Liquid Acquisition Devices Research Articles

Phase Separation through Screen Channel Liquid Acquisition Devices in Microgravity

To enable future deep space exploration, orbital refueling of spacecraft is essential. However, transferring liquid in a microgravity environment is a complex process dependent on various factors. One of the basic and critical tasks is to separate phases to allow the supply of gas-free liquid from one tank to another. For this purpose, a liquid acquisition device is essential. In this work, a screen channel liquid acquisition device was designed and used to investigate phase separation and liquid removal from an experiment tank in a microgravity environment. The experiments were performed using the drop tower facility at the University of Bremen, with HFE-7500 as the test liquid under isothermal conditions. This investigation explored the interdependent effects of various phenomena, including the reorientation of liquid in the tank, capillary rise between parallel plates, flow through screen pressure variation, and bubble point breakthrough. Under subcritical conditions, the SC-LAD was found to supply gas-free liquid at the outlet, as long as the pressure drop across the screen was lower than the bubble point threshold. At the critical point, the screen started to ingest bubbles, resulting in a sharp peak in the differential pressure signal. The wetted area of the screen was obtained by analyzing images captured with a high-speed camera and used to calculate the analytical pressure drop. The experimental results were compared with the analytical solution and discussed in detail.

Warm pressurant gas bubble point experiments for coarse mesh screen channel liquid acquisition devices in liquid nitrogen

The most crucial aspect in screen channel liquid acquisition device (LAD) design is the bubble point pressure (ΔPBP). Historically, results have shown that cryogenic liquid nitrogen (LN2) ΔPBP values can be increased when using helium (GHe) pressurant and decreased when using gaseous nitrogen (GN2) pressurant due to evaporative cooling and condensation heating of the liquid-vapor interface within the screen, respectively. Historical results show a reduction in ΔPBP performance when using warm pressurant, regardless of pressurant gas type. This paper presents warm pressurant ΔPBP tests in LN2 using both GHe and GN2 with pressurant bulk gas temperatures TGB between 77−160K for 14 screen types, focusing on coarser meshes. Results from this study show a degradation in GHeΔPBP but no degradation in GN2ΔPBP at elevated TGB, the latter of which contradicts historical trends. To help explain these results and to provide a level of physical background to the warm pressurant ΔPBP experiments, a noncondensable pressurant sweat cooling heat and mass transfer model is developed as part of this study. Based on current and historical results, it is concluded that the flow velocities on the gas side of the screen could degrade ΔPBP significantly, especially when warm pressurant is used.

Liquid nitrogen wicking rate experiments for screen channel liquid acquisition devices

A screen channel liquid acquisition device (LAD) commonly employed in microgravity space applications uses a finely woven mesh of metal wires along with capillary forces to separate liquid and vapor phases in storage tanks used for propellant transfer. Successful implementation of LADs in flight propulsion systems, particularly for cryogenic systems, depends on analytical design models that are anchored to experimental data. Screens are characterized using parameters such as bubble point pressure, flow-through-screen pressure drop, and wicking rate. The last parameter is especially important to cryogenic LAD systems due to the high propensity for screens to experience evaporation dry out during a mission. This paper presents new experimental wicking rate data for 12 screens covering a wide range of weave types, mesh counts, and metal type with liquid nitrogen (LN2) as a working fluid using a continuous flow method. The horizontal wicking rate data is used to validate the room temperature fluid-based wicking rate model from Grebenyuk and Dreyer (2016) with the gravitational term neglected. Results are examined parametrically, with respect to the effect of wicking rate direction, dewar test pressure, fineness of the screen, shute to warp wire ratio, warp wire orientation, and using cryogenic vs. room temperature fluid. The main takeaway from the current work is that the effective wicking diameter from cryogenic testing lies within experimental uncertainty as wicking diameters from room temperature data for all screens, implying that the room temperature based-model from Grebenyuk and Dreyer (2016) can be used to compute wicking velocities for cryogenic nitrogen for most screen types.

SiOC Screens with Aligned and Adjustable Pore Structure for Screen Channel Liquid Acquisition Device.

