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Publication Date: 0
pp. 429-463
Most of the weight of the proton exchange membrane (PEM) fuel cell stack is in the bipolar plates. The main function of bipolar plates is uniform distribution of gas reactants as well as distribution of cooling fluid (water or air) inside the fuel cell. Therefore, the plate design and the characteristics of the gas and cooling channels inside them are essential to the operation of the PEM. Although reactive gas channels and cooling channels perform separately, there are many similarities between them. For example, gas channels should be designed so that distribution of reactive gases on the electrode surfaces is uniform. Also, cooling channels should be designed so that temperature distribution inside the fuel cell is uniform. Further, pressure drop of reactive gases inside the gas channels and the fluid inside the cooling channels must be minimal. In this chapter, initially the characteristics, functions and making materials of bipolar plates along with the to make channels inside of them are investigated. Afterwards, gas channels, cooling channels and effects of the shape and size of channels on the PEM fuel cell performance are studied. Finally, different configurations of gas and cooling channel with emphasizing on the new configurations of these channel are researched simultaneously. © 2022 Elsevier Inc. All rights reserved.
Publication Date: 0
2pp. 1343-1352
The ultra-fast charging capability, distinct properties, fine performance and high capacity of nickel cadmium (Ni-Cd) and nickel metal hydride (Ni-MH) batteries along with their limited weight and size are very attractive for use in many applications including cordless and portable devices, emergency and standby power, telecommunication equipments, photovoltaic systems, electric vehicle, satellite and space craft and power plant supporting equipments. However, the limitation on their temperature requires a detail thermal analysis of these batteries. Thermal behavior of batteries are effected by their boundary conditions, type and construction, and more importantly by their chemical reaction. The purpose of this study is to investigate the effect of temperature on thermal behavior of the Ni-Cd and Ni-MH batteries. The governing equation is the transient and non-linear differential energy equation subjected to non linear radiation boundary conditions and source term. To solve the transient and non-linear governing differential energy equation a control volume based finite difference code is utilized. In formulation of the governing differential energy equation, the Ni-Cd and Ni-MH properties (K, C, ρ) are not constant and the chemical characteristic of the Ni-Cd and Ni-MH batteries, source term, vary with location and time. Calculated thermal characteristic of each battery is then compared to experimental results. The result shows that Ni-MH battery is thermally more suitable for space application and satellite. Copyright © 2004 by ASME.
In this entry, photo-reactors for catalytic solar hydrogen production are introduced and explained. To be an economical environmentally benign and sustainable pathway, hydrogen should be produced from a renewable energy source, i.e., solar energy. Solar driven water splitting combines several attractive features for sustainable energy utilization. The conversion of solar energy to a type of storable energy has crucial importance. In the first part of the entry, background information is presented regarding different photo-reactor configurations for water dissociation with light energy to generate hydrogen. The photo-electrochemistry of water splitting is discussed, as well as photo-catalytic reaction mechanisms. The design and scale-up of photo-reactors for photo-catalytic water splitting are explained by classification of light-based hydrogen production systems. At the end, a new photo-catalytic energy conversion system is analyzed for continuous production of hydrogen at a pilot-plant scale. Two methods of photo-catalytic water splitting and solar methanol steam reforming are investigated as two potential solar-based methods of catalytic hydrogen production. The exergy efficiency, exergy destruction, environmental impact, and sustainability index are investigated for these systems. The light intensity is found to be one of the key parameters in design and optimization of the photo-reactors, in conjunction with light absorptivity of the catalyst. © Springer Science+Business Media New York 2013. All rights reserved.
In this paper, an exergy-economic model is developed to analyze the performance of a direct steam solar tower - steam turbine - organic Rankine cycle (ORC) power plant under different working conditions. The solar power plant is connected to a power grid, and it is integrated with a hydrogen storage system. The hydrogen storage system is composed of an electrolyser, fuel cell, steam turbine and organic Rankine cycle. When solar energy is not available, electrical power is generated by the fuel cell, steam turbine and ORC using the hydrogen produced by the electrolyzer. The analyses are made for the maximum solar irradiation that is available in the city of YAZD in Iran. The effects of the current density and operating temperature on the performance of the solid oxide electrolyzer cell (SOEC) and solid oxide fuel cell (SOFC) are investigated. The effect of solar irradiation on the energy and exergy efficiencies of the cycle is investigated. The results indicate that increase of the solar irradiation leads to an increase of the energy and exergy efficiencies of the cycle. The solar tower has the highest exergy destruction and capital investment cost. © 2022 Proceedings of WHEC 2022 - 23rd World Hydrogen Energy Conference: Bridging Continents by H2. All rights reserved.
Determination of forming limit in sheet metal forming processes is very important and can reduce the number of costly trials. Therefore numerous numerical and experimental analyses have been reported. In this paper, 3D model of hydro-forming process of T-shape tube was simulated by finite element method. An integral ductile damage model, coupled with von Mises plastic criterion, has been applied to predict where and when onset of ductile rupture occurs in the process. Model is based on damage evolution and accounts nonlinear strain paths. Results have been compared with experimental tests and empirical observations. Because of bending effects and nonlinear strain paths assumptions, the ductile damage model showed good agreement with experimental tests and empirical observations. The results were satisfactory and acceptable. Hence ductile damage model can be used as a reliable criterion in prediction of ductile fracture in sheet metal forming processes.
