Kazu Nishigaki

The Superheat-Limit of Liquid Oxygen and Nitrogen at 1 atm

The superheating of bimolecular cryogenic liquids (oxygen, nitrogen) was measured at one atmospheric pressure. The maximum superheating data obtained here were compared with the results of calculation based on the Becker-Doring-Zeldovich homogeneous nucleation theory. Good agreement between theory and experiment was found, and the magnitude of the super-heat-limit Tnucleation-Tcoexist was well represented as a function of the temperature gap Tcritical-Tcoexist, as Tnucleation-Tcoexist0.68 (Tcritical-Tcoexist) at 1 atm.

Elementary study on superconducting electromagnetic ships with helical insulation wall

Abstract We, Kobe University of Mercantile Marine (KUMM) and Institute of Electrical Engineering (IEE) research teams, have carried out in Japan, the joint experimental test of the high magnetic field (∼14 T) superconducting electromagnetic ship performance in co-operation with the researchers of NRIM. In this experimental study, the major system components are thruster, seawater circulating system and various measuring instruments. The NRIMs 15 T class superconducting magnet that forms the outmost member of the 40 T class hybrid magnet was used. The flow guide and flow rectifier are of same lengths of 0.2 m, and the length of the electrodes are 0.6 m. The anodes outer diameter is 0.1 m, and the cathodes inner diameter is 0.346 m. The helical insulation wall is 10 mm thick and the pitch number is 3.8. During the experiment, magnetic fields were changed to six stages 3, 5, 8, 10, 12 and 14 T, whereby seawater pressures, temperatures and flow rates were measured. Electric currents were changed from 10 to 700 A. In one of results, the thruster efficiency increases in association with the increase of the magnetic field. It has been demonstrated that the helical-type superconducting electromagnetic thruster is superior, in terms of thruster efficiency, than that of earlier works by Iwata et al. and YAMATO-1s group. So, it is considered that this thruster is better suited to commerical application than earlier works.

Thermal test of the insulation structure for LH2 tank by using the large experimental apparatus

Abstract Conceptual designs of large mass LH 2 (liquid hydrogen) storage systems, whose capacity is 50,000 m 3 , have been studied in the Japanese hydrogen project, World Energy Network (WE-NET) [K. Fukuda, in: WE-NET Hydrogen Energy Symposium, 1999, P1–P41]. This study has concluded that their thermal insulation structures for the huge LH 2 tanks should be developed. Their actual insulation structures comprise not only the insulation material but also reinforced members and joints. To evaluate their thermal performance correctly, a large test specimen including reinforced members and joints will be necessary. After verifying the thermal performance of a developed large experimental apparatus [S. Kamiya, Cryogenics 40 (1) (2000) 35] for measuring the thermal conductance of various insulation structures, we tested two specimens, a vacuum multilayer insulation (MLI) with a glass fiber reinforced plastic (GFRP) support and a vacuum solid insulation (microtherm ® ) with joints. The thermal background test for verifying the thermal design of the experimental apparatus showed that the background heat leak is 0.1 W, small enough to satisfy apparatus performance requirement. The thermal conductance measurements of specimens also showed that thermal heat fluxes of MLI with a GFRP support and microtherm ® are 8 and 5.4 W/m 2 , respectively.

Influence of NaCl Concentration on the Gas–Liquid Interface Deformation of Water in Magnetic Fields

To clarify the deformation characteristics of a seawater surface in magnetic field, the gas–liquid interface deformation of water and NaCl aqueous solution at room temperature was investigated. In this research, a uniform magnetic field (UMF) and a gradient magnetic field (GMF) were used. The deformation of water was rarely observed in UMF of 0 to 10 T, but it was clearly observed in GMF. The deformation of water and NaCl aqueous solution in GMF decreased in proportion to the increase of NaCl concentration. The decrease was mainly affected by the increase of density in the aqueous solution as the NaCl concentration increased. In addition, it is considered that the deformation of NaCl aqueous solution depends not only on the magnetic force but also on the osmotic pressure of the concentration gradient.

