Cryogenic Two-phase Flow Research Articles

A Direct Numerical Simulation of Axisymmetric Cryogenic Chill Down in a Pipe in Microgravity

Cryogenic two-phase flow with phase change heat transfer, consisting of a saturated liquid slug translating in its own superheated vapor in a circular pipe, was numerically simulated. The cryogenic chill down process was simplified by assuming ideal inverted annular flow regime. The method used is based on a sharp interface concept and developed on an Eulerian Cartesian fixed-grid with a cut-cell scheme and marker points to track the moving interface. The unsteady, axisymmetric Navier–Stokes equations in both liquid and vapor phases are solved separately and used to compute the velocity, pressure, and temperature fields and the deformation of the liquid core very accurately. Three most common cryogenic fluids, viz. nitrogen, oxygen, and argon were included in the study. The influence of non-dimensional parameters like Reynolds number \(Re,\) Weber number \(We\), and Jakob number \(Ja\) on flow characteristics was studied by systematically varying only one at a time. \(Re\) was found to affect the mass flow rates, but did not have a significant influence on the wall cooling or the Nusselt number. \(We\) affected the interface shape at the leading edge of the liquid slug, also influencing the heat transfer and velocity field there. \(Ja\) affects all three quantities of interest, i.e., mass flow rate, wall cooling, and the Nusselt number.

LNGC 디젤기관 크랭크 챔버용 액체질소 불활성가스 시스템에 관한 연구

It is necessary to install the inert gas system(IGS) for preventing fire and explosion in LNGC main diesel engine crankcase besides oil mist detector(OMD) unit with CO₂ gas injector. Therefore, to design the liquid nitrogen IGS, analytical work is conducted for predicting the heat input load of liquid nitrogen heater with two-phase stratified flow model. This paper also presents the effects of changes in pipe diameter, saturated pressure, and inclination angle by ship’s movement on cryogenic two-phase stratified flows. It is found that the stratified model gives reasonable predictions, and the model is effective to predict the heat input load of liquid nitrogen IGS.

A direct numerical simulation of axisymmetric cryogenic two-phase flows in a pipe with phase change

An accurate finite-volume based numerical method for the simulation of a cryogenic two-phase flow with phase change heat transfer, consisting of a saturated liquid slug translating in its own superheated vapor in a circular pipe is presented. This method is built on a sharp interface concept and developed on an Eulerian Cartesian fixed-grid with a cut-cell scheme and marker points to track the moving interface. The unsteady, axisymmetric Navier–Stokes equations in both liquid and vapor phases are solved separately. The mass continuity, momentum flux conditions and conservation of energy are explicitly matched at the true boundary between the two phases to determine the interface shape and movement. A quadratic curve fitting algorithm with marker points is used to yield smooth and accurate information of the interface curvatures. It is uniquely demonstrated for the first time with the current method that conservation of mass is strictly enforced for continuous infusion of flow into the domain of computation. The method has been used to compute the velocity, pressure and temperature fields and the deformation of the liquid core. It is also shown that the current method is capable of producing accurate results for a wide range of Reynolds number, Re, Weber number, We, Jakob number, Ja and large property jumps at the interface.

Experimental study of detonation in a cryogenic two-phase H 2–O 2 flow

Direct initiation and propagation of detonation through a cryogenic two-phase flow constituted by liquid oxygen droplets in gaseous hydrogen at 100 K are experimentally investigated. The influence of droplet size distribution is characterized in a cryogenic gaseous helium and liquid oxygen two-phase flow. Droplet sizing and detonation experiments are conducted by varying different parameters: distance from the injector, helium and hydrogen mass flow rates, global equivalence ratio and addition of gaseous nitrogen. Droplet size distributions reveal quick vaporization of the smallest droplets of the cryogenic jet. Results in terms of wave velocity, pressure, and detonation cells show that a detonation wave can be directly initiated, with a propagation wave velocity of 20% higher than the Chapman–Jouguet value. Cell size measurements show that the mixture sensitivity is not affected by the presence of droplets. Addition of gaseous nitrogen reduces only slightly the peak pressure, but the detonation velocity is reduced by about 30%.

Optical velocimetry in cryogenic two-phase flows

This paper presents the design and implementation details of an optical sensor for velocity measurements in cryogenic two-phase flows. The proposed sensor utilises a spatial filtering technique to robustly estimate the velocity of optically inhomogeneous phase boundaries based on the power spectral density of the detector signal. We address implementation issues arising from the application of the sensor to cryogenic media and present experimental results showing the applicability of the sensor to both low and high velocity measurements.

Experimental study on boiling flow of liquid nitrogen in inclined tube—liquid slug length distribution and velocity

An experimental study was carried out to understand the phenomena of the boiling flow of liquid nitrogen in an inclined tube with closed bottom by using a high speed motion analyzer. The experimental tube is 0.018 m ID and 1.0 m in length. The range of the inclination angle is 45-90° from the horizontal. The liquid slug length and velocity were studied. The mean liquid slug lengths increased first, and then decreased with decreasing θ, maximum at 60°, which showed the Taylor bubble was easier to coalescence from vertical to inclined, but coalescence lessening at 45°. The standard deviations of liquid slug lengths increase with increasing x/D at all inclination angles. The liquid slug propagation velocity increases first, and then decreases with decreasing θ, maximum at θ=60°, and is almost stable at 50D and 55D positions. These conclusions provide a basis for further study of the cryogenic two-phase slug flow.

