Hiroshi Tsukamoto

Bio: Hiroshi Tsukamoto is an academic researcher from Kyushu Institute of Technology. The author has contributed to research in topics: Centrifugal pump & Impeller. The author has an hindex of 19, co-authored 67 publications receiving 1255 citations.

Fabrication and characterization of bismuth–telluride-based alloy thin film thermoelectric generators by flash evaporation method

Abstract: Bismuth–telluride-based alloy thin film thermoelectric generators are fabricated by a flash evaporation method. We prepare Bi 0.4 Te 3.0 Sb 1.6 (p-type) and Bi 2.0 Te 2.7 Se 0.3 (n-type) powders for the fabrication of the flash evaporated thin films. The overall size of the thin film thermoelectric generators, which consist of seven pairs of legs connected by aluminum electrodes, is 20 mm by 15 mm. Each leg is 15 mm long, 1 mm wide and 1 μm thick. We measure the output voltage and estimate the maximum output power near room temperature as a function of the temperature difference between hot and cold junctions of the thin film thermoelectric generators. In order to improve the performance of the generators, a hydrogen annealing process is carried out at several temperatures from 25 °C to 250 °C. The highest output voltage of 83.3 mV and estimated output power of 0.21 μW are obtained from a hydrogen annealing temperature of T a = 250 °C and a temperature difference of Δ T = 30 K. The hydrogen annealing temperature of T a = 250 °C also results in the best electrical performance for both p-type thin film (Seebeck coefficient = 254.4 μV/K, resistivity = 4.1 mΩ cm, power factor = 15.9 μW/cm K 2 ) and n-type thin film (−179.3 μV/K, 1.5 mΩ cm, 21.5 μW/cm K 2 ).

Effect of grain size on thermoelectric properties of n-type nanocrystalline bismuth-telluride based thin films

Abstract: bismuth-telluride-based thin films with the average grain size of 60 nm by a flash-evaporation method and shown the re- duction of thermal conductivity. 12 To further reduce the thermal conductivity of the nano- crystalline bismuth-telluride-based thin films and investigate the effect of grain size on thermoelectric properties, we pre- pare the nanocrystalline thin films by the flash-evaporation method with an improved annealing condition. The grain size of the thin films is estimated using an x-ray diffraction XRD and atomic force microscopy AFM. The thermo- electric properties, in terms of the electric conductivity, the Seebeck coefficient, and the thermal conductivity, are mea- sured at room temperature. The measured thermal conductiv- ity is divided into the lattice thermal conductivity l and electronic thermal conductivity e. Then we investigate the grain size dependence of the lattice thermal conductivity of the nanocrystalline thin films using a simplified phonon transport model.

Numerical Study of Pressure Fluctuations Caused by Impeller-Diffuser Interaction in a Diffuser Pump Stage

Abstract: Two-dimensional and three-dimensional, unsteady state Reynolds-averaged Navier-Stokes (RANS) equations with standard k-e turbulence models were solved within an entire stage of a diffuser pump to investigate pressure fluctuations due to the interaction between impeller and diffuser vanes. A complete solution of transient flows due to the interaction between components in the whole pump without approximating the blade count ratio of impeller to diffuser was obtained by employing an Arbitrary Sliding Mesh. The unsteady numerical results were compared with experimental data and values calculated by the singularity method

Transient characteristics of a centrifugal pump during stopping period

Abstract: A theoretical and experimental study has been made on the transient characteristics of a centrifugal pump during its rapid acceleration from standstill to final speed Instantaneous rotatinal speed, flow-rate, and total pressure rise are measured for various start-up schemes Theoretical calculations for the prediction of transient characteristics are developed and compared with the corresponding experimental results As the results of this study, it becomes clear that the impulsive pressure and the lag in circulation formation around impeller vanes play predominant roles for the difference between dynamic and quasi-steady characteristics of turbopump during its starting period

Thermoelectric properties of n-type nanocrystalline bismuth-telluride-based thin films deposited by flash evaporation

Abstract: The thermal conductivity of n-type nanocrystalline bismuth-telluride-based thin films (Bi2.0Te2.7Se0.3) is investigated by a differential 3ω method at room temperature. The nanocrystalline thin films are grown on a glass substrate by a flash evaporation method, followed by hydrogen annealing at 250 °C. The structure of the thin films is studied by means of atomic force microscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy. The thin films exhibit an average grain size of 60 nm and a cross-plane thermal conductivity of 0.8 W∕m K. The in-plane electrical conductivity and in-plane Seebeck coefficient are also investigated. Assuming that the in-plane thermal conductivity of the thin films is identical to that of the cross-plane direction, the in-plane figure of merit of the thin films is estimated to be ZT=0.7. As compared with a sintered bulk sample with average grain size of 30 μm and nearly the same composition as the thin films, the nanocrystalline thin films show approximately a 50% redu...

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Advanced Thermoelectric Design: From Materials and Structures to Devices

Abstract: The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

A wearable thermoelectric generator fabricated on a glass fabric

Abstract: The conversion of body heat into electrical energy using a thermoelectric (TE) power generator is useful for wearable self-powered mobile electronic systems such as medical sensors or smart watches. We herein demonstrate a glass fabric-based flexible TE generator using a screen printing technique and the self-sustaining structure of a TE device without top and bottom substrates. With this technique it is possible to make the device thin (∼500 μm), lightweight (∼0.13 g cm−2), and flexible. In addition, the developed TE generator achieved an unprecedentedly large output power density which is several tens of times higher than that of flexible TE generators reported to date. The developed TE generator shows an allowable bending radius of as low as 20 mm and no change in performance by repeated bending for 120 cycles. This work can expedite the development of wearable self-powered mobile devices.

Smart Textiles for Electricity Generation.

Abstract: Textiles have been concomitant of human civilization for thousands of years. With the advances in chemistry and materials, integrating textiles with energy harvesters will provide a sustainable, environmentally friendly, pervasive, and wearable energy solution for distributed on-body electronics in the era of Internet of Things. This article comprehensively and thoughtfully reviews research activities regarding the utilization of smart textiles for harvesting energy from renewable energy sources on the human body and its surroundings. Specifically, we start with a brief introduction to contextualize the significance of smart textiles in light of the emerging energy crisis, environmental pollution, and public health. Next, we systematically review smart textiles according to their abilities to harvest biomechanical energy, body heat energy, biochemical energy, solar energy as well as hybrid forms of energy. Finally, we provide a critical analysis of smart textiles and insights into remaining challenges and future directions. With worldwide efforts, innovations in chemistry and materials elaborated in this review will push forward the frontiers of smart textiles, which will soon revolutionize our lives in the era of Internet of Things.

A review of the state of the science on wearable thermoelectric power generators (TEGs) and their existing challenges

Abstract: Thermoelectric generators are solid state energy harvesters which can convert thermal energy into electrical energy in a reliable and renewable manner. Over the last decade, the human body has been considered as a good source of heat to harvest electrical energy through wearable thermoelectric generators. It may become an alternative power generation technique compared to other conventional ones used for many wearable devices. The wearable thermoelectric generator has potential to generate sufficient energy for any wireless sensor nodes (typically power requirements