Performance analysis of no-vent fill process for liquid hydrogen tank in terrestrial and on-orbit environments

Two finite difference computer models, aiming at the process predictions of no-vent fill in normal gravity and microgravity environments respectively, are developed to investigate the filling performance in a liquid hydrogen (LH₂) tank. In the normal gravity case model, the tank/fluid system is divided into five control volume including ullage, bulk liquid, gas–liquid interface, ullage-adjacent wall, and liquid-adjacent wall. In the microgravity case model, vapor–liquid thermal equilibrium state is maintained throughout the process, and only two nodes representing fluid and wall regions are applied. To capture the liquid–wall heat transfer accurately, a series of heat transfer mechanisms are considered and modeled successively, including film boiling, transition boiling, nucleate boiling and liquid natural convection. The two models are validated by comparing their prediction with experimental data, which shows good agreement. Then the two models are used to investigate the performance of no-vent fill in different conditions and several conclusions are obtained. It shows that in the normal gravity environment the no-vent fill experiences a continuous pressure rise during the whole process and the maximum pressure occurs at the end of the operation, while the maximum pressure of the microgravity case occurs at the beginning stage of the process. Moreover, it seems that increasing inlet mass flux has an apparent influence on the pressure evolution of no-vent fill process in normal gravity but a little influence in microgravity. The larger initial wall temperature brings about more significant liquid evaporation during the filling operation, and then causes higher pressure evolution, no matter the filling process occurs under normal gravity or microgravity conditions. Reducing inlet liquid temperature can improve the filling performance in normal gravity, but cannot significantly reduce the maximum pressure in microgravity. The presented work benefits the understanding of the no-vent fill performance and may guide the design of on-orbit no-vent fill system.     

Preparation of JEREMI Experiment: Development of the Ground Based Prototype

This study has been performed in the frame of preparing the space experiment JEREMI (Japanese and European Research Experiment on Marangoni Instabilities). The use of forced coaxial gas flow is proposed as a way to stabilize the Marangoni convection in liquid bridges, which might have important technological applications in the floating zone technique. A new set-up is under development and all sub-systems have passed severe tests. Here we present the design of this set-up and preliminary results of experiments for shear-driven two-phase flows in a confined volume of liquid under conditions of normal gravity. The geometry corresponds to a cylindrical liquid bridge concentrically surrounded by an annular gas channel with external solid walls. Gas enters into the annular duct, flows between solid walls and upon reaching the liquid zone entrains initially quiescent liquid. The test liquids are ethanol, n-decane and 5?cSt silicone oil, which have different degrees of viscosity and of volatility. The gas flow along the interface strongly enhances the evaporation and, correspondingly, affects the interface shape. Silhouette measurements are used for optical determination of the interface shape. From the digital images the variation of the liquid volume as a function of flow rate is calculated.     

Sloshing in microgravity

The International Space Station provides a low gravity environment for experiments that require very low acceleration. The steady component of acceleration due to the gravity gradient is in the microgravity range. It is possible to achieve microgravity levels for the variable component by using isolation racks. For experiments cooled by liquid cryogens sloshing may increase the variable acceleration at the experiment beyond acceptable levels. Sloshing of cryogens in microgravity can be predicted using a surface wave model. The model should include: a calculation of the shape of the unperturbed liquid–gas interface; a listing of the normal modes and resonant frequencies for the container; a prediction of the amplitude of the modes in response to the motion of the container; and a test to detect the breakdown of linear theory. A model is presented that contains these components. The shape of the interface is calculated and it is found that for most anticipated applications the interface is nearly cylindrical or spherical. Since gravity is not aligned with the symmetry of the container, the depth of the liquid is variable. Examples are presented to show how to estimate the extent of variable depth and curved interface on the normal modes and resonant frequencies. Equations are derived for the dynamic interaction of the isolation rack, the dewar and the sloshing motion. Damping is introduced by using boundary layer theory. Random vibration theory is applied to the incoherent component of the driving spectrum while standard resonance formalism is used for the coherent component. The model cannot be used if the wave amplitude becomes so large that linear theory does not apply. A procedure is developed to check for nonlinear difficulties.     

The influence of film structure on the interfacial friction in annular two-phase flow under microgravity and normal gravity conditions

Results for the interfacial friction factor and relative interfacial roughness on the gas-liquid interface are reported for an air-water annular flow in a small inner diameter tube (9.53 mm i.d.). The film structure was obtained through processing the time trace signal of film thickness measurements using conductance probes. The interfacial friction factor and the wave height were altered through changing the gravity level and gas Reynolds number. It was found that the wave height decreased with increasing the gas Reynolds number. The wave height in microgravity is less than half of that in normal gravity, while the friction factor was about 10% smaller in microgravity than that in normal gravity. It was shown that the annular two-phase flow friction factor decreased less dramatically as the relative interfacial roughness decreased compared to the single-phase case. It is interesting to note that the interfacial shear stress values at microgravity were very close (or even larger than) those at normal gravity. This was attributed to the thicker substrate at microgravity.     

