The Simulation And Optimization Of The Gas Flow Field And Heat Exchanging Of The High Power Fast Axial Flow CO₂ Laser

The high power fast axial flow (FAF) CO2 laser is a very well established processing tool in the manufacturing industry. With the development of processing industry, the FAF CO2 laser needs not only a higher power, but also a smaller, lighter and more compact structure. The key factors in achieving all these characteristics are the optimization of heat exchanging and flow field of the gas circulation system. According to the analysis of the influence of the heat exchanging and flow field on the efficient laser output and the long-time stable work, the gas circulation system is divided into four parts. The three key parts which affect the heat exchanging and flow field are studied. The main work of this paper is:(1) The optimization method of the internal flow field distribution of the discharge region which is the first critical part of the gas circulation system is studied. The influence of the nozzle structure and tube diameter on the internal flow field stability is analyzed, and an efficient and accurate optimization method for the discharge tube design is provided. According to the comparison of different numerical simulation results, the following conclusions can be obtained:the vortex of the working gas is benefit in the anode region, but disadvantaged in the straight length. Moreover, the situation that the tube diameter increase from 19 mm to 23 mm is considered, the internal flow field variation tendency is studied. The optimization design principle is obtained:there is an optimum ration between the tube diameter and the inflow nozzle size. The inflow nozzle size should be determined by this ratio after increasing the tube diameter. The influence of the inflow nozzle size on the gas flow filed is also further studied.(2) The heat balance equation of the FAF CO2 laser is established. Meanwhile, in view of the heat exchanging characteristics of the high power laser, various types of heat exchangers are compared; the rectangle fin circle tube heat exchanger is chose as the laser radiator because of its prominent heat transfer capacity and compact structure. Further more, the traditional empirical formula method is used to design the heat exchanger for the 7 kW FAF CO2 laser. The results indicate that the rectangle fin circle tube heat exchanger is suitable to the FAF CO2 laser we designed.(3) The numerical simulation method of the heat exchanging region is studied. According to the analysis of the inner heat exchanging process characteristics of the FAF CO2 laser, the geometric model, physical model and mathematical model of the heat exchanger are established, moreover, the inner gas distribution is obtained. The results between the numerical simulation and the empirical formula calculation are compared. The results are in good agreements, so the reasonableness of the numerical simulation method is proved to be an efficient method to the heat exchanger design for the gas circulation system. Moreover, the inner gas distribution in different structures of the heat exchangers is compared, and then the most reasonable structure for the 4 kW FAF CO2 laser is selected. The results can not only meet the requirements of the heat transfer capacity, but also achieve a compact structure.(4) According to the analysis of the characteristics of the blower given gas circulation system, the importance of the inlet pressure of the turbo blower is studied, and the key part to the optimization design of the gas circulation system is identified. According to the working characteristics and structure of this region, the geometrical model and the physical model is established. Moreover, the flow field distribution is calculated by using the computational fluid dynamics method. The following optimization design principles are obtained:the inlet of the flow region should be ensured enough space, in order to facilitate the high-speed and hot gas fully spread to the entire fin area of the heat exchanger; the obstacles block should be avoided in the outlet region, in order to suppress the influence of the swirl. According to those principles, an optimized structure is designed. Compare to the traditional structure, the 34% length and 6% pressure loss is saved.The research of this thesis improve the traditional design method of the heat exchanging process and flow field of the FAF CO2 laser, and make the design process more efficient and more accurate. The research provides an efficient tool for simulation and optimal design to promote the FAF CO2 towards higher power and more compact structure development.