Deep Cryogenic Research Articles

Three-part superposition quasi-static stress model for PTFE across a broad low-temperature range based on ZWT and higher-order stress corrections

The widespread application of cryogenic liquid fuels in aerospace necessitates an accurate description of the mechanical properties of sealing materials such as Polytetrafluoroethylene (PTFE) at low temperatures. This study aims to develop a stress prediction model to describe the tensile stress response of PTFE across a broad low-temperature range. Quasi-static tensile tests on PTFE samples were conducted to obtain the uniaxial tensile properties of PTFE in the low-temperature range. Data fitting revealed significant errors and a loss of physical significance in the classical Zhu–Wang–Tang (ZWT) constitutive model and its modified versions when describing PTFE's mechanical response at low temperatures or large strains. Based on these theoretical models, a three-part superposition (TPS) model, incorporating asymptotic growth, linear growth, and exponential growth terms, is proposed. The TPS model demonstrates excellent predictive accuracy for PTFE's mechanical response from 77 K to 293 K, and from initial strain to fracture. Additionally, the physical connections and interpretations between the three parts of the TPS model and the macroscopic mechanical behavior and microscopic crystalline characteristics of semi-crystalline polymers are analyzed, providing a unified description and a comprehensive understanding of PTFE's mechanical behavior over this temperature range.

Experimental study on sloshing mechanical characteristics in a partially filled storage tank

AbstractDue to excellent performance, hydrogen is treated as the most promising energy carrier. However, during the storage of liquid hydrogen, there are still some thorny issues that need to be addressed urgently, such as fluid thermal stratification and sloshing phenomenon. To efficiently grasp fluid sloshing mechanical characteristics, a simple visual sloshing experiment rig was established by using a rectangle transparent water vessel. The variations of the interface shape and the impact force during sloshing were monitored and analyzed. The effects of sloshing frequency, horizontal acceleration, and initial liquid height on fluid sloshing mechanical mechanism were investigated. The results show that when the external sloshing excitation is close to the first order natural frequency, obvious interface fluctuation and large amplitude sloshing force variation are observed. The present work is of significance to strengthen the understanding of fluid sloshing mechanical performance and may lay a solid foundation for fluid sloshing suppression and long‐term storage of cryogenic fuels.

Cryogenic energy assisted power generation utilizing low flammability refrigerants

Cryogenic carbon-neutral fuels are potential alternatives as future marine fuels, releasing waste cryogenic energy during regasification and waste thermal energy during combustion. Organic Rankine Cycles (ORCs), using flammable hydrocarbon working fluids, are the preferred waste energy reutilization technology, prioritized over Brayton and Kaline cycles due to their compact system configuration. However, hydrocarbon flammability and explosiveness poses a huge safety risk. Therein lies the novelty of this study which presents an advanced dynamic model of a cryogenic enhanced ORC utilizing low flammability hydrofluorocarbons as working fluids for simultaneous reutilization of waste thermal and cryogenic energy from carbon-neutral cryogenic fuels. The evaporation temperature exhibits a direct correlation with energy and an inverse correlation with the exergy performance. System overcharging leads to a drastic performance decline, while undercharging can be tolerated to a certain liquid-to-volume ratio until critical failure. Marine classification societies’ recommendations-based scenarios were employed to gauge the emission reduction potential of low flammability working fluids for cryogenic ORCs, pitted against traditional combustion technologies. A maximum specific net-work, thermal efficiency, exergy efficiency, and cryogenic energy efficiency of 45.64 kJ/kg, 10.43 %, 12.75 %, and 11.8 % was achieved, respectively, with 85 % reduction in GHG emissions, using R452B as the working fluid.