The development of porous ceramic screens with high chemical stability, low density, and thermal conductivity can lead to promising screen channel liquid acquisition devices (SC-LADs) for propellant management under microgravity conditions in the future. Therefore, SiOC screens with aligned pores were fabricated via freeze-casting and applied as a SC-LAD. The pore window sizes and open porosity varied from 6 µm to 43 µm and 65% or 79%, depending on the freezing temperature or the solid loading, respectively. The pore window size distributions and bubble point tests indicate crack-free screens. On the one hand, SC-LADs with an open porosity of 79% removed gas-free liquid up to a volumetric flow rate of 4 mL s-1. On the other hand, SC-LADs with an open porosity of 65% were limited to 2 mL s-1 as the pressure drop across these screens was relatively higher. SC-LADs with the same open porosity but smaller pore window sizes showed a higher pressure drop across the screen and bubble ingestion at higher values of effective screen area when increasing the applied removal volumetric flow rate. The removed liquid from the SC-LADs was particle-free, thus representing a potential for applications in a harsh chemical environment or broad-range temperatures.

Investigation of flow and pressure drop through porous metallic screens with different weave densities

Metallic screens have been frequently used for cryogenic propellant management system under microgravity conditions due to the superior properties to separate the liquid and vapor phases. The flow through screens (FTS) characteristics as the main factor to determine the separation performance is greatly influenced by the pore structure of metallic screens. However, the actual flow behavior through the pore structure cannot be readily observed by the experiments and macroscopic simulation. Therefore, in the present study, three-dimensional pore-scale models are established to investigate flow behavior through the pore structure, and meanwhile the FTS characteristics for four of types Dutch Twill Weave (DTW) screens with different weave densities are presented. The influence of cryogenic temperature on the volume porosity and specific surface area of the metallic screens with different weave densities are firstly examined based on periodic structure unit for accurate estimation in the following study. Based on the pore-scale model, numerical simulations of laminar flow through screens for various liquid are carried out, and the accuracy of the model is verified by comparing to the experimental results. The simulation results show that the cross-sectional hydraulic diameter of the screen in the thickness direction imposes a significant effect on local FTS pressure drop. Moreover, the dimensionless correlations of the FTS pressure drop for the DTW screens are obtained based on the simulation results. Furthermore, the permeability and Forchheimer coefficient of the screen are acquired on the basis of the Darcy-Forchheimer law for facilitating the design of Liquid Acquisition Device (LAD).

A transient hydrodynamic model of screen channel liquid acquisition devices for in-space cryogenic propellant management

Screen channel liquid acquisition devices (LADs) will play a crucial role in future deep space travel. It is essential that vapor-free delivery of propellants during tank-to-tank transfer is ensured to maximize yield from storage tanks and prevent potential combustion instabilities. The screen channel LAD utilizes a fine screen wire mesh that can separate phases in a low Bond number (i.e., microgravity) environment using surface tension forces. This study presents the development and verification of a new model for transient screen compliance, one of the influential factors for screen channel LAD design. Screen compliance is crucial during LAD channel outflow transients because the slight deflection of the screen can provide needed mass to satisfy rapid outflow demands and reduce the pressure difference across the screen. The model is successfully verified against computational fluid dynamics simulations. In addition, the characteristic speed for the governing screen compliance equations is derived, which allows for numerical stability criteria to be established. As shown in this study, the transient maximum pressure difference across the screen can greatly exceed the steady state maximum pressure difference across the screen in many cases.

Cold pressurant gas bubble point experiments for coarse mesh screen channel liquid acquisition devices in liquid nitrogen

Screen channel liquid acquisition devices (LADs) will play a crucial role in future deep space travel. It is essential that vapor-free delivery of propellants during in-space transfer is ensured to maximize yield from storage tanks and prevent potential combustion instabilities. The screen channel LAD utilizes a fine screen wire mesh that can separate phases in a low Bond number (i.e. microgravity) environment using surface tension forces. This paper presents cryogenic liquid nitrogen (LN2) screen channel LAD bubble point experiments focused on coarser mesh screens. A total of 14 different screen types are tested across a range of cryogenic liquid temperatures near the screen (70.8 − 80.0 K) and dewar pressures (∼101.3 – 156.5 kPa or ∼0 – 8 psig) for two pressurization schemes (noncondensable gaseous helium and autogenous pressurization with gaseous nitrogen) to examine the effect of pressurant gas type on LAD performance. Cold pressurant gas bubble point test results for coarser meshes shown here agree almost perfectly with historical trends using fine mesh screens. Pressurization with a noncondensable generally leads to higher bubble point due to evaporative cooling at the LAD screen while pressurization with the vapor generally leads to degradation in performance due to condensation of the vapor and subsequent interfacial heating.