Spatial High-Speed-Imaging of Projectile Impacts into Fluids in Microgravity

Impacts of rigid metal projectiles into fluid targets were observed under microgravity conditions using a technique which simultaneously generates multiple images from different angles with microsecond resolution. The impact experiments were performed with velocities of 15 ± 3 km/h into a water surface on the ground and during parabolic flights. To obtain comparable impacts, the fluid was forced to maintain a planar surface in weightlessness by a sharp metal ring attached in a transparent ultrahydrophobic-coated cylinder. The resulting continuous ‘Frozen Reality’® camera pan shots show the liquid surface deformation due to projectile water-entry. While an impacted liquid surface in gravity forms a wine-glass-shaped air cavity, in microgravity, the air cavity is tear-drop-shaped. Shortly after the impact into liquid, the air cavity closes and a large air bubble remains in the fluid due to microgravity. The escaped fluid forms a columnar liquid jet which tears approximately one second after the impact and leaves a satellite drop above the impact surface. The experiments help to understand collisions of kilometer-sized low-gravity bodies in space as they behave fluid-like at high impact velocities.     

Bubble rupture in a vibrated liquid under microgravity

The response of an air bubble surrounded by a liquid in a sealed cell submitted to vibrations was investigated experimentally under microgravity conditions and compared to experiments under normal gravity conditions. As in normal gravity [1], it was observed that the bubble split into smaller parts when the acceleration of the vibrations reached a threshold. This threshold in microgravity is substantially smaller than that in normal gravity. Experimental results are presented in terms of an acceleration based Bond number which has been found to characterize the bubble behaviour in the laboratory experiments [1].     

Microstructure analysis of samples sintered at different gravitational conditions

Tungsten heavy alloy samples liquid phase sintered under normal gravity and microgravity conditions are examined in this study for microstructure, phase, grain orientation, and lattice misorientation comparison. The focus is on understanding gravitational effects on the microstructure evolution as a function of location in the samples sintered using different holding times. This analysis shows that gravity has sub-grain level effects. The main differences are observed at the grain boundaries and in the relative orientation of the touching grains. Microgravity sintering is conducive for solid grain rotation into low lattice misorientation angle arrangement and potentially coalescence.     

Investigation of the influence of free convection on the heat transfer of cylinders with different aspect ratios

Electrically heated cylindrical wires are used in research and industry for fluid velocity and turbulence measurements. At very low free-stream velocities (u≤0.1 m/s), hot-wire measurements are significantly influenced by buoyant convection. Below a certain Reynolds number Re* this effect degrades the accuracy of the measurements. To assess the contribution of free-convection heat transfer to the heat balance of hot-wires in cross flow, measurements under normal gravity and microgravity (µg) conditions are compared keeping all other parameters constant. Under gravity conditions, the acceleration of gravity, the hot-wire axis and the direction of the free stream are all perpendicular to each other. The microgravity experiments were carried out in the Drop-Tower Bremen in which the residual acceleration is less than 10^?5 g during a period of 4.7 s. The present investigation is concerned with a velocity range of 0≤u≤0.35 m/s corresponding to a Reynolds number range Re<0.1 in standard air. This range includes pure free convection for Re→0 and forced-convection-dominated heat transfer for Re=0.1. At intermediate Reynolds numbers both transport mechanisms must be considered.     

Gravitational Effects on Multi-component Droplet Evaporation

This paper focuses on the analysis of multi-component droplet heating and evaporation under microgravity and normal gravity conditions. This analysis is based on the conventional conservation equations of species and energy for the gas phase, and the energy balance equation at the liquid?Cgas interface. The species diffusion is based on the Hirschfelder law, rather than on the less general Fick??s equation. Moreover, the heat flux due to species diffusion is taken into account in addition to the classical conduction heat flux between the gas and the liquid droplets. The liquid phase analysis is based on the infinite thermal conductivity liquid phase model, which has been justified by a reasonably good agreement between the predicted and experimental results. Indeed, the developed evaporation model has been validated against experimental data reported by Chauveau et al. (2008), where the droplets evaporation has been observed in microgravity and normal gravity conditions. The effects of gravity have been taken into account by introducing the Grashof number in the expressions of the Sherwood and Nusselt numbers. This model has been implemented in the multidimensional IFP-C3D industrial software. The modeling and experimental results have been shown to be reasonably close and the gravitational effects have been revealed to be significant especially for multi-component liquids including heavy components.     