Simulation analysis of cryogenic mechanical properties of carbon fiber reinforced silicon-containing epoxy resin composite

The use of carbon fiber-reinforced resin matrix composites instead of metals to manufacture cryogenic propellant tanks for spacecrafts is a development trend in the world aerospace industry. Cryogenic mechanical properties of the composites should be investigated in detail due to that the ultra-low temperature environment may cause micro cracks in the composites, leading to propellant leakage. In the present study, cryogenic tensile properties of a carbon fiber reinforced silicon-containing epoxy resin aomposite are investigated using experimental and numerical simulation methods. A silicon-containing epoxy resin with excellent cryogenic mechanical properties is developed by introducing a synthesized organic silicon polymer epoxidized polysiloxane and Nano-SiO2 into bisphenol F type epoxy resin. The tensile strength and modulus of the silicon-containing epoxy resin at −180 °C are 202.63 MPa and 7.81 GPa, which are 16.71% and 3.03% higher than those of bisphenol F type epoxy resin. The tensile strength of the silicon-containing epoxy resin at −180 °C is increased by 107.7% compared to that at room temperature, and the modulus at −180 °C is nearly twice that at room temperature. The carbon fiber reinforced silicon-containing epoxy resin composite is prepared by vacuum injection molding. The finite element model for the representative volume element of the composite unidirectional plate is established. The random sequence expansion method is used to randomly distribute the carbon fibers and simulate the thermal residual stress, the elastic performance, and the damage of the composite at cryogenic environments. Through comparison, it is found that the simulation results are in good agreement with the experimental results. The simulation reliability for cryogenic mechanical properties of carbon fiber reinforced resin matrix composites is verified. It is expected to provide a reference for the analysis and evaluation of cryogenic mechanical properties of composite tanks.

Modeling of cryogenic heated-tube flow boiling experiments of hydrogen and helium with the Generalized Fluid System Simulation Program

Accurate modeling of cryogenic boiling heat transfer is vital for the development of extended-duration space missions. Such missions may require the transfer of cryogenic propellants from in-space storage depots or the cooling of nuclear reactors. Purdue University in collaboration with NASA has assembled a database of cryogenic flow boiling data points from steady-state heated-tube experiments dating back to 1959, which has been used to develop new flow boiling correlations specifically for cryogens. Computational models of several of these experiments have been constructed in the Generalized Fluid System Simulation Program (GFSSP), a network flow code developed at NASA’s Marshall Space Flight Center. The new Purdue-developed universal correlations cover the full boiling curve: onset of nucleate boiling, nucleate boiling, critical heat flux, and film boiling. These correlations have been coded into GFSSP user subroutines. The fluids modeled in this study are liquid hydrogen and liquid helium. Predictions of local wall temperature and pressure drop are presented and compared to the test data.

Microscopic damage behavior in CFRP cross-ply laminates at cryogenic temperature

For the practical use of cryogenic propellant tanks made of CFRP laminates, experimental elucidation of the laminates’ microstructural damage propagation behavior at cryogenic temperatures is important. This paper presents a newly developed tensile test rig that enables in-situ observation of microscopic damage using an optical microscope at cryogenic temperatures using a Gifford–McMahon refrigerator. In-situ observations of microscopic damage under uniaxial tensile loading were done at room temperature (290 K, 17 °C) and at 30 K (−243 °C) on cross-ply thin-ply CFRP specimens of three kinds with different 90° layer thicknesses. The results demonstrated that the crack propagation behavior is independent of temperature, that the matrix crack density is higher, and that the onset of matrix crack initiation strain is lower at 30 K than at 290 K. Furthermore, the thermal strain within 90° layer at 30 K and at 290 K was estimated using finite element analyses (FEA). The FEA results suggest that the decrease in onset strain of matrix crack initiation at 30 K is mainly attributed to the increase in the thermal strains within the 90° layer.

Coupled modeling and simulation of tank self-pressurization and thermal stratification

Numerical analysis of thermo-fluid dynamics for cryogenic propellant storage primarily consists of nodal and computational fluid dynamics (CFD) modeling approaches. While nodal approaches prioritize faster computation over fidelity, CFD approaches promise accuracy and fidelity at the expense of significant computational resources. This paper presents an efficient coupling methodology developed to facilitate the simulation of a long-term self-pressurization process of a cryogenic propellant tank as well as associated thermal stratification phenomenon under both normal and reduced gravity conditions. Key highlight of the methodology is the development of a coupling scheme based on a domain decomposition approach that separates the tank into two computational regions at the liquid-vapor interface. SINDA/FLUINT, the nodal code, is utilized to simulate the liquid region, while ANSYS Fluent, the CFD code, handles the vapor region. A data exchange algorithm was developed to compute required boundary conditions for each region using the local thermodynamic properties of assumed infinitely thin interface. The coupling between the nodal and CFD codes was demonstrated by simulating a self-pressurization process in a small size tank using hydrogen as the working fluid. A sensitivity study on the grid sizing and coupling time step was conducted to determine appropriate spatial and ensure a divergent-free explicit data exchange time step size. Using the coupling approach, two numerical case studies were performed to study tank self-pressurization by considering two initial hydrogen fill levels. The effectiveness and efficiency of the coupling methodology was assessed by comparing the temperature and pressure evolution results of the coupled simulation with those obtained solely from the CFD simulation. Results showed that the coupling scheme and data exchange algorithm were successfully implemented, and the coupled simulation agreed well with the CFD simulations. In addition, a stratification number was used to characterize the transient dynamic development of the thermal stratification. Lastly, the computational costs associated with both approaches were compared. Significant reductions in simulation time were achieved for both cases.

