Air-water two-phase flow experiments were conducted to investigate the centrifugal gas-liquid separation performance in the scale of a BWR separator. Two-phase flow features in the standpipe and the separation performance in the barrel were evaluated mainly by radial distribution of void fraction, measured with dual optical void probes. From the flow measurement results in the standpipe, the flow would reach quasi-developed state within about H/D=10. This finding can be supported by previous studies of two-phase flow in vertical large-diameter pipes, for not only air-water system but also for steam-water system. The standpipe length in the BWR was evaluated by applying these results.

View full abstract

This paper describes the estimation of flow pattern by using such statistical parameters as power spectrum and auto-correlation function based on measured data of void-fluctuation. Experimental conditions were the following: the test section was a vertical tube of 20mm in inner diameter and the measurements were carried out for bubbly and slug flows. Time series of cross-sectional area-averaged void fraction in gas-liquid two-phase flow were measured by means of fluid conductance technique. It was shown that the minimum value of auto-correlation function estimates the flow pattern transition of gas-liquid two-phase flow well.

View full abstract

Vapor bubbles in water subcooled flow boiling were observed visually to investigate the bubble rise characteristics after the departure from a nucleation site and the mechanism of the increase of void fraction with wall heat flux. Three typical bubble rise paths were observed in the present experimental setup: some bubbles slid upward the vertical wall for long distance, while other bubbles were detached from the wall after sliding for several millimeters and then migrated toward the bulk liquid; after the migration, some of the detached bubbles were collapsed in subcooled liquid but others remained close to the wall and were reattached eventually to the wall. It was suggested that the variation in bubble shape from flattened to more rounded was of primary importance for the occurrence of bubble detachment. The dependence of void fraction on heat flux was influenced significantly by the mass flux: the void fraction increased smoothly with heat flux at low mass flux while the increase of void fraction with heat flux was almost negligible near the onset of nucleate boiling (ONB) at high mass flux. It was considered that the difference in bubble size caused the difference in the dependence of void fraction on heat flux.

View full abstract

In this research, the influence on the condensation heat transfer according to the transition of gas-liquid contact area, temperature conditions, and a mixing non-condensable gas with the condensation of the single steam bubble that rises continuously in water is observed with a high-speed camera. And, the condensation heat transfer coefficient was evaluated by adding the image data processing to the obtained observation results. It was shown that the condensation heat transfer coefficient was calculated from the obtained transition of gas-liquid contact area and ran from 10^4 through 10^5 according to the effect of each parameter.

View full abstract

In particle methods, complex behavior of interfaces of multi-phase flow can be analyzed by fully Lagrangian treatment. Thus, detailed analysis of multi-phase flow in nuclear reactor cores is carried out using a particle method. Droplet and liquid film behaviors are analyzed in Boiling Water Reactors. In the droplet analysis, it is clarified that re-entrainment accompanied by the deposition process cannot be neglected. In the liquid film analysis, a new approach, a particle-mesh hybrid method, is developed for efficient calculations.

View full abstract

For single-phase turbulent mixing rate between triangle tight lattice subchannels, a new prediction method was developed by modifying Sadatomi et al.'s model (1996). The method could predict well the present data as well as the data for several triangle lattice channels in literatures.

View full abstract

The Reduced-Moderation Water Reactor (RMWR) adopts a tight-lattice core with triangular fuel rod arrangement and remarkably narrow gap spacing between rods. The criteria of boiling transition (BT) is one of most important subjects for such reactor but there has been no sufficient information from previous experimental or analytical studies about the effects on the gap spacing, grid spacer shapes on the BT characteristics. Thus, we start to develop a detailed two-phase flow simulation code with interface tracking method to get information of two-phase flow in tight-lattice bundles. In this paper, the simulation code results are compared to existing experimental results of 2-channel air water mixing tests to verify code performance, and the existing two-phase flow correlation for fluid mixing is evaluated using detailed numerical simulation data.

