Computational Fluid Dynamic Simulation of Liquid-Liquid Mixing in a Static Double-T-shaped Micromixer

The laminar flow structure and mixing performance of T-shaped and double-T-shaped micromixers with rectangular cross-section have been investigated using computational fluid dynamic (CFD) simulation. FLUENT software is used to evaluate the mixing efficiency. The numerical simulation results show that the presented double-T-micromixer is highly efficient over T-shaped micromixer. The performance of double-T-micromixer with and without static mixing elements (SME) is also investigated. The enhancement in mixing performance is thought to be caused by the generation of eddies and lateral velocity component when the mixture flows through these elements. Mixing efficiency as higher as 97% is reached within a mixing length of 320 μm downstream from the first T-junction with the enhancement of three SMEs.

Two-dimensional Simulation for Hydrogen/Air Combustion in a Monolith Reactor

Recent studies on hydrogen combustion were reviewed briefly. The laminar flow and combustion of premixed hydrogen/air mixture in a cylindrical channel of a monolith reactor with and without catalytic wall was numerically modeled by solving two-dimensional (2-D) Navier-Stokes (N-S) equations, energy equation, and species equations. Eight gas species and twenty reversible gas reactions were considered. The control volume technique and the SIMPLE algorithm were used to solve the partial differential equations. The streamlines of the flow field, temperature contours, the entrance length, and the concentration fields were computed. It is found that the entrance zone plays an important role on flow and temperature as well as species distribution. Therefore, the flow cannot be assumed either as fully developed or as plug flow. There is a small but strong thermal expansion zone between the wall and the entrance. Both diffusion and convection affect the heat and mass transfer processes in the expansion zone. Thus the equations of momentum, energy and species conservations should be used to describe hydrogen/air combustion in the monolith reactor. The hot-spot location and concentration field of the homogeneous combustion is strongly influenced by the inlet velocity and temperature, and the equivalence ratio. The catalytic combustion of premixed hydrogen/air mixture over platinum catalyst-coated wall in a cylindrical channel was also simulated.

Experimental and Numerical Investigations of an Ice-slurry Generator

A new test facility equipped with refrigerant and brine circulation systems, and a rotating-scraper ice-slurry generator was constructed to analyze the ice-slurry flow and heat transfer accompanied by phase change in an industrial generator. The axial and transverse brine temperature and ice fraction concentration profiles in the ice generator were measured. The heat transfer efficiency lower than the average was identified in the upper half of the ice generator and its cause was determined by conducting three-dimensional numerical simulation using a commercial CFD code, FLUENT. Approaches of improving the brine-side heat transfer rates were investigated by incorporating extra mixing blades from numerical simulation.

Coupling System for Food Wastes Anaerobic Digestion and Polyhydroxyalkanoates Production with Ralstonia eutropha

A new technology was developed to couple the anaerobic digestion of food wastes with production of polyhydroxyalkanoates (PHAs). Acetic, propionic, butyric and lactic acids were produced during food wastes anaerobic digestion and their concentrations reached 5.5, 1.8, 27.4 and 32.7 g/L, respectively under appropriate digestion conditions. The fermentative acids were transferred through a dialysis membrane to an air-lift reactor for PHA synthesis by Ralstonia eutropha. Dry cell concentration and PHA content reached 22.7 g/L and 72.6%, respectively. The obtained PHA was a copolymer of b-hydroxybutyrate (HB) and b-hydroxyvalerate (HV) with 2.8% (mole ratio) of HV units in polymer.

Effects of Supports and Promoter Ag on Pd Catalysts for Selective Hydrogenation of Acetylene

SiO2,α-Al2O3,γ-Al2O3,ZrO2 and CeO2 were used as supports and Ag as promoter to study their effects on Pd catalysts for selective hydrogenation of acetylene.The catalysts were prepared by impregnated synthesis and characterized by XRD,BET and TEM.The catalytic reaction was carried out in a fixed-bed reactor.Overall,the low specific surface area supports were better to increase the ethylene selectivity at high conversion rate of acetylene.Among the four Pd catalysts on low specific surface area supports,the catalyst on low specific surface area SiO2(LSA-SiO2) retained a high ethylene selectivity even at complete conversion,while the other catalysts showed significant decrease in the selectivity at complete conversion.The performance of Pd/LSA-SiO2 was important to decrease the loss of ethylene in selective hydrogenation of trace acetylene in ethylene.Addition of Ag to Pd/LSA-SiO2 significantly decreased the formation of ethane,C4 alkenes and green oil,and improved the ethylene selectivity to 90% when Pd:Ag=1:1 and 1:3(ω).When the ratio of Pd to Ag was above 1,the activity of Pd-Ag bimetallic catalyst was similar to that of Pd monometallic catalyst,and the selectivity of ethylene increased with increasing of amount of Ag.When the ratio of Pd to Ag was below 1,the activity of bimetallic catalyst decreased with increasing of amount of Ag,while the selectivity of ethylene was kept unchanged.The optimum temperature was 200-230℃ for 0.02%(ω)Pd-0.02%(ω)Ag/LSA-SiO2 to give a high ethylene selectivity and low formation of green oil.

Experimental Study on Hydrogenation of SiCl_4 to SiHCl_3 in a Stirred Bed Reactor

The hydrogenation of SiCl_4 to SiHCl_3 was studied in a stirred bed reactor with CuCl catalyst.The properties of the CuCl catalysts and silicon particles before and after the reaction were characterized by SEM,XRD and XPS.The XRD showed that the active component of Cu3Si was formed during the reaction,and the EDX proved the molar ratio of Cu and Si on the region of apertures.The valent of Cu was discussed by XPS before and after the hydrogen reaction.Then the effects of the reaction temperature,pressure,molar ratio of H2 to SiC l4,weight hourly space velocity(WHSV),and catalyst loading were studied.The results showed that the conversion rate of Si Cl4 was about 38%at WHSV of 190 Nm3/(t·h),temperature of 540℃,pressure of 1.8 MPa,catalyst loading of 0.9%(ω),and molar ratio of H2 to Si Cl4 1.7:1.Based on the experemental results,a reaction mechanism was proposed,which involved the continuous consumption of silicon(many apertures was showed on SEM image)and formation of new Cu3Si active component during the hydrogenation reaction.