Multilayer Insulation Material Research Articles

Numerical Study on Composite Multilayer Insulation Material for Liquid Hydrogen Storage

This study investigated the heat transfer characteristics of composite multilayer insulation (MLI) materials used for the storage and transport of liquid hydrogen at cryogenic temperatures. This research focused on analyzing the effects of thermal boundary temperature, total layer count, and vacuum level on the heat flux through the insulation material. Based on the layer-by-layer model, a heat transfer model of composite MLI was constructed. This research introduces a novel method for analyzing the heat transfer properties of composite MLI in the liquid hydrogen temperature range. Results indicate that heat flux increases with higher thermal boundary temperatures, with the MLI layers near the cold boundary playing a critical role in overall insulation performance. Additionally, numerical analysis was conducted to examine the impact of different material combinations and variations in vacuum level on heat transfer characteristics. Findings reveal that adding spray-on foam insulation reduces heat flux by 20.76% compared to using MLI alone. Furthermore, increasing the total number of MLI layers effectively mitigates heat flux increase, achieving an optimal heat flux of 0.5377 W/m2 with a total of 50 layers.

Harmonizing lightweight and ablation resistance: Design and performance of multilayer composite insulation materials for solid rocket motors

AbstractThe realization of lightweight insulation materials is often accompanied by a decrease in ablation performance. Coordinating the contradiction between lightweight and ablation resistance is the key to the development of thermal protection technology. Addressing the need for high‐performance insulation materials within solid rocket motors (SRMs) combustion chambers, we designed three multilayer composite structural insulation materials and studied their properties. The results show that among these constructed multilayer composites, the bilayer structure exhibited the lowest density at a mere 0.72 g/cm3, marking a 27% reduction compared to the basic structure. Remarkably, the bilayer configuration demonstrated superior ablation resistance, showcasing a 25% decrease in the line ablation rate in contrast to the basic structure after oxygen‐acetylene test. This achievement embodies the successful harmonization of lightweight properties with ablation resistance. Furthermore, based on the performance and microstructure of the char layer, a further analysis revealed the enhancement mechanism of ablative performance by the multilayer composite structure. It was found that the synergistic effect of the compact/porous structure of the char layer grants the bilayer structure thermal insulation material optimal ablative performance. This work provides strong support for improving the performance of SRMs.Highlights Insulation materials with multilayer composite structures are designed. The materials exhibit both lightweight and superior ablation resistance. Compact/porous char layers enhance material ablation performance.

Modeling the performance of multilayer insulation in cryogenic tanks undergoing external fire scenarios

Multilayer Insulation (MLI) is frequently used in vacuum conditions for the thermal insulation of cryogenic storage tanks. The severe consequences of the degradation of such materials in engulfing fire scenarios were recently evidenced by several large-scale experimental tests. In the present study, an innovative modelling approach was developed to assess the performance of heat transfer in polyester-based MLI materials for cryogenic applications under fire conditions. A specific layer-by-layer approach was integrated with an apparent kinetic thermal degradation model based on thermogravimetric analysis results. The modeling results provided a realistic simulation of the experimental data obtained by High-Temperature Thermal Vacuum Chamber tests reproducing fire exposure conditions. The model was then applied to assess the behavior of MLI systems for liquid hydrogen tanks in realistic fire scenarios. The results show that in intense fire scenarios degradation occurs rapidly, compromising the thermal insulation performances of the system within a few minutes.

SFSNet: An Inherent Feature Segmentation Method for Ground Testing of Spacecraft

In the final approach stage of rendezvous and docking of a spacecraft, the pose parameters of the target spacecraft need to meet docking or berthing capture conditions. Visible light visual measurement systems are increasingly employed in spacecraft ground tests to extract the geometric features of spacecraft to calculate and verify the accuracy of pose parameters. Most current feature-segmentation algorithms are unable to break through the scale transformation problem of spacecraft movement and the noise interference of multi-layer insulation materials in imaging. To overcome these challenges, we propose a novel feature segmentation algorithm based on the framework of deep convolutional neural networks. Firstly, a full convolution model of the encoding-decoding structure is constructed based on data for the ground test. A feature concatenation module is applied and combined with a network backbone to improve the segmentation performance. Then, a comprehensive loss function is presented and optimized by the pose characteristics of the spacecraft in the approach phase. Furthermore, a specific spacecraft simulation dataset to train and test our segmentation model is built through data augmentation. The experimental results verify that the proposed method achieves accurate segmentation of spacecraft of different scales, suppresses the interference caused by multilayer insulation material, and has strong robustness against motion ambiguity. The pixel accuracy of our proposed method reaches 96.5%, and the mean intersection over union is 93.0%.

