This paper reports output increase of conventional thermal power plants by the method of feed water bypassing feed water heaters, in order to deal with tight supply-demand situation of electric power in our business area. A method to let a certain amount of boiler feed water bypass several water heaters was chosen, since thermal influence on the plants of this method is less than other methods. Then, we analyzed the relation between the output increase and the ratio of bypassing heaters prior to the first application, using a heat balance analysis program for conventional power plants that we developed before. As a result, an output increase of over 30 MW was observed under the condition of 20 % of the feed water flow rate bypassing four high pressure heaters in a conventional thermal power plant of 1000 MW output. The procedures of bypassing heaters method were established and discussed in detail. This method was applied to two actual thermal power plants on trial. As a result, output increase over 30 MW was observed respectively, and it almost equals that of the calculation. The thermal efficiency for the output increase was calculated to be more than thirty percent by the heat balance program. Consequently, this method is considered having a possibility for the practical use.
The successful development of oxygen-blown integrated coal gasification combined cycle (IGCC) technology requires gas turbines capable of achieving the dry low nitrogen oxides (NOx) combustion of hydrogen-rich syngas for low emissions and high plant efficiency. The authors have been developing a “multiple-injection burner” to achieve the dry low-NOx combustion of hydrogen-rich syngas. This burner consists of multiple fuel nozzles and a perforated plate with multiple air holes. At each injection point, one fuel nozzle and one air hole are installed coaxially, so that a fuel jet surrounded by a sheath air jet is injected. The burner achieves low-NOx combustion by mixing fuel and air rapidly with multiple fuel-air coaxial jets, and prevents flashback into the burner by lifting the flame from itself. The purpose of this paper is to present the test results of multi-can combustors equipped with multiple-injection burners in an IGCC pilot plant, and evaluate combustor performance by focusing on the effects of flame shapes. The syngas fuel produced in the plant contained approximately 50% carbon monoxide, 20% hydrogen, and 20% nitrogen by volume. In the tests, the combustor with slenderer flames achieved lower NOx emissions of 10.9 ppm (at 15% oxygen) diluent-free with high stability and high reliability, and reduced both combustor liner and burner plate metal temperatures at the maximum gas turbine load. These findings demonstrated that the multiple-injection combustor achieved the dry low-NOx combustion of the syngas fuel in the plant.
Integrated coal Gasification Combined Cycle (IGCC) is a highly effective power generation system that the gas turbine is operated with the gasified coal in the gasifier. Clean Coal Power R&D Co., Ltd. had been conducting various tests for commercialization with the Nakoso IGCC demonstration plant since September 2007. The plant consists of air-blown gasifier, wet gas clean-up system and 1,200°C class gas turbine to produce 250 MW-gross electricity. Reliability was confirmed by 2,238 h of continuous operation, 18,788 h of accumulated operation and the resulting net thermal efficiency was 42.9% (LHV basis). Various types of coal have been successfully tested, such as North American coal, Indonesian coal, Russian coal and Columbian coal in addition to Chinese plant-designed coal. Although the Great East Japan Earthquake and Tsunami has caused severe damages to plant in March 2011, our IGCC swiftly restored its operation within 4.5 month and has been maintaining stable operation for demonstration project. The demonstration project was finished in March 2013 and the Nakoso IGCC plant is operated commercially by Joban Joint Power Co., Ltd. as high efficiency power generating station.
Trilateral cycle is one of the heat cycles for waste heat recovery system. In the heat exchange process of the trilateral cycle, pressurized working fluid is kept as a single liquid phase. Therefore, temperature-profile matching between the heat source and the working fluid should be improved, and exergy loss can be minimized. In the present study, thermodynamic performances of Rankine, trilateral and supercritical cycles are assessed. In the cycle simulation, maximum pressures of these three cycles are optimized to give the highest exergy efficiency. Cycle performance criteria are sink-temperature-based exergy efficiency, isentropic expansion ratio and maximum pressure. Exhaust gas (400℃) and hot water (80℃) are assumed for the heat sources. Simulation results show that the sink-temperature-based exergy efficiency of trilateral cycle is 78 %, which is 1.36 times larger than that of Rankine cycle for the hot water case. For the exhaust gas case, water is the optimal working fluid for the trilateral cycle, and the sink-temperature-based exergy efficiency is 80 %. Especially in the trilateral cycle, the optimum expansion ratio shows large variation depending on the working fluids and working conditions. Thus, a reciprocating expander should be suitable from the view point of adaptability to various working conditions. In the present study, the effect of volumetric expansion ratio with reciprocating expander is also investigated. Simulation results show that the volumetric expansion ratio of 100 or even higher is needed to reduce the expander loss.
The purpose of this study is to develop the compact auxiliary water heater using tubular flame for home CHP (combined heat and power). The tubular-flame water-heater consists of the tubular flame burner, the coiled tube heat exchanger and the inserted tube installed at the center of the coiled tube as an additional heat exchanger. The tubular flame is formed in a rotating flow field by injecting the air-fuel mixture tangentially into the cylindrical chamber. The swirling flow of the combustion gas flows through the gap between the coiled tube and inserted tube. The high heat transfer performance can be achieved on these heat exchangers without the expanded heat transfer surface due to the swirling flow. Thus, the compact water heater can be constructed by using the tubular flame burner. At the first stage of the development, the maximum thermal efficiency achieves 81 % at the combustion rate of 15 kW. The heat transfer characteristics on the coiled tube and the inserted tube is investigated under the combustion and non-combustion conditions. Heat transfer coefficient on the coiled tube has about 5.6 times higher than that under the no-swirling flow condition at the same flow rate. Nusselt number on the coiled tube heat exchanger and the inserted tube can be estimated by Dhir's correlation equation for the swirling flow, which was provided as a function of the ratio between tangential momentum and axial momentum. The heat transfer characteristics on not only the coiled tube but the inserted tube was dominated by the swirling convection flow.
In order to determine the effect of triple junction on the crack initiation, we use the finite element method to investigate the effect of misorientation between Cu grains on the stress concentration near the triple junction in comparison to that near a free edge. The results reveal that the triple junction represents a greater danger for crack initiation than the free edge in nano-components over a wide range of grain combinations. The stress concentration near the triple junction is governed by the difference in stiffness between the grains. Thus, the combination of the stiffest and softest grains induces the highest stress concentration.
Quasi-static and dynamic tensile testing was performed upon machined tensile specimens fabricated from bulk primitives produced by the consolidation of water atomized, 17-4 precipitation hardened stainless steel powder by layer-based, selective laser melting. Such mechanical evaluation was performed by a screw-driven uniaxial tension testing machine and a split-Hopkinson tensile bar apparatus. Strain rates evaluated include 10-3, 10-1 and 103 s-1. Prior to tensile testing, specimens underwent additional thermal processing in accordance with industry standards. Evaluations of the solution heat treatment and peak-age conditions were made alongside similarly prepared, but traditionally processed specimens meeting the same material standard for chemistry (drawn rod). Tensile strength across all strain rates is higher for these selective laser melted (SLM) specimens as a result of microstructure refinement through rapid melt, solidification and cooling during processing. Ultimate tensile and yield strengths increase with increasing strain rate and show no preferential direction relative to the building direction. Elongation anisotropy is observed as a consequence of directional porosity stemming from pores limited to within individual layers. Specimens loaded normal to the SLM building plane commonly rupture at small elongation because of this mechanical fibering from the selective laser melting process.
Thermal fatigue cracking may initiate at a T-junction pipe where high and low temperature fluids mix. In this study, wall temperature characteristics at a T-junction pipe were investigated to improve the evaluation method for thermal fatigue. The stainless steel test section consisted of a horizontal main pipe (diameter, 150 mm) and a T-junction connected to a vertical branch pipe (diameter, 50 mm). The inlet flow velocities in the main and branch pipes were set to 0.99 m/s and 0.66 m/s respectively to produce a wall jet pattern in which the jet from the branch pipe was bent by the main pipe flow and made to flow along the pipe wall. The temperature difference was 34.1 K. A total of 148 thermocouples were installed to measure the wall temperature on the pipe inner surface in the downstream region. The maximum of temperature fluctuation intensity on the pipe inner surface was measured as 5% of the fluid temperature difference at the inlets. The dominant frequency of the large temperature fluctuations in the region downstream from z = 0.5Dm was equal to 0.2 of the Strouhal number, which was equal to the frequency caused by the vortex streets generated around the jet flow. The large temperature fluctuation was also observed with the period of about 10 s. The fluctuation was caused by spreading of the heated region in the circumferential direction.
The main characteristics of robot are the precision work with a high degree of reliability and the repetitive over long period that makes it suitable for use in the medical field. In this paper, the control and analysis of robot arm for the human wrist rehabilitation by using flexible pneumatic cylinder is introduced. The system consists of a slave arm, a master arm, a high-speed microcomputer, compact and inexpensive quasi-servo valves, a potentiometer and accelerometers to give the references for the attitude control. The robot arm has three degrees-of-freedom that is bending, extending and contracting. The control performances of the robot arm were investigated and the analytical model of the whole robot arm system including the flexible pneumatic cylinder, the quasi-servo valves and an embedded controller was proposed and tested for estimating the performance theoretically. We also made comparisons between the calculated and experimental results to confirm the validities of the proposed model and the identified system parameters. The results from experiments show that the proposed models accurately predict the behavior of the tested flexible robot arm using flexible pneumatic cylinders. The proposed master-slave control system has a potential for application for robot-assisted rehabilitation and training especially for human wrist.
To prevent noise generated by devices such as compressors, generators, or motors, a noise-proof cover is usually installed around them. It is also installed to protect ultra precise devices from ambient noise. Because of space considerations, the noise radiating device or ultra precise devices to be protected from outer noise are generally situated at the center of the cover. However, this often lowers the performance of the noise-proof cover at some frequencies because of the occurrence of its inner cover acoustic modes. To solve these problems from the standpoint of the cover's dimensions and the occurrence frequency of the inner acoustic mode in the cover, which protect devices within the cover from outer ambient noise, we used a simplified one-dimensional Transfer Matrix Method (TMM) to investigate the most effective arrangement of acoustic tubes on the inside of the cover to restrain the acoustic mode. The results show that the most effective arrangement depends on the width of the target frequency range. If the target frequency range is plus-minus 10 to 17 % around the peak caused by the acoustic mode, for example, the most effective arrangement is one in which tubes 1/4 as long as the longest length of the cover edge are set at both ends and at the center along the longest direction of the cover. Finally, the effect of the proposed structure was investigated by numerical acoustic calculations using the Boundary Element Method (BEM) and validated by experimental measurements. The BEM results correspond well to those of the experiment; the experimental results show that the sound pressure level is reduced about 6 dB over all of the frequency range around the original peak frequency plus or minus 50%.
As the small-sized high speed diesel engine used for construction machinery and generator is operated under continuous heavy load condition, a gear train is employed to drive the fuel injection pump and valve train. When a loading torque is small at the idling condition, the gear tooth separation and impact are caused by the fluctuating torque and they increase the engine noise level. Particularly when the torsional vibration of the crankshaft occurs and its rotational amplitude is magnified at a specified rotational speed, the gear impact is intensified and it leads to increase of engine noise. Author has developed the theoretical procedure using FEM, modal analysis technique and BEM to predict the vibratory response and radiated noise of the engine block coupled with the rotating crankshaft and gear train shafts which drives the fuel injection pump and valve system. This method is applied to reveal the effect of torsional vibration of crankshaft on the gear impact force and engine noise of the four-stroke four-cylinder engine. Countermeasure to reduce vibration and noise by changing the location of the gear train from pulley side to flywheel side of the crankshaft is evaluated and its result indicates the prospects which can reduce the radiated noise from the engine block.
Vibration modes of a rotating circular membrane with extremely small thickness are investigated. In the previous papers, the author has conducted theoretical analysis of the membrane's equilibrium states and small vibration modes under gravity, employing the membrane theory of shell of revolution and von Karman's vibration equation and taking buckling of the thin membrane into account. In this paper, the vibration mode analysis is briefly summarized and the vibration modes are experimentally investigated in detail. An experimental system that can rotate and vibrate the circular membrane simultaneously in vacuum is created, and forced vibration experiments are performed with a wide range of rotation and excitation frequencies. Several vibration modes are observed and two kinds of resonance points are obtained by the experiments. Experimental results are compared with analytical results, and the resonance points and a few basic vibration modes are found to appear similarly in both. It is also found that the frequencies of the lowest vibration mode observed in the experiment are higher than those of the vibration mode analysis. In view of the compressive stress, i.e. wrinkling in circumferential direction due to finite amplitude vibration of the thin membrane, the vibration mode analysis is modified and the difference of the mode frequency is explained.
We have developed and evaluated polycarbonate (PC)-based dual cantilever sensors as part of a low-cost sensor network system for monitoring VOCs (volatile organic compounds). The PC-based dual cantilever sensor consists of a PC cantilever and a PBD (polybutadiene)-coated PC cantilever with PVDF (polyvinylidene fluoride) piezoelectric films. We began by investigating the size and mode dependences of resonant frequencies and quality factors of PC cantilevers and PBD-coated PC cantilever as output signal of PVDF piezoelectric film. Next, we examined the change of resonance frequency in the presence of VOCs vapor by setting up a resonance sensor evaluation system equipped with a dilution flow system, temperature-controlled chamber, oscillation circuit, and frequency counter. The resonant frequency of both PC cantilever and PBD-coated PC cantilever shifted significantly downward depending VOCs.
In this paper, an active safety device for skid control of a small in-wheel electric vehicle that uses a hydraulic-mechanical brake system (HMBS) is proposed. An anti-lock braking system (ABS) which is a basic skid control method is difficult to install at the driving tire because the space is insufficient. To improve the stability and the safety of the small electric vehicle with two in-wheel motors, we have constructed a simulation model of the HMBS with ABS and regenerative brake control. During braking, when skid occurs, especially on an icy road, ABS will maximize the slip ratio and cornering force, thus, assuring the stability control of the vehicle and eliminating the possibility of accident. However, due to the rigidness and low response performance of the rear mechanical braking system, ABS is still not enough to maximize the slip ratio and cornering force of the rear tire. To obtain the optimum slip ratio and cornering force at the rear tire, we proposed the regenerative brake control timing. During braking, we consider that an in-wheel motor at the rear tire will produce the regenerative braking force. The regenerative brake control timing operates similar as ABS. When the slip ratio increased more than the optimum value, the regenerative brake is turned off and the excessive energy is used to charge the battery. On the other hand, when the slip ratio decreased more than the optimum value, the regenerative brake force is again restored. The effectiveness of our proposed model has been evaluated by a MATLAB/Simulink. The results of the numerical analysis indicate that the combination of the HMBS with ABS and regenerative brake control can prevent the vehicle to skid and improve the stability of the vehicle.