Examples of CHARM Use
CHARM Software can perform a number of simulations that are not available in
standard air dispersion models. The most recent version of the CHARM® software
has been extended to allow multiple releases; multiple species; particle
formation, coagulation, evaporation / condensation, deposition, and interaction
with gases; and chemical reactions. Some examples of these non-standard uses are
below.
Liquid Release with Terrain Influenced Flow
CHARM has the capability to allow a liquid release to follow terrain contours and
evaporate as it flows. The emission rate into the atmosphere from the amorphous
source is time varying as the surface temperature and wind speed can change with
location and time.
The model can visually display the location of the liquid with depth indicated by
color. An example of such a display is shown in Figure 1. In the figure the
liquid release is assumed to occur at the top of a ridge (a small red S marks
the spot) with a steep slope to the left of the figure and a ditch to the right.
The liquid depth is indicated by color. Blue is the deepest liquid and white is
shallower. The liquid is deepest in the ditch. Some liquid goes down the steep
slope and pools at the bottom.
Figure 1. Example display of CHARM liquid flow calculation.
Cooling Tower Droplet Deposition
Cooling towers can create droplets that can coagulate, evaporate, and be deposited
on the ground. CHARM is capable of handling all these processes. In some cases
the droplets formed may have toxic material mixed with the water, for example,
sulfuric acid. A specified droplet size distribution for the source was entered
into the model. The droplets were allowed to evaporate, coagulate, and deposit
on the ground.
A more detailed description of the use of the
software for this case is available.
Figure 2. Deposition as a function of time at two distances downwind (500 and 1,000
meters).
Water Curtain Scavenging Efficiency
CHARM was used to model a ground release of ammonia vapor with a source of water
droplets higher than the release site and downwind. To test the effect of
different flow rates a number of water emission rates are used. One simulation
is performed with only the ammonia emission to determine the non-mitigated case.
Most scenarios were run with 50% humidity. One scenario used 95% humidity to
investigate the effects of evaporation on the droplets.
A chemical reaction that allows ammonia vapor to be absorbed by particles was
defined in the chemical database. The assumed reaction for the analysis is:
NH3(g) + H2O(l) -->NH4+ + OH-
The reaction rate is assumed as:
Reaction Rate = 4 π D r
Where D = binary diffusion coefficient of ammonia in air;
r = radius of particle absorbing the ammonia.
A more detailed description of the use of the
software for this case is available.
Figure 3. Ammonia Scavenging Efficiency at Ground Level as a Function of Downwind
Distance.
Multiple Buildings
In most modeling that takes buildings into account, only one building upwind is
assumed to effect the dispersion. The CHARM Software allows for multiple
buildings at arbitrary locations with respect to the release site. Multiple
buildings near each other can have a much different effect on the wind field
affecting the dispersion of the released material than a single building.
Buildings downwind can have split or deflect the released material.
Figure 4. Example 3D display of plume affected by buildings and terrain.
Sarin Release in an Urban Environment
A PDF example of concentration impacts from a release of 100 pounds of Sarin in an urban area (terrain and buildings). A CHARM created animation of the plume moving over and around buildings is also available.
Pool Fire
A PDF example of thermal radiation and concentration impacts from a release of a flammable liquid that forms a pool and catches fire.
Vapor Cloud Explosion
A PDF example of a vapor cloud explosion from the release of LNG on water.
Multi-building Impact
A PDF example of concentration impacts at a building downwind of another building with a release.
Release Inside Building
A PDF example of concentration impacts inside and outside from a release inside a building. A CHARM created animation of the plume leaving the building is also available.