Koji Matsubara

• Doctor of Engineering
• Professor at Niigata University

Next-generation drone needs a high energy density, long life, and light weight portable power source. This work focus on a combined power system consists of micro gas turbine and high-speed generator. In recent years, combustion using porous media has been attracting attention due to factors such as high power output relative to weight. Combustion...

Modern society faces major social problems such as the future depletion of fossil fuels and the acceleration of global warming due to the increase in greenhouse gases resulting from their use. On the other hand, the demand for energy will continue to increase due to population growth and economic growth. In response, carbon recycling and decarboniz...

In order to collect the data required to further improve the design of solar porous receiver/reactor, we use open-source software to conduct simulations and study the effect of radiative heat transfer and convection inside. By using Gaussian heat flux distribution to simulate differing focal length and study their effects on the absorption and dist...

In order to produce electricity beyond insolation hours and supply to the electrical grid, thermal energy storage (TES) system plays a major role in CSP (concentrated solar power) plants. Current CSP plants use molten salts as both sensible heat storage media and heat transfer fluid, to operate up to 560°C. To meet the future high operating tempera...

Direct simulation was performed for the solar porous receiver having cubic lattice as elementary structure with high porosity (0.80 - 0.98). The cell size was changed in four steps from 0.49 mm to 2.94 mm at three levels of the power over air mass (POM). Silicon carbide (SiC) was assumed as receiver material, and the absorptivity of the wall surfac...

Solar thermochemical energy storage systems, utilize the entire spectrum of solar radiation to drive endothermic chemical reactions, have received great interest in concentrated solar power applications during the past years. Storing solar radiation as chemical energy during the day can be utilized at night times and cloudy days. In these solar the...

Heat transfer between solids and gases plays an important role in various fields of engineering. In this study, we perform three-dimensional unsteady conjugate heat transfer numerical simulations of solids and fluids in a rectangular computational domain by arranging columns of cylinders parallel to the flow direction. Air is used as the fluid and...

This study focused on porous-inserted channel with radiative heating. A cubic lattice structure is assumed as an elementary porous structure. Open-source CFD code “OpenFOAM” was used to calculate conductive heat transfer in the solid region and heat transfer between fluid and solid region, simultaneously. Heat transfer medium is air. Flow is assume...

Considerable attention is being paid in recent years to develop and improve alternative technologies to replace fossil fuels due to pollution problems and limited conventional energy sources. Solar thermal energy has been considering as one of the most attractive renewable sources to provide solution to the aforementioned problems. In recent years,...

Direct numerical simulation was performed for the entrance region of a channel with repeated ribs under iso-thermal wall heating condition. Heat transfer performance was discussed for the case of the Reynolds number of 20,460 which was based on the mean velocity and the hydraulic diameter. Numerical results indicated that turbulence are generated i...

Conjugate radiation-convection-conduction simulation was conducted for a solar volumetric receiver of silicon carbide honeycomb for high temperature heat absorption at 1,000°C and higher. Simulation was made for three cases of channel cell size: 0.6mm; 1.5mm; 2.9mm. At two levels of incident heat flux 1,400 kW m⁻² and 4,200 kW m⁻², air mass flux wa...

The volumetric solar receiver is a promised technology for high-temperature solar absorption in the concentrated solar power, industrial solar thermal usage and solar fuel production. Existing numerical simulation separated computations of light and convective flow and two-way coupling was not perfectly integrated between radiation and convective t...

The concentrated solar power is utilized for industrial thermal usage, electricity generation and fuel production. To increase the solar thermal temperature is essential for enhancing the thermal efficiency of the energy conversion and for widening application. The synthetic oil, widely used for solar thermal storage, pylorizes at 400 °C, and this...

A transient three dimensional numerical model of the heat transfer and fluid flow of a windowed fluidized bed reactor for solar thermochemical conversions is formulated and solved using discrete element method coupled to computational fluid dynamics. Radiation transfer equation is solved by discrete ordinate radiation model and the particle collisi...

This paper describes and presents the direct numerical simulation of a volumetric solar receiver under concentrated irradiation. The simulations systematically analyze the receiver performance and thermal loss mechanisms for operating conditions when outlet temperatures are in the 1000–1500 °C range. The implemented numerical method fully considers...

