高圧下で合成された部分充填スクッテルダイトRxCo4Sb12 (R = La, Ce および Nd) の熱電特性

Thermoelectric (TE) materials have been utilized for power generation devices by the direct conversion of waste heat into electrical power. The efficiency of TE materials is determined by the dimensionless figure of merit ZT=S2T/ρκ, where S is the Seebeck coefficient, T is the absolute temperature, ρ is the electrical resistivity, and κ is the thermal conductivity. CoSb3-based skutterudite compounds have attracted considerable attention as one of the best candidates of TE materials. Although CoSb3 shows excellent thermoelectric properties, κ is very high. The reduction in κ for a partially filled CoSb3-based skutterudite is one promising method for improving the TE performance. Partially filled skutterudite compounds with high filling ratio are expected for high-performance TE materials. High pressure benefits the entrance of guest ions into the voids of the filled skutterudite structure than ambient pressure. In this study, we have tried to synthesize partially filled skutterudites LaxCo4Sb12, CexCo4Sb12 and NdxCo4Sb12 were prepared by the high-pressure and high-temperature (HPHT) synthesis method. The structure and chemical composition of the samples were studied and the actual La, Ce and Nd filling ratios were estimated. The electrical and thermal transport properties were studied for selected compounds. The actual filling ratio x of La, Ce or Nd was estimated by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX). SEM-EDX results indicate that the maximum x values of La, Ce, and Nd can be increased to 0.28, 0.37 and 0.33, respectively. These values have been considered the highest for any LaxCo4Sb12, CexCo4Sb12, and NdxCo4Sb12 reported thus far. The electrical resistivity, thermal conductivity, and Seebeck coefficient measurements of the compounds were performed from 5 to 760 K. Furthermore, the Hall coefficient and specific heat of the compounds were also measured below 300 K. The Seebeck and Hall coefficients of La-, Ce-, and Nd-filled samples exhibited the n-type conductor behavior. The maximum ZT values of NdxCo4Sb12 were determined to be 0.48 at 700 K. This results contribute development of next-generation TE materials.熱電変換材料は，効率的に熱エネルギーを電気エネルギーに直接変換可能な材料であり，熱電発電や熱電冷却に不可欠な電子材料である。熱電変換材料の性能は，性能指数Z＝S2/pk (S：ゼーベック係数，p：電気抵抗率，k：熱伝導率)で評価され，これに絶対温度Tを乗じた無次元性能指数ZT≧1 が実用化の目安となっている。熱伝導率 kは，さらに電子による寄与（kE）と格子による寄与（kL）の和で表される。熱電性能を決定する各パラメータS，p，kEは，いずれもキャリア濃度の関数であり独立に制御することはできない。しかし，格子熱伝導率kLは，結晶構造等で決まり，キャリア濃度に依存しないため，独立に制御可能である。キャリア濃度を最適化した上で，さらにZTを向上させる方法として，kLの低減は重要である。CoSb3は，その特殊な結晶構造・電子構造から，熱電変換材料への応用が期待されている物質であるが，kLが高いことが欠点である。しかし，CoSb3に希土類元素等を部分的に充填することで，kLが大きく低減することが知られており，充填率が高いほどkLの減少率も高くなることが報告されている。本研究では，高温高圧合成法により， 高い充填率の部分充填スクッテルダイト化合物LaxCo4Sb12, CexCo4Sb12, NdxCo4Sb12 の合成を試みた。その結果，純良な試料の合成に成功し，La, Ce，Nd の最大充填率xは，それぞれ 0.28，0.37，0.33となった。 これらの値は，これまでに報告されている常圧下で合成されたLaxCo4Sb12, CexCo4Sb12, NdxCo4Sb12の充填率よりも高い値であった。得られた試料に関して，電気抵抗率，熱伝導率，ゼーベック係数，ホール係数，比熱の測定を行い，熱電特性を評価した。その結果， La, Ce，Ndを充填した試料は，いずれもn型半導体の性質を示した。 また，最大のZT値は，NdxCo4Sb12の700Kにおいて0.48 と高い値を示した。室蘭工業大学 (Muroran Institute of Technology)博士（工学

Thermoelectric properties of partially filled skutterudites RxCo4Sb12 (R = Ce and Nd) synthesized under high pressures

