Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/jtst.22-00057

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Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The effects of doping manganese ions into a cerium oxide lattice for a thermochemical two-step water-splitting cycle to produce oxygen and hydrogen and new synthesis methods were experimentally investigated. In order to comparison of oxygen/hydrogen producing performance, pristine CeO2, a coprecipitation method for Mn-CeO2, and a direct depositing method for Mn-CeO2 with different particle sizes (50~75, 100–212, over 212 μm) and doping extents (0, 5, 15 mol%) were tested in the context of synthesis and fabrication processes of reactive metal oxide coated ceramic foam devices. Sample powders were coated onto zirconia (magnesium partially stabilized zirconia oxide, MPSZ) porous foam at 30 weight percent using spin coating or a direct depositing method, tested using a solar reactor at 1400 °C as a thermal reduction step and at 1200 °C as a water decomposition step for five repeated cycles. The sample foam devices were irradiated using a 3-kWth sun-simulator, and all reactive foam devices recorded successful oxygen/hydrogen production using the two-step water-splitting cycles. Among the seven sample devices, the 5 mol% Mn-CeO2 foam device, that synthesized using the coprecipitation method, showed the greatest hydrogen production. The newly suggested direct depositing method, with its contemporaneous synthesis and coating of the Mn-CeO2 foam device, showed successful oxygen/hydrogen production with a reduction in the manufacturing time and reactants, which was lossless compared to conventional spin coating processes. However, proposed direct depositing method still needs further investigation to improve its stability and long-term device durability.

DOI： 10.3390/en14216919

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Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

A copper–germanium alloy (Cu–Ge alloy) was examined as a phase change material, at temperatures exceeding 600°C, for latent heat storage in solar thermal applications. First, the thermo-physical properties of the Cu–Ge alloy were examined using differential scanning calorimetry, thermomechanical analysis, and laser flash analysis. Second, to evaluate the thermal response and reliability of the Cu–Ge alloy, the cyclic properties of thermal charge/discharge were examined under various thermal conditions. The alloys obtained after the tests were examined for their chemical compatibility with the stainless steel container using an electron probe micro analyzer. The elemental distribution of each Cu–Ge alloy was evaluated using cyclic performance tests. Finally, the chemical compatibility of the Cu–Ge alloy was evaluated using a high-temperature test with candidate materials of a phase change material container vessel [stainless steel (SUS310S), Inconel625, silicon carbide (SiC), and alumina (Al2O3)]. The Cu–Ge alloy exhibited significant potential as a latent heat storage material in next-generation solar thermal power plants because it demonstrates various advantages, including a superior storage capacity at a temperature of 644°C, temperature coherence to the phase diagram, a quick thermal response, satisfactory cyclic behavior of charge/discharge modes, a thermodynamically stable metallographic structure, and non-reactivity with container ceramic materials (SiC and Al2O3).

DOI： 10.3389/fenrg.2021.696213

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Publishing type：Research paper (international conference proceedings)  

A thermochemical two-step water-splitting cycle using perovskite oxide of La0.7Sr0.3Mn0.9Cr0.1O3 was examined for hydrogen production from water using concentrated solar radiation. The impact of the thermal reduction temperatures of 1000–1350 °C on oxygen/hydrogen productivity and repeatability was examined for hydrogen production at a water decomposition temperature of 1200 °C. The sample displayed relatively high evolution rates of oxygen at TR temperatures of 1350-1300°C, and showed similar rate at TR temperatures of 1000-1200 °C. After the sample was subjected to the TR step at temperatures of 1350-1300 °C, the obtained samples were superior hydrogen production rate to the others. On the other hand, the sample provided relatively good reactivities and repeatabilities for oxygen release and hydrogen production with a small production level without coagulation or sintering during the TR temperatures of 1000-1200 °C.

DOI： 10.1063/5.0028720

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Publishing type：Research paper (international conference proceedings)  

In this paper, the effect of doping of Manganese on to Cerium oxide for thermochemical two-step water splitting cycle for produce the hydrogen was experimentally studied. In order to compare the oxygen/hydrogen productivity, pure CeO2, coprecipitation method applied Mn-CeO2, and direct doping calcination method adopted Mn-CeO2 were used to thermo-chemical two-step water splitting cycle tests. The synthesized sample powders were coated on the reticulated porous foam device and tested in the fixed bed type reactor for the temperature of 1400 C for thermal reduction step, and 1200 C for water decomposition step through 5 cyclic tests. The redox reactive foam devices were irradiated by 3kW sun-simulator, and all samples recorded successful oxygen/hydrogen production. Among the 3 sample devices, the 15 mol% Mn-CeO2 foam device which synthesized by direct doping calcination method shows highest hydrogen production amount and H2/O2 conversion ratio. o o

DOI： 10.1063/5.0029890

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Publishing type：Research paper (international conference proceedings)  

A thermochemical two-step water-splitting cycle using perovskite oxide of La0.7Sr0.3Mn0.9Cr0.1O3 was examined for carbon monoxide production from CO2 using concentrated solar radiation. Previously, the authors proved the perovskite oxide can thermochmically split H2O via two-step process into oxygen and hydrogen in an individual step. In this study, a thermochemical two-step CO2 splitting cycle using the perovskite oxide was examined for the reactivity and repeatability of redox reaction at CO2 spitting temperatures of 1000-1200 °C. The reactivity and repeatability for two-step CO2 splitting was compared to those for H2O splitting operating at the same temperature level.

