1. Aero/Hydrodynamic Properties
Air and water are used to remove foreign material from products
How much air required depends on the drag force FD ( sum of skin friction and pressure drag)
FD affected by density, abs. viscosity, area and velocity (equation 10.1)
Reference Figure 10.1
Dr. C. L. Jones
Biosystems and Ag. Engineering
3/31/08
BAE 2023 Physical Properties

2. BAE 2023 Physical Properties
Figure 10.1
3/31/08
BAE 2023 Physical Properties

3. Aero/Hydrodynamic Properties
FD depends on the drag coefficient CD which is quantified using the Reynolds number.
NRe = Vdpρf/η Where:
V = fluid velocity
dp = particle dimension
ρf= fluid density
η = absolute viscosity
NRe<1.0, Stokes flow, FD=3πdpμV (sphere)
NRe<1,000 Laminar flow
NRe >20,000 Turbulent flow
Dr. C. L. Jones
Biosystems and Ag. Engineering
3/31/08
BAE 2023 Physical Properties

4. Aero/Hydrodynamic Properties
Terminal velocity: occurs when drag force balances gravitational force
See Table 10.1
For a sphere
Fdrag=CD(πd2/4)(ρfv2/2)
CD depends on the Reynold number of the particle: Rep= ρfvd/μ (restated from eqt in different terms)
If Rep<0.2, CD=24/Rep
If Rep>200,000, CD=0.44
If Repis between 500 and 200,000,
CD=(24/Rep)( (Rep)0.687)
Dr. C. L. Jones
Biosystems and Ag. Engineering
3/31/08
BAE 2023 Physical Properties

5. Lecture 17 – Aero/Hydrodynamic Properties (Ch. 10)
Dr. C. L. Jones
Biosystems and Ag. Engineering
3/31/08
BAE 2023 Physical Properties

6. Aero/Hydrodynamic Properties
Read Example Problem You will need to be familiar with it. This examples shows how to find a Reynolds number for a particle, the drag coefficient and the terminal velocity
Dr. C. L. Jones
Biosystems and Ag. Engineering
3/31/08
BAE 2023 Physical Properties

7. Aero/Hydrodynamic Properties
Application example: Can corn stalks be separated from corn cobs pneumatically? What minimum air velocity can be used?
How well will it be separated?
How could we improve the separation?
Dr. C. L. Jones
Biosystems and Ag. Engineering
3/31/08
BAE 2023 Physical Properties

8. Aero/Hydrodynamic Properties
Application example: A seed company would like to move soybeans through a pipe (5.25” inside diameter) pneumatically. What capacity should the air source (the fan) be rated for?
Dr. C. L. Jones
Biosystems and Ag. Engineering
3/31/08
BAE 2023 Physical Properties