Diagnostics of blast-furnace linings

Hatch (Canada) has developed a system for the nondestructive monitoring of the residual lining thickness in blast furnaces and eletrofurnaces. This system, which is based on an acoustic–ultrasound echo signal (AU-E), supplements the traditional thermal simulation of the furnace lining by means of built-in thermocouples or on the basis of the thermal load on the cooling units in the blast furnace. By this means, the position of cracks and anomalies may be determined, and the boundary between the coating and the refractory may be identified. The constraints and sources of error in the AU-E method are analyzed, and an improved version is outlined. The improved method takes account of the influence of the following factors on the wave propagation: high temperatures; the furnace shape and size; and the difference in acoustic resistance of different layers in a multilayer refractory lining. The AU-E method permits reliable and nondestructive monitoring of the refractory lining in smelting furnaces. The hardware and software of the AU-E system have been significantly improved, so as to obtain measurements of satisfactory accuracy. Estimates of the method’s precision are confirmed by physical measurements on inoperative blast furnaces. Examples of the utilization of this diagnostic system at various Russian and non-Russian plants are presented. Some technological measures that extend the blast-furnace run are noted. As shown in the present study, the use of several successive measurements permits the determination of the lining’s wear rate and the time remaining before major repair. The AU-E method continues to operate well at more than 70 blast furnaces around the world, including those at the Novolipetsk, Cherepovets, Nizhny Tagil, Western Siberian, and Magnitogorsk steel works, as well as at electrofurnaces producing ferroalloys, copper, and platinum.     

Multi‐Objective Optimization of a Cross‐Flow Plate Heat Exchanger Using Entropy Generation Minimization

Multi‐objective optimization of a cross‐flow plate fin heat exchanger (PFHE) by means of an entropy generation minimization technique is described. Entropy generation in the PFHE was separated into thermal and pressure entropy generation as two objective functions to be minimized simultaneously. The Pareto optimal frontier was obtained and a final optimal solution was selected. By implementing a decision‐making method, here the LINMAP method, the best trade‐off was achieved between thermal efficiency and pumping cost. This approach led to a configuration of the PFHE with lower magnitude of entropy generation, reduced pressure drop and pumping power, and lower operating and total cost in comparison to single‐objective optimization approaches.     

An experimental study on thermal conductivity and viscosity of nanofluids containing carbon nanotubes

Recently, there has been considerable interest in the use of nanofluids for enhancing thermal performance. It has been shown that carbon nanotubes (CNTs) are capable of enhancing the thermal performance of conventional working liquids. Although much work has been devoted on the impact of CNT concentrations on the thermo-physical properties of nanofluids, the effects of preparation methods on the stability, thermal conductivity and viscosity of CNT suspensions are not well understood. This study is focused on providing experimental data on the effects of ultrasonication, temperature and surfactant on the thermo-physical properties of multi-walled carbon nanotube (MWCNT) nanofluids. Three types of surfactants were used in the experiments, namely, gum arabic (GA), sodium dodecylbenzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS). The thermal conductivity and viscosity of the nanofluid suspensions were measured at various temperatures. The results showed that the use of GA in the nanofluid leads to superior thermal conductivity compared to the use of SDBS and SDS. With distilled water as the base liquid, the samples were prepared with 0.5 wt.% MWCNTs and 0.25% GA and sonicated at various times. The results showed that the sonication time influences the thermal conductivity, viscosity and dispersion of nanofluids. The thermal conductivity of nanofluids was typically enhanced with an increase in temperature and sonication time. In the present study, the maximum thermal conductivity enhancement was found to be 22.31% (the ratio of 1.22) at temperature of 45°C and sonication time of 40 min. The viscosity of nanofluids exhibited non-Newtonian shear-thinning behaviour. It was found that the viscosity of MWCNT nanofluids increases to a maximum value at a sonication time of 7 min and subsequently decreases with a further increase in sonication time. The presented data clearly indicated that the viscosity and thermal conductivity of nanofluids are influenced by the sonication time. Image analysis was carried out using TEM in order to observe the dispersion characteristics of all samples. The findings revealed that the CNT agglomerates breakup with increasing sonication time. At high sonication times, all agglomerates disappear and the CNTs are fragmented and their mean length decreases.     

High-output-impedance transadmittance type continuous-time multifunction filter with minimum active elements

A new transadmittance multifunction filter with single input and three outputs employing only three positive-type second-generation current conveyors and five passive elements is presented. The proposed filter realizes three basic filter functions simultaneously, all at high impedance outputs. No component matching is required and all the passive sensitivities are low. Experimental verification is also performed.     

