Influence of chain length in nonyl-phenol ethoxylate surfactants on the film formation behaviour of methylmethacrylate-2-ethylhexyl acrylate copolymer latexes: part 1. Differential scanning calorimetry and atomic force microscopy

A comparison of the film forming characteristics of methylmethacrylate-2-ethylhexyl acrylate latex copolymers stabilised with nonyl-phenol ethoxylate molecules of varying chain lengths is presented. The ability of the stabiliser to segregate and diffuse from the interfacial layer into the surrounding media influences both the rate of coalescence process and structure of the film formed. Dynamic mechanical analysis, minimum film formation temperature measurements, particle size analysis, differential scanning calorimetry (DSC) and atomic force microscopy reveal the complexity of the mechanism involved in the coalescence process. A model that describes the various stages of coalescence and compaction of the latex particles indicates the effects of chain length on the film forming properties. For the stabiliser with a chain length of 20, coalescence is observed at room temperature; whereas for the stabiliser with chain lengths of 30 and 40, coalescence only occurs if the films are raised above 315 K. For the longer chain stabilisers, the effect of stabiliser-stabiliser interaction inhibits the coalescence process and DSC data indicate the occurrence of crystalline phase structure in the thin film.     

Bubble coalescence efficiency near multi-orifice plate

Bubble coalescence reduces specific area and weakens the work performance of bubble column. The bubble coalescence near gas sparger which is caused mainly by bubble growing is different from the ones occurring in major liquid. Bubble coalescence efficiency near gas sparger is influenced by many factors including sparger configuration, gas flow rate, bubble deformation, solution composition, etc. This work has conducted a set of visual experiments to study the coalescence characteristics near multi-orifice plate. The experiment parameters cover a wide range of conditions including large scope of gas flow rate,different kinds of solution and orifice configurations. The experimental results suggest that coalescence time is applicable to reflect the influence of the pitch of orifices and gas flow rate on bubble coalescence efficiency. As the number of orifices increases, bubble coalescence efficiency is reduced by the disturbance from the bubbles at adjacent orifices. A hindering coefficient is used to consider the hindering effect of additives on bubble coalescence efficiency. Finally a new calculation expression is established to predict bubble coalescence efficiency near multi-orifice plate whose fundamental form is based on the logistic curve of binary response. The calculated values that refer to this calculation expression are well consistent with the experimental results.     

A SIMPLE CORRELATION FOR COALESCENCE RATE CONSTANT IN BATCH TURBULENT LIQUID LIQUID DISPERSIONS

A model for prediction of the coalescence rate in batch turbulent dispersions is developed using the various relevant time scales involved in the process of binary coalescence. The model requires only the knowledge of the steady-state drop volume distribution and not its transient development.     

Bubble mechanisms and characteristics at pore scale in a packed-bed reactor

An image processing technique was used to study dominant bubble mechanisms in a two-dimensional packed-bed at pore level under the bubbly flow regime. Bubble breakup and coalescence were identified as dominant mechanisms using a large number of image samples. Two types of coalescence mechanisms were identified that occur due to compression and deceleration associated with the bubbles and three breakup mechanisms were identified that are result of liquid shear force, bubble acceleration, and bubble impact. Data on various two-phase parameters, such as local void fraction, bubble velocity, size, number, and shape were obtained from the images. Results indicated that when a flow regime changed from bubbly to either trickling or pulsing flow, the number of average sized bubbles significantly decreased and the shape of the majority of the bubbles was no longer spherical. Although a mean bubble velocity of all sized bubbles was uniform for given gas and liquid superficial velocities, individual bubble velocities were quite different depending on the bubble location in the pore. The present bubble size distributions were compared with previous studies and the results on bubble size are in general agreement.     

CFD simulation of bubble columns incorporating population balance modeling

A computational fluid dynamics (CFD)-code has been developed using finite volume method in Eulerian framework for the simulation of axisymmetric steady state flows in bubble columns. The population balance equation for bubble number density has been included in the CFD code. The fixed pivot method of Kumar and Ramkrishna [1996. On the solution of population balance equations by discretization—I. A fixed pivot technique. Chemical Engineering Science 51, 1311-1332] has been used to discretize the population balance equation. The turbulence in the liquid phase has been modeled by a k-ε model. The novel feature of the framework is that it includes the size-specific bubble velocities obtained by assuming mechanical equilibrium for each bubble and hence it is a generalized multi-fluid model. With appropriate closures for the drag and lift forces, it allows for different velocities for bubbles of different sizes and hence the proper spatial distributions of bubbles are predicted. Accordingly the proper distributions of gas hold-up, liquid circulation velocities and turbulence intensities in the column are predicted. A survey of the literature shows that the algebraic manipulations of either bubble coalescence or break-up rate were mainly guided by the need to obtain the equilibrium bubble size distributions in the column. The model of Prince and Blanch [1990. Bubble coalescence and break-up in air-sparged bubble columns. A.I.Ch.E. Journal 36, 1485-1499] is known to overpredict the bubble collision frequencies in bubble columns. It has been modified to incorporate the effect of gas phase dispersion number. The predictions of the model are in good agreement with the experimental data of Bhole et al. [2006. Laser Doppler anemometer measurements in bubble column: effect of sparger. Industrial & Engineering Chemistry Research 45, 9201-9207] obtained using Laser Doppler anemometry. Comparison of simulation results with the experimental measurements of Sanyal et al. [1999. Numerical simulation of gas-liquid dynamics in cylindrical bubble column reactors. Chemical Engineering Science 54, 5071-5083] and Olmos et al. [2001. Numerical simulation of multiphase flow in bubble column reactors: influence of bubble coalescence and breakup. Chemical Engineering Science 56, 6359-6365] also show a good agreement for liquid velocity and gas hold-up profiles.     