Solar Absorptivity Degradation of Spacecraft Materials Due to UV and Charged Particles in the Gateway Environment

Gateway will be an outpost in cislunar space designed to survive a 15-year mission to support human Moon landings and future deep space exploration. The Gateway Passive Thermal Control System (PTCS) Group has identified charged particle and UV degradation of potential Gateway materials as a knowledge gap for the Near Rectilinear Halo Orbit (NRHO) and transit environment, especially the slow spiral transit planned for the first two modules. Solar absorptivity degradation is important to quantify because the end-of-life absorptivity impacts thermal performance of the system. To address this, ground testing has been completed at NASA Goddard Space Flight Center in which potential Gateway materials, including radiators, multi-layer insulation (MLI), and structural materials are subjected to the expected transit plus 15-year on-orbit charged particle fluence (9.86x1015 protons/cm2 at 2.5 keV and 3.1x1016 electrons/cm2 at 10 keV) and 5093 Equivalent Solar Hours (ESH). Reflectivity of a single sample of each material was measured in atmosphere and in vacuum inside the chamber after exposure to incremental levels of ESH and charged particle fluence. Increase in absorptivity of most samples were seen throughout the test including large differences in absorptivity of materials of the same category. Future planned testing will validate these results and include additional materials of interest.

EXPERIMENTAL STUDY ON THE FACTORS AFFECTING THE INSULATION PERFORMANCE OF FLAME-RETARDANT MULTILAYER INSULATION MATERIALS

Flame-retardant multilayer insulation materials act as effective thermal insulation blankets of cryogenic containers that store flammable and explosive cryogenic liquids. This study used standard static liquid nitrogen boil-off calorimetry to test the insulation performance of eight groups of flame-retardant multilayer insulation materials with different wrapping parameters. The effects of four factors, namely the layer density, seaming process, number of reflector layer, and variable-density multilayer insulation arrangement, on the insulation performance were analysed. Three layer densities were considered: 4.47, 3.08, and 2.50 layers/mm. Two types of seaming processes were discussed: the overlapped and fold-over seaming processes. Three numbers of reflector layers were considered: 60, 70, and 80. Two variable-density multilayer insulation arrangements with similar thicknesses were discussed: 10-10-40 and 20-20-20 layers of reflectors allocated for low-, medium- and high-density segments. The conclusions are as follows: Decreasing the layer density enhances the performance of multilayer insulation; Using the fold-over seaming process results in less heat flux and lower apparent thermal conductivity; An increase in the number of reflector layers weakens radiative heat transfer, resulting in better thermal insulation; Furthermore, for a given wrapping thickness, reducing the number of reflectors appropriately in low- and medium-density segments improves the insulation performance; Optimizing and controlling the layer density of each density segment are also essential for variable-density multilayer insulation effects. This study provides supporting theories and reference data for practical engineering applications.

Mussel-inspired design of a catechol-polydimethyl siloxane covalent hybrid polymer for atomic oxygen resistant coating application

Design of materials embodying the adhesive and cohesive nature of mussel byssal protein mimics have long served to inspire material developers in uncommon areas. Herein, a Catechol-Polydimethyl Siloxane Covalent Hybrid polymer (PGDX) derived from mussel chemistry is demonstrated as a highly effective atomic oxygen resistance (AOR) coating/adhesive, a yet unreported activity. The rational design of PGDX through a greener route is derived from poly dimethyl siloxane diglycidyl ether (PG) and dopamine (D). PGDX coating achieved excellent AOR on commonly used aluminised polyimide (AI-PI) and polyimide (PI) multilayer insulation materials for satellites as exposure to AO fluence of 2.5 × 1020 atom/cm2 resulted in 47 % and 71 % reduction in mass-loss rate for AI-PI and PI respectively. The hybrid morphology of the polymer enabled its solubility in solvents having different polarities thus widening the scope of coating perspectives of dopamine. The coated substrates possessed lower surface energy (PI/Al-PI, 23.6/24.8 mN/m) than their uncoated counterparts (Al-PI/PI, 29.60/34.4 mN/m) and lower work of adhesion that denoted the hydrophobicity of the coating owing to the siloxane segment. The modified PDMS backbone with mussel chemistry show potential for application as a coating and adhesive for protecting delicate satellite components from the highly degrading AO rich Low Earth Orbit (LEO) environment.

