Zero Boil-Off Research Articles

Simulation test platform for the controlled storage and transfer of liquid hydrogen

Clean-energy propulsion machines, including trucks, tractors, ships, and aircraft, for heavy-duty and long-range mobility have moved, by necessity, to onboard liquid hydrogen (LH2). However, the established method of storage and transfer is problematic due to losses and for any duty-cycle of a sporadic or on/off nature. Integral servicing system methodology is needed for both safety and cost effectiveness in the key drivers of time savings, product savings, and venting exposures. Modern controlled storage technology enables quick and effective vehicle servicing at the point of use. Simulations of controlled storage/transfer (CS/T) methodologies are performed using a multi-purpose LH2 simulation test platform comprised of two primary systems: Cryostat CS900 tank and transfer system and the LS20 liquefaction/refrigeration and storage system. Testing includes both steady-state and transient modes of operation to demonstrate both zero boiloff (ZBO) and zero-loss transfer (ZLT) modes. Technical areas of use include product development for tanks, refrigeration, transfer systems (lines, dispensers, pumps, valves); experimental validation of analytical models and thermofluidic properties; thermal insulation performance test data under relevant conditions; thermophysical characterization of materials and structures; instrumentation and sensors development; tank boiloff and heat flux engineering design data. Descriptions and preliminary test results are given along with thermal performance analyses from real-world testing and experimentation.

Multi-objective optimization of precooled JT cryocooler working at liquid hydrogen temperature

With the advantages of no moving parts at low temperature, flexibility and simple structure, the precooled Joule-Thomson (JT) cryocooler working at liquid hydrogen temperature has the potential to be applied in the liquid hydrogen zero boil-off (ZBO) storage system in space. For JT cryocooler used in aerospace, cooling capacity, efficiency and mass are key parameters which should be considered simultaneously. For this reason, in this study, a theoretical model of the precooled JT cryocooler working at liquid hydrogen temperature which is composed of the heat exchangers, the JT compressor and the precooler is established. The target cooling capacity of the cryocooler is 10 W at liquid hydrogen temperature. Multi-objective optimization method is introduced to comprehensively optimize input power and mass. The Pareto frontier consisting of a series of non-dominated solutions is obtained. The linear programming technology of multidimensional analysis preference (LINMAP) method is used to select the final optimal solution from the Pareto frontier. The multi-objective optimization results of input power and mass of the cryocooler are 3484.72 W and 40.92 kg, respectively.

Study of thermal transport in highly anisotropic materials for space recuperator applications

A high-effectiveness, low-pressure-drop recuperator is one of the critical components of energy-efficient, high-capacity, low-temperature cryocoolers for long-term storage of cryogens including hydrogen. This paper presents an investigation of the thermal transport mechanisms in highly anisotropic materials. These materials enable the development of compact, lightweight, high-effectiveness recuperative heat exchangers. The high in-plane thermal conductivity allows effective heat transfer from the hot stream to the cold stream, while the low out-of-plane thermal conductivity keeps undesirable axial conduction to a minimum. The concept suggested in this paper could lead to a disruptive technology which affects how future space heat exchangers are designed and built. This is the first time an investigation is carried out to exploit the unique thermophysical properties of lightweight, highly anisotropic materials to enable the development of high-effectiveness, compact and lightweight recuperators for cryocoolers. A very attractive design feature of the recuperator is its modularity, so that high gas flow rates can be obtained by simply increasing the number of modules. NASA Space Technology Roadmap indicates that compact cryocoolers capable of removing 20 W or greater of heat from liquid hydrogen storage tanks could offer significant mass savings of cryogenic propellants through zero boil-off (ZBO), and thus enable long-duration space missions.

