Mixing characteristics in microchannels with biomimetic superhydrophobic (Lotus leaf replica) walls

We demonstrate here the mixing characteristics in microchannels with a biomimetic superhydrophobic (lotus leaf replica) wall. The lotus leaf replica is fabricated using a frugal, yet efficient, double-step soft lithography method. In microchannels with a lotus leaf replica wall, the unidirectional laminar flow pertaining to the low hydrodynamics regime changes into an erratic flow field beyond a critical flow rate. We show here that such lotus leaf replica-induced erratic flow, even for low Reynolds number, can be used for enhanced mixing at the microscale. The enhancement in the mixing is quantified by the reduction in the mixing length in the microchannels with the biomimetic lotus leaf replica wall as compared to identical microchannels with flat walls. We believe that the simple cost-effective methodology for enhancing mixing in microchannels, as demonstrated here, can be integrated into lab-on-a-chip devices, which may be beneficial for applications requiring microscale mixing like DNA sequencing, enzyme reaction, and medical diagnostics.     

Fuzzy rule extraction from ID3-type decision trees for real data

This paper proposes a method to construct a fuzzy rule-based classifier system from an ID3-type decision tree (DT) for real data. The three major steps are rule extraction, gradient descent tuning of the rule-base, and performance-based pruning of the rule-base. Pruning removes all rules which cannot meet a certain level of performance. To test our scheme, we have used the DT generated by RIB3, an ID3-type classifier for real data. In this process, we made some improvements of RID3 to get a tree with less redundancy and hence a smaller rule-base. The rule-base is tested on several data sets and is found to demonstrate an excellent performance. Results obtained by the proposed scheme are consistently better than C4.5 across several data sets.     

QFD-based expert system for non-traditional machining processes selection

Selection of an optimal non-traditional machining (NTM) process for generating a desired feature on a given material requires the consideration of several factors among which the type of the workpiece material and shape to be machined are the most significant ones. This paper presents a quality function deployment (QFD) based methodology to ease out the optimal NTM process selection procedure. It includes the design of a QFD-based expert system that can automate the decision making process with the help of graphical user interfaces and visual aids. The developed expert system employs the use of a house of quality (HOQ) matrix for comparison of the relevant product and process characteristics. The weights obtained for various process characteristics are utilized to estimate an overall score for each of the NTM processes. Finally, if some of the NTM processes satisfy certain critical criteria, they are again compared with each other on the basis of their overall scores and the process having the maximum score is selected as the optimal choice.     

A Critical Assessment of Kriging Model Variants for High-Fidelity Uncertainty Quantification in Dynamics of composite Shells

This paper presents a critical comparative assessment of Kriging model variants for surrogate based uncertainty propagation considering stochastic natural frequencies of composite doubly curved shells. The five Kriging model variants studied here are: Ordinary Kriging, Universal Kriging based on pseudo-likelihood estimator, Blind Kriging, Co-Kriging and Universal Kriging based on marginal likelihood estimator. First three stochastic natural frequencies of the composite shell are analysed by using a finite element model that includes the effects of transverse shear deformation based on Mindlin’s theory in conjunction with a layer-wise random variable approach. The comparative assessment is carried out to address the accuracy and computational efficiency of five Kriging model variants. Comparative performance of different covariance functions is also studied. Subsequently the effect of noise in uncertainty propagation is addressed by using the Stochastic Kriging. Representative results are presented for both individual and combined stochasticity in layer-wise input parameters to address performance of various Kriging variants for low dimensional and relatively higher dimensional input parameter spaces. The error estimation and convergence studies are conducted with respect to original Monte Carlo Simulation to justify merit of the present investigation. The study reveals that Universal Kriging coupled with marginal likelihood estimate yields the most accurate results, followed by Co-Kriging and Blind Kriging. As far as computational efficiency of the Kriging models is concerned, it is observed that for high-dimensional problems, CPU time required for building the Co-Kriging model is significantly less as compared to other Kriging variants.     

Semi-analytical solutions for electroosmotic flows with interfacial slip in microchannels of complex cross-sectional shapes

In this article, we investigate the implications of electroosmosis with interfacial slip on electrohydrodynamic transport in microchannels having complex (yet symmetric) cross-sectional shapes, by employing a generic semi-analytical approach. We also devise an approximate technique of flow rate prediction under these conditions, using a combined consideration of electroosmotic slip (under thin electrical double layer limits) and Navier slip conditions (originating out of confinement-induced hydrophobic interactions) at the fluid–solid interface. We further assess the effectiveness of the approximate solutions in perspective of the exact solutions, as a parametric function of the relative thickness of the electrical double layer with respect to the channel hydraulic diameter. We illustrate the underlying consequences through examples of elliptic, polygonal, point star-shaped, and annular microchannel cross sections.     

