Simulation And Optimization Study Of Supercritical CO₂ Spraying Nozzle

Supercritical CO₂spraying is a new and environmentally friendly spraying method.Currently,there is limited research on nozzle atomization simulation for supercritical CO₂spraying processes.In this study,a new process flow for a high-viscosity supercritical CO₂coating spraying device was designed,and relevant prototypes were manufactured.Subsequently,a comprehensive Fluent simulation method for supercritical CO₂spray nozzle atomization was proposed.The flow field characteristics of supercritical CO₂spray nozzle atomization were analyzed.The nozzle parameters were optimized through the use of a response surface methodology,yielding the optimal spraying conditions.Finally,the simulated results were experimentally validated using the spray prototype developed in this study.The specific research contents are as follows:（1）Based on the atomization simulation method of supercritical CO₂spraying nozzle proposed in this paper,using ANSYS Fluent software,with the average diameter D[3,2]as the measurement criterion,the influence of spraying temperature,spraying pressure,supercritical CO₂mass fraction,and nozzle inner diameter on the atomization of high-viscosity Type A butadiol coating with supercritical CO₂spraying was investigated.A simulation scheme was constructed using the response surface methodology to optimize the spraying process parameters and nozzle structure.The optimal simulation parameters were determined as follows:spraying pressure of 10MPa,spraying temperature of 53.144℃,supercritical CO₂mass fraction of 50wt%,nozzle inner diameter of 0.3302mm,and the optimal average diameter D[3,2]was 69.642μm.The significance order of the respective variables on the response variable was found to be:nozzle inner diameter>spraying pressure>supercritical CO₂mass fraction>spraying temperature.In addition,the nozzle slit opening angle had the most significant influence on the spray angle,while the auxiliary atomization pore pressure and the spray angle adjustment pore pressure played a fine-tuning role in the spray angle.（2）The supercritical CO₂high-viscosity coating prototype developed in this paper was used to carry out spraying experiments on Type A and Type B butadiol coatings,and the particle size characteristics of the atomized droplets during the spraying process were measured using a PW180-B laser particle size analyzer.The diameter distribution of atomized particles obtained from the airless spray gun was significantly smaller than that of the air-assisted spray gun,but the average diameter D[3,2]and D50 were slightly larger than those of the air-assisted spray gun.Three repeated experiments were performed on both types of coatings without the addition of solid fillers,and the obtained average diameter D[3,2]was consistent with the simulation results.Through experimental research,the organic solvent usage required for spraying Type A and Type B butadiol coatings was reduced by more than 70%,and good spraying results were achieved.The above research results can provide theoretical guidance for the industrialization of supercritical CO₂spraying technology.