Manifold Homotopy via the Flow Complex

It is known that the critical points of the distance function induced by a dense sample P of a submanifold Σ of ℝⁿ are distributed into two groups, one lying close to Σ itself, called the shallow , and the other close to medial axis of Σ, called deep critical points. We prove that under (uniform) sampling assumption, the union of stable manifolds of the shallow critical points have the same homotopy type as Σ itself and the union of the stable manifolds of the deep critical points have the homotopy type of the complement of Σ. The separation of critical points under uniform sampling entails a separation in terms of distance of critical points to the sample. This means that if a given sample is dense enough with respect to two or more submanifolds of ℝⁿ, the homotopy types of all such submanifolds together with those of their complements are captured as unions of stable manifolds of shallow versus those of deep critical points, in a filtration of the flow complex based on the distance of critical points to the sample. This results in an algorithm for homotopic manifold reconstruction when the target dimension is unknown.     

From logic programming towards multi‐agent systems

In this paper we present an extension of logic programming (LP) that is suitable not only for the “rational” component of a single agent but also for the “reactive” component and that can encompass multi‐agent systems. We modify an earlier abductive proof procedure and embed it within an agent cycle. The proof procedure incorporates abduction, definitions and integrity constraints within a dynamic environment, where changes can be observed as inputs. The definitions allow rational planning behaviour and the integrity constraints allow reactive, condition‐action type behaviour. The agent cycle provides a resource‐bounded mechanism that allows the agent’s thinking to be interrupted for the agent to record and assimilate observations as input and execute actions as output, before resuming further thinking. We argue that these extensions of LP, accommodating multi‐theories embedded in a shared environment, provide the necessary multi‐agent functionality. We argue also that our work extends Shoham’s Agent0 and the BDI architecture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Information source tracking method: efficiency issues

This paper is devoted to the study and analysis of query processing efficiency in the information source tracking (IST) technique, an approach to the representation and manipulation of uncertain and inaccurate data. We show that the efficiency depends on the average number of information sources confirming the same data in the database. If this number is close to unity, then the efficiency of query processing for the IST model is comparable to conventional relational database systems. For the case where multiple information sources confirm the same data in the database, we present a variation of IST, called the Dual IST method, which provides efficient query processing. Extended relational algebra operations are presented for Dual IST, and proven to be correct under the “alternate worlds” semantics interpretation. The complexity of reliability calculation in IST and Dual IST methods is also studied     

The effect of PVD coatings on the corrosion behaviour of AZ91 magnesium alloy

In this study, multilayered AlN (AlN + AlN + AlN) and AlN + TiN were coated on AZ91 magnesium alloy using physical vapour deposition (PVD) technique of DC magnetron sputtering, and the influence of the coatings on the corrosion behaviour of the AZ91 alloy was examined. A PVD system for coating processes, a potentiostat for electrochemical corrosion tests, X-ray difractometer for compositional analysis of the coatings, and scanning electron microscopy for surface examinations were used. It was determined that PVD coatings deposited on AZ91 magnesium alloy increased the corrosion resistance of the alloy, and AlN + AlN + AlN coating increased the corrosion resistance much more than AlN + TiN coating. However, it was observed that, in the coating layers, small structural defects e.g., pores, pinholes, cracks that could arise from the coating process or substrate and get the ability of protection from corrosion worsened were present.     

An intelligent scheduling system using fuzzy logic controller for management of services in WiMAX networks

The appearance of media applications with high bandwidth and quality of service requirements has made a significant impact in telecommunications technology. In this direction, the IEEE802.16 has defined wireless access systems called WiMAX. These systems provide high-speed communications over a long distance. For this purpose some service classes with QoS requirements are defined; but the QoS scheduler is not standardized in IEEE802.16. The scheduling mechanism has a significant effect on the performance of WiMAX systems for use of bandwidth and radio resources. Some scheduling algorithms have been introduced by researchers; but they only provide some limited aspects of QoS. An intelligent decision support system is therefore necessary for scheduling. In this paper a fuzzy based scheduling system is proposed for compounds of real-time and non-real-time polling services which provide QoS requirements and fairness in dynamic conditions. A series of simulation experiments have been carried out to evaluate the performance of the proposed scheduling algorithm in terms of latency and throughput QoS parameters. The results show that the proposed method performs effectively regarding both of these criteria and achieves proportional system performance and fairness among different types of traffic.