Dynamic modeling and simulation of air-breathing proton exchange membrane fuel cell

Small fuel cells have shown excellent potential as alternative energy sources for portable applications. One of the most promising fuel cell technologies for portable applications is air-breathing fuel cells. In this paper, a dynamic model of an air-breathing PEM fuel cell (AB-PEMFC) system is presented. The analytical modeling and simulation of the air-breathing PEM fuel cell system are verified using Matlab, Simulink and SimPowerSystems Blockset. To show the effectiveness of the proposed AB-PEMFC model, two case studies are carried out using the Matlab software package. In the first case study, the dynamic behavior of the proposed AB-PEMFC system is compared with that of a planar air-breathing PEM fuel cell model. In the second case study, the validation of the air-breathing PEM fuel cell-based power source is carried out for the portable application. Test results show that the proposed AB-PEMFC system can be considered as a viable alternative energy sources for portable applications.     

Identification of bioactive compounds with GC–Q-TOF–MS in the extracts from Clinacanthus nutans using subcritical carbon dioxide extraction

Subcritical carbon dioxide Soxhlet extraction of biologically active compounds from Clincanthus nutans was investigated by full factorial design to identify and optimize the factors (particle size and co-solvent) affecting extract yield, antioxidant activity, total phenolic content, total flavonoid content, and α-glucosidase inhibitory activity. An average of 3.103% yield, 98.90% antioxidant activity, 49.40 mg/g (GAE) TPC, 43.76 mg/g (RE), and 88.58% AGI activity can be achieved using the optimum levels of independent variables. The GC-Q-TOF MS identification of optimized extract shown that different classes of phytoconstituents were successfully separated by CO₂-Soxhlet to produce potential antioxidant and α-glucosidase inhibitory activity.     

Metallurgical and tribological investigations of aluminium bronze bushes made by a novel centrifugal casting technique

Aluminium bronzes have been used as high strength, corrosion and wear resistance alloys for many decades. However, the alloy has a narrow solidification range and a complex nature which has confined its use to a limited field of applications. Published data on the wear characteristics and the metallurgical nature of the alloy system is limited, leaving wide possibilities for research. In the work described in this paper a study has been made of the metallurgical and tribological characteristics of aluminium bronzes conforming to BS 1400 AB2 specification. A novel centrifugal casting technique using a bonded sand lining integrated into a standard rotating die was adapted to cast a series of test bushes. Mechanical and microscopic aspects are studied and an attempt is made to correlate the physical properties with the tribological behaviour of the bushes. The results show that the test behaviour of the test bush was in some respects better than that of commercially produced bushes made by forging techniques. Detrimental embrittlement, due to ‘self annealing’ is significantly reduced by the adoption of the novel centrifugal casting technique referred to above.     

Thermoeconomic optimization for a finned‐tube evaporator configuration of a roof‐top bus air‐conditioning system

This paper presents a methodology of a design optimization technique that can be useful in assessing the best configuration of a finned‐tube evaporator, using a thermoeconomic approach. The assessment has been carried out on a direct expansion finned‐tube evaporator of a vapor compression cycle for a roof‐top bus air‐conditioning (AC) system at a specified cooling capacity. The methodology has been conducted by studying the effect of some operational and geometrical design parameters for the evaporator on the entire cycle exergy destruction or irreversibility, AC system coefficient of performance (COP), and total annual cost. The heat exchangers for the bus AC system are featured by a very compact frontal area due to the stringent space limitations and structure standard for the system installation. Therefore, the current study also takes in its account the effect of the variation of the design parameters on the evaporator frontal area. The irreversibility due to heat transfer across the stream‐to‐stream temperature difference and due to frictional pressure drops is calculated as a function of the design parameters. A cost function is introduced, defined as the sum of two contributions, the investment expense of the evaporator material and the system compressor, and the operational expense of AC system that is usually driven by an auxiliary engine or coupled with the main bus engine. The optimal trade‐off between investment and operating cost is, therefore, investigated. A numerical example is discussed, in which a comparison between the commercial evaporator design and optimal design configuration has been presented in terms of the system COP and evaporator material cost. The results show that a significant improvement can be obtained for the optimal evaporator design compared with that of the commercial finned‐tube evaporator that is designed based on the conventional values of the design parameters. Copyright © 2007 John Wiley & Sons, Ltd.     

Designing feedforward command shapers with multi-objective genetic optimisation for vibration control of a single-link flexible manipulator

This paper presents investigations into the design of a command-shaping technique using multi-objective genetic optimisation process for vibration control of a single-link flexible manipulator. Conventional design of a command shaper requires a priori knowledge of natural frequencies and associated damping ratios of the system, which may not be available for complex flexible systems. Moreover, command shaping in principle causes delay in system's response while it reduces system vibration and in this manner the amount of vibration reduction and the rise time conflict one another. Furthermore, system performance objectives, such as, reduced overshoot, rise time, settling time, and end-point vibration are found in conflict with one another due to the construction and mode of operation of a flexible manipulator. Conventional methods can hardly provide a solution, for a designer-oriented formulation, satisfying several objectives and associated goals as demanded by a practical application due to the competing nature of those objectives. In such cases, multi-objective optimisation can provide a wide range of solutions, which trade-off these conflicting objectives so as to satisfy associated goals. A multi-modal command shaper consists of impulses of different amplitudes at different time locations, which are convolved with one another and then with the desired reference and then used as reference (for closed loop) or applied to system (for open loop) with the view to reduce vibration of the system, mainly at dominant modes. Multi-objective optimisation technique is used to determine a set of solutions for the amplitudes and corresponding time locations of impulses of a multi-modal command shaper. The effectiveness of the proposed technique is assessed both in the time domain and the frequency domain. Moreover, a comparative assessment of the performance of the technique with the system response with unshaped bang–bang input is presented.     