DOI： 10.1063/5.0028681

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Publishing type：Research paper (international conference proceedings)  

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, latent thermal energy storage systems using phase change materials (PCMs) have been developed to aid energy supply and demand of solar thermal power plants. As one of the obstacles of these systems is the low thermal conductivity of PCMs, ceramic fin has been used in this study to enhance heat transfer rate between the PCM and heat transfer fluid. To assess the heat transfer characteristics of the triplex-tube thermal energy storage system with ceramic fin, a numerical model has been developed and the effect of fin for various Stefan numbers has been studied numerically. The heat transfer and solidification rates are significantly enhanced when connecting the fins between the inner and outer tubes.

DOI： 10.1063/5.0028873

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Publishing type：Research paper (international conference proceedings)  

Latent heat storage technology in CSP plant has been studied to enhance the dispatchability of solar energy in order to meet fluctuating electricity needs. A novel concept using metal alloys as latent heat storage material gives way to achieve this technology. In this paper, we analyzed the structural and thermal properties of Cu-Ge alloy to evaluate the potential of metallic PCM for high temperature TES application. Containment options for metallic PCM were explored and the materials are selected for long term operation. Compatibility tests of stainless steel, alumina and SiC ceramics under inert atmosphere were performed at high temperatures (800°C) for a duration of 1 month (720 h) in order to develop a suitable container material for thermal energy storage system.

DOI： 10.1063/5.0028722

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Publishing type：Research paper (scientific journal)  

In this study, an iron–germanium alloy (Fe–Ge alloy) was examined as a phase change material at temperatures exceeding 800°C for thermal energy storage in solar thermal applications. The cyclic properties of the thermal charge/discharge of the Fe–Ge alloy were examined at various thermal cycles. A thermal reliability test was performed in the form of a multi-cyclic performance assessment to evaluate the short- and long-term thermal stability of this alloy. Eutectic and hypereutectic chemical compositions of the Fe–Ge alloy were placed in a graphite container under vacuum and an inert atmosphere. The Fe–Ge alloy was experimentally examined for its compatibility with the container material of graphite-carbon. The element distribution of each Fe–Ge alloy was examined via a cyclic performance test. The heat storage capacities were evaluated and compared with those of chloride molten salts. The Fe–Ge alloy exhibits significant potential as a latent heat storage material in next-generation solar thermal applications as it demonstrates various advantages, namely: a higher storage capacity than that of chloride molten salts, temperature followability to the phase diagram, a quick thermal response, satisfactory cyclic behavior of charge/discharge modes, a thermodynamically stable metallographic structure, and non-reactivity with capsulation materials of graphite carbon.

DOI： 10.1016/j.est.2020.101420

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.renene.2019.07.039

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Publishing type：Research paper (international conference proceedings)  

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 cannot be used for very high temperatures. The authors used quartz sand as thermal storage medium in the fluidized bed receiver, and achieved the thermal receiver temperatures beyond 1000 °C in the previous report. The research work was further made on using the particle steady flow for high-temperature solar thermal storage. The steady-flow-type particle receiver was designed through visualization of cold model and numerical simulation. The experimental apparatus was fabricated and tested using beam-down sun simulator of 1.0 kWth. The apparatus comprises of the internal-circulating fluidized bed receiver placed between a loop seal with an inlet port and another loop seal with a weir and an exit port of the particles. The tested particles are quartz sand of 0.1 - 0.2 mm and fused brown alumina of 0.09 - 0.1 mm. The experimental set up produces hot particles of quartz sand at 428°C and those of fused brown alumina at 491°C. The highly efficient steady-flow-type particle receiver created steady particle flow smoothly. This apparatus takes in the concentrated light through the quartz window to continuously discharge the particles at high temperatures beyond the criterion in synthesis oil (400°) for solar thermal storage.

DOI： 10.1088/1757-899X/556/1/012059

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

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 transport. This paper describes conjugate analysis of radiation, convection and conduction heat transfer in the volumetric receiver for perfect three-way coupling between three mechanisms of heat transfer. The numerical scheme was used for the volumetric receiver with plane surface and that with cut-back inlets for optimization of the geometry. The simulation was made for single cell of honeycomb with 2.4 mm pitch and 0.5 mm wall thickness. Two cases of surface geometry was computed: plane surface
cut-back inlet with 10 mm depth. Basic equations are momentum and energy equations with radiation transport equation. The discrete ordinates method was applied for solving the radiation intensity to consider perfect interaction between radiation, convection and conduction. The material of the receivers are assumed as stainless steel. The numerical simulation demonstrated the superiority of the cut-back receiver which increased the exit temperature by 30 K and decreased 2 Pa for the smallest beam angle of 10°. The contour plot of total heat flux on the wall revealed that the shadow effect was attenuated by the cut-back inlet leading to heat transfer enhancement. The novelties of this work are to treat perfect interaction between radiation and convection in volumetric receiver and to demonstrate the excellence of cut-back inlet receivers.