Characterization Of Cryogenic Sloshing Via Image Velocimetry, Free Surface Tracking And Data Assimilation

Cryogenic fuels such as liquid hydrogen (LH_2 ) and liquified natural gas (LNG) are promising energy carriers for the future. Their thermal management is significantly challenged by the liquid sloshing induced by external acceleration because sloshing strongly impacts the evaporation rate and, thus, the reservoir’s pressure control. This work presents a unique experimental characterization of liquid sloshing in cryogenic conditions combining interface tracking, image velocimetry and physics-constrained data assimilation. The experiments were conducted in a reduced-scale cryogenic tank partly filled with liquid nitrogen undergoing lateral harmonic sloshing. A combination of floating and neutrally buoyant seeding particles was used to simultaneously carry out interface tracking using a moving-window Radon transform and image velocimetry using Particle Tracking Velocimetry (PTV). The data assimilation was carried out using constrained radial basis function (RBF) regression, imposing kinematic boundary conditions at the walls and interface. The assimilation allows for unprecedented super-resolution of the velocity field.

Simulation of the micro-gas desublimation crystallization during pressurization of cryogenic propellant

The desublimation crystallization of trace impurity gas at the temperature of liquid hydrogen and liquid oxygen is a common problem in cryogenic engineering, which usually leads to the failure of cryogenic liquid transportation. Liquid hydrogen and liquid oxygen are important aerospace propellants. In the pressurization process of cryogenic liquid propellant, a small amount of water vapor and other gases in the pressurized gas would appear desublimation and crystallization at low temperature. Inevitably, as the tail gas of hydrogen combustion, water vapor sometimes diffused into cryogenic liquid. This kind of desublimation crystallization was accompanied by heat and mass transfer, accompanied by gas-solid phase transition, moving boundary, random and extremely complicated crystallization growth process. It was of great engineering practical significance to study the heat and mass transfer mechanism and law of this complex desublimation phase change phenomenon for the progress and development of engineering technologies such as refrigeration, cryogenics and aerospace. In this paper, based on the homogeneous desublimation theory, the pressurization system of liquid oxygen tank with oxygen containing trace water vapor was taken as the research object, and the basic data of ice crystal formation and growth during pressurization, such as crystallization quantity, crystallization speed and size distribution, were calculated theoretically. It provided a theoretical basis for the experimental study of the real dynamic characteristics and laws of desublimation crystallization in the propulsion system. The research methods and conclusions in this paper also had some guiding significance for the use of liquid hydrogen in the storage, transportation and use of the hydrogen energy.

Demonstration of charge-hold-vent (CHV) and no-vent-fill (NVF) in a simulated propellent storage tank during tank-to-tank cryogen transfer in microgravity

The space exploration from a low earth orbit to a high earth orbit, then to Moon, Mars, and possibly asteroids and moons of other planets is one of the biggest challenges for scientists and engineers for the new millennium. The enabling of in-space cryogenic rocket engines and the Lower-Earth-Orbit (LEO) cryogenic fuel depots for these future manned and robotic space exploration missions begins with the technology development of advanced cryogenic thermal-fluid management systems for the propellant transfer line and storage tank system. One of the key thermal-fluid management operations is the chilldown and filling of the propellant storage tank in space. As a result, highly energy efficient, breakthrough concepts for quenching heat transfer to conserve and minimize the cryogen consumption during chilldown have become the focus of engineering research and development, especially for the deep-space mission to Mars. In this paper, we introduce such thermal transport concepts and demonstrate their feasibilities in space for cryogenic propellant storage tank chilldown and filling in a simulated space microgravity condition on board an aircraft flying a parabolic trajectory. In order to maximize the storage tank chilldown thermal efficiency for the least amount of required cryogen consumption, the breakthrough quenching heat transfer concepts developed include the combination of charge-hold-vent (CHV) and no-vent-hold (NVF). The completed flight experiments successfully demonstrated the feasibility of the concepts and discovered that spray cooling combined with hold and vent is more efficient than the pure spray cooling for storage tank chilldown in microgravity. In microgravity, the data shows that the CHV thermal efficiency can reach 39.5%. The CHV efficiency in microgravity is 6.9% lower than that in terrestrial gravity. We also found that pulsing the spray can increase CHV efficiency by 6.1% in microgravity.

