Multilayer Insulation Research Articles

Feasibility analysis of a new thermal insulation concept of cryogenic fuel tanks for hydrogen fuel cell powered commercial aircraft

Of cryogenic liquid hydrogen tanks for future airliners, their volumetric and gravimetric efficiencies, their robustness and their environmental adaptability are all strengthened via a novel thermal insulation concept proposed in this work.A conventional cryogenic tank is insulated either purely by a layer/layers of Polyurethane (PU) foam or by a vacuum-based multilayer insulation (MLI). In the new concept, an extra layer is inserted into the PU foam. The intermediate layer can be filled with liquid nitrogen while on the ground or with ambient air during flight.By this new design, analysis shows an approximate 33% volumetric saving compared to PU insulation. Furthermore, a 6-fold amount of passive heat input during cruise flight is easily achieved compared to the rest two concepts. This showcases an increased robustness against possible failure of the tank's active heating system, and the potential for significant parasitic power loss reduction.

An Improved Design Procedure for a 10 kHz, 10 kW Medium-Frequency Transformer Considering Insulation Breakdown Strength and Structure Optimization

Medium-frequency transformer (MFT) is an essential device in the smart solid-state transformer (SST) prototype. Compared with the well-defined principle design of magnetic core and windings in MFT, insulation issues are barely concerned. This article focuses on improved design optimization of an MFT, considering the main insulation strength and structure. Dielectric breakdown characteristics of epoxy resin insulating material were studied. An obvious reduction of dielectric strength occurred at high frequency and high temperature in thick samples, which is used for the design of insulation clearance and margin. Moreover, a modified insulation loss evaluation was used, involving the square wave with spike voltages. Through introducing a strategy of multilayered insulation in the windings, the insulation structure is optimized. A 10-kW, 10-kHz, 1-kV/750-V MFT used in the 10-kV SST system was designed by considering the insulation research. Finally, experimental verifications of the MFT performance were carried out by a resonant dc–dc converter. It appears that the optimized MFT exhibits low electric field, small temperature rise, and high efficiency at a 10-kW load. This research provides the basic principles for insulation design in high-voltage and high-power MFT.

Performance of high-temperature lightweight multilayer insulations

Multilayer insulation (MLI) is a kind of high-temperature insulation which employs multiple high-reflective screens to retard the radiation heat, but analyzing and optimizing its heat transfer characteristics by experimental and theoretical models remains low-efficiency and non-visualization. In this work, finite element analysis (FEA) models verified by comparing the simulation and experiment results are established to systematically reveal the numerous and complex effect factors, including the number of layers, thermal boundary, fibrous insulation density and emissivity of reflective screens. The results show that the top temperature of MLIs can be reduced by increasing the number and the emissivity of reflective screens, and the density of fibrous insulation, but there is a reasonable number of layers to achieve the best comprehensive performance of MLI. In addition, the proportion of radiative heat transfer in the total heat transfer increases with increasing heating temperature. The feasibility of optimizing thermal insulation performance based on the FEA models is confirmed by designing the MLIs with stainless steel and aluminum as reflective screens. And the results indicate that the FEA methods can significantly reduce the number of trials and realize the optimal design of MLI.

Thermal Characteristic of Novel Insulation Materials Designed for Solar Simulator

The solar simulator is an important device for simulating solar irradiation in cold black and vacuum environments and has a wide range of application prospects. In this work, a method of thermal conductivity measurement by a double specimen protection thermal plate method under vacuum conditions was proposed, and the thermal conductivity of a new thermal insulation material under a cryogenic vacuum environment was studied. By designing a vacuum adjustment device and a multi-layer insulation structure with a low outgassing rate, it is possible to adjust the vacuum pressure from 10−4 Pa to atmospheric. A temperature control and thermal conductivity test can be realized from −160 °C to 280 °C by the joint temperature control of liquid nitrogen cooling and electric heating. Then, the measurement accuracy of the device was checked by the national standard sample, the thermal conductivity of the sample was measured under different vacuum and temperature conditions, the uncertainty analysis of the device was given, and, finally, the thermal conductivity of the new material was tested.

Design and test of vacuum system for 40 T hybrid magnet superconducting outsert of China

The vacuum system for 40 T hybrid magnet superconducting outsert in the Chinese High Magnetic Field Laboratory has been successfully designed, fabricated, installed, and tested. The vacuum system has achieved stable operation after several rounds of optimization. The influence of the pressure and strong magnetic field on the long-term stable operation of the 40T hybrid superconducting outsert was investigated. In the process of structural verification of the vacuum system, the stress distribution of the vacuum system under the influence of assembly, cooling, and quench is analyzed, and the correctness of the analysis results is verified by the theoretical calculation results of circumferential stress. On this basis, the membrane stress, bending stress, and secondary stress were calculated, and the safety of a large vacuum chamber is evaluated by using ASME international vacuum standard code. According to the outgassing test data of the multilayer insulation under real working conditions, the pumping calculation formula was fitted for outgassing rate estimation. The results show that the vacuum system was pumped down from the atmospheric pressure to 5.0 × 10−3 Pa in approximately 72 h and that it worked stably for a fairly long time, affected little by the strong background magnetic field.

