Papers by Keyword: Supercritical Fuid

Abstract: This study was aimed at understanding how the process conditions affected the dimensional stability of glass fiber reinforced PP by microcellular injection molding. A design of experiments (DOE) was performed and plane test specimens were produced for the shrinkage and warpage analysis. Injection molding trials were performed by systematically adjusting six process parameters (i.e., Injection speed, Injection pressure, Shot temperature, SCF level, Mold temperature, and Cooling time). By analyzing the statistically significant main and two-factor interaction effects, the results showed that the supercritical fluid (SCF) level and the injection speed affected the shrinkage and warpage of microcellular injection molded parts the most.

Abstract: The supercritical fluid flow jetted out from a nozzle was divided into two stages, free jetting and passing through the porous media, in a supercritical spray dyeing process. According to the nature of the flow, the free jetting model and passing through porous media model were established separately. Based on the established models, the characteristics of supercritical fluid flow field in the supercritical fluid spray dyeing process were investigated firstly in this paper. Distributions of the temperature and pressure and their influencing factors in the flow field, which are the determinants of the spray dyeing process, were obtained and analyzed. Besides, the mass flow and covering diameter sprayed by supercritical fluid were studied. The simulating analysis may provide a theoretical basis and guidance for the actual process of supercritical fluid spray dyeing.

Abstract: In this work, a novel method was reported for preparation of Ru/activated carbon (Ru/AC) catalysts. Supercritical carbon dioxide (SC CO₂) was employed as medium for the impregnation of ACs with inorganometallic precursor of RuCl3. The Ru/AC catalysts displayed excellent activity for the catalytic hydrogenation of D-glucose. Selected Ru/AC catalysts were characterized by N₂ adsorption-desorption, TPR and TEM analysis. The results show that the order of effects on catalytic activity are supercritical temperature > supercritical pressure > amount of co-solvent > time of impregnation. The optimal supercritical parameters for preparing Ru/AC catalyst were 313 K, 8 MPa, 4 ml of methanol and 9 h, respectively. The highest reaction rate of hydrogenation reached 86.35 mmol•min-1g-1Ru, upgrading 42.96% compared with the activity of conventional Ru/AC prepared using aqueous impregnation. The SC CO2 impregnation could result in Ru uniformly dispersed on the outer surface and in the pore of AC, leading _{Subscript text}to higher dispersion of Ru and enhanced interaction between AC and Ru. Furthermore, the enhanced interaction induces improved reduce temperature. Consequently, the catalytic activity of Ru/AC catalysts is improved significantly.

Abstract: Microcellular foam injection parts have many advantages such as saving material and energy, reducing cycle time, and processing excellent dimensional stability. Despite these advantages, the low surface quality problems limit its application scope seriously. In this study, the microcellular foam injection molding principle and some surface defects were introduced, and the technologies to improve surface quality, such as Gas Counter Pressure (GCP), Rapid Heat Cycle Molding (RHCM), and Film Insulation were summarized in detail. Finally, the prospect of CAE technologies about microcellular foam injection molding was proposed.

Abstract: Based on the creative design of nozzle structure, the application fields of the micro-particles production using supercritical fluids (SCF) can be further broaden. According to the analysis of the structural characteristics of the nozzles, a new kind of nozzle with a tunable annular gap is proposed in this research, which includes a cover, movable trays, unmovable trays, seal fittings and connecting components. By virtue of FLUENT software, the flow field of the nozzle in outer mixing mode with two passages is numerically simulated. The effects of the passing length of SCF before mixing and the height of conic convexity on the flow-field are analyzed. The simulation results show that the above length does adverse effect on enhancing mixing extent, however, the smaller height of convexity can help achieve better mixing level. Then the nozzle is redesigned in which a movable tray and an unmovable tray are removed. The improved nozzle has simple and reasonable structure and can do better work on improving gas-liquid mixing extent.

