Rapid Expansion Of Supercritical Fluid Solutions Research Articles

The characteristics of coherent structures in the rapid expansion flow of the supercritical carbon dioxide

By the use of a tiny pressure-transferring probe and capacitor-type sensor, the dynamic pressure signals in the jet flow of the rapid expansion of supercritical carbon dioxide are measured, which distinctively shows the characteristics of quasi-periodical coherent structures. After Fast Fourier Transform (FFT) conversion of the time series signals of the dynamic pressure, there exist three dominant frequency bands in the power spectrum, which correlate with the scale of the dominant eddies in the turbulent field. The dominant frequencies change little with the distance from the nozzle exit or the pre-expansion pressure, while the power density of the dominant frequencies, which correlates with the energy of the dominant eddies in the turbulence, attenuates along the axial direction and with the decrease of the pre-expansion pressure. Through analysis, it is inferred that the nozzle structure and initial conditions remarkably affect the coherent structures in the expansion flow which should be the important factors in the particle nucleation and its growth process in ultra-fine particle preparation by rapid expansion of supercritical fluid solution (RESS).

Mechanism of particle coating granulation with RESS process in a fluidized bed

In this study, the rapid expansion of supercritical fluid solution (RESS) process was employed for the coating granulation of fine particles in a fluidized bed and its mechanism was examined. The rapid expansion of the supercritical solution causes very high supersaturating ratio of solute in the spraying flow, forming a large number of superfine nuclei. The superfine nuclei deposited on the surface of the particles form a thin film. It was found that the fine particles were all covered with the thin film. This coating mechanism has been confirmed by SEM inspection. The granules with fine particles adhered were circulated through the spraying region and were covered with the binder or coating material (solute) in the region in the form of a film, resulting in the fine particles being cumulatively coated on core particles layer by layer. The temperature at the nozzle inlet was found to be an important factor affecting the coating granulation process.

Rapid expansion of supercritical fluid solutions(RESS)

Rapid expansion of supercritical fluid solutions(RESS)

ChemInform Abstract: Preparations of Nickel, Cobalt, and Iron Nanoparticles Through the Rapid Expansion of Supercritical Fluid Solutions (RESS) and Chemical Reduction.

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Preparations of Nickel, Cobalt, and Iron Nanoparticles through the Rapid Expansion of Supercritical Fluid Solutions (RESS) and Chemical Reduction

A method based on the rapid expansion of supercritical fluid solutions (RESS) coupled with chemical reduction was developed to produce nickel, cobalt, iron, and iron oxide nanoparticles of reasonably narrow size distributions. Under the protection of a polymer stabilization agent, the largely amorphous metal nanoparticles form stable suspensions in room-temperature solvents.

Strong Optical Limiting of Silver-Containing Nanocrystalline Particles in Stable Suspensions

Metal and metal sulfide nanoparticles are prepared using a method that is based on the rapid expansion of supercritical fluid solution (RESS) into a liquid solution and characterized using transmission electron microscopy and X-ray diffraction methods. The nanoparticles form solution-like stable suspensions in the presence of a stabilization agent such as poly(N-vinyl-2-pyrrolidone) (PVP) polymer. The stable suspensions allow systematic nonlinear optical measurements. The nanocrystalline silver metal and silver sulfide particles in PVP polymer-stabilized ethanol suspensions of high linear transmittance exhibit excellent optical limiting properties, with the optical limiting responses toward nanosecond laser pulses at 532 nm being much stronger than those of benchmark materials [60]fullerene and chloroaluminum phthalocyanine in solution. A comparison of the results with those of stable suspensions of other nanoparticles including cadmium sulfide, lead sulfide, and nickel suggests that the optical limiting ...

A novel fluidized-bed coating of fine particles by rapid expansion of supercritical fluid solutions

A novel fluidized-bed coating process using the rapid expansion of supercritical fluid solutions (RESS) is described for the coating of fine particles. Experiments were conducted in a 50 mm i.d. circulating fluidized bed with an internal nozzle in the center of the riser. Microspheroidal catalyst particles (average particle size 56 μm) were used as the core particles. Supercritical carbon dioxide solutions of paraffin were expanded through the nozzle into the bed that was fluidized by air. The coating mass and coating rates were measured by a sampling method. Mercury porosimetry was used to determine the quality of the coated particles. A stable coating of fine particles was achieved without the formation of agglomerates at room temperature. The present study examines the effects of hydrodynamics and solute concentration on coating rate and coating efficiency.

Radial Model for Particle Formation from the rapid expansion of supercritical solutions

A numerical model for the rapid expansion of supercritical-fluid solutions (RESS) is presented. Considering the complete expansion of the fluid into a vacuum, the process is modeled as inviscid, radial flow. The particulate material is described by the moments of the particle size distribution by numerically integrating the moments with the equations describing an inviscid flow of a non-ideal solution. By varying the initial process conditions, we examine the trends due to changes in specific operational parameters for typical RESS solutions. These calculations show that in the limit of a very rapid expansion with no precipitation in the nozzle itself, an increase in solute concentration produces a large increase in the particle size of the solids produced. Increasing the initial temperature causes a decrease in the calculated mean particle size, while an increase in pressure produces larger particles. However, both temperature and pressure have a much smaller effect on the calculated particle sizes than does concentration. The calculations demonstrate that small particles with a narrow size distribution can be achieved by using as low a solute concentration as possible and operating at relatively low preexpansion pressures and high preexpansion temperatures.

Production of powders and films by the rapid expansion of supercritical solutions

A new process utilizing the rapid expansion of supercritical fluid solutions (RESS) is described for the production of fine powders and thin films by the rapid nonequilibrium precipitation of nonvolatile compounds from dense gas solutions upon expansion. A variety of the fluid solution expansion parameters, including solute and solvent identity, solute concentration, expansion temperature, and expansion nozzle configuration, has been shown to affect the product characteristics of materials formed during the RESS process. Conditions favouring thin film formation include very dilute solutions and short nozzles minimizing residence time during expansion. Particle formation is favoured by more concentrated solutions. The process has been demonstrated to produce products of widely varying morphology by the adjustment of RESS parameters, and examples of SiO2 GeO2 and various polymeric materials are presented. Unique features of the RESS process relevant to other powder and film production methods are described and potential applications are discussed.