View full abstract

In order to improve predictability of detailed void distributions in BWR fuel bundles, the Lahey's void settlement model has been modified by implementing the anisotropic void diffusion coefficient that is determined based on the detailed velocity reconstruction model. Through CFD analyses and existent velocity measurements in rod bundles, the wall law was applied as the basic physical mechanism of this reconstruction model. The improved void settlement model was verified based on the past partial bundle void distribution database, GE3x3 and ISPRA4x4.

View full abstract

We started R&D project to develop the predictable technology for thermal-hydraulic performance of Reduced-Moderation Water Reactor (RMWR) in collaboration with power company/reactor vendor/university since 2002. The RMWR can attain the favorable characteristics such as effective utilization of uranium resources, multiple recycling of plutonium, high burn-up and long operation cycle, based on matured BWR technologies. MOX fuel assemblies with tight lattice arrangement are used to increase the conversion ratio by reducing the moderation of neutron energy. Increasing the in-core void fraction also contributes to the reduction of neutron moderation. The confirmation of thermal-hydraulic feasibility is one of the most important R&D items for the RMWR because of the tight lattice configuration and the high void fraction. This presentation shows the advances of thermal/hydraulic feasibility study using large-scale test facility and advanced numerical simulation technology.

View full abstract

To develop the design correlation for the critical power in rod bundles is indispensable for R&D of Reduced-Moderation Water Reactor (RMWR) which adopts a triangular tight-lattice fuel rod configuration. In this research, critical power correlation developed for tight-lattice rod bundles is improved by using newly obtained 37-rod bundle data with 1.0mm gap between rods. Compared to the existing correlation, which based on the data obtained in 37-rod bundle data with 1.3mm gap, the improved one expands its adaptability to tighter rod bundles whose rod gap is 1mm, by revising the dependencies on mass velocity and equivalent heated diameter. The improved correlation is confirmed being able to give good critical power predictions to both its based datasets and Bettis Atomic Power Laboratory (BAPL) data. The standard deviation of ECPR (Experimental Critical Power Ratio) to JAERI 37-rod data and BAPL data are 7.3% and 8.4%, respectively. Moreover, the improved correlation is implemented into TRAC code, with which the analyses of transient processes postulated for the RMWR are carried out. For the postulated transients for the RMWR, it has been confirmed that BTs can be predicted within the accuracy of the implemented critical power correlation.

View full abstract

The critical heat fluxes and the temperature excursion heat fluxes of narrow-annular flow passages (d=0.5〜4.0mm) were examined under the counter-current flow condition by using water at 0.2, 0.1, 0.05 and 0.02MPa. As the heat flux was increased, the heat transfer began to deviate from the nucleate boiling first, and then the temperature excursion was initiated. When the clearance was narrow; d=0.5〜2.0mm, water penetration was restricted by upward vapor flow. This restriction was well correlated by the falling film type flooding correlation. When d=4.0mm, the restriction was expressed with the flooding correlation of the mixture level swelling with a falling film. The restriction caused the critical heat flux condition and finally resulted in the temperature excursion. The correlation of the temperature excursion heat fluxes was developed based on the Kutateladze type flooding correlation.

View full abstract

We are developing technologies for "Innovative Simplified Nuclear Power Plants" in order to improve the economy and safety for the further nuclear power plants. The purpose of our developing technologies is to significantly simplify equipment and reduce physical quantities by applying "High-Efficiency Steam Injector (SI)". It is applicable to wide operational ranges beyond the performance and applicable range of existing steam injectors. We adapted the multistage SI and parallel operation to replace the low-pressure feedwater heaters with SIs. Emergency Core Cooling Systems of nuclear power plants can be replaced by SIs to achieve high inherent safety free from severe accidents by keeping the core covered with water (Severe Accident-Free Concept). This report describes the demonstration test of the visualization of water injection into the core by applying a Low-Pressure SI to validate the capability of a SI-driven Core Coolant Passive Injection System. This research project is carried out by Tokyo Electric Power Company, Toshiba Corporation, and six Universities in Japan, funded from the Institute of Applied Energy of Japan as the national public research-funded program.

