Micro-mixing in chemical reactors:A perspective

Micro-mixing is an important mechanism, which works simultaneously with macro-mixing in chemical reactors in process industries, for achieving the best selectivity with respect to desired products. In about a half century, a huge amount of data and knowledge has been accumulated from theoretical and experimental studies on micromixing. Nevertheless, those results are mostly composites of simplified theoretical and empirical models, and the true nature of interactions of flow inhomogeneity and micro-mixing with chemical reaction has not been fully unveiled. This article reviews the progress in micro-mixing study in chemical reactors to date. A few important topics related to the nature, experimental evaluation, and numerical simulation of micro-mixing are addressed.Some suggestions are given hopefully to motivate more chemical engineers to devote their efforts to better understanding of micro-mixing in chemical reactors.

Optimum design of welding transformer

Welding transformer is widely used in industry manufacturing, depleting a large portion of electricity energy.Based on modern computer technology and mathematical programming, optimum design of electro-magnetic devices leads to highly efficient use of energy and materials. Are welding transformer is optimized here. A mathematical model,considering both productive cost and operating losses, which is called or Economical-through-Life transformer, is established. Mixed penalty function method, mixed dispersing variable method and improved orthogonal method have been applied to carry out the optimization calculations. Result shows that the power factor is quite important in an Economi-cal-through-Life transformer, and that some principles must be followed in the design work. Also discussed are the advantages and disadvantages of the three methods. In the end, the prospect of optimum design of welding transformer is forecast.

Ultra broadband flat dispersion tailoring on reversed-rib chalcogenide glass waveguide

In this paper,we introduce a horizontal slot in the reversed-rib chalcogenide glass waveguide to tailor its dispersion characteristics.The waveguide exhibits a flat and low dispersion over a wavelength range of 1080 nm,in which the dispersion fluctuates between-10.6 ps·nm-1·km-1 and ＋11.14 ps·nm-1·km-1.The dispersion tailoring effect is due to the mode field transfer from the reversed-rib waveguide to the slot with the increase of wavelength,which results in the extension of the low dispersion band.Moreover,the nonlinear coefficient and the phase-matching condition of the fourwave mixing process in this waveguide are studied,showing that the waveguide has great potential in nonlinear optical applications over a wide wavelength range.

Normalized solutions for a fourth-order Schrődinger equation with a positive second-order dispersion coefficient

In this paper,we study normalized solutions to a fourth-order Schrődinger equation with a positive second-order dispersion coefficient in the mass supercritical regime.Unlike the well-studied case where the second-order term is zero or negative,the geometrical structure of the corresponding energy functional changes dramatically and this makes the solution set richer.Under suitable control of the second-order dispersion coefficient and mass,we find at least two radial normalized solutions,a ground state and an excited state,together with some asymptotic properties.It is worth pointing out that in the considered repulsive case,the compactness analysis of the related Palais-Smale sequences becomes more challenging.This forces the implementation of refined estimates of the Lagrange multiplier and the energy level to obtain normalized solutions.

Recent improvements on the pulsed optically pumped rubidium clock at SIOM

We report the recent progress of our pulsed optically pumped（POP） vapor cell rubidium clock with dispersive detection.A new compact physics package is made.A rubidium cell with a high precision buffer gases mixing ratio is obtained,and the temperature controlling system is renovated to reduce fractional frequency sensitivity to temperature variation.The resolution of the servo control voltage is also optimized.With these improvements,a clock frequency stability of 3.53×10-13 at 1s is obtained,and a fractional frequency stability of 4.91×10-15 is achieved at an average time of τ=2000 s.

Effect of pH on rheology of aqueous Al_(2)O_(3)/SiC colloidal system

The rheological behavior of aqueous Al_(2)O_(3)/SiC suspensions at different pH values was investigated by rheological measurement.Experimental results showed that at pH=3-6,Al_(2)O_(3) and SiC particles have opposite surface charges,and the binary suspensions have lower viscosity than the unary suspensions at shear rates of 0-300 s^(-1).Furthermore,at pH=3-12,the stability of the Al_(2)O_(3) component seemed to dominate the overall rheological behavior of the Al_(2)O_(3)/SiC binary suspensions.The tendency mentioned above showed little variations in various ionic strengths,particle diameters and component fractions.