Passivity breakdown due to discontinuous precipitation during ageing of 21Cr-10Mn-5Ni stainless steel

Discontinuous precipitation in a 21Cr-10Mn-5Ni steel was found to result in breakdown of passivity when tested in a 0.5 m H₂SO₄ + 0.01 m KSCN solution. The electrochemical response was similar to that due to sensitization of conventional stainless steels. The ageing time and temperature affected the resistance of the passive film, with lower ageing temperatures being more severe in terms of passivity breakdown. The effect of interlamellar spacing on the chromium depletion, the effect of volume diffusion on the healing of the matrix, and the solubility product reaction for precipitation, were considered to explain the observed different strengths of passive films formed on specimens aged at different temperatures and times. The observance of good corrosion protection in spite of the presence of profuse precipitates was in contrast to the effect of grain-boundary carbide proliferation on the corrosion resistance of conventional stainless steels.     

Non-adiabatic polaron hopping conduction in semiconducting V2O5-Bi2O3 oxide glasses doped with BaTiO3

BaTiO₃-doped (5–40 wt %) 90V₂O₅-10Bi₂O₃ (VB) glasses have been prepared by a quick quenching technique. The d.c. electrical conductivities, _d.c., of these glasses have been reported in the temperature range 80–450 K. The electrical conductivity of these glasses, which arises due to the presence of V⁴⁺ and V⁵⁺ ions, has been analysed in the light of the small-polaron hopping conduction mechanism. The adiabatic hopping conduction valid for the undoped VB glasses (with 80–95 mol % V₂O₅), in the high-temperature region, is changed to a non-adiabatic hopping mechanism in the BaTiO₃-doped VB glasses. At lower temperatures, however, a variable range hopping (VRH) mechanism dominates the conduction mechanism in both the glass systems. Such a change-over from adiabatic to non-adiabatic conduction mechanism is a new feature in transition metal oxide glasses. Various parameters, such as density of states at the Fermi level N(E_F), electron wave-function decay constant, , polaron radius, r _p, and its effective mass, m _p ^* , etc., have been obtained for all the glass samples from a critical analysis of the electrical conductivity data satisfying the theory of polaron hopping conduction.     

A comparative experimental and numerical study to investigate the relative merits of convectors and “C” inserts in cooling cold-rolled coils

The coil cooling and storage unit (CCSU) is used to cool cold-rolled coils to the temper rolling temperature after the annealing cycle is over at the batch annealing furnace (BAF) in a cold rolling mill (CRM). In the CCSU, the coils are kept on the cooling bases for any fixed time irrespective of the grade and tonnage. Therefore, the need for a mathematical model to accurately predict the cooling time of the coils was felt. The current study involves experimental and numerical analysis of a stack of coils with respect to heat transfer and fluid flow. A comparative study was carried out to ascertain the relative merits of convectors and “C” inserts (CIs) in the cooling the coils. The air flow distribution for the case of different convectors and CIs was measured by means of a full scale physical model. Two different mathematical models were applied to model the fluid flow and flow distribution through the stack of coils. The first flow model uses the hydraulic resistance concept for estimating the air flow rate distribution, whereas the second flow model uses commercial computational fluid dynamics (CFD) software and predicts the velocity distribution in the flow path between two coils in a stack. The predictions from these two models compare well with the experimental data. The flow models were used to calculate the average heat-transfer coefficient in different flow passages in a stack. The heat-transfer coefficients thus obtained were used to tune and validate a two-dimensional transient heat-transfer model of coils. The heat-transfer model predicts the cooling time of coils accurately and also suggests a possible reduction of cooling time if CIs are used in place of convectors.     

Compatibility of Lead-Bismuth Eutectic with SiC-Coated Graphite at Elevated Temperature

Uniform coating of β-silicon carbide (β-SiC) was formed over a graphite pellet through slurry-based silicon coating followed by in situ reaction at 1873 K (1600 °C). The coated pellet was exposed to molten lead-bismuth eutectic (LBE) at 1173 K (900 °C) in static condition for 200 h. Weight loss measurement, X-ray diffraction, and secondary electron microscopy–energy-dispersive spectroscopy confirmed that the SiC coating could effectively prevent molten LBE from attacking the inner graphite material.