View full abstract

A steam injector (SI) is a passive jet pump with no movable parts, able to drive water by supersonic steam jet, reaching a discharge pressure even higher than the supply steam pressure. Moreover the SI works as a direct contact heat exchanger between steam and water. We have developed multi-stage SIs by using steam directly extracted from the turbine, which has high performance in wide operation range and can be used in parallel-operation to simplify feed-water heating system of nuclear and thermal-power plant. In this study, we carried out endurance test in order to verify the performance and resistance of the SI under operation during prolonged time period. The SI has undergone a global amount of 80 hours operation with steam and no performance degradation has been evidenced. According to inspection of inner parts of SI, good resistance of the component was shown in continuous operation under conditions similar to those for which it is designed.

View full abstract

In order to clarify the fragmentation mechanism of a metallic alloy (U-Pu-Zr) fuel on liquid phase formed by metallurgical reactions (liquefaction temperature=650℃), which is important in evaluating the sequence of core disruptive accidents in metallic fuel fast reactors, a series of basic experiments was carried out using molten aluminum (m.p.=660℃) and sodium under the thermal condition that the boiling of sodium does not occur. The thermal fragmentation of a molten aluminum drop with a solid crust is caused by transient pressurization within the drop confined by the crust even in such a thermal condition. This indicates the possibility that the metallic alloy fuel on liquid phase formed by metallurgical reactions can be fragmented without occurring the boiling of sodium on the surface of the melt.

View full abstract

Spontaneous vapor explosion can occur when a layer of the high temperature molten material lies on the water pool or on the moisture floor. This is so-called base-triggered vapor explosion. The base-triggered vapor explosion is supposed to occur in the case of a severe accident in a nuclear reactor and in other industrial facilities. It is very important to clarify the base-triggered vapor explosion from the viewpoints of the prediction and the prevention of the vapor explosion. In order to evaluate the heat transfer and fluid dynamic behavior of the base-triggered vapor explosion, the experimental apparatus is designed and constructed. The experiments using U-Alloy95 as a stimulant material are conducted. Consequently, the behavior of the molten material can be observed in detail with this experimental apparatus. Image processing including the digital auto-correlation method are also applied to the visual observation data obtained on the experiments in order to evaluate the velocity of the molten material. Based on the velocity, the conversion ratio of kinetic energy in initial thermal energy at the vapor explosion is also evaluated.

View full abstract

We investigated the water hammer caused by striking of water mass pushed up by a rapidly growing bubble and its scale effects using three cylindrical model containment vessels of 0.428, 1.0 and 2.0m diameters. We also closely observed the movement of water mass and the growing bubble in the vessels. In these experiments, rapid bubble growth was simulated by injecting high-pressure air into a water pool. It was clarified that the water mass was pushed up without any air penetration until the water level reached a certain elevation. The acceleration of the water mass was almost constant. On the basis of all data, scale effect of the vessels and the water hammer pressure for exerting large forces on the structures were quantitatively evaluated.

View full abstract

Shown below are experimental results on characteristics of reactor instrumentations including a coolant mass tracking method and core exit thermocouples (CETs) which are necessary to precise operator actions for accident management (AM) during a loss-of-coolant accident (LOCA) at a pressurized water reactor (PWR). The experiments at the ROSA-V/LSTF facility of the Japan Atomic Energy Research Institute simulated small break LOCAs at the PWR vessel bottom and clarified effects of secondary depressurization as one of the AM measures in case of high pressure injection system failure and non-condensable gas inflow from the accumulator injection system. It was shown that the coolant mass tracking method based on three types of water level instruments could detect most of the primary coolant mass change between the initial state and core-heatup starting condition. The CET characteristics to detect the core heatup conditions were significantly degraded by the condensed water fall-back during the secondary depressurization action.

