Thermophotovoltaic generation of electricity was investigated through near-field and far-field radiation experiments by making use of a schottoky diode and a p-n junction cells made of GaSb semiconductor. The maximum power for the far-field was not dependent on a gap between the cell and an emitter surfaces, provided that its view factor was almost unity. On further decrease in gap, the output powers for the schottoky and the p-n junction cells became 4.4 and 3.9 times higher than those for the far-field radiation regime, respectively. The increase in output power might be originated from a near-field radiation effect, that is, an evanescent wave effect.

View full abstract

This paper describes on the energy saving experiment by using the smart meter. In Japan, last summer, the power shortage was concerned and the limited use of electric power had been issued from the government. We constructed display system of the electric power consumption of Tokyo University of Marine Science and Technology (TUMSAT) on the web. This system could provide the average power usage during 10 minutes to promote the energy saving actions of each consumer. From the energy saving experiment in our university, it was found that the display on web was significantly effective to suppress the consumption of electric power without the compulsory cut off.

View full abstract

Microgrid is paid attention as the system that can reduce CO₂ emission from residential area. Microgrid can absorb the fluctuation of electricity power which might be originated from several kinds of renewable energy system, therefore it does not negatively affect on the stability of the utility grid. In addition, microgrid has the capability to control the heat-and-power ratio in demand and supply by optimizing the combination of several kinds of high efficiency residential devices in the area. Depending on the area where microgrid is applied, the reductions of CO₂ and cost might be changed. However, here are few researches on the effect of areal characteristics. Hence in this report, microgrid was evaluated environmentally and economically in several kinds of areal characteristics; specifically, 12 kinds of demand patterns, 4 kinds of photovoltaics capacities, and 3 kinds of CO₂ emission coefficients of electricity. As a result of the analysis, microgrid has economic advantages in each area.

View full abstract

The aim of this study is to propose a new energy system ”trigeneration”, which is developed from cogeneration system. In this system, comparing with ordinal cogeneration system, CO₂ in exhaust gas is also used as an energy resource for photosynthesis etc., for example, in order to grow plant or cultivate microalgae which include the component of liquid fuel. In this paper, the characteristics of ratio of heat-electricity, and CO₂ emissions were investigated in the case of using fatty acid methyl ester derived from waste cooking oil. And by using these experimental results the CO₂ emissions from trigeneration system was simulated. As the result, it is shown that CO₂ emissions are possible to decrease considerably compared with using petro-diesel fuel.

View full abstract

Some cracks were found at the first stage discs of gas turbine rotors made of Ni-base superalloy. There were inter-granular cracking and observed to be highly stressed and damage sensitive locations with less potential for oxidation, which is thought to occur due to hold-time cracking. In this study, laser peening technology was developed to improve fatigue properties of Ni-base superalloy Alloy 706, and the effects on the material properties were examined. Laser peening is a novel process to induce compressive residual stress on material surface by irradiating focused high-power laser pulses. Several durability tests, such as thermal aging treatment test and stress aging test, were performed under thermal power plant operation conditions, and the effectiveness of laser peening treatment was confirmed.

View full abstract

Specimens with a gage section diameter of 1 mm and 6 mm were prepared from 12 Cr steel used over a long period in a power plant, and were compared for the difference of creep rupture strength depending on the gage-section diameter. Specimens of 2.25 Cr steel with a gage section diameter of 1 mm and 6 mm were also compared for the difference of creep rupture strength. As a result, 12 Cr and 2.25 Cr steels were found to have different size dependence of creep rupture strength, and the difference was studied on the effect of specimen diameter and thickness of oxidation film.

View full abstract

In the present study, the distributions of time-averaged and fluctuated wall shear stresses downstream from an orifice were measured using a Flow Vector Sensor of MEMS (Micro Electro Mechanical System). The air flow was supplied to a circular pipe from a blow-down wind tunnel. The diameter of the pipe is D = 194 mm and the diameter of the orifice is d = 97mm, yielding a diameter ratio of 0.5. The axial distance from separation (orifice) to reattachment was approximately 2.5D. Near the wall in the recirculating region, the minimum mean wall shear stress was located at approximately x/D = 1.75, and the maximum rms value of the wall shear stress was approximately x/D = 1 - 2. The experimental results were found to approximately agree with the numerical results obtained previously by Large-eddy simulation. It seems that using the fluctuated wall shear stress to estimate the FAC(Flow-Accelerated Corrosion) rate of the circular pipe wall downstream from the orifice is appropriate.

