Rapid expansion of supercritical solution is one of techniques for generation nanoparticles. This process has different and unique advantages; producing very fine particles with the same and narrow size distribution, controllability particle size, high purity of particle without solvent … Modeling of this process help to known effective parameters and how effect of them. Modeling results of RESS showed that; increasing the pre-expansion temperature produced larger particles because temperature is an effective parameter on the growth of particles. Smaller particles obtain by increasing preexpansion pressure lead to. Modeling results of RESS showed that, heat flux of expansion device (nozzle), if driving process to isotherm path lead to smaller particles. another effective parameter is nozzle geometry , modeling results show that increasing nozzle diameter lead to larger particles , on the other side increasing converging angle generated smaller particles so that small diameter and large angle of nozzle is appropriate (suitable) . In some experimental reports of rapid expansion of supercritical solution recommended adding capillary after nozzle. Its effect is considered in model and to become distinct that smaller particles generated, because addition capillary exceed residence time in subsonic part and in more time nucleation and condensation have majority mechanism. Expansion chamber pressure is another independent and controllable parameter of this process. Modeling results show that increasing this pressure lead to larger particles its increase appropriate suitable collision.
