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Air Movement in granular mass

Air Movement in granular mass

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Air Movement in granular mass

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  1. Air Movement in granular mass (Flow through beds of solids)

  2. objective • To estimate pressure drop in a bed of granular materials (packed or grain bed) and pump power http://www.scielo.br/scielo.php?pid=S0104-66322004000100004&script=sci_arttext

  3. Factors affected on P • Porosity • Particle size • Exposed surface area • Moisture content • Surface roughness • Container size • Etc… 3 main methods • Ergun’s equation • Leva’s equation • ASAE data (American Society of Agricultural Engineering)

  4. Kozeny-Carman’s equation

  5. Ergun’s equation • Modified for specific materials • Noted that Ergun uses  darcy friction factor (not fanning) dp = average diameter of particle

  6. Moody Diagram for the Darcy friction factor

  7. Ergun proposed a modified friction factor E Laminar contribution Turbulent contribution

  8. Leva’s equation • ’ =modified fanning friction factor n = 1 for laminar flow, n = 2 for turbulent flow G = mass velocity (kg/s.m2)

  9. Shape factor or sphericity • For non spherical particles,  is a shape factor (also called sphericity and used with symbol ), defined by: • For spheres =1 by definition. For other typical filter bed materials irregular shapes  ~ 0.75

  10. ’ =modified fanning friction factor

  11. Given: • Voidage = 45% • Density of air = 5.239 kg/m3 • Height of bed = 3 m • Diameter = 0.005 m • Air mass flow rate = 3000 kg/hr.m2 • Entrance pressure = 5 bar • Determine the pressure of exit air using Ergun Equation Example 1

  12. Example 2