View full abstract

In order to establish a safety evaluation method of a steam generator in sodium-cooled fast reactors, a computer program called SERAPHIM to calculate compressible multicomponent multiphase flow with sodium-water chemical reaction under tube failure accident has been developed. In this study, a numerical model for liquid droplet entrainment from an interface of the gaseous jet and its transport was newly constructed to evaluate the environment of the liquid droplet impingement erosion. Applicability of the SERAPHIM program which incorporates the droplet entrainment / transport model was investigated through the analysis of vertical discharging of water vapor in the liquid sodium pool. The numerical analysis reproduced the underexpansion of the vapor jet, which appears under the actual condition of the tube failure accident. The calculated peak temperature agreed with the experimental results well. Also, appearance of the dispersed phase of droplets in the reacting jet and movement with the supersonic gaseous flow were calculated successfully.

View full abstract

Wastage phenomena on adjacent tubes (target-wastage) arise from water/steam leak in steam generators of sodium-cooled fast reactors. Target-wastage is likely to be caused by liquid droplet impingement erosion and flow-accelerated corrosion in an environment marked by high-temperature and high-alkali (reaction jet) due to sodium-water reaction. The static and flow-accelerated corrosion experiments have been carried out as a part of phenomena elucidation experiments for target-wastage by using actual tube material under high-temperature sodium-hydroxide and sodium monoxide conditions which are mainly generated by sodium-water reaction. The authors evaluated the dependence of liquid/tube material temperature and liquid velocity upon the flow-accelerated corrosion rate on the tube and derived the new correlation of flow-accelerated corrosion for target-wastage taking into account local wastage environment in this report.

View full abstract

For the purpose of elucidating the mechanism of the sodium-water surface reaction in a steam generator of sodium-cooled fast reactors, kinetic study of the sodium (Na)-sodium hydroxide (NaOH) reaction has been carried out by using Differential Thermal Analysis (DTA) technique. Based on the measured reaction temperature, the first-order rate constant of sodium monoxide (Na₂O) generation was obtained by the application of the laws of chemical kinetics. From the estimated rate constant, it was reconfirmed that Na₂O generation should be considered during the sodium-water reaction in spite of variation of volume fraction (Na:NaOH). Na, NaOH and Na₂O as major chemical species were identified from the X-ray diffraction (XRD) analysis of the residues after the DTA experiment. It was inferred that Na₂O could be generated as a reaction product.

View full abstract

This paper describes a gas turbine inlet air cooling system using high pressure spray nozzle. Thermal characteristics and fluid properties were studied by performing the wind tunnel test that simulated an actual gas turbine intake cooling duct part. A result of examining the cooling performance due to differences in the inlet relative humidity 30～50%RH, the cooling performance was the same. Furthermore, as a result of investigating the cooling performance due to the difference in a spray nozzle number, in one case, it became clear from 33°C that it is possible for 28°C to cool ,and in three case, it became clear from 33°C that it is possible for 23°C to cool. The air humidifying cooling process of an actual gas turbine inlet duct part was clarified.

View full abstract

It is suggested that a steam injector (SI) is applied to heat pump systems as an effective condenser or compressor in the battle against global warming to downscale them. SI which consists of a compact structure has high heat transfer performance due to the direct contact condensation, and the downsizing of a condenser is expected. And it is expected that the feature to act as a static jet pump without any rotating power source may enable to downscale a compactor. Thus the objective of the present study is to investigate the internal flow mechanism of an ultra micro steam injector (UMSI) in an effort to develop the further small SI. In particular the flow observation in UMSI whose throat diameter is 600 μm is conducted. As the results, the formation of water jet and the back stream in the mixing nozzle which are the operating characteristics of SI is confirmed.