We report the thermoelectric properties of the partially Ce or Nd filled skutterudite compounds CexCo4Sb12 and NdxCo4Sb12 prepared under high pressures and temperatures. The samples were characterized by X-ray diffraction. The actual filling ratio x of Ce or Nd was estimated by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX). SEM-EDX results indicate that the maximum x values of Ce and Nd can be increased to 0.37 and 0.33, respectively. These values have been considered the highest for any CexCo4Sb12 and NdxCo4Sb12 reported thus far. The electrical resistivity, thermal conductivity, and Seebeck coefficient measurements of the compounds were performed from 5 to 760 K. Furthermore, the Hall coefficient and specific heat of the compounds were also measured below 300 K. The Seebeck and Hall coefficients of both Ce- and Nd-filled samples exhibited the n-type conductor behavior. The maximum dimensionless figure-of-merit (ZT) values of CexCo4Sb12 and NdxCo4Sb12 were determined to be 0.26 and 0.48 at 700K, respectively. (C) 2018 The Japan Society of Applied Physic

Investigation of the temperature distribution models for phase change material (PCM) in one-dimensional direction

The modern insulation material for buildings is developed to prevent the overconsumption of energy by the building. The phase change material (PCM) is an excellent thermal insulation for the walls of a building, and it has become popular to study and apply this material for the construction industry. The heat transfer through the PCM is a conduction mechanism because the PCM is a medium that has no bulk motion. For this conduction mechanism, the temperature gradient is needed to calculate the amount of heat transferred through the construction wall to the inside of the building. Therefore, the investigation of the temperature gradient is beneficial for the design and energy management of the building. This study aims to investigate the temperature distribution of the PCMs related to the spatial axes of PCMs along the heat conduction direction. The purpose of this study is finding the correlation of the temperature related to the thickness of the PCM, which this purpose is useful for design the insulation wall for air-conditioned room. The methodology was to set the heat flow through the PCM in one dimension. An electric heater was used to generate heat for the hot side of the PCM. Constant temperatures of the hot side as 35, 40, 45, 50, and 55 °C were achieved. Thermocouples were used to measure the temperature at different points in one-dimension. The result shows that the thickness of the PCM has a significant effect on the temperature change. The correlation of the temperature gradient was reported. From this study, it can be concluded that the correlations of the temperature related to the thickness of the PCM and the temperature gradient are beneficial for the building design and energy management in future work

Towards net-zero energy school: A case study in Thailand

Most of the schools in Thailand consumes electricity, which is available through the national grid. It is nearly impossible for these schools to achieve net-zero energy because of very limited access to the renewable resources. This research explores the possibility of achieving net-zero energy in a school that is located near the Thailand–Myanmar​ boarder. The school utilizes locally available solar energy and hydropower. An appropriated electrification system for the school is proposed. The system consists of 2 sets of PV modules (24 kWp and 30 kWp), 288 kWh LiFePO 4 battery, and an inverter. It was found that the system was able to supply sufficient amount of electricity generated by solar energy and hydropower. The estimated annual diesel consumption was drastically reduced from 10,668 kg to 380 kg. Ultimately, the annual greenhouse gas emissions reduction was estimated at 3650 kg-CO2e. It was concluded that the school could achieve net-zero energy if further energy efficiency is applied

Electricity peak load reduction of a refrigerator using phase change material

Phase change material (PCM) has become a topic of study in thermal management, as it has a high-energy storage density. Most refrigerators have a fixed-speed compressor, which operates randomly (on/off) during their cycle. This leads to a high-power peak of electricity when the refrigerators start at the same time. Therefore, this study aims to investigate the reduction potential of the power peak and energy consumption of a refrigerator using PCM as a heat absorber. Nine testing conditions were performed by using water as the internal thermal load, at 1, 2, and 3 kg. Besides, each internal thermal load condition was varied with a PCM mass of 500, 1,500, and 2,500 g. The necessary data, such as the internal temperature and power of a refrigerator and the outside ambient temperature, were collected. The results show that the mass of PCM significantly affected the peak power of the refrigerator and energy consumption. Moreover, the results clearly show that the PCM can be used to reduce the peak power and energy consumption of the refrigerator. The correlation of the power, related to the mass of the internal heat load, and the mass of PCM was also reported. The conclusion of this study is that the PCM is suitable for reducing the peak power and energy consumption of a household refrigerator

Investigation of the Mechanical Properties of Additively Manufactured Metal Parts with Different Relative Densities

Currently, metal additive manufacturing (MAM) has been receiving more attention in many sectors for its production of metal parts because MAM effortlessly enables the fabrication of complex metal parts and provides faster and more sustainable manufacturing than conventional processes. Recently, a MAM-using bound metal deposition (BMD) has been proposed as a user-friendly manufacturing method that can provide low-volume production, economical metal parts, and operation safety. Since the BMD technique is new, information on the mechanical properties of MAM parts using this technique has not been sufficiently provided. This paper aims to study the mechanical properties of MAM parts manufactured by the BMD technique, examining the elastic modulus, yield strength, ultimate strength, and fatigue behavior of the parts with different relative densities. The MAM parts made from 316L and 17-4PH stainless steel were investigated using tensile and fatigue tests. Some mechanical properties of the infill parts in this study were validated with formulas from the literature. The weight efficiency is used as an index to assess the efficiency of the infill parts with different densities by examining the relationship between the mechanical properties and the weight of the MAM parts. The experimental results and a discussion of the weight efficiency assessment are presented as a novel information report on MAM products fabricated by BMD technology

