Experimental setup for the investigation of bubble mediated gas exchange

An experimental setup for the measurement of the contribution of air bubbles to gas exchange is presented. The bubble size distribution was measured as a function of the position in a 1.3m deep glass tank using an imaging method based on the depth from focus principle. Bubble radii from 100 to 1000 micro;m can be resolved with the recent image processing algorithm. The optical apparatus is automated to move horizontally and vertically along the tank walls in order to capture the whole bubble cloud. The bubble cloud is generated by a water jet which impinges on the water surface from above. The bubble distribution is similar to that produced by whitecaps, but stationary in a statistical sense. The flow rate of the air entrainment can be controlled. In a pilot experiment, the evasion of a set of trace gases was measured by means of UV absorption spectroscopy. The effect of the tracer solubility on the bubble-mediated gas exchange is demonstrated./p>