On the effect of phase fraction on drop size distribution of liquid–liquid dispersions in agitated vessels

The theory of Kolmogorov–Hinze is the base for many studies that have been done on mean drop size and drop size distribution of liquid–liquid dispersions in agitated vessels. Although this theory has been used extensively in the literature, but it does not always give a satisfactory result in the studies and therefore needs to be modified. This paper addresses the effect of phase fraction on drop size distribution in agitated vessels and on the proportionality coefficient and Weber number exponent in the relation d₃₂/D ∝ We^m. The experimental data that were taken from Pacek et al. (1998) and Desnoyer et al. (2003) have been applied to this relation to investigate the effect of phase ratio. It is shown that even at low phase fractions, the Kolmogorov–Hinze theory necessarily does not give the best result with the −0.6 exponent for the Weber number. Furthermore, for the non-coalescing system, a range of exponent for the Weber number typically from −0.6 to −0.43 can be considered where the system may be approximated as a pseudo-coalescing system at Φ = 0.4 in which the obtained results are in good agreement with the results of Pacek et al. (1998).     

DEM modeling of crack coalescence between two parallel flaws in SiC ceramics

A discrete element model (DEM) of SiC ceramics containing two parallel flaws was used to study crack coalescence under uniaxial compression with different flaw inclination angles, ligament lengths, and ligament angles. A relationship is proposed between coalescence stress state, flaw inclination angle, and horizontal component of the ligament length during the failure process. The effects of coplanar flaws on various characteristics of the specimen, viz. compressive strength, Young's modulus, crack initiation stress, and Poisson's ratio, were studied. Coalescence modes between two parallel flaws observed in the DEM model were in good agreement with nine crack coalescence categories summarized in experimental studies. Meanwhile, the corresponding stress state at the moment of coalescence can be classified into three types – pre-peak, mid-peak, and post-peak. The results also showed that the horizontal component d of the ligament length of parallel flaws significantly influences the coalescence stress state. When parallel flaws overlap in the loading direction (d < 0), with an increase in the inclination angle, the occurrence of crack coalescence changes from pre-peak period to mid-peak period and post-peak period and eventually to non-coalescence. When d = 0, coalescence between the flaw pair mainly occurs before the peak stress and the corresponding flaw geometries are the most dangerous. As distance d increases, the possibility of crack coalescence decreases.     

新型过滤器结构分析及改进

天然气中的粉尘影响仪表、阀门设备正常运行。根据常用的天然气过滤方法及过滤分离设备的工作原理及过滤分离器的结构构成，以重庆气矿的在役过滤分离器为例，通过对其运行状况及工作过程中所存在问题的详细分析，找出了存在的问题，提出了新型过滤分离器内部结构的改进方案，并且探讨了新型天然气过滤分离设备的发展方向。     

Behaviour of an oil-in-water emulsion stabilized by β-lactoglobulin in an in vitro gastric model

The behaviour of β-lactoglobulin (β-lg)-stabilized emulsions (1.0 wt% protein and 20.0 wt% soy oil) using pepsin digestion under simulated gastric conditions (37 °C, pH 1.2 and 34 mM NaCl ionic strength, with continuous shaking at approximately 95 rev/min for 2 h) was investigated. Changes in particle size, ζ-potential and microstructure were monitored as a function of incubation time in the gastric fluid. Initially, β-lg formed a stable anionic emulsion at pH 7, but the emulsion underwent extensive droplet flocculation, with some coalescence, on mixing with the simulated gastric fluid. The ζ-potential values gradually changed from −57.1 ± 0.5 mV to +17.6 ± 1.2 mV because of pH change and peptic hydrolysis of the interfacial layer. Native β-lg was largely resistant to pepsin attack but, when β-lg was present at the interfacial layer of the oil-in-water emulsion, it was rapidly hydrolysed by pepsin, as shown by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The droplet flocculation and the coalescence observed during hydrolysis were markedly dependent on the digestion time.     

Utilizing the thermodynamic nanoparticle size effects for low temperature Pb-free solder

Development of a Pb-free Sn nanosolder paste with an initial melting temperature near or below the melting temperature of eutectic Sn-Pb solder (183 °C) has been investigated using the size-dependent melting behavior of small particles. Three to five nanometer Sn nanoparticles were fabricated by sonochemical reduction and observed to melt at temperatures near or below 183 °C. Prototype nanosolder pastes were produced by combining the nanoparticles with flux and were characterized by differential scanning calorimetry (DSC) in terms of their melting, solidification, coalescence, and metal particle loading properties. The results indicate that, although target melting temperatures were achieved, nanoparticle coalescence was limited by low volume loading of the metal, due in part to the capping layer (an organic layer adsorbed on the metal surface during chemical synthesis).