Fluid Dynamics Viscosity. Dave Foster Department of Chemical Engineering University of Rochester

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1 Fluid Dynamics Viscosity Dave Foster Department of Chemical Engineering University of Rochester che.rochester.eduedu 1

2 Chemical Engineering What do Chemical Engineers Do? Manufacturing Research Biotech Chemical Medical Pharmaceutical 2

3 OK, first a little background Fluid Mechanics is the study of fluids either in motion (Fluid Dynamics) or at rest (Fluid Statics) Fluids are either gas or liquid Solids are NOT fluids Properties of the fluid are things like density, pressure, temperature, and VISCOSITY! 3

Fluids are either gas or liquid Solids are NOT fluids Properties of

4 Fluid a definition A substance that deforms continuously under the action of shear stress Gas or Liquid Solids can resist a shear stress, a fluid can t 4

5 Applications of Fluid Mechanics Explains blood flow in capillaries of a few microns in diameter to crude oil flow through an 800 mile long, 4 ft diameter pipe Explains why airplanes are streamlined with smooth surfaces Explains why golf balls are made will dimpled surfaces for most efficient travel 5

diameter pipe Explains why airplanes are streamlined with smooth surfaces

6 Effect of Dimples on Golf Balls Drag (Pounds of Force) Drag for Sphere Drag for Golf Ball Velocity (Feet per Second) 6

7 A List of Some Applications Coating Breathing Blood flow/pipe flow Swimming Pumps (traditional and your heart) Fans Turbines Airplanes & Rockets Missiles Ships Kidney dialysis machines Heart-Lung bypass machines Membrane oxygenators Engines And lots more! 7

Airplanes & Rockets Missiles Ships Kidney dialysis machines

8 For everything FLUID - Flow is key How fast What direction How changing with time (differential equations) Flow properties deal with things like the velocity, changes in temperature, concentration. 8

9 Isaac Newton Key player in much of basic science Three Laws 1. A body will remain at rest or in motion unless acted upon by an external force 2. Σ F = m a 3. For every action there is an equal and opposite reaction 9

10 Newton s Law of Viscosity: τ = µ dv dy Shear stress viscosity Shear Strain 10

11 Viscosity What is it? A property of a fluid to resist the rate of deformation a quantitative measure of a fluid s resistance to flow (water vs. syrup) Takes place when a fluid is acted upon by a shear stress Simply stated, it s s how thick a fluid is We easily move through air It s s more difficult to move through water which is 50X higher in viscosity than air 11

12 A couple common examples: Most Viscous Air < Water < Paint < Pancake Syrup < Tooth Paste Least Viscous 12

13 Units (yep units, very important) If we talk about how deep a swimming pool is and I tell you that it s 10,, would you dive in? Not if it s s 10 inches But you might if it was 10 feet Units are key in all of science, never accept a number without a unit if it s supposed to have one 13

Not if it s s 10 inches But you might if it was 10 feet Units are key

14 Units of Viscosity Poise (the most common units used to describe viscosity, but not the only one) Named after the French physician Jean Louis Poiseuille ( ) One-hundredth of a Poise is a centipoise or cp 14

after the French physician Jean Louis Poiseuille

15 Viscosity of Some Common Materials (all are in units of Centi-Poise) Hydrogen Carbon Dioxide Air Blood 0.40 Gasoline 0.29 Water 1.0 Mercury 1.5 Corn Oil 72 SAE 30 oil 290 Heinz Ketchup 50,000 15

015 Air 0.018 Blood 0.40 Gasoline 0.29 Water 1.

16 Changing a Material s Viscosity Easiest ways: Change the Temperature Heat it Up! Strong Effect Change the Pressure not as easy Weak Effect: Decrease pressure, viscosity decreases 16

17 In a perfect world: τ Fluids obey Newton s s Law of Viscosity dv = µ dy τ Straight line passing through the origin Slope = viscosity (Format: y = m x + b) dv/dy 17

18 Newtonian Fluids Fluids that obey Newton s s Law of Viscosity Linear relationship between shear stress and shear strain Some Examples of Newtonian Fluids: Water Simple Alcohols Simple Organic Solvents 18

stress and shear strain Some Examples of Newtonian

19 Everything Else is a Non-Newtonian Fluid 19

20 Non-Newtonian Fluids Examples: Honey, toothpaste, paint, blood, ketchup, syrup, many polymers The list goes on and on 20

21 Non-Newtonian Fluids Pseudoplastic shear-thinning- Fluid decreases resistance with increasing stress. (ex: hair gel) Newtonian τ Dilatant shear-thickeningfluid increases resistance with Increasing applied stress (ex. Rarely encountered, Cornstarch + water, Silly putty) dv/dy 21

22 Why do we care? The primary parameter correlating the viscous behavior of Newtonian Fluids is the dimensionless Reynolds Number: Re = velocity*distance viscosity 22

23 Why do we care? The first thing a fluids researcher should do is estimate the Reynolds Number range of flow under study. Low Re = laminar flow (no change with time) High Re = turbulent flow (changes with time) 23

24 Reynolds Number and Viscosity Viscosity Re Viscosity Re Re = velocity*distance viscosity 24

25 How can we use Viscosity (and Fluid Dynamics)? Flow measurements in human body Heart valve flow volumes Coating technologies Lots of applications Moving fluids from one place to another Blood flow in your body Chemicals in pipes Moving objects through fluids 25

26 Thanks!! Any Questions? 26

CE 204 FLUID MECHANICS

CE 204 FLUID MECHANICS Onur AKAY Assistant Professor Okan University Department of Civil Engineering Akfırat Campus 34959 Tuzla-Istanbul/TURKEY Phone: +90-216-677-1630 ext.1974 Fax: +90-216-677-1486 E-mail: