Output increase of combined cycle power plants is highly expected in order to deal with tight supply-demand situation of electricity and to save fuel consumption. This paper reports improvement of the output increase method by cooling their suction air using water spray nozzles. The spray nozzles installed previously are pointing to downstream of air flow or downward. We tried to improve its cooling efficiency by optimizing the spray nozzle angle. Laboratory experiments were conducted for that purpose. Suction air area was 2 meter square, and air flow velocity was set to approximately 2 meter/sec. by a blower. Temperature and relative humidity were set to 33 degrees centigrade and 60 percent respectively by air-conditioning units. As a result, a method that the spray nozzles are pointing upstream of air flow showed the best performance. The same tendency was also observed by finite volume analysis using a CFD program. This method was applied at both a working combined cycle power plant of 380 MW and that of 500 MW on trial. Temperature of cooled air was measured using a number of thermocouples set in suction air room at each plant. Consequently, it was observed that the cooling efficiency was improved by ten percent and several percent respectively, and plant output was increased by approximately 2 MW at the 380 MW plant.
Sugar production is the main industry in Tanegashima, Japan. Whilst the sugar mill recycles sugarcane bagasse as a fuel, it concurrently generates large amounts of unused 200 °C heat during operation. Raw sugar is shipped to a refinery in Osaka for the final stages of production, which uses a city gas boiler to continuously generate a large quantity of 150 °C heat. However, factories in Tanegashima need a continuous supply of process steam at temperatures of up to 120 °C. To resolve this spatial and seasonal mismatch of heat, we propose a thermal energy storage and transport system using a zeolite adsorption/regeneration cycle. A process flow diagram of the sugar mill has been developed, and the amount of available heat, the potential storage capacity, and the transportable amount of heat have been calculated. Two scenarios were analyzed, in which the stored heat is shipped to Osaka, or used on the island. This was achieved by calculating the rate-based storage capacity of zeolite, based upon an adsorption and regeneration test. The transportable quantity of zeolite determines the feasibility of using waste heat. In the first case, transport of heat to the sugar refinery in Osaka has little possibility of being implemented. In the second case, transport of heat to a liquor factory in Tanegashima can potentially reduce its usage of heavy oil by 83 %, equivalent to 33 kL/year.
Natural convective flows around V-shaped cavities are encountered in some engineering applications such as over the heat-transfer plates or roofs having triangular-shaped grooves. In order to assess the heat transfer performance of these plates or roofs, detailed information on their flow and heat transfer will be needed. Thus, the experimental investigations have been carried out on natural convection of water induced around a heated, V-shaped open cavity. The open angles, θ, and the side lengths, W / 2, were varied systematically as θ = 90-180° and W / 2 = 25, 50, 100 mm. The flows in the cavity and the surface temperatures were visualized with fine nylon particles and a thermo-chromic liquid crystal sheet, respectively. The results showed that the ambient fluid first descends to the bottom edge of the cavity, and, then, directs to the upper edge of cavity when θ<135°. The local heat transfer coefficients were also measured. The results showed that the heat transfer is enhanced markedly when θ =120°. It is also found that the overall heat transfer coefficients from the cavity θ = 120° and W / 2 = 25 mm became 17% higher than that from the horizontal plate.
Solution and diffusion process of carbon dioxide (CO2) in seawater is important in the research and development of CO2 ocean sequestration technology to mitigate global warming. In this study, solution and diffusion process of single CO2 bubble in seawater and pure water were experimentally studied under various pressures and temperatures to evaluate the transport process of CO2 in seawater. The solution process was conducted in a test vessel. CO2 bubble was generated by a CO2 bubble generator installed at the bottom of the vessel. The diameter of CO2 bubble was recorded using a high speed video camera. The pressure and temperature of liquids were measured by using a pressure transducer and thermocouples. Experimental conditions for the temperature ranged from 277 K to 297 K, and the pressure ranged from around 101 kPa up to 400 kPa. It was obtained that the complete solution time decreases with the increase in pressure due to its higher solubility at a higher pressure. It decreases with an increase in temperature arising from a higher diffusivity at a high temperature. It was clarified that the complete solution time for CO2 in seawater is longer than that in pure water due to its relatively lower solubility compared with pure water.
Carbon Capture and Storage (CCS) is regarded as a countermeasure for global warming, but introduction of conventional CCS system deteriorates thermal efficiency of power station. To find out its solution, a project has started by NEDO to develop the High-efficiency Oxy-fuel IGCC system, which can keep high efficiency even after capturing CO2. In this system, gasifying agent and combustion air is substituted by oxygen diluted by exhaust gas recirculated from gas turbine combustor. The target of this project was set as to achieve net thermal efficiency more than 42% at HHV basis, which is equivalent to state of the art coal-fired power station. Various approaches were done to confirm the concept of this system and to develop fundamental technologies necessary for the system since 2008 to 2014 under the support by NEDO. As good achievements were obtained till 2014, the project made another step for developing high efficiency oxy-fuel IGCC since 2015 as a 5 year joint project with MHI and MHPS under the support by NEDO. This paper introduces the latest status of this project executed by CRIEPI by referring several related papers.
For improving performance of the stationary Polymer Electrolyte Fuel Cell (PEFC) system, the cell operating temperature up to 90°C will be preferred in Japan during the period from 2020 to 2030. To understand the operation of the PEFC system under relatively high temperature conditions, detail heat and mass transfer analysis is required. The main focus of this study is to analyze the PEFC performance under operational conditions, such as initial operational temperature of cell (Tini), relative humidity of supply gas, and the cathode gas type, temperature distribution in a cell of PEFC (using Nafion membrane) under relatively higher operating temperature conditions. The in-plane temperature distributions on backside of gas separator of cell under power generation were measured using thermograph and it was observed that the in-plane temperature distribution at the anode was more uniform than that at the cathode under the O2 supply condition, irrespective of Tini, relative humidity of supply gases except Tini of 100°C. As to Tini of 100°C, the in-plane temperature distribution at the anode was broader since the back diffusion of water from the cathode to the anode was helped compared to the other Tini. The temperature at the cathode was raised through the gas channel toward the outlet of cell for the relative humidity of supply gases of 100 %RH at Tini of 90°C, while the temperature increase was relatively smaller at Tini of 80°C. The in-plane temperature distribution at the anode under the air supply condition was broader compared to not only that at the cathode, but also that at the anode under the O2 supply condition. It is necessary to manage the water concentration (liquid water accumulation in gas channel and gas diffusion layer (GDL) as well as relative humidity in PEM and catalyst layer) and required O2 supply in order to obtain a good power generation performance of PEFC under relatively higher temperature operating conditions than usual.
Low calorific value of lignite, mostly attributed to high moisture content, undermines usability of this low rank coal. Upgrading the quality of this energy carrier, which benefits coal-fired power plant's thermal efficiency, can be effectively realized by means of drying. The kinetics of superheated steam drying was studied for 30 mm spherical samples from Belchatow lignite mine in Poland. The experiment featured simultaneous and continuous measurements of weight and temperature. The drying kinetics, described by curves of moisture content, drying rate and temperature profile, were evaluated using the data acquired. The appearance of the sample throughout the process was video-recorded. Widespread cracking and shrinkage, which differ depending on the conditions, along with series of droplets typical for larger sample, were observed. The examined particles were suitable for predictions of thermodynamically derived drying rate and time, as proposed in the previous study for 5 and 10 mm particles from the same coal deposit. However, in comparison they exhibited more uniform density distribution. On the basis of experimental results and material properties, the numerical model of drying process was applied. Simulated drying behavior was consistent with empirical observations. Extensive investigation, revealing features of variously-sized samples as well as diameter dependence on drying process, is required for purposes of designing industrial drying system dedicated to specific type of coal.
Polymeric materials are now major materials used in various situations. However, most polymers are usually unsuitable for use in high temperature environments because of low glass transition temperature. In polymers, however, polyimide is one of polymers having relatively higher glass transition temperature and high strength. This means that the mechanical property of polyimide has been said not to be changed very much by temperature. Therefore, polyimide foam is expected to show good mechanical performance over wide temperature range. In order to increase the use of a polyimide foam in industrial applications, it is necessary to know its deformation behavior in wide range of strain rates and temperature. In this study, a series of compression tests at various strain rates, from 10-3 to 103 s-1 were carried out in order to examine the effect of strain rate on the compressive properties of polyimide foam. It was found that the flow stress of polyimide foam increased dramatically at dynamic strain rates. The effect of ambient temperature on the properties of polyimide foam was also investigated at temperature from -190 °C to 270 °C. The flow stress decreased with increasing temperature in the range from room temperature to 270 °C. At -190 °C, the deformation behavior of polyimide foam changed to be brittle.
Batteries or electric wires are currently in wide use for sensor energy supply. However, industrial waste caused by battery disposal are recognized as a social issue. In addition, the weight of the electric wires supplying electric energy to sensors can reach several kilograms in a car or several hundred kilograms in a passenger aircraft. Thus, reduction of electric wire weight can bring weight saving for a car or a plane. We performed a basic study of development of generation system using ferromagnetic powders and fluid. Such an electrical generator is inexpensive, uses kinetic energy naturally available in the living environment such as wave force, vibration, or shock, is maintenance-free and safe. Magnetic field of a permanent magnet is used in the electrical generator using ferromagnetic powders, that significantly contributes to generation. Electromagnetic fluid simulation and liquid metal magnetohydrodynamic power generation considering dynamic behavior of magnetic particles in magnetic field was studied before. However, electromagnetic analysis for magnetic particle in magnetic field for energy harvesting purposes is not studied. Therefore, in this work, we performed electromagnetic analysis using a general-purpose finite element simulation program and studied the efficiency of the electrical generator using ferromagnetic powders. We were able to assess generation efficiency by analyzing the magnetic flux distribution of the permanent magnet used for electricity generation.
In s-version finite element method (s-FEM) proposed by Fish (1992), a local mesh that represents the local feature such as a hole or a crack is superposed on a global mesh that represents the shape of the whole analysis model. The interaction between global and local meshes is represented by coupling stiffness matrices. Since the global and local meshes can be generated independently, mesh generation efforts are reduced remarkably. However, s-FEM has a common issue. The generation of coupling stiffness matrices takes a considerable amount of program development efforts, which include constructing accurate cross-element integration methodology and programming it for various element types. For such an issue, we propose an iterative s-FEM that does not require the generation of coupling stiffness matrices at all. The coupling term is now evaluated by global and local stresses that are computed on the respective mesh and then transferred to the other by interpolation techniques. The global and local stresses are treated as initial stress in the finite element computations. The global and local analyses are performed alternately under assumed initial stress, and converged solution is achieved by iteration with a monitored residual being sufficiently small. In proposed iterative s-FEM, an issue about linear independence of global and local elements, which is known to occur in the original s-FEM, does not occur. In numerical experiments, converged solution was successfully obtained within several hundred iteration counts. Accurate stress distribution for a stress concentration problem and an accurate stress intensity factor for a linear elastic fracture mechanics problem were computed by proposed iterative s-FEM. In addition, several stress interpolation techniques were compared in the numerical experiments. Nearest neighbor interpolation for the global stress and local least squares interpolation for the local stress showed good convergence and accurate solution.
The appropriate size of the representative volume element (RVE) for filled rubber composite is investigated where the volume fraction of the filler is about 20%. The micro structures of the composite are obtained by the measurement with 3-dimensional transmission electron microscope tomography (3D-TEMT) at resolution of about 1nm in each direction. Numerical simulations of static elongation have been conducted by finite element method (FEM) with various sizes of RVEs where the FEM models are created by applying voxel technique to the measured data. A highly parallelized FEM program, FrontISTR, and up to 4096 cores of K computer are utilized because the largest FEM models have nearly 200-million degrees of freedom (DOFs). Two different filler dispersion states of the composite material are examined.
