Durability and economics investigations on triple stack configuration and its power management strategy for fuel cell vehicles

The durability and cost are the most important bottlenecks in fuel cell vehicle (FCV) commercialization. To alleviate these two drawbacks, a new power management strategy (PMS) is proposed on a triple fuel cell stack configuration (TFSC) to enhance the fuel cell lifetime in a commercialized FCV such as Toyota-Mirai. The two main innovations of the present study are summarized to: (i) lifetime assessing study of the proposed TFSC under the vehicular condition and comparing them with those of single fuel cell stack configuration (SFSC), and (ii) performing an economics analysis to compute and compare the stack costs of triple and single configurations. The lifetime is calculated based on all the operating modes during the combined driving cycle including start/stop cycles, idling or constant potential operation, load cycling, and high current operation. The result reveals that TFSC improves the lifetime by 18.93% compared to the SFSC. It also indicates that during the FCV lifespan, the stack cost of the TFSC is around 14% less than that of the SFSC, which makes triple stack more feasible.     

Evaluation of tube to collector connection by hydraulic expansion method in PGV-1000 steam generators

Investigations on steam generators failure due to cracking in collector ligaments at perforated parts determined that connection process of the tubes to collector could be one of the main breakdown causes. The stability and strength of tube to collector joint is dependent to the geometry of tube and collector, the joining process and the operational conditions. In this research hydraulic expansion method has been considered as connection method of tube to collector. The Finite Element Method (FEM) was used to simulate the hydraulic expansion process and determine stress condition of the joints. The contact stresses between the tube and collector interface were modeled using contact elements of ANSYS program. Furthermore, the effect of clearance between tube and collector on the residual stresses around of joints was investigated. Some specimens from collector and tube materials were tested at various temperatures and their results were used at rate-independent multi-linear Mises plasticity model for FE analysis. Required connection strength between tube and collector is estimated based on ASME rules and compared with FE results. The results show that the residual tensile stresses could be greatly increased by decreasing of initial clearance. The highest value of residual stresses was observed around of collector holes nevertheless it was considerably lesser than obtained residual stresses in explosive method. The contact pressure and other parameters were in allowable ranges and the friction stresses were negligible.     

Scheduling multi-product tree-structure pipelines

The problem discussed in this paper is short-term scheduling of distribution of petroleum derivatives from a single oil refinery to a number of depots through a tree-structure pipeline. Scheduling product batches in pipelines is a very complex task with many constraints to be considered. Batches of refined products and grades are pumped back-to-back in the pipeline, often with no separation device between batches. In this work a continuous-time, MILP problem representation for tree-structure pipelines is proposed. The approach is successfully applied to a number of pipeline scheduling problems, including a real-world problem. The data and experimental results are reported.     

An investigation on the capability of equal channel angular pressing for consolidation of aluminum and aluminum composite powder

In this study equal channel angular pressing (ECAP) was used as a technique for consolidation of attritioned aluminum powder (45 μm) with varying concentration of nano alumina powders (35 nm) in tube at 200 °C. The effect of ECAP on consolidation behavior of composite powder and mechanical properties of subsequent compacts are presented. It is found that ECAP has the capability of consolidating pure aluminum powder, Al-5 vol% Al₂O₃ and Al-10 vol% Al₂O₃ to near their theoretical density and also declustering of the agglomerated alumina particles after maximum four passes. However full consolidation of Al-15 vol% Al₂O₃ before emanating the cracks on the tube material was not possible and about 7% porosity remains in the compacted composite which degrades the mechanical properties of this composite in comparison to the aluminum composites with 5 vol% and 10 vol% alumina.     

Longitudinal Legendre polynomial expansion of electromagnetic fields for analysis of arbitrary-shaped gratings

The Legendre polynomial expansion method (LPEM), which has been successfully applied to homogenous and longitudinally inhomogeneous gratings [J. Opt. Soc. Am. B24, 2676 (2007)], is now generalized for the efficient analysis of arbitrary-shaped surface relief gratings. The modulated region is cut into a few sufficiently thin arbitrary-shaped subgratings of equal spatial period, where electromagnetic field dependence is now smooth enough to be approximated by keeping fewer Legendre basis functions. The R-matrix propagation algorithm is then employed to match the Legendre polynomial expansions of the transverse electric and magnetic fields across the upper and lower interfaces of every slice. The proposed strategy then enhances the overall computational efficiency, reduces the required memory size, and permits the efficient study of arbitrary-shaped gratings. Here the rigorous approach is followed, and analytical formulas of the involved matrices are given.     