Numerical simulation and experimental investigation of the thermal insulation performance of multi-layer insulation material at 20-298 K

Thermal insulation plays a major role in the use of cryogenic systems. Due to its superior thermal insulation property, Multi-layer insulation materials (MLI) are widely used in various cryogenic systems, such as superconducting magnets, space propellant storage, satellites and so on. Thus, it is crucial to estimate and measure the insulation performance of it. This paper has carried out a numerical simulation of the performance of one kind of MLI through a modified Layer-by-Layer model. The thermal insulation propriety of the test specimen is also measured by a newly designed measurement system, which is based on the steady-state axial heat flux method. Finally, the simulation and test results are compared and discussed.

Analysis of the factors influencing the precooling process of cryogenic compressed hydrogen storage tank

Cryogenic compressed hydrogen has attracted much attention recently. Its volume and weight hydrogen storage density are relatively high, which can meet the long-distance driving demand of hydrogen fuel cell vehicles. It is considered as a very promising physical storage method. In the process of transportation, the precooling process of cryogenic compressed hydrogen storage tank is very important. It is necessary to establish a reasonable mathematical model, analyse the precooling process of the storage tank theoretically, and use the hydrodynamics software for numerical simulation to analyse the influencing factors of the precooling process. On the basis of theoretical analysis, this paper uses ANSYS FLUENT software to simulate the precooling process of intake pipe length, intake pipe diameter, length diameter ratio of storage tank, insulation performance of high vacuum multilayer insulation material, lining material, initial temperature of storage tank and hydrogen filling rate. By comparing the distribution of internal temperature field and enclosure temperature field as well as precooling time, the design suggestions of Cryogenic compressed hydrogen storage tank and hydrogenation suggestions are given.

Studying Breakdown and Electrical Hardening of Crystal Materials with Proton Conductivity

The breakdown mechanism of a number of crystal materials with hydrogen bonds is investigated. The contribution of the proton component is considered and it is shown that the formation of an avalanche-streamer discharge is characteristic of multilayer electrical insulation materials. As a result of the breakdown, a discharge channel is formed, along which the protons that form the reverse proton conductivity will move in the opposite direction. In the process of directed translational diffusion of protons, the formation and decay of H3O+ and OH-ions occur, which move in opposite directions, resulting in the formation of a reverse positive streamer from the anode to the cathode. For layered samples of phlogopite, muscovite, and magnesium hydrosilicate, it is shown that for thin samples, a volume charge is formed as a result of a multi-avalanche-streamer discharge that significantly exceeds the volume charge that occurs in thick samples, which is determined by the value of high temperature maximum of the spectrum of thermally stimulated depolarization currents. The field of the volume charge reduces the external electric field, as a result of which the breakdown field strength in thin samples increases. That is, the material is electrically strengthened. Based on the results of the research, a non-destructive method of electrical hardening of electrical insulation materials was developed, which was confirmed by the patent.

Characterization and monitoring of vacuum pressure of tank containers with multilayer insulation for cryogenic clean fuels storage and transportation

Liquid natural gas and liquid hydrogen are promising and economical clean energy sources for reducing CO2 emissions and slowing global warming. Characterization and monitoring of the vacuum pressure inside tank containers with multilayer insulation (MLI) are essential for the safe storage and convenient transportation of these cryogenic fuels. Herein, a new method for characterizing the vacuum pressure of tank containers with MLI is proposed. A theoretical analysis revealed that the temperature of the outer surface of the MLI material (To) is a good indicator of the vacuum pressure inside the tanks. Experimental verification was conducted using an MLI performance-testing apparatus, To was measured under 10 different vacuum pressures. The results showed that when the vacuum pressure was <10-1 Pa, To kept almost. However, when the vacuum pressure was >1 Pa, To decreased sharply with the increase of vacuum pressure.The mechanism of the proposed method was also discussed based on the thermal analysis of the experimental system at different vacuum pressures. This study provides a simple and reliable method for vacuum pressure monitoring of tank containers with MLI, which allows the large-scale and safe utilization of clean energy with a low boiling temperature.

