Circuit model for microfluidic bubble generation under controlled pressure

We explore the microfluidic generation of bubbles in a flow-focusing junction using a pressure-controlled device rather than the more common flow rate-controlled devices. This device is a prototype for extending microfluidic drop generation methods to molten polymers. We show that the bubble generation process is highly sensitive to pressure: small changes in pressure induce large changes in bubble size and bubble formation frequency. A simple resistance circuit model can explain this pressure dependence. Briefly, we show that bubble generation is possible only within a finite pressure range. Near the ends of this pressure range, the ratio of the flow rates of the dispersed to continuous phase is highly sensitive to pressure, and therefore so also is the bubble generation process. The circuit model offers a way to use existing models of drop generation (which are based on flow rate-controlled operation) to predict pressure-controlled operation. We also examine drop formation using a highly viscous polymer as the dispersed phase. Drops are formed far downstream of the flow-focusing junction, and they are far smaller than the microfluidic channel dimensions. These results suggest that existing microfluidic drop generation methods may be exploited to make complex particles from thermoplastic polymers.     

A solvothermal approach for the size-, shape- and phase-controlled synthesis and properties of CuInS2

In this work, Copper Indium disulfide (CIS) nanoparticles of size ∼ 5 nm were prepared via solvothermal approach in ethanol under the nitrogen atmosphere using copper chloride, indium chloride and thiourea (Tu) as starting materials, without any assistance through organic ligands at the reaction temperature of 150 °C. The factors which might affect the morphology, structure, phase of the product during the synthesis were discussed. It was found that the products were significantly affected by the reaction time and solvent. The morphology, structure, phase constituents and optical properties of the as prepared CIS powders were characterized by X-ray diffraction (XRD), Energy dispersive Spectroscopy (EDS), scanning electron microscopy (SEM) and ultraviolet–visible (UV–Vis) spectrometry respectively. The result shows that the CIS nanoparticles can be synthesized by solvothermal method at a reaction time of 2 h and shows that when the reaction time was increased from 2 h to 48 h, CIS porous flower like nanoparticles were obtained as we increase the reaction time. We also observed that in this process, the phase selection of WZ-CIS or CH-CIS is greatly influence by solvent. We also observed that, in this process sulfur source did not influence the phase but participated in the growth of the nanoparticles.     

Understanding Melt Flow Behavior for Al-Si Alloys Processed Through Vertical Centrifugal Casting

The objective of this article is to investigate the appearance, microstructure, and hardness of Al-Si alloys Al-12Si and Al-17Si in vertical centrifugal casting process. During rotation of the mold, molten metal flow affects the formation of uniform cylinder. In this study, flow of molten metal for Al-Si alloys at different rotational speeds is focused. It is found that for Al-17Si alloy a uniform cast tube is observed for 1000 rpm, whereas for Al-12Si it is at 1200 rpm; above and below these speeds, irregular cast tubes are formed. Finally, fine structured grain size with high hardness value is found in a uniform cast tube in comparison with others.     

Prediction of gel-time in the cure of unsaturated polyester resins: Phenomenological modeling vs. statistical analysis

A series of kinetic and rheological measurements were carried out using a differential scanning calorimeter (DSC) and a Rheometrics Dynamic Analyzer (RDA). The effects of temperature, inhibitor level, initiator level, and initiator type on the curing of unsaturated polyester resins were investigated. Two models based on the free radical polymerization mechanism were developed for predicting the time to reach liquid-solid transition. These models adapted a concept that gelation occurred at a critical radical concentration. The applicability of these models was compared to that of a statistical analysis.     

Stochastic fracture analysis of laminated composite plate with arbitrary cracks using X-FEM

In this paper, second order statistics of mixed mode stress intensity factors (MSIFs) and crack propagation analysis of the symmetric angle ply laminated composite plate with through thickness arbitrary curve cracks subjected to tensile and shear stress is presented. The fracture behaviour is analysed using extended finite element method (X-FEM). The cracks like line, semi elliptical, semi circular and arbitrary curves are considered for the detailed numerical study. The material properties, lamination angle, loading, crack width and crack depth are modelled as independent, combine uncorrelated and correlated input random Gaussian variables. The interaction integral (M-integral) is adopted for calculating the MSIFs. The second order perturbation technique and Monte Carlo simulations are proposed to obtain the mean and coefficient of variance of MSIFs by random change in input system parameters. This work signifies the accurate and realistic evaluation of fracture response by handling the various levels of uncertainties. The effect of crack propagation on MSIFs using tensile and shear stresses using global tracking algorithm is also highlighted.     

Open contact analysis of single bit failure in 0.18 μm technology

Single bit failure is the most common failure mode in static random access memory. Although a failing cell can be easily localized with bitmap data, the exact defect location within the failing cell cannot be found immediately, especially when a defect is related to contact. In this paper, a technique of contact-level passive voltage contrast has been proposed to detect such defects for a single bit failure. After an open contact was identified, subsequent transmission electron microscope analysis was performed and it was found that the root cause for the open contact was poly residue.     

Capacity investment and the value of operational flexibility in manufacturing systems with product blending

A distinct feature of process industries such as food, chemical and consumer packaged goods is the blending of intermediates into finished goods. In the context of such manufacturing systems the levels of different inputs that can be blended to process a final good define the range of flexibility. Likewise, the cost for using (blending) different inputs defines the mobility element of flexibility. In this paper, we investigate capacity investment and the value of flexibility in the presence of such product blending constraints. We are motivated by recent case studies of food manufacturers, in particular, those manufacturers that seek to increase flexibility via blending of intermediates. We analyse stochastic programs under demand uncertainty of such manufacturing systems. We provide analytical insights into trade-offs when range and mobility are interdependent. Our analytical work gives structural insights into subtle complementarity and substitution effects between dedicated and shared resources in the presence of blending. We analytically show that there is a degradation in the cost performance of such systems with an increase in correlation. We characterise the optimal blending fraction that balances the benefits of higher range with higher costs (lower mobility). Our numerical work shows that a moderate level of blending can significantly improve flexibility and that well-known guidelines for designing limited flexibility change in the presence of blending. For example, blending, even if optimally designed, weakens the appeal of chaining configurations. Overall our work guides resource configuration in industries where product blending is an integral part of the production process.     

Prediction of residual stress distribution in plastic pipe extrusion

In thermoplastic pipe extrusion, the extrudate emerging from the die is typically sized and cooled from outside in a quench tank. This process causes quick solidification of the external layer, while the inner mass of molten material cools only gradually. The slow cooling and crystallization, and the associated shrinkage of this material, can lead to build-up of severe stresses in the final part that can affect the long term service performance. In this paper, a simple theoretical analysis of this process of residual stress build-up is presented. The pipe undergoing quenching is modeled as an annular cylinder of molten polymer being cooled at a controlled rate from outside. The overall stresses are derived numerically by adding up the stress contributions due to incremental advance of the solidification boundary. The results of the analysis are found to be in qualitative accord with the experimentally measured stress profiles in thermoplastic pipe.