View full abstract

The carbon-doped copper oxide is devised as an electrocatalyst to reduce carbon dioxide under ambient pressure and temperature. The electrode was immersed into a KHCO₃ aqueous solution with CO₂ bubbling. The electric potential was maintained at -1.64 V vs SHE. The electrode prepared at 900°C gives the maximum production rate of ethylene (25 %), ethanol (6.9 %) and 1-propanol (3.6 %). The production rate of methane, from which is harmful to separate ethylene, was suppressed to one fifteenth of that of ethylene. In contrast to a thermally-oxidized copper-oxide layer, the doped-carbon and a high ratio of Cu₂O to CuO in the devised electrocatalyst may result in the higher productivity and selectivity.

View full abstract

Effects of the cylinder wake in a freestream on statistical properties of a turbulent boundary layer over a flat plate are investigated by means of wind tunnel experiments. The cylinder is set horizontally over the flat plate and the interactions between its wake and the zero-pressure-gradient turbulent boundary layer are investigated. Instantaneous velocity is measured by using hot wire anemometry. The bursting events are detected by the variable interval time average (VITA) technique. The results show that the time-averaged mean velocity in the inner layer with the cylinder wake coincides with that without the cylinder wake. However, turbulence intensities normalized by the inner parameters are suppressed by the cylinder wake. It is found that the peak value of the velocity fluctuation during the sweep phase in the bursting event is increased by the cylinder wake.

View full abstract

High-Schmidt-number scalar mixing layers in a turbulent flow generated by regular and fractal grids are investigated by means of experiments using particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) technique. The Reynolds number based on the mesh size is 2,500. Rhodamine B is used as a fluorescent dye. The Schmidt number is about 2,100. The flow is separated into upper and lower layers by a splitter plate installed upstream of the grids; thus, the turbulent scalar mixing layers develop downstream of the grids. The results show that fractal grid turbulence has stronger turbulence intensity than that in regular grid turbulence. The decay exponent of turbulence intensity, n, is n = 1.21 for the regular grid and n = 1.40 for the fractal grid. The eddy diffusivity for mass in fractal grid turbulence is approximately four times larger than that in regular grid turbulence. The scalar dissipation in fractal grid turbulence is smaller than that in regular grid turbulence. Finally, it is concluded that turbulent scalar mixing is more enhanced by the fractal grid than by the regular grid.

View full abstract

Three-dimensional numerical predictions are presented for a laminar flow through a square channel with a sudden expansion of area ratio 4 : 1 in the range of Reynolds numbers Re = 20 to 700, using an Open Source CFD Toolbox (OpenFOAM). In particular, the vortex structure in the recirculation zone behind the sudden expansion was examined from the fluid particle trajectory based on Lagrangian method. The results showed that the main flow diverged through the expansion, and at the constant x section, the flow vector of the duct centerline is directed towards the wall in the vertical plane, while the secondary flow vector of the duct corner is directed toward the centerline in the diagonal plane. So that, the overall regular flow structure consisted of the eight regions that is 1/8 part of the flow field surrounded by two diagonal plane, vertical plane, horizontal plane and peripheral wall. The results of the particle trajectory in the 1/8 area clarifies that the fluid particles enter into the recirculation zone behind the sudden expansion from upstream diagonal corner, and move toward spanwise direction with helical motions, and then they flow out to the downstream region near the lower wall. It seems that the helical type vortex is formed. Moreover, the other particles have been recirculated accompany with longitudinal small scale vortex motion inside the helical type vortex. We call it the ring type vortex. These structures could not be explained by two-dimensional flow structure and showed the characteristics of three-dimensional vortices.

View full abstract

The yields of consecutive reactions in a micro-fluid device were predicted by using Monte Carlo simulation. It was found that the yield of main product was improved by using a micro-fluid device when the ratio of the reaction rate constants is k₁/k₂ >1. The yield prediction map was also made by using non-dimensional Damkohler Number Da and the ratio of the reaction-rate constants k₁/k₂. The validation experiments of four kinds of consecutive reactions were conducted. Next, the micro-fluid system of 20 parallel-connected micro-fluid devices was developed. The maximum flow rate of the micro-fluid system was 10 mm³/s, which corresponds to 315 t/year. Evaluation of the chemical performance of the micro-fluid system was conducted using a nitration reaction. It was found that the micro-fluid system increased the production scale without decreasing the yield of the products.