Abstract: The aim of this study was to obtain nanoparticles and improve solubility of ursolic acid (UA), using supercritical antisolvent process (SAS). The four effects of process variables on drug particle formation during SAS process were investigated. Particles with mean particle size ranging from 139.4 ± 19.4 to 1039.8 ± 65.2 nm were obtained. The UA was characterized by scanning electron microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, specific surface area and dissolution test. The XRD analyses showed that the processed UA was amorphous. The processed UA had solubility 4.4 times higher than the unprocessed UA.

Abstract: The characteristics of heat transfer enhancement and deterioration in supercritical water reactor core is essential to the reactor efficiency and security. At present, there exists deficiency in the study of core enhanced channels. Two different fins arrangements of the enhanced channels are designed in present paper, which are long-strip fins and equal-distance short fins. At the conditions of the supercritical pressure of 25MPa, the inlet temperature of 350°C and different inlet velocities, the heat transfer enhancement and deterioration characteristics of water flowing in the two different fins arrangements of the enhanced channels were studied and comparatively analyzed. The results show that the heat transfer is enhanced in the channels with fins. The heat transfer enhancement is better in the channel with equal-distance short fins when lower input velocity, better in the channel with long-strip fins when high input velocity. The surface heat transfer coefficients increase with the velocity increases; the surface heat transfer coefficients in equal-distance short fins is two to three times than that in the channel without fins. There exists heat transfer deterioration when the input velocity is lower in the channel without fins and with long-strip fins, no deterioration occurs in the channel with equal-distance short fins. The channel with equal-distance short fins is a relatively reasonable of the three channels.

Abstract: In consideration of the similarities of supercritical fluid extraction (SFE) kettles, the parameterized finite element analysis system was developed based on ANSYS and Visual Basic. The parameterized model building, stress analysis and fatigue analysis for shell, nozzle and quick-opening sealing structure were realized by second development of ANSYS using APDL language. The program which can deal with design parameters was developed based on Visual Basic, and the command stream files, which can be recognized by ANSYS, were modified according to design parameters and sent to ANSYS solver by the program. With the system, the stress and fatigue analysis process for SFE kettle is simplified and the analysis efficiency of SFE kettle is improved.

Abstract: The aim of this study was to evaluate the possibility of preparing chitosan porous matrixes using supercritical fluid technology. Supercritical immersion precipitation technique was used to prepare scaffolds of a natural biocompatible polymer, chitosan, for tissue engineering purposes. The physicochemical and biological properties of chitosan make it an excellent material for the preparation of drug delivery systems and for the development of new biomedical applications in many fields from skin to bone or cartilage. Immersion precipitation experiments were carried out at different operational conditions in order to optimize the processing method. The effect of different organic solvents on the morphology of the scaffolds was assessed. Additionally, different parameters that influence the process were tested and the effect of the processing variables such as polymer concentration, temperature and pressure in the chitosan scaffold morphology, porosity and interconnectivity was evaluated by micro computed tomography. The preparation of a highly porous and interconnected structure of a natural material, chitosan, using a clean and environmentally friendly technology constitutes a new processing technology for the preparation of scaffolds for tissue engineering using these materials.

Abstract: Nano-sized nickel particles were dispersed on multi-walled carbon nanotubes (MWCNTs) via an improved electroless deposition route using a supercritical CO2 fluid. The microstructure, chemical composition and crystallinity of the Ni-decorated CNTs were examined using a transmission electron microscope (TEM), an X-ray energy dispersive spectrometer (EDS), and an X-ray diffractometer (XRD), respectively. The analytical results indicate that, with assistance of the supercritical fluid, Ni nanoparticles with a diameter of approximately 10 nm can be uniformly dispersed on the surface of CNTs. The hydrogen storage capacity of the Ni-decorated CNTs was evaluated with a high-pressure microbalance at room temperature and under a hydrogen pressure of 6.89 MPa. The measured hydrogen adsorption amount of the Ni/CNTs nanocomposite was 1.06 wt%, which was much higher than 0.33 wt% found for the plain CNTs.