Filtration characteristics of Clarke-Bumpus samplers

Abstract

The Australian and American models of the sampler were tested at water velocities up to 3.5 kt. A calibration tank designed to simulate normal flow conditions through the flowmeter was used to calibrate flowmeter rate against flow rate measured at a 90º V-notch exit. This calibration was used to determine the discharge through samplers towed for a measured distance in a water channel. Thus the filtration characteristics of the samplers were examined.

The filtration coefficient for the American sampler without a net averaged 88 %, compared with 92% for the Australian sampler. Australian nets reduced the filtration coefficient of the Australian sampler by 2-15 %. The American net had little effect on the filtration coefficient of the American sampler.

The filtration coefficient varied with mesh aperture and clogging but was largely independent of towing velocity. Other experiments suggested that net length was less important, and the flow of water around the net more important, than previously thought.

Above approximately 1 kt, the calibration value was nearly independent of velocity and hardly altered with net attachment no matter how fine the mesh.