Comparison of Single-Point Injections in Pipe Flow

For applications such as using tracer techniques for discharge measurements in pipes or using a segment of a pipe as a mixing chamber, it is desirable to know the rate at which the concentration of injected material becomes mixed within the pipe cross section. The distance required to achieve a given degree of mixing depends on the injection system and the pipe flow characteristics. The mixing for three single-point injection systems is compared. The three systems are a center line source, a wall source, and a jet at the wall issuing perpendicularly to the pipe flow. A center line source can provide the most rapid mixing, but it is extremely difficult to maintain the symmetry necessary to achieve the rapid mixing. The wall source gives the slowest mixing. The mixing for a jet injection depends on M, the ratio of the jet momentum to the pipe momentum. For a jet injection, there is an optimum M which gives the most rapid mixing for given flow characteristics, and this mixing is more rapid than either a wall source or most practically achievable center line sources.