EDU liquid acquisition device outflow tests in liquid hydrogen: Experiments and analytical modeling

This paper presents experiments and modeling of the most recent set of liquid acquisition device (LAD) vertical outflow tests conducted in liquid hydrogen. The Engineering Development Unit (EDU) was a relatively large tank (4.25 m³) used to mimic a storage tank for a cryogenic storage and transfer flight demonstration test. Six 1-g propellant tank outflow tests were conducted with a standard 325 × 2300 rectangular cross-section curved LAD channel conformal to the tank walls over a range of tank pressure (158–221 kPa), ullage temperature (22–39 K), and mass flow rate (0.0103–0.0187 kg/s) per arm. An analytical LAD channel solver, an exact solution to the Navier-Stokes equations, is used to model propellant outflow for the LAD channel. Results shows that the breakdown height of the LAD is dominated by liquid and ullage gas temperatures, with a secondary effect of flow rate. The best performance is always obtained by exposing the channel to cold pressurant gas and low flow rates, consistent with the cryogenic bubble point model. The model tracks the trends in the data and shows that the contribution of flow-through-screen pressure drop is minimized for bottom outflow in 1-g, versus the standard inverted outflow.     

Screen channel liquid acquisition device outflow tests in liquid hydrogen

This paper presents experimental design and test results of the recently concluded 1-g inverted vertical outflow testing of two 325 × 2300 full scale liquid acquisition device (LAD) channels in liquid hydrogen (LH₂). One of the channels had a perforated plate and internal cooling from a thermodynamic vent system (TVS) to enhance performance. The LADs were mounted in a tank to simulate 1-g outflow over a wide range of LH₂ temperatures (20.3–24.2 K), pressures (100–350 kPa), and flow rates (0.010–0.055 kg/s). Results indicate that the breakdown point is dominated by liquid temperature, with a second order dependence on mass flow rate through the LAD. The best performance is always achieved in the coldest liquid states for both channels, consistent with bubble point theory. Higher flow rates cause the standard channel to break down relatively earlier than the TVS cooled channel. Both the internal TVS heat exchanger and subcooling the liquid in the propellant tank are shown to significantly improve LAD performance.     

Cryogenic capillary screen heat entrapment

Cryogenic liquid acquisition devices (LADs) for space-based propulsion interface directly with the feed system, which can be a significant heat leak source. Further, the accumulation of thermal energy within LAD channels can lead to the loss of subcooled propellant conditions and result in feed system cavitation during propellant outflow. Therefore, the fundamental question addressed by this program was: “To what degree is natural convection in a cryogenic liquid constrained by the capillary screen meshes envisioned for LADs?” Testing was first conducted with water as the test fluid, followed by liquid nitrogen (LN₂) tests. In either case, the basic experimental approach was to heat the bottom of a cylindrical column of test fluid to establish stratification patterns measured by temperature sensors located above and below a horizontal screen barrier position. Experimentation was performed without barriers, with screens, and with a solid barrier. The two screen meshes tested were those typically used by LAD designers, 200 × 1400 and 325 × 2300, both with Twill Dutch Weave. Upon consideration of both the water and LN₂ data, it was concluded that heat transfer across the screen meshes was dependent upon barrier thermal conductivity and that the capillary screen meshes were impervious to natural convection currents.     

PVT gauging with liquid nitrogen

Experimental results are presented for pressure–volume–temperature (PVT) liquid quantity gauging of a 0.17 m³ liquid nitrogen tank pressured with ambient temperature helium in the normal gravity environment. A previously reported PVT measurement procedure has been improved to include helium solubility in liquid nitrogen. Gauging data was collected at nominal tank fill levels of 80%, 50% and 20% and at nominal tank pressures of 0.3, 1.0, and 1.7 MPa. The test tank was equipped with a liquid pump and spray manifold to circulate and mix the fluid contents and therefore create near-isothermal conditions throughout the tank. Silicon diode sensors were distributed throughout the tank to monitor temperatures. Close-spaced arrays of silicon diode point sensors were utilized to precisely detect the liquid level at the nominal 80%, 50%, and 20% fill levels. The tests simulated the cryogenic tank-side conditions only; helium mass added to the tank was measured by gas flowmeters rather than using pressure and temperature measurements from a dedicated helium supply bottle. Equilibrium data for cryogenic nitrogen and helium mixtures from numerous sources was correlated to predict soluble helium mole fractions. Results show that solubility should be accounted for in the PVT gauging calculations. Mole fractions predicted by Dalton’s Law were found to be in good agreement with the compiled equilibrium data within the temperature–pressure range of interest. Therefore, Dalton’s Law was deemed suitable for calculating ullage composition. Gauging results from the PVT method agreed with the reference liquid level measurements to within 3%.     

