Evaluation of turbulence parameters in laboratory flasks used for dispersant effectiveness testing

The effectiveness of dispersants used as countermeasures for oil spills is commonly evaluated by conducting tests in laboratory flasks. The success of the test relies on the replication of sea conditions in the flasks. We used a Hot-wire Anemometer (HWA) to characterize the hydraulics in the Swirling Flask (SF) and the Baffled Flask (BF) at orbital shaker speeds of 150 and 200 rpm's. We used these measurements to compute velocity gradient, G, turbulence microscale, η, and energy dissipation rate per unit mass, ε. The flask average energy dissipation rates in the SF were about hvo orders of magnitude smaller than those in the BF. The sizes of the microscales in the BF were found to be much smaller than that in the SF. Also, in the BF, the sizes of the microscales approached the size of oil droplets observed at sea (50 to 400 micron), which means that the hydraulics in the BF closely resembles the hydraulics occurring in the top few cm of a breaking wave. Hence, the BF is preferable for dispersant effectiveness testing in the laboratory.