Abstract: Assembly pressure plays an important role in the factors affecting the performance of a PEM fuel cell. An insufficient clamping pressure may cause large contact resistance and thus lower the cell performance. On the other hand, over-clamping may reduce the porosity and permeability of the gas diffusion layer (GDL) and also result in poor cell performance. Therefore, it is very important to determine the proper assembly pressure for obtaining optimal performance. In this study, we design a special test fixture to evaluate the effect of assembly pressure on the performance of a PEM fuel cell. Without disassembling the fuel cell, the clamping pressure can be adjusted in situ to measure the cell performance directly and precisely. The unique single cell design eliminates the influence of gasket around the membrane electrode assembly (MEA) and makes it possible to estimate the compression effect of GDL independently. Three different types of carbon paper are used in the experiments as the GDLs. The variations of water contact angle, gas permeability, and in-plane electrical resistivity with the assembly pressure are also measured to explore the effects of assembly pressure on these physical properties. The results show that an optimal assembly pressure is always observed in each case, indicating an adequate compression on GDL is quite necessary for fuel cells.
Abstract: In this paper, Self Phase Modulation (SPM) in chalcogenide As2Se3 glass Photonic Crystal Fiber (PCF) is numerically studied by combining the fully vectorial effective index method (FVEIM) and Split Step Fourier Method (SSFM). The FVEIM is used to calculate the variation of effective refractive index of guided mode (neff), effective area (Aeff), dispersion and non-linear coefficient (γ) with wavelength for different designs of chalcogenide As2Se3 PCF. The FVEIM solves the vector wave equations and SSFM solves non linear Schrödinger Equation (NLSE) for the different designing parameter of As2Se3 PCF. In case of Self Phase Modulation (SPM), spectral width of the obtained output pulse at d/Λ=0.7 is 1.5 times greater than width of the output pulse obtained at d/L=0.3 using SSFM. Thus we can get the desired spectral broadening just by tailoring the design parameters of the PCF.
Abstract: In this paper, we compare the dispersion properties (flattened, zero and negative dispersion) and effective area in hexagonal and square lattice PCF with different hole-to-hole spacing (Λ) and air hole diameter (d) by using Fully Vectorial Effective Index Method (FVEIM). The analysis is carried out in wavelength range from 1.3 µm to 1.6 µm. We also use plane wave expansion method for comparison of effective cladding index in both above lattices.
Abstract: Piezoelectric transformers are electronic devices made from piezoelectric materials. The piezoelectric transformers as the name implied are used for changing voltage signals from one level to another. Electrical energy carried with signals is transferred by means of mechanical vibration. Characterizing in both electrical and mechanical properties leads to extensively use and efficiency enhancement of piezoelectric transformers in various applications. In this paper, study and analysis of electrical and mechanical properties in forms of potential and displacement distribution throughout the volume, respectively, are discussed and especially focused on around its natural frequency. This paper proposes a set of quasi-static mathematical model of electro-mechanical coupling for piezoelectric transformer by using a set of partial differential equations. Computer-based simulation utilizing the three-dimensional finite element method (3-D FEM) is exploited as a tool for calculation in two purposes. The first use is developed the 3-D FEM for identifying its natural frequencies while the second use is for visualizing potentials and displacements distribution within the piezoelectric transformer. The computer simulation based on the use of the FEM has been developed in MATLAB programming environment. In addition, which satisfactory results of natural frequencies are compared with those obtained from the experiment and the accuracy of 3-D FEM model is confirmed.
Abstract: In this paper, an in house production of a 0.5hp induction motor’s rotor is investigated. This investigation considers the induction motor’s efficiency and losses dissipation as an important aspect to determine the rotors efficiency. Through out this project, a new rotor which has 0.35mm steel sheet thickness and 10mm rotor bar slot size is constructed and compared with the existing rotor which has 0.50mm steel sheet thickness and 10mm rotor bar slot size. Once the construction phase of the rotor has been completed an in house motor experiment is done such as the no load, blocked rotor and dc resistance test. Result shows that thinner steel sheet (0.35mm) of the constructed rotor increase the efficiency up to 3.2% and reduces the losses to 17.2 watts compare to the thicker steel sheet rotor (0.5mm). An economical aspect is presented to show the amount of energy and money that can be saved from replacing the existing rotor (0.5mm) with a thinner rotor (0.35mm). As for the annual energy saving (AES) and total cost saving (TCS), the new rotor manage to save 138.7kWh per year and utility billing by RM45.51 per year per motor.