Investigation of cryogenic level sensors for LN2 and LOX

Investigations of two different types of cryogenic level sensors (capacitance and High Temperature Superconductor (HTS) for level measurement of liquid nitrogen (LN₂) and liquid oxygen (LOX) are presented here. They were tested for an active length of 400 mm in LOX and LN₂. A discrete diode array level sensor was used as a primary standard for calibrating these sensors. Comparative studies on linearity, sensitivity and other parameters at the operating temperatures are presented.     

Cracking of Al–4.5Zn–1.5Mg aluminium alloy propellant tank – A metallurgical investigation

The medium strength aluminum alloy AFNOR 7020 (Al–4.5Zn–1.5Mg) is extensively used in the fabrication of common bulk head propellant tank of liquid propulsion engine. The rings used in fabrication of the tank were of different sizes and were processed almost 4 years back in T651 condition. The propellant tank developed a leak at 2.7 bar(a) during proof pressure charging to 5 bar. The cracked portion of the ring was removed from the failed tank and subjected to detailed metallurgical investigations to understand the cause of failure. This paper brings out the details of investigations carried out and thereafter conclusion arrived on.     

Spark plasma sintering synthesis of intermetallic T2 in the Mo–Si–B system

Mo₅SiB₂ (T2) was synthesized by sparking plasma sintering (SPS) under different heating rates and sintering temperatures. The powder mixture with a T2 composition (Mo–12.5Si–25B (at.%)) failed to produce the T2 single-phase alloy due to the volatilization of Si during SPS process. Extra 0.5 at.% Si added to this mixture offset the volatilization loss. It has been found that heating of the mixture at low heating rates favored the formation of binary phases in the solid state at medium temperatures. In this work, the T2 alloy with a fine-grained microstructure was obtained via a liquid–solid reaction when the mixture was heated fleetly to the temperatures above the silicon melting point at the rapid heating rate of 200 °C/min. The sintering temperature at 1500 °C for T2 synthesis is beneficial to enhance further densification, as well as to avoid abnormal grain growth at higher temperatures.     

Design and experimental investigation of a cryogenic system for environmental test applications

This paper is concerned with the design, development and performance testing of a cryogenic system for use in high cooling power instruments for ground-based environmental testing. The system provides a powerful tool for a combined environmental test that consists of high pressure and cryogenic temperatures. Typical cryogenic conditions are liquid hydrogen (LH2) and liquid oxygen (LO2), which are used in many fields. The cooling energy of liquid nitrogen (LN2) and liquid helium (LHe) is transferred to the specimen by a closed loop of helium cycle. In order to minimize the consumption of the LHe, the optimal design of heat recovery exchangers has been used in the system. The behavior of the system is discussed based on experimental data of temperature and pressure. The results show that the temperature range from room temperature to LN2 temperature can be achieved by using LN2, the pressurization process is stable and the high test pressure is maintained. Lower temperatures, below 77 K, can also be obtained with LHe cooling, the typical cooling time is 40 min from 90 K to 22 K. Stable temperatures of 22 K at the inlet of the specimen have been observed, and the system in this work can deliver to the load a cooling power of several hundred watts at a pressure of 0.58 MPa.     

