<p></p><p>In the grain handling and
processing industry, dust emission and accumulation are major concerns for the
safety of workers and for explosion risks. Dust emission and accumulation
locations highly depend on the facility design and equipment used for handling
and processing. To prevent an explosive atmosphere, monitoring the amount of
dust accumulated or dispersed is extremely important. However, methods of
measuring the dust concentration require the installation of equipment. The
Occupational Safety and Health Administration (OSHA) regulations and National
Fire Protection Association (NFPA) standards restrict the thickness of dust
layers on floors for fine powder materials such as starch. The objective of
this dissertation was to better understand the rate of dust layer accumulation,
dust suspension patterns, and the optical properties of suspended dust. For
this purpose, The Discrete Phase Model (DPM) was combined with a Computational
Fluid Dynamics Model (CFD) and the hybrid model was used to model dust
dispersion. Dust dispersion patterns under pressure, such as primary explosions
or leakage from equipment, were simulated using the unsteady CFD-DPM approach.
The particle-wall interaction based on energy conservation was also introduced
in this model. Both one-time and continuous dust dispersion in an enclosed
chamber were simulated to mimic secondary explosions and the dust emission from
processing equipment. In addition, the light extinction property of suspended
dust was studied as a method of measuring suspended dust concentration. </p>
<p>For a one-time dust dispersion
incident, the predicted dust concentration agreed with the simulation result
for the trial conducted at a dust injection velocity of 2 m/s with injection
rates of 0.05 and 0.10 kg/m³ and at a dust injection velocity of 10 m/s with an
injection rate of 0.05 kg/m³. The dust concentration in the entire chamber
increased with dust injection velocity and the mass of injected dust. As dust
injection velocity increased, dust spread out and formed a larger explosive
dust cloud. However, the dust concentration inside the chamber was non-uniform.
Considering the minimum explosive concentration, the largest explosive cloud
was created at a dust injection velocity of 10 m/s with an injection rate of
0.10 kg/m³. Explosive concentrations of dust were found somewhere in the
chamber for all dispersion rates. At an injection velocity of 10 m/s with an
injection rate of 0.10 kg/m³, the predicted dust concentration was 10% more
than the measured dust concentration. Thus, this model is suitable for dilute
dust particle dispersion flows, where the volume fraction of particles is less
and only a single particle layer settles.</p>
<p>Continuous dispersion was simulated
to determine the suspended dust concentration and particle deposition patterns.
Dust was dispersed for 30 s at dispersion rates of 2, 4 and 6 g/min at a dust injection
velocity of 2 m/s. The dust concentration increased at a constant rate after a
few seconds of dispersion, regardless of the dust dispersion rate. Most dust
particles were deposited near the dust dispersion nozzle. Large particles were
more affected by gravitational force and inertia compared with small particles,
which traveled with airflow and settled behind the nozzle. The dust accumulated
close to the dispersion nozzle faster than behind the nozzle location. However,
specific attention must be paid to small particles, because they are more
likely to cause an explosion, as their minimum explosive concentration is lower
than that of large particles.</p>
<p>The light extinction coefficients
of cornstarch, grain dust, and sawdust were measured using a two-target method.
The suspended dust concentration was measured using a calibrated laser
instrument. The light extinction coefficient was linearly related to the
suspended dust concentration. The correlation coefficient between the light
extinction coefficient and suspended dust concentration depended on particle
size, particle shape, and chemical properties. </p>
<p>Controlling dust cloud generation
and minimizing the concentration and volume of dust clouds are some key
measures to prevent dust explosions. The mathematical models developed in this
study to predict dust dispersion, suspension, and rate of settling will help
solve a few of the challenges in the particulate material handling and
processing industry. This method of measuring the light extinction coefficient
can be applied development of a dust safety monitoring system. The result
presented in this dissertation will help the industry prevent the formation of an
explosive atmosphere.</p><br><p></p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12749408 |
| Date | 05 August 2020 |
| Creators | Yumeng Zhao (9193676) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Relation | https://figshare.com/articles/thesis/Modeling_and_Measurement_of_Dust_Dispersion_Patterns_in_Confined_Spaces/12749408 |
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