# Study on Two-Phase Mixing Inside Flow Focusing/Blurring Nozzle by Gray Distribution Analysis Method
## 4 Results and Discussions
### The Influence of Flow and Structure Parameters on Two-Phase Mixing Inside the Nozzle  
Experiments were carried out on the flow focusing/blurring nozzle under different conditions and the gray distribution of the two-phase flow images in the mixing zone of the nozzle was extracted and analyzed. Because we mainly study the gas-liquid mixing in the mixing zone, the conditions that make the flow blurring or close to the flow blurring inside the nozzle are selected in the experiment. Figure 7 shows the gray distribution curves of the two-phase flow images in the mixing zone under different water flow rates. As can be seen from Figure 7, with the increase of the water flow rate, the gray scale level of the two-phase flow image in the mixing zone increases and the concentration of the gray distribution curve decreases. This indicates that the mixing intensity and uniformity of the gas and liquid in the mixing zone will be weakened with the increase of the water flow rate in a certain range. This indicates that the increase of the water inertia force is not conducive to the full mixing of the two-phase fluids in the nozzle. Figure 8 shows the gray distribution curves of the two-phase flow images in the mixing zone under different air flow rates. Figure 8: The gray distribution curves of the two-phase flow images under different air flow rates: the water flow rate, tube-hole distance and orifice diameter are 100 mL/min, 1 mm and 5 mm, respectively. For cases 1 to 4, the air flow rates are 10 L/min, 20 L/min, 40 L/min and 60 L/min, respectively. Figure 7: The gray distribution curves of the two-phase flow images under different water flow rates: the air flow rate, tube-hole distance and orifice diameter are 80 L/min, 1 mm and 5 mm, respectively. For cases 1 to 4, the water flow rates are 100 mL/min, 200 mL/min, 400 mL/min and 600 mL/min, respectively. Figure 8 shows that with the increase of the air flow rate, the gray scale level of the two-phase flow image in the mixing zone decreases. When the air flow rate is small (such as in case 1), the flow pattern in the mixing zone is closer to flow focusing and the single-phase uniformity is better, so the concentration of the gray distribution curve is better. Therefore, it indicates that, with the increase of the air flow rate, the mixing intensity and uniformity of the two-phase will become stronger. Different from the water, the increase of the air inertia force can make the mixing effect of the gas-liquid phase better in the mixing zone. Figure 9 shows the gray distribution curves of the two-phase flow images in the mixing zone under different tube-hole distances. As can be seen from the figure, the gray scale level of the two-phase flow image in the mixing zone decreases with the decrease of the tube-hole distance; when the flow pattern is flow blurring, the concentration of gray distribution curve will be enhanced with the tube-hole distance's decreases. In other words, the increase of the tube-hole distance will weaken the mixing intensity and uniformity of gas and liquid in the mixing zone. This indicates that the increase of the tube-hole distance is also not conducive to the full mixing of the two phases in the nozzle. Figure 10 shows the gray distribution curves of the two-phase flow images in the mixing zone under different orifice diameters. The influence of the orifice diameter on two-phase mixing in a mixing zone is relatively simple. Figure 10 shows that, when the orifice diameter is larger than the inner tube, the two-phase mixing intensity and uniformity inside the mixing zone are weak. When the orifice diameter is equal to or less than the inner tube, the concentration of the gray distribution curve is significantly enhanced, which indicates that when the orifice diameter is equal to or less than the inner tube, the two-phase mixing in the mixing zone is significantly better than that when the orifice diameter is larger than the inner tube.