Elevated Gravity Research Articles

DNS of laboratory-scale turbulent premixed counterflow flames under elevated gravity conditions

In the present work, direct numerical simulations (DNSs) of laboratory-scale turbulent premixed counterflow flames are performed to understand the effect of elevated gravity on flame structures. In the DNS, a turbulent jet of CH4/N2/O2 mixture is injected in opposition to a stream of combustion product. Three cases were considered, i.e., one case with normal gravity and two cases with elevated gravity in different directions. The DNS results of the case under normal gravity conditions were found to be in good agreement with the experimental data. The turbulent flame speed is the highest in the case with elevated gravity aligned with the mean flame propagating direction, which is due to the increase in flame surface area and stretch factor. The gravity levels have a substantial influence on the flame extinction characteristics. It was observed that the flame front is pushed toward the direction of the gravity. When the elevated gravity antialigns with the mean flame propagating direction, the flame front travels across the stagnation plane toward the combustion product stream, leading to significant reactant dilution and flame extinction. The flame normal vector preferentially aligns with the most compressive strain rate for various gravity conditions. The tangential strain rate is the greatest (smallest) when elevated gravity antialigns (aligns) with the mean flame propagating direction. The impact of elevated gravity on the tangential strain rate at the flame fronts ultimately leads to a displacement in the flame front location relative to the stagnation plane, thereby influencing flame extinction.

Reduction of edge beading defects on rectangular substrates using a rotation about an axis perpendicular to the spin axis

Here, we consider the coating dynamics of a binary liquid on a rectangular substrate that both spins and rotates about an axis perpendicular to the spin axis. This rotation causes not only a force parallel to the substrate but a large normal force on the horizontal region of the substrate, known as elevated gravity. This force not only smooths out any irregularities in the film, it also causes an increase in the evaporation rate, resulting in a higher viscosity, which in turn decreases the thinning of the coating due to centrifugal forces. We derive the lubrication form of the governing equations for such a geometry that includes surface tension and body forces acting on the liquid due to the spinning and rotation of the substrate, as well as viscosity changes and surface tension gradients due to evaporation of the volatile component. The resultant coupled nonlinear differential equations are solved numerically using an efficient alternating direction implicit method. The numerical results indicate that the rotation can reduce edge beading defects for parameters typically employed by the spin coating industry. It is particularly effective for small average coating thicknesses, where it can almost eliminate edge beading. Surface tension gradients, which act in the post rotation dry phase, can also further affect edge beading, particularly in the corner regions.

Microstructure and resolution of etched patterns of Photoresist (AZP4620) layers spin-coated under artificially elevated gravity accelerations by two-axis spin coating technology

Microstructure and resolution of etched patterns of Photoresist (AZP4620) layers spin-coated under artificially elevated gravity accelerations by two-axis spin coating technology

Predicting the efficiency of oxygen-evolving electrolysis on the Moon and Mars

Establishing a permanent human presence on the Moon or Mars requires a secure supply of oxygen for life support and refueling. The electrolysis of water has attracted significant attention in this regard as water-ice may exist on both the Moon and Mars. However, to date there has been no study examining how the lower gravitational fields on the Moon and Mars might affect gas-evolving electrolysis when compared to terrestrial conditions. Herein we provide experimental data on the effects of gravitational fields on water electrolysis from 0.166 g (lunar gravity) to 8 g (eight times the Earth’s gravity) and show that electrolytic oxygen production is reduced by around 11% under lunar gravity with our system compared to operation at 1 g. Moreover, our results indicate that electrolytic data collected using less resource-intensive ground-based experiments at elevated gravity (>1 g) may be extrapolated to gravitational levels below 1 g.

Compressibility and crystalline structures of PVDF membranes under elevated gravity acceleration by two-axis spin coating technology.