View full abstract

The Advanced Energy System Project (AESP) aims to develop commercially viable systems and technologies that provide electricity and heat such as hydrogen, methane, methanol, fuel cells using heat from small nuclear reactors, gas-turbine power plants and the sun. AESP has three objectives: (1) Save energy resources and reduce global warming gas emissions, attaining total energy utilization efficiency higher than 85% through waste heat recovery and utilization. (2) Foster a recycling society that consumes that garbage, waste wood and used paper that are produced in urban centers, along with excreta produced through farming to generate hydrogen, methane and methanol for fuel cells using waste heat and solar energy. (3) Consume trans-uranium elements produced in light water reactors as fuel for the small fast reactors, and reduce long-lived radioactive wastes or environmental loads of long term geological disposal.

View full abstract

This paper describes results of cycle efficiency calculation and gas turbine aerodynamic design for the supercritical CO_2 gas turbine coupled to the Na cooled fast reactor indirectly. In this system, the turbine inlet temperature is 527℃ and thermal capacity is 600MW. The pressure was varied from 12.5MPa to 20MPa. Effect of providing an intercooler was also examined. For the cycle of non-intercooling at 20MPa, an aerodynamic design of turbine and compressors was carried out based on the method for the air gas turbine. The values of number of stages, dimensions of bladed section and adiabatic efficiency were revealed. The marked feature of the supercritical CO_2 gas turbine is large values of gas-bending force.

View full abstract

The application of a supercritical carbon-dioxide (CO_2) turbine cycle to FBR could enhance its economy and reliability because the compact CO_2 turbine system is to replace the steam turbine system and the intermediate heat transport sodium system of the conventional LMFBR. Thus, three experimental studies have been started concerning the subjects such as the system performance of the supercritical CO_2 cycles, the CO_2 corrosion on component materials, and the Na-CO_2 reaction in case of a heat exchanger tube failure. While the construction of the test rigs was finished and experiments have started as for the former two items, the Na-CO_2 reaction proves to be exothermal which has threshold on the sodium temperature.

View full abstract

This paper describes the development of high performance Micro Channel Heat Exchanger (MCHE) with supercritical CO_2 as a working fluid. MCHEs are made by etching and diffusion bonding. MCHEs have flow channels with a small hydraulic diameter. Many fins are disposed on the heat transfer surface in order to improve thermalhydraulic performance. The experimental study of MCHE thermalhydraulic performance using a supercritical CO_2 loop has been performed. The comparison of experimental data and calculated results are presented in this paper. The further optimization of heat transfer and pressure loss was done by three dimensional calculations using FLUENT CFD code. As a result the pressure drop is reduced by factor five keeping the same heat transfer performance.

View full abstract

The zero waste heat release cogeneration system for power generation plant is described. In order to demonstrate the applicability of waste heat recovery system with supercritical CO_2 as a working fluid the experimental study has been done. The thermohydraulic performance of condenser and hot water supply heat exchanger was estimated. The advanced Printed Circuit Condenser (PCC) for steam condensation and Micro Channel Heat Exchanger (MCHE) for hot water supply were designed. The application of cogeneration system results in increasing the energy utilization factor up to 85%. The described waste heat recovery system might be used for any power cycle with steam condensation at low pressure.

View full abstract

Conceptual design studies of supercritical CO_2 gas turbine system applied in both cases of high temperature operation reactor(〜950℃) such as HTGR and medium temperature (〜600℃), such as fusion reactor have been developed and performance and optimization of control conditions of both reactor systems were evaluated. Maximum cycle efficiency of 49% and 46% were optimized in the case of HTGR Brayton cycle and fusion partial cooling cycle, respectively.

View full abstract

As an application of supercritical CO_2 cycle, computational fluid dynamics (CFD) with conjugate heat transfer was performed to analyze performance of printed circuit heat exchanger (PCHE). Massively parallel computation with 1200 CPUs was used to reduce the computational time of huge models including more than 100M DOF. For the connection between plates of solid regions, non conformal or coupled mesh was adopted. Finite volume method fluid analysis code "FLUENT" coupled with a fluid property package "PROPATH" was employed. As results of analyses, effectiveness of parallel computing method was verified for the application to PCHE.