Development of a hybrid screen channel liquid acquisition device for reliable microgravity transfer of cryogenic fluids

Refueling spacecraft in orbit offers potential benefits to future extended duration missions including increased spacecraft payload capacity and reduced launch cost. However, a key challenge for refueling cryogenic propellants in microgravity conditions is the acquisition of vapor-free liquid propellants from an in-orbit supply tank. This is especially true when the required liquid flow rate is high but residual liquid in the tank must be minimal. Vane-type Propellant Management Devices (PMDs) excel in stabilizing and distributing liquid, but are more susceptible to gas ingestion, and generally only perform well at lower flow rates and/or under favorable acceleration gradients. Screen channel PMDs do not stabilize and distribute the liquid as well, but are less susceptible to gas ingestion, and perform well at higher flow rates and/or under adverse accelerations. Screened channel LADs appear to hold many advantages for a flight cryogenic system with high demand flow rate, however there are currently no flight cryogenic fluid-based screen channel LADs. To address this need, Creare has been working with NASA Glenn to develop a hybrid Liquid Acquisition Device (LAD) for cryogenic propellants consisting of screened channels with attached guide vanes, and a screened sump. Creare’s design forms the flow channel from screen material itself, allowing much higher acquisition surface area per unit volume as compared to existing designs. The screened channel LAD and screened sump are assembled by Creare’s advanced laser welding processes to reliably maintain the pore structure of the screen adjacent to the bonding joints. After completing a series of fabrication trials to validate the reliability and repeatability of the approach, a prototype screen channel was fabricated, and its performance was characterized in LN2 outflow. Results were found to be consistent with single-phase CFD predictions of this geometry for a partially exposed screen channel. Two-phase CFD analysis was conducted to evaluate the performance of the guide vanes in favorably distributing liquid to enhance expulsion efficiency. Preliminary structural analysis was performed on representative geometry for the LAD assembly to assess stresses of the under 5 g acceleration. Using this screen channel geometry and overall design approach, Creare assembled a laboratory-scale hybrid LAD with four parallel gallery arms, a screened sump, and guide vanes. The assembly has been installed in a large dewar for preliminary evaluation in LN2. This unit is planned for delivery to NASA for follow-on investigations using liquid hydrogen.

The Effect of Liquid Withdrawal Rate on Screen Channel Liquid Acquisition Device Screen Compliance

The Effect of Liquid Withdrawal Rate on Screen Channel Liquid Acquisition Device Screen Compliance

A three-dimensional flow model of screen channel liquid acquisition devices for propellant management in microgravity

Screen channel liquid acquisition devices (LADs) are among the most promising technologies for separating liquid and vapor phases in propellant storage tanks under microgravity conditions and thus ensuring vapor-free propellant supply to spacecraft engines. However, the prediction of the critical flow rate of a screen channel LAD relies on the full understanding of the three dimensional distribution of injection velocity. In this study, the flow characteristics at the entrance region of the LAD were investigated via particle image velocimetry (PIV) technique and numerical simulations under various working conditions. The experimental results illustrated that the velocity component normal to the porous woven mesh is non-uniform in both streamwise and spanwise directions of channel flow and that this phenomenon has a significant influence on the critical flow rate. Hence, a model that accounts for the three-dimensional flow field was proposed to predict the critical flow rate. The average error in the critical flow rate, which was determined by comparing the proposed model’s predictions and the experimental results, was less than 8.4%.

Performance analysis and improved design of screen channel liquid acquisition device for hydrogen

The screen channel liquid acquisition device is vital to in-orbit management of liquid propellant, when it is applied to large hydrogen tank, an improved design is necessary to obtain higher outflow rate with less device mass. To get this purpose, we established a model through an innovative route: motivating the resolution by the driving-pressure boundary condition. Based on this new model, we analyzed the influential factors of outflow rate: the geometric parameters of channel, the driving pressure, and the selection of screen. Further, we derived a set of dimensionless numbers that characterize the outflow process. Finally, we proposed creatively two suggestions for optimizing design: (1) reducing the ratio of L to H by rearranging the channel outlet; (2) combining the use of different screens with an appropriate mixing ratio. By numerical calculation, it is proved that both of these two suggestions could help to improve the device.

