Lecture 10 – Viscosity and Flow (Ch. 6) This chapter is a study of the shear stress as a function of the shear rate for Newtonian and non-Newtonian biological materials. 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 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 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 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. 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 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 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 6) http://www.answers.com/topic/viscosity?cat=biz-fin 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Dynamic viscosity (Figure 6.1) Lecture 10 – Viscosity and Flow (Ch. 6) Dynamic viscosity (Figure 6.1) 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 6) Kinematic viscosity: dynamic viscosity/density Gives a quantity that is dependent only on the type of fluid, not density or concentration 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 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. Reference article: http://www.hofstra.edu/Academics/SOEAHS/TEC/tec_nyspdc_newsletter_Jun05.cfm 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 6) Most common: pseudoplastic…convex curve towards the shear stress axis (Fig. 6.1b) Apparent viscosity will decrease as shear rate increases Dilatant fluids: concave toward shear stress axis (corn flour, wet beach sand: stiffens when walked on..select pumps carefully!) Apparent viscosity increases as shear rate increases Plastic: linear but intercept is at the yield stress (toothpaste: must stay on brush but must be exudable) Casson-type plastic: has a yield stress but is not linear (chocolate) 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 6) Apparent viscosity = shear rate ratio at any given shear rate Pseudoplastic and Dilatant materials, eqtn. 6.2, Table 6.2) Newtonian: n=1, k=dynamic viscosity 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 6) Plastic and Casson-type plastic behavior (more general case…Herschel-Bulkley model, eqtn. 6.3 Table 6.3) Chocolate and other Casson materials follows this where N = ½ and the yield stress is taken to the ½ power 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 6) Temperature Dependency: Viscosity decreases with an increase in Temp. Typically 2% per degree C For some materials (fruit juices) the T effect follows an Arrhenius relationship (Eqtn. 6.5 page 193) 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Time dependent Viscosity (figure 6.2 page 196) Lecture 10 – Viscosity and Flow (Ch. 6) Time dependent Viscosity (figure 6.2 page 196) 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Lecture 10 – Viscosity and Flow (Ch. 6) Time dependent Viscosity Thixotropic examples (viscosity decreases with time) Gelatin, shortening, cream, paints Rheopectic examples (viscosity increases with time) Highly concentrated starch solutions…gravy 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Flow in a pipe: Darcy-Weisbach Newtonian -Non-newtonian Lecture 10 – Viscosity and Flow (Ch. 6) Flow in a pipe: Darcy-Weisbach Newtonian -Non-newtonian 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Examples of viscometers Lecture 10 – Viscosity and Flow (Ch. 6) Examples of viscometers 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

Viscosity and Flow of Liquids and Semisolids…Chapter 6 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity

HW#6 Assignment Due 2/18 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. Problem 3: 6.1 in the Stroshine Book 1/13/2019 BAE2023 Physical Properties of Biological Materials Lecture 10 Viscosity