View full abstract

A 10×10mm micro flow circuit of 1×1mm cross-sectional flow area was manufactured. The circuit filled with water had two tanks with free surface and one dead-end branch with a closed tank. A single bubble was cyclically generated and condensed in the dead-end branch tank so as to create forth and back oscillatory flow in the branch pass. A flow state in the flow circuit was visualized by dissolving dye in fluid. The flow state was also recorded with a high speed video camera to derive a flow velocity by utilizing the PTV method. It was confirmed that uni-directional circulation flow was created in the flow circuit without any pumps and valves. Although the created flow was oscillatory, back ward flow was never observed. The time averaged velocity in the flow circuit was 2.71×10^<-3>m/s. Numerical simulations of the flow in the micro flow circuit were also performed by using STAR-CD code.

View full abstract

The flow behavior in the wake region of the thin wire of 1mm and the heat transfer were examined. The flow field was visually observed by using fluorescent dye and a YAG laser beam. Numerical analyses were also performed by a STAR-CD code. The vortex shedding rates of the STAR-CD analyses for the 10mm wire were close to the existing correlation, however, much lower for 1mm. The measured rates for the 1mm wire were larger than correlation's values. Measured heat transfer rates were close to existing correlation's values. However, the variation trend for the Reynolds number was a little bit different from the correlation. STAR-CD analytical values were a large different from correlation's values.

View full abstract

In the present study, micro gas-liquid separator using surface tension is investigated by water-air experiment. The gas bubbles are forced out from the liquid flow which is confined inside the groove at the expanding part of the separator by the minimization effect of excess gas-liquid interface free energy. Perfect separation is obtained for low velocity and high quality conditions.

View full abstract

In this paper, we investigate the effects of fuel supply conditions on the power generation characteristics of a small tubular solid oxide fuel cell (SOFC), In the experiments, the furnace inside temperature is fixed at 800℃ or 850℃, and the hydrogen/nitrogen mixture (1%/99% or 10%/90%) is fed into the single cell as the fuel with the different flow rate conditions. The results show that the flow rate affects the current-voltage characteristics, that is, the net voltage becomes higher with increasing the fuel flow rate. The data of the fuel utilization and the power generation efficiency at the operating points, which give the maximum power output individually, are estimated. Therefore, it is found that excess fuel supply leads to the increase of power output, but the fuel utilization and efficiency decrease simultaneously. The optimum flow rate does exist according to the respective hydrogen concentration. Under the operation with 10% hydrogen, the power generation efficiency reaches to 4.0% with the fuel flow rate of 20mL/min.

View full abstract

In the present study, numerical simulation of thermo-fluid dynamics and electrochemical reaction in a small tubular solid oxide fuel cell (SOFC) was carried out. An experiment was carried out to compare the measured output characteristics with the simulation result. The simulation result was formed in good agreement with the experimental data. The simulation revealed that the effect of radiation heat transfer on the temperature distribution is significant. Additionally, the inline arrangement with a small pitch in the air flow direction shows the most uniform temperature distribution.

View full abstract

A micro ejector for butane catalytic combustor is investigated. Quasi-1-D computation and CFD analysis are conducted to investigate the effect of various design parameters on ejector performances. A truly 3-D micro convergent-divergent nozzle having a throat diameter of 42μm is fabricateed by electro-discharge machining. It is shown in experimental evaluation of the present micro ejector that the volume flow rate of entrained air can reach 43 times the value of butane when the back pressure of ejector is set as 11.6 Pa.

View full abstract

Computational fluid dynamics (CFD) simulation was performed to investigate flow inside MEMS-based ejectors. The ejector is a microdevice to supply air to microcombustors using the jet of liquid gas fuel ejected from a nozzle. The simulation results were compared with experimental results, and found to show fair coincidence with them. Thus, the CFD simulation is useful to understand the experimental results, find problems and finally improve the performance of the ejector. For example, the CFD simulation confirmed that sudden increase in sucked air at a certain flow rate of ejected gas was due to supersonic flow outside the nozzle. It also found the problem that the ejected gas and sucked air were not fully mixed in the ejector.

