Characterization of Turbulent Properties in the EPA Baffled Flask for Dispersion Effectiveness Testing

Abstract

The baffled flask test (BFT) has been proposed by United States Environmental Protection Agency to be adopted as the official standard protocol for testing dispersant effectiveness. The mixing energy in the baffled flask is investigated in this paper. Particle image velocimetry (PIV) was used to measure the water velocity in the flask placed at an orbital shaker that was rotated at seven rotation speeds: 100, 125, 150, 160, 170, 200, and 250 rpm. Two dimensional velocity fields in large and small vertical cross sections of the flask for each rotation speed were obtained. The one-dimensional (1D) energy spectra indicates the existence of inertial subrange. The estimated average energy dissipation rates were in the range 7.65×10−3 to 4 W/kg for rotation speeds of Ω=100–250 rpm, of which it is larger than the one estimated by prior studies using single-point velocity measurement techniques for Ω=100 and 200 rpm. Factors such as instruments used, velocity components measured, and different analysis methods could contribute to the discrepancies in the results. The Kolmogorov scale estimated in this study for all seven rotation speeds approached the size of oil droplets observed at sea, which is 50–400 μm. The average energy dissipation rate,ε and Kolmogorov microscale, η, in the flasks were correlated to the rotation speed, and it was found that ε¯=9.0×10−5 Exp(0.043Ω) with R2=0.97 and η¯=1,463 Exp(−0.015Ω) with R2=0.98.