Formation mechanism and size prediction of bubble in opposite-flowing T-shaped microchannel

Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.     

不锈钢铝合金半固态连接工艺参数研究

By using semisolid joining technique,the bonding of stainless steel and semisolid aluminum alloy is successfully realized.The relationships between interracial shear strength and solid fraction of aluminum alloy,bonding pressure and time of keeping pressure were studied by the method of orthogonal experiment.The interfacial structure and the fracture structure of the bonding plate are studied by means of optical microscope (OM) and scanning electron microscope (SEM).The results show that there is the best solid fraction between the solid phase line and the liquid phase line of the semisolid aluminum alloy,with the increase of bonding pressure and pressure time,the interfacial shear strength increases rapidly,and then with further increase of bonding pressure and pressure time,the shear strength rises little.Along the interface,solid phase and liquid phase bond with stainless steel by turns because of the different diffusion ability.So,a new type of non-equilibrium diffusion interfacial structure is constructed at the interface of stainless steel and aluminum alloy,compound mechanism of plastic and brittle fracture interface was formed at the shear fracture interface.     

Coaxial liquid-liquid flows in tubes with limited length

Coaxial liquid-liquid flows were numerically studied in a nesting two-tube system. Calculations were carried out when various exit-lengths （meaning length differences between the two tubes） were used. Numerical results indicated that there exists a certain range of exit-length for the liquid-liquid flows to form stable and smooth interfaces, which requires that the exit-length should roughly be less than 5.6 times the outer tube diameter. In this range, interface instability is effectively restrained and the core fluid shows a phenomenon of die swell. When the exit-length is about 1.6 times the outer tube diameter, the core fluid has the greatest diameter size in the shell fluid. Velocity distributions at the outer tube exit favor formation of a continuous and stable core-shell structure.     

Science Letters： In-situ synthesis and luminescence properties of titanium oxide gels containing 1,10-phenanthroline europium（Ⅲ） complex

It is difficult to directly dope europium complexes in gel because the excessive water or high acidic condition may lead to their decomposition. We prepared a novel homogeneous TiO2 gel containing Eu-phen complexes by using an in-situ synthesis method. The formation of Eu-phen complexes in sol-gel derived TiO2 was confirmed by luminescence excitation spectra. The effects of temperature and aging time on in-situ synthesis are discussed. The luminescence spectra of gel containing europium complexes were also compared with the pure Eu-phen complexes.     

Numerical and Experimental Study on Nugget Formation Process in Resistance Spot Welding of Aluminum Alloy

The weld nugget formation in the resistance spot welding(RSW) of aluminum alloy was investigated in the present study. The nugget formation process was directly observed by using a digital high-speed camera. Numerical simulation was also employed to investigate the nugget formation process. The results showed that for the RSW of two aluminum alloy sheets, a nugget was first formed in the workpiece/workpiece(W/W) interface and grew along the radial direction and axial direction of the sheets, and then it became a large elliptical nugget. For the RSW of three aluminum alloy sheets, two small nuggets were firstly formed in two W/W interfaces and grew along the axial direction and radial direction; finally they fused into one nugget. Besides, there existed a critical welding time, after which the nugget size remained nearly unchanged. This indicates that a long welding time is unnecessary for the RSW of aluminum alloy. In addition, the calculated nugget radius was compared with the experimental results, which showed that the simulation results agreed well with the experimental results.     

Experimental study and numerical simulation of the sludge concentration in a sedimentation tank

Sedimentation tanks and clarifiers play a significant role in an active sludge system, and the efficiency of the whole system is closely related with the design and operation of the sedimentation tanks. This paper focuses on the sludge concentration in each cross-section of the sedimentation tank. We measured the sludge concentration to explore its distribution inside the tank, carried in-situ tests to research the fluid pattern and real operational rules of the sedimentation tank. We also used the computational fluid dynamics (CFD) software, PHOENICS 3.5, to simulate the solid-liquid two-phase fluid inside the tank and describe the sludge concentration distribution. The numerical results indicate obviously a sludge-water interface and a compression interface inside the sedimentation tank, a stratified sedimentary region with uniform concentration and a compression region with high concentration at the bottom of the tank. Although the simulated concentrations deviated slightly from those of in-situ tests, they were still acceptable for identifying the sludge interfaces and fluid pattern inside a sedimentation tank, which are important parameters for optimizing the tank size and improving the settling efficiency.     

RESEARCH ON THE MECHANISM OF ORGANIC MATTER DEGRADATION IN FLUIDIZED BED

Aiming at the defects in previous research and based on porous pelletmodel,the kinetics model of organic matter degradation in FBBR has been estab-lished.By means of synthesis phenolic wastewater treatment experiment,the reliabil-ity of the model is tested and the result shows that the precision is satistactory.De-pending on the model,the paper analyses in detail the mechanism of organic matterdegradation and the effect of biofilm thickness on reactor performance in FBBR.Theresearch result indicates that high efficiency of FBBR lies in high value of ηX and thebiofilm thickness is a significant factor affecting η,X and reactor performance.     

