Screen Channel 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.

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.

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%.

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.

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.

Investigation on cryo-wicking performance within metallic weaves under superheated conditions for screen channel liquid acquisition devices (LADs)

In order to investigate the wicking performance of cryogenic propellants within metallic screens for space liquid acquisition devices (LADs), a vertical wicking experiment was carried out in a one-species test system with liquid nitrogen (LN2). Screens of Dutch twill weave (DTW) type 200 × 1400 were tested in both warp and shute directions. Two different degrees of superheat (∼2 K and ∼25 K) were achieved with a novel porous cooling shield element. A modified one-dimensional macroscopic model is proposed which considers the thermal effect of the solid weave and the vapor environment. Good agreement with experimental data is achieved. Results show that the cryo-wicking process is sensitive to the superheat condition. The wicking velocity as well as the maximum wicking height decreases with increasing superheat. For the same superheat condition, the wicking velocity was always higher in the warp direction than that in the shute direction.

Investigation on isothermal wicking performance within metallic weaves for screen channel liquid acquisition devices (LADs)

Wicking performance within the metallic screen is one of the key foundation to preventing gas penetration for screen channel liquid acquisition devices (LADs), which are designed to provide vapor free propellant for space crafts. In this study, based on the theoretical analysis on screen microscopic structure and wicking characteristics, a vertical isothermal wicking experiment was carried out using three selected Dutch Twill Weaves (DTWs) with HFE-7500 as the test fluid. According to the agreement between experimental results and the wicking theory, three macroscopic structural parameters named porosity, equivalent capillary diameter (ECD) and permeability were obtained both in warp and shute directions for 200 × 1400 DTW (woven with 200 warp wires and 1400 shute wires per square inch), 325 × 2300 DTW and 510 × 3600 DTW, respectively. Results show that, a finer mesh screen at the same direction is of a larger porosity, a smaller ECD and a smaller permeability, while the same mesh is of a smaller ECD and a larger permeability at the warp direction over the shute direction. In general, the wicking velocity is higher in a coarser mesh and is higher along the warp direction.

Room temperature bubble point, flow-through screen, and wicking experiments for screen channel liquid acquisition devices

This paper presents fundamental performance data for three of the influential factors that are required to design, size, and analyze screen channel liquid acquisition devices (LADs) for future in-space cryogenic propulsion systems. Bubble point, flow-through-screen, and wicking rate experiments are conducted on 14 different screen meshes, including three different metals (steel, aluminum, titanium), two different diameter screen samples (1.25″ and 2.50″), using multiple room temperature fluids (acetone, isopropyl alcohol, and water). Emphasis in the current work is on coarser meshes where there is a lack of reliable data. Corresponding analytical models from Hartwig and Darr (2014) are updated for each of the three influential factors, including a new evaporation rate-corrected wicking rate equation. Data obtained from this experiment will allow for efficient and accurate computational fluid dynamics simulations for flow out of a storage tank using LADs with mesh screens.

Propellant Management Devices for Low-Gravity Fluid Management: Past, Present, and Future Applications

This paper presents a comprehensive background and historical review of propellant management devices used throughout space flight history. The purpose of a propellant management device is to separate liquid and gas phases within a propellant tank and to transfer vapor-free propellant from a storage tank to a transfer line en route to either an engine or a receiver depot tank, in any gravitational or thermal environment. The design concept, basic flow physics, and principle of operation are presented for each type of propellant management device. The three primary capillary-driven propellant management device types of vanes, sponges, and screen channel liquid acquisition devices are compared and contrasted. For each propellant management device type, a detailed review of previous applications using storable propellants is given, which include space experiments as well as space missions and vehicles, in storable and cryogenic propellants. Future needs and recent technology developments are also discussed for future in-space cryogenic propellant management.

Hydrodynamic model of screen channel liquid acquisition devices for in-space cryogenic propellant management

Technologies that enable the storage and transfer of cryogenic propellants in space will be needed for the next generation vehicles that will carry humans to Mars. One of the candidate technologies is the screen channel liquid acquisition device (LAD), which uses a metal woven wire mesh to separate the liquid and vapor phases so that single-phase liquid propellant can be transferred in microgravity. In this work, an experiment is carried out that provides measurements of the velocity and pressure fields in a screen channel LAD. These data are used to validate a new analytical solution of the liquid flow through a screen channel LAD. This hydrodynamic model, which accounts for non-uniform injection through the screen, is compared with the traditional pressure term summation model which assumes a constant, uniform injection velocity. Results show that the new model performs best against the new data and historical data. The velocity measurements inside the screen channel LAD are used to provide a more accurate velocity profile which further improves the new model. The result of this work is a predictive tool that will instill confidence in the design of screen channel LADs for future in-space propulsion systems.

The static reseal pressure model for cryogenic screen channel liquid acquisition devices

Inside a propellant tank in microgravity, surface tension forces dominate, and porous screen channel liquid acquisition devices (LADs) are required to separate fluid phases, control flow, and ensure vapor free liquid transfer out of the tank. The bubble point pressure based on Adamson and Gast (1997) and reseal pressure of the screen define LAD performance. This paper presents a predictive equation for modeling the reseal pressure in both storable as well as cryogenic liquids. Seven parameters affect the reseal pressure, including surface tension (liquid type), contact angle, screen reseal diameter, liquid temperature, degree of subcooling, and pressurant gas type and temperature. Decreasing the temperature decreases reseal pressure. Pressurization with a non-condensable gas always yields higher reseal points over pressurization with a condensable gas. Subcooling the liquid at the screen adds margin in reseal point whereas elevating the temperature of the pressurant gas is a degradation factor. The reseal pressure model is validated across a wide range of experimental ground data and the mean absolute error between 4815 data points and model is only 2.4%.