View full abstract

A hydroinertia micro-high speed gas bearing to realize high-speed operation of a micro-rotor at 870,000 rpm for a micromachine-gas turbine of the impeller diameter 10mm, has been developed. The diameter of the journal bearing is 4mm. The outer and inner diameters of the thrust bearing are 10mm and 5mm, respectively. Hydroinertia gas bearing is a type of hydrostatic gas bearing with larger bearing gap than usual. The flow in the wider side of the gap becomes supersonic and generate suction forces to pull them back. The loading capacity can be larger than that of usual hydrostatic bearings. The target speed of 870,000 rpm has successfully been achieved by increasing the supply pressure of the thrust bearings, and shortening the bearing length.

View full abstract

Hydrostatic air bearings for MEMS-based turbines with low L/D (bearing length/diameter) were designed and fabricated. The radial bearing is a 12-port inherent orifice air bearing, and the thrust bearing is a hydroinertia air bearing. The thrust bearing was tested, and stable levitation of the φ4mm rotor with 50μm gap was demonstrated at a bearing pressure of 0.2〜0.3 MPa. This result fairly agrees with the design calculation.

View full abstract

Wet biomass comprises diverse organic wastes, which are discarded vastly in our society. Energy production from them, therefore, is significant. In this paper, an energy-saving dryer named VCC (vapor compression and condensation) is proposed to dehydrate wet biomass. The dried biomass could be used as a fuel to generate electricity. It was estimated the VCC dryer process would generate more electricity than anaerobic digestion. A scheme employing the VCC dryer was proposed to utilize various biomass resources regardless of wet and dry.

View full abstract

High efficiency drying is one of the challenges to utilize wet biomass as solid fuel. In addition, usually wet biomass has stinky smell and includes hazardous bacteria, so to collect and convey wet biomass is difficult. We propose a novel pretreatment technology for wet biomass. It is the hydrothermal reforming employing saturated steam at 473K with mixing rice husk. This pretreatment technology has two features; one is increasing effect of apparent drying rate of solid products, another is reforming effect of stinky and distinct odor of sewage sludge. As results of experiments used sewage sludge as model wet biomass, the apparent drying rate of the solid product became four times as large as that of the reactant. And, concerning the stinky smell, the concentrations of H_2S and NH_3 originated from the solid product decreased compared with the sewage sludge by this reforming. This hydrothermal reforming needs little energy compared with conventional indirect heating drying. So, this hydrothermal treatment is appropriate as pretreatment for wet biomass fuelization.

View full abstract

Development of high-efficient gasification technology is now under way as an R&D project entrusted by NEDO in collaboration with KOBELCO, IHI, Kyoto University, Hokkaido University and CRIEPI. This R&D project is directed to develop pretreatment technology realizing calorie-improvement of biomass by applying dehydration-in-oil technology, and to develop pyrolytic gasification technology realizing highly effective gasification. In this project CRIEPI is involved in the study on the gasification reactivity for biomass reformed in oil and on the CFD for gasification. This report shows both the gasification reactivity & modeling of the coffee-residue reformed in oil and the simulation results of gasifier based on CFD technology.

View full abstract

From a viewpoint of environmental preservation and resource protection, the recycling of wastes has been promoting. Expectations to new energy resource are growing by decrease of fossil fuel. Biomass is one of new energies with prevent global warming. This study is an attempt to burn pelletized woody biomass (Bio-pellet) made from sawdust and logging residue in order to thermally recycle waste products of forestry and lumbering industry. Fundamental data on Bio-pellet combustion were obtained in an electric furnace. Combustion appearance, weight and temperature of pellets were investigated under specified furnace temperatures and sizes to obtain combustion characteristics such as ignition delay, burning period, char-combustion time and the change of weight decrease and temperature rise.

View full abstract

While a number of examples are shown in co-generation system (CGS) in recent years, it is not so easy to build up the effective systems in heat energy usage at digestive gas plants. The reason is hard to seize the difference of the exhaust heating energy in the system, which always tends to be variable in each season. Especially in cold circumstances, most of co-generation energy was forced to exhaust to heat up the tanks, since it needs to keep the digested sludge temperature over 39℃. In the study, CGS of MGT plant operated in digestive gas was tested and analyzed to achieve smoothing use of digestive gas through the year, in order to solve the shortage problem of heating energy. One of the methods is to make methane hydrate (MH) production and to use in cold seasons, and it was also tried to simulate its probability to use in this CGS system.