INVESTIGATION ON THE STABILITY OF A PLANAR INTERFACE DURING SOLIDIFICATION OF A DILUTE BINARY ALLOY(Ⅱ)

By introducing a sinusoidal cylindric ripple of infinitesimal amplitude into aplanar interface when there is convection in the liquid,an expression q(ω)=(t)/δ(t)isobtained for determining the stability of planar interface.The destabilizing perturbationfrequency interval and dangerous frequency for planar interface during solidification of adilute binary alloy under the condition of a sinusoidal cylindric perturbation have been in-vestigated.In comparison with the sinusoidal planar perturbation,the results obtained aremore conformable with the actual situation.     

Preparation of a mesoporous sorption complex catalyst and its evaluation in reactive sorption enhanced reforming

A mesoporous sorption complex catalyst was prepared by pore-forming modification and evaluated by the COz reactive sorption enhanced reforming （ReSER） process, which is used to produce hydrogen from methane. Three samples of polyethylene glycol （PEG） with molecular weights between 2000 and 20 000 were added as templates into a mixed slurry to create catalysts with different pore properties by further formation and calcination. The pore characteristics determined by Brunauer- Emmett-Teller （BET） analysis showed that one of the mesoporous catalysts, named M-NiAICa-6000, had a pore size of 9.2 nm and a surface area of 70.52 m2/g and the CO2 sorption capacity of this catalyst was 44% higher than that of the catalyst without the PEG 6000 modification. The catalyst was evaluated in the ReSER process in a fixed-bed reactor system at 0.1 MPa and 600 C with an H20/CH4 molar ratio of 4. An H2 concentration of 94.2% and a CH4 conversion of 86.0% were obtained at a carbon space velocity of 1700 h 1 while CO2 was hardly detected.     

Study on Particle Pushing in Front of Growing Interface During Soldification

For in -situ composite materials,the interaction between the second-phase particles and the solidification interface attracts more attentions of people,for concerning the final distribution of the particles on the matrix.With the conception of the local solidification time,a kinematics mechanism of particle pushing into the crystal boundary during the solidification process was assumed.Through the analysis of forces acted on the particle in front of the solid /liquid interface the critical velocity criterion for the particles pushing was given.The calculation results show when the growth rate of the interface V is less than or equals to the critical velocity Vc,the particles on the solid/liquid interface is pushed into the boundary region of cellular crystals,where they are distributed as a chain-like straight,which forms a particle-strengthened in-situ composite materials.     

Acid Separation, Catalytic Oxidation and Coagulation for ATC Waste Liquid Treatment

It is difficult to treat 2-amino-thiazoline- 4-carboxylic acid (ATC) waste liquid effectively at present for its characteristics of high chemical oxygen demand (COD), high salinity and low biodegradability. In order to solve this problem, this paper presents several kinds of physical-chemical treatment unit techniques, including acid separation, catalytic oxidation and coagulation. First of all, acid separation was adopted to precipitate relevant organics at isoelectric point. When the temperature and pH value of acid separation were controlled at about 5 ℃ and 2.2 respectively, the COD removal rate could reach 27.6%. Secondly, oxidation was used to break chemical constitution of refractory organics. The optimal reaction parameters of catalytic oxidation should be 20 ℃, pH adjusted to 5.0 and [Fe^2 ] 300 mg/L. Then with 5% H2O2 added and after one-hour reaction, the COD removal rate could achieve about 52%. Finally, coagulation was adopted to remove a portion of refractory organics, and 15% polymeric molysite flocculant was the best for the coagulation, and the COD removal rate could reach about 15%. Therefore, the proposed feasible process of physicalchemical pretreatment for ATC waste liquid could have about 70% COD removed in total.     

Hydrodynamics and oxygen transfer in a novel extra-loop fluidized bed bioreactor

In this paper, the characteristics of fluid mixing time in a novel extra-loop fluidized bed were studied. The results showed that the mixing time was shortened with the increase of fluid velocity. All the discrete numbers of the reactor were above 0.2. The serial number n was 2.5 -3.0. It was judged accordingly that the reactor fluid state was continous stirred tank reactor （CSTR） mainly. When the inspiratory capacity increased the mixing time of the reactor was shortened. Thus the air input was beneficial for the fluid mixing. During the three phases mixing process, the mixing time of the reactor could be decreased by the n increase of carrier and air loading together, but the change was not significant. The parameters affecting the reactor fluid state were fluid velocity, inspiratory capacity and carrier. KLa could be increased with the air loading increase, and at the same gas/liquid ratio when the pressure drop was high, KL~ value was increased. The amount of carrier complex influence on KLa. As the carrier loading continued to increase, its value had been dropped but the changes was not significant, and optimization condition was found at above 800 1 000 g carrier loading （pouzzolane） or 600 g PVC. Under gas/liquid ratio of 0.8% -5.2%, KLa was （0.62-1.37）×10^-2· s^-1.     