Improved pressure–volume–temperature method for estimation of cryogenic liquid volume

One of the most important issues in a liquid propellant rocket is to measure the amount of remaining liquid propellant under low gravity environment during space mission. This paper presents the results of experiment and analysis of a pressure–volume–temperature (PVT) method which is a gauging method for low gravity environment. The experiment is conducted using 7.4 l tank for liquid nitrogen with various liquid-fill levels. To maximize the accuracy of a PVT method with minimum hardware, the technique of a helium injection with low mass flow rate is applied to maintain stable temperature profile in the ullage volume. The PVT analysis considering both pressurant and cryogen as a binary mixture is suggested. At high liquid-fill levels of 72–80%, the accuracy from the conventional PVT analysis is within 4.6%. At low fill levels of 27–30%, the gauging error is within 3.4% by mixture analysis of a PVT method with specific low mass flow rate of a helium injection. It is concluded that the proper mass flow rate of a helium injection and PVT analyses are crucial to enhance the accuracy of the PVT method with regard to various liquid-fill levels.     

Thermodynamic vent system performance testing with subcooled liquid methane and gaseous helium pressurant

LCH₄ testing was conducted at the Marshall Space Flight Center using the multipurpose hydrogen test bed (MHTB) to evaluate the performance of a spray-bar thermodynamic vent system (TVS) with subcooled LCH₄ and gaseous helium (GHe) pressurant. Thirteen days of testing were performed in November 2006, with total tank heat leak conditions of about 715 W and 420 W at a fill level of approximately 90%. A total of 23 TVS cycles were completed. The TVS successfully controlled the ullage pressure within a prescribed control band but did not maintain a stable liquid saturation pressure. This was likely due to a TVS design not optimized for this particular propellant and test conditions, and possibly due to a large artificially induced heat input directly into the liquid.     

Elevated temperature low cycle fatigue of grey cast iron used for automotive brake discs

This paper evaluates the fatigue life properties of low carbon grey cast iron (EN-GJL-250), which is widely used for automotive brake discs. Although several authors have examined mechanical and fatigue properties at room temperatures, there has been a lack of such data regarding brake discs operating temperatures. The tension, compression and low cycle fatigue properties were examined at room temperature (RT) and at brake discs’ working temperatures: 500 °C, 600 °C and 700 °C. The microstructure of the material was documented and analysed. Tensile stress–strain curves, cyclic hardening/softening curves, stress–strain hysteresis loops, and fatigue life curves were obtained for all the above-mentioned temperatures. It was concluded, that Young’s modulus is comparable with both tension and compression, but yield its strength and ultimate strength are approximately twice as great in compression than in tension. All the mechanical properties remained quite stable until 500 °C, where at 700 °C all deteriorated drastically. During fatigue testing, the samples endured at 500 °C on average at around 50% of cycles at room temperature. Similar to other materials’ properties, the cycles to failure have dropped significantly at 700 °C.     

Ab initio study of AlCu2M (M = Sc,Ti and Cr) ternary compounds under pressures

The structural, electronic and elastic properties of the AlCu₂M (M = Sc, Ti and Cr) compounds in the pressure range of 0–100 GPa was investigated based on density functional theory. The calculated lattice parameters of the AlCu₂M compounds at zero pressure and zero temperature are in very good agreement with the existing experimental data. The bulk modulus, shear modulus and Young’s modulus increases with the increase of pressure, which indicates that higher materials hardness may be obtained when increasing pressures. The bulk modulus and Young’s modulus of AlCu₂Cr is the greatest under pressure. The shear modulus of AlCu₂Ti is the highest above 30 GPa, while that of the AlCu₂Sc is the strongest below 30 GPa. The calculated B/G values at zero and higher pressure indicated that they are ductile materials. The electronic densities of states and bonding charge densities have been discussed in details, revealing these compounds exhibit half-metallic behavior. In addition, the pressure dependences of Debye temperatures of AlCu₂M compounds have also been calculated. The results indicate that Debye temperatures increase with increasing pressure.     

