A graphical approach for confidence limits of optimal preventive maintenance cycles

Facilities management (FM) is the management of infrastructure resources and services to support and sustain the operational strategy of an organization over time. Maintenance is often the business process that has not been optimized and is considered as a liability of business operations. Therefore, extensive studies have been done to determine the optimal replacement interval for irreparable parts of repairable systems where typically the time between failures is characterized by lifetime distribution in which the parameters are estimated from failure data. As a result, the optimal preventive maintenance (PM) interval computed is exposed to sampling risk as the repair cost and failure data used for estimation are typically highly censored due to issues related to data collection and unobserved failures. In this paper, we present a graphical approach to obtain the confidence interval for the optimal PM interval that resulted from sampling variations parameter estimates. The proposed methodology is applied in the context of FM as a strategy for opportunistic replacement and for the purpose of validating the cost components in maintenance. Copyright © 2008 John Wiley & Sons, Ltd.     

Development and test of a new catalytic converter for natural gas fuelled engine

This paper presents characteristics of a new catalytic converter (catco) to be used for natural gas fuelled engine. The catco were developed based on catalyst materials consisting of metal oxides such as titanium dioxide (TiO₂) and cobalt oxide (CoO) with wire mesh substrate. Both of the catalyst materials (such as TiO₂ and CoO) are inexpensive in comparison with conventional catalysts (noble metals) such as palladium or platinum. In addition, the noble metals such as platinum group metals are now identified as human health risk due to their rapid emissions in the environment from various resources like conventional catalytic converter, jewelers and other medical usages. It can be mentioned that the TiO₂/CoO based catalytic converter and a new natural gas engine such as compressed natural gas (CNG) direct injection (DI) engine were developed under a research collaboration program. The original engine manufacture catalytic conveter (OEM catco) was tested for comparison purposes. The OEM catco was based on noble metal catalyst with honeycomb ceramic substrate. It is experimentally found that the conversion efficiencies of TiO₂/CoO based catalytic converter are 93%, 89% and 82% for NO_x, CO and HC emissions respectively. It is calculated that the TiO₂/CoO based catalytic converter reduces 24%, 41% and 40% higher NO_x, CO and HC emissions in comparison to OEM catco respectively. The objective of this paper is to develop a low-cost three way catalytic converter to be used with the newly developed CNG-DI engine. Detailed review on catalytic converter, low-cost catalytic converter development characteristics and CNGDI engine test results have been presented with discussions.     

Synthesis and Characterization of Molecularly Imprinted Polymer Membrane for the Removal of 2,4-Dinitrophenol

Molecularly imprinted polymers (MIPs) were prepared by bulk polymerization in acetonitrile using 2,4-dinitrophenol, acrylamide, ethylene glycol dimethacrylate, and benzoyl peroxide, as the template, functional monomer, cross-linker, and initiator, respectively. The MIP membrane was prepared by hybridization of MIP particles with cellulose acetate (CA) and polystyrene (PS) after being ground and sieved. The prepared MIP membrane was characterized using Fourier transform infrared spectroscopy and scanning electron microscopy. The parameters studied for the removal of 2,4-dinitrophenol included the effect of pH, sorption kinetics, and the selectivity of the MIP membrane. Maximum sorption of 2,4-nitrophenol by the fabricated CA membrane with MIP (CA-MIP) and the PS membrane with MIP (PS-MIP) was observed at pH 7.0 and pH 5.0, respectively. The sorption of 2,4-dinitrophenol by CA-MIP and PS-MIP followed a pseudo–second-order kinetic model. For a selectivity study, 2,4-dichlorophenol, 3-chlorophenol, and phenol were selected as potential interferences. The sorption capability of CA-MIP and PS-MIP towards 2,4-dinitrophenol was observed to be higher than that of 2,4-dichlorophenol, 3-chlorophenol, or phenol.     

Integrated decision support system for waste minimization analysis in chemical processes

The need to build and operate environmentally friendly plants has challenged the chemical industry to consider waste minimization or even elimination starting from the early stages of process development. A thorough waste minimization analysis requires specialized expertise and is laborious, time-consuming, expensive, and knowledge-intensive. This has caused a major technical barrier for implementing waste minimization programswithin the industry. Previously, we had reported a systematic methodology and a knowledge-based system, called ENVOPExpert, for identifying waste minimization opportunities in chemical processes. In this paper, we propose an integrated qualitative-quantitative methodology to identify waste minimization alternatives and assess their efficacy in terms of environmental impact and process economics. A qualitative analysis is first conducted to identify the sources of wastes and to propose alternatives for eliminating or minimizing them. Environmental impact of each alternative is then calculated by doing a quantitative pollutant balance. The capital expenditure required for implementing the alternative and the resulting plant operating costs are also calculated and used in the evaluation of the waste minimization alternatives. Through this, practical and cost-effective options can be identified. This methodology has been implemented as an integrated decision support system and tested using the hydrodealkylation process case study with satisfactory results.     

