by a thixotropic model where the typical structure parameter, used in thixotropic modeling, is replaced by fluidity (i.e., reciprocal of viscosity). In this rheological model, the mechanical response is described by two evolution equations: one for the stress and the other for the fluidity. The set of differential equations is solved by the Finite Element Method. The results show how the rheological parameters affect the flow behavior for both cases: thixotropic and GNM simulations. Moreover, the results reveal at which conditions time-dependency can be neglected.
Keywords
Thixotropy, Generalized Newtonian fluid, Finite Element Method, Avalanche and construction times, capillary, slot coating flow