Circulation intensity and axial dispersion of non-cohesive solid particles in a V-blender via DEM simulation

In this study, discrete element method （DEM） was employed to simulate the movement of non-cohesive mono-dispersed particles in a V-blender along with particle-particle and particle-boundary interactions. To validate the model, DEM results were successfully compared to positron emission particle tracking （PEPT） data reported in literature. The validated model was then utilized to explore the effects of rotational speed and fill level on circulation intensity and axial dispersion coefficient of non-cohesive particles in the V-blender. The results showed that the circulation intensity increased with an increase in the rotational speed from 15 to 60 rpm. As the fill level increased from 20% to 46%, the circulation intensity decreased, reached its minimum value at a fill level of 34% for all rotational speeds, and did not change significantly at fill levels greater than 34%. The DEM results also revealed that the axial dispersion coefficient of particles in the V-blender was a linear function of the rotational speed. These trends were in good agreement with the experimentallv determined values reported bv previous researchers.

A single-cell encapsulation method based on a microfluidic multi-step droplet splitting system

Single cell analysis is of great significance to understand the physiological activity of organisms.Microfluidic droplet is an ideal analytical platform for single-cell analysis. We developed a microfluidic droplet splitting system integrated with a flow-focusing structure and multi-step splitting structures to form 8-line droplets and encapsulate single cells in the droplets. Droplet generation frequency reached1021 Hz with the aqueous phase flow rate of 1 m L/min and the oil phase flow rate of 15 mL /min. Relative standard deviation of the droplet size was less than 5% in a single channel, while less than 6% in all the8 channels. The system was used for encapsulating human whole blood cells. A single-cell encapsulation efficiency of 31% was obtained with the blood cell concentration of 2.5 ？ 104cells/mL, and the multicellular droplet percentage was only 1.3%. The multi-step droplet splitting system for single cell encapsulation featured simple structure and high throughput.

JETS,PLUMES AND BUOYANT JETS IN STATIC ENVIRONMENT

Turbulence represents an essential aspect in atmospheric and oceanic circulations.In particu- lar,it is a preponderant factor in the dispersion of pollutants of artificial or natural origin.The vertical turbulent jets,plumes and buoyant jets discharging into static environment is one of the most important and basic flow patterns related with the environment pollution.These flows have numerous important applications,for example,thrust augmentors,waste disposal plumes from stacks and combustion systems,and significant problems of turbulent diffusion.

Melt emulsification-Is there a chance to produce particles without additives?

Melt emulsification is a well known process. Milk is thus homogenized for over 100 years. In the melt emulsification process, the future disperse phase is melted and dispersed into droplets, the size of which is controlled by an emulsification process. After emulsification, the droplets are cooled down and solid particles of spherical shape are formed. In order to realize melt emulsification processes, we developed the new SHM （Simultaneous Homogenizing and Mixing） nozzle, which enables us to mix separate phases directly into the droplet forming zone of homogenization nozzles. This molten milk fat globule can be homogenized at elevated fat content （up to 42 vol% instead of max. 17 vol%） and elevated temperatures （up to 150 ℃ instead of max. 70 ℃） without loosing product quality as for conventional homogenization processes. In addition, more than 80% of the energy costs can be saved and additional mixing units can be spared. This is realized by a controlled and quick dilution and cooling down of molten fat globules directly after their disruption in the nozzle itself. SHM-technology also allows for the dispersing of molten waxes. Instant cooling down after adjusting particle sizes also allows us to work without emulsifiers or other additives as absolutely required in conventional melt emulsification processes where molten droplets will coalesce upon their collisions in the homogenization nozzle. SHM-melt emulsification is thus an alternative to conventional milling processes, which are often limited by the stickiness of these products.