This study analyzed efficiency and heat loss of three types of simple and cut-back receivers. The conjugate simulation was made for situation where the honeycomb receiver receives concentrated radiation heating air stream through square cells. The DO (Discrete Ordinate) approach was adopted to calculate the radiation intensity and to fully couple t...

Two-point correlation and integral scale of curved channel turbulent flow were examined for onset and growth of large-scale vortex. Away from the two walls of the straight channel, the two-point correlation of streamwise velocity has large negative values around local minimum at y/δ = 1.6 and those of radial and spanwise components take small negat...

This paper describes conjugate radiation-convection-conduction simulation of a porous solar receiver irradiated by beam-down concentrated light. Simulation was made for three cases where cell sizes and porosity were changed in each of two steps. It was demonstrated that receiver efficiency increased when cell size decreases and porosity increases....

The first performance test of a novel windowed solar fluidized bed reactor was carried out for a two-step water splitting cycle with ceria particles by using a 30-kWth sun-simulator. O2 and H2 were successfully produced by the reactor system. During the thermal reduction step of the two-step water splitting, a fluidized bed of ceria particles was c...

In this research, heat transfer and hydrodynamics of a solar thermochemical fluidized bed reactor filled with ceria particles have been studied numerically and experimentally for beam-down solar concentrating system. A CFD-DEM model has been developed, in which the contact forces between the particles have been calculated by the spring-dashpot mode...

Gasification of carbonaceous materials using concentrated solar thermal radiation has been considered as one of the promising renewable pathways to produce syngas. In this study, thermal performance of a recently developed solar thermochemical reactor is presented. To analyze the gas–solid flow and heat transfer characteristics of the reactor, a tr...

To perform thermochemical cycles using non-volatile metal oxides to split water and produce hydrogen, a directly irradiated fluidized bed reactor is designed and fabricated for beam-down configuration. As the main aim of this investigation is to analyze the heat transfer and particulate flow of the reactor, chemically inert particles are used. A tr...

This study analyzes the effect of cut-back inlets on the conjugate heat transfer of honeycomb-channel solar receivers. Two-way coupling simulations are reported for a plane-surface inlet, and five kinds of cut-back inlet receivers. The receivers are based on a 1.9-mm × 1.9-mm square cell with a 1.0-mm wall thickness. The cut-back inlet receivers ha...

A loop thermosiphon thermal collector was developed for the waste heat recovery power generation with electric capacity of 500 W. The heat collector with heat transfer area of 0.159 m² (500 mm width and 300 mm depth) was connected to the condenser with a shrunken heat transfer area by a loop. The thermal performance of the apparatus was declined wh...

Solar gasification is one of the promising techniques to convert the carbonaceous materials to clean chemical fuels, which offers the advantages of being transportable as well as storable for extended period of time. In this study, thermal performance of a recently developed 5 kWth fluidized bed reactor for solar gasification has been investigated...

A combined numerical and experimental investigation of hydrodynamics and heat transfer of internally circulating fluidized bed reactor for solar gasification of coal coke to produce syngas is reported. As the main objective of this study is to study the thermal performance of the reactor, chemically inert quartz particles have been used. A numerica...

This study investigates conjugate heat transfer problem for honeycomb structure under concentrated irradiation. This simulation model focuses on a unit rectangular channel made by stainless steel. The problem assumes the condition that the honeycomb structure is installed in vertical orientation and heated up by beam-down concentrated irradiation,...

Improving heat storage system is needed to effective operation for concentrate solar power. In order to consist and evaluate packed-bed latent heat storage system, melting experiment of phase change material (PCM) inside a ceramic container in forced convection is operated. An axisymmetric model of heat transfer and fluid flow during melting proces...

Heat transfer between the high temperature fluid and the cylindrical ceramic capsule and the melting process of the PCM inside the capsule were experimented and simulated. Realizable k-ε turbulence model is used in this simulation. Numerically solved results showed trends consistent with the experiment. In the down flow, it was confirmed that the m...

The particles flow and heat transfer characteristics of a high temperature solar thermochemical fluidized bed reactor have been studied for solar beam-down concentrating systems. A numerical model has been developed by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) collisional model since it is an effe...

We performed a direct numerical simulation (DNS) of the turbulent natural convection between two parallel plates at a Rayleigh number of Ra = 8.0 × 10⁶, focusing on the turbulent natural convection affected by radiation in an optically thick fluid . When the effects of the radiation were considered, the flow structure and temperature distribution i...