Preparation and Properties of TiO_2-Coated Hollow Glass Microspheres as Thermal Insulation Materials for Energy-Saving Buildings

A hollow glass microsphere(HGM)/TiO_2 composite hollow sphere was successfully prepared via a simple precipitation method. The TiO_2 coating layers grew on the surface of the HGMs that range from 20 to 50 μm in diameter as nanoparticles with the formation of the SiO Ti bonds. The growth mechanism accounting for the formation of the TiO_2 nanolayers was proposed. The morphology, composition, thermal insulation properties, and visible–near infrared(VIS–NIR) refl ectance of the HGMs/TiO_2 composite hollow spheres were characterized. The VIS–NIR refl ectance of the HGMs/TiO_2 composite hollow spheres increased by more than 30% compared to raw HGMs. The thermal conductivity of the particles is 0.058 W/(m K). The result indicates that the VIS–NIR refl ectance of the composite hollow spheres is strongly infl uenced by the coating of TiO_2. The composite hollow spheres were used as the main functional fi ller to prepare the organic–inorganic composite coatings. The glass substrates coated by the organic–inorganic coatings had lower thermal conductivity and higher near infrared refl ectivity. Therefore, the HGMs/TiO_2 composite hollow spheres can refl ect most of the solar energy and eff ectively keep out the heat as a thermal insulation coating for energy-saving constructions.     

Performance of Methanol-to-Olefins Catalytic Reactions by the Addition of PEG in the Synthesis of SAPO-34

SAPO-34, a silicoaluminophosphate zeolite, has been synthesized by the hydrothermal method with the addition of different molecular weights of polyethylene glycol(PEG), and has been characterized with XRD, SEM,N_2 adsorption–desorption, FT-IR, and NH_3 temperatureprogrammed desorption(NH_3-TPD). We studied SAPO-34 as a catalyst in the methanol-to-olefins(MTO) reaction, in a fixed-bed reactor. The results show that the chain length of PEG has a great influence on the particle size and morphology of SAPO-34. PEG acts as inhibitor in the crystallization process. With the increase of the chain length of PEG used in the synthesis, from a relative molecular weight of 400-6000, the morphology of SAPO-34 changes gradually from cubic to nanoplate-like and then changes to cubic again. The particle size decreases markedly at first and then increases to some extent. The catalytic stability in the MTO reaction also increases first and then decreases, with all the catalysts having almost the same selectivity to olefins. When the sample is synthesized with PEG800, the particles become nanoplate-like with a thickness of 46 nm on average, and the catalytic stability is appreciably prolonged, which is attributed to the shorter diffusion paths of the reactants in the zeolite.     

Experimental investigation of the factors affecting accuracy and resolution of the pore structure of cement-based materials by thermoporometry

Thermoporometry （TPM） is a calorimetric-based technique for characterizing pore structure according to the freezing and melting point depression of liquid confined in pores which attributes to a varying phase-transition free energy by interface curvature. TPM has demonstrated an emerging success in applications for determining the mesopores of cement-based materials in recent decades. To improve its resolution and accuracy, this paper discussed these factors which show a great influence on the baseline heat flow and the derived pore structure using two molecular sieves with discontinuous size for calibration, referring to the sample handling, the mass of sample and the varying temperature. The pore size distributions of ordinary and high-strength concrete by TPM were favorably compared to the results taken by nitrogen adsorption/desorption （NAD） and mercury intrusion porosimetry （MIP）. The results illustrated that both the accuracy and resolution improve with the decreasing cooling/heating rate until 1 ℃/rain; however, if the rate is too slow, it can lead to an unstable result. The mass of the sample tested has much less an effect on the accuracy when it increases to more than 30 mg. TPM is demonstrated to be more accurate to characterize the mesopores with the size bigger than 4 nm as compared to NAD and MIP.     

Absorption of NO2 into Na2S solution in a stirred tank reactor

To understand the absorption mechanism of nitrogen dioxide into a sodium sulfide solution, a stirred tank reactor with a plane gas-liquid interface was used to measure the chemical absorption rate of diluted nitrogen dioxide into sodium sulfide solution. The absorption rates under various experimental conditions were measured and the effects of experimental conditions on nitrogen dioxide absorption rate were discussed. The results show that, in the range of this study, nitrogen dioxide absorption rate increases with increasing sodium sulfide concentration, nitrogen dioxide inlet concentration, and flue gas flow rate, but decreases with increasing reaction temperature and oxygen content in flue gas.     