Integrated refrigeration and storage of LNG for compositional stability

Growing interest in liquefied natural gas (LNG) as a rocket fuel necessitates a greater technical understanding of the compositional changes due to preferential boil-off (or weathering) that occurs during long duration storage. The purity of methane in LNG can range from 90 to 98%, and is subject to preferential boil-off due to its low boiling point compared to other constituents despite the use of high-performance thermal insulation systems. Active heat extraction (i.e. refrigeration) is required to completely eliminate weathering. For future operational safety and reliability, and to better understand the quality and efficiency of the LNG as a cryofuel, a 400-liter Cryostat vessel was designed and constructed to measure the composition and temperatures of the LNG at a number of different liquid levels over long durations. The vessel is the centerpiece of a custom-designed lab-scale integrated refrigeration and storage (IRaS) system employing a pulse tube cryocooler capable of roughly 50 W of lift at 100 K. Instrumentation includes ten temperature sensors mounted on a vertical rake and five liquid sample tubes corresponding to five liquid levels. Two modes of operation are studied. The first is without refrigeration in order to determine a baseline in the change in composition, and to study stratification of the LNG. The second is performed with the cryocooler active to determine the operational parameters of the IRaS system for eliminating the weathering as well as stratification effects in the bulk liquid. The apparatus design and test method, as well as preliminary test results are presented in this paper. As a bonus in cost-saving and operational efficiency, the capability of the IRaS system to provide zero-loss capabilities such as zero boil-off (ZBO) keeping of the LNG and zero-loss filling/transfer operations are also discussed.

Development of zero boil-off cooling systems for superconducting self-shielded MEG

A mobile Magneto encephalography (MEG) of Sumitomo Heavy Industries, Ltd. (SHI) uses a high temperature superconducting magnetic shield (HTSMS), Superconductor-Normal-metal-Superconductor (SNS) type Superconducting Quantum Interface Device (SQUID) sensors, and they are cooled by a zero boil-off cooling system. The zero boil-off cooling system consists of a circulating cooled helium gas system for cooling the HTSMS below temperature 90 K and a helium recovery system for cooling the SNS type SQUID sensors to liquid helium temperature. The zero boil-off cooling system are designed to allow measurement in an operating state, allowing arbitrarily long usage. We succeeded first measurement of neuron current in brain by using SHI’s MEG with Helium zero-boil off cooling system at April, 2018. This paper describes overview of SHI’s MEG, the thermal design of the zero boil-off cooling system for our MEG and the results of cooling tests.

Helium Re-condenser for 1.5T Zero-Boil-Off (ZBO) MRI cryostat

Superconducting MRI magnet is the most exhaustive commercial application of superconductivity and helium cryogenics. Cryocooler based Zero-Boil-Off (ZBO) technique is inevitable for the present-day scanner. An MRI cryostat for a 1.5T MRI magnet has been designed with the ZBO technique using a fin-based helium recondenser. A cryocooler based test rig has been developed to characterize the performance of the helium recondenser made of OFHC copper. A two-stage GM cryocooler is used to cool the thermal shield and the helium recondenser. Four liters of liquid helium has been produced using the same heat exchanger. The recondensation test of the heat exchanger is performed up to 6 psi of bath pressure. At 1psi, the recondensation capacity is found to be ~1.5W. This paper briefly discusses the experimental details of the recondensation test along with an analytical calculation.

Thermodynamic optimization of composite insulation system with cold shield for liquid hydrogen zero-boil-off storage

The study of zero-boil-off (ZBO) storage is of great significance for the long-term storage of liquid hydrogen (LH2). Preliminary experimental research on the utilization of cryocooler to achieve ZBO storage has been reported, but the optimization of the total power consumption has barely been considered. This paper will fully consider the working characteristics of the cryocooler, that is, refrigerator efficiency increases with the increase of its working temperature. A novel method to realize the cascade utilization of the cooling power of cryocooler is proposed, which can effectively reduce the total power consumption of ZBO system. A thermodynamic model has been developed to optimize the input power of cryocooler in LH2 ZBO storage with cold shied and multilayer insulation (MLI). Thermal coupling characteristics of cryocooler, cold shield and MLI has been studied at the minimum input power. The mechanism and optimization strategy have been explained quantitatively. By optimizing position and temperature of cold shield, the input power of cryocooler can be reduced by 69.5%–74.4%. In addition, the effects of MLI thickness and boundary temperature on the optimization of the cold shield have been studied. The influence of LH2 pressure in tank on cryocooler input power has also analyzed.