Screen Channel Liquid-Acquisition-Device Bubble Point Tests in Liquid Oxygen

This paper examines the key parameters that affect the bubble point pressure for screen channel liquid acquisition devices in cryogenic liquid oxygen at elevated pressures and temperatures typical of a high-pressure propellant tank. An in-depth analysis of the effect of varying liquid temperature, pressure, and pressurization gas type on the bubble point is presented. Testing of a and Dutch twill screen sample was conducted at the NASA John H. Glenn Research Center at Lewis Field in Cleveland, Ohio. Test conditions ranged from 92 to 130 K and 0.138 to 1.79 MPa. The bubble point is shown to be a strong function of temperature with a secondary dependence on the amount of liquid subcooling. The subcooling dependence is believed to be a function of the amount of evaporation and condensation occurring at the liquid–gas interface at the screen. Good agreement exists between the data and theory for normally saturated liquid, but the model generally underpredicts the bubble point in subcooled liquid. Using the liquid temperature at the screen as opposed to the bulk liquid temperature to determine the surface tension of the fluid results in better correlation with the data.

Screen Channel Liquid-Acquisition-Device Bubble Point Tests in Liquid Methane

This paper examines the effect of varying the thermodynamic state and type of pressurant gas on the bubble point pressure for screen channel liquid acquisition devices in cryogenic liquid methane across a wide range of pressures and temperatures. Testing of a Dutch twill screen sample was conducted at the NASA John H. Glenn Research Center at Lewis Field in Cleveland, Ohio. Test conditions ranged from 106 to 160 K and 0.0618 to 1.78 MPa, using helium, methane, and nitrogen as pressurant gases. The bubble point is shown to be a strong function of temperature and a weak function of liquid subcooling. Pressurizing the propellant above the saturation pressure increase the overall margin in the total allowable pressure drop across a liquid acquisition device when using helium or nitrogen pressurant above the current predicted value. The model predicts well for saturated liquid and autogenous pressurization but underpredicts for a subcooled liquid using a noncondensible gas for pressurization.

A steady state pressure drop model for screen channel liquid acquisition devices

This paper presents the derivation of a simplified one dimensional (1D) steady state pressure drop model for flow through a porous liquid acquisition device (LAD) inside a cryogenic propellant tank. Experimental data is also presented from cryogenic LAD tests in liquid hydrogen (LH2) and liquid oxygen (LOX) to compare against the simplified model and to validate the model at cryogenic temperatures. The purpose of the experiments was to identify the various pressure drop contributions in the analytical model which govern LAD channel behavior during dynamic, steady state outflow. LH2 pipe flow of LAD screen samples measured the second order flow-through-screen (FTS) pressure drop, horizontal LOX LAD outflow tests determined the relative magnitude of the third order frictional and dynamic losses within the channel, while LH2 inverted vertical outflow tests determined the magnitude of the first order hydrostatic pressure loss and validity of the full 1D model. When compared to room temperature predictions, the FTS pressure drop is shown to be temperature dependent, with a significant increase in flow resistance at LH2 temperatures. Model predictions of frictional and dynamic losses down the channel compare qualitatively with LOX LADs data. Meanwhile, the 1D model predicted breakdown points track the trends in the LH2 inverted outflow experimental results, with discrepancies being due to a non-uniform injection velocity across the LAD screen not accounted for in the model.

A PREDICTIVE BUBBLE POINT PRESSURE MODEL FOR POROUS LIQUID ACQUISITION DEVICE SCREENS

This article presents a simplified model for porous screen channel liquid acquisition devices based on a maximum bubble point pressure method from Adamson and Gast (1997). To validate the model, three 304 stainless steel (325 × 2300, 450 × 2750, and 510 × 3600) mesh samples were tested in methanol, acetone, isopropyl alcohol, and water. Screen pores are estimated based on analysis from scanning electron microscopy, historical data, and current test data. Results show that the bubble point pressure is proportional to the surface tension of the fluid only when accounting for nonzero contact angles. The previous assumption that bubble point pressure scales inversely with effective pore diameter is shown to be invalid, as the second finest 450 × 2750 produced the highest bubble point of the three screens. The simplified bubble point model can be used to make predictions for any pure fluid when pore diameters are based on bubble point tests and not SEM analysis.

Screen channel LAD bubble point tests in liquid hydrogen

This paper presents experimental results for the liquid hydrogen bubble point tests for liquid acquisition devices (LADs) operating in low gravity cryogenic propulsion systems. The purpose of the test was to investigate parameters that affect screen channel LAD performance in a low pressure liquid hydrogen (LH2) propellant tank and to demonstrate several ways to increase the LH2 bubble point pressure. Three fine mesh screen channel LAD samples were tested in LH2 over the range of 16.7 K < T < 21.1 K and 31.5 kPa < P < 155 kPa using gaseous helium and hydrogen as pressurant gases. Results show that bubble point pressure is affected by screen mesh type, liquid temperature and pressure, and type of pressurization gas. Higher bubble points are achieved by using a finer mesh screen and pressurizing and subcooling the liquid with gaseous helium. In addition, there is evidence that the screen pore is itself temperature dependent.