DOI： 10.1088/1757-899X/556/1/012060

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Language：English   Publishing type：Research paper (scientific journal)  

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 transient 3D heat and mass transfer model is formulated by the combined approach of discrete element method and computational fluid dynamics. The radiative transfer is solved using the discrete ordinate radiation model. Experimental validation is accomplished by the measured temperatures, obtained with the fluidized bed reactor prototype tested under 30 kW high-flux solar simulator. The model is applied to analyze the granular flow characteristics and efficiency of the reactor for various superficial gas velocities and bed masses. The results indicate that higher gas flow rate increases the velocity and convection loss of the bed and decreases the bed temperature and efficiency of the reactor. th

DOI： 10.1016/j.ces.2018.09.012

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Language：English   Publishing type：Research paper (scientific journal)  

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 transient three dimensional numerical model has been developed using discrete element method and computational fluid dynamics. Particle collision dynamics has been solved by the spring-dashpot model based on the soft-sphere method. To perform model verification, experiments have been performed using 30kW fluidized bed reactor prototype under high flux solar simulator. The particulate and thermal characteristics of spout, annulus and fountain of the fluidized bed are analyzed for different irradiation power, loaded powder and gas flow rates. The results indicate that large and small size particles govern the bottom and fountain part of the bed respectively due to gravitational force, and the peak temperature is moved from fountain core to the fountain periphery of the bed when increasing the gas flow rate. th

DOI： 10.1016/j.cej.2018.10.111

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Language：English   Publishing type：Research paper (scientific journal)  

The operational mode of a batch-type fluidized bed reactor containing quartz sand and coal-coke particles was tested under xenon arc lamp (Xe-light) illumination to develop processes for the continuous feeding and gasification of coke particles in the quartz sand fluidized bed. This paper focuses on the fluidizing, heating, and steam gasification performances of a windowed internally circulating fluidized bed reactor. The operational modes explored in this study were: (1) elevated temperature processes associated with the use of Xe-light radiation to reach gasification temperatures, and, (2) the gasification process driving steam gasification at high-temperatures, working with stream gasification of continuously-fed coal-coke. The gasification performances were used to evaluate the performance of quartz sand as a thermal-transfer/sensible heat-storage medium. The peak rate of gas production was greatly enhanced for the high volume fraction of coal-coke. In addition, the light-to-energy conversion rate of 11.0–13.2% and carbon conversion rate up to 80% were reached in the simplified distributor structure of gasification reactor.

DOI： 10.1016/j.energy.2018.10.036

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Language：English   Publishing type：Research paper (scientific journal)  

La Sr (Mn, Fe, Co)O , and Ba Sr CoO perovskite oxide powders were investigated as potential thermochemical energy storage (TES) materials operated at high temperatures above 600 °C. The purpose of the research is to provide complete characterization of the impact of partial A- and B-site substitution on the reactivity, kinetics, redox reaction repeatability and charging/discharging storage capacity. The perovskite oxides were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) at temperatures of 500–1100 °C. Thermal energy storage was evaluated in terms of the enthalpy of the reversible reactions of oxygen release (reduction) and uptake (oxidation) upon heating the oxide materials in air stream. Among the perovskites tested, Ba Sr CoO and Ba Sr CoO powders were suitable thermochemical storage materials operating at above 600 °C in terms of chemical reactivity, charging/discharging temperatures and storage capacities, kinetics of oxygen uptake/release, and repeatability of thermochemical cycling. Further, charging/discharging capacity for both perovskites was comparable to that for Fe-doped manganese oxide. x 1-x 3-δ y 1-y 3-δ 0.3 0.7 3-δ 0.7 0.3 3-δ

DOI： 10.1016/j.energy.2019.01.081

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A thermochemical two-step water-splitting cycle using perovskite oxides based on LaSrMnAlO was examined for hydrogen production from water using concentrated solar radiation. Concurrent Sr and Mn substitutions in La Sr Mn Al O , Sr and Al substitutions in La Sr Mn Al O , and substitution of Al by Cr in La Sr Mn Cr O were examined, and their kinetics, oxygen/hydrogen productivity, and repeatability were compared against LaSrMnAlO . The impact of the chemical compositions of the perovskite oxides was systematically examined at a thermal reduction temperature of 1350 °C and water decomposition temperatures of 1000–1200 °C. From the viewpoints of average amounts of oxygen and hydrogen produced and the H /O ratios, La Sr Mn Cr O and La Sr Mn Cr O provided the most reproducible productions of oxygen and hydrogen in the thermochemical two-step water-splitting cycle. 3 1-x x x 1-x 3 1-y y 1-y y 3 0.7 0.3 1-z z 3 3 2 2 0.7 0.3 0.9 0.1 3 0.7 0.3 0.8 0.2 3