Numerical Analysis of Two-Phase Pipe Flow of Liquid Helium Using Multi-Fluid Model

The two-dimensional characteristics of the vapor-liquid two-phase flow of liquid helium in a pipe are numerically investigated to realize the further development and high performance of new cryogenic engineering applications. First, the governing equations of the two-phase flow of liquid helium based on the unsteady thermal nonequilibrium multi-fluid model are presented and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the two-phase flow of liquid helium is shown in detail, and it is also found that the phase transition of the normal fluid to the superfluid and the generation of superfluid counterflow against normal fluid flow are conspicuous in the large gas phase volume fraction region where the liquid to gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase. According to these theoretical results, the fundamental characteristics of the cryogenic two-phase flow are predicted. The numerical results obtained should contribute to the realization of advanced cryogenic industrial applications.

Two-Dimensional Numerical Simulation of Boiling Two-Phase Flow of Liquid Nitrogen.

Two-dimensional characteristics of the boiling two-phase flow of liquid nitrogen in a duct flow are numerically investigated to contribute to the further development of new high-performance cryogenic engineering applications. First, the governing equations of the boiling two-phase flow of liquid nitrogen based on the unsteady drift-flux model are presented and several flow characteristics are numerically calculated taking account the effect of cryogenic flow states. Based on the numerical results, a two-dimensional structure of the boiling two-phase flow of liquid nitrogen is shown in detail, and it is found that the phase change of liquid nitrogen occurs in quite a short time interval compared with that of two-phase pressurized water at high temperature. Next, it is clarified that the distributions of pressure and the void fraction in a two-phase flow show a tendency different from those of fluids at room temperature because of the decrease in sound velocity due to large compressibility and the rapid phase change velocity in a cryogenic two-phase mixture flow. According to these numerical results, the fundamental characteristics of the cryogenic two-phase flow are predicted. The numerical results obtained will contribute to advanced cryogenic industrial applications.

Numerical Analysis on Two-Phase Flow Characteristics of Liquid Nitrogen.

Gas liquid two-phase flow characteristics in a pipe flow of liquid nitrogen are numerically investigated. Firstly, the government equations on two-phase flow of liquid nitrogen based on the unsteady drift-flux model are presented and several characteristics are numerically calculated taking into consideration the effect of cryogenic flow state. It is found that phase change of liquid nitrogen occurs in quite short time interval compared with that of pressurized water in high temperature. Next, it is clarified that the pressure wave in two-phase flow forms strongly steep shape with the time progress because of the nonlinearity based on a compressibility of cryogenic two-phase mixture. According to these theoretical results, it seems reasonable to predict the fundamental characteristics of cryogenic two-phase flow, and the obtained numerical results would contribute to advanced cryogenic engineering applications.

A contribution to the characterization of liquid-liquid dispersion

An accurate finite-volume based numerical method for the simulation of a cryogenic two-phase flow with phase change heat transfer, consisting of a saturated liquid slug translating in its own superheated vapor in a circular pipe is presented. This method is built on a sharp interface concept and developed on an Eulerian Cartesian fixed-grid with a cut-cell scheme and marker points to track the moving interface. The unsteady, axisymmetric Navier–Stokes equations in both liquid and vapor phases are solved separately. The mass continuity, momentum flux conditions and conservation of energy are explicitly matched at the true boundary between the two phases to determine the interface shape and movement. A quadratic curve fitting algorithm with marker points is used to yield smooth and accurate information of the interface curvatures.It is uniquely demonstrated for the first time with the current method that conservation of mass is strictly enforced for continuous infusion of flow into the domain of computation. The method has been used to compute the velocity, pressure and temperature fields and the deformation of the liquid core. It is also shown that the current method is capable of producing accurate results for a wide range of Reynolds number, Re, Weber number, We, Jakob number, Ja and large property jumps at the interface.

A cryogenic pressure regulator

A pressure regulator especially suited for cryogenic fluid and two-phase (gas and liquid mixture) flow application such as an aircraft fuel tank inerting system wherein the regulator controls the pressure and rate of flow of inerting fluid, e.g. nitrogen, into the fuel tank to pressurize the tank and to inert the tank ullage gases to render them noncombustible, said regulator being characterized in that the flow control valve has large and small variable area orifices which operate in sequence to minimize overshoot and undershoot, in that resonant oscillation is predictably damped and the damping remains substantially constant despite wear or change in clearances of the parts, and in that the valve actuator is thermally isolated from the cryogenic fluid flow path. The use of the tandem or sequential valve seat arrangement aforesaid also allows the larger seat to have an extended life and greater resistance to contamination and wear because at low flow demands, the larger valve portion remains seated and thus does not operate extremely close to its seat while the smaller valve portion partakes of greater stroking relative to its seat to satisfy such low flow demands. Furthermore, the regulator herein has a configuration such as to produce a large mechanical advantage to enable the regulator to provide a narrow pressure control band even with large variations in inlet fluid pressures and flow demands, this large mechanical advantage being obtained by the use of the rotary motion of a crank shaft having long and short crank arms.