View full abstract

In order to clarify dominant aerodynamic sound sources with regard to the sound generated from flows around a rectangular cylinder, decoupled simulations based on Lighthill's acoustic analogy are performed. The freestream Mach number is 0.2 and 0.4, and the Reynolds number based on the side length and the freestream velocity is 150. In these decoupled simulations, acoustic fields are predicted by the acoustic simulations using Lighthill's tensor, which is computed by incompressible flow simulations. It is clarified that the predicted acoustic fields are in good agreement with those by direct simulations. Moreover, it is presented that the shift of the propagation angle of the acoustic waves due to the Doppler effects can be captured by the present decoupled simulations. Also, the scattered sound is predicted by the force exerted on the flow by the cylinder, which is computed by the results of the above-mentioned decoupled simulation. The direct sound is computed by subtracting the scattered sound from the total sound. As a result, the effects of the freestream Mach number on the contributions of the scattered and direct sounds to the total sound are clarified. Moreover, by investigating the effects of filtering out a part of the acoustic sources in the wake on the predicted acoustic fields, the dominant acoustic sources contributing to the far acoustic field are identified.

View full abstract

Ultrasonic pulse Doppler method has been widely used in many engineering field referred to as UVP (ultrasonic velocity profiler). Analysis algorithm in the UVP, number of pulse repetition (N_pulse), noise and reflector conditions, etc. may affect on the measurement accuracy. The N_pulse is related to the temporal resolution, and must be set as low as possible in order to improve the temporal resolution. However, it is known that accuracy of instantaneous velocity becomes worse with decreasing of the N_pulse. In this study, effect of analysis algorithm in the UVP on velocity data was investigated with changing of the N_pulse and SNR by simulation and experiments. As a result, it is shown that there is an appropriate N_pulse in each algorithm depending on the SNR. An algorithm which decides the Doppler frequency from maximum value in the power spectrum, FFT-max, was relatively hard to be affected by noise. Difference of velocity standard deviation was small between lower and higher noise conditions when FFT-max with N_pulse over the appropriate value was used for the calculation. Hence, FFT-max was the best analysis algorithm for measuring flow field compared with the autocorrelation.

View full abstract

In the present study, we treat the dirty (small) and the adsorbing (large) particles as charged and anti-charged spheres and investigate the behavior of these particles under the gravity field by means of Brownian dynamics simulations. As an interaction potential between these charged particles, we have employed the electrical interaction energy based on the electrical double layers formed around the particles. The large particles will adsorb small particles due to the electrical interaction during the translational Brownian motion and sediment under the gravity field toward the bottom surface of the simulation region. Hence, we have here discussed mainly the dependence of the adsorption rate on the particle diameter ratio, the volumetric fraction and the input amount of large particles. The main results obtained here are summarized as follows. Although putting a numerous number of large particles enhances the adsorption rate, the number of inefficient large particles that do not contribute to the adsorption performance increases. This implies that an adsorption performance becomes worse with the input amount of large particles from the viewpoint of the adsorption rate per unit input amount. If it is necessary to remove the dirty particles during a short period, adsorbing particles with larger diameter may be used, but in this case the number of dirty particles that remain without adsorption increases. If it is desirable to obtain a significant adsorption performance even if a long time period is necessitated, adsorbing particles with smaller diameter may be adopted. From these results, we understand that there is an optimal input amount of adsorption agents, for example, from a commercial point of view.

View full abstract

In order to realize a premixed compression ignition (PCI) engine by utilizing bio-alcohol, combustion characteristics of bio-alcohol blended with gas oil were compared between ethanol and n-butanol in a diesel engine. The effects of the ethanol blend ratio and the butanol blend ratio on ignition delay, premixed combustion, diffusion combustion, fuel consumption and exhaust emissions such as smoke density, nitrogen oxide (NOx) and so on were investigated experimentally. It is found that ethanol almost burns out together with low evaporation temperature composition of gas oil in the premixed combustion period and the heat release in the diffusion combustion is based on mainly high evaporation temperature composition of gas oil, then, soot is formed in the diffusion combustion of gas oil. On the other hand, a part of butanol burns in the diffusion combustion, and the combustion of butanol in the diffusion stage is not the cause of soot formation. Butanol is more useful in diesel engine compared with ethanol because butanol can be blended with gas oil without surface-active agent, and fuel consumption and smoke are almost equal in both blend fuels if the alcohol blend ratio is the same.