View full abstract

The Ring Type Reflector solves the problems on the mechanical integrity of central reflector against wind force, wider focus and dilution of beam concentration at receiver aperture. The power generation cost for the Beam-Down system was estimated to be 8.98 US cents/kWh. And, about half of the capital cost of 8.17 US cents/kWh of the Beam-Down is the heliostat cost, therefore the capital cost will be 5.37 US cents/kWh, when the heliostat cost is reduced by 30% (the total cost=6.19 US cents/kWh). This figure is near the cost of the fossil fuels of coal (4.38 US cents/kWh) and natural gas (4.81 US cents/kWh). The total cost of 6.19 US cents/kWh can be further reduced by 20%, when the new heliostat arrangement process of the Dual Tower Concept is applied (the number of the heliostat and tower height can be reduced). Then the total cost of the Beam-Down will become 4.90 US cents/kWh, which can be competitive with coal and natural gas. This cost is about 1/4 of the solar PV cost (16.48 US cents/kWh).

View full abstract

A novel receiver concept is established for a solar thermal concentrating system. The receiver enables solar heat concentrated by beam-down method to be transferred to heat transfer medium (molten salt) efficiently. Conventional receiver is an indirect type of heat exchanger in which solar heat is transferred to the molten salt through the wall of a pipe containing the molten salt. To the contrary, the present receiver is of a direct type where concentrated solar beam directly heats the molten salt forming a liquid film gravity flow along inner surface of a cavity container. Theoretical expression for the thickness of the liquid film is derived and examined by the simulated experiment using water. Using the expression, surface temperature of the liquid film is evaluated to a typical heat flux from the concentrated solar beam transferred from the surface, which results in much lower value than the temperature limitation where chemical decomposition of the molten salt is anticipated.

View full abstract

This paper presents the concepts and results of a study aimed at developing and demonstrating a direct solid polymer electrolyte (SPE) fuel cell stack that operates on dimethyl ether (DME). As a preliminary work, a test stack (three cells stack) was developed for understanding the requirements for the auxiliary operation systems including fuel supply and gas humidification.

View full abstract

A fuel cell was made to allow direct observation of the phenomena in the cell, 2-D temperature measurement in cathode channels, and local current density measurements in anode side. The experimental results showed good correlation among direct view in the cell, temperature distribution and local current density. The experiment indicates transition phenomena of dry out and flooding depending on the flow and current conditions. The results suggests the possibility of different current density distribution for the same experimental conditions depending on the previous MEA condition history.

View full abstract

In PEFC at low temperature, the freezing of produced water induces the extreme deterioration of cell performance. The characteristics of start-up below freezing in a wide variety of current densities was investigated and the cell impedance measurements was conducted to clarify the freezing phenomenon in PEFC. It was confirmed that the characteristics can be related to the amount of produced water and the rise in cell temperature by reaction. It was also showed that increase of reaction resistance, which was considered to be mainly due to increase gas transfer resistance, has much effect on freezing phenomenon.

View full abstract

The performance of a polymer electrolyte fuel cell (PEFC) operating on pure hydrogen and air is primarily limited by the performance of the cathode side. At high current densities, the transport of the reactant (O_2) to the catalyst layer is limited by accumulated liquid water inside the gas diffusion layer (GDL), which causes flooding. A carbon cloth GDL displays better performance than a carbon paper GDL under humidified conditions. To investigate these phenomena, neutron radiography was used to compare the amount of liquid water that accumulated in the cell with different GDL materials. It was found that a larger amount of water accumulated in a carbon cloth GDL than in a carbon paper GDL. From the standpoint of cell performance, the carbon cloth GDL was less influenced by the accumulated water than the carbon paper GDL. A carbon cloth GDL has a larger porosity distribution than a carbon paper GDL. It is assumed that carbon cloth allows O_2 transportation through the GDL due to the material's larger pores even though water accumulates in the layer.