Measurements of the Surface Tension of Liquid Oxygen in High Magnetic Fields

Using a capillarity method and a split type superconducting magnet, the surface tension of liquid oxygen has been measured in various magnetic fields up to 5 T at 65.3 K and 77.1 K. Experimental data are compared with the numerical calculations obtained on the basis of the theory of surface tension. It is found that the dependence of surface tension on magnetic field is so small that it can not be the main cause of the shape deformation of the meniscus.

Basic study on velocity‐flow urodynamics using Doppler sonography: Simultaneous detection of cavitation and Doppler signals in an artificial urethral model

Abstract  Background:  We have developed velocity‐flow urodynamics using Doppler sonography based on the hypothesis that microbubbles formed in the urethra are responsible for Doppler signals. In order to confirm this hypothesis derived from Bernoullis principle, we investigated the simultaneous detection of cavitation noise and Doppler signals in an experimental system.

Flow control of seawater with a diverging duct by MHD separation method

A unique control method for a diverging seawater flow based on electromagnetic force, the so-called MHD (magnetohydrodynamics) separation method, is performed. The experimental apparatus is composed of a 10-T class superconducting magnet, a separation cell, a seawater tank, and a flow system. The constructed separation cell contains parallel electrodes, 18 mm wide, 40 mm long and 20 mm apart, and a diverging duct divided into equal parts, A (not affected by electromagnetic force) and B (affected by electromagnetic force). The dependence of flow ratio (mass of side-A sample solution/total mass of sample solution) on electric current, magnetic field, NaCl concentration and sample velocity has been studied experimentally using NaCl aqueous solution. The possibility of flow control of seawater with a diverging duct by the MHD separation method as well as experimental results are discussed.

A large experimental apparatus for measuring thermal conductance of LH2 storage tank insulations

Abstract In the Japanese hydrogen project, WE-NET (World Energy Net Work), the conceptual design of the large mass liquid hydrogen storage systems for ground tanks and transportation, whose scales would reach to that of commercialized LNG (liquid national gas), has been studied. This study has concluded that the thermal insulation for a mass storage tank, providing the excellent thermal performance with the optimized strength, should be developed. In order to evaluate thermal conductance of various devised insulations, we have manufactured a large-scale experimental apparatus. This apparatus, which adopts a double guarded flat plate boil-off calorimeter method, can provide the thermal data needed for designing a full-scale tank. It would be possible to test various kinds of specimens with allowable dimensions: diameter 120 cm, thickness up to 30 cm. In the case of a rigid specimen contacting bottom surfaces of liquid hydrogen vessels, the good flatness of their bottom plates is desirable to reduce the thermal resistance between vessels and a specimen surface. This paper describes the abstract of the developed apparatus, its structural design and also the experimental results for verifying its structural design.

Superheat Limit of 4He and Its Quantum Deviation from Classical Behavior

The superheating of normal liquid 4 He was investigated by means of continuous heating of liquid specimen in a small glass capillary over a temperature range 2.26 K to 4.88 K. The maximum superheating data obtained were compared with the prediction from the homogeneous nucleation theory and the data for various liquids in terms of the reduced coordinates. It is confirmed that the agreement between the homogeneous nucleation theory and experiment on 4 He is satisfactory, and the scaled superheating depends parametrically on the quantum parameter \(\varLambda^{*}\), i.e., the deviations of the data for quantum liquids from the classical behavior become pronounced as the parameter is increased.

Gas-Liquid Interface Deformation of Flowing Water in Gradient Magnetic Field-Influence of Flow Velocity and NaCl Concentration.

To clarify the deformation characteristics of flowing seawater surfaces in a gradient magnetic field, the influence of flow velocity and NaCl concentration on the gas–liquid interface deformation of flowing water was carefully examined. The gas–liquid interface under the condition of flow was asymmetrically deformed for the magnetic center differing from the interface deformation under the rest condition. The deformation of water and NaCl aqueous solution increased as initial velocity and magnetic field increased. Also, the deformation at a constant initial velocity decreased with increasing NaCl concentration. It was found that the deformation under the condition of flow was affected not only by the magnetic field but also by the pressure drop at the interface, pressure loss induced by the viscosity and decrease of concentration gradient due to increasing flow velocity.