Yoichi Fujii-E

MHD pressure drop of NaK flow in stainless steel pipe

An experiment on electric potential and pressure drop for NaK flow in uniform transverse magnetic fields was conducted. A test channel was constructed using 45.3 mm (or 28 mm) I.D. and 1.65 mm thick 304-SS circular pipe in the NaK-Blowdown MHD Experimental Facility of Osaka University. The experimental range covered had a driving gas pressure <8 bar, an applied magnetic flux density: B/sub 0/=0.3 about1.75 T, a mean flow velocity of NaK: U/sub 0/=2 about 15 m/sec, a Reynolds number Re = 8 X 10/sup 4/ about6.2 X 10/sup 5/ and a Hartmann number: Ha = 740 about4150. A theoretical analysis is given on the basis of a uniform-velocity thick-wall model. Good agreement between the theory and the experiment were obtained both for the potential and for the pressure drop, except a small deviation of the experimental pressure drop towards values lying above the theoretical ones in a weak B/sub 0/ and high U/sub 0/ region (Ha/sup 2//Re <15).

Flow and heat transfer characteristics in lithium loop under transverse magnetic field

A medium-scale lithium-loop with 40 l/min and 3bar ratings was constructed to gain basic information on MHD effects on the flow and heat transfer characteristics. The loop has two parallel test sections for pressure drop and heat transfer experiments, which were made of 15.75 mm I.D. and 19.05 mm O.D. 316-SS tubes and placed between magnet poles of 500 mm vertical length. The pressure drop test section was provided with two strain gage type pressure transducers and the heat transfer test section with a 300 mm long 7.6 mm O.D. high flux electric heater pin. The experiment covered the ranges of the magnetic flux density: 0-1.0 T, The Li flow velocity: 0.2 -5.0 m/sec, the heat flux: 0-120 W/cm/sup 2/ and the Li temperature: 350-400/sup 0/C. The experimental results of potential and pressure drop agreed well with the theoretical prediction based on the uniform-velocity thick wall model. The heat transfer coefficient, or Nusselt number, was decreased with increasing magnetic flux density, but not monotonically in a weak magnetic field region of 0.2-0.4 T, where a singular phenomenon, i.e. an elevation of Nusselt number was observed.

Condensing Heat Transfer in Steam-Water Condensing-injector

An experiment on the direct heat transfer process between supersonic steam and subcooled water jet was performed, using a steam-water condensing-injector. Photographic observation provided information on the state of flow, and establishment of a critical separate steam-water flow was confirmed. The temperature and pressure distributions along the flow were measured and the effective coefficients of condensing heat transfer were evaluated from the observed data, based on a model embodying an idealized interface between vapor and liquid. In the vicinity of the water nozzle exit, where the vapor-liquid interface was distinct, the heat transfer coefficients obtained were 14–28 (cal/°C.cm2.sec), and some correlation was observed among Nusselt, Reynolds and Jakob numbers, upon adopting the velocity and the physical properties of the steam phase. The relations Nu=6.0.Re 0.9(Pr=1.04–1.10), and Re=1.8×108.Ja 3.0, i.e., Nu=1.6×108.Ja 2.7 were derived as a rough estimation. No clear correlation could be discerned in...

Propagation of Pressure Wave in Air-Water Two-Phase System, (II)

In an attempt to gain information on the propagation characteristics of pressure waves in a two-phase system consisting of gas and liquid, experiments were performed on a nonflowing air-water mixture in a range of pressures from 1.0 to 7.5 bar and void fractions from 0 to 60%. Stepwise pressure disturbancies were applied to a water column dispersed with rising air bubbles by bursting diaphragm. The pressure transients at several points down the fluid column were measured with strain gage type pressure transducers and recorded on magnetic tapes. The nonlinearity of the pressure wave records was scarcely marked. The propagation velocity of pressure wave front down the fluid column was found almost independent of the magnitude of the pressure change applied, nor whether it was depressive or compressive. At higher void fractions where the flow regime became sluggy, the measured propagation velocities showed increasing deviation from the calculated values based on the nonslip homogeneous adiabatic model, thoug...

