## 4 Results and Discussion
### Comparative Analysis of Experimental Results  
To verify the feasibility and effectiveness of the impeller optimization scheme, this study takes the VHGQ-D-9912 dual-chamber vacuum gas quenching furnace as the application scenario, with its main structure shown in Figure 18. Flow field and temperature field experiments are conducted on the gas quenching furnace using both the original and modified impellers. Figure 17: Blockage factor distribution in the flow passages A and B of the original and modified impellers. Figure 18: Main structure of the vacuum quenching furnace. The flow velocity measurement device used is the Kanomax 6243 multi-channel hotwire anemometer from Japan, with a measurement range of 0 m/s to 50 m/s. For velocities less than 10 m/s, its accuracy is 0.01 m/s. The working principle involves placing a fine electrically heated metal wire perpendicular to the airflow. As the airflow passes over the wire, heat is transferred, causing a temperature change in the wire, which in turn alters its electrical resistance. This change in resistance is used to convert the airflow velocity signal into an electrical signal, which is then transmitted to the anemometer's main unit. The testing process is shown in Figure 19, and the on-site installation diagram of the modified structure is shown in Figure 20.  
The velocity measurement section is located at the central cross-section of the workpiece area of the quenching furnace, with a total of 7 \(\times\) 7 measurement points. Figure 21 shows the velocity distribution at the test section. From the figure, it can be observed that both the original and optimized impellers exhibit a velocity distribution with the highest velocity at the center and lower velocities at the periphery. However, the original structure further demonstrates a distribution where the flow velocity on one diagonal side is significantly greater than that on the opposite side. After the impeller optimization, the overall velocity distribution becomes more uniform compared to the original, with a substantial increase in velocity at the periphery. Figure 19: Schematic diagram of the testing process. Figure 20: On-site installation diagram of the modified structure: (**a**) disassembly diagram of the air chamber (**b**) schematic of the workpiece area, (**c**) exterior view of the gas quenching furnace. The velocity test data for the original and modified impellers were statistically analyzed, and the standard deviation was used to measure the uniformity of the velocity distribution, as shown in Figure 22. It can be seen that the standard deviation of the velocity data is significantly reduced after optimization. The average velocity standard deviation at the test section is 42.78% lower than that of the original impeller. Specifically, the standard deviations at Y = 400, Y = 600, and Y = 800, located at the center of the test section, are reduced by 62.97%, 60.69%, and 57.14%, respectively, compared to the original, indicating a more uniform flow. The temperature tests were conducted by placing a 400 mm \(\times\) 400 mm \(\times\) 400 mm H13 hot work steel specimen at the center of the workpiece area. During the cooling process of the gas quenching furnace, nine thermocouples were passed through flange holes and fixed at nine measurement points evenly distributed at the lower part of the workpiece. The temperature was recorded using these thermocouples. The temperature recorder selected was the DAQ970A model from KEYSIGHT, which includes 14 thermocouple input ports, enabling simultaneous data recording from 14 channels. This system was able to meet the measurement requirements for the nine temperature points in this experiment. A comparison of the temperatures at the measurement points when the average workpiece temperature is 523 K is shown in Figure 23. After the optimization of the blades, the temperature differences at each measurement point are significantly reduced.