Definition of Rheology Rheology TX UTA [Greek rheos-"to flow"]is the study of deformation and flow of matter Name was coined by Dr. Marcus Reiner instead of the more obscure “continuum mechanics” Motto of the Society of ☒ Rheology:"Panta Rhei"or “everything flows'" -after Heraclitus THE VISCOSITY OF LIQUIDS -SOME SIMPLE EVERYDAY IDEAS _ryhing osimple色es地t motsmper.Ens时e电 English rheology words:viscosity,consistency,and texture Thick,creamy,watery,runny Gluey,gelatinous,sticky,tacky,goocy,gummy,cohesive laundry liquids,surface cleaning liquids om cabinet onal products tool shed paints.glues,mastics 1
1 Definition of Rheology • Rheology [Greek rheos - “to flow”] is the study of deformation and flow of matter • Name was coined by Dr. Marcus Reiner instead of the more obscure “continuum mechanics” • Motto of the Society of Rheology:“Panta Rhei” or “everything flows” - after Heraclitus English rheology words: viscosity, consistency, and texture Thick, creamy, watery, runny Gluey, gelatinous, sticky, tacky, gooey, gummy, cohesive
WHAT IS FLOW AND DEFORMATION? 'Insufficient facts aluays inite danger,Captain',Mr Spock o。8 velocity A Force dx y For solids dx is constant and is a function of F/A and y For liquids dx changes with time and a resulting velocity of The upper plane is a result. The velocity is constant and is a function F/A and y 2
2 y Force A dx velocity For solids dx is constant and is a function of F/A and y For liquids dx changes with time and a resulting velocity of The upper plane is a result. The velocity is constant and is a function F/A and y
Terms and Units Flow shear stress=F A velocity dx shear straln=y y Foree Ares=A shear rate=y==y 3 Modulus(solids)=G= 么 )=刀=g Extensional Viscosity a,=4 Force → Velocity cdhy =% w. w.p 10.1 3
3 Flow y v y dt dx shear rate y dx shear strain A F shear stress = = = = = = = γ γ σ & γ σ η γ σ & = = = = cos ( ) ( ) Vis ity liquids Modulus solids G Terms and Units y Area = A Force velocity dx Extensional Viscosity Force Velocity ε σ η ε ε σ & & e e e h V h dh A F = = = = h dh
Newtonian Fluids "The beginning of wisdom is to call things by their right names" A Chinese proverb O slope=n 0=7形 Newtonian Viscosity of Common Foods Viscosity mPa s Temp C Water 0.89 25 Milk 1.45 25 Coconut oil 26 40 Cocoa butter 41 4 Cream 40% 210 48 Glycerine 954 Honey 10.000 25 Newtonian Fluids Honey Glycerine O Cream 40% Coconut 4
4 Newtonian Fluids σ =ηγ& σ γ& slope =η “ The beginning of wisdom is to call things by their right names” A Chinese proverb Newtonian Viscosity of Common Foods Viscosity mPa s Temp °C Water 0.89 25 Milk 1.45 25 Coconut oil 26 40 Cocoa butter 41 40 Cream 40% 210 48 Glycerine 954 25 Honey 10,000 25 Newtonian Fluids σ γ& Water Coconut Oil Cream 40% Glycerine Honey
Viscous M女ous Intermediate Mobile Mobile Shear rate Shear rate y Liquid or gas Approx viscosity in Pas Hydrogen 105 Air 2x103 Petrol 3x10 Water 10 Lubricating oil 101 Glycerol 10e.1) Com syrup Bitumen Approximate viscosities of some common ewtonian fluids. the viscosity of the solvent or continuous phase.Pa.s dimensionless relative viscosity,n which is the ratio of the viscosity of a suspension to its continuous phase viscosity.n/n: the dimensionless specific viscosity,n,given byn-1: ·the intrinsic viscosity.【nl(with dime )which is the specific ity divided by the dis the kinematic viscosity,pwhich in pre e(你-1/c: centi-Stokes,c5,for thin liquids,with water at 20C-1 cS. The effect of temperature on viscosity The most widely-used expression is that due to Andrade logis n =A+B/T where T is the temperature in degrees absolute (C+273.15).i.e.K.Note that this equation is also known by other names for instance the Arrhenius law where B is replaced by E/R where E is an activation energy for viscous flow and R is the universal gas constant.The activation energy E is said to be a measure of the height of a potential energy barrier associated with the force needed to produce elemental quantum steps in the movement of molecules. Arrhenius =4eh) 5
5 The effect of temperature on viscosity Arrhenius η = A exp −Ea RT ⎛ ⎝ ⎜ ⎞ ⎠ ⎟