View full abstract

For the purpose of examining feasibility of COSMOS (CO_2 Sending Method for Ocean Storage), we conducted seven in situ CO_2 storage experiments off California in the United States. As a result, we confirmed that liquid CO_2 could be stored stably without 'overflow' at the depth of 3,960m, and that surface of stored CO_2 was almost always protected from dissociation into seawater by thick layer including CO_2 hydrate membrane at natural flow condition. Also, we found that hydration rate of CO_2 molecules was slower than their diffusion rate at various depths, and that the hydration rate varied according to pressure.

View full abstract

The diameter of dissolving CO_2 drops with CO_2 hydrate films wider conditions with slight water flow was measured and compared with that predicted from a dissolution model including flow effect to investigate the effect of water flow on the dissolution of CO_2 drops stored on the deep sea-floor for ocean storage of CO_2. The dissolution of CO_2 drops was enhanced by water flow. The dissolution rate almost agreed with the model during the period that the amount of dissolved CO_2 was relatively small while an increase in dissolved CO_2 with both of time passing and an increase in flow velocity provided lower dissolution rate than that predicted from the model. The measurement of pH showed the dissolution of CO_2 drops lowered pH near the drops, and the pH lowering was enhanced by an increase in flow velocity. These results suggest that a lowering of the difference of CO_2 concentration between on the surface of the drop and nearby would provide lower dissolution rate than that predicted from the model.

View full abstract

The Japanese Ministry of Economy, Trade and Industry began, in 2002, a five year project on CO_2 sequestration in coal seams, entitled as "Japan CO_2 Geosequestration in Coal Seams Project (JCOP)". The purpose of this project is to develop a series of processes that can extract the CO_2 discharged from thermal power plants and other large scale emitters, fix it within coal seams in a stable state, and in the process, recover methane as a clean energy source. This paper describes overview of the project and introduces CO_2 sequestration test results at the Ishikari coal filed test site. The results indicated the advantage of CO_2 sequestration in coal seams, that is, CO_2 was sequestrated and at the same time, the recovery of coalbed methane was enhanced.

View full abstract

In the concept of the Carbon dioxide Capture and Storage (CCS), the CO_2 is captured from emission source and stored into geological reservoirs at a depth about 1000m. The injected CO_2 is less dense than water to migrate upward so that the reservoirs should be covered with a sufficiently impermeable seal, i.e. cap rock, for trapping the injected CO_2. However, the cap rock may contain imperfections such as faults and fractures which will be a high permeability path to arise leakage of the injected CO_2 from reservoirs. To overcome such problem, we will present here an idea to reduce artificially the permeability of the leakage paths and rock itself for trapping enhancement. In this idea, a solution is supposed to be injected into the fractures and rocks in concern, and then the permeability should be reduced by clogging the pore space in the fractures and rocks with a material produced by chemical reaction between the injected solution and CO_2.

View full abstract

We experimentally investigated the characteristics of dissolution rate of CO_2 into water in porous media and the behavior of emitted CO_2 from porous media in sequestration conditions. Dissolution rate of CO_2 were summarized as a relationship between the modified Sherwood number and Reynolds number. Liquid CO_2 shows a high mass transfer rate as compared with gas and supercritical states. Carbon dioxide is emitted from porous rock in bubble form with diameters of about 1mm in gas state and much finer in liquid state.

View full abstract

This paper describes experimental research on two-phase flow of supercritical CO_2 and water in a Berea sandstone core. We used a magnetic resonance imaging (MRI) technique to directly visualize the distribution of supercritical CO_2 injected into the sandstone core containing water. In-situ saturation distributions were successfully visualized under the temperature and pressure conditions corresponding to the aquifers at the depth of about 900m with a projection method every 10 seconds. A new coreflood interpretation method proposed by Good field et al. was applied to in-situ saturation data to evaluate two-phase flows in sandstone directly. We have experimentally demonstrated that capillary dispersion rate could be evaluated as a function of water saturation independent of viscosity and buoyancy.

View full abstract