Ionic mass transfer at horizontals disc electrodes under longitudinal vibration

A dimensionless correlation for ionic mass transfer at horizontal discelectrodes under longitudinal vibration has been obtained. Within a certain range of amplitude and frequency the flow is confined to a cylinder adjacent to the electrode. The fluid boundary layer thickness is rapidly reduced when either the frequency or the amplitude is increased. The longitudinal vibration, under controlled potential conditions, produces an ac component in the total current. A comparison of the mass transfer rate equation with others corresponding to different flow regimes reveals that a critical flow rate exists, above which vibration is more efficient than conventional agitation in increasing the mass transfer rate.     

声表面波传感器温度频率特性的数值分析

利用ANSYS软件对声表面波传感器进行温度频率特性的数值模拟研究。分析了在一定压力情况下,基于氮化铝压电薄膜铝叉指换能器的延迟型传感器结构内部的温度有限元分布情况。结果表明外界自然对流对传感器内部的温度场及应力场分布影响很小。并模拟计算出温度与输出串联谐振频率变化的关系,通过数据拟合得出,SAW传感器的输出谐振频率与环境温度变化呈良好的线性关系,因此可应用于温度的精确测试。     

Nonlocal material properties of single-walled carbon nanotubes

Natural frequencies of single-walled carbon nanotubes (SWCNTs) obtained using a model based on Eringen's nonlocal continuum mechanics and the Timoshenko beam theory are compared with those obtained by molecular dynamics simulations. The goal was to determine the values of the material constant, considered here as a nonlocal property, as a function of the length and the diameter of SWCNTs. The present approach has the advantage of eliminating the SWCNT thickness from the computations. A sensitivity analysis of natural frequencies to changes in the nonlocal material constant is also carried out and it shows that the influence of the nonlocal effects decreases with an increase in the SWCNT dimensions. The matching of natural frequencies shows that the nonlocal material constant varies with the natural frequency and the SWCNT length and diameter.     

含能粘结剂低温动态力学性能的临界温度

采用ＤＭＡ（动态机械热分析仪）研究了几种含能粘结剂的机械松弛,从动态力学性能的ＴＴＳ（时温叠加１）原理,求得时间位移与频率对数的关系曲线及ＷＬＦ方程的常数Ｃ１和Ｃ２,应用ＷＬＦ方程,把时间位移与频率对数曲线的拐点作为材料由高弹态变为玻璃态的判据,计算求得火箭发动机点火瞬间粘结剂系统的临界温度Ｔｃ,根据自由体积理论模型和结晶理论解释了Ｔｃ的物理意义。并研究了临界温度与玻璃化转变温度之间的关系     

Mass transfer by free convection during electrolysis at inclined electrodes

The limiting electrolysis current technique has been used to obtain experimental measurements of mass transfer in natural convection at rectangular plane plates. Inclinations varying from horizontal down facing to horizontal upfacing at intervals of 10° have been employed with plate height and electrolyte concentration as additional variables. For attached boundary layer flow conditions, all results are well correlated by the equation: Attached flow conditions are obtained for all downfacing inclined orientations the vertical position and for upfacing inclinations where θ (the angle from the vertical) is small. Separation of the flow occurs at higher values of θ in upfacing orientations and is demonstrated by Schlieren photography, as is the existence of longitudinal vortices in the flow. The critical Rayleigh number for separation instability is estimated from the mass transfer measurements and compared with results of other authors.     

流动换热强化的能量传递转换机制及其最小熵产原理

在线性非平衡区域,对熵产率方程进行了相位拓展,建立了流动换热熵流变化与体系总熵产之间的关系。结果表明,熵产越小时熵流越大,则换热强度越大。当传热与传质均为自发过程,质量流与热流之间同相位时,两者的相位差越小,流动换热的强度越大,它反映了两个正熵产率过程间能量传递的场协同机制;当传热与传质分别为非自发及自发过程,质量流与热流之间反相位时,两者的相位差越大,流动换热的强度越大,它反映了正熵产率过程与负熵产率过程间能量转换的热力学耦合机制。质量流与热流之间由同相位到反相位,分别对应着场协同时的能量传递机制及热力学耦合时的能量转换机制,共同反映了体系流动换热时能量传递转换的最小熵产原理。     

APPLICATION OF LINEARIZED MODELS OF MULTICOMPONENT MASS TRANSFER FOR CALCULATION OF EVAPORATION-CONDENSATION PROCESS IN TERNARY SYSTEMS

