Experimental Investigation And Numerical Simulation Of Supercritical Impinging Streams

Technology of supercritical carbon dioxide (SCCO2) impinging streams is a new which process developed recently for microparticles preparation. It has some advantages as followed: supercritical fluid (SCF) technology and impinging streams technology are combined; heat and mass transfer are significantly enhanced. However, the present research is still in the early stage of the process feasibility. There are few reports on the systemically experimental and theoretical research of the process, especially the aspect of hydrodynamics behavior which plays a key role in the process of microparticles preparation. This research is aimed to study the basic hydrodynamics behavior of SCCO2 impinging streams from both of experimental and numerical simulation. The main contents and achievements of this study are as followed:(1) By numerical simulation of the throttling process, the effects of inlet pressure and throttling valve opening on the throttling process were investigated, the evolutions of the pressure, temperature and density of CO2 are revealed. The results show that the pressure, temperature and density of CO2 have decreased rapidly in the throttling valve.(2) By orthogonal experimental study of the throttling process, the effects of throttling valve opening, extractor pressure and extractor temperature on CO2 pressure after throttling were investigated, the key factors of impinging streams are determined. The results show that the effects of throttling valve opening, extractor pressure and temperature on CO2 pressure after throttling are gradual decrease.(3) By numerical simulation of impinging streams, the effects of inlet pressure and impingement distance on the flow field were investigated, the evolutions of the pressure, Mach number, temperature and density of CO2 are revealed. The results show that the pressure, temperature and density of CO2 are decreased in the nozzle, while the Mach number increases rapidly. The pressure, temperature and density of CO2 are relatively high in the impingement zone, while the Mach number is relatively low.(4) Impinging streams were tested experimentally and analyzed quantitatively by using particle image velocimetry (PIV), velocity vector figures are obtained and the impingement zone is determined. The results show that the evolutions of the jet velocity from the nozzle exit to the impinging face including surge, plummet, leveled off, and replunge. The nozzle axial velocity decreases rapidly and the direction is changed to radial velocity and then leaves the impingement zone. Increasing the flow rates from 0.2 to 0.8 m3/h, the width of the impingement zone increases from 0.25 to 0.5.