| OCR Text |
Show * = _*•' C = itc.A, =i A ,_, M is often called unmixedness. 5. RESULT 5.1 F L O W P A T T E RN The typical model incinerator with four nozzles was calculated. For the comparative evaluation, the values of jet velocities from 3(m/s) to 200(m/s) and the nozzle diameters (10,20.30.40.50.60mm) were calculated. The jet temperature of 498K was selected because the reburning gas is usually mixed with E G R gas to penetrate into primary combustion gas. The velocity of primary combustion gas was 1 m/sec and the temperature was 1170K for all cases. A typical flow pattern is shown in the contour plot of Figure 4. The plane of the plot intersects the center of the injection nozzle. The fluid injected from the nozzle penetrates into the primary combustion gas flow and is mixed with it. It is obvious that the mixing degree strongly depends on the penetration degree. Turbulent mixing is generally promoted by the turbulent intensity in the mixing region. In the case of (a) . the jet can not penetrate sufficiently and the mixing speed is slow. In the case of (b) . the jet penetrate adequately and the mixing is promoted by the turbulence caused by the jet. O n the other hand, in the case of (c). the jet penetrates completely and mixes with primary combustion gas sufficiently by the turbulence caused by the jet impacting. From these flow patterns, mixing mechanisms in the model incinerator can be classified into three groups; wall source, jet mixing and jet impacting"1. 5.2 UNMIXEDNESS In order to evaluate the mixing degree for various jet conditions of the nozzle diameters and the jet velocities, the unmixedness at x/D=1.0 was calculated. The contour plot of the unmixedness was shown in Figure 5. The unmixedness decreases as the nozzle diameter is longer and the velocity is higher. 5.3 CRELLATION EQUATION It is clear from Figure 5 that the unmixedness at x/D=1.0 plane from the injection points is determined by the nozzle diameter and the jet velocity. When engineers select the nozzle configuration for the good mixing performance.% it is convenient that the important parameters such as the nozzle diameters and the jet velocities can be selected without confusion by generalized correlation equations. |