Pressure-Driven Phase Separation Based on Modified Porous Mesh for Liquid Management in Microgravity.

Surface tension becomes the main force influencing the gas-liquid interface in microgravity environment. The instability of the gas-liquid distribution is a menace for spacecraft missions. Passive phase separation based on porous material is a promising technique for microgravity liquid management and advanced life support systems. Here, the mechanism of pressure-driven phase separation based on porous material is experimentally investigated, highlighting the synergistic influence of single-phase flow, breakthrough failure, and self-healing ability on liquid acquisition capability. The major parameters characterizing the separation efficiency are the breakthrough threshold pressure and the flow resistance. A fabrication strategy which elicits the surface wettability and maintains the original surface morphology is proposed and verified to increase the critical breakthrough threshold pressure without introducing extra flow resistance. Moreover, the modified mesh is integrated into a screen channel liquid acquisition device. The improvement of the overall separation performance is evaluated in an antigravity delivery experiment, where the acceleration of liquid is -g0. It has been demonstrated that the fabrication strategy increases the achievable flow rate over 80% and the reseal flow rate over 200% for gas-free water delivery. This work enriches the understanding of phase separation based on porous material and provides an alternative method for liquid management in microgravity.

The Impact of Vapor Blockage on the Outflow Rate of Screen Channel Liquid Acquisition Devices.

The outflow rate of screen channel liquid acquisition devices (LADs) is a key indicator of the liquid acquisition capacity, but would be decreased when a portion of its screen is blocked by the vapor. So far, the quantitative research about the consequent loss of outflow rate seems not enough, though it is important and inevitable. In this paper, a modified model by introducing an “available rate” to describe the blocked degree is established to analyze and compare the cases with and without vapor blockage. We found that the loss of outflow rate is mainly decided by the total area of the blocked screen, while the distribution of blockage position barely has any effects. Besides, a “characteristic curve” is proposed to describe the robustness of LAD against blockage (i.e., loss rate of outflow velocity versus total area of the blocked screen). Higher driving pressure, coarser mesh of screen, and higher ratio of length to height of the channel would bring about greater robustness.

Space Screen Channel Liquid Acquisition Device Experiments in Liquid Nitrogen for Coarse Meshes. I. Cold Pressurant Gas Bubble Point Tests

Space Screen Channel Liquid Acquisition Device Experiments in Liquid Nitrogen for Coarse Meshes. I. Cold Pressurant Gas Bubble Point Tests

Space Screen Channel Liquid Acquisition Device Experiments in Liquid Nitrogen for Coarse Meshes. Ii. Investigation of Effects of Temperature Gradients During Bubble Point Tests

Space Screen Channel Liquid Acquisition Device Experiments in Liquid Nitrogen for Coarse Meshes. Ii. Investigation of Effects of Temperature Gradients During Bubble Point Tests

Liquid Acquisition Device Screen Compliance Experiments with Rectangular Geometry for Microgravity Applications

Liquid Acquisition Device Screen Compliance Experiments with Rectangular Geometry for Microgravity Applications

Cryogenic wicking of liquid nitrogen in the metallic screens with different weave densities

Liquid wicking in porous media has been applied to the management and transportation of propellant in microgravity. The flow and heat transfer characteristics during wicking of cryogenic fluid in the metallic screens play significant roles in determining the wicking performance. However, the experimental investigations of cryogenic wicking are relatively rare due to experimental difficulties. In the present study, the experimental visualization of wicking of liquid nitrogen is carried out, where five typical Dutch Twill Weaves (DTW) with different weave densities are employed as the test samples. The evolutions of the wicking front during cryogenic wicking are experimentally traced. Moreover, the cryogenic wicking in the DTW has been numerically investigated by considering the thermal non-equilibrium equation in the porous media, which yields a good agreement between the experimental and numerical results due to better accounting the evaporation of liquid nitrogen resulted from the heat conduction of the DTW. As an example, the wicking height of liquid nitrogen in the DTW 200 × 1400 reaches a maximum wicking height of about 0.0851 m, which is improved by about 36.4% ∼ 75.0% compared to the results in the literature. Furthermore, the effect of the weave densities of the DTWs on the flow and heat transfer characteristics are investigated, which provides useful information for the screen channel liquid acquisition device of cryogenic propellant.

