Lecture 10 Announcements HW#7 due MONDAY, 2/12 Lab #2 due Wednesday 2/14 HW#8 due Wednesday 2/14 HW#9 due Friday 2/16 Upcoming test #1: Feb. 21 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 “When a fluid or semisolid is subjected to a constant shearing force it flows, ie., it deforms continuously at a velocity that increases as the applied shearing force increases.” Viscosity: quantifies the resistance of the fluid to flow 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Liquids and semisolids are usually pumped during processing Viscosity plays a huge part in pump and conveyance system design Viscosity may be dependent on moisture content, concentration, composition and prior treatments. 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Newtonian Fluids Simplest model Covers most, but not all, ag products Velocity behaves linearly w/ distance Shear stress is linear function of the shear rate Dynamic viscosity: proportionality constant for this relationship 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Dynamic viscosity (Figure 6.1) 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Kinematic viscosity 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Non-Newtonian Fluids Relationship between shear stress and shear rate is NOT linear Some also have a yield stress which must be obtained before flow begins. Plastic: linear but intercept is at the yield stress Casson-type plastic: has a yield stress but is not linear Most common: pseudoplastic…convex curve towards the shear stress axis (Fig. 6.1b) Dilatant fluids: concave toward shear stress axis 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Apparent viscosity = shear rate ratio at any given shear rate Pseudoplastic and Dilatant materials Newtonian: n=1, k=dynamic viscosity 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Plastic and Casson-type plastic behavior (more general case…Herschel-Bulkley model) Chocolate and other Casson materials follows this where N = ½ and the yield stress is taken to the ½ power 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Temperature Dependency: Viscosity decreases with an increase in Temp. Usually 2% per degree C For some materials (fruit juices) the T effect follows an Arrhenius relationship; 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Time dependent Viscosity 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Flow in a pipe: Darcy-Weisbach Newtonian -Non-newtonian 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 Examples of viscometers 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

Viscosity and Flow of Liquids and Semisolids…Chapter 6 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials

BAE2022/BAE4400 Physical Properties of Biological Materials HW#8 Assignment Problem 1: Name three applications where knowing the viscosity of a food product would be important. Are the food products Newtonian or non-Newtonian? How do you know which it is? (because the book says so is not the right answer!) Problem 2: Pick one of the different kinds of viscometers, explain briefly how it works and where or how it would be used. 2/16/2019 BAE2022/BAE4400 Physical Properties of Biological Materials