The Design and Validation of a Zero Boil-Off LAr System for CDEX-10 Experiment

The China Dark Matter Experiment (CDEX) is an experiment of detecting light weakly interacting massive particles by using the p-type point contact germanium (pPCGe) detector. The underground laboratory of the CDEX is situated in Jinping Mountain in Sichuan province of China. In this experiment, a 1200-L liquid argon (LAr) scintillator is employed as anti-coincidence veto detector to maximally rule out the background radiation, and to provide a stable low-temperature surrounding for the pPCGe detector. A self-circulation argon liquefaction system with three Pulse Tube Refrigerators is developed to satisfy the zero boil-off condition of the LAr detector; bubbles formed during system operation are prevented by LAr sub-cooling condition. Meanwhile, an actively cooled LAr shield outside the LAr detector is used to prevent the external heat radiation from propagating inside to keep the required 1.0 K temperature gradient inside the LAr detector. The structure of the cryogenic system and the testing results of this cryogenic system by using liquid nitrogen are presented in the paper. The testing results indicate that the cryogenic system satisfies the dark matter experiment requirements.

Development of molecular tagging velocimetry for the ZBOT experiment

We present the development of molecular tagging velocimetry (MTV) capability for the NASA Zero Boil-Off Tank (ZBOT) experiment. The challenges of chemical solubility posed by the fluorocarbon working fluid and small range of velocities in the experiment are met using MTV based on the photobleaching of coumarin-153. The feasibility of measurements is demonstrated by one-component velocimetry (1c-MTV) in a setup with geometric characteristics that mimic the actual ZBOT test section.

Calculation and position optimization on vapor cooled shield for liquid hydrogen storage

The ZBO (zero boil off) storage of liquid hydrogen (LH2) has broad prospects in aerospace and civil market. Because of low critical temperature and volatility, LH2 tank poses severe requirements to the insulation system (multilayer insulation (MLI) is considered to be the most promising). In order to reduce heat leak into tank, vapor cooled shield (VCS) was set up to cool the MLI by retrieving the cold energy of discharged low temperature GH2. In this study, a simplified physical model is established to investigate the optimal position of VCS in MLI, and the influence of various factors on the performance of VCS has been analysed. Taking the minimum heat leak as the target, the best installation position is around 50% in MLI (inside looking outward) for the given condition. The heat leak of the tank can be reduced by 48.03% at most.

Reduction of helium loss from a superconducting accelerating cavity during initial cool-down and cryostat exchange by pre-cooling the re-condensing cryostat

A Zero-Boil-Off (ZBO) cryostat is designed to realize a compact, stand-alone cryogenic system for the AIST superconducting accelerator (SCA). Under normal operation there is no evaporative helium loss from the cryomodule and therefore operating costs associated with the supply of liquid helium can be eliminated. The only significant loss of helium from the module occurs during the initial cavity cool-down procedure or when the re-condensing cryostat is replaced. It takes about 3h to cool down the cryostat head from room temperature (300K) to 4K. During this time around 100L of liquid helium is lost due to evaporation. By pre-cooling the cryostat inside a low heat load vacuum tube before transfer to the cryomodule, this evaporative loss could be essentially eliminated, significantly reducing the volume of liquid helium required for the initial cryomodule cool-down. The pre-cooling system also provides an efficient method to test the cryostat prior to use.

Design, fabrication and test of Load Bearing multilayer insulation to support a broad area cooled shield

Improvements in cryogenic propellant storage are needed to achieve reduced or Zero Boil Off of cryopropellants, critical for long duration missions. Techniques for reducing heat leak into cryotanks include using passive multi-layer insulation (MLI) and vapor cooled or actively cooled thermal shields. Large scale shields cannot be supported by tank structural supports without heat leak through the supports. Traditional MLI also cannot support shield structural loads, and separate shield support mechanisms add significant heat leak. Quest Thermal Group and Ball Aerospace, with NASA SBIR support, have developed a novel Load Bearing multi-layer insulation (LBMLI) capable of self-supporting thermal shields and providing high thermal performance.We report on the development of LBMLI, including design, modeling and analysis, structural testing via vibe and acoustic loading, calorimeter thermal testing, and Reduced Boil-Off (RBO) testing on NASA large scale cryotanks.LBMLI uses the strength of discrete polymer spacers to control interlayer spacing and support the external load of an actively cooled shield and external MLI. Structural testing at NASA Marshall was performed to beyond maximum launch profiles without failure. LBMLI coupons were thermally tested on calorimeters, with superior performance to traditional MLI on a per layer basis. Thermal and structural tests were performed with LBMLI supporting an actively cooled shield, and comparisons are made to the performance of traditional MLI and thermal shield supports. LBMLI provided a 51% reduction in heat leak per layer over a previously tested traditional MLI with tank standoffs, a 38% reduction in mass, and was advanced to TRL5. Active thermal control using LBMLI and a broad area cooled shield offers significant advantages in total system heat flux, mass and structural robustness for future Reduced Boil-Off and Zero Boil-Off cryogenic missions with durations over a few weeks.