This paper describes a volumetric solar receiver that is vertically integrated with beam-down optics for condensed light irradiation. The heat-transfer performance of a silicon carbide honeycomb receiver was investigated using a 30-kWth solar simulator and numerical simulation. The experiments achieved an air temperature of 840 K at the receiver ou...

A window-type, solar fluidized bed receiver with quartz sand particles was tested by a 100-kWth novel beam-down solar concentrating system at Miyazaki, Japan. A compound parabolic concentrator (CPC) was placed above the quartz window of the receiver to increase the concentration of the solar fluxes from the beam-down solar concentrating system. The...

This paper presents a numerical analysis of unconstrained melting of high temperature(>1000K) phase change material (PCM) inside a cylindrical container. Sodium chloride and Silicon carbide have been used as phase change material and shell of the capsule respectively. The control volume discretization approach has been used to solve the conservatio...

Numerical simulation was made for high-temperature solar and thermal receivers of pressurized air for solar micro gas turbine system. The solar / biomass hybrid gas turbine was considered to generate 30kW to 100kW power. The gas turbine system was provided with the concentrated solar light from the dish reflector at the solar receiver and the combu...

In this study, a numerical model has been developed by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) collisional model to study the particle-fluid flow of the fluidized bed reactor for solar beam-down concentrating system. The contact forces between the particles have been calculated by the spring-das...

The flow and heat transfer in a curved channel were numerically analyzed for their spatial advancement under the influence of streamline curvature. The simulation was made for the curved channel of the radius ratio 0.92. The curved channel was provided with the fully developed velocity and thermal profile in a straight channel at the mean velocity...

One of the merits of a solar thermal utility is that the cost of heat storage is lower than that of an electrical battery. Furthermore, a power generation system using solar thermal energy with heat storage equipment is capable of stabilizing its output. For a parabolic trough solar concentrator, molten salt is adopted as the heat storage material...

A new particle receiver for continuous supply and discharge of particles was proposed for high-temperature solar thermal acquisitionin concentrating solar power (CSP) combined with Solid Oxide Electrolysis Cell (SOEC). The quartz sand or ceramic particles with high melting point will be used in the new system since conventional molten salt is therm...

Direct numerical simulation was performed for the heat transfer of airflow in the entrance region of a channel with repeated rib protrusions. The rib-pitch to rib-height ratio (Pi/H) was increased from 2.0 to 16.0 by four steps. The rib-height ratio (H/δ) was maintained constant at 0.20. The distribution of heat transfer coefficient numerically sim...

A novel concept of particles fluidized bed receiver/reactor with a beam-down solar concentrating optics was performed using a 30-kWth window type receiver by a big sun-simulator. A fluidized bed of quartz sand particles was created by passing air from the bottom distributor of the receiver, and about 30 kWth of high flux visible light from 19 xenon...

In 2014, Niigata University and the Institute of Applied Energy developed a point-concentration receiver-evaluation system using a silicon carbide (SiC) honeycomb and a three-dimensional simulation method. The system includes several improvements over its forerunner, including the ability to increase/decrease the power-on aperture (POA), air-mass f...

One of merits of a solar thermal utility is that the cost of heat storage is lower than electrical battery. Furthermore, a power generation system using solar thermal energy with a heat storage equipment is able to control its output to be stable. For parabolic trough solar concentrator, molten salt is adopted as the heat storage material by using...

There has been growing interest on renewable energy because of the recent environmental and energy problems. Among them, solar thermal and biomass can be applied to the existing gas turbine cycle as good options to solve current problems. In the EFGT (externally fired gas turbine) cycle, one of the key components is heat exchanger, and improving it...

A new particle receiver for continuous supply and discharge of particles was proposed for high-temperature solar thermal aquisition in concentrating solar power (CSP) combined with Solid Oxide Electrosys Cell (SOEC). The quartz sand or ceramic particles with high melting point will be used in the new system since conventional molten salt is thermal...

Niigata University and TERI collaborated in developing a biomass gas turbine system with an enhanced fuel applicability for rural villages in south Asia. This paper describes a mixed and standard type gas turbine system for this purpose. The mixed type gas turbine employs a regenerated Brayton cycle with a secondary combustor to burn various fuels....

This paper proposes the improvement of microfluidic mixture using the unsteady electroosmotic vortices induced by a staggered array of electrodes. The unsteady electroosmotic forces near two walls, having opposite directions near two walls, were shown to drive organized vortices to contribute for the enhanced mixing. Examination was given to the fl...

