Hiromitsu Ohta

Flashing Phenomena of Liquid Nitrogen in a Pressure Vessel Under Rapid Depressurizations

In recent years in Japan, the demand of cryogenic fluids like a LH2, LNG is increasing because of the advance of fuel cell device technology, hydrogen of engine, and stream of consciousness for environmental agreement. The purpose of this study is to clarify some fundamental features of the flashing of cryogenic fluids. Experiments on flashing of liquid nitrogen were conducted to clarify the effect of surface roughness of a vessel. Two types of pressure vessel were used. One is a vessel made of stainless steel, the other is a vessel made of glass. In the case of glass vessel, many types of boiling have been observed. The degree of superheat at the start of boiling was found to depend strongly on the rate of depressurization.Copyright

Active noise control‐like performance of a spherical reflector

The principle of cancellation of tonal noise by using a spherical reflector, the designing method of an appropriate reflector for canceling jet screech, the advantage of a spherical compared to a flat reflector for canceling a tonal noise, and a prospective application for an aircraft to protect the fuselage from acoustic fatigue are discussed. The thrust loss due to the new technique was also evaluated directly with a vertical wind tunnel. The change in the aerodynamic structure was optically observed by using a schlieren apparatus along with a high‐speed video camera. [Work supported by grant of JSPS, Japan.]