Abstract: The Issue of daylight inclusion in the office buildings has got the significant importance in the recent years. Using this light, dependence on artificial lighting sources can be reduced which results in the energy efficiency. This study aims to determine the optimal Window Wall Ratios in the office buildings of Tehran to take the advantage of daylight abundance regarding the climatic features without making the designers involved with the complicated calculations. All the research analyses have been done based on the window models comparison through the computational simulations. After the primary analyses, the models were developed and put to the test again. The study shows that among from all the tested models, an optimal WWR range for the office buildings of Tehran can be proposed.
Abstract: A thermodynamic analysis was performed for hydrogen production from ethanol reforming and oxidation in supercritical water (SCW) conditions. The minimization of Gibbs free energy was used to calculate the equilibrium composition to investigate the effect of operating conditions, pressure, temperature, H2O2:EtOH molar ratio and H2O:EtOH molar ratio, on product yields. The theoretical results indicated that the yields of hydrogen and carbon monoxide decreased as the pressure increased but a H2/CO ratio at atmospheric pressure was lower than that at SCW conditions. High temperatures increased the efficiency of hydrogen production although the amount of carbon monoxide also increased. The presence of oxygen led to great decreases in methane oxidized to carbon dioxide and water. The spending of some hydrogen oxidized to water resulting in a lower hydrogen yield. High H2O:EtOH ratios increased the yields of hydrogen and carbon dioxide but decreased the methane and carbon monoxide production. It is possible to conclude that high temperature, high H2O:EtOH ratio and low addition of oxygen should lead to best results in the SCWO of ethanol.
Abstract: The purpose of this study was to investigate the effect of particle size distribution on the mechanical properties of granular sulphur and its relation to silo blockage at South Pars Gas Complex Phases 2 & 3. Solid elemental sulphur is a relatively hard, friable crystalline material that tends to break up into smaller particles when subjected to force or stress of any magnitude. Conglomeration of the dust so produced clogs storage silos, making truck loading difficult. Grain size selection is based on the “friability value” and “maximum entropy” for granules in a static state. The model of the behavior of confined granular sulphur is based on the principle of continuum mechanics. Granules were formed by feeding liquid sulphur and water to a rotating granulation drum. Sample granules were classified into different size fractions (300 μm – 4.75 mm) by sieve analysis, and friability tests were done by the Fines 28-inch tumbler S5-77 test. Friability and granule size data collected over four years were studied. The implication of field analysis and laboratory tests is that the granule size should be controlled during sulphur solidification while ensuring that only granular material with the correct mechanical characteristics is stored in the silo and shipped.
Abstract: The numerical solution for an edge crack problem in a two-dimensional (2-D) finite piezoelectric media has been discussed using extended finite element method. The four-fold standard enrichment functions are taken in conjugation with the interaction integral to evaluate the intensity factors (IFs). The intensity factors as well as the mechanical energy release rate and the total energy release rate has been analyzed for different electro-mechanical boundary conditions. It is observed that the IFs results are coupled and contrary to analytic solution which shows uncoupled behaviour.
Abstract: The industrial development of the world has increased the demand of petroleum-based fuels sharply which are obtained from limited in certain regions of the world. As a result, most of the countries have to face energy crisis. Hence, it is necessary to look for alternative fuels which can be produced from resources available locally within the country. Lots of researches on biofuels such as alcohol, biodiesel and vegetable oils have been conducted to accelerate the development of a next generation of clean, green biofuels that can compete with fossil fuels in economics and well as performance. Biodiesel is a renewable, domestically produced fuel that has been shown to reduce particulate, hydrocarbon, and carbon monoxide emissions from combustion. In the present study an experimental investigation on emission characteristic of a liquid burner system operating on several percentage of biodiesel and gas oil is carried out. Samples of exhaust gas are analysed with Testo 350 Xl. The results show that biodiesel can lower some pollutant such as CO, CO2 and particulate matter emissions while NOx emission would increase in comparison with gas oil. They also demonstrate growth in temperature of exhaust gas with increase of percentage of biodiesel from B0 to B40. The results indicate there may be benefits to using biodiesel in industrial processes.