Study On The Flow Of Supercritical CO₂Spraying

Excessive volatile organic compounds（VOC）have been produced by traditionalspraying. The flammable and explosive VOC which have strong toxicity have beenbeginning to be replaced by environmental friendly solvents, which has become oneof research highlights nowadays. In addition, supercritical carbon dioxide（SC-CO2）has been considered as an ideal substitute for VOC, contributing to the close attentionin SC-CO2spraying technique. Based on this background, the process of supercriticalCO2spraying is studied numerically in the present dissertation. The main work andresearch results are as follows:(1) SC-CO2coating material analysis. SC-CO2paint ingredient and phasebehavior have been studied. Meanwhile, various physical properties of SC-CO2coating material have been calculate, which brings important parameters fornumerical simulation.(2) The study of SC-CO2spraying model. The simplified physical model,mathematical model and numerical analysis method have been established byanalyzing the process of SC-CO2spraying. The results of numerical calculation ofRapid Expansion of Supercritical Solution（RESS）, the experimental results ofParticles from Gas Saturated Solutions（PGSS） and SC-CO2spraying model havebeen verificated by FLUENT software. The results reveal that the research methods ofthis subject are feasible.(3) The3D numerical simulation of two-phase mixed flow in the nozzle. Theeffects of the nozzle diameter, inlet pressure and inlet temperature on the flow field,axial pressure distribution and axial density distribution have been studied. The resultsare as follows: The flow velocity and the pressure drop in the leading portion of pipeare minor. At the same time, the smaller the nozzle diameter, the higher the outletpressure and the better the spraying effect. Supercritical fluid spraying contained twoatomization mechanisms, one is pressure atomization and the other is gas explosionatomization. Meanwhile, the outlet velocity, outlet density and outlet temperature oftwo-phase flow increase with the raise of the inlet pressure. In addition, the temperature condition of supercritical CO2spraying which is a great reference valueto optimal design on SC-CO2spraying has been proposed.(4) The3D numerical simulation of rapid expansion. The influences of thenozzle diameter, pre-expansion pressure and pre-expansion temperature on theresidence time, diameter, number, velocity and temperature of particles have beeninvestigated. The results show that some spray particles can move away from primaryjet direction because of the impact of atomization; the smaller the jet diameter, thegreater the temperature drop of spray particles; the particle size decreases and theparticle size distribution narrows with the increasing of the pre-expansion pressure;the effect of gas explosion atomization weakens and the function of pressureatomization enhances as pre-expansion temperature rises.