Characteristics of a four-nozzle, slotted short mixing stack with shroud, gas eductor system

Abstract

Cold flow tests were conducted on a four nozzle (nozzles tilted at a 15 degree angle) gas educator system to evaluate the system's performance utilizing a short slotted missing stack and two shrouds with diffuser rings. The stack length-to-diameter ratio, (L/D), was 1.0, and with the shroud and diffuser rings extended to L/D to 1.5. The difference in the two shrouds was the separation distance between stack and shroud and between shroud and diffuser rings. This separation distance resulted in exit diffuser angles of 10.8 and 7.3 degrees. The nozzles were constructed with a ratio of total area of primary flow to area of mixing stack of 2.5. Secondary and tertiary pumping coefficients, mixing stack pressure distributions, and exit velocity profiles were used to evaluate the shrouded mixing stacks. The stack and shrouds were evaluated with the stack slots closed and then with the slots open. Secondary pumping was found to be independent of changes in diffuser angle. Tertiary pumping decreased with the separation distance and only showed a slight increase when the slots were opened. The 7.3 degree shroud had a lower tertiary flow; however, in the regions of low flow at the exit plane, the severity of the velocity fluctuations was much reduced and hence better overall performance was achieved.