Polymers play an important role in designing and manufacturing lithium-ion batteries and sensors. This study investigates the compressibility and crystalline structure of polyvinylidene fluoride (PVDF) membranes spin-coated under different gravity conditions. Particle Flow Code (PFC) numerically models the compressibility of membranes. The models show a 10% reduction in the thickness of the membrane when the gravity is artificially elevated to 500g. The time of solvents' release from the free surface of membranes based on Stokes' law is simulated by MATLAB. The results show that the solvents' release time decreases significantly when the artificial gravity increases. Novel experiments are conducted to validate the results of numerical modeling and MATLAB simulations. Four PVDF membranes are spin-coated by a novel two-axis spin coater under 1, 100, 300, and 500g. The SEM images experimentally report a 21% reduction in the thickness of the membrane spin-coated under 500g. The weights of membranes are measured to verify the results of MATLAB simulations. The results show that 99% of the whole solvents are evaporated while increasing the gravity to noticeable values. XRD, FTIR, and SEM characterize the polymeric crystalline structure of membranes. The crystalline structure of spin-coated PVDF membranes varies under various gravity conditions. The XRD measurements report phase transitions, while the gravity is artificially elevated during membranes' fabrication. FTIR spectroscopy revealed that the observed phase transition is from γ toward β while increasing the gravity acceleration.

Performance of elevated energy pile groups with different pile spacing in clay subjected to cyclic non-symmetrical thermal loading

There is an increasing interest and use of energy foundation worldwide. Full-scale tests, physical model tests at one Earth’s gravity and at elevated gravity in a geotechnical centrifuge and numerical simulations have been widely reported in the literature. Almost all studies have focused on single energy piles (EPs) and pile groups subjected to symmetrical thermal loads, although it is not unusual to have energy pile groups stressed by non-symmetrical thermal loads. In this study, a series of non-symmetrical thermal loading centrifuge model tests were conducted in saturated soft clay (OCR = 1.7), which is much vulnerable to temperature changes. The tests aim to investigate the effects of pile spacing on the serviceability of floating energy pile groups. Fifteen cycles of non-symmetrical thermal loading are applied to three EPs in 2 x 2 elevated energy pile groups with 3D and 5D (D denotes pile diameter) pile spacing. The thermally induced irreversible settlement and tilting in the 3D-pile group are 200% and 300% larger than those in the 5D one, respectively. Contrary to the 5D-pile group where the serviceability criteria (EN 1997-1:2004) are satisfied, the settlement and tilting are 30% and 200% larger than the criteria in the 3D one, respectively.

Effects of the ratio between body forces and inter-particle forces on maximum void ratio

Relative density has been shown to be useful for interpreting soil behaviour and for estimating the strength and other soil characteristics in geotechnical engineering. Previous studies have shown that the index void ratios (maximum and minimum void ratios) used to determine relative density depend on the particle shape and the shape of the grain size distribution. However, the effect of the median grain size on the index void ratios has not been resolved. In this study, the effects of the particle weight and the particle size relative to the inter-particle attractive forces are examined by conducting maximum void ratio (emax) tests in elevated gravity fields through the use of a centrifuge. The results indicate that both an increasing particle size and increasing gravity affect emax, providing evidence that inter-particle forces affect the packing of materials in this limit state. The change in emax, occurring in an elevated gravity field, implies that the relative densities estimated for centrifuge model experiments may not be accurate.

Quality enhancement of copper oxide thin film synthesized under elevated gravity acceleration by two-axis spin coating

Two-Axis spin coating as a new modified technique is employed to enhance the quality and surface leveling of thin films. The modified technology utilizes a synthetic centrifugal force perpendicular to the surface which generates an elevated gravity acceleration while spreading the coating on the entire wafer surface. In this paper, copper acetate sol-gel is coated by conventional and Two-Axis spin coating techniques. The coated layers are sintered in an air furnace at 275 °C. The fabricated layers are characterized by GIXRD, EDX, AFM and SEM devices. Wettability and Surface Free Energy (SFE) of sintered films using the contact angle technique are measured, and evaluated by the Owens-Wendt method. XRD and EDX spectra show a higher intensity of copper oxide phase using Two-Axis spin coating technology. AFM micrographs showed an improvement in the surface leveling within the Two-Axis spin coated layer. A comparison between the SFE of conventional and Two-Axis spin coated layers shows an increase in SFE of the layer synthesized under 200g artificial gravity acceleration.