Frictional Pressure Drop for NaK-N2 Two-Phase Flow in Rectangular Cross Section Channel of Large Aspect Ratio

In this paper, the frictional pressure drop in an isothermal liquid metal-gas two-phase flow through a rectangular channel with large width-to-height ratio is treated semiempirically for a NaK-N2 two-phase flow system. The frictional pressure drop in the two-phase flow is compared with the following two reference values : 1. The frictional pressure drop in the liquid flowing alone in single phase with the same velocity as that of the liquid in the two-phase mixture. 2. The frictional pressure drop in the liquid flowing alone in single phase with the same mass flow rate as that of the liquid in the two-phase mixture. The comparison with the former reference value is necessary for the prediction of friction loss in a liquid metal MHD generator channel whose medium would be two-phase mixture. The semiempirical analysis was performed assuming the two-phase mixture to be a continuous medium with its properties, e.g. viscosity and density, defined by void fraction and the velocity determined by the total mass f...

Energy loss in liquid metal MHD induction converter due to discrete tooth-slot arrangements

In this paper, the performance characteristics of a linear channel LM-MHD induction converter operated in both constant current and constant voltage mode are obtained analytically, appling the slit channel approximation but taking account of variations in the traveling magnetic field intensity in the direction of the fluid flow according to differences in the disposition of the teeth and slots in the stators. The analytically obtained solutions were verified with the experimental converter with and without copper side bars operated in constant voltage mode at room temperature using NaK-78 as the electrically conducting working fluid. The experimental results obtained with the converter with copper side bars agreed with the analytically obtained solutions, though the plots of power output shifted toward greater values of negative slip compared with the theoretical curves, due to the additional ohrnic losses in both the side walls of channel and the copper side bars, which were not taken into account in the...

Measurement of incipient boiling pressure signal and evaporation coefficient of liquid metal.

In the liquid metal boiling with the incipient boiling superheat, the pressure transient is large enough to be measured. In this paper the time constant of pressure transient τ in the growing stage of the vapor bubble is measured and its dependence on the channel geometry, the dynamic constraint and the liquid temperature is made clear. The evaporation coefficient C is also obtained by measuring the vapor pressure and the liquid column velocity. For potassium C is constant in our experiment and its value is (3.8±0.6)X10−3. Using the measured C, the τs are computed with the momentum equation, the state equation and the Hertz-knudsen equation in the kinetic theory.

Experimental studies on characteristics of pressure attenuation and recovery to saturation for decompressive disturbances in low pressurized water

Slightly pressurized water (P sat = 1.2–6.0 bar) was flashed into steam void by step decompression to atmospheric pressure, using a shock tube type device with vertical test section, made of stainless steel pipe about 2 m long, with an inner diameter of 40 mm. The transient pressure depression below saturation and the time constant of pressure recovery to the saturation were measured, based on the observed transient pressure response signals. The transient pressure curve could be approximated by the expression P(t) = P min +(P sat −P min )(1−e −t/τ) for the period immediately following step decompression. This time constant τ represents the effective relaxation time of thermodynamic nonequilibrium. Defining the term decompression ratio e as the ratio of the excess transient depression below saturation pressure to the difference between saturation and atmospheric pressure, i.e., e=(P sat −P min )/(P sat −P fin ), the dependence of e on the vertical position along the test column z and P sat was found to fo...

Decrease in Power Density due to Finite Electrode Conductivity in Liquid Metal MHD Generator

In the liquid metal MHD power generator, the electric conductivity of the working fluid is so large as to be comparable with that of the electrode. Under such circumstances the perfect conductor approximation no longer holds for the electrode, because the electric potential loses its constancy and acquires a certain pattern of distribution in the electrode as well as in the fluid. The extent of distortion in the electric equipotential lines and lines of force depends on the ratio of conductivity between electrode and fluid, and on the load connection. The power density becomes non-uniform, and furthermore the average power density becomes smaller than in the case of a generator with the perfect conductor electrode. The effect due to this finite conductivity of the electrode is contrary in trend to that due to end loss, as analyzed by Sutton with both aspect ratio and load factor as parameters. The results obtained in our present experiments with a mercury blow-down facility have agreed very well with the ...

Control systems and transient analysis

Abstract Characteristics governing a marine reactor operation include: (1) occurrence of abrupt load changes in association with maneuvering operations; (2) subjection to ship motion such as rolling, heaving and piching. The effects of abrupt load changes appear on the reactor primary system as well as on the secondary steam generator. However, the effects of ship motion appear only on the steam generator since enough subcooling is given to primary coolant and no steam void is found in the primary coolant. This paper contains the following subjects: (1) description of the part of the reactor system which has an intimate relation to reactor operation; (2) description of the functions of the control system and the safety system; (3) transient behaviour of the reactor and the steam generator under load change; (4) transient behaviour of the steam generator due to ship motion.