Ultrafiltration of polyethylene glycol aqueous solutions was analyzed using concentration polarization-gel layer model. The model is based on coupling concentration polarization layer and gel layer growth. The concentration polarization layer development is given by the convective-diffusion equation. However, the gel layer growth model is obtained by using the experimental observations. The limiting flux was found to be proportional to the square root of the axial velocity. Beyond the critical concentration, both concentration polarization and gel formation are the main factors controlling the limiting flux in the tubular UF system. The developed semi-empirical model, which contains a single empirical constant to be evaluated from experiments, predicted satisfactorily the limiting flux data over the range of experimental variables examined in this study. 相似文献
This paper deals with the regulator problem for linear continuous-time systems with asymmetric saturations on the control. The main contribution of this work is to extend the available results for symmetrical saturations, in term of LMIs, to systems with asymmetric saturations. Hence, LMIs formalism is obtained for the first time for asymmetrical saturation. New less conservative result on saturation is used. An example is presented to illustrate the obtained results. 相似文献
The context of this study is the modelling of reactive extrusion process based on an alginate extraction protocol. Residence Time Distribution (RTD) is one important part to predict the kinetics of reactive compounds. A simple model is proposed to predict RTD in fully intermeshing co-rotating twin-screw extruders without reaction. This model, which can be easily extended to reactive case in a future work, is based on the extension of an axial dispersion model, including control parameters (screw speed and flow rate) and geometrical parameters (screw profile and die design). Simulations were performed for various operating and geometrical conditions so as to illustrate possibilities offered by the proposed model. Validation was conducted for two different extrusion applications, seaweed extrusion and polymer extrusion. This highlighted the model ability to predict RTD for various kinds of materials after adjusting only one parameter thanks to a unique experimental RTD curve. 相似文献
This paper focuses on the bond between near-surface mounted (NSM) reinforcement and low-strength concrete. In order to investigate this, eight beams made of low-strength concrete were made. The compressive strength of this concrete varied from 14.22?MPa to 16.83?MPa. These beams were then tensioned under monotonic loading until failure. The test setups differed in terms of their groove size and the type of reinforcement (a rod and plate of carbon fiber reinforced polymer, prestressing steel). Based on the achieved results and analysis, it was found that the NSM method can be applied to low-strength concrete. Furthermore, the application of a NSM reinforcement rod and plate, made of the carbon fiber reinforced polymer, and prestressing steel showed a satisfactory bond strength when compared to low-strength concrete. However, the carbon plates performed better in terms of failure load and rate use than the rods made of carbon and the prestressing steel. Moreover, the results showed that the increase of groove size for the near-surface mounted reinforcement made of prestressing steel did not have an effect on the failure mode. In addition, a significant increase of the failure load was observed for the prestressing steel. Finally, the effect of concrete strength was analyzed and compared with the results found in literature. 相似文献
The antibacterial activity of chitosan (CS) nanospheres, in comparison with other physical forms, was investigated against Salmonella enterica serovar Typhimurium and Staphylococcus aureus, which are 2 foodborne harmful pathogens. Results showed that the antibacterial efficacy of CS nanospheres: (1) was superior to that displayed by CS in powder and solution form; (2) was higher against S. aureus than against Salmonella Typhimurium; and (3) was dependent on the temperature and pH of the medium depending on the strain. For S. Typhimurium, a higher activity was displayed at 37 °C, in which 99.9% of the population was eradicated independently of the pH, followed by 20 °C and 7 °C, in which acidic pH conditions favored a higher susceptibility of bacteria to the effect of CS. On the contrary, S. aureus was less susceptible to the pH and temperature conditions of the medium, and no statistical difference in the antibacterial effect was observed for pH 5.8 and 8.0 at 20 °C and 37 °C. However, at 7 °C a slightly higher activity was displayed at pH 5.8 than at 8.0. 相似文献
In this paper, an integrated solar heat pipe wall space heating system, employing double glazed heat pipe evacuated tube solar collector and forced convective heat transfer condenser, is introduced. Thermal performance of the heat pipe solar collector is studied and a numerical model is developed to investigate the thermal efficiency of the system, the inlet and outlet air temperatures and heat pipe temperature. Furthermore, the system performance is evaluated based on exergy efficiency. In order to verify the precision of the developed model, the numerical results are compared with experimental data. Parametric sensitivity for design features and material associated with the heat pipe, collector cover and insulation is evaluated to provide a combination with higher thermal performance. Simulation results show that applying a solar collector with more than 30 heat pipes is not efficient. The rate of increasing in temperature of air becomes negligible after 30 heat pipes and the trend of the thermal efficiency is descending with increasing heat pipes. The results also indicate that at a cold winter day of January, the proposed system with a 20 heat pipe collector shows maximum energy and exergy efficiency of 56.8% and 7.2%, which can afford warm air up to 30°C. At the end, the capability of the proposed system to meet the heating demand of a building is investigated. It is concluded that the best method to reach a higher thermal covered area is to apply parallel collectors. 相似文献
The paper presents a numerical analysis of the behavior of single-layered graphene sheet (SLGS) using a mesh-free approach based on a nonlocal continuum plate model (NCPM). The adopted NCPM constructed by incorporating the nonlocal elasticity theory into the first order shear deformation elastic plate theory is able to capture small length scale effects. Through the NCPM, the SLGS is modeled as a continuous orthotropic nanoplate. the obtained nonlocal nonlinear partial differential equations completed by boundary conditions are solved numerically by a mesh-free approach associating the asymptotic numerical method with the mesh-free collocation method based on moving least square approximation. The effects of the small-scale parameter and aspect ratio on the nonlinear bending and post-buckling behaviors of SLGS are considered. Good agreement has been established between the obtained results and those of the literature.