Naoto Hagino

Field Experiment of Top-Heat Thermosyphon

Three types of thermosyphon were tested. Type-1 has a horizontal condenser with a 536ml volume buffer chamber. The vertical heat transfer height was 3m. In type-2, condenser and connecting pipe were tilted by 10° to the ground with 3776ml buffer chamber. In type-3, only condenser was tilted and the others were the same as type-2. In type-2 and -3, the vertical heat transfer height was 4 m. The maximum coefficient of the heat transfer was 60% for type-1 and 40% for type-2 and -3. Detailed difference in performance of type-1, -2, and -3 were not elucidated because of the limited field data. However, the present results indicated the promising capability of thermosyphon without using circulation pumps. Optimizing the performance of the thermosyphon was left for the future study.Copyright

Performance of a Self-Circulating Thermosyphon

A series of laboratory experiments on self-circulating thermosyphon (SCT) was carried out. The thermosyphon system consists of heating section, condenser, reservoir, and heat exchanging section. The basic performance was elucidated. The present thermosyphon system works by itself under certain conditions of tilting angle of the condenser, the water filling rate, and the input power. The startup time of the present system is remarkably improved. The effect of the buoyancy on the driving force is indicated through the tilting angle of the condenser.Copyright

Ultrasonic Wave Propagation Analysis for In-Process Monitoring of Stamping

The servo press has high potential for producing high precision mechanical parts. However, small gaps between dies and workpieces tend to exist even in servo press stamping, and the potential of the servo press has not yet been fully utilized. The reason for this is conventional presses do not have feedback control systems, and the lack of a suitable method of sensing contact information in real time causes deterioration in the accuracy of products. If slide motion could be controlled by contact information, the small gaps could be removed. To solve this problem, the authors have developed a method of monitoring the contact states between dies and workpieces during the stamping process. The method uses ultrasonic wave reflection and transmission at the contact surfaces and was proved to be able to monitor contact pressure by using a simple geometry experimental die apparatus. Finite-difference time-domain (FDTD) numerical simulation was conducted in this study to obtain better understanding of wave propagation through dies and workpieces. The results obtained from this FDTD simulation visualized wave propagation that could not be experimentally measured. Some of the major results obtained are as follows. 1) When a thin metal sheet is pressed between dies that have inclined stamping surfaces, ultrasonic elastic waves are reflected and transmitted multiple times. 2) Modal conversion occurs at the die-workpiece boundary in such a way that normal waves with an inclined incident angle are transformed into normal and shear waves. 3) Elastic waves sent out from an ultrasonic transducer are mixtures of normal waves with flat wave fronts along the propagation path axis, normal waves with circular or spherical wave fronts expanding from both sides of the transducer, and shear waves. These results brought about much useful information for setting ultrasonic transducers and analyzing collected signals.

Hydropower Generation by a Self-Circulating Solar Thermosyphon

A self-circulating solar thermosyphon (TS) was applied to hydropower generation for the first time. A TS consists of a solar thermal collector, condenser, buffer chamber, hydropower section, heat exchanger, and recuperator. In the present study, the power output level was 10−6 W for the solar irradiation input of 102 – 103 W. The coefficient is 10−9. Considering the Carnot’s coefficient, 0.13, for the heat source and sink of temperatures 70°C and 25°C, there is room for remarkable improvement in TS hydropower generation. Moreover, the solar thermosyphon hydropower generation may provide us with new ways of utilizing heat below a temperature of 100°C, which until now has been merely used for things such as hot water supply and floor heating.Copyright

Basic Characteristics of a Compact PV/T Simulator

This paper presents the development and experimental results of photovoltaic and thermal hybrid (PV/T) simulator. The light source of the simulator consists of 16 halogen lamps with 4×4 arrangements. The PV/T collector is constructed from the mono-crystalline type of PV cell and backed by the 8 mm thick polyvinyl chloride (PVC) thermal collector. In order to understand and evaluate precise behavior of PV/T system, we applied 3 different mass flow rates; 200, 250, and 300 g/min. The result shows that the PV output behavior of the simulator for the radiation seems to be similar to that done under the sunlight experiment. At certain surface temperatures of PV, the collector thermal efficiency of PV/T system increases with the mass flow rate. This may be due to the internal heating of the PV cell.Copyright