Investigation on spray and flame stabilization of a LOX/methane swirl coaxial injector

Variable-thrust cryogenic propellant rocket engines are gaining significant research interest in space exploration. However, low-frequency unstable combustion is still a challenging scenario, especially in fuel-rich preburner and low-thrust operating conditions of deep variable thrust. To deeply understand the mechanism of low-frequency unstable combustion, chemiluminescence images of CH* and background light images of the spray were obtained synchronously by chemiluminescence imaging and laser background light imaging, respectively. Both the spray and flame stabilization of liquid oxygen/methane swirl coaxial injector were studied through the continuous regulation of liquid oxygen mass flow rate. The results showed that low-frequency unstable combustion occur in both the start-up stage and the throttled stage under the fuel-rich condition at a frequency of 39.1∼48.1 Hz and an amplitude of 30% of the average combustor pressure. It is found that the two-phase flow instability of liquid oxygen is likely to induce spray and flame instability, resulting in low-frequency unstable combustion. The dimension subcooling degree of liquid oxygen is an important factor affecting unstable combustion. When the dimensionless subcooling degree is larger than 0.7, the low-frequency unstable combustion is suppressed. On the other hand, as the mixing ratio decreases, the flame oscillation mode gradually transforms from the longitudinal oscillation mode to contraction/expansion mode. Flame filling up and flashback processes can be observed in both flame oscillation modes, and the entropy coupling mechanism of the oscillation mode is explained in detail. Furthermore, an oscillation period is determined to include four processes: propellants filling up and flame liftoff; heat release of the combustion products and entropy disturbance; acceleration of the entropy wave through the nozzle creating an acoustic disturbance; and flame flashback, in which the heat release time of combustion products and entropy disturbance is the longest.

A numerical study on thermal-structural characteristics of cryogenic common bulkhead propellant tanks for various tank lengths and core thicknesses

Common bulkhead (CBH) propellant tanks have the advantage that its structural and space efficiency are high. The tank is a form in which an oxidizer tank and a fuel tank are integrally combined, and the oxidizer and fuel are separated by the CBH. The CBH propellant tank in which two tanks are integrated can reduce unnecessary space between the two tanks. However, there are other difficult problems regarding effectively designing the CBH propellant tanks even though there are structural and space benefit. This paper is a study on the thermal-structural characteristics of CBH tanks containing LOX/LH2 propellant. In order to conduct the thermal-structural analysis, the thermal analysis model was constructed using 2-dimensional axisymmetric elements to reflect the shape features of the tank, and the structural analysis model was built using 3-dimensional elements. The thermal-structural analysis was performed on the length of the bottom tank and the foam core thickness of the CBH. In the structural analysis of the tank, when the thermal load was ignored and only the pressure load was applied, there was a difference in the buckling load factor depending on the thickness of the CBH foam core, but as the thermal load was taken into consideration, there was also a difference in the bottom tank length. The analysis results show that the thermal-structural characteristics of the CBH propellant tank were influenced by the length of the bottom tank as well as the thickness of the foam core.

