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CUSTOM APPLICATIONS | ENVIRONMENTAL ENGINEERING

                                                          container and keep it         water levels and oil types? Could
                                                                                        different hydrophobic coatings work for
                                                          connected to a pump for       different ocean depths?

                                                          continuous extraction            The answers lay in nding the best
                                                                                        combination of mesh properties for
                                                          as oil is collected. They     different oil spill conditions. The team
                                                                                        set up numerical simulations to help
                                                          could also be tailored        them in their search to nd the best
                                                                                        designs to collect the most oil.
                                                          to many different
                                                                                        ð HOW DOES MESH
                                                          operating conditions,”        DESIGN AFFECT OIL FLUX?

                                                          he continued. “We’re          Seeking the solution to a problem no
                                                                                        one has solved can sometimes feel like a
                                                          hoping to offer               needle-in-a-haystack hunt, even though
                                                                                        you may have a general idea of where
                                                          something to R&D              to start. But mathematical modeling
                                                                                        techniques vastly simplify the process.
                                                          engineers trying to
                                                                                           Coene, Silva, and Jorge Molinero,
FIGURE 2. Concept: a boom towed by boats hems in the oil  design cleanup tools,         partner and modeling solutions
while hydrophobic meshes collect it.                      environmental companies       director at Amphos 21, used
                                                          doing research, and the       COMSOL Multiphysics® software to
                                                                                        set up a simulation of a hydrophobic
                                                          oil companies that have       mesh in order to analyze how different
                                                                                        mesh designs would behave at different
the spilled oil without having to                               to gure out how to      water depths and to assess factors
process it — which is often another         contain a very large problem                in uencing the mesh performance.
costly step in the cleanup process,” said   very quickly.”
Emilie Coene, consultant at Amphos                                                         The success of a mesh is ultimately
21. “These meshes could be used for            One challenge arises with the            measured by the oil recovery rate
continuous operation, are very clean,       hydrophobic mesh collection method:         and the purity of the recovered oil.
and potentially have good recovery                                                      The team’s modeling work therefore
ef ciency and capacity.”                      uid height. At a certain water depth,     involved testing different polymer
                                            hydrostatic pressure will reach a           coating properties and mesh operation
   Hydrophobic meshes could,                “breakthrough” level, causing water to      at different ocean depths, and analyzing
hypothetically, be used alongside           intrude into the mesh and the collection
equipment designed for blocking the oil     container. If enough water gets mixed         ow rates for different oils.
from spreading out. For instance, while     in with the salvaged oil, the oil needs to     To see how different geometries
a boom surrounded the spill, meshes         be treated and processed in order           would affect the oil ux, they also
and collection containers could be          to be usable.                               parameterized the mesh wire radius
deployed directly into the oil to collect                                               as well as the hole size and spacing. In
it (see Figure 2). The collected oil could     The retention properties of the mesh     COMSOL® software, they conceptualized
then be pumped out of the container at      are a function of the oil-air and water-    the mesh as a porous medium coupled
regular intervals to ensure the correct     air surface tensions, and the contact       with two-phase ow to represent water
pressure difference from one side of the    angles of oil and water on the mesh
mesh to the other.                          surface. The coating on the mesh creates
                                            water repellency, but this is overcome
    “You can envision a large cylindrical   at certain water depths. The ow of oil
container (the mesh) that could be left     and water through the mesh depends
in the ocean until saturated with oil       on uid properties such as viscosity,
and then emptied,” added Orlando            density, and surface tension — which
Silva, senior consultant and project        vary for different types of oil — and the
manager. “Or you could deploy the           mesh porosity and permeability.

                                               Given this, how could the team at
                                            Amphos 21 design a mesh for different

   FIGURE 3. COMSOL® software results showing how oil ux through the mesh (left) and fractional water ow (center) vary with wire radius and
   water depth. Pore analysis showing the relationship between uid height, pore radius, and oil ux (right).
22 COMSOL NEWS 2016
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