Two-phase Flow in Fuel Cells in Short-term Microgravity Condition

A visual observation of liquid–gas two-phase flow in anode channels of a direct methanol proton exchange membrane fuel cells in microgravity has been carried out in a drop tower. The anode flow bed consisted of 2 manifolds and 11 parallel straight channels. The length, width and depth of single channel with rectangular cross section was 48.0 mm, 2.5 mm and 2.0 mm, respectively. The experimental results indicated that the size of bubbles in microgravity condition is bigger than that in normal gravity. The longer the time, the bigger the bubbles. The velocity of bubbles rising is slower than that in normal gravity because buoyancy lift is very weak in microgravity. The flow pattern in anode channels could change from bubbly flow in normal gravity to slug flow in microgravity. The gas slugs blocked supply of reactants from channels to anode catalyst layer through gas diffusion layer. When the weakened mass transfer causes concentration polarization, the output performance of fuel cells declines.     

Numerical Simulation of Bubble Dynamics in Microgravity

A numerical method for the simulation of two-phase flows under microgravity conditions is presented in this paper. The level set method is combined with the moving mesh method in a collocated grid to capture the moving interfaces of the two-phase flow, and a SIMPLER-based method is employed to numerically solve the complete incompressible Navier-Stokes equations, and the surface tension force is modeled by a continuum surface force approximation. Based on the numerical results, the coalescence process of two bubbles under microgravity conditions (10^???2×g) is compared to that under normal gravity, and the effect of gravities on the bubbles coalescence dynamics is analyzed. It is showed that the velocity fields inside and around the bubbles under different gravity conditions are quite similar, but the strength of vortices behind the bubbles in the normal gravity is much stronger than that under microgravity conditions. It is also found that under microgravity conditions, the time for two bubbles coalescence is much longer, and the deformation of bubbles is much less, than that under the normal gravity.     

Experimental Study of Nucleate Pool Boiling of FC-72 on Smooth Surface under Microgravity

Experiments of highly subcooled nucleate pool boiling of FC-72 with dissolved air were studied both in short-term microgravity condition utilizing the drop tower Beijing and in normal gravity conditions. The bubble behavior and heat transfer of air-dissolved FC-72 on a small scale silicon chip (10 × 10 × 0.5 mm³) were obtained at the bulk liquid subcooling of 41 K and nominal pressure of 102 kPa. The boiling heat transfer performance in low heat flux region in microgravity is similar to that in normal gravity condition, while vapor bubbles increase in size but little coalescence occurs among bubbles, and then forms a large bubble remains attached to the heater surface during the whole microgravity period. Thermocapillary convection may be an important mechanism of boiling heat transfer in this case. With further increasing in heat flux to the fully developed nucleate boiling region, the vapor bubbles number as well as their size significantly increase in microgravity. Rapid coalescence occurs among adjacent bubbles and then the coalesced large bubble can depart from the heating surface during the microgravity period. The reason of the large bubble departure is mainly attributed to the momentum effects caused by the coalescence of small bubbles with the large one. Hence, the steady-state pool boiling can still be obtained in microgravity. In the high heat flux regime near the critical heat flux, significant deterioration of heat transfer was observed, and a large coalesced bubble forms quickly and almost covers the whole heater surface, leading to the occurrence of the critical heat flux in microgravity condition.     

Heat Transfer Through the Interface and Flow Regimes in Liquid Bridge Subjected to Co-Axial Gas Flow

We present results of an extensive numerical study on the thermocapillary (Marangoni) convection and a heat transfer through the interface in a liquid bridge of Pr?=?68. The geometry of the physical problem is a cylindrical and non-deformable liquid bridge concentrically surrounded by an annular gas channel under conditions of zero gravity. The gas flow is co- or counter-directed with respect to the Marangoni flow. The forced gas flow along the interface provides two actions: via shear stresses and heat exchange. Usually the cooling of the interface enhances the flow while the heating slows down. This general trend may not hold when shear and thermocapillary stresses are comparable. The results show that when gas enters from the cold side the heat transfer through the interface is considerably larger than that when gas enters from the hot side.     

Effect of non-planar geometry on diffusion kinetics during brazing repair process

A new finite difference numerical model is used to study the influence of non-planar (cylindrical and spherical) solid–liquid interface geometry on the kinetics of isothermal solidification during diffusion brazing or transient liquid phase repair process. Notwithstanding that limited work had been reported on non-planar systems, this study shows that non-planarity of the solid–liquid interface can have significant effects on the kinetics of solid–liquid phase transformation during the repair process, which are crucial to the understanding and optimisation of the repair process in non-planar systems.     