DOI： 10.1016/j.tca.2019.178374

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ijheatmasstransfer.2019.03.153

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

A novel concept of a windowed, particle fluidized bed solar reactor was proposed by Niigata University for performing a two-step thermochemical water splitting cycle with redox metal-oxide particles. The solar reactor concept needs to be combined with a beam-down type solar concentrator. A new type of 100kW beam-down solar concentrating system with a secondly elliptical reflector was built at the campus of University of Miyazaki, Japan. The solar reactor and the CPC were fabricated for demonstrating the concept of the windowed, particle fluidized bed solar reactor. The first performance tests of the solar reactor with pulverized ceria particles with 100 - 300 μm in diameter were carried out using the Miyazaki beam-down solar concentrating system. th

DOI： 10.1063/1.5117691

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Language：English   Publishing type：Research paper (international conference proceedings)  

Fe-doped manganese oxides for solar thermochemical storage are studied using thermogravimetric reactor in a laboratory scale. The operation process of Fe-doped Mn O /Mn O redox pair for two-step thermochemical cycle are optimized from the viewpoint of redox temperatures and thermochemical storage capacity, and the impact of operation temperatures on redox performances were experimentally evaluated. In addition, the thermochemical storage potentials of some Fe-X-doped manganese oxides are examined with regards to reaction rate, short-term cycling stability, storage capacity and redox temperatures. 2 3 3 4

DOI： 10.1063/1.5117752

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Language：English   Publishing type：Research paper (international conference proceedings)  

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 collision dynamics is solved by spring-dashpot model based on soft-sphere method. The instantaneous granular flow behavior of the irradiated bed is presented along with the incident radiation and particle size distribution. The results indicate that as time progresses the average velocity of the particle increases due to high temperature and bed expansion effect.

DOI： 10.1063/1.5117684

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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 effective approach for studying the gas-solid flow. The discrete ordinate model has been used to solve the radiation heat transfer. An experimental visualization of particles circulation pattern and mixing of two-tower fluidized bed system has been presented. A good agreement has been found between the experimental measurements and numerical predictions. The effect of gas superficial velocity, bed mass and inlet gas temperature on the flow pattern and temperature characteristics of the bed have been investigated. The results showed that the maximum and average temperature of the bed, depends on the top layer position and focal point of the concentrated radiation, decreased when increasing the total mass of the bed. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2017.09.015

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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 kW fluidized bed reactor for solar gasification has been investigated and reported. Discrete element method (DEM) has been used for modeling the granular flow, and computational fluid dynamics (CFD) method has been used for modeling the multiphase flow. To validate the developed model, experiments were preformed and compared with modeling results. Discrete ordinate radiation model has been used to solve the radiative transfer equation. The thermal performance of the reactor and particulate flow behavior have been predicted and the effect of particle size, particle size distribution and gas flow rate are analyzed. The results indicate that the performance of the bed increases when fluidizing the annulus region particles as the high porosity increases the diffusion rate of radiation throughout the bed. th

DOI： 10.1016/j.ijhydene.2018.06.033

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.solener.2018.06.006

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Language：English   Publishing type：Research paper (scientific journal)  

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 numerical model has been developed by the combined approach of computational fluid dynamics and discrete element method (CFD-DEM). The radiation transfer equation has been solved by the discrete ordinate (DO) model. The experimental data have been used for model validation. The thermal performance of the reactor and the spout-annulus flow have been predicted by the model and other hydrodynamic parameters such as internal solid volume fraction, velocity and temperature of the particles are analyzed as a function of superficial gas velocity (gas flow rate) at different initial conditions.

DOI： 10.1016/j.energy.2018.06.212

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Language：English   Publishing type：Research paper (international conference proceedings)  

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-kW sun-simulator. O and H 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 created by passing N gas through the perforated bottom plate of the reactor, and about 30 kW of high flux visible light from 19 xenon-arc lamps of the sun-simulator was directed inside the reactor through a quartz window to directly irradiate the top of the fluidized bed. The central bed temperature reached the temperature of 1400 to 1500°C in the thermal reduction step. The subsequent water decomposition or hydrolysis step was performed at the central bed temperature of 800 - 900°C. About 6 - 12 Ndm of hydrogen was produced by one cycle. th 2 2 2 th 3

DOI： 10.1063/1.5067143

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Language：English   Publishing type：Research paper (international conference proceedings)  

A laboratory-scale prototype windowed internally circulating fluidized-bed reactor made of quartz sand and coal coke particles was investigated for steam gasification using concentrated Xe-light radiation as the energy source. The quartz sand was used as a chemically inert bed material for the fluidized bed, while the coal coke particles functioned as the reacting particles for the endothermic gasification reaction. The purpose of this study is a preliminary tests of batch type fluidized bed reactor that assuming a continuous feeding process of carbonous materials (cokes, coal, and biomass et al.) into the fluidized bed reactor with a thermal transfer/storage medium (quartz sand). The gasification performances such as the production rates of CO, H , and CO were evaluated for the fluidized bed reactor. 2 2

DOI： 10.1063/1.5067140

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Begell House Inc.  