Effect of micro- and elevated gravity condition on the evolution of stratification and self-pressurization in a cryogenic propellant tank

An efficient way of handling and storing cryogenic propellant is required for future space exploration. In rocketry applications, propellants are stored at subcooled conditions in foam-insulated tanks. Any kind of heat infiltration may lead to stratification and self-pressurization of the tank. The supply of warm propellant beyond the cavitation limit to a turbo-pump is dangerous and hence additional propellant has to be loaded, which affects the payload capacity. The evolution of stratification during lift-off and accelerated conditions and coast phase will be different from those during normal ambient conditions. During lift-off the gravity value can reach up to 6g and microgravity (μg) conditions at the coast phase. Hence, accurate prediction of the state of propellant at all stage is required for the successful mission planning. A multiphase axis-symmetric CFD model is developed, which can simultaneously account for heat transfer from the ambient and heat exchanges within the fluids during different gravity conditions. The results show that the self-pressurisation in microgravity condition is due to phase change rather than thermal stratification. The flow velocity will be maximum during lift-off and accelerated condition. Hence, greater self-pressurisation happens during the initial period and reduction in pressure rise rate is noticed later, which is due to turbulence of the fluid.

On the role of powder flow behavior in fluid thermodynamics and laser processability of Ni-based composites by selective laser melting

Abstract A deep understanding of the underlying relation of powder paving and subsequent melting/solidification behavior is critical in predicting and tailoring the processing quality of components fabricated by selective laser melting (SLM) additive manufacturing technology based on the mesoscopic scale. Combining discrete element method (DEM) and finite volume method (FVM), the present work proposed a newly developed three-dimensional DEM physical model coupling with mesoscopic FVM model to give a unique insight into the influence of powder particle size on the flow behavior of powder and resultant melting/solidification characteristics of SLM-processed WC/Inconel 718 composites. The contacting force among powder particles, transition of solid/liquid, and surface tension of melt were considered in the model. By characterizing the packing profiles, velocity vectors and packed state of particles, the simulation results and corresponding experimental validations generally revealed that the powder possessed an elevated flow-ability as increasing the average diameter of powder below 25 μm, due to the alleviation of the domination of adhesive force among neighboring particles. The considerably high-quality SLM-processed surface without apparent laser-induced defects was obtained with a significantly low surface roughness of 2.2 μm, attributing to the formation of a denser and more homogeneous powder-bed during SLM. However, when the average diameter of powder particles was elevated over 25 μm, the combined influence of the elevated gravity of large-scaled powder and the considerable space between neighboring powder particles worsened the flow-ability of powder. The discontinuous and loose powder-bed with a low packing density of particles had a high tendency to produce the top surface with a higher surface roughness, resulting in the formation of a number of defects in SLM-processed parts such as cave-like porosities, balling and discontinuous laser-melted tracks.

Two-dimensional spin coating with a vertical centrifugal force and the effect of artificial gravity on surface leveling

This study focuses on an innovative method for spin coating called the two-dimensional (2D) spin coating method. Using a centrifugal force applied by a rotary machine perpendicular to the wafer surface body, a vertical centrifuge force (VCF) was generated. The VCF allowed controllable artificial gravity acceleration to be generated and caused the coating to face this elevated gravity acceleration to adjust and normalize the high and low surface tension stresses. Previous surface leveling mathematics were analyzed and modified. The modified calculations indicate that the effect of additional gravity exerted on the liquid’s surface can reduce the amplitude of surface leveling. To experimentally investigate this phenomenon, a 2D spin coater was designed and manufactured. Higher artificial gravity overcame some common coating defects, such as cloudiness, edge beading, inner layer bubbling, and unsmooth surface leveling. Photoresist (AZP4620) was used as the coating material. The surface roughness was analyzed by atomic force microscopy (AFM) and the layer properties were also imaged by scanning electron microscopy (SEM). The AFM results (average and root-mean-square roughness) indicated a decrease in surface leveling amplitude by increasing the VCF. SEM images showed condensed layers without any porosity or rupture. The experimental results agreed with the simulations and calculated values.