MATHEMATICAL MODEL FOR DETERMINE OF THE MESH BUBBLE POINT PORE DIAMETER

The article presents mathematical models for determining the bubble point diameter of the pores of meshes with micron sizes square cells of plain and full twill weaving. Analyzed are mathematical models developed by a number of researchers to determine the bubble point pore diameter of the meshes and their point pore pressure. The analysis of the mathematical models showed that they were developed on the basis of a number of assumptions that, to varying degrees, take into account the spatial shape of the mesh cells and the physicochemical processes when the free surface through the mesh. This undoubtedly affects the accuracy of analytical calculations that are based on the use of these models. In the presented work, mathematical models have been developed that take into account the complex spatial shape of the wires from which the mesh is made. Mathematical models have been developed for plain and twill weaving meshes. When developing mathematical models, it was assumed that the free surface is formed on a hole with elliptical edges. In this case, it is assumed that the points of contact of the free surface of a plain weave mesh correspond to the most distant points of the projection of the mesh cell. For full twill meshes, taking into account the structure of their weaving, it is assumed that the free surface is formed on two adjacent cells. The influence of the contact angle between the mesh surface and the working fluid was taken into account by analyzing the spatial shape of the mesh wires. The developed models make it possible to take into account the effect of liquids with a contact angle from zero to 90 degrees. Simplified mathematical models of the meshes have also been developed for the case of perfect wetting of the mesh surface with a liquid, when the contact angle is zero. The obtained mathematical models can be used in the design of capillary phase separators of liquid acquisition devices in zero gravity of spacecraft, as well as in the calculation of capillary devices of various technical systems, such as heat exchangers, gas-liquid mixers, chemical reactors, bubble filters, etc.

Using Tapered Channels to Improve LAD Performance for Cryogenic Fluids: Suborbital Testing Results

Abstract Improvement of cryogenic fluid storage and transfer technology for in-space propulsion and storage systems is required for long-term space missions. Screened channel liquid acquisition devices (LADs) have long been used with storable propellants to deliver vapor-free liquid during engine restart and liquid transfer processes. The use of LADs with cryogenic fluids is problematic due to low temperatures associated with cryogenic fluids. External heat leaks will cause vapor bubbles to form within the LADs that are difficult to remove in the existing designs. A tapered LAD channel has been proposed to reliably remove vapor bubbles within the device without costly thrusting maneuvers or active separation systems. A model has been developed to predict bubble movement within tapered LAD channels, and subsequent ground testing was completed with a simulant fluid to provide model validation data. Suborbital microgravity testing of tapered LAD technology was recently completed with two different simulant fluids and demonstrated that the concept can passively expel vapor bubbles within the channel. Two additional suborbital flights have been funded to further develop this technology by investigating the performance of larger scale versions of the design.

Phase Separation in Porous Media Integrated Capillary Channels

Phase separation in space is critical for gas-free propellant supply, life support systems, refueling of spacecraft in low earth orbit (LEO), and for deep space exploration missions. In the absence of gravity, the stability of the liquid-gas interface depends on capillary forces. High liquid flow rates, sudden accelerations, and vibrational disturbances can cause the free surface of the liquid to collapse, which results in the ingestion of gas. Propellant tanks may have screen channel liquid acquisition devices (SCLADs) to position and maintain a gas-free propellant supply to the outlet. A saturated porous screen permits liquid to pass through but acts as a barrier to the gas. We investigated phase separation in porous media integrated capillary channels during parabolic flights (33rd DLR parabolic flight campaign in March 2019). An open side of a rectangular channel was covered with a dutch twill weave 200×1400. The liquid was ingested into the channel from its surroundings by establishing a differential pressure across the screen section. The gas-phase was blocked during the liquid withdrawal. We could show that the gas breakthrough occurs when the pressure difference across the screen exceeds the bubble point pressure. The experimental results showed good agreement with correlations from literature.