Results of calculations based on a linearized multicomponent mass transfer theory developed by Burghardt and Krupiczka are compared with experimental data of Modine for condensation-evaporation process in ternary systems. These data have been obtained for acetone-benzene-nitrogen and acetone-benzene-helium in a welted wall column. Models I and II, which take into account diffusional interactions of components in a mullicomponent mixture show good agreement with the experiments as well as with other calculation methods (Krishna-Standart and Toor-Stewart-Prober). When multicomponent mass transfer occurs in the presence of inert species, a straightforward Model II is recommended. Model I, which is more universal, requires some iterative calculations with respect to the sum of mass fluxes. According to theoretical considerations the latter model is limited to the case of low total mass flux. The results of calculations for the systems studied were reasonably good though the total mass fluxes were not small. The calculation procedure based on the presented linearized models are convergent to the proper solutions in contrast to the Krishna-Standart Model IV which in some cases can be unstable.     

Modelling of fluidized bed reactors—VI(a): An isothermal bed with stochastic bubbles

A two-phase stochastic isothermal fluidized bed reactor model with first order reaction in the dense phase is developed to investigate the significance of the fluctuating nature of fluidized beds on reactor performance. Several stochastic processes are employed as the overall mass transfer coefficient between phases. Analytical moment solutions are obtained for white noise coefficients while hybrid computer simulation was used for correlated stochastic coefficients. Results indicate that a gamma distributed coefficient is preferred over white noise and Gaussian correlated coefficients. When compared with the deterministic model, randomness in the mass transfer coefficient is seen to lead to a decrease in reactor performance. Deviation from the deterministic model increases with increasing variance and decreasing fluctuation frequency of the correlated stochastic coefficients.     

APPLICATION OF LINEARIZED MODELS OF MULTICOMPONENT MASS TRANSFER FOR CALCULATION OF EVAPORATION-CONDENSATION PROCESS IN TERNARY SYSTEMS

Results of calculations based on a linearized multicomponent mass transfer theory developed by Burghardt and Krupiczka are compared with experimental data of Modine for condensation-evaporation process in ternary systems. These data have been obtained for acetone-benzene-nitrogen and acetone-benzene-helium in a welted wall column. Models I and II, which take into account diffusional interactions of components in a mullicomponent mixture show good agreement with the experiments as well as with other calculation methods (Krishna-Standart and Toor-Stewart-Prober). When multicomponent mass transfer occurs in the presence of inert species, a straightforward Model II is recommended. Model I, which is more universal, requires some iterative calculations with respect to the sum of mass fluxes. According to theoretical considerations the latter model is limited to the case of low total mass flux. The results of calculations for the systems studied were reasonably good though the total mass fluxes were not small. The calculation procedure based on the presented linearized models are convergent to the proper solutions in contrast to the Krishna-Standart Model IV which in some cases can be unstable.     

液液两相混合中液滴的凝并频率

液液两相混合中液滴的凝并频率的直接观察和建模都存在一些困难 .由此建立了一种喷雾 -搅拌两相混合器 ,获取液滴分布的即时值 .因为液滴很小时破裂频率可以忽略 ,影响液滴分布的只有凝并频率 ,可以从液滴的分布获得液滴的凝并频率 .验证了液滴的自我维持性质并利用反问题的方法求取液滴的凝并频率 ,与从理论推导的液滴凝并频率比较 ,判断该方法的优势之处     

In situ investigation of lysozyme adsorption into polyelectrolyte brushes by quartz crystal microbalance with dissipation

A well understanding about protein adsorption into charged polymer brushes is of importance in the elucidation of mechanism and important phenomena (such as “chain delivery” effect) in protein adsorption on polymer-grafted ion exchange adsorbents. In this work, quartz crystal microbalance with dissipation (QCM-D) was introduced to in situ investigate lysozyme adsorption on QCM sensors grafted with poly(3-sulfopropyl methacrylate) (pSPM) via atom transfer radical polymerization. It was achieved by analyzing frequency (f) and energy dissipation (D) shift simultaneously on pSPM-grafted sensors. The result showed that an initial decrease in ΔD was typical of lysozyme adsorption on pSPM-grafted sensor and more significant with an increase of chain length and grafting density. It was attributed to significant water release in the hydration layer of protein and polymer chains in lysozyme adsorption into pSPM brushes. On pSPM-grafted sensors with long and dense chains, furthermore, lysozyme transitioned from monolayer to multilayer adsorption and the maximum adsorbed amount was obtained to be 374.0?ng·cm^?2 among all pSPM-grafted sensors in this work. The results in D-f plot further revealed that lysozyme adsorption into pSPM brushes increased the rigidity of adsorbed layer and little structure adjustment of adsorbed lysozyme. It was unfavorable for “chain delivery” effect for facilitated transport of adsorbed protein. This work provided valuable insight into protein adsorption in pSPM brushes and outlined a feasible approach to increasing mass transport in polymer-grafted ion exchange adsorbents.     