Characterization of a thermoelectric/Joule–Thomson hybrid microcooler

Micromachined Joule–Thomson (JT) coolers are attractive for cooling small electronic devices. However, microcoolers operated with pure gases, such as nitrogen gas require high pressures of about 9 MPa to achieve reasonable cooling powers. Such high pressures severely add complexity to the development of compressors. To overcome this disadvantage, we combined a JT microcooler with a thermoelectric (TE) pre-cooler to deliver an equivalent cooling power with a lower pressure or, alternatively, a higher cooling power when operating with the same pressure. This hybrid microcooler was operated with nitrogen gas as the working fluid at a low pressure of 0.6 MPa. The cooling power of the microcooler at 101 K operating with a fixed high pressure of 8.8 MPa increased from 21 to 60 mW when the precooling temperature was reduced by the thermoelectric cooler from 295 to 250 K. These tests were simulated using a dynamic numerical model and the accuracy of the model was verified through the comparison between experimental and simulation results. Based on the model, we found the high pressure of the microcooler can be reduced from 8.8 to 5.5 MPa by lowering the precooling temperature from 295 to 250 K. Moreover, the effect of TE cooler position on the performance of the hybrid microcooler was evaluated through simulation analysis.     

Investigation of turbulent heat transfer performance of aviation turbine fuel multi-wall carbon nanotube nanofluid

Nanofluid is a novel heat transfer fluid prepared by suspending high thermal conductivity nano-sized particles in conventional fluids (water, engine oil and ethylene glycol). Thermo-physical properties (Thermal conductivity, dynamic viscosity and specific heat) and turbulent heat transfer performance of Aviation Turbine Fuel (ATF) based Multiwall Carbon Nanotube (MWCNT) nanofluid are investigated experimentally for particle volume concentrations of 0–1% and at mean fluid temperatures of 30οC and 50οC for a potential regenerative heat transfer application in semi-cryogenic liquid propellant rocket engine. The experimental results show that the heat transfer coefficient of the nanofluid increases with particle volume concentration, with a maximum enhancement at 1% particle volume concentration of approximately 23% and 50% observed at 30οC and 50οC respectively. Two different numerical modelling approaches (a single phase fluid model with enhanced thermo-physical properties and an Eulerian-Lagrangian model called the “discrete phase model”) are employed to simulate the experimental conditions. The predictions from both numerical modelling approaches are found to compare reasonably well with the experimental data. The enhanced heat transfer performance is expressed on an equal power penalty basis to clearely show the advantage of the nanofluid.     

Modeling of the dynamics of a slug of liquid oxygen in a magnetic field and experimental verification

This study presents the theoretical basis for the dynamics of a slug of liquid oxygen in a quartz tube when displaced by a pulsed magnetic field. The theoretical model calculated slug movement by balancing the forces due to magnetism, pressure, and damping and was verified with experimental data for a slug 1.3 cm long and 1.9 mm in diameter. During the experiments, the hidden slug length and damping factor were unknown, but quantifiable through the numerical solution. The hidden slug length accounted for the mass of LOX which cannot be seen during the experiment and was calculated as 10–14.5 cm. The damping factor was an empirical augmentation to represent increased damping from various phenomena and was calculated as 5.76–6.3. The experiments generated damped pressure waves of 6–8 Hz with maximum amplitudes of 0.8–1.3 kPa. Outside these ranges, the model indicated that the oscillation frequency decreased logarithmically with the hidden slug length, and the maximum amplitude decreased logarithmically with the damping factor. Measurement uncertainties of the visible length and slug initial position (0.8 mm) were also evaluated for their effects on the frequency and amplitude of the oscillations. The visible slug length did not seem to significantly affect the pressure waves, but the initial position strongly altered the amplitudes and mean of the oscillations. The predictive model matched the experiment well and could be used to design advanced flow control systems for cryogenic applications.     

The microscopic features of cavitation erosion and the solution in the plastic injection moulding machines

The premature failure mode of the nozzle unit in the plastic injection moulding machines was discovered to be cavitation erosion, rather than corrosion. The microscopic features of the cavitation erosion on the soft aluminium alloy have its own distinct characteristics. Three types of erosion pits in different size order have been discovered: a large round pit with very smooth surface are in the size range of 1–2 mm, small round overlapping pits in the pattern of parallel line are approximately 100 μm, and micro erosion pits are about 5 μm. These different size order erosion pits might be associated with the different size order of bubbles imploding. The root cause of the bubble formation was the alteration in surface tension and the vapour pressures due to the dosing chemicals in the coolant. The solution to the cavitation erosion with substituting stainless steel to aluminium alloy has been successful.     

