上海交通大学：《食品物性学 Physical Properties of Foods》教学资源（英文PPT课件）2007_SJTU2

Definition of Rheology o Rheology TXVTC [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 :l

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

THE VISCOSITY OF LIQUIDS SOME SIMPLE EVERYDAY IDEAS 'Everything should be as simple as possible,but not simpler',Einstein English rheology words:viscosity,consistency,and texture Thick,creamy,watery,runny Gluey,gelatinous,sticky,tacky,gooey,gummy,cohesive kitchen laundry liquids,surface cleaning liquids ● bathroom cabinet personal products ● garage oils,greases pantry sauces,salad dressings ● tool shed paints,glues,mastics

English rheology words: viscosity, consistency, and texture Thick, creamy, watery, runny Gluey, gelatinous, sticky, tacky, gooey, gummy, cohesive

Sugars ·Flavours ·Polysaccharides ●Vitamins ·Lipids ●Preservatives ·Proteins ·Minerals ●Colours 。Water

Having considered the consistency of a product,we now need to think about its packaging and means of delivery.These probably range over the following sequence of packaging,consistency and delivery action: Package Consistency Action Example pressure cans thin and watery Spray paint,hair spray bottles,cans oily Squirt washing-up liquid,oil tubes pasty Squeeze toothpaste,tomato paste tubs soft-solid like Scoop face cream, Clearly anyone interested in these areas should be thinking very carefully about rheology

WHAT IS FLOW AND DEFORMATION? Insufficient facts always invite danger,Captain',Mr Spock SHEAR FLOW 4—。 0◆ Adjacent particles moving over or past each other original shape EXTENSIONAL FLOW ←-00→ I Adjacent particles moving away from or towards each other T 1 Particle motion in shear and extensional flows

velocity Force A 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

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 F Flow shear stress =o A dx velocity dx shear strain=y y Force Area=A d shear rate y dt 2 y y Modulus(solids)-G= Visquds）=7=7

Flow y v y dt dx shear rate y dx shear strain A F shear stress                      cos ( ) ( ) Vis ity liquids Modulus solids G Terms and Units y Area = A Force velocity dx

Extensional Viscosity o=% h ,dh Force Velocity 6 h 6-

Extensional Viscosity Force Velocity         e e e h V h dh A F     h dh

Situation Shear Rate Examples Range/s1 Sedimentation of fine 10-6-103 Medicines,paints,salad powders in liquids dressing Levelling due to surface 102-101 Paints,printing inks tension Draining off surfaces 10-1-101 Toilet bleaches,paints,coatings under gravity Extruders 100-102 Polymers,foods soft solids Chewing and 101-102 Foods swallowing Dip coating 101-102 Paints,confectionery Mixing and stirring 101-103 Liquids manufacturing Pipe flow 100-103 Pumping liquids,blood flow Brushing 103-104 Painting Rubbing 104-105 Skin creams,lotions High-speed coating 104-106 Paper manufacture Spraying 105-106 Atomisation,spray drying Lubrication 103-107 Bearings,engines

Newtonian Fluids "The beginning of wisdom is to call things by their right names" A Chinese proverb O slope n 0=7y

Newtonian Fluids       slope   “ The beginning of wisdom is to call things by their right names” A Chinese proverb