Tohru Miyashita

On the performance limit of closed two-phase thermosyphons.

This paper discusses an experiment conducted to investigate the performance limit of closed two-phase thermosiphons, together with visual observations of the flow state in the adiabatic section. The working fluids were R-113, methanol, and water. The flow state at the performance limit conditions was a violently disturbed slug type, in which the vapor plugs held up the liquid slugs periodically to a high level, causing a local circulation of liquid in the adiabatic section. This phenomenon is somewhat different from the flooding observed in open systems. An equation correlating the vapor velocity at the performance limit to the rising velocity of vapor plugs in stagnant liquid columns is proposed. This correlation compares satisfactorily with the performance limit data covering a wide range of parameters.

Rising Velocity of a Gas Plug in Vertical-Rectangular-Narrow Channels

A bubble rising velocity in stagnant water in rectangular channels was examined. The width of the flow channels and the gap space between parallel walls were varied from 10 mm through 150 and from 1 mm through 10 mm, respectively. When the bubble had plug shape in the long side and also the short side, the bubble velocity took the same velocity as that in a circular pipe that had the same periphery. When the bubble lost the plug shape in the long side, the rising velocity became fast as the long side shape departed from the plug shape. When the long side was large enough for the bubble to have the shape of a bubble in open space, the bubble rising velocity was expressed well with the expression for the bubble rising velocity in open space. As the long side became narrow, the bubble rising velocity became slower than that for open space. When the gap spacing was quite narrow; 1 mm, and the long side was less than 20mm, the bubble stopped rising halfway in the flow channel.Copyright

Development of Technologies on Innovative-Simplified Nuclear Power Plant Using High-Efficiency Steam Injectors: Part 13—Study on Heat Transfer of Direct Condensation of Steam on Subcooled Water Jet

Characteristics of thermal-hydraulic phenomena in the steam injector were examined. In experiments, a water jet from a nozzle of 5 mm diameter flowed into the condensing test section pipe concentrically. The inner diameter of the condensing section was 7, 10, or 20 mm and the length was 105 mm. Steam flowed into the peripheral space between the water jet and the inner wall of the test section and condensed on the ware jet surface. The radial and the axial distributions of velocity and temperature of the water jet were measured. Analyses by using the STAR-CD code were also performed. The temperature measured in the central portion of the water jet was higher than the predicted assuming the ordinary turbulent flow in a pipe. The temperature measured in the peripheral region was lower than the predicted. The radial temperature distribution measured was flatter than the predicted. When the steam condensation rate was large, the measured radial velocity distribution in the water jet was flatter than the predicted. In the case that the steam velocity was quite high, the velocity measured in the peripheral region was higher than that in the center portion. These results implied that the steam condensing on the water jet brought momentum in the water jet to result in more effective radial transport of heat and momentum. The STAR-CD code analyses to allow the interface between the wall that simulated the steam flow part and the water flow that stood for the water jet to move, i.e. creating momentum in-flux at the water jet interface, provided better results to support the experimental results. To increase the interfacial friction had a minor effect on the radial velocity distribution in the tested range.Copyright