Performance improvement of a pulse tube cryocooler with a single compressor through cascade utilization of cold energy

The high-frequency pulse tube cryocooler (HPTC) has been attracting increasing and widespread attention in the field of cryogenic technology because of its compact structure, low vibration, and reliable operation. The gas-coupled HPTC, driven by a single compressor, is currently the simplest and most compact structure. For HPTCs operating below 20 K, in order to obtain the mW cooling capacity, hundreds or even thousands of watts of electrical power are consumed, where radiation heat leakage accounts for a large proportion of their cooling capacity. In this paper, based on SAGE10, a HPTC heat radiation calculation model was first established to study the effects of radiation heat leakage on apparent performance parameters (such as temperature and cooling capacity), and internal parameters (such as enthalpy flow and gas distribution) of the gas-coupled HPTC. An active thermal insulation method of cascade utilization of the cold energy of the system was proposed for the gas-coupled HPTC. Numerical simulations indicate that the reduction of external radiation heat leakage cannot only directly increase the net cooling power, but also decrease the internal gross losses and increase the mass and acoustic power in the lower-temperature section, which further enhances the refrigeration performance. The numerical calculation results were verified by experiments, and the test results showed that the no-load temperature of the developed cryocooler prototype decreased from 15.1 K to 6.4 K, and the relative Carnot efficiency at 15.5 K increased from 0.029% to 0.996% when substituting the proposed active method for the traditional passive method with multi-layer thermal insulation materials.

Numerical simulation and optimization of heat-insulation material and structure for CFB boiler

Performance of different thermal insulator structures for CFB boilers was studied in this work. Taking a 220-t/h CFB boiler as the research object, physical models of the furnace wall, cyclone separator wall and tail flue wall were established. The outer wall temperature for different design schemes was calculated, and the adiabatic properties of some materials were verified experimentally. It is found that the thermal-insulation property for the monolayer material is, in increasing order, PSC, ASFF, and RWIF. The adiabatic effect of the furnace wall multi-layer insulation material depends on the weighted-average thermal conductivity. If RWIF is used as heat-insulation material of furnace wall, the thickness could be less than 110 mm. If PSC or combined material is selected, their thickness should exceed 130 mm. The isotherm for the cylinder and cone of the cyclone separator is a cluster of concentric circles with a uniform distribution. A lower thermal conductivity yields a denser isotherm. For a three-layer material insulation structure, the second layer plays a decisive role in the thermal-insulation property. For tail flue, the insulation effect of the outermost insulation material is most obvious. The temperature field is evenly distributed, and the distribution tightness is related to the thermal conductivity of the material used. A combination of RFB, AIT, and ORB could be selected if the flue-wall thickness needs to be reduced. An optimal heat-insulation point exists for each material, at which the insulation efficiency reaches an extreme value. Various insulation materials could be combined based on the insulation efficiency.

Thermal performance assessment of cryogenic transfer line with support and multilayer insulation for cryogenic fluid

Cryogenic transfer lines are very important to transport cryogenic fluid in the fields of fusion energy and hydrogen energy. The main aim of this work is to assess and minimize heat leakage of cryogenic transfer line. A three-channel coaxial liquid helium pipe with three support structures and typical multilayer insulation (MLI) materials was designed. Cryogenic transfer lines installed three support structures and MLI with different layer density & number of layer were studied based on a horizontal cryogenic transfer line test platform with liquid nitrogen. Thermal performance including heat leakage and temperature distribution of straight and elbow pipe have been numerically and experimentally analyzed for boundary temperature 77 K–293 K. By comparing simulated results with experimental heat leakages of supports, MLI and cryogenic transfer lines, the largest deviations are less than 10%, 10.7% and 6.6%, respectively. Based on above analysis, the minimal heat leakages of two-plate support and MLI with 50 layers and 25 layers/cm are 0.200 W and 0.488 W, respectively. Furthermore, the minimal heat leakages of straight pipe and elbow pipe were acquired as the values of 0.688 W and 0.858 W with two-plate support and MLI under 50 layers and 25 layers/cm. The results have been successfully applied in 250 W@4.5 K helium cryogenic refrigerator. The new and useful assessment method could also be applied to minimize heat leakage of cryogenic transfer lines with different size, support and MLI, etc, and then to improve the energy efficiency of system.

Design of a multi-layer insulation(MLI) measurement system with a G-M cryocooler

Multi-layer insulation (MLI) is widely used in cryogenic systems such as Aerospace propulsion systems and various cryostats. The effective thermal conductivity of MLI used in lab is measured by typical systems using bath cryostat, which is only able to maintain boundary temperatures at critical point of cryogen. A liquid cryogen-free apparatus based on a two stage G-M cryocooler has been developed to measure the effective thermal conductivity of multi-layer insulation(MLI) materials at temperatures ranging from 20-300 K. Unlike traditional measurement systems utilizing evaporation rate of liquid cryogen, a calorimeter supported by a calibrated rod is installed in this system to determine the heat flow through the testing blanket. This design eliminates the error caused by variation of environment pressure to the measured evaporation rate, and meanwhile, simplifies the system structure.

