FLUIDIZATION
Testing with the REVOLUTION
Powder Analyzer
A powder is fluidized when a gas is injected into
the powder causing the powder particles to separate and
enter a fluid like state. The properties of the
powder, as well as the pressure and temperature of the
gas, determines the degree of fluidization. For
fine powders, the gas pressure required to fluidize the
particles is very low. This low pressure can be created
by rotating the powder in a drum. Varying the rate
of drum rotation results in changes of the fluidization
pressure. The
fluidization of a fine powder can be studied by
measuring the volumetric expansion of the powder in a
rotating drum as a function of the rotation rate of the
drum.
Fluidization Process
In addition, the rate at which a fluidized fine
powder settles to its original state can be measured by
stopping the rotation and reducing the fluidization
pressure to zero.
The
REVOLUTION Fluidization
Test measures a
powder's volume increase at specified angular velocity
intervals in a rotating drum to create a fluidization
function for the powder. During the fluidization test,
the rate of decrease in the powder's volume is measured
to create a settling function for the material.Appropriate powders
for the REVOLUTION
Fluidization test include: toners, catalysts,
powder coatings, and other powders with low pressure
fluidization potential.
There are
four optional process steps to the Fluidization
Analysis: Prep, Settling, Analysis, and Settling. These
four steps are discussed below.
Prep
Step
Within the Prep
Step, the user can rotate the
powder at a chosen rotation rate and length of time to
completely fluidize the material.
This step will allow the user establish a
repeatable initial fluidized state for this
analysis. This
prep step can be skipped if the user wishes to
study the fluidization of the material in its
original state.
Powder in a Fluidized State
Figure
C - Fluidization Rate of Two Samples - Time vs. Sample Height
Settling
Step
If the material has
been fluidized in the prep step, the material must
return to its un-fluidized state to perform the
fluidization analysis. In this step, the rotation
of the drum is stopped for a specific length of
time or until the volume of the sample reaches its
original state. The rate at which the
powder's volume decreases is measured and is used
to create a settling function.
Powder Settling after Fluidization
Fluidization Analysis
Step
During the
analysis, the user sets the
start and end drum rotation rate with the desired step rate.REVOLUTION will begin the
drum rotation at the
specified start rotation rate, stepping up the rate at
the desired intervals until the end rotation rate is
achieved. The user can chose to ramp up the
angular speed at any desired intervals to achieve
the equilibrium fluidized state.
Fluidization Process
After
a specified equilibration time
has elapsed at the end rotation rate, REVOLUTION will
begin computing the statistical measurements described
below for this fluidization analysis step. In
Figure A, the statistical analysis shows the
operator the rate at which the powder fluidized by
the increase in the overall volume. In Figure
B, the fluidization test results are shown for
two different powder samples: one sample fluidizes
at a faster rate than the other.
Figure
A - Rate of Fluidization - Rotation
Speed vs. Sample Height
Figure
B - Comparison of Fluidization Rate of Two Powder Samples
- Rotation Speed vs. Sample Height
Settling Step
After
the fluidized analysis, the REVOLUTION
measures
the settling time of the powder. This settling time
is valuable for anyone who is fluidizing a coating
for example and needs to know the amount of time
required for the powder to settle on the coating surface.
In Figure C, the analysis shows the operator the
rate at which the powder settled after the
fluidization operation had been stopped.
Powder Settling after Fluidization
Figure
C - Settling Rate of Two Samples - Time vs. Sample
Height
This fluidization test will provide the
following statistical analysis at each of
the process steps: prep, settling
and
analysis. Please doubleclick
on any of the parameters for a brief
measurement description.