Colloidal Material Box: In-situ Observations of Colloidal Self-Assembly and Liquid Crystal Phase Transitions in Microgravity

To study the self-assembly behavior of colloidal spheres in the solid/liquid interface and elucidate the mechanism of liquid crystal phase transition under microgravity, a Colloidal Material Box (CMB) was designed which consists of three modules: (i) colloidal evaporation experimental module, made up of a sample management unit, an injection management unit and an optical observation unit; (ii) liquid crystal phase transition experimental module, including a sample management unit and an optical observation unit; (iii) electronic control module. The following two experimental plans will be performed inside the CMB aboard the SJ-10 satellite in space. (i) Self-assembly of colloidal spheres (with and without Au shell) induced by droplet evaporation, allowing observation of the dynamic process of the colloidal spheres within the droplet and the change of the droplet outer profile during evaporation; (ii) Phase behavior of Mg₂Al LDHs suspensions in microgravity. The experimental results will be the first experimental observations of depositing ordered colloidal crystals and their self-assembly behavior under microgravity, and will illustrate the influence of gravity on liquid crystal phase transition.     

Granular Flow Under Microgravity: A Preliminary Review

The complex macroscopic rheological behavior of granular flow contains elements of both solid and liquid flow. Furthermore, under microgravity, granular flow exhibits novel flow features. To overcome a lack of comprehensive analyses of granular flow under microgravity, this study reviews the microgravity platforms and devices under which granular flow can be observed, the experimental findings made in such settings, and the range of numerical simulations that can be used to examine granular flow under microgravity. Differences in experimental research between normal gravity and microgravity are highlighted. These differences are found in the modifications made to conventional granular flow experimental devices, in new or unique granular flow behaviors, and in the numerical simulation methods needed for microgravity modeling. Additionally, the benefits of numerical simulation methods for examining rapid and dense flows under microgravity are also discussed. This study may have wide-ranging implications in such fields as investigations of the surface geology of asteroids or the efficient design and development of anchoring mechanisms or space vehicles.     

A dynamic technique for thermophysical measurements at high temperatures in a microgravity environment

Millisecond-resolution dynamic techniques for thermophysical measurements, when utilized in the laboratory, are limited to the study of materials in their solid phase because the specimen becomes geometrically unstable during melting and collapses, due (at least in part) to the influence of gravity. Therefore, a millisecond-resolution dynamic technique is being developed for use in a microgravity environment in order to extend accurate measurements of selected thermophysical properties of electrically conducting refractory materials to temperatures above their melting point. The basic method involves heating the specimen resistively from ambient temperature to temperatures above its melting point in about 1 s by passing an electrical current pulse through it, while simultaneously recording the pertinent experimental quantities. A compact pulse-heating system, suitable for microgravity simulations with NASA's KC-135 aircraft, has been constructed and initial experiments have been performed to study the geometrical stability of rapidly melting specimens. Preliminary results show that rod-shaped specimens can be successfully pulseheated into their liquid phase.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.Formerly National Bureau of Standards     

A Review on InGaSb Growth under Microgravity and Terrestrial Conditions Towards Future Crystal Growth Project Using Chinese Recovery Satellite SJ-10

The paper reviewed the previous microgravity experiment using Chinese recovery satellite, the in-situ measurement of composition profile in the solution by X-ray penetration method and homogeneous growth of InGaSb by temperature freezing method under terrestrial condition for making clear the effect of gravity on the growth of InGaSb ternary alloy semiconductor crystals. The previous experimental results showed that the shape of solid/liquid interfaces and composition profile in the solution were significantly affected by gravity. Based on the previous microgravity experimental results, experimental conditions were investigated to grow homogeneous In _xGa _1?xSb with higher indium composition at Chinese recovery satellite SJ-10 in near future.     

Numerical Prediction of Eutectic Temperature Using a Multi-phase-Field Model

To evaluate the reliability of metal-carbon eutectic systems as fixed points for the next generation of the international temperature scale, the effect of the eutectic microstructure on the temperature at the solid/liquid (s/l) interface during solidification and melting is preliminarily investigated using a multi-phase-field model. First, the effects of furnace temperature, lamellar spacing, and interface energy on the average temperature of the s/l interface are studied in the solidification process. With increased furnace undercooling, the s/l interface temperature was found to decrease. Calculated eutectic microstructures are then adopted as initial conditions for a melting simulation. The interface undercooling during melting is observed to be smaller than that observed during solidification. This difference in interface undercooling is attributed to the solute/solvent concentration profiles in the liquid phase near the s/l interface being different for melting and solidification.     

Mathematical and Numerical Modelling of Microconvection in the Long Rectangular Domains

The thermal gravitational convection of liquids under conditions of microgravity is studied in a 2D long rectangular domain elongated in the direction of the gravity force. The liquid is located between two solid regions of equal thickness. The solid parts are heat conducting. The mathematical modelling of the coupled problem is presented. Two mathematical models of convection are used to describe a motion of liquid: the classical Oberbeck-Boussinesq model and the microconvection model of isothermally incompressible liquid. The numerical experiments of convection are performed and demonstrate the qualitative and quantitative differences in the flow characteristics.