Enhanced Axial Dispersion in Oscillating Pipe Flow With Different Solute Concentrations at Its Ends

Abstract

The problem of the enhanced axial contaminant dispersion by sinusoidal oscillation of fluid in a cylindrical pipe connected to reservoirs filled with contaminated groundwater involving different concentrations of species has been examined. It is found that the axial contaminant transfer along the pipe can be greatly enhanced by the fluid oscillation, which leads to a rapid removal of contaminants from groundwater and develops a relative low concentration region in the neighborhood of the subsurface collector. The enhanced dispersion coefficients, Deff , of several heavy metal ions and organic compounds with water as carrying fluid were computed, and the results show they are about four to six orders of magnitude larger than those in the absence of fluid oscillation. The operational energy cost is low. For example, by operating the presented U-type enhanced mass pump, whose total cross-section area in one leg is 0.0154 m2 , it takes 15 days to extract and remove acetone from a contaminated groundwater body that is 12 m below grade and 10 m3 in volume, such that the acetone concentration can be decreased from 650 mg/l to 325 mg/l (i.e:, 50 percent lower than its original level) and the averaged daily (24 hours) operational energy cost is only 12.6 kJ (1.56 Btu).