Pose Estimation of Non-Cooperative Target Coated With MLI

The relative pose estimation between the chaser and the non-cooperative target is a significant prerequisite for performing on-orbit servicing (OOS) missions. The chaser could design the close-range rendezvous trajectory to approach the non-cooperative target only when the relative pose parameters are obtained effectively and efficiently. In this paper, a pose estimation scheme is designed to obtain the relative pose parameters between the chaser and the non-cooperative target coated with multilayer insulation material (MLI). The scheme utilizes a time-of-flight (TOF) camera to acquire 3D point clouds of the non-cooperative target, and uses the iterative closest point (ICP) method to achieve the point cloud registration between every two frames. Aiming at decreasing the non-systematic errors caused by MLI in the data acquisition of the TOF camera, the corresponding point median filtering approach is adopted to filter out the bad corresponding point pairs generated in the ICP method. A semi-physical experiment is carried out to evaluate the performance of the proposed scheme, the result of which shows that the proposed scheme could notably improve the accuracy of pose estimation of the non-cooperative target, meanwhile the computational efficiency is also ensured.

Investigation for heat transfer mechanisms in multi-layer insulation materials

Investigation for heat transfer mechanisms in multi-layer insulation materials

Flexible, controllable, and high-strength near-infrared reflective Y2O3 nanofiber membrane by electrospinning a polyacetylacetone‑yttrium precursor

High-quality reflective screens constitute an important part of multi-layer insulation materials. However, the metal foils currently used as thermal reflective screens are easily oxidized in an oxidizing environment. Nanoscale yttrium oxide exhibits high reflectivity in the near-infrared (NIR) region, as well as excellent stability in an oxidizing environment. The material also shows potential for application as a high-temperature reflective screen. A high near-infrared reflective Y2O3 nanofiber membrane was successfully prepared by electrospinning a synthetic polyacetylacetone‑yttrium (PAY) precursor into precursor fibers, followed by heat treatment. The new polyorganometallic precursor PAY with 42% Y2O3 content was synthesized by adjusting the ratio of acetylacetone to YCl3·6H2O. The crystallization, microstructure and NIR reflectivity of the Y2O3 nanofiber membrane were analyzed. The tensile strength of the Y2O3 nanofiber membrane was evaluated. The strength of the Y2O3 nanofiber membrane with good flexibility, prefect morphology and high crystallinity could reach 1.6 MPa, and its NIR reflectivity could reach 95%. High-temperature heat-reflective testing shows that the Y2O3 nanofiber membrane exerts a reflective effect on thermal radiation at 1500 °C. It could be continuously used as a reflective screen for high-temperature insulation materials in a high-temperature oxidizing environment.

Simulation Analysis of Outboard Gas Status for Spacecraft Gas Leakage In-Orbit

Due to high vacuum environment of spacecraft orbiting and complex external surface structure of spacecraft cabin, outboard leak detection of spacecraft in-orbit cannot directly adopt existing mature technology. In this article, outboard gas status of spacecraft leakage in-orbit is simulated through computational mechanics and Monte Carlo simulation methods. The simulation results show that complex external surface structure of spacecraft cabin, especially external thermal control layers composed of multilayer insulation material, obviously blocks leakage gas into astrospace and reduces detection sensitivity of outboard leak detection methods. This simulation process and results can provide analyze method and theoretical data for detection scheme design and testing instrument selection of outboard leak detection in the future.

Preparation and properties of the multi-layer aerogel thermal insulation composites

Multi-layer insulation materials possess low radiation thermal conductivity, and excellent thermal insulation property in a vacuum environment. However, the spacers of the traditional multi-layer insulation materials are mostly loose fibers, which lead to more sensitive to the vacuum environmental of serviced. With the vacuum degree declining, gas phases thermal convection increase obviously, and the reflective screen will be severe oxidation, all of these make the thermal insulation property of traditional multi-layer insulation deteriorate, thus limits its application scope. In this paper, traditional multi-layer insulation material is combined with aerogel and obtain a new multi-layer aerogel thermal insulation composite, and the effects of the number, thickness and type of the reflective screens on the thermal insulation properties of the multi-layer composites are also studied. The result is that the thermal insulation property of the new type multi-layer aerogel composites is better than the pure aerogel composites and the traditional multi-layer insulation composites. When the 0.01 mm stainless steel foil as the reflective screen, and the aluminum silicate fiber and silica aerogel as the spacer layer, the layer density of composite with the best thermal insulation property is one layer per millimeter at 1000 °C.