AUTHOR=Boniewicz-Szmyt Katarzyna , Pogorzelski Stanisław Józef 

TITLE=Influence of Surfactant Concentration and Temperature Gradients on Spreading of Crude-Oil at Sea*

JOURNAL=Frontiers in Marine Science

VOLUME=5

YEAR=2018

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2018.00388

DOI=10.3389/fmars.2018.00388

ISSN=2296-7745

ABSTRACT=<p>Spreading kinetics measurements were carried out on crude oils surfactant-containing sea water of well-controlled thermo elastic surface properties in laboratory conditions. It was found that oil lens expansion rates, predicted from the classical surface tension-driven spreading theory, were higher by a factor of 6–9 than those experimentally derived for Baltic collected sea water. Previously, in order to explain such a discrepancy, the initial spreading coefficient <italic>S</italic><sub>0</sub>–entering the lens radius vs. time dependence was replaced with the temporal one <italic>S</italic><sub><italic>t</italic></sub> dependent on the water phase surface viscoelasticity of Boniewicz-Szmyt and Pogorzelski (<xref ref-type="bibr" rid="B5">2008</xref>). Now, natural surfactant concentration and temperature gradients perpendicular to the surface were shown to drive a particular cell-like flow at the surface microlayer, as a result of the classic and thermal Marangoni phenomenon. The balance of interfacial forces was taken as<italic>: –</italic>μ∂<italic>U</italic><sub><italic>s</italic></sub><italic>/</italic>∂<italic>z</italic> = ∂γ<italic>/</italic>∂<italic>T</italic>·∂<italic>T/</italic>∂<italic>x</italic>+∂γ<italic>/</italic>∂<italic>c</italic>·∂<italic>c/</italic>∂<italic>x</italic> where: μ is the dynamic viscosity, <italic>U</italic><sub><italic>s</italic></sub>—the velocity, <italic>z</italic> and <italic>x</italic> axes oriented perpendicularly and horizontally to the main flow direction, <italic>T</italic>, γ<italic>, c</italic> are the temperature, surface tension, and concentration of surfactants. Computations performed on original seawater (Baltic Sea) systems, shown that the natural surfactant concentration term ∂γ<italic>/</italic>∂<italic>c</italic> is several times lower than the thermal ∂γ<italic>/</italic>∂<italic>T</italic> one (Boniewicz-Szmyt and Pogorzelski, <xref ref-type="bibr" rid="B6">2016</xref>). Such a surface tension gradients induce the Benard-Marangoni instability, for high enough the so-called Marangoni numbers that could significantly slow down the spreading process. On the basis of thermo-physical model liquids properties, the critical temperature difference Δ<italic>T</italic><sub><italic>c</italic></sub> required to initiate the process under an evaporative cooling condition was evaluated. In this just concept study, the preliminary results suggest that the vertical processes are involved, and that a realistic model of oil dispersion should include vertical velocity shears appearing in the final surface tension-driven stage of oil pollution development.</p>