Afshari, E. ,
Asghari, S. ,
Jahantigh, N. ,
Shamsizadeh, P. Publication Date: 0
pp. 417-440
Work production systems cannot convert all input energy into useful work, and in these systems, always a part of the input energy is rejected to the environment in the form of heat. Therefore, the efficiency of work production systems is limited. In these systems, one of the limiting factors of the work production rate is the disposal of the produced heat during the process. The lack of proper heat dissipation increases the temperature of the system and its various parts of damages. Cooling system is an inseparable part of work production systems. The cooling system can be very simple (a natural circulation air-cooling system) or very complex (a nuclear facility cooling system). Simple cooling systems are usually used for low energy production rates (a few watts) and complex systems for high production rates (several hundred megawatts). The polymer electrolyte membrane (PEM) fuel cell is not excluded from this issue. In addition to the production of electric power, heat is produced in the PEM fuel cell, which is even slightly more than the production power. Therefore, one of the most important challenges that affects the use of this fuel cell is the issue of heat removal from the cell and heat management in it, which is done by a cooling system. © 2023 Elsevier Inc. All rights reserved.
Publication Date: 2004
1pp. 921-927
This paper deals with design and analysis of intermittent supersonic wind tunnels. System can be constructed by allowing air at atmospheric pressure to pass through a converging-diverging nozzle, a test section and a diffuser into a vacuum tank. The governing equations of compressible fluid flow have been solved numerically using flux vector splitting method to obtain running time under which it works at the design Mach number. The formulation has been tested on the theory of quasi one-dimensional compressible flow. The numerical results are in good agreement with the results of the theory.
Poursina, M. ,
Antonio c.a.c., ,
Castro c.f., ,
Parvizian j., ,
Sousa l.c., Publication Date: 2004
Engineering Computations (02644401) 21(6)pp. 631-650
A numerical method for shape optimisation in forging is presented. The god of the optimisation is to eliminate work-piece defects that may arise during the forging process. A two-dimensional finite element code has been developed for the simulation of the mechanical process. The material is incompressible and it follows the Norton-Hoff law. To deal with contact constraint the velocity projection algorithm is used. The optimisation process is conducted using a genetic algorithm supported by an elitist strategy. A new genetic operator called adaptive mutation has been developed to increase the efficiency of the search. The developed scheme is used to design optimal preform shapes for several axisymmetric examples. Continuous and discrete design variables are considered. The objective function of the optimisation problem is associated with the quality of the final product. Comparing the obtained optimal results with the literature validates the proposed optimisation method.
Publication Date: 2005
6pp. 291-298
Seat cushion is in the primary load path between the seat and the occupant, and the potential for injuries to an occupant in an accident highly depends on it. The seat cushion is able to dissipate the kinetic energy due to impact in a controlled manner. Wide varieties of energy absorbing materials are used in aircraft interiors for occupant safety and ergonomic purposes. Flexible polyurethane foams are one among those used in seat cushions. Although comfort and aesthetics play an important role in the seat cushion design, safety is among the top criteria. Studies on seat cushions have demonstrated that the seat cushions generally amplify the lumbar/pelvis transmitted load to the occupant, making the seat cushion design further complicated for crashworthy design. The certification of seat cushion requires that their performance be demonstrated by dynamic full scale sled testing. Due to the high costs involved in dynamic testing, a mathematical hybrid multi-body model is developed in this study to simulate the dynamic responses of a bare iron seat, the seat cushion and the occupant represented by crash test dummy. The model is utilized to predict the lumbar load sustained when subjected to the FAR Part 23 and 25 dynamic test conditions for transport and general aviation category aircraft. The model is also used to determine the relative displacement and velocity of occupant against the seat pan. The results from the dynamic model are validated with full-scale sled tests performed at the National Institute for Aviation Research (NIAR), and hence can be utilized as a design tool for the selection of proper seat cushions. Copyright © 2005 by ASME.
Alshaer b.j., ,
Nagarajan h., ,
Beheshti, H. ,
Lankarani, H.M. ,
Shivaswamy s., Publication Date: 2005
Journal of Mechanical Design (10500472) 127(3)pp. 493-498
Clearances exist in kinds of joints in multibody mechanical systems, which could drastically affect the dynamic behavior of the system. If the joint is dry with no lubricant, impact occurs, resulting in wear and tear of the joint. In practical engineering design of machine, joints are usually designed to operate with some lubricant. Lubricated journal bearings are designed so that even when the maximum load is applied, the joint surfaces do not come into contact with each other. In this paper, a general methodology for modeling lubricated long journal bearings in multibody mechanical systems is presented. This modeling utilizes a method of solving for the forces produced by the lubricant in a dynamically loaded long journal bearing. A perfect revolute joint in a multibody mechanical system imposes kinematic constraints, while a lubricated journal bearing joint imposes force constraints. As an application, the dynamic response of a slider-crank mechanism including a lubricated journal bearing joint between the connecting rod and the slider is considered and analyzed. The dynamic response is obtained by numerically solving the constraint equations and the forces produced by the lubricant simultaneously with the differential equations of motion and a set of initial conditions numerically. The results are compared with the previous studies performed on the same mechanism as well a dry clearance joint. It is shown that in a multibody mechanical system, the journal bearing lubricant introduces damping and stiffness to the system. The earlier studies predict that the order of magnitude of the reaction moment is twice that of a perfect revolute joint. The proposed model predicts that the reaction moment is within the same order of magnitude of the perfect joint simulation case. Copyright © 2005 by ASME.
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