Terminal velocity
- 1. ENGINEERING PROPERTIES OF FOOD MATERIALS- PFE 502 AERODYNAMIC PROPERTIES Presented by, NAGARAJU BUDIGAM FMPE (previous)
- 2. Aerodynamic properties of Biological materials The aerodynamic properties are important from the point of view of : 1.Coneying grains 2.Seperation of grains from foreign materials. The main aerodynamic property is terminal velocity. The drag coefficient and other properties are required for calculating the terminal velocity of the material in air conveying.
- 4. Fig. Seperation of grain from foreign materials
- 5. The drag coefficient is given by, C = 2 mg / Ap ρf V2 Where , mg = weight of the object Ap= projected area of the object ρf= fluid density V= terminal velocity. Drag coefficient in the direction of the flow exerted by the fluid on the solid is called drag. It consists, 1. wall drag or shear drag 2.form or pressure drag
- 6. Terminal velocity: Terminal velocity of a particle is the air velocity at which the particles remains in suspended state in a vertical pipe. Fig .terminal velocity illustration Terminal velocity of grain graph:
- 7. Methods of measurement of drag coefficient and terminal velocity: 1.Free fall method By Time distance relation , the displacement of fall of object is S=Vt 2/g ln cosh a gt 2.Photographic method: By determining the acceleration of a falling seed by photographic means, V=
- 8. In the condition of free fall , the particles attain a constant terminal velocity , V at which the net gravitational acceleration force equals the resisting upward drag force. Under steady state condition , when the terminal velocity has been achieved , if a particle density is greater than the fluid density, the particle motion will be downward. If the particle density is smaller than the fluid density, the particle will rise. Expression for terminal velocity is given as , V= Where, W=weight of the particle, kg Ap=projected area of the particle normal to the motion ρf=mass density of the fluid , kg mass/m3 ρp=mass density of the particle, kg mass/m3 C= drag coefficient.
- 9. Fig . Darg coefficient of different shapes of objects For a sphere of diamter dp, terminal velocity, V= For a thin disk (normal to face), V= For a circular cylinder, V=
- 10. The relationship between terminal velocity and drag coefficient is , 3ErCd V2t=4dn(Ep-Ef)g1/2 where, Er = density of air Vt = terminal velocity Cd = drag coefficient Ep = particle density dn = nominal diameter g = acceleration due to gravity