Centrifuge modelling of displacement and replacement energy piles constructed in saturated sand: a comparative study

Energy piles serve as supporting structures and heat-exchange elements. They can provide thermal comfort much more efficiently than traditional air-sourced systems as the ground offers high thermal conductivity and a stable temperature below a certain depth. Energy piles are commonly installed as bored piles (replacement); however, driven (displacement) energy piles are also used in practice. A direct comparison of the performance of these two different types of energy piles subjected to thermal cycles is rarely explored not fully understood. In this study, two centrifuge energy model piles, one wished-in-place at one gravity (i.e. at low stress, simulating bored pile) and the other pile was jacked in at elevated gravity were constructed in saturated Toyoura sand. After construction, they were subjected to five heating and cooling cycles (7–37°C) under a constant working load. Cumulative settlement with a ratcheting pattern was observed for the ‘bored’ energy pile after five thermal cycles. In contrast, a slight heave was recorded for the jacked-in energy pile. The observed heave can be attributed to the densification effect and particle crushing of soil when the pile was jacked in, reducing or even eliminating thermal-induced contraction of sand and hence decreasing the reduction of horizontal stress during thermal cycles.

Abstract WMP84: Worse Functional Outcome in Stroke Patients With Elevated Urine Specific Gravity

Introduction: An estimated 44-70% of stroke patients present to the hospital in a dehydrated state. Prior studies suggest that volume contraction contributes to worsened neglect syndromes and reduced chance of early recovery. Thus we hypothesized that patients who were clinically dehydrated at the time of stroke carried a higher probability of worse functional outcome at three months. Methods: We enrolled a consecutive series of ischemic stroke patients who presented to the hospital within 12 hours from stroke symptom onset. Patients were excluded if they had baseline kidney disease, presented with signs of active infection, or were unable to complete MRI. Clinical function was measured via daily NIHSS and 3 month modified Rankin scale (mRS). A priori, we defined a volume contracted state as BUN/creatinine ratio > 15 or urine specific gravity (SG) > 1.010. Results: One hundred and four patients were eligible for inclusion after 1 year of recruitment, of whom 83 (80%) had urinalysis measured and were thus included in this analysis. 62/83 patients (75%) had elevated urine SG consistent with a clinically dehydrated state. Independent of age, sex, and baseline NIHSS score, patients with elevated urine SG > 1.010 had a 3.6 increased odds (95% CI; 1.31-9.93) of being in a higher (worse) modified mRS category (Figure). A combined model defining volume contraction using both elevated BUN/creatinine ratio and urine SG did not demonstrate a statistically meaningful difference in outcomes. Conclusions: Elevated urine specific gravity at the time of ischemic stroke is associated with worse 3 month outcome. This objective marker may represent a readily available, standardized way to measure clinical dehydration syndromes as we attempt to define structured rehydration strategies for this population of patients.

Layering in sedimenting nanoparticle suspensions: The order-inducing role of randomness

Abstract Sedimentation of nanoparticles (NPs) is common in science and technology; yet, the dynamics of sedimentation is sometimes unexpected. We study the sedimentation of NPs under an elevated gravity in a centrifuge, in presence of a small temperature gradient, transverse to the axis of sedimentation. We observe spontaneous ordering of the sedimenting fluids into well defined layers of constant number density; the corresponding density profiles thus adopt a staircase-like appearance. While the physical mechanism of these phenomena has been very recently elucidated [8] , the quantitative description of these effects still remained incomplete. We fill this gap by direct quantitative measurements of the layering effect. In this work, we employ much smaller Fe2O3 NPs, in addition to the previously-used Ag and Cu@Ag NPs; the Fe2O3 particles are suspended in water, while only organic solvents were used in our previous work. Remarkably, in both cases, the layering effect remains largely unchanged. We demonstrate that particle polydispersity, an archetypal source of disorder, counterintuitively, promotes formation of ordered density staircase structures. Furthermore, we demonstrate complex layer dynamics and ‘glitches’ of particle concentration at the interfaces between the layers; these phenomena have been predicted by theory, yet their experimental validation was missing.