View full abstract

A new technique of micro/nanoscale temperature measurement is developed using an individual carbon nanotube (CNT) on a platinum hot-film, which can control the heat flow through the CNT probe and sense its own average temperature. A feedback control to extinct the heat flow enables us to neglect the effect of contact thermal resistance and to know the real surface temperature. Spatial resolution of 70 nm, temperature uncertainty of less than 0.5 K and enough robustness are achieved. Using this method, quantitative temperature profiles are obtained around a line heater of 604 nm-width and 9.73 μm-length.

View full abstract

Diesel engines, in recent years, come to apply high pressure charging and high EGR to improve engine performance. In this situation, it is important to study on diesel spray behavior and mixture formation under those kinds of condition. This study investigates diesel spray development and micro-scale characteristics of droplets evaporation including atomization under high density and high temperature atmosphere. Experiment was carried out by shadowgraph photography method. Our system has a nano-spark light source to illuminate spray injected into spray chamber. The image analysis can reveal droplets size-distribution and droplets dynamic behavior at spray boundary. Results indicate that, at early stage of injection, high atmospheric density accompanied with high temperature greatly affects droplets atomization and evaporation at spray boundary. High density atmosphere produces small-size droplets. Evaporation of large-size droplets is improved with high density and high temperature atmosphere.

View full abstract

The water emulsified fuel consists of base fuel oil and water doped with or without a trace content of emulsifier. It is known that the water emulsified fuel is effective for suppressing NOx and soot emissions. In this study, the water emulsified fuel was produced without addition of any emulsifiers. And the combustion characteristics of heavy oil C and its water emulsified fuel were investigated on a small-scale combustion furnace. To investigate the effect of water content ratio on thermal efficiency and exhaust gas characteristics at the condition of constant excess air ratio. As a result, it is clarified that the optimum water content ratio to reduce NOx and dust emissions as well as to improving the thermal efficiency is about 10%.

View full abstract

Mainly steam is utilized as a means for thermal energy supply in industrial fields. It is important to be aware of the steam flow rate in the view point of energy management. However, steam becomes wet in many cases in the process to be sent through steam pipes to machinery using steam. It is well known that the wetness of steam sometimes causes measurement errors of the steam flow rate, and there has scarcely been the established method for estimating the error caused by the wetness of steam flow. Accordingly, we conducted the experiments of wet steam flow rate measurement to clarify the measurement error caused by the wetness of steam. This paper reports the measurement using a vortex flow meter, following our previous paper using an orifice flow meter⁽¹⁾. The experiments were conducted with the conditions in changing the flow rate, pressure and wetness. As a result, the correlation between the measurement error and the flow condition was clarified.

View full abstract

This paper reports about a centrifugal heat pump producing high temperature water. The heat pump is charged a single refrigerant HFC-134a and is adopted for a high efficiency centrifugal compressor and a brazed plate heat exchangers. Rated performance of the heat pump confirmed COP=3.0. The heat pump was applied for a transformer manufacturing factory as an alternative to the boilers. Low temperature heat source of the heat pump is exhaust gas in the factory. As a result, the heat pump has been satisfied high COP at factory operations. In addition primary energy consumption of manufacturing system has been reduced by 27%. And CO₂ emissions of manufacturing system has been reduced by 44%.

View full abstract

The role of turbulence in the combustion systems of flame propagation and diffusion combustion is to mix burned region with unburned region to promote combustion. Meanwhile homogeneous charged compression ignition (HCCI) is a combustion system which goes through the chemical reaction in overall field. It makes no rigid distinction between unburned region and burned region, and differs from the systems of flame propagation and diffusion combustion. Therefore, the role of turbulence in HCCI differs from other combustion systems. Three-dimensional direct numerical simulation (DNS) of auto-ignition process of n-heptane/air mixture was performed to analyze the interaction between chemical reaction and turbulence. In conclusions, the progress of chemical reaction delays under the area where rotation dominants in comparion with the area where distortion dominants under higher temperature region. Turbulence makes complicated structure of heat release which includes sheet and coherent structures.