In concentrated solar thermal industry, fluidized-bed technology has been used to produce hydrogen and synthetic gas by two-step water splitting cycles and gasification of coal cokes respectively. A two tower fluidized bed reactor has been developed in this study for solar thermochemical conversions. To study the granular flow and heat transfer characteristics of the two tower fluidized bed reactor, a numerical model has been developed by combined approach of discrete element method and computational fluid dynamics. Particle collision dynamics has been solved by the spring-dashpot model based on the soft-sphere method. Discrete ordinate radiation model has been used to solve the radiative transfer equation. To validate the model, the predicted heat transfer characteristics of the bed have been compared with the reported experimental data. A reasonable agreement has been found between the predicted and experimental results. Particulate flow dynamics of the bed filled with ceria powder is presented with temperature distributions. Using this model, the key operating parameters can be optimized.

DOI： 10.1615/ihtc16.mpf.023665

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Begell House Inc.  

This study focuses on the conjugate radiation-convection-conduction heat-transfer problem for a square channel of volumetric solar receiver with concentrated irradiation for Concentrated Solar Power (CSP). A single channel of a honeycomb receiver is directly irradiated from the outside, via a transparent wall. Atmospheric air flows through the channel and absorbs the sensible heat. Governing equations are continuity, Navier-Stokes and energy equations for solid/fluid region, and radiative transfer equation. Radiation was solved by the Discrete Ordinates (DO) model. The effects of the number of mesh grids and direction vectors on the DO model were confirmed to be negligible. This study analyzed the heat-transfer performance of stainless-steel receivers with different channel geometry. Three different types and sizes of channels were treated
L-shaped cuts were made at the channel top. The heat transfer performance of these channels, i.e. bulk air temperature and pressure drop at the outlet were improved by the L-shape cutting. The wall heat flux difference between simple and cut channel was clarified by the contour plots of inner walls. Across the entire inner wall, the conduction heat flux contributed to the heating of the flowing air, while the radiation heat-flux dominated near the inlet due to high incident radiation. As a result, the wall heat-flux had characteristic profile along the channel depth (-z) direction. This study elucidates conjugate heat transfer mechanism in the honeycomb-like channel receivers with highly concentrated radiation.

DOI： 10.1615/ihtc16.nee.023436

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

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 outlet by varying the operational parameters. Numerical simulations were performed for a vertical honeycomb block with beam-down irradiation and a horizontal honeycomb block with tower-type irradiation to elucidate the effects of buoyancy. Three blocks with different sizes were simulated for a variety of operational parameters. When the block was oriented vertically, the flow and temperature fields remained nearly symmetric in and near the receiver. In contrast, when it was oriented horizontally, the flow and temperature became asymmetric, with the hot spot moving toward the receiver's side wall and the stream in the receiver being reversed. The vertical orientation's robustness to buoyancy effects prevented any reduction in the receiver efficiency or outlet temperature and suppressed the thermal leakage.

DOI： 10.1016/j.energy.2017.11.147

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Utilization of solar thermal power for high temperature fuel production has the potential to significantly reduce the fossil fuel dependence of our current economy. Over the past two decades, remarkable progress has been made in the development of solar driven thermochemical reactors for the production of hydrogen and syngas as they are promising energy carriers for transportation, domestic and industrial applications. However, there are solar peculiarities in comparison to conventional thermochemical processes high thermal flux density and frequent thermal transients because of the fluctuating insolation-, and conventional industrial thermochemical reactors are generally not suitable for solar driven reactors. Therefore, solar-specific modifications of reactor design are necessary to realize efficient solar driven thermochemical processes. In solar thermochemical reactors, the methods for solar-heating particulate solid feedstock to high temperatures can be broadly classified as solar "directly" and "indirectly" absorbing reactors. On solar thermochemical processes involving reacting solid particles at high temperatures, such as "solar two-step water splitting with metal oxides" and "solar gasification", various types of solar directly and indirectly absorbing particle reactors have been developed. In this review, recent development of solar particle reactors for the above solar thermochemical processes is described. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.solener.2017.05.084

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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-dashpot model, based on the soft-sphere method. An experimental visualization of particles circulation pattern and mixing of two-tower fluidized bed system has been presented. A good agreement has been found between the experimental measurements and numerical predictions. To investigate the influence of fluid flow rate and particle size on the flow pattern of the reactor, simulations have been performed for various conditions. The results indicate that the large size particles induce three-dimensional effects as they are accumulated at the central axis region. The average bed height of the left tower increased by 23.4% when increasing the flow rate about 70%. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.powtec.2017.06.060