Measurement of permeability using a bench-top centrifuge

The commonly used British Standard constant head triaxial permeability test for testing of fine-grained soils is relatively time consuming. A reduction in the required time for soil permeability testing would provide potential cost savings to the construction industry, particularly in the construction quality assurance of landfill clay liners. The purpose of this paper is to evaluate an alternative approach of measuring permeability of fine-grained soils benefiting from accelerated time scaling for seepage flow when testing specimens in elevated gravity conditions provided by a centrifuge. As part of the investigation, an apparatus was designed and produced to measure water flow through soil samples under conditions of elevated gravitational acceleration using a small desktop laboratory centrifuge. A membrane was used to hydrostatically confine the test sample. A miniature data acquisition system was designed and incorporated in the apparatus to monitor and record changes in head and flow throughout the tests. Under enhanced gravity in the centrifuge, the flow through the sample was under ‘variable head' conditions as opposed to ‘constant head' conditions as in the classic constant head permeability tests conducted at 1g. A mathematical model was developed for analysis of Darcy's coefficient of permeability under conditions of elevated gravitational acceleration and verified using the results obtained. The test data compare well with the results on analogous samples obtained using the classical British Standard constant head permeability tests.

Integrative geophysical approach for assessing the prospectivity of the Idlewilde intrusion, NSW

The Idlewilde Intrusion (IWI) sits below ~150 m-thick sediment overburden and consists of a Palaeozoic basement of presumed Ordovician Macquarie Arc volcanics and the Nyngan Intrusive Complex. The geological setting is similar to the gold-rich Cadia and Northparkes porphyry-style deposits. Geophysical data include ground gravity, airborne magnetic and electromagnetic.Gravity data define a negative ovoid with an elevated gravity inner zone. Magnetic data show a central high surrounded by a circular low zone as part of a broader regional low. Electromagnetic data outline: (a) ?150 m- thick dual conductor corresponding to the overburden; (b) a medium conductor associated with the volcanics; (c) a resistor linked to the intrusion and (d) a slightly conductive annulus around the resistor interpreted as alteration, but may instead reflect the lack of sensitivity below the conductive overburden. The central part of the intrusion associated to gravity and magnetic highs could conceivably correspond to: (1) a magnetite-altered potassic core characteristic of gold-rich porphyry, (2) eroded granite with volcanics close to the surface, (3) roof pendant volcanics above a barely-eroded granite, and (4) a late monzonite pulse.From an exploration point of view, gravity data delineate the extent of the IWI. The regional low magnetisation suggests that the intrusion may be a later intrusive phase. Electromagnetic data identify the footprint of a granitic body which cannot be clearly associated with an alteration system because of conductive overburden. A mineralised system is yet to be identified, and one of the first company priorities is now to resolve the inner part of the IWI.

Numerical Study of a Granular Material in Various Gravity Environments

AbstractThis paper presents the material response of a granular material under different gravity fields using the discrete element method (DEM). A bidispersive porous medium is prepared and sheared under various gravity conditions. The medium is composed of two kinds (shape and size) of ellipsoids. Each type of particle occupies 50% of the whole mass. The ellipsoids are randomly generated and deposited in lunar gravity (1/6g), Earth’s gravity (1g), and elevated gravity (10g). Various friction coefficients are used during the deposition stage, which yields samples of different initial densities. Afterward, samples are isotropically consolidated to different initial confining pressures, and the friction coefficient between particles is 0.5. A total of 25 numerical samples have been created. Very large strain is applied to the sample under drained or undrained conditions. The granular material comes into the critical state. Overall, the gravity effect on peak friction angle (shear strength of the material) i...