Review of the Liquid Hydrogen Storage Tank and Insulation System for the High-Power Locomotive

Hydrogen has been attracting attention as a fuel in the transportation sector to achieve carbon neutrality. Hydrogen storage in liquid form is preferred in locomotives, ships, drones, and aircraft, because these require high power but have limited space. However, liquid hydrogen must be in a cryogenic state, wherein thermal insulation is a core problem. Inner materials, including glass bubbles, multi-layer insulation (MLI), high vacuum, and vapor-cooled shields, are used for thermal insulation. An analytic study is preferred and proceeds liquid hydrogen tanks due to safety regulations in each country. This study reviewed the relevant literature for thermodynamic modeling. The literature was divided into static, dynamic, and systematic studies. In summary, the authors summarized the following future research needs: The optimal design of the structure, including suspension, baffle, and insulation system, can be studied to minimize the boil-off gas (BOG). A dynamic study of the pressure, mass flow, and vaporizer can be completed. The change of the components arrangement from the conventional diesel–electric locomotive is necessary.

Theoretical and experimental study on a compound insulation system for high temperature applications

• Designed a test setup for determining high temperature thermal performance of CFMLI. • Measured the temperature profile and effective thermal conductivity of CFMLI at 800–1325 K. • Discussed CFMLI thermal performance with gas pressure, spacing materials and foil numbers. • Validated the accuracy of experimental data by comparison with theoretical predictions. High temperature thermal insulation performance plays a crucial role in the application of thermal contact resistance precision measurement to reduce systematic heat loss and ensure 1D axial heat flow. In this paper, a compound insulation system composed of carbon fibrous materials and multilayer insulation (CFMLI) with non-interlayer-contact space was proposed in terms of high temperature sustainability, low thermal conductivity and thermal performance stability. An experimental set-up was designed and fabricated to measure the temperature distribution and the effective thermal conductivity of CFMLI as a function of temperature (800 K−1325 K). The experimental results showed that the temperature gradually decreases from inner to external radius of CFMLI, and a temperature jump of 40 K−80 K appears at the interface between two segments under vacuum conditions. It also reveals that the thermal performance of CFMLI is strongly dependent on the gas pressure and the number of reflective layers, while it is hardly affected by the filling materials when the temperature is above 1050 K. Meanwhile, the effective thermal conductivity of CFMLI varies around 0.2 W/m/K for two levels of pressure (10 -4 Pa and 0.1 MPa), and it decreases by 14.7% when the number of reflective layers increases from 6 to 21 at 1325 K. Additionally, a theoretical model with thermal resistance network was developed for heat transfer analysis of CFMLI. The model could predict the external temperature of CFMLI with high accuracy so that the difference between the theoretical results and experimental data was less than 2.61%.

Multilayer 2D insulator shows promise for post-silicon electronics

Multilayer 2D insulator shows promise for post-silicon electronics

Space Charge Behavior of Thermally Aged Polyethylene Insulation of Track Cables.

The interface of multi-layer insulation is a relatively weak point in the cable system during the long-term high-temperature service. Space charge is prone to continuously accumulate in the interface area, leading to the deterioration of electrical properties and even insulation failure in advance. The knowledge about thermal oxidation of polyethylene (PE) materials at the molecular level is still urgent to explore. Herein, single-layer and double-layer PE insulation, representing the typical insulation structure of frequency-shift pulse voltage track cables, were prepared and thermally aged in the oven for up to 360 h. Thermal, mechanical, electrical, and space charge characterizations were systematically carried out. Thermogravimetric analyzer and oxidation induced temperature (OIT) measurements confirmed that LDPE’s thermal-oxidative aging temperature range was the lowest among the three PE groups in the O2 atmosphere. After 360 h thermal aging, the tensile property of HDPE material kept relatively stable, while the elongation at break of the other two groups was lower than 50%. Unaged HDPE exhibits apparent charge injection and migration, leading to the severe electric field distortion of 20%. Noticeable charge accumulation can be observed at the unaged double-layer sample interface due to the mismatching of DC conductivity, which play a significant role in the aged double-layer samples. This work utilizes precise thermal analysis to provide new information about the resistance ability of thermal oxidation of LDPE, FPE, and HDPE, and its influence on space charge behaviors, which is helpful for the insulation design and evaluation in cable applications.

