Liquid CO2 Droplet Spectra

Abstract

Sequestration of anthropogenic CO2 in the deep ocean is being evaluated as a means to reduce the rate of accumulation of this greenhouse gas in the atmosphere. The two primary issues that must be addressed are the effectiveness of this strategy in reducing atmospheric CO2 levels over time and its impacts on the marine environment. An important parameter in predicting local acute changes in sea water chemistry induced by deep ocean injection of liquid CO2 is the size of the resultant CO2 droplets. Jets of liquid CO2 discharging into seawater are hydrodynamically unstable and will break-up into a dispersed droplet phase. The droplets are advected by buoyancy and currents while they dissolve and acidify the sea water. Models of CO2 droplet plumes consistently predict that although the vertical extent of affected sea water is greater for large droplets, the magnitude of induced changes in sea water chemistry is less than that associated with smaller droplets. The majority of effort to date has been directed toward studies of liquid jets in air. While instability phenomena in liquid-gas and liquid-liquid systems are similar, they are not identical; break-up is affected by the properties of the continuous (ambient) phase and the condition of the jet-ambient fluid interface, which can be significantly different in the two systems. Investigations of liquid-liquid instability are limited, and largely confined to the laminar flow regime. Little information exists on droplet sizes produced by transitional flow and turbulent break-up events. To address this deficiency, laboratory experiments have been conducted to obtain droplet size spectra and to investigate the mechanisms of instability of liquid CO2 jets discharging into pressurized water under simulated deep ocean conditions.