Brookfield PFT Powder Flow Tester Operating Instructions Manual page 58

Software can be used to estimate pressures in a container based on measurements of the bulk
density ρ, wall friction ϕ
pressure σ at depth Z is given by the following equation. This equation is used for Rat-hole
1
calculation.
ρ · g · D
=
σ
1
4 · λ · tanϕ
We assume:
This applies only to the vertical section of the bin or silo. "Kick-pressure" has an effect when
the powder gets into the hopper section.
The wall friction angle represents the angle to which a wall surface must be inclined as shown
in Figure A-7 to cause powder to slip. The wall friction angle is typically in the range of 10 to
45 degrees.
The wall friction angle is also called the chute angle.
AMETEK Brookfield
0
0.5
1
1.5
2
2.5
3
3.5
4
Major Principal Consolidation Stress σ
Figure A-6: Stress distributions in vertical walled vessels
, internal friction δ
w
(
1 – e 4 · λ · tanϕ
·
W
λ = 0.4
Powder slip
Figure A-7: Wall friction
wall friction = 0 deg
wall friction = 20 deg
wall friction = 40 deg
Hydrostatic pressure increase
(pgh)
40 20 0
and container diameter D. The principal consolidation
j
)
·Z
w
D
w
Page 58
1
Manual No. M09-1200-F1016