JET MIXING OF LIQUIDS IN LONG HORIZONTAL CYLINDRICAL TANKS

Large storage tanks may require mixing to achieve homogeneity of conte nts for several reasons: prior to sampling for mass balance purposes, for blending in reagents, for suspending settled solids for removal, o r for use as a feed tank to a process. At Oak Ridge National Laborator y, mixed waste evaporator concentrates are stored in similar to 190-m( 3) (50000-gal) horizontal tanks, about 3.7 m (12 ft) in diameter and 1 8 m (60 ft) in length. This tank configuration has the advantage of pe rmitting transport by truck and therefore fabrication in the shop rath er than in the field. A survey of the literature revealed no informati on on mixing large storage tanks with length-to-diameter ratios greate r than 2. Jet mixing experiments were carried out in two model tanks: a 0.87-m(3) (230-gal) Plexiglas tank that was similar to 1/6 linear sc ale of the actual waste tanks and a 95-m(3) (25000-gal) tank that was about 2/3 linear scale of the actual waste tanks. Mixing times were me asured by the use of a sodium chloride tracer and several conductivity probes distributed throughout the tanks. Several jet sizes and config urations were tested. In the 0.87-m(3) tank, jet diameters of 0.016, 0 .022, and 0.041 m (0.62, 0.87, and 1.61 in.) were used. In the 95-m(3) tank, jet diameters of 0.035 and 0.049 m (1.38 and 1.93 in.) were use d. One-directional and two-directional jets were tested in both tanks. Mixing times for each tank were correlated with the jet Reynolds numb er and for the two tank sizes using the recirculation time for the dev eloped jet.