1. 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

2. 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

3. 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

4. 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

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

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

7. 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

8. 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

9. 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

10. 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

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

12. 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

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

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

15. 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