Minimum superficial fluid velocity in a gas–solid swirled fluidized bed

A swirl flow is achieved in a bed of solids by passing air through multiple fluid inlets, which are tangentially located at the base of a flat-based circular column. The minimum superficial velocities needed to achieve swirling of the bed are measured experimentally under varied conditions. An empirical correlation for the minimum swirl velocity has been proposed. The results indicate that a stable swirling regime operation of the bed is possible. There exists an upper limit of static bed depth beyond which stable swirling of entire bed is not possible. The minimum swirl velocities are found to be 1.2–1.3 times the minimum fluidization velocities predicted for conventional fluidized beds.     

Tribological study of elastomeric bearings for marine propeller shaft system

Elastomeric compounds, due to their favourable properties like sufficient hardness, toughness and natural resistance to abrasion and corrosion, are commonly used as bearing material for propeller shaft system of Indian Coast Guard Ships. Recently unequal and non-uniform wear of these bearings has resulted in unscheduled lay off of the Coast Guard Ships. To solve this problem of bearing wear, a mixed lubrication analysis of sea-water lubricated journal bearing has been attempted in the present study. A computer code was written to estimate lubricating film thickness for a given set of load and speed condition, and to predict the lubrication regime for the specified surface roughness parameters. To validate the theoretical analysis performed in the present study, the results obtained from the computer simulation have been compared with the established studies on the water lubricated bearing.To understand the uneven wear of marine bearings, actual geometric clearances of new and worn out bearings recorded by the ship maintenance team, and the operational data (load, speed and operating hours), obtained from the log books of ICGS Sangram (AOPV) of Indian Coast Guard, are listed in the present paper. The dynamic viscosity of sea water, surface roughness of propeller shaft and bearings, and particulate contamination has been measured. Finally, the suggestions have been enlisted for proper operation of shaft-bearing system so as to maintain the wear within the permissible limits during ship's operational cycle.     

Dry sliding wear behaviour of AA 6351-ZrB2 in situ composite at room temperature

In the present work, AA 6351-xZrB₂ [x = 0, 3, 6 and 9 weight percentage (wt.%)] in situ composites have been prepared by the reaction of mixture of K₂ZrF₆ and KBF₄ with molten aluminium alloy at a reaction temperature of 850 °C. The in situ prepared composites were characterized by using scanning electron microscope (SEM), X-ray diffractometer (XRD), and microhardness analysis. The sliding wear properties of the prepared composite at room temperature were estimated by a pin-on-disc wear testing equipment using the composite material; the pins were machined according to standard sizes, and the tests were conducted as per the standards recommended by the ASTM G99-95a designation of different weighing percentage at room temperature. The wear characteristics of the composite in the as-cast, the solutionized and the solutionized-aged conditions were studied by conducting sliding wear test at the load of 9.81 N. The results indicated that the wear rate was decreased with an increase in the weight percentage of ZrB₂ and the wear resistance was increased with an increase in the fraction of ZrB₂ particulates in composite before and after heat treatment.     

Cold deformation of dezincification resistant yellow brass for plumbing applications

In the present work, the room temperature deformation behavior of dezincification-resistant (DZR) brass was performed by varying strain rates (1?×?10^?4?s^?1, 0.55?×?10^?3?s^?1, 1?×?10^?3?s^?1, 0.55?×?10^?2?s^?1, 1?×?10^?2?s^?1) and percent cold works (15 to 65% with step of 10%). These parameters are important to plumbing parts of its forming. Room temperature deformation workability map was developed that provides the selection of safe deformation parameters without cracking. The as-received and deformed DZR brass samples were carefully characterized by various microscopes. The results revealed that more dislocations lines and twinning were observed through transmission electron microscope images as the strain rate (SR) increases which led to early failure of the sample before reaching the set height reduction. It was determined that more amount of strain hardening with designed height reduction was achieved at lower SR whereas less amount of strain hardening was achieved at higher SR due to strain mismatching phenomenon and various deformation mechanisms.     