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

The present authors (Niigata University, Japan) have developed a tubular reactor system using novel "double-walled" reactor/receiver tubes with carbonate molten-salt thermal storage as a phase change material (PCM) for solar reforming of natural gas and with Al-Si alloy thermal storage as a PCM for solar air receiver to produce high-temperature air. For both of the cases, the high heat capacity and large latent heat (heat of solidification) of the PCM phase circumvents the rapid temperature change of the reactor/receiver tubes at high temperatures under variable and uncontinuous characteristics of solar radiation. In this study, we examined cyclic properties of thermal storage/discharge for Cu-Si alloy in air stream in order to evaluate a potentiality of Cu-Si alloy as a PCM thermal storage material. Temperature-increasing performances of Cu-Si alloy are measured during thermal storage (or heat-charge) mode and during cooling (or heat-discharge) mode. A oxidation state of the Cu-Si alloy after the cyclic reaction was evaluated by using electron probe micro analyzer (EPMA).

DOI： 10.1063/1.4984465

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

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 conservation equations of mass, momentum and energy. The enthalpy-porosity method has been used to track the solidliquid interface of the PCM during melting process. Transient numerical simulations have been performed in order to study the influence of radius of the capsule and the Stefan number on the heat transfer rate. The simulation results show that the counter-clockwise Buoyancy driven convection over the top part of the solid PCM enhances the melting rate quite faster than the bottom part.

DOI： 10.1063/1.4984427

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

A novel concept of particles fluidized bed receiver/reactor with a beam-down solar concentrating optics was performed using a 30-kW(th) 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 kW(th) of high flux visible light from 19 xenon-arc lamps of the sun-simulator was directly irradiated on the top of the fluidized bed in the receiver through a quartz window. The particle bed temperature at the center position of the fluidized bed went up to a temperature range from 1050 to 1200 degrees C by the visible light irradiation with the average heat flux of about 950 kW/m(2), depending on the air flow rate. The output air temperature from the receiver reached 1000 - 1060 degrees C.

DOI： 10.1063/1.4949206

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Dispatchable electricity generation on demand is a fundamental issue for commercial deployment of Concentrated Solar Power (CSP) plants. One of the promising routes to overcome the intermittence of the solar resource is the use of thermochemical energy storage systems based on redox reactions of metal oxides. Different metal oxides might potential candidates as storing material depending on the foreseen working temperature range. In the framework of the FP7 European project TCSPower, a particle-based reactor is used to analyze this type of materials. The lab-scale thermochemical reactor is initially tested using an inert material (alumina particles) instead of reactants in order to study its thermal performance. Thermocouples installed inside the system at various positions monitor the experiments. A three dimensional numerical model is developed to investigate the flow and heat transfer in the reactor. The governing equations - mass, momentum and energy conservation - are solved by the finite element method in the commercial software COMSOL Multiphysics. Simulations are performed for the experimental conditions. Experimentally measured and numerically predicted temperature profiles at various locations inside the system are compared and presented in this paper.

DOI： 10.1063/1.4949103

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In order to avoid intermittent energy supply problems, thermal energy storage system plays an important role in concentrated solar power plants. Thus, a significant focus has been given on the improvement of thermal energy storage systems from the past few decades. In this paper, the dynamic thermal performance of high temperature latent thermal energy storage system packed with spherical capsules is analyzed experimentally and numerically. The spherical capsules are encapsulated by sodium nitrate and air is used as heat transfer fluid. Transient two-dimensional continuous solid phase and effective packed bed models are developed and validated by comparing to the experimental results. Using these models, detailed characteristics of the heat transfer between the capsules and heat transfer fluid are analyzed. Parametric analyses are conducted to study the influence of mass flow rate, Stefan number, thickness and the thermal conductivity of the shell. The results indicate that the Stefan number plays a vital role on the total heat storage capacity due to sensible heat, and the shell properties of the capsule significantly influence the thermal performance of the system; the influence of the shell thickness increases (decreases) when the thermal conductivity of the shell is low (high). (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.applthermaleng.2015.07.056

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

A latent thermal energy storage system, which consists of sodium nitrate filled spherical capsules in a cylindrical tank, is analyzed for concentrating solar power plant applications. The high temperature synthetic oil, Therminol 66, is used as heat transfer fluid. A numerical model is developed to investigate the behavior of the system. The developed model is validated using the reported experimental and numerical data. The influence of capsule size and the flow rate of heat transfer fluid (HTF) on the temperature distribution, fluid flow, melting and solidification of the system is studied. The natural convection effect present in the liquid region during melting is resolved by the effective thermal conductivity, which is calculated by enthalpy formulation method. The results indicated that the heat transfer rate is increased and eventually the charging/discharging time is decreased when the capsule size is decreased, or the HTF flow rate is increased. (C) 2015 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2015.03.086

