VORTEX-TUBE SEDIMENT EXTRACTORS .1. TRAPPING EFFICIENCY

The vortex tube is a device for extracting sediment from canals that c onsists of a tube laid horizontally across the canal bed with an open slit along its top edge. Flow from near the canal bed is collected in the vortex tube and is extracted from the canal. Its trapping efficien cy is defined as the proportion of the canal sediment load that is ext racted. The present paper provides a theory for predicting the trappin g efficiency of vortex tubes that is based on a theoretical sediment f lux profile for the canal upstream from the vortex tube. The theory is compared with field measurements of trapping efficiency at six sedime nt extractors. The ratio of observed trapping efficiency to predicted trapping efficiency has a mean value of 1.0 and a standard deviation o f 0.25 over 120 measurements. The present paper also provides quantita tive guidance on locating vortex tubes so that local effects, such as canal bends, do not reduce trapping efficiency. (A design method for v ortex tubes, which uses trapping efficiency predictions, is presented in a companion paper.)