This study proposes a t wo-tower t ype fluidized receiver for receiving concentrated s olar light at high temperatures is proposed. This fluidized receiver is coupled with the Miyazaki beam-down reflector system. The visualization and the numerical simulation was made for the laboratory model to show the fluid-dynamics and the heat transport as wel...

This paper describes the thermal collector type loop thermosiphon for low-temperature waste heat recovery. Water is used as the working fluid for heat transport at temperatures 100°C and higher. The loop thermosiphon comprises of a thermal receiver, a condenser, and riser and downcomer tubes. The thermal receiver is made of a cupper plate brazed by...

Mechanisms for dissimilarities between momentum and heat transport in a disturbed turbulent channel flow of air were studied through direct numerical simulations. A square rib protrusion with an aspect ratio of up to 64 was used to minimize constraints that the side boundary imposed on the wake and the related heat transfer. Channel walls were heat...

The point-concentration receiver evaluation system was developed using the world class 30 kWth light source of 19 arc xenon lamps. The system comprises of a receiver unit, heat exchanger, blower, chiller and light source. Precise measurement of the thermal power absorbed by air was performed by the enthalpy rise of the coolant water and that of the...

This study describes the flow and thermal field ofatwo-tower fluidized receiver, aimed tobeincorporated into a beam-down reflector system.Anexperimental visualization and numerical simulation were made to accumulate phenomenological knowledge, in order to complete the design of ademonstration model.Visualization of the cold particle bed with no irr...

This study proposes a novel fluidized receiver for absorbing concentrated solar light at high temperatures. Previously, a tubular receiver and a volumetric receiver were developed to make high-temperature air for a solar gas turbine system. The aim was to combine these elements with a tower reflector; however, it was challenging to install these he...

Steam reforming of methane is a candidate process for converting concentrated high-temperature solar heat to chemical fuels because it is a high-temperature, highly endothermic process. We developed a tubular reformer system using novel double-walled reactor tubes with molten-salt thermal storage for solar reforming to produce hydrogen or synthetic...

A two-step thermochemical water splitting cycle using nonstoichiometric cerium oxide is a promising solar thermochemical hydrogen production process. One of the present authors has developed new solar reactors using “internally circulating fluidized beds” with cerium oxide particles for the high-temperature cycle. These solar reactors need to be co...

We tested a thermosyphon loop with water as the working fluid using heating rates between 100W and 400W. Four kinds of core blocks were installed in the evaporator and tested: a hollow block, and blocks with narrow holes: ϕ 2.2mm×90; ϕ 2.5mm×55; and ϕ 4.0mm×30. The temperature distribution indicated stable flow circulation inside the thermosyphon a...

Direct numerical simulation was performed for a spatially advancing turbulent flow in a two-dimensional curved channel. The radius ratio of the curved part, α , was set at 0.92, the same as Kobayashi et al.'s experiment. And the friction Reynolds number, Re_<τ0>, was set at 550. Numerically solved mean velocity field showed trends consistent with t...

Direct numerical simulation is performed for a two-dimensional turbulent jet dispersed by sphere particles in the jet core region. The temporary evolving jet in a periodic domain is solved by the Fourier Spectral method. The particle is treated by the immersed boundary to consider the fluid disturbance from the sphere particles. The Reynolds number...

Direct Numerical Simulation was performed for a spatially advancing turbulent flow and heat transfer in a channel with some ribs on one wall. The rib was square shape and uniform in spanwise direction. The rib height was set at 0.2δ, where δ was channel half width. Rib pitch to height ratios, Pi/H = 2, 4, 8, and 16 were considered. Total stream len...

A direct numerical simulation is made for the incompressible turbulent flow in the 180 deg curved channel with a long straight portion connected to its exit port. An examination is made for how the organized coherent vortex grows and decays in the curved channel: the radius ratio of 0.92, the aspect ratio of 7.2, and the succeeding straight section...

Turbine engines have been used as high reliable, safe engines in airline transportation. Safety is the most important factor in the social use of aerial robots. We started research on Aerial Cargo Robots (ACR) in 2004. The first flight of an ACR prototype was successfully achieved on November 22, 2005. The ACR prototype consists of a flexible airfo...

It's necessary to further improve technology of energy-saving with increasing energy consumption. And there is a current situation that low-temperature exhaust heat has been discarded from a factory. So we have started a study of the heat pipe for utilizing this exhaust heat. It's necessary to carry out heat transportation of long distance and high...

An experimental study was performed for freeze-concentration of 1 % water-solution of sodium chloride in a cylindrical container, where a heat transfer pipe was set vertically. Experimental results denoted that temperature gradient in the ice promote solute rejection. When the ice is given a temperature gradient for long time , solute is eliminated...

A newly developed electric furnace was used to pyrolyze benzene, methane or acetylene diluted by a non-reactive gas, and the carbon aggregates were separated from the hydrogen-rich gases. Temperature was changed up to 2200 K for various levels of initial concentration of hydrocarbon and residence time, and examination was given to how the experimen...

抄録 The estimation of thermal sensation at the instant when a certain object is touched is becoming an important consideration in material evaluation. In a previous paper, we showed that the effective contact temperature of the object –when covered with a thin surface of a different material– could be implied from the thermal contact resistance of t...

The purpose of this study is to clarify the radiation effects on mixed turbulent convection in a horizontal channel. The present study provides turbulence statistics using direct numerical simulation (DNS) in an optically thin medium. When the radiation effect is considered, the flow structure and the temperature distribution in the channel change...

The near-wall turbulent heat transport of the three orthogonal directions was directly solved for the Prandtl numbers ranging from 0.025 to 5.0 to validate the algebraic models of the turbulent heat flux. Two kinds of thermal situations were considered in the low Reynolds number turbulent flow: (a) the case with a uniform heat flux in the spanwise...

Heat transfer and fluid flow in a single-rib mounting channel were investigated by directly solving Navier-Stokes and energy equations. The flow and thermal fields were considered to be fully developed at the inlet of the channel, and the simulation was made for spatial advancement of turbulent heat transfer. The Reynolds number based on the fricti...

Direct numerical simulation was performed for air turbulent flows and heat transfer in a channel with square ribs attached to one wall. The spatially advancing cases and the fully advanced cases were both treated for the bulk Reynolds number of about 4,560. The rib height, H, was kept constant at 0.2 times the channel half-width, whereas the rib pi...

Thermal radiation in a turbulent natural convection plays an important role in a wide area of engineering and nature. The purposes of this study are to investigate the effects of turbulent fluctuation on radiative heat transfer, and to evaluate radiative heat transfer models applied to turbulent natural convection. The present radiative heat transf...

Direct numerical simulation was performed for a spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel. A rib was placed on either an inner-or outer-wall of the straight part nearby curved-channel inlet for controlling the flow and thermal fields. Outer-wall was heated at the constant temperature and inner-wall was...

Direct numerical simulation was performed for a spatially advancing turbulent flow in a two-dimensional curved channel. The radius ratio of the curved part, α, was set at 0.92, the same as Kobayashi et al.'s experiment. And the friction Reynolds number, Re_<τ0>, was set at 550 and 300. Numerically solved mean velocity field showed trends consistent...

Direct numerical simulation was performed for a spatially advanced turbulent flow in a two-dimensional curved channel. In the past research, the influence of radius ratio was not discussed. Therefore, the radius ratio of the curved part, a=0.92, the same as Kobayashi et al.'s experiment, and 0.8 were calculated. Then, we carried out simulations of...

Direct numerical simulation was performed for the spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel equating the radius ratio to 0.92 or 0.8. The frictional Reynolds number was fixed at 150, whereas the Prandtl number was set at 0.71. According to the numerical result, the remarkable enhancement of heat transf...

Direct numerical simulation was performed for the spatially advancing turbulent flow in a two-dimensional curved channel. The fully developed turbulence was introduced into the curved channel through a straight part, and observation was made for how the near-wall turbulence advanced along curved walls. The frictional Reynolds number, Retau0, was fi...

Studies of curved channel flows are clearly important since the flow over curvatures is related to various applications such as turbines, heat exchangers and combustors. Since Wattendorf (1935), many works have been made for the flow instability near the concave wall, and it was pointed out that the organized flow called Taylor-Görtler vortex grew...

Importance of turbulence and radiation interaction (TRI) has been investigated in a turbulent channel flow by using direct numerical simulation (DNS) to clarify detailed turbulent flow structure and heat transfer mechanisms. To investigate the effect of correlation functions between gas absorption and temperature fluctuation, the two cases of corre...