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The objective of this paper is to develop a two dimensional two-phase model to study the dynamic behavior of a packed bed thermal energy storage system, which is composed of spherical capsules of encapsulated phase change material (PCM-sodium nitrate) and high temperature synthetic oil (Therminol 66) as heat transfer fluid. The heat transfer coefficient is calculated based on the phase change process inside the capsule by enthalpy formulation model and the flow inside the system is predicted by solving the extended Brinkman equation. After model validation, the developed model is used to investigate the influence of capsule size, fluid temperature (Stefan number), tank size (length and diameter), fluid flow rate and the insulation layer thickness of tank wall on the performance of the system. The dynamic behavior of the system, subjected to partial charging and discharging cycles, is also analyzed. It is found that increasing the capsule size, fluid flow rate, or decreasing the Stefan number, results in an increase in the thermocline region which finally decreases the effective discharge time and the total utilization. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.applthermaleng.2014.07.009

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

A lab-scale solar thermochemical reactor is designed and fabricated to study the thermal reduction of non-volatile metal oxides, which operates simultaneously as solar collector and as chemical reactor. The main purpose of this reactor is to achieve the first step in two-step thermochemical cycles. The chemical conversion rate strongly depends on the temperature and fluid flow distribution around the reactant, which are determined by the reactor geometry. The optimal design depends on the constraints of the problem and on the operating parameters. Hence, the objective of this investigation is to analyze the heat and mass transfer in the vertically-oriented chemical reactor by a CFD model and to optimize the reactor design. The developed numerical model is validated by comparing the simulation results with reported model. The influence of different technical and operating parameters on the temperature distribution and the fluid flow of the reactor are studied.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

Thermal energy storage in the form of latent heat of fusion of phase change material gained considerable attention in solar energy applications since it significantly increases the energy density and reduces the storage tank size compared to the sensible heat storage system. Several numerical and experimental studies have been conducted to enhance the performance of the system. In this study, 2-D continuous solid phase and effective packed bed models are developed to study the behavior and performance of a thermal energy storage system for high temperature applications, which is composed of spherical capsules encapsulated by phase change material (Sodium nitrate) and high temperature synthetic oil (Therminol 66) as heat transfer fluid. Temperature distribution, fluid flow, melting, solidification and thermocline behavior of the system are predicted and the influence of capsule size on the performance of the system is studied.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

A lab-scale thermochemical reactor is designed and fabricated for the solar-driven thermal reduction of non-volatile manganese oxide to produce hydrogen by water splitting thermo chemical cycles. A time dependent three dimensional numerical model is developed to investigate the performance of the reactor since the chemical kinetics strongly depends on irradiance, temperature and fluid flow distribution around the reactant. Radiation heat transfer is calculated by using surface-to-surface (S2S) radiation model. Thermo-fluid flow, absorption efficiency and the temperature distribution of the sample are predicted as a function of time and the model is validated by experimental measurements. (C) 2013 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2014.03.079

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

This paper presents numerical analysis on the performance of latent heat packed bed thermal energy storage system, which is composed of spherical capsules filled with sodium nitrate as phase change material and high temperature synthetic oil (Therminol 66) as Heat Transfer Fluid. The influence of capsule size, fluid temperature (Stefan number), Tank size (length and diameter) and fluid flow rate on the performance of the thermal energy storage system is investigated in the temperature range between 300 and 400 degrees C. The phase change process inside the capsule is modeled by enthalpy formulation method and the flow inside the system is predicted by extended brinkman equation. This model is validated using the already reported models. The ultimate aim of this investigation is to develop a packed bed thermal energy storage model to study and optimize the main components of the storage tank to use in concentrating solar power plants. (c) 2014 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2014.10.222

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Numerical simulation of in-flight particles in thermal plasma jet is one of the most important research fields. It has been used to analyze the influence of spray parameters on jet characteristics and to improve the quality of coating during plasma spraying. In this study, in-flight behavior of a group of lanthanum zirconate (La2Zr2O7) particles with different diameters (10-60 mu m) in gas tunnel type plasma jet is investigated by numerical modeling. The influence of torch power on the plasma jet is investigated and its interaction with different sizes of La2Zr2O7 particles is studied under optimized spraying conditions. The resultant coating properties are also investigated and correlated with simulation results. The simulation results showed that the plasma jet temperature and velocity increased while increasing the torch power. Consequently, the in-flight particle temperature and velocity profile also increased with respect to the torch power. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2012.02.002

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MANEY PUBLISHING  

Plasma sprayed coatings of yttrium oxide, exhibiting good adhesion and thermal shock resistance, were developed on various substrates using thermal spray grade yttrium oxide powder developed in our laboratory. Numerical simulation of particle behaviour in the thermal plasma jet was combined with experimental method to develop the coatings. Phase structure and microstructural characterisation of the deposits were evaluated by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Deposition efficiencies and adhesion strength of the coatings deposited at different power levels could be well explained with the predictions provided by the model. The process was optimised using deposition efficiency as the response parameter.

