A novel approach for obtaining bubble dissolution measurements at sea

Abstract

A hybrid system for measuring the dissolution of gas bubbles in an oceanic environment was developed utilizing the Coastal Systems Station’s Light Scattering Bubble Counter (LSBC). The LSBC independently measures flow velocity and bubble size, and is capable of distinguishing bubbles from particulate matter. In the hybrid system, the dynamic range of the LSBC measurements is 50 μm to about 300 μm in radius. The system is filled at depth (30 feet maximum without internal pressurization) and initially purged of all free gas. Pneumatically controlled valves are used to establish a closed recirculating system in which a flow can be generated in either direction using a large-volume peristaltic pump driven at low-volume velocity. Clear air is forced through a ceramic fritted disk to create the initial bubble population. This bubbly mixture is recirculated through the system at a nominal flow rate of 22 l/min, which corresponds to a velocity of 30 cm/s through the LSBC aperture. The bubble radii are continuously measured using the LSBC, resulting in time-dependent bubble size distributions. These distributions are used to estimate bubble dissolution rates for the size range indicated. [Work supported by ONR.]