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# Dr. C. L. Jones Biosystems and Ag. Engineering - PowerPoint PPT Presentation

Aero/Hydrodynamic Properties. Air and water are used to remove foreign material from products How much air required depends on the drag force F D ( sum of skin friction and pressure drag) F D affected by density, abs. viscosity, area and velocity (equation 10.1) Reference Figure 10.1.

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• 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

BAE 2023 Physical Properties

BAE 2023 Physical 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

BAE 2023 Physical 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. 10.1 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)(1.0 + 0.15(Rep)0.687)

Dr. C. L. Jones

Biosystems and Ag. Engineering

BAE 2023 Physical Properties

Dr. C. L. Jones

Biosystems and Ag. Engineering

BAE 2023 Physical Properties

Read Example Problem 10.1. 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

BAE 2023 Physical 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

BAE 2023 Physical 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

BAE 2023 Physical Properties