In s-version finite element method (s-FEM), a local mesh is superposed on a global mesh, and they are solved monolithically. The local mesh represents the local feature such as a hole, whereas the global mesh does the shape of a structure. Since the two meshes are generated independently, mesh generation becomes very tractable. However, s-FEM has a difficulty that the generation of coupling stiffness matrices takes a lot of computational efforts. To overcome this difficulty, the authors proposed coupling-matrix-free iterative s-FEM. In this method, the coupling stiffness matrices are computed implicitly by stress integration on one mesh and stress transfer from one mesh to the other mesh. Converged solution is obtained by iteration. However, in practical cases, unnatural stress oscillations can occur with conventional Gaussian quadrature. In this paper, in order to smooth unnatural stress oscillations, element subdivision technique is applied. Element subdivision technique can deal with the discontinuity of discretized stress along element interfaces. The stress transfer scheme in coupling-matrix-free iterative s-FEM is designed to work harmoniously with element subdivision. Moreover, element subdivision strategy to obtain smooth stress distribution is investigated in the numerical experiments of a circular hole problem. We propose the element subdivision strategy as the following two items. First, at least 4×4 element subdivision should be adopted to obtain smooth stress distribution. Second, the local mesh should be fine enough to evaluate stress concentration accurately. To confirm this strategy, global and local meshes for elliptical hole problems are designed by following this strategy. Even in severe stress concentration problems, unnatural stress oscillations, which occur with conventional quadrature, is smoothed obviously with 4×4 element subdivision. In addition, stress concentration is evaluated accurately due to the second item of the strategy.
Conventionally, the evaluation of wear in the cutting tools have been focused mainly on the rake and flank face, but there is little research (consideration) that paid attention to the cutting edge of the tools. The reason for this is the cutting edge is having a large scale chip, a small scale chipping, and edge shape varies complicatedly due to abrasion and wear. Therefore, by extracting its features, a valid technique for evaluating this matters has not been established. That is why this research is carried out to focus on the cutting edge of the tool. In other words, it is an evaluation from the point of the cutting edge that is the line of intersection of rake face and flank face of the cutting tool. The scope involve a quantitative evaluation of its complexity due to the change of this edge line by the fractal dimension. The fractal dimension is a theory that is capable of reasonably indicates the complexity of the shape by a non-integer dimension. Therefore, as a result in the 3-dimensional cylindrical turning using this method, tendency that the fractal dimension of the nose corner part of the cutting edge approached 1.08, and the fractal dimension of the straight part approached 1.12 when the tool reached its end life are obtained.
Radio frequency-microelectromechanical system (RF-MEMS) switches, which use physical Ohmic contacts, are recently focused for high performance in the high-frequency ranges. Typically, the contact areas of the electrodes in RF-MEMS switches are less than 0.01 mm2, and they generate just very low normal loads of less than 1 mN. The limited real contact area of the electrodes leads to high electrical contact resistances and wear on the switches. Carbon nanotube (CNT) films, formed with many vertically aligned CNTs on a silicon substrate, are one candidate electrode material for RF-MEMS switches. However, CNT films have a high electrical contact resistance with metals. In this study, precious-metal electroplating (Ag, Au, Pt, Rh, and Cu) on CNT films was performed to decrease the electrical contact resistances of the films and increase their wear resistances. The contact resistances of the electroplated CNT films as a function of normal loads up to 1 mN were measured by φ2 mm Cu balls. In this study, the Ag-electroplated CNT film with a hydrogen annealing had the lowest electrical contact resistance of 0.10 Ω. Durability experiments of cyclic connection switching were conducted under direct applied voltages of 3 V or 10 V between the films and Cu balls, and with a load of 1 mN for 3 × 105 cycles. The electrical contact resistance of the Ag-electroplated CNT film with the hydrogen annealing was stable during this durability experiment.
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