Cooling system optimization of cryogenic propellant storage on lunar surface

A cooling system using a cryocooler and boil-off gas was proposed for cryogenic propellant storage on the lunar surface. The cryogenic tank was covered with an advanced non-interlayer-contact multi-layer-insulation and coolant from the cryocooler and boil-off gas flow in the layers to remove the heat load. The proposed system included optimization factors for fluid tubes location, cryocooler temperature, and flow rate. A simple uniform-temperature thermal model was developed to optimize boil-off rates and system weights, and the results revealed a Pareto front. A three-dimensional model was developed to discuss the effect of temperature nonuniformity. Finally, the proposed concept was compared to other candidates. The results showed that the proposed system offered a well-balanced system in terms of boil-off rate, system mass, and electric power consumption, which drastically reduced the boil-off rate when compared to only multi-layer insulations, which reduced the weight and power consumptions as compared to zero-boil-off systems.

Symmetric Mass Generation in the 1+1 Dimensional Chiral Fermion 3-4-5-0 Model.

Lattice regularization of chiral fermions has been a long-standing problem in physics. In this Letter, we present the density matrix renormalization group simulation of the 3-4-5-0 model of (1+1)D chiral fermions with an anomaly-free chiral U(1) symmetry, which contains two left-moving and two right-moving fermions carrying U(1) charges 3,4 and 5,0, respectively. Following the Wang-Wen chiral fermion model, we realize the chiral fermions and their mirror partners on the opposite boundaries of a thin strip of (2+1)D lattice model of multilayer Chern insulator, whose finite width implies the quantum system is effectively (1+1)D. By introducing two sets of carefully designed six-fermion local interactions to the mirror sector only, we demonstrate that the mirror fermions can be gapped out by the interaction beyond a critical strength without breaking the chiral U(1) symmetry, via the symmetric mass generation mechanism. We show that the interaction-driven gapping transition is in the Berezinskii-Kosterlitz-Thouless universality class. We determine the evolution of Luttinger parameters before the transition, which confirms that the transition happens exactly at the point when the interaction term becomes marginal. As the mirror sector is gapped after the transition, we check that the fermions in the light chiral fermion sector remain gapless, which provides the desired lattice regularization of chiral fermions.

Experimental and numerical investigation of self-pressurization with different methods of insulation for ground and space applications

The necessity of precise estimation and understanding of self-pressurization in a cryogenic storage vessel has increased rapidly over the years because of the influence of self-pressurization phenomena on the design of cryogenic engines. Since propellants are stored at their boiling temperature or subcooled condition, very small heat infiltration itself causes self-pressurization. When heat is transferred to the propellant tank, the liquid near the sidewall is heated up, and a warm stratified layer is developed at the liquid vapor interface, which causes self-pressurization. A numerical model is developed, and experiments are conducted to investigate the self-pressurization effects of cryogenic storage vessels to precisely understand the mechanisms causing it and the effect of methods of insulations, including multi-layer insulations in tanks. The numerical model is developed based on the available correlation to predict the self-pressurization and related parameters of a double wall cryogenic storage tank with different sets of insulations such as air, foam, vacuum, and MLI and different cryogens; hydrogen, nitrogen, and oxygen. A double wall cryogenic storage tank using SS 304 is also developed, conducted self-pressurization studies using liquid nitrogen under different methods of insulation. The experimental results were compared with the numerical model and found in good agreement. Comparing the self-pressurization rate of different cryogens, the value is higher for hydrogen. Since the boiling point of hydrogen is less, the axial heat flux acting will be higher. The low-density fluids will quickly move towards the interface and deposit, causing a warm layer at the liquid-vapour interface. The amount of phase change is also higher for liquid hydrogen, which in turn aid in rapid self-pressurization. Among the insulations used, multi-layer insulation shows the best performance in terms of thermal resistance. The analytical and heat transfer model developed predicts and compared well with the experimental results and can be used for a variety of situations in ground and space for self-pressurization and roll over phenomenon studies and prediction of results in advance.

Results of use of heat flux sensors on liquid hydrogen tanks

Heat flux sensors were used to characterize the performance of insulation on the Structural Heat Intercept, Insulation, and Vibration Evaluation Rig (SHIIVER), a large-scale test article designed to simulate upper stage cryogenic propellant tank thermal performance in simulated space environments. Usually, the insulation heat loads are derived from calculations removing all other heat sources and attributing the residual heat load to the insulation system. Testing for SHIIVER included the tank being just insulated with spray-on-foam insulation as well as covering the domes with multilayer insulation while leaving the barrel section insulated with spray-on-foam. Heat flux sensors were located at multiple locations on both domes as well as on the barrel section of the tank. Results from the SHIIVER testing using the heat flux sensors are compared to other calculated heat inputs for both liquid nitrogen and liquid hydrogen testing as a function of tank fill level. Further investigation into the transient nature of the SHIIVER testing including the heat flux sensors provided insight into heat flow patterns that may not have been otherwise seen using temperature sensors and calculated insulation heat loads. While the demonstrated uncertainties in the absolute values in the heat flux sensors are high, the values and the trends match well with other calculation methods. The results of SHