Mass Movement: What causes the different types of mass movement? 1.
Air Movement in granular mass
description
Transcript of Air Movement in granular mass
AIR MOVEMENT IN GRANULAR MASS
(Flow through beds of solids)
OBJECTIVE
To estimate pressure drop in a bed of granular materials (packed or grain bed) and pump power
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746
.)(
QPhpPower
ghP
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)
KOZENY-CARMAN’S EQUATION
ERGUN’S EQUATION
Modified for specific materials Noted that Ergun uses darcy friction factor
(not fanning)
dp = average diameter of particle
2
21
v
dLP
fp
6
Moody Diagram for the Darcy friction factorMoody Diagram for the Darcy friction factor
Ergun proposed a modified friction factor E
factorfrictiondarcyf
porosity
ff
p
pE
)1(2
3
Laminar contribution
Turbulent contribution
75.1Re
)1(150
75.1,36
150
1000ReRe
)1(C 63
21
21
E
E
f
CC
for
Cf
LEVA’S EQUATION
n = 1 for laminar flow,n = 2 for turbulent flowG = mass velocity (kg/s.m2)
’ =modified fanning friction factor
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
spheres of ratio surface tovolume
particles of ratio surface tovolume
’ =modified fanning friction factor
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
Example 2