Katsuhide Ohira

PRESSURE DROP REDUCTION OF SLUSH NITROGEN IN TURBULENT PIPE FLOWS

Slush fluid such as slush hydrogen and slush nitrogen is a two-phase (solid-liquid) single-component cryogenic fluid containing solid particles in liquid, and consequently its density and refrigerant capacity are greater than for liquid state fluid. Experimental tests were performed with slush nitrogen to obtain the frictional pressure drop flowing in a 15 mm internal diameter, 400 mm long, horizontal, stainless steel pipe. The primary objective of this study was to investigate the pressure drop reduction phenomenon with changes in velocity and solid fraction. From the experimental results, the pressure drop correlation between the friction factor and the Reynolds number was obtained and an empirical correlation was derived. Flow patterns for slush nitrogen inside a pipe and the behavior of solid particles were also observed using a high speed camera.

Experimental Study on Magnetic Refrigeration for the Liquefaction of Hydrogen

An experimental study of magnetic refrigeration has been conducted for the liquefaction of hydrogen. The magnetic material selected is GGG (Gd3Ga5O12). The experimental magnetic refrigeration system principally consists of a superconducting pulsed magnet, a Gifford-McMahon type refrigerator as heat expelling portion and a thermal siphon type heat pipe as a thermal switch on the low temperature side. In the GGG heat-pipe system, gaseous hydrogen coming up from liquid hydrogen reservoir condenses on the GGG surface, then falls down to the reservoir. Liquefaction rate is measured from the input power of the electrical heater in the hydrogen bath. The authors try to find the suitable gap width of the GGG heat-pipe system considering heat capacity around GGG and interaction between liquefied and gaseous hydrogen. Subsequently we conducted a hydrogen liquefaction test and obtained a liquefaction rate of 3.55 g/h (50 cc/h) or refrigeration power of 0.4 W at 20.3 K, and these experimental results agreed with the calculated results of cycle simulation.

HEAT TRANSFER CHARACTERISTICS OF SLUSH NITROGEN IN TURBULENT PIPE FLOWS

Slush fluids, such as slush hydrogen and slush nitrogen, are two-phase (solid-liquid) single-component cryogenic fluids containing solid particles in a liquid, and consequently their density and refrigerant capacity are greater than for liquid state fluid alone. This paper reports on the experimental results of the forced convection heat transfer characteristics of slush nitrogen flowing in a pipe. Heat was supplied to slush nitrogen by a heater wound around the copper pipe wall. The local heat transfer coefficient was measured in conjunction with changes in the velocity and the solid fraction. The differences in heat transfer characteristics between two-phase slush and single phase liquid nitrogen were obtained, and the decrease in heat transfer to slush nitrogen caused by the previously observed pressure drop reduction was confirmed by this study. Furthermore, for the purpose of establishing the thermal design criteria for slush nitrogen in the case of pressure drop reduction, the heat transfer correlat...

Development of Density and Mass Flow Rate Measurement Technologies for Slush Hydrogen

Slush hydrogen is a two-phase solid-liquid cryogenic fluid consisting of solid hydrogen particles in liquid hydrogen. Compared to liquid hydrogen, the density is about 16% greater at a solid mass ratio (solid fraction) of 50%, and the cryogenic heat capacity (enthalpy) is about 18% higher. Various applications are anticipated, including fuel for reusable space shuttles, coolant for cold neutron generation, as well as the transport and storage of hydrogen as a clean energy source. At a solid fraction of within 50%, piped transport can be conducted in the same way as for normal fluids. This paper reports on the slush hydrogen technology in terms of the measurement of the density and the mass flow rate. (Translation of the article originally published in Cryogenics 44 (2004) 59-68)

Pressure-drop Reduction and Heat-transfer Deterioration of Slush Nitrogen in Horizontal Pipe Flow

Cryogenic slush fluids such as slush hydrogen and slush nitrogen are two-phase, single-component fluids containing solid particles in a liquid. Since their density and refrigerant capacity are greater than those of liquid-state fluid alone, there are high expectations for the use of slush fluids in various applications such as clean-energy fuels, fuels for spacecraft to improve the efficiency of transportation and storage, and as refrigerants for high-temperature superconducting equipment. Experimental tests were performed using slush nitrogen to obtain the flow and heat-transfer characteristics in two different types of horizontal circular pipes with inner diameters of 10 and 15 mm. One of the primary objectives for the study was to investigate the effect of pipe diameter on the pressure-drop reduction and heat-transfer deterioration of slush nitrogen according to changes in the pipe flow velocity, solid fraction and heat flux. In the case of an inner diameter of 15 mm, pressure drop was reduced and heat-transfer characteristics deteriorated when the pipe flow velocity was higher than 3.6 m/s. On the other hand, in the case of an inner diameter of 10 mm, pressure drop was reduced and heat-transfer characteristics deteriorated when the pipe flow velocity was higher than 2.0 m/s. From these results, it can be seen that a larger pipe diameter produces a higher onset velocity for reducing pressure drop and deteriorating heat-transfer characteristics. Furthermore, based on observations using a high-speed video camera, it was confirmed that pressure drop was reduced and heat-transfer characteristics deteriorated when the solid particles migrated to the center of the pipe and the flow pattern of the solid particles inside the pipe was pseudo-homogeneous.

Integrated Numerical Prediction of Atomization Process of Liquid Hydrogen Jet

The 3-D structure of the liquid atomization behavior of an LH2 jet flow through a pinhole nozzle is numerically investigated and visualized by a new type of integrated simulation technique. The present Computational Fluid Dynamics (CFD) analysis focuses on the heat transfer effect on the consecutive breakup of a cryogenic liquid column, the formation of a liquid film, and the generation of droplets in the outlet section of the pinhole nozzle. Utilizing the governing equations for a high-speed turbulent cryogenic jet flow through a pinhole nozzle based on the thermal nonequilibrium LES-VOF model in conjunction with the CSF model, an integrated parallel computation is performed to clarify the detailed atomization process of a high-speed LH2 jet flow through a pinhole nozzle and to acquire data, which is difficult to confirm by experiment, such as atomization length, liquid core shape, droplet-size distribution, spray angle, droplet velocity profiles, and thermal field surrounding the atomizing jet flow. According to the present computation, the cryogenic atomization rate and the LH2 droplets-gas two-phase flow characteristics are found to be controlled by the turbulence perturbation upstream of the pinhole nozzle, hydrodynamic instabilities at the gasliquid interface and shear stress between the liquid core and the periphery of the LH2 jet. Furthermore, calculation of the effect of cryogenic atomization on the jet thermal field shows that such atomization extensively enhances the thermal diffusion surrounding the LH2 jet flow. (Translation of the article originally published in Cryogenics 48 (2008) 238–247)