Predicting the critical pre-aging time in ECAP processing of age-hardenable aluminum alloys

Age-hardenable Al alloys may be successfully processed by equal channel angular pressing (ECAP) at room temperature, if the processing is carried out immediately after water quenching from the solution treatment temperature. It is important to estimate the critical time for any age-hardenable alloys, since after this time, ECAP processing will cause catastrophic cracking or segmentation at room temperature. In this study, ECAP processing was carried out on two age-hardenable Al alloys (2014 and 7075) at room temperature. The results demonstrated that the critical time could be predicted successfully by using tensile test curves related to different times after quenching. It is also shown that room temperature ECAP processing of these materials for more than a single pass is not possible and causes damage. However, a single pass will have significant effects on the strength of the material.     

Aging Characteristics of RTV Silicone Rubber Insulator Coatings

The paper reports on tests done on four commercial room temperature vulcanized (RTV) silicone rubber high voltage insulator coatings aimed at achieving information on the relative performance of the coatings with respect to aging. The initial characterization of the coatings includes the identification of the primary filler type, concentration of filler, the amount of free fluid, and the molecular species of the free fluid. Soxhlet extraction and gas chromatography tests show considerable depletion of fluid after accelerated aging tests in acid-water and the associated changes to the physical properties is assessed by standard mechanical tests on coupon size specimens. The effect of acid-water aging on the hydrophobicity is assessed by measurements of the static contact angle and the onset of leakage current in an incline plane test. Several field aged coatings are assessed for residual LMW fluid which is compared to accelerated aging tests.     

Prediction of leakage current of non-ceramic insulators in early aging period

The paper presents a neural network based prediction technique for the leakage current (LC) of non-ceramic insulators during salt-fog test. Nearly 50 distribution class silicone rubber (SIR) insulators with three different voltage classes have been tested in a salt-fog chamber, where the LC has been continuously recorded for at least 100 h. A boundary for early aging period is defined by the rate of change of the LC instead of a fixed threshold value. Consequently, the Gaussian radial basis network has been adopted to predict the level of LC at the early stage of aging of the SIR insulators and is compared with a classical network. The initial values of LC and its rate of change at 10 min intervals for the first 5 h are selected as the input to the network, and the final value of LC of the early aging period is considered as the output of the network. It is found that Gaussian radial basis function network with a random optimizing training method is an appropriate network to predict the LC with a 3.5–5.3% accuracy, if the training data and the testing data are selected from the same type of SIR insulators.     

Developing Equations for Estimating Reference Evapotranspiration in Australia

Quantifying reference evapotranspiration (ET₀) is essential in water resources management. Although, many methods have been developed with different level of accuracy, in this study, two new equations were developed and optimized for estimating ET₀ using Honey-Bee Mating Optimization (HBMO) algorithm. The first eq. estimates ET₀ from extraterrestrial radiation (R_a), relative humidity (RH) and mean daily temperature (T_mean), while the second uses the same parameters except that mean daily temperatures is replaced with maximum daily air temperature (T_max). Both equations were developed using climatic data from eight weather stations in Western Australia and subsequently verified using data from ten sites across Australia. The estimated ET₀ values from both equations versus the FAO56-Penman-Monteith have a coefficient of determination, R², of larger than 0.96. Moreover, the performance of six commonly used methods of estimating ET₀ including Hargreaves-Samani, Thornthwaith, Hamon, Mc Guinness-Bordne, Irmak and Jensen-Haise were assessed and the Hargreaves-Samani method performed better than others. An attempt was made to calibrate the Hargreaves-Samani equation; however, its overall performance did not improved and the two newly proposed equations are suggested to be used in Australia.