扁平纤维熔融纺丝动力学模型

根据熔融纺丝的基本原理,推导了扁平纤维的动力学模型。根据所建立的模型,模拟了纺丝工艺条件对纤维异形度的影响。模拟的结果表明:扁平纤维的异形度随着纺丝温度及特性黏度的升高而降低;泵供量一定时,纺速对异形度的影响不大;纺丝速度一定,异形度随着泵供量的增大而增大;吹风条件对异形度的影响较大;随着喷丝孔的长宽比的增大,异形度增加的幅度也较大;异形度在纺程上较小的区间内有明显的下降趋势,并随着泵供量的增加其下降的趋势变缓。     

Mechanical Property, Thermal Property and Crystal Structure of Isotactic Polypropylene Samples Prepared by Vibration Injection Molding

Summary A self-designed pressure vibration injection device was used to study the effect of vibration frequency and vibration pressure on tensile strength and impact strength of iPP F401 vibration injection molding samples. Furthermore, vicat softening temperature, WAXD measurements and polarized microscopic observation were conducted. According to the results, tensile strength and impact strength increase with increasing vibration frequency and vibration pressure. The maximum increment of tensile strength is 26.1%. Under certain process conditions, there is a transition of the impact strength, whose maximum increment is 85%. The vicat softening temperatures have a significant increase of 6∼8 °C for the samples obtained at high vibration frequencies compared with that of static samples. According to pole figures, α-PP of vibration samples orientates much stronger than that of static samples. PM micrograghs show that vibration changes the crystal structure of samples and enhances their orientation.     

Effect of adhesive on the performance of piezoelectric elements used to monitor structural health

The effect of adhesive thickness and its modulus on the performance of adhesively bonded piezoelectric elements for the purpose of monitoring structural health has been experimentally investigated. All the piezoelectric elements were adhesively bonded to aluminum plates. Experimental results revealed that an increase in adhesive thickness alters the electromechanical impedance and the resonant frequency of the piezoelectric elements as well as the amplitude of the sensor signal. When the modulus is within a certain range, the modulus of adhesive slightly affects the impedance of PZT element and the amplitude of sensor signal at lower frequency, while at high frequency, the impedance response and sensor signal are more sensitive to the modulus of adhesive.     

Density Measurements of Single Granules Using the Atomic Force Microscope

The density of single spray-dried granules has been determined with a new method based on atomic force microscopy (AFM). Spherical granules with a well-defined diameter are attached to the AFM cantilever, which acts as a beam-type spring, and the mass of a granule is estimated from the shift in the resonant frequency. The error of the measurements associated with the method was estimated to vary between 1% and 5%, depending on the size and shape of the granule. Density measurements of spray-dried WC–Co granules are presented, and the effect of a polymeric binder and dispersant on the consolidation during drying is discussed.     

Determination of thermal stress distribution in a model microelectronic device encapsulated with alumina filled epoxy resin using fluorescence spectroscopy

A method for measuring residual and applied stresses in particulate polymer systems, which utilizes the piezo-spectroscopic effect of the optical fluorescence of filled particles, is presented. Fluorescence piezo-spectroscopy (PS) is non-destructive and provides microscopic lateral resolution upon using an optical microprobe system. Epoxy resin filled with α-alumina particles is used in this study. Stress values are obtained by frequency shift measurement of the characteristic optical fluorescence lines produced by Cr³⁺ impurities in alumina. The relationships between peak frequency shift of these lines and stress are derived by using a 4-point-bending test. The peak frequency shift shows linear correlation with tensile stress, while a non-linear relation between peak frequency shift and stresses is found in the compressive stress region. To a first order approximation, residual stresses were calculated by the frequency shift divided by the linear correlation coefficient in the tensile stress region. As an application of the PS method, we determined micron order residual stress distributions in a model plastic encapsulated silicon substrate for microelectronic devices and compared the stress data with those calculated using a two-dimensional finite element analysis of the device. The experimental results were in good agreement with the tensile stress components that have been obtained by theoretical calculation. Therefore, PS techniques can be used to measure residual stresses in polymer compounds utilizing the information obtained from the fluorescence lines of a dispersed ceramic powder.     