Cryogenic thermal system analysis for orbital propellant depot

In any manned mission architecture, upwards of seventy percent of all payload delivered to orbit is propellant, and propellant mass fraction dominates almost all transportation segments of any mission requiring a heavy lift launch system like the Saturn V. To mitigate this, the use of an orbital propellant depot has been extensively studied. In this paper, a thermal model of an orbital propellant depot is used to examine the effects of passive and active thermal management strategies. Results show that an all passive thermal management strategy results in significant boil-off for both hydrogen and oxygen. At current launch vehicle prices, these boil-offs equate to millions of dollars lost per month. Zero boil-off of propellant is achievable with the use of active cryocoolers; however, the cooling power required to produce zero-boil-off is an order of magnitude higher than current state-of-the-art cryocoolers. This study shows a zero-boil-off cryocooler minimum power requirement of 80–100W at 80K for liquid oxygen, and 100–120W at 20K for liquid hydrogen for a representative Near-Earth Object mission. Research and development effort is required to improve the state-of-the-arts in-space cryogenic thermal management.

Cryogenic Boil-Off Reduction System

A computational model of the cryogenic boil-off reduction system being developed by NASA as part of the Cryogenic Propellant Storage and Transfer technology maturation project has been applied to a range of propellant storage tanks sizes for high-performing in-space cryogenic propulsion applications. This effort focuses on the scaling of multi-layer insulation (MLI), cryocoolers, broad area cooling shields, radiators, solar arrays, and tanks for liquid hydrogen propellant storage tanks ranging from 2 to 10m in diameter. Component scaling equations were incorporated into the Cryogenic Analysis Tool, a spreadsheet-based tool used to perform system-level parametric studies. The primary addition to the evolution of this updated tool is the integration of a scaling method for reverse turbo-Brayton cycle cryocoolers, as well as the development and inclusion of Self-Supporting Multi-Layer Insulation. Mass, power, and sizing relationships are traded parametrically to establish the appropriate loiter period beyond which this boil-off reduction system application reduces mass. The projected benefit compares passive thermal control to active thermal control, where active thermal control is evaluated for reduced boil-off with a 90K shield, zero boil-off with a single heat interception stage at the tank wall, and zero boil-off with a second interception stage at a 90K shield. Parametric studies show a benefit over passive storage at loiter durations under one month, in addition to showing a benefit for two-stage zero boil-off in terms of reducing power and mass as compared to single stage zero boil-off. Furthermore, active cooling reduces the effect of varied multi-layer insulation performance, which, historically, has been shown to be significant.

Systems Design, Fabrication, and Testing of a High‐Speed Miniature Motor for Cryogenic Cooler

The long‐term storage of liquid hydrogen for space missions is of considerable interest to NASA. To this end, the Reverse Turbo‐Brayton Cryocooler (RTBC) is considerably lighter than conventional designs and a potentially viable and attractive solution for NASA′s long‐term Zero‐Boil‐off (ZBO) hydrogen storage system for future space missions. We present the systems design, fabrication, and performance evaluation of the Permanent Magnet Synchronous Motor (PMSM) powering a cryocooler capable of removing 20 W of heat at 18 K with a COP of 0.005 and driven by two 2‐kW permanent magnet synchronous motors operating at 200 000 rpm and at room temperature and 77 K. Structural, thermal, and rotordynamic aspects of system design are considered.

An overview of NASA efforts on zero boiloff storage of cryogenic propellants

Extended cryogenic propellant storage periods have become increasingly important within NASA. Furthermore, cryocooler and passive insulation technology advances have substantially improved the prospects for zero boiloff (ZBO) storage of cryogenics. Accordingly, a cooperative effort by NASA's Ames Research Center, Glenn Research Center, and Marshall Space Flight Center has been implemented to develop ZBO concepts for in-space storage of cryogenic propellants. Accomplishments include analytical modeling; an early subscale liquid hydrogen (LH 2) demonstration; a flight-like 10 W, 95 K pulse tube cryocooler; and assembly of a large-scale test article for an LH 2 system-level demonstration. Future testing with flight-like cryocoolers is planned.