Aviation fuels of the future − A techno-economic assessment of distribution, fueling and utilizing electricity-based LH2, LCH4 and kerosene (SAF)

This paper investigates the techno-economic implications on air travel when fossil-based kerosene is phased out of the market, specifically focusing on the comparison between liquid hydrogen, liquid methane and renewable kerosene for ten exemplary flight routes to estimate the cost of air travel per passenger and 100 km distance travelled €2020PAX100km for every fuel type. By considering the entire supply chain, including hydrogen production from renewable sources, synthesis, oversea transport, domestic distribution, and utilization, this study addresses the overarching question of whether it is more economical to change the fuel source or the fuel itself to reduce fossil kerosene usage in the aviation industry. It is demonstrated that aircraft acquisition costs play a minor role compared to fuel supply costs and specific fuel demand. The study shows that for electricity-based fuels, liquid hydrogen is the most economic option, even with a potential energy penalty, followed by liquid methane and renewable kerosene. The results for an aircraft with a capacity 180 passengers are 3.08, 4.57 and 5.11 €PAX100km for liquid hydrogen, liquid methane and renewable kerosene, respectively. Challenges regarding storage and isolation requirements for cryogenic fuels in aviation are discussed, with assumptions made that these obstacles can be overcome to realize economic benefits. Additionally, the study suggests potential shifts in aircraft size selection by airlines to mitigate rising fuel prices in the future. The study advocates for the aviation industry's openness to new fuels like liquid hydrogen and liquid methane to alleviate the cost increase associated with phasing out fossil kerosene.

Study of long-term in-orbit pressure control of liquid krypton cryogenic storage tank

Due to its high specific impulse, low toxicity, contamination, safety, and cost, krypton has gradually replaced other propellants as the primary choice for electric thrusters on deep-space exploration and large-orbit transfer missions with long-range, long-duration, and large-thrust requirements. However, due to the cryogenic propellant itself having a low boiling point, controlling the pressure change of krypton cryogenic propellant during the process of long-term cryogenic storage has emerged as one of the most important issues that must be resolved and proven to achieve non-destructive storage of cryogenic propellant. This paper examines the necessity and viability of a cryogenic gas propellant liquefaction storage scheme and quantifies the effectiveness of tank pressure control of the supercooled liquid krypton injection mixing scheme to solve the problem at present. Its purpose is to offer scheme examples for the design of a krypton thruster propellant storage unit and the in-tank pressure control during the long-term application process.

Parametric analysis of the Charge-Hold-Vent method for cryogenic propellant tank chilldown

In the absence of external heat exchangers, the on-orbit transfer of cryogenic propellants requires the receiver tank to first be quenched to a sufficiently low energy state to allow for a continuous no-vent fill to avoid unnecessary venting of liquid. One proposed method for tank chilldown that minimizes the potential for venting liquid is the charge hold vent (CHV) method. CHV follows a cyclic process that gradually removes thermal energy from the receiver tank by injecting liquid with the vent valve closed and allowing the fluid and wall to reach near-thermal equilibrium before venting the superheated vapor. However, the CHV method must be optimized to minimize complexity, mass, and time. This paper presents a modular CHV analytical model used to quantify the number of cycles and propellant mass consumed based on first principles. The model is used to examine the effect of eight parameters: receiver tank material, volume, mass, maximum expected operating pressure, and initial pressure, liquid injection pressure and temperature, and the target temperature. The model is validated against the only two available CHV datasets. Based on results, the tank mass-to-volume ratio is the most important factor in determining the number of CHV cycles and thus degree of difficulty in tank chilldown. The model can easily be used for early-stage design, sizing, and analysis of cryogenic propellant transfer systems.

Impact of Internal Baffle Designs on Liquid Hydrogen Sloshing in Cryogenic Aircraft Fuel Tanks

Hydrogen because of its zero carbon emissions and highly energy-dense nature has a strong potential to be used as an aviation fuel. There are currently two main ways that hydrogen is being considered for use in aircraft: it can be vaporized and mixed with air before being burned in the jet engine, or it can be used to power fuel cells that generate electricity, which can be used to power electric motors. Both these scenarios would require storing liquid hydrogen (LH2) in cryogenic tanks on board as it minimizes the tank size. But a major challenge with cryogenic hydrogen storage is the dynamic movement of the fuel which can lead to fuel boil off and bubble formation. In the current paper, the sloshing motion of LH2 in a CHEETA type thin-walled composite fuel tank, under acceleration data obtained from an Airbus A-320 in cruising conditions, is investigated. The dynamic fluid structure interaction problem is solved numerically using the Coupled Eulerian-Lagrangian (CEL) technique in ABAQUS. The developed modelling strategy is then employed to study the impact of various internal baffle designs on the sloshing behavior of the fuel under different fill levels. This study not only establishes that sloshing is a major cause for concern when it comes to LH2 aircraft fuel storage, but also advances our understanding in devising potential mitigative strategies.