Effect of heating location and size on mixed convection in lid-driven cavities

A numerical study is performed to analyze the mixed convection heat transfer and fluid flow in lid-driven cavities with different lengths of the heating portion and different locations of it. The left wall has been heated fully or partially to a higher temperature, whereas the right wall is maintained at a lower temperature. Three different lengths of the heating portion and three different locations of it are used along the hot wall. The remaining portions of the left wall, and the top and the bottom walls of the cavity are insulated. The finite volume method is used to discretize the governing equations which are then solved iteratively. The velocities and pressure are coupled by the SIMPLE algorithm. Results are presented graphically in the form of streamlines, isotherms and velocity profiles. It is concluded that the heat transfer rate is enhanced on reducing the heating portion and when the portion is at middle or top of the hot wall of the cavity.     

Tile Complexity of Approximate Squares

The standard Tile Assembly Model (TAM) of Winfree (Algorithmic self-assembly of DNA, Ph.D. thesis, 1998) is a mathematical theory of crystal aggregations via monomer additions with applications to the emerging science of DNA self-assembly. Self-assembly under the rules of this model is programmable and can perform Turing universal computation. Many variations of this model have been proposed and the canonical problem of assembling squares has been studied extensively. We consider the problem of building approximate squares in TAM. Given any $\varepsilon \in (0,\frac{1}{4}]$ we show how to construct squares whose sides are within (1±ε)N of any given positive integer N using $O( \frac{\log \frac{1}{\varepsilon}}{\log \log\frac{1}{\varepsilon}} + \frac{\log \log \varepsilon N}{\log \log \log \varepsilon N} )$ tile types. We prove a matching lower bound by showing that $\varOmega( \frac{\log \frac{1}{\varepsilon}}{\log \log\frac{1}{\varepsilon}} + \frac{\log \log \varepsilon N}{\log \log \log \varepsilon N} )$ tile types are necessary almost always to build squares of required approximate dimensions. In comparison, the optimal construction for a square of side exactly N in TAM uses $O(\frac{\log N}{\log \log N})$ tile types. The question of constructing approximate squares has been recently studied in a modified tile assembly model involving concentration programming. All our results are trivially translated into the concentration programming model by assuming arbitrary (non-zero) concentrations for our tile types. Indeed, the non-zero concentrations could be chosen by an adversary and our results would still hold. Our construction can get highly accurate squares using very few tile types and are feasible starting from values of N that are orders of magnitude smaller than the best comparable constructions previously suggested. At an accuracy of ε=0.01, the number of tile types used to achieve a square of size 10⁷ is just 58 and our constructions are proven to work for all N≥13130. If the concentrations of the tile types are carefully chosen, we prove that our construction assembles an L×L square in optimal assembly time O(L) where (1?ε)N≤L≤(1+ε)N.     

Parameter consistency and quadratically constrained errors-in-variables least-squares identification

In this article, we investigate the consistency of parameter estimates obtained from least-squares identification with a quadratic parameter constraint. For generality, we consider infinite impulse-response systems with coloured input and output noise. In the case of finite data, we show that there always exists a possibly indefinite quadratic constraint depending on the noise realisation that results in a constrained optimisation problem that yields the true parameters of the system when a persistency condition is satisfied. When the noise covariance matrix is known to within a scalar multiple, we prove that solutions of the quadratically constrained least-squares (QCLs) estimator with a semidefinite constraint matrix are both unbiased and consistent in the sense that the averaged problem and limiting problem produce, respectively, unbiased and true (with probability 1) estimators. In addition, we provide numerical results that illustrate these properties of the QCLS estimator.     

