The Application of Free Jets to the Mixing of Fluids in Bulk

Abstract

A laboratory investigation with scale models was made to determine the performance figures of free jets for mixing fluids in large circular tanks, primarily for the war-time purpose of utilizing existing underground storage tanks for blending aviation petrol. The investigation showed that a simple jet directed across a diameter of the tank caused complete mixing in a time approximately equal to 8D²/√QU seconds, where D was the tank diameter, Q the volumetric rate of flow through the nozzle, and U the velocity at the nozzle—all expressed in self-consistent units—provided the time taken to inject the second fluid was less than half the total time. The model tests also showed the necessity of using a sufficiently large vertical component of the jet velocity to avoid stratification when mixing fluids of different densities, and quantitative values depending on a modified type of Froude number have been determined. The tests predicted that mixing by simple jets would occur in a time much shorter than is usually taken by conventional mixing devices, and this has been confirmed in full-scale practice in a number of cases varying from relatively small lubricating-oil tanks to four million gallon petroleum tanks. Possible applications to other mixing problems, such as the sterilization of swimming baths, are briefly discussed.