A study of mass transfer from single large oscillating drops

A study was made of mass trasfer rates from single large oscillating drops of pure liquid-liquid systems, in the size range of 5 to 10 mm. A thrermostatically-controlled, 50 mm in diameter, 1000 mm long, rising drop column was used, in which mirrors in the jacket enabled front and side views of drops to be photographed simultaneously. The systems studied were (1) toluene and acetone (dispersed)-water (continuous), and (2) n-heptane and acetone (dispersed)-water (continuous). High concentrations of acetone (up to 3.75 kmol/m³) were used to examine the effect of different parameters on the mass transfer rate, frequency and amplitude of oscillation in countercurrent operation. Previous theories and empirical correlations [2–6, 12, 13, 15] for the prediction of overall mass transfer coefficients showed large deviations from measured values. These may have aarisen because the models do not represent droplet oscillation accurately, and/or apply only to oscillations of small droplets. Fair agreement was obtained for small oscillating droplets as low solute concentrations. The oscillations of a travelling drop were asymmetrical; the period of oscillation was uniform for mutually-saturated systems but changed when mass transfer was taking place. The periods were longer than those predicted by the Lamb [7] and Shroeder and Kintner [37] correlations. Terminal velocities predicted from literature correlations [32, 34] did not give reasonable agreement with experimental data when there was mass transfer of solute. The drag coefficient increased with increasing mass transfer rate from the drop. Correlation of the results and the dispersed phase mass trasfer coefficients by dimensional analysis resulted in the correlation

1 List of symbols at the end of the paper.

with a mean deviation of ±23%, by insertion of experimental oscillation frequency data. This will facilitate more accurate prediction of the dispersed phase mass transfer coefficients relating to equipment containing droplets in the oscillating regime, e.g. pulsed columns or agitated tanks.     

Analysis for relationship of transmembrane potential–pulsed electric field frequency

The paper presents a model of a spherical cell. The transmembrane potential on cell membrane is obtained by solving the Laplace's equation. The frequency dependence of the transmembrane potential in pulsed electric fields is described. The value of transmembrane potential decreases as the frequency of external electric field increases. And there is a range of frequency for the value of transmembrane potential to decrease fast. It is shown that there is a strong relationship between the value of transmembrane potential and frequency components contained in the pulse. With more low-frequency components, the value of transmembrane potential is increasing and thus a better sterilization effect can be obtained. By comparing the frequency components contained in square wave pulse, exponentially decaying pulse, oscillatory pulse and their sterilization effect respectively, the analysis results about the relationship of transmembrane potential-frequency presented in this paper is validated.     

气固流化床中双组分混合颗粒的流态化特性

在一套φ500 mm×12500 mm大型有机玻璃冷模实验装置中,采用FXC-П/32型压力巡检仪测量了双组分混合颗粒体系沿流化床轴向的颗粒浓度分布,采用容积法测量了不同操作条件下自由空域内双组分混合颗粒的饱和夹带量,并根据稀相空间的轴向颗粒浓度获得了双组分混合颗粒的输送分离高度(TDH)。实验结果表明：混合颗粒在密相床的平均空隙率在小颗粒质量分数为0.4时存在一最小值;双组分混合颗粒的TDH随表观气速的增加而增大,随小颗粒质量分数的增加也增大。在自由空域内双组分混合颗粒的饱和夹带量随表观气速的增加而增加,当表观气速小于0.6 m•s^-1时,随表观气速增加明显;当表观气速大于0.6 m•s^-1时,增加趋势减缓。而当表观气速小于0.5 m•s^-1时,双组分混合颗粒的饱和夹带量随小颗粒质量分数增加,变化趋势不明显;当表观气速大于0.5 m•s^-1时,则随小颗粒质量分数的增加而增大明显。通过对实验结果的分析,建立了双组分混合颗粒TDH的数学模型,模型值与实验值吻合较好。     

Dielectric and viscoelastic studies of poly(ethyl methacrylate) containing cholesteric compounds

Poly(ethyl methacrylate) (PEMA) containing small amounts of cholesteryl additives was studied by dielectric and dynamic mechanical spectroscopy. Dielectric data from pure PEMA and PEMA + additive systems were fitted to the WLF equation. Using the WLF constants obtained from the data for pure PEMA, the To values for PEMA + additive systems were determined in order to get the best fit of the experimental points to the WLF curve. Values of tan δmax (dielectric and mechanical) for all the PEMA + additive systems shift to higher temperatures compared with that for pure PEMA. In the glassy region, the moduli of PEMA + additive systems are higher than that of pure PEMA. Viscometric studies of PEMA + additive systems indicate the presence of some interaction. FTIR spectra of the polymer + additive systems show no shift in carbonyl bond frequency. The shift of Tg to higher temperatures indicates that chain motion in this region is hindered greatly by these additives and the reason for this may be the fitting or aligning of the additive molecules in the polymer matrix.