Particle Settling in a Non-Newtonian Fluid Medium Processed by Using the CEF Model

In this study, the settling of small particles in a non-Newtonian fluid medium is considered. The simulation of this problem according to the fluid mechanics principles may be realized by the flow of a non-Newtonian fluid around a sphere falling along the centerline of a cylindrical tube. The knowledge of the rate of settling of particles in practice is particularly significant in determining the shelf life of materials such as foodstuffs, cleaning materials and many others. Thus, this problem has great importance in many natural and physical processes and in a large number of industrial applications such as chemical, genetic and biomedical engineering operations. The majority of the theoretical, experimental and numerical studies available in the literature deal with Newtonian fluids. Conversely, for non-Newtonian fluids the problem is considerably more complex. It is well-recognized that extensional behaviour in non-Newtonian fluids plays a major role in complex flows. Most non-Newtonian fluids such as polymeric solutions and melts exhibit shear-thinning behaviour. In this study it is aimed to determine the equations governing this process and some important conclusions about the properties of polymeric liquids related to their viscoelastic constitution are drawn. Effectively, it is found that for polymeric liquids, the elastic behaviour characterized by the normal stress coefficients, implies relatively increased normal stresses with respect to the generalized Newtonian fluids, whereas the shear stresses tend to decrease, thus changing somewhat the category of the flow from shear-flow into extensional flow in a small rate. Hence, the viscoelastic property of the polymeric liquids must be stressed by their constitutive equation choice, which led us to the CEF model

The flow of non-Newtonian fluids around a sphere falling along the centreline of a cylindrical tube

Silindirik bir tüpün ekseni boyunca düşen bir küre etrafında non-Newtonian akışkanların akım modeli, küçük taneciklerin bir non-Newtonian akışkan ortamında çökelmesi probleminin akışkanlar mekaniği esaslarına göre simülasyonudur. Pratikte küçük taneciklerin çökelme oranının bilinmesi, gıda maddeleri, temizlik malzemeleri ve benzerlerinin raf ömrü bakımından özellikle anlamlıdır. Bu problem pratikte, kimyasal, genetik, biyomedikal ve diğer endüstriyel alanlardaki uygulamalarda önem taşımaktadır. Eldeki çalışmada bu problemi düzenleyen denklemler elde edilmek istenmiş ve polimerik akışkanların viskoelastik özelliklerine ait bazı önemli sonuçlar bulunmuştur.Gerçekten, polimerik akışkanlarda, normal gerilme katsayıları ile karakterize edilen elastik davranış, genelleştirilmiş Newtonian akışkana oranla normal gerilmelerde bir artış meydana getirmekte, kayma gerilmeleri ise azalmaktadır.   Anahtar Kelimeler: Non-Newtonian, CEF denklemi, kayma-oranı, FEM.We consider the settling of small particles in a non-Newtonian fluid medium. The simulation of this problem according to the fluid mechanics principles may be realized by the flow of a non-Newtonian fluid around a sphere falling along the centreline of a cylindrical tube. The knowledge of rate of settling of particles in practice is particularly significant in determining the shelflife of materials such as foodstuffs, cleaning materials and many others. Thus, this problem has great importance in many natural and physical processes and in a large number of industrial applications such as chemical, genetic and biomedical engineering operations. In this study we tried to determine the equations governing this process and we drew some important conclusions about the properties of polymeric liquids related to their viscoelastic constitution. Effectively we found that, for polymeric liquids, the elastic behaviour characterized by the normal stress coefficients, implies relatively increased normal stresses with respect to the generalized Newtonian fluids, whereas the shear stresses tend to decrease, thus changing somewhat the category of the flow from shear-flow into elongational flow in a small rate. Hence, the viscoelastic property of the polymeric liquids must be stressed by their constitutive equation choice, which led us to the CEF model.  Keywords: Non-Newtonian, CEF equation, shear-strain rate, FEM.

Study of the axisymmetric and steady motion of a sphere in a non-newtonian fluid filling a restrained volume

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2005Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 2005DoktoraPh.D