Velocity field and pressure distribution around a collapsing cavitation bubble during necking and splitting

The hydrodynamic behavior of the fluid around a cavitation bubble located above a rigid boundary is investigated numerically. The liquid around the cavitation bubble is assumed to be incompressible, inviscid and irrotatational and surface tension is assumed to be negligible. Boundary-integral-equation and finite-difference methods are employed to study the problem. Three cases are investigated: (1) when the Bjerknes force is negligible in comparison with the buoyancy force, (2) when the buoyancy force is negligible in comparison with the Bjerknes force, (3) when the Bjerknes attraction force through the rigid surface and the buoyancy force are comparable. It is shown that during the collapse phase in the third case, an annular liquid jet develops around the bubble, causing it to take the shape of an hour-glass. This phenomenon is called necking which is followed by splitting the bubble into two parts. Features to note are the large lateral pressures and the high relative velocities of the fluid particles near the annular liquid jet of the bubble. This large lateral pressure may be the cause of bubble collapse. The velocity field of the liquid domain around the two parts of the cavitation bubble after splitting shows that a stagnation point exists between the two parts of the bubble. Because of the unsteady nature of the problem, the stagnation point and the point of maximum pressure do not coincide.     

Partial transient liquid phase diffusion bonding of Zircaloy-4 to stabilized austenitic stainless steel 321

An innovative method was applied for bonding Zircaloy-4 to stabilized austenitic stainless steel 321 using an active titanium interlayer. Specimens were joined by a partial transient liquid phase diffusion bonding method in a vacuum furnace at different temperatures under 1 MPa dynamic pressure of contact. The influence of different bonding temperatures on the microstructure, microindentation hardness, joint strength and interlayer thickness has been studied. The diffusion of Fe, Cr, Ni and Zr has been investigated by scanning electron microscopy and energy dispersive spectroscopy elemental analyses. Results showed that control of the heating and cooling rate and 20 min soaking at 1223 K produces a perfect joint. However, solid-state diffusion of the melting point depressant elements into the joint metal causes the solid/liquid interface to advance until the joint is solidified. The tensile strength of all the bonded specimens was found around 480–670 MPa. Energy dispersive spectroscopy studies indicated that the melting occurred along the interface of the bonded specimens as a result of the transfer of atoms between the interlayer and the matrix during bonding. This technique provides a reliable method of bonding zirconium alloy to stainless steel.     

Influences of temperature and contact pressure on thermal contact resistance at interfaces at cryogenic temperatures

The microscopic heat transfer between solid and solid at cryogenic temperatures exists in many application fields. This paper employed the Laser Photothermal Method (LPM) which is a transient and non-contact method to measure the Thermal Contact Resistance (TCR) between solid and solid in the temperature range of 70–290 K and the pressure range of 0.2–0.7 MPa. This paper analyzed the effects of the temperature and the contact pressure on the TCR at interfaces. The relationship between the TCR and the temperature at certain contact pressure was established, and the explanation about this phenomenon was given. Following, the TCR of SS 304–AlN, SS 304–Cu and SS 304–SS 304 were compared at different temperatures and contact pressures.     

Liquid nitrogen energy storage unit

An energy storage unit is a device able to store thermal energy with a limited temperature drift. After precooling such unit with a cryocooler it can be used as a temporary cold source if the cryocooler is stopped or as a thermal buffer to attenuate temperature fluctuations due to heat bursts. In this article, after a brief study of the possible solutions for such devices, we show that a low temperature cell filled with liquid nitrogen and coupled to a room temperature expansion volume offers the most compact and light solution in the temperature range 60–80 K. For instance, a low temperature cell as small as 23 cm³ allows the storage of 3.7 kJ between 76 K and 81 K. Experimental results were obtained varying the expansion volume size, the filling pressure and the temperature range. These results agree with our simple model based on thermodynamical properties of nitrogen. A cell filled with porous material was tested to confine the liquid in the cell independently of the gravity. This material enhances the thermal exchange for high liquid filling ratio whereas below ≈16% a solution must be found to improve the heat exchange coefficient between the fluid and the cell walls. Our calculations are extended to the 80–120 K temperature range for nitrogen and argon in order to clarify the various parameters to take into account for an energy storage unit dimensioning.