Effect of Ba and Zn doping in Bi2Pb0.6Sr2Ca2Cu3Oδ superconductors using ac susceptibility measurements

Ac complex susceptibility, = – i, measurements were done on the samples doped with barium and zinc (Bi₂Pb_0.6Sr₂Ca_{2 – x}M_xCu₃O, M = Ba, Zn and x = 0.02 and 0.10). The data of shows that coupling of the grains in Zn-doped samples are weaker than that of Ba-doped samples and hence it could be concluded that Zn-doped samples are dominated by the S-I-S type of weak links, whereas the Ba doped samples are dominated by the S-N-S weak links. Calculated values of I₀ is three times higher in the Ba doped samples such that the values of Josephson coupling energy, E_j is four times that of Zn doped samples. Analysis based on the sensitivity of the data of d(T)/dT versus temperature furnished further information on the two-step transitions related to the coupling of the grains in both systems.     

An adaptive sliding mode differentiator for actuator oscillatory failure case reconstruction

This paper proposes an adaptive sliding mode super-twisting differentiator which allows the gains to adapt based on the ‘quality’ of the sliding motion. A Lyapunov based analysis for the adaptive super-twisting scheme is presented to demonstrate its properties. As an example, the adaptive differentiator proposed in this paper has been used as part of a nonlinear FDI scheme for an Oscillatory Failure Case (OFC) in an actuator. The FDI scheme requires an estimate of the rod speed which is provided by the adaptive super-twisting differentiator. Due to the conditions in which the actuator operates, normally the differentiator gains are initialised at low values to ensure good rod speed estimation in fault free conditions. However for large amplitude/frequency OFCs, the gains must adapt in order to maintain sliding and provide a good estimation. Simulations on a high fidelity nonlinear aircraft benchmark model have been carried out for both liquid and solid OFCs.     

Modeling of vial and ball motions for an effective mechanical milling process

Mechanical milling (MM) is referred to a solid state size reduction process where work materials in the form of coarse particulates are broken into the ultimate fineness by means of mechanical impact created by collisions of the work materials and the milling media which are placed inside a reciprocating vial. Many milling techniques have been so far developed to improve the process. However, the efficiency of MM process is still below satisfactory in terms of energy balance, where the energy consumed by the process of reduction is still very low compared to the energy supplied to perform the milling process itself. This contributes to high energy losses and proportionally to the span of processing time. Other major problems inherent in the process are contamination by the balls and the vial materials into the work materials, and process temperature that could influence the properties of milled materials. Since MM process utilizes the energy generated by impact upon the collisions of the balls against the work materials, it is important to understand the motions of the balls, the work materials, and the vial, which are the sources of the generation of impact energy. To obtain an optimized processing condition, the motions of vial and ball in relationship with the work materials should be designed in such a way to ensure the optimum impact energy is consumed by the work materials for the size reduction purposes. This paper presents a physical model for work materials, balls, and vial collisions based on different ways of motions. Using this model, higher impact could be achieved. These would lead to the reduction of milling time, contamination, as well as milling temperature.     

Application of micromechanical models for predicting fracture toughness of sulphide controlled Fe 510 steels

As cleavage fracture follows a tensile stress criterion, it is possible to predict fracture toughness K_Ic as a function of temperature when small scale yielding stress distribution in combination with the Ritchie, Knott and Rice criterion is used. With increasing temperature and thus pronounced plasticity the crack tip blunts and the experimental values are underestimated. The Schmidtmann and Nierhoff proposal for modifying the cleavage stress criterion and introducing the effect of crack tip blunting is compared with the RKR-model and with experimentally determined K_Ic-values for four different qualities of Fe 510 steels. The steels mainly differ in sulphur content and sulphur shape control. Thus the effect of sulphur on cleavage fracture will be discussed.     

Improvement of mechanical performance of epoxy resins filled with cobalt and chromium powders

Epoxy/ powder metal composites have interesting electrical properties, becoming conductors above the percolation threshold. To complete this study, mechanical investigations have been carried out to show the influence of the fillers on the mechanical performance of these composites. In this framework, different epoxy/metallic powders (Cobalt, Chromium) composites were prepared. Scanning Electron Microscopy showed that the dispersion of the metallic fillers in the matrix is almost homogeneous. The dynamic mechanical thermal analysis (DMTA) measurements showed the dependence of the viscoelastic parameters with the frequency, temperature, nature, and content of fillers. The main relaxations observed are the primary α relaxation (associated to the glass transition, T_g) and a secondary β relaxation. A second DMTA run on the same samples showed a slight increase of the T_g. It clearly showed that the used metallic fillers improve the mechanical properties of the obtained composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hydrolytic Depolymerization of PET in a Microwave Reactor

Recycling of PET was examined using hydrolytic depolymerization in an alkaline solution under microwave irradiation. The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. The main products were the monomers TPA and EG. The effect of reaction temperature, time, amount of PET and alkaline concentration on the degree of PET depolymerization and TPA recovery was investigated. Microwave irradiation was found to reduce the time needed to achieve a specific degradation of PET significantly, with almost complete depolymerization occurring in 30 min at 180 °C and only 46 W of microwave power. Using a phase transfer catalyst (TOMAB) resulted in the same amount of unreacted PET but at significantly lower depolymerization temperatures.