Development Of Supercritical CO₂ Spray Jet Mixing Device

Compared with traditional spraying methods,supercritical CO₂ spraying can solve the problem of organic solvent pollution from the source,and has higher coating utilization and better film quality.However,the mixing device of supercritical CO₂spraying still has many problems such as long mixing time,difficult equipment cleaning,and poor mixing effect for high viscosity coatings.To solve the above problems,a jet mixing device for high viscosity coatings is developed in this paper.The mixing effect of the jet mixer is optimized by CFD simulation and applied to a supercritical CO₂spraying device to test the spraying effect.The details of the study are as follows:（1）Design a supercritical CO₂ jet mixing and spraying device,using a supercritical CO₂ jet mixer instead of a high-pressure mixing kettle as the mixing device of the spraying system.The structural dimensions of the nozzle section,contraction section,mixing section and diffusion section of the jet mixer are determined by a theoretical calculation method based on the conservation law,and a three-dimensional model is established.（2）Analyze the variation law of pressure field,velocity field,temperature field and concentration field in the jet mixer by CFD simulation.The optimal mixing section inlet cross-section to nozzle cross-section area ratio was determined to be 6.25 and the relative pressure was 0.16 to complete the optimization of the efficiency of the jet mixer.The statistical relative standard deviation was used as the mixing index to measure the macroscopic mixing effect of supercritical CO₂ and coatings.（3）Using the mixing index and priming ratio as response values,the surface response analysis method was used to determine the optimal priming pressure of the jet mixer as 8MPa,the priming temperature as 50℃,the length of the mixing section as30mm,and the diffusion angle as 7°.At this time,the mixing index is 0.043.The larger the energy difference between supercritical CO₂ and paint,the more sufficient mixing space,the better the material mixing effect.The priming ratio under the optimal mixing index condition was determined to be 1.071.（4）The processing and manufacturing of the jet mixer,the selection of key equipment,and the construction and commissioning of the complete device were completed.By comparing the spraying effect of A-butyl hydroxyl rubber coating with PW180-B particle size analyzer,it was found that the average atomization particle size D_[4.3]of the jet mixer was between 165.41μm and 173.21μm,and the Uniformity index of particles was 0.8244,which was basically consistent with the mixing effect of the mixing kettle and met the mixing requirements of the supercritical CO₂ spraying system.The jet mixing device developed in this paper not only effectively solves the problems of low mixing efficiency and difficult equipment cleaning,but also adds an automatic control system,which can realize continuous spraying under optimal working conditions.It is of great significance to optimize the supercritical CO₂ spraying process.