Controlling Gravity Impact on Diffusion Flames by Magnetic Field

The ability to use a magnetic field as a means for controlling the role of gravity buoyancy on the combustion process is demonstrated by applying a strong vertical magnetic field gradient on a laminar gas jet diffusion flame. The confirmation is based on a comparison of flame appearance; in particular, length variation, to both elevated gravity (higher than earth’s gravity) and zero-gravity combustion experimental data. The comparison parameter is the dimensionless number G, defined as the ratio of gravity level generated by magneto-gravity buoyancy to earth’s gravity. The more important results are as follows. First, for G > 1, good agreement between magnetic and centrifuge length scaling laws reveals that the slight decrease of flame length according to L ∼ G−1/8 is the result of increasing artificial magnetically induced gravity strength. It ensues that flame thinning, bluing, lifting, and extinction are produced by similar mechanisms previously identified in centrifuge diffusion flames. Thereafter, at G ≅ 0, the flame assumes a nearly hemispheric shape and a blue color in perfect similarity to nonbuoyant flames under zero-gravity conditions generated in drop towers. Another important fact is that the magnetic field offers the ability to observe the flame behavior at low gravity levels 0 < G < 1. A primary interesting result is that flame length varies strongly, following the scaling law L ∼ G−1/2.

Foam Evolution and Stability at Elevated Gravity Levels

Foaming experiments in order to understand the evolution of the foam structure blown in different directions and levels of gravity have been carried out. The key elements of the experiment are the foam generator body (henceforth FG) and the controlled blowing apparatus. The FG was a polymer foam infiltrated with a suspension (distilled water, pure tenside (SDS, 0.05m%) and SiO2 nanoparticles (2m%)) Foams were blown out at 1.5, 2, 4, 6, 10 and at 15g levels in three different directions (0, 90 and 180o, measured to the direction of the gravity vector). The elevated gravity condition was implemented in a hyper-g centrifuge (ZARM Bremen). Results show that foams can be created even at high gravity levels though the foamability and foam structure alters a lot by varying gravity level and foaming direction. At higher g-levels, under fixed gas flow rate and blowing time less foam could be produced. The average cell size varied with the blowing directions but proved constant on any gravity levels. On base of the gravity direction dependent pressure curves the foaming process was interpreted in detail. It was found that the sedimentation ruled capillary clogging is the main process by causing the gravity direction dependent foaming phenomena. The unexpected observation is that the foam stability does not depend on the gravity level.

Cooling Performance of a 16-Nozzle Array in Variable Gravity

The objective ofthis paper was to investigate the cooling performance of 16-nozzle spray array using FC-72 as the working fluid in variable-gravity conditions. A flight-test experiment was modified to accommodate a 16-nozzle spray array, which was then tested in the parabolic flight trajectory environment of NASA's C-9 reduced-gravity aircraft. The 16-nozzle array was designed to cool a 25.4 x 25.4 mm 2 area on a thick-film resistive heater used to simulate an electronic component. Flight tests were conducted over the course of two flight weeks (each week consisting of four flights and each flight consisting of 40 to 60 parabolas). The mass flow rate through the 16-nozzle spray array ranged from 13.1 ≤ m ≤ 21.3 g/s. The heat flux at the thick-film resistor ranged from 2.9 ≤ q ≤ 25 w / 2 , the subcooling of the working fluid ranged from 1.6 ≤ ΔT sc ≤ 18.4°C, the saturation temperature ranged from 37.4 ≤ T sat ≤ 47.2°C, and the absorbed air content in the working fluid was C = 10.1,14.3 and 16.8% by volume. The spray chamber pressure ranged from 42 ≤ P ≤ 78 kPa and the acceleration ranged from -0.02 ≤ a ≤ -2.02 g. Two-phase cooling was emphasized, but some single-phase data were also collected. A one-dimensional model was used to predict the heater surface temperature from the heat input and mean heater base temperature. It was found that the cooling performance was enhanced in microgravity over terrestrial and elevated gravity. In addition, a sudden degradation in performance was found at high mass flow rates in microgravity, possibly due to liquid buildup on the surface between the nozzle impact zones. A high degree of subcooling was found to be beneficial, but the dissolved air content had little effect on the heat transfer performance in either microgravity or elevated gravity.