Gas exchange in seawater with special emphasis on open-cycle ocean thermal energy conversion

This study examines gas transfer characteristics of seawater. Special emphasis is on gas transfer processes in connection with Open-Cycle Ocean Thermal Energy Conversion (OC-OTEC) applications. Experiments probe the mechanism regulating gas transfer in bubbles and in a packed column. In order to compare gas transfer in seawater with extensively documented transfer characteristics of fresh water, all tests are conducted using both seawater and fresh water in the same experimental setting.;The main findings are: (1) Bubble coalescence is significantly less in seawater than in fresh water. Bubbles coalesce in seawater to a limited extent if flow conditions promote bubble collisions; the magnitude of coalescence increases with the frequency and intensity of collisions. (2) Gas transfer in seawater exceeds that of fresh water due primarily to the increased liquid-gas interfacial area resulting from the different coalescence behaviors. (3) Gas transfer rates in bubble aeration are the same in offshore and filtered Hawaiian coastal seawater. Suspended matter and surfactant in unfiltered coastal seawater reduce the overall transfer coefficient. (4) If bubbles do not coalesce, the magnitude of gas transfer is similar in fresh water and in seawater. (5) The liquid film transfer coefficient k...