Determination of the depletion of furazolidone residues in chicken tissues using a Bacillus stearothermophilus test

This study assessed the applicability of a Bacillus stearothermophilus test for detection of the depletion of furazolidone anticoccidial drug residues in chicken tissues. Thirty-three Ross breed chicken were dosed orally with furazolidone (2 mg/kg body weight) daily for 5 days. After the last treatment the birds were sacrificed in groups of three at intervals of 1, 3, 6, 10, 24, 48, 144, 240, 360 and 480 h. Liver, kidney and breast muscle samples were collected and immediately analysed at each interval for furazolidone residues. Serum was separated from the blood collected from jugular veins into bottles containing glass beads and analysed. Supernatant from the homogenates was analysed for the presence or absence of furazolidone residues using the B. stearothermophilus test. Semi quantification of furazolidone residues was done by comparing the obtained zones of inhibition on a Bacillus subtilis test plates and the zones from calibrated standard curves. Qualitatively the B. stearothermophilus test was positive for furazolidone residues up to 480 h post treatment in serum samples, 360 h in liver samples, 480 h in kidney samples and 360 h in muscle samples. Semi quantitatively from the B. subtilis test plates, serum samples were observed to have the highest furazolidone concentration of 3.2 μg/ml. The lowest furazolidone concentration was recorded in kidney tissues at 0.21 μg/ml. Kidney and serum tissues appear to be good tissues for testing of furazolidone tissues. The Kidney samples would appear best for post-mortem screening of furazolidone residues while serum could be used antemortem screening of depletion in chicken.     

Static expansion primary vacuum standard — Part 1: Determination of the volume ratio of the expansion stage

Measurement of volume ratio forms an essential part of the characterization of a static expansion system (SES) for the generation of pressures in the medium and high vacuum region. Because of the complexity of the vacuum chambers, it is not possible to determine the absolute volumes of the chambers involved. Hence an expansion process is resorted to, in which the gas enclosed in the small volume at a known pressure is allowed to expand, under isothermal conditions, into the large volume. The accuracy of the volume ratio thus determined depends on the stability of the vacuum gauges used for the measurement of initial and the final pressures and the ambient temperature. High accuracy resonant silicon gauges (RSGs) of two different ranges, one 130 kPa full scale and the other 1 kPa full scale for measurement of the initial and final pressures are found to be useful. This paper reports the results obtained with these RSGs for the measurement of the volume ratio of the National Physical Laboratory, India (NPLI) SES which is nominally 2820. With the use of the RSGs, and calibrated platinum resistance thermometers (PRTs) mounted inside the vacuum chambers, it has been possible to measure the volume ratio within the relative expanded uncertainty (k = 2) of 0.0014. The results of the volume ratio determination exercise are given in this paper while the Part 2 of this paper will discuss the procedure for the calibration of spinning rotor gauges on the Static expansion primary standard.     

An inverse-measure-based unilevel architecture for reliability-based design optimization

Reliability-based design optimization (RBDO) is a methodology for finding optimized designs that are characterized with a low probability of failure. Primarily, RBDO consists of optimizing a merit function while satisfying reliability constraints. The reliability constraints are constraints on the probability of failure corresponding to each of the failure modes of the system or a single constraint on the system probability of failure. The probability of failure is usually estimated by performing a reliability analysis. During the last few years, a variety of different formulations have been developed for RBDO. Traditionally, these have been formulated as a double-loop (nested) optimization problem. The upper level optimization loop generally involves optimizing a merit function subject to reliability constraints, and the lower level optimization loop(s) compute(s) the probabilities of failure corresponding to the failure mode(s) that govern(s) the system failure. This formulation is, by nature, computationally intensive. Researchers have provided sequential strategies to address this issue, where the deterministic optimization and reliability analysis are decoupled, and the process is performed iteratively until convergence is achieved. These methods, though attractive in terms of obtaining a workable reliable design at considerably reduced computational costs, often lead to premature convergence and therefore yield spurious optimal designs. In this paper, a novel unilevel formulation for RBDO is developed. In the proposed formulation, the lower level optimization (evaluation of reliability constraints in the double-loop formulation) is replaced by its corresponding first-order Karush–Kuhn–Tucker (KKT) necessary optimality conditions at the upper level optimization. Such a replacement is computationally equivalent to solving the original nested optimization if the lower level optimization problem is solved by numerically satisfying the KKT conditions (which is typically the case). It is shown through the use of test problems that the proposed formulation is numerically robust (stable) and computationally efficient compared to the existing approaches for RBDO.