Thermal Modeling of CryoFILL liquefaction tests

Proposed NASA missions to Moon and Mars involve producing cryogenic propellant in-situ to reduce launch mass and requirements. One technique for liquefaction of the gases produced through electrochemical processes is to circulate cold gaseous neon or helium through broad area cooling tubes attached to the outside of the propellant tanks. To determine the performance of this liquefaction process tests were conducted at NASA Glenn Research Center in a 2.1 cubic meter tank with a broad area cooling network (CryoFILL). A thermal/fluid model of the tank and its cooling loop is developed in Thermal Desktop. Details of the model and the model predictions and comparison to some of the experimental data from the CryoFILL liquefaction tests are presented here.

Development of test rig for optical diagnostics of cryogenic spray

Spray cooling is the primary method for conducting chilldown and fill of cryogenic propellant tanks. In a typical spray injection process, a liquid sheet/jet that exits the spray nozzle undergoes primary breakup by the development of surface instabilities. Droplets and ligaments generated after the primary breakup undergo secondary breakup to create a dispersion of droplets, which extract heat on impact with the tank walls. In the existing literature, there is limited data on the primary breakup of cryogenic sprays and their detailed visualization. Moreover, an insight into the spray characteristics such as primary breakup length and cone angle is vital to the development of computational models. In this investigation, optical diagnostics of cryogenic spray breakup and measurements of cryogenic spray characteristics have been conducted. Liquid nitrogen is the selected cryogen for the present analysis. To capture the transient nature of spray breakup after the injection, a novel shadowgraph technique is developed to photographically freeze the spray motion. Cryogenic spray characteristics such as cone angle and primary breakup length are obtained from the shadowgraph. In addition, droplet velocity measurement using Particle Image Velocimetry is explored. The comprehensive experimental dataset obtained herein not only provides insights into the mechanism of spray formation for cryogenic fluids but also helps in designing of spray cooling system for tank chilldown.

Liquid hydrogen tank chill and no-vent fill prediction using computational fluid dynamics

Cryogenic tank chill and fill is an important cryogenic fluid management technology that supports and enables many of NASA’s long-duration space missions. For no-vent fill, the receiver tank pressure remains below the supply tank pressure during the entire duration of the fill so that the tank does not require venting. This is especially advantageous for tank fill operations in low gravity where the position of the liquid is not always known and venting the tank may cause loss of propellant by venting liquid. In lieu of expensive tests conducted on-orbit, accurate computational models capable of predicting receiver tank pressure during cryogenic propellant tank fill may be used to reduce system and propellant mass as well as mission risk. However, these numerical models must be validated or anchored to test data. This study presents computational fluid dynamics (CFD) models with conjugate heat transfer that are used to predict a liquid hydrogen tank chill and no-vent fill ground test conducted at Lewis Research Center (now Glenn Research Center) in 1991. The specific test case chosen for model validation implemented an upward-facing jet near the bottom of a cylindrical 34 liter tank. CFD predictions are compared to experimental measurements of tank pressure, fill level, and wall temperature. The CFD results show reasonable agreement to the test data but overpredict the pressure collapse near the end of the fill despite the liquid jet penetrating the liquid-vapor interface.

Modeling of cryogenic heated-tube flow boiling experiments of nitrogen and methane with Generalized Fluid System Simulation Program

Accurate modeling of cryogenic boiling heat transfer is vital for the development of extended-duration space missions. Such missions may require the transfer of cryogenic propellants from in-space storage depots or the cooling of nuclear reactors. Purdue University in collaboration with NASA has assembled a database of cryogenic flow boiling data points from heated-tube experiments dating back to 1959, which has been used to develop new flow boiling correlations specifically for cryogens. Computational models of several of these experiments have been constructed in the Generalized Fluid System Simulation Program (GFSSP), a network flow code developed at NASA’s Marshall Space Flight Center. The new Purdue-developed correlations cover the full boiling curve: onset of nucleate boiling, nucleate boiling, critical heat flux, and post-critical heat flux boiling. These correlations have been coded into GFSSP user subroutines. The fluids modeled are nitrogen and methane. Predictions of wall temperature are presented and compared to the test data.