Monodisperse Ultra-Large-Pore Silica Coated Polystyrene Core-Shell Microbeads via Layer-by-Layer Assembly for Nano-Micro Composite

Polystyrene(PS)@Si O2 core-shell microbeads with large pore and large particle size were prepared via layer-by-layer(LBL)assembly technique for potential applications in nano-micro composites. Negative silica nanoparticles synthesized via modified St?ber method and cationic poly(diallyldimethylammonium chloride)were alternately adsorbed on the surface of microbeads. Zeta potential, size, and morphology of the microbeads were monitored during LBL assembly process to ensure the successful deposition of silica nanoparticles. The porous shell was characterized using nitrogen adsorption and desorption analyses, and the surface area, volume and diameter of the pores were derived. It is found that the porous shell thickness and the pore size can be tuned by changing the coating times of silica nanoparticles. Finally, PS@Si O2 core-shell microbeads with 5,μm PS solid core and 350,nm mesoporous shell(mean BJH pore diameter is ~27,nm)were used to load Cd Se/Zn S quantum dots(QDs). The fluorescence microscopic image and the optical amplification of the QDs-embedded microbeads(QDBs)indicate that the as-prepared core-shell microbeads can provide adequate space for QDs and may be useful for further application of nano-micro composites.     

Bounded space algorithms for variant of variable-sized bin packing

Given a list of items and a sequence of variable-sized bins arriving one by one, it is NP-hard to pack the items into the bin list with a goal to minimize the total size of bins from the earliest one to the last used. In this paper a set of approximation algorithms is presented for cases in which the ability to preview at most k（〉=2） arriving bins is given. With the essential assumption that all bin sizes are not less than the largest item size, analytical results show the asymptotic worst case ratios of all k-bounded space and offiine algorithms are 2. Based on experiments by applying algorithms to instances in which item sizes and bin sizes are drawn independently from the continuous uniform distribution respectively in the interval [0,u] and [u,l ], averagecase experimental results show that, with fixed k, algorithms with the Best Fit packing（closing） rule are statistically better than those with the First Fit packing（closing） rule.     

Heat of Boron Trifluoride–Methanol System Determined by Bunsen Ice Calorimeter

The complex heat of BF_3 with methanol was measured by utilizing the principle of the Bunsen ice calorimeter. The complex heat of BF_3 –methanol was found to be 49.2 and 58.1 kJ/mol when the molar ratio of BF_3 to methanol was 1:2 and 1:1,respectively. In addition,the complex heat of BF_3 –anisole was also measured to test the apparatus error. The BF_3 –anisole result showed a calorimeter value of 53.1 kJ/mol with a system error of 2.3% as compared with the value reported in the literature. The mechanism of the reaction of BF_3 and methanol was interpreted based on our obtained results. This apparatus is useful and suitable for measuring the heat of other liquid–gas and liquid–liquid reactions.     

Activation of Akt and cardioprotection against reperfusion injury are maximal with only five minutes of sevoflurane postconditioning in isolated rat hearts

It had been proved that administration of sevoflurane for the first two minutes of reperfusion effectively protects the heart against reperfusion injury in rats in vivo.Our aim was to investigate the duration of effective sevoflurane administration and its underlying mechanism in isolated rat hearts exposed to global ischemia/reperfusion(I/R) injury.Adult male Sprague-Dawley rats were randomly divided into six groups(n=12):a sham-operation group,an I/R group,and four sevoflurane postconditioning groups(S2,S5,S10,and S15).In the S2,S5,S10,and S15 groups,the duration times of sevoflurane administration were 2,5,10,and 15 min after the onset of reperfusion,respectively.The isolated rat hearts were mounted on the Langendorff system,and after a period of equilibrium were subjected to 40 min global ischemia and 120 min reperfusion.Left ventricular(LV) hemodynamic parameters were monitored throughout each experiment and the data at 30 min of equilibrium and 30,60,90,and 120 min of reperfusion were analyzed.Myocardial infarct size at the end of reperfusion(n=7 in each group) and the expression of myocardial phosphorylated Akt(p-Akt) after 15-min reperfusion were determined in a duplicate set of six groups of rat hearts(n=5 in each group).Compared with the I/R group,the S5,S10,and S15 groups had significantly improved left ventricular end-diastolic pressure(LVEDP),left ventricular developed pressure(LVDP),and the maximal rate of rise or fall of the LV pressure(±dP/dtmax),and decreased myocardial infarct size(P<0.05),but not the S2 group.After 15 min of reperfusion,the expression of p-Akt was markedly up-regulated in the S5,S10,and S15 groups compared with that in the I/R group(P<0.05),but not in the S2 group.Sevoflurane postconditioning for 5 min was sufficient to activate Akt and exert maximal cardioprotection against I/R injury in isolated rat hearts.