48
surveys of the DSD of a vertical oil discharge for several exit velocities and discharge diameters ranging from 1 to 5 mm. A pulse-free gear pump was used to
inject the oil from a pressure-free reservoir into a water depth of approximately 1 m.
Droplet sizes were determined using a Phase Doppler Particle Analyzer (PDPA).
Brandvik et al. (2013) performed a series of experiments using the “Tower Basin”
facility at SINTEF, Norway, to measure oil droplet sizes with and without subsea
dispersant injection (SSDI). The water tank used was 3 m wide and 6 m deep; oil
was injected vertically upward by pressurizing the oil reservoir with nitrogen and
releasing the pressurized oil through a controlled valve. Size measurements were
taken with both a LISST-100X laser diffractometer and a macro camera 2 m above
the nozzle. On the same scale, Belore (2014) investigated the effect of varying
dispersant- to-oil ratio (DOR) and gas void fraction on the DSD at Ohmsett Wave
Tank. In this study, two LISST-100X laser diffractometers were used to measure the
DSD. Zhao et al. (2016) performed experiments at a larger scale also at Ohmsett
Wave Tank in 2016 with a discharge of 6.3 L/s from a 1 inch horizontal nozzle; DSD
was again determined using two LISST-100X.
These and other similar studies provide key information on the DSD of an oilonly discharge in shallow waters. But because of the limitations of the facilities, the
effects of a deep-sea environment such as in the DWH spill could not be investigated. A deep-sea oil discharge will alter from one in shallow waters not only with
regard to the water temperature and hydrostatic pressure but also to the high amount
of short-chained, gaseous hydrocarbons dissolved in the oil and a pressure difference between the oil reservoir and the surrounding seawater. Recently, two research
groups investigated these effects by generating jets under artificial deep-sea conditions. Brandvik et al. (2017) used a holocam (Davies et al. 2017) to determine the
DSD of “live oil”, i.e. oil saturated with natural gas, with and without an additional
gas void fraction and/or chemical dispersants. The experiments took place in a
2.3-m-wide pressure tank at the Southwest Research Institute (SwRI) at elevated
hydrostatic pressures between 59 and 172 bar; jets were generated by overpressure
in the oil reservoir. Malone et al. (2018) at Hamburg University of Technology
performed several studies at 151 bar hydrostatic pressure to quantify the effects of
gas dissolution, outgassing and sudden pressure loss at the nozzle. Oil DSD was
determined from an endoscopic imaging system at the centreline of the jet. Oil flow
was generated either isobarically or with a defined pressure difference using an
equal- volume cylinder (Seemann et al. 2014), enabling a wide range of spill
scenarios.
4.2.2 Stirrer Cells
A different approach to determine the DSD of an accidental oil discharge is based
on the turbulent nature of such a discharge. This approach uses a stirrer cell to simulate not the oil jet itself, but rather its turbulent flow field by stirring an oil-in-water
K. Malone et al.
surveys of the DSD of a vertical oil discharge for several exit velocities and discharge diameters ranging from 1 to 5 mm. A pulse-free gear pump was used to
inject the oil from a pressure-free reservoir into a water depth of approximately 1 m.
Droplet sizes were determined using a Phase Doppler Particle Analyzer (PDPA).
Brandvik et al. (2013) performed a series of experiments using the “Tower Basin”
facility at SINTEF, Norway, to measure oil droplet sizes with and without subsea
dispersant injection (SSDI). The water tank used was 3 m wide and 6 m deep; oil
was injected vertically upward by pressurizing the oil reservoir with nitrogen and
releasing the pressurized oil through a controlled valve. Size measurements were
taken with both a LISST-100X laser diffractometer and a macro camera 2 m above
the nozzle. On the same scale, Belore (2014) investigated the effect of varying
dispersant- to-oil ratio (DOR) and gas void fraction on the DSD at Ohmsett Wave
Tank. In this study, two LISST-100X laser diffractometers were used to measure the
DSD. Zhao et al. (2016) performed experiments at a larger scale also at Ohmsett
Wave Tank in 2016 with a discharge of 6.3 L/s from a 1 inch horizontal nozzle; DSD
was again determined using two LISST-100X.
These and other similar studies provide key information on the DSD of an oilonly discharge in shallow waters. But because of the limitations of the facilities, the
effects of a deep-sea environment such as in the DWH spill could not be investigated. A deep-sea oil discharge will alter from one in shallow waters not only with
regard to the water temperature and hydrostatic pressure but also to the high amount
of short-chained, gaseous hydrocarbons dissolved in the oil and a pressure difference between the oil reservoir and the surrounding seawater. Recently, two research
groups investigated these effects by generating jets under artificial deep-sea conditions. Brandvik et al. (2017) used a holocam (Davies et al. 2017) to determine the
DSD of “live oil”, i.e. oil saturated with natural gas, with and without an additional
gas void fraction and/or chemical dispersants. The experiments took place in a
2.3-m-wide pressure tank at the Southwest Research Institute (SwRI) at elevated
hydrostatic pressures between 59 and 172 bar; jets were generated by overpressure
in the oil reservoir. Malone et al. (2018) at Hamburg University of Technology
performed several studies at 151 bar hydrostatic pressure to quantify the effects of
gas dissolution, outgassing and sudden pressure loss at the nozzle. Oil DSD was
determined from an endoscopic imaging system at the centreline of the jet. Oil flow
was generated either isobarically or with a defined pressure difference using an
equal- volume cylinder (Seemann et al. 2014), enabling a wide range of spill
scenarios.
4.2.2 Stirrer Cells
A different approach to determine the DSD of an accidental oil discharge is based
on the turbulent nature of such a discharge. This approach uses a stirrer cell to simulate not the oil jet itself, but rather its turbulent flow field by stirring an oil-in-water
K. Malone et al.