Degradability of kenaf dust-filled chitosan biocomposites

Degradability of environmentally friendly of kenaf dust-filled chitosan biocomposites was investigated. Biocomposites of chitosan/kenaf was prepared via solution blending method. Diluted acetic acid was used as solvent for dissolving the chitosan powder. High speed homogenizer was used to assist the dispersion of kenaf dust in chitosan solution. Five types of composites containing different amounts of kenaf dust; 0%, 7%, 14%, 21% and 28% were fabricated. Degradability of each composites were evaluated against seven different solutions; (0.1, 0.5, 1.0) M of H₂SO₄, (0.1, 0.5, 1.0) M of NaOH and distilled water. Degradation behaviors were evaluated based on percent of weight gain, percent of water absorption and degree of swelling. It was noted that, chitosan film which contains higher kenaf dust content showed greater stability against seven different solutions due to lower degree of swelling compared to chitosan film having lesser amount of kenaf dust. It was observed that the composites showed greater resistance towards alkaline and acidic solution as compared to distilled water.     

Prediction of sand mass and organic matter distribution via in situ measured wet sediment bulk density profile

The objective of the study is to develop a spatial prediction model of sand mass and organic matter distribution in an urban stormwater holding pond using in situ measured wet sediment bulk density profile data to spatially distinguish the most likely contaminated sediment deposit areas. The wet bulk density profiles of deposited sediment at 25 locations in the Berembang (Malaysia) stormwater holding pond were measured using a single-probe nuclear density gauge. The sand and organic matter compositions of the surface sediment sample, 5 cm thickness from the bed surface, were determined. Discriminant analysis (DA) was conducted to generate two Fisher’s linear discriminant functions for the prediction of sand mass and organic matter composition areas, respectively. The linear discriminant functions generated better area classifications of surface organic matter composition compared to the sand mass distribution using wet sediment bulk density data measured at more than 15 cm depth levels.     

Circulation rates of boiling liquids in a vertical tube

An experimental study of heat transfer to boiling liquids under natural convective flow has been carried out in a single tube vertical thermosiphon reboiler to investigate the effect of heat flux and submergence on circulation rates. The test liquids used were distilled water, various concentrations of propan-2-ol in water and their azeotrope. The test section was an electrically heated stainless steel tube of 25.56 mm i.d., 28.85 mm o.d. and 1900 mm long with twenty-one spot welded copper constantan thermocouples to measure the variations in wall temperature along its axis. The uniform heat fluxes in the range of 3.5–42.4 kW/m² were employed while inlet liquid sub-cooling varied from 0.2 to 30.7 °C. The liquid submergence levels were maintained in the range 30–100%. The typical experimental data has been graphically presented and discussed. An empirical correlation has been developed from the experimental data of the present study through regression analysis.     

Extraction and separation of molybdenum(VI) from acidic media by fatty hydrazides

BACKGROUND: The increasing demand for molybdenum has encouraged the development of low‐cost and environmentally friendly extractants to recycle and recover this metal. In the present study, solvent extraction of Mo(VI) from acidic media using a mixture of fatty hydrazides synthesised from palm olein as the extractant was carried out. The effects of various parameters such as acid, diluent, contact time, extractant concentration, metal ion concentration and stripping agent and the separation of Mo(VI) from other metal ions such as Co(II), Ni(II), Al(III) and Mn(II) were investigated. RESULTS: It was found that the extraction of Mo(VI) into the organic phase involved the formation of 1:3 complexes. Mo(VI) was successfully separated from commonly associated metal ions such as Ni(II), Co(II), Al(III) and Mn(II). Mo(VI) stripping from the loaded organic phase was studied using different acidic and alkaline solutions and was found to be optimal with ammonium hydroxide solution. CONCLUSION: These results are useful for the development of a method to recover Mo(VI) from acidic media utilising fatty hydrazides as the extractant. Copyright © 2008 Society of Chemical Industry     

Social learning for adaptive delta management: Tidal River Management in the Bangladesh Delta

ABSTRACT

The article analyzes Tidal River Management in Bangladesh from a social learning perspective. Four cases were investigated using participatory assessment. Knowledge acquisition through transformations in the Tidal River Management process was explored as an intended learning outcome. The study finds that social learning occurred more prominently at the individual stakeholder level and less at the collective level. For Tidal River Management to be responsive and sustainable, especially in times of increased uncertainty and climate vulnerability, more attention needs to be paid to coordination and facilitation of multi-level learning that includes all stakeholders.