View full abstract

Fundamental examinations were carried out about the influence of turbulent fluctuation of temperature and gas composition on the radiative heat flux arriving at the wall of large-scale industrial furnaces, where the absorption of radiative energy on its path until furnace wall cannot be disregarded. Line-by-line analysis based on detailed absorption line database is utilized in this study to avoid confusing the influence of turbulence radiation interaction and the error raised by radiation models. Paying attention to a typical optical path in radial direction, growth of radiative intensity along the optical path was evaluated for some cases where the fluctuation of temperature and/or gas composition is taken into consideration or neglected. The results show that radiative heat transfer toward the wall of large-scale furnaces is considerably underestimated by neglecting the fluctuation of both temperature and composition. And the negligence of only one of temperature fluctuation or composition fluctuation leads to fair underestimation of almost same level. In addition, whether the spatial correlation of turbulence fluctuation extends to near or far hardly changes the radiative wall heat flux, though the fraction of radiative energy absorbed on the optical path is fairly large in the test case of this study.

View full abstract

An effective method is proposed for handling turbulent fluctuations of temperature and partial pressure of infrared-active gas in order to evaluate radiative heat transfer under the influence of turbulence-radiation interaction with fair accuracy and feasible calculation load, assuming large-scale industrial furnaces where the re-absorption of radiative energy by combustion gas on optical path toward objects to be heated cannot be neglected. The proposed method realizes feasible calculation load suitable to simulation tools based on two kinds of simplification. Firstly, assuming that temperature fluctuations of arbitrary two positions are independent from each other, local emission of radiative energy from turbulent combustion gas is treated as steady emission though its value is evaluated by averaging the fluctuating intensity corresponding to turbulence. Secondly, absorption of radiative energy by turbulent combustion gas on the optical path is evaluated based on the steady spatial distribution of absorption coefficient in correspondence to spatial distribution of time-averaged temperature. Validity of the proposed method is examined on a model optical path imaging the typical course of radiative energy in large-scale industrial furnaces. H₂O is selected as fuel taking the reliability of absorption line database into consideration. Examination results indicate that the validity of proposed method is secured even if the cross-correlation of temperature fluctuation extends over realistic distance and even if the fluctuation intensity is fairly large. The error attendant to proposed method is sufficiently smaller than the error raised by entire neglect of turbulent fluctuation of temperature and gas composition.

View full abstract

The purpose of this study is to clarify the fundamental and general features of N₂O formation during the combustion of pulverized biomass under low temperature. First, the effect of various important factors, i.e., combustion temperature, volatilization process (i.e., either slow or rapid dispersion), and nitrogen content in biomass on N₂O formation were investigated by numerical analysis. The analysis of the effect of combustion temperature on the formation of nitrous oxide showed that N₂O emission level increases with the decrease in combustion temperature, and both N₂O and NO levels are strongly dependent on the combustion temperature. In other words, there is a trade-off relationship between the formation of NO and that of N₂O. The analysis of the effect of the slow/rapid volatilization process on the formation of nitrous oxide showed that the conversion ratio of biomass-N to N₂O increases with the decrease in the dispersion of volatile matter per unit time; it means that biomass-N is effectively converted to N₂O during slow volatilization. Further, the gasification reactions among CO₂, O₂, and C occur simultaneously on the surface of biomass particles during combustion. With respect to the effect of nitrogen content in biomass, the N₂O emission level increases with the increase in N-content of the biomass, while the NO emission level remains constant during low-temperature combustion.

View full abstract

To investigate the front shape and fluctuation of cellular flames on a flat burner, we treated CH₄/Air mixtures and two types of CH₄/O₂/CO₂ mixtures. We obtained the front shape of cellular flames, i.e. the cell width and cell depth, by the planar laser-induced fluorescence of CH radicals (CH-PLIF) and measured the light emission to clarify the characteristics of fluctuation of premixed flames. As the flow rate of methane decreased, the cell width and cell depth became larger, and the size of attractors increased. Compared with CH₄/Air mixtures, cellular fronts were observed at large flow rates of methane in CH₄/O₂/CO₂ mixtures, and the trajectory of attractors was complicated. These were because of high intensity of diffusive-thermal instability resulting from the replacement of N₂ with CO₂.

View full abstract