Investigation of the Mechanical Properties of Additively Manufactured Metal Parts with Different Relative Densities

Currently, metal additive manufacturing (MAM) has been receiving more attention in many sectors for its production of metal parts because MAM effortlessly enables the fabrication of complex metal parts and provides faster and more sustainable manufacturing than conventional processes. Recently, a MAM-using bound metal deposition (BMD) has been proposed as a user-friendly manufacturing method that can provide low-volume production, economical metal parts, and operation safety. Since the BMD technique is new, information on the mechanical properties of MAM parts using this technique has not been sufficiently provided. This paper aims to study the mechanical properties of MAM parts manufactured by the BMD technique, examining the elastic modulus, yield strength, ultimate strength, and fatigue behavior of the parts with different relative densities. The MAM parts made from 316L and 17-4PH stainless steel were investigated using tensile and fatigue tests. Some mechanical properties of the infill parts in this study were validated with formulas from the literature. The weight efficiency is used as an index to assess the efficiency of the infill parts with different densities by examining the relationship between the mechanical properties and the weight of the MAM parts. The experimental results and a discussion of the weight efficiency assessment are presented as a novel information report on MAM products fabricated by BMD technology

Energy reduction for commercial freezer by force convection cooling of heatsink

Commercial freezers are commonly used the outer wall as a heatsink. This heatsink needs surrounded ambient air for cooling, which is the natural convection mechanism. However, in theory the force convection provides more heat transfer than the natural convection. Therefore, energy consumption of the force convection is generally less than the natural convection. This study aims at testing and comparing the heat transfer between the natural convection and force convection of the heatsink of the commercial freezer. Moreover, this study investigated the potential of energy reduction of the freezer by using the natural convection and the force convection of the heatsink. In this study, the unmodified commercial freezer installed with the wind tunnel over the heatsink of the freezer was made. The necessary parameters such as heatsink surface temperature, cooling air temperature, ambient air temperature, velocity of cooling air, and power consumption of the freezer were collected. The testing conditions were varied the internal heat load of the freezer by using water as 0, 3, and 6 kg, and varied the cooling air velocity as 0, 1, 2, and 3 m/s. The results showed that the convection mechanism was significantly affected by energy consumption. Furthermore, it was clearly found that the heat transfer for the force convection was higher than the natural convection. Moreover, the use of force convection resulted in a lower energy consumption. In particular at the internal heat load of 6 kg, the energy consumption of the force convection decreased by 17.5%, 17.7%, and 20.5% as compared to the natural convection at the cooling air velocity of 1, 2, and 3 m/s, respectively. Based on the results obtained it can be concluded that the force convection for the freezer heatsink can be used to reduce energy consumption, which could be efficiently applied in the future works

Energy harvesting from air conditioners by using a thermoelectric application

Air conditioners operate according to a simple refrigeration cycle, where evaporators are used to provide cooled air to air-conditioned rooms. This process normally involves making condensed water at the evaporator. Otherwise, the heat absorbed from the evaporator is directed to the outside environment by the cooled air at the condenser. This working cycle led to an idea to use low-temperature condensed water and high-temperature air for energy generation by using a thermoelectric module. The purpose of this study was to harvest energy from air conditioners by using thermoelectric power generation. This study used eight thermoelectric power generators (TEGs) attached to an aluminum heat sink, where the TEGs were heated on one side. The cooled side of the TEGs was attached to three aluminum water-cooled blocks. The necessary data, such as the condensed water temperature, heated air temperature, the condensed water rate, and the power generation, were collected. The thermostat of the air conditioner was set at 20, 21, 22, 23, 24, and 25 °C. The results show that the thermostat setting significantly affected the power generation of thermoelectric power generation module because the condensed water rate increased when the thermostat setting decreased. The condensed water rate, the hot-side and cool-side of TEG, and the condensed water temperature were reported. The power generation values were 4.28, 4.05, 3.74, 3.56, 3.36, and 3.15 mW for the thermostat settings of 20, 21, 22, 23, 24, and 25 °C, respectively. The correlation of the power generation of the TEGs and the condensation rate were related to the thermostat temperature and are reported. Moreover, the multiple linear models for the power generation of the TEGs were related to the influence independent variables and are reported. Based on the results, the energy harvesting from air conditioners by using a TEG can be used for applications such as monitoring systems