# Study on Two-Phase Mixing Inside Flow Focusing/Blurring Nozzle by Gray Distribution Analysis Method
## 4 Results and Discussions
### Comparison of the Influence of Different Parameters on Two-Phase Mixing  
The influence of the nozzle structure and flow parameters on two-phase mixing in a mixing zone is analyzed and discussed by using gray scale level distribution. In the nozzle design and practical application adjustment, in most cases, multiple parameters will change simultaneously to affect the operation of the flow focusing/blurring nozzle. Therefore, it is meaningful to study and compare the effects of different parameters on two-phase mixing in the mixing zone. In this section, the effects of different parameters on two-phase mixing in the mixing zone are compared and analyzed. The effect of the liquid flow rate, the tube hole distance and the orifice diameter on gas-liquid mixing is similar, while the effect of the gas flow rate on gas-liquid mixing is opposite. Therefore, after increasing gas flow rate and liquid flow rate, gas flow rate and tube hole distance, gas flow rate and orifice diameter, in equal proportion, the influence degree of these four parameters on gas-liquid mixing can be qualitatively studied through the change of the gray distribution curve. Figure 11 shows the gray distribution curves of the two-phase flow images in the mixing zone with different air and water flow rates. As can be seen from Figure 11, as the air flow rate and the water flow rate increases proportionally, the gray scale level of the two-phase flow image in the mixing zone increases slowly, indicating that the degree of two-phase mixing decreases. This indicates that the liquid inertia force has a slightly stronger effect on the two-phase mixing in a mixing zone than the gas inertia force. This is due to the difference in inertia forces between the gas and liquid: when the gas-liquid phase is mixing in the mixing zone, although the gas velocity is higher than the liquid, the water density is much higher than air, so as the two-phase flow rate increases proportionally, the air inertia force will be lower than water. Therefore, the effect of the liquid flow rate on two-phase mixing is slightly greater than gas flow rate. Figure 10: The gray distribution curves of the two-phase flow images under different orifice diameter: the water flow rate, air flow rate and tube-hole distance are 100 mL/min, 100 L/min and 1 mm, respectively. For cases 1 to 3, the orifice diameter is 3 mm, 5 mm and 7 mm, respectively. Figure 12 shows the gray distribution curves of the two-phase flow images in the mixing zone under different air flow rates and tube hole distances. As can be seen from the figure, when the air flow rate and the tube hole distance increase proportionally, the gray scale level of the two-phase mixing image does not change much at the beginning, and then the gray scale level of the image increases significantly. The air velocity in the mixing zone will decrease with the increase of the tube hole distance, thus reducing the mixing degree of gas and liquid in the nozzle. At the initial stage, when the air flow rate and the tube hole distance increase proportionally, the decrease in air velocity caused by the increase of the tube hole distance in the mixing zone is compensated by the increase of the air flow rate, so the gray scale level of the two-phase mixing image does not change much. However, when the tube hole distance is large, the increase of the air flow rate is not enough to make up for the air velocity decrease in the mixing zone, resulting in a significant decrease in the degree of the two-phase mixing. Therefore, when the tube hole distance is small, the air flow rate and the tube hole distance have the same effect on the two-phase mixing, while when the tube hole distance is large, the effect of the tube hole distance on two-phase mixing is more obvious than the gas flow rate. Figure 11: The gray distribution curves of the two-phase flow images under different air and water flow rates: the tube-hole distance and orifice diameter are 1 mm and 5 mm.