DOI： 10.1179/1743294412Y.0000000019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Substrate heating in the plasma spray process is one of the important parameters, which affects the microstructure of coatings and bonding between coating and substrate. In this study, a three-dimensional numerical model is developed to study the thermal exchange between the plasma jet and the substrate. The plasma jet temperature and velocity distributions and thermal flux to the substrate surface are predicted. The effects of arc current, gas flow rate, and stand-off distance on the temperature and velocity fields of the impinging plasma jet and thermal flux to the substrate are clarified. Results indicate that the three-dimensional effect has a very weak influence on the substrate heating. The air entrainment is compared for different cases. The present model is validated by comparing the present results with previous predictions and measurements. The temperature distributions in the substrate for different stand-off distances are predicted.

DOI： 10.1007/s11666-010-9587-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Temperature of the substrate during plasma heating and spraying plays an important role on quality of the substrate and coating. In this study a three dimensional numerical model is developed to simulate the Ar-N(2) plasma jet and conjugate heat transfer between plasma and substrate. The influencing of operating parameters on thermal flux from the plasma to the substrate and substrate temperature are discussed. Transient simulations are carried out to predict the substrate temperature with heating time. The arc current, gas flow rate, stand-off distance, substrate material and environment around the substrate significantly affect the thermal flux to the substrate. Heat flux to the substrate cannot be neglected in the coating built-up models. Present model is validated by comparing the results of present model with previous predictions and measurements.

DOI： 10.1140/epjd/e2010-10443-1

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

One of the challenging problems in the plasma spray technique is reproducibility of the coating quality. This problem is mainly associated with arc fluctuations, which affect the plasma jet temperature and velocity inside the plasma torch. In this study, three-dimensional numerical models are developed to study the behaviour of Ar-N-2 plasma arc inside a non-transferred torch and plasma jet. Ar-N-2 plasma arc is simulated for given arc current and gas flow rate. Different arc sizes, which correspond to given torch power, are predicted. A most feasible arc size, which corresponds to an actual physical situation of the arc inside the torch, is identified using thermodynamic principle of minimum entropy production for particular torch power. Predicted torch efficiency is comparable with measured one. Cathode and anode losses are reported. Predicted temperature and velocity profiles at the nozzle exit are used to simulate the plasma jet. Since plasma gas is mixed with cold air, plasma jet is diffused in the radial direction. Three-dimensional effect on plasma jet temperature and velocity is diminishes along the axial direction.

DOI： 10.1088/1742-6596/208/1/012047

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Simulation studies on the thermal behaviour of yttrium oxide particles in a thermal plasma jet was carried out with the objective of controlling and optimization of the plasma spray process. The 'in-flight' behaviour of yttrium oxide particles in the plasma jet was studied by solving the heat transfer and momentum transfer equations using the velocity and temperature distribution in the plasma jet obtained from a two-dimensional model. In particular, the effect of particle size, thermal power of the torch and the torch operating parameters like gas flow rates were considered to calculate the heat transfer and momentum transfer to the particle. Results of simulation studies agree quite well with the experimental results on variation of deposition efficiency with power and particle size. The complete description of the model with the results obtained for the typical operating parameters of our plasma spray torch is presented in the paper.

DOI： 10.1088/1742-6596/208/1/012116

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Several numerical models have been developed to study the characteristics of an arc inside the nontransferred plasma torch. A few of them have considered complete geometry of cathode and anode nozzle (type I) whereas others have considered only anode nozzle with cathode tip (type II). In this work, a three-dimensional model is developed to simulate Ar-N(2) arc in type I and type II geometries. Various combinations of the arc length and arc core radius are predicted for the torch power that corresponds to given gas flow rate and current. Various combinations of the same and minimum entropy production for all cases could not be predicted in type II geometry. The difference between velocities predicted in both geometries is larger than that between temperatures. Three-dimensional effect in the plasma jet thermo-fluid fields demises along the axial direction. Torch efficiencies and arc voltages predicted in both geometries are comparable with measurements.

DOI： 10.1007/s11666-009-9343-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

A three-dimensional numerical model is developed to study the behaviour of an argon-nitrogen plasma arc inside a non-transferred torch. In this mode, both the entire cathode and anode nozzle are considered to stimulate the plasma arc. The argon-nitrogen plasma arc is simulated for different arc currents and gas flow rates of argon. Various combinations of arc core radius and arc length, which correspond to a given torch power, are predicted. A most feasible combination of the same, which corresponds to an actual physical situation of the arc inside the torch, is identified using the thermodynamic principle of minimum entropy production for a particular torch power. The effect of the arc current and gas flow rate on the plasma are characteristics and torch efficiency is explained. The effect of nitrogen content in the plasma gas on the torch power and efficiency is clearly detected. Predicted torch efficiencies are comparable to the measured ones and the effect of the arc current and gas flow rate on predicted and measured efficiencies is almost similar. The efficiency of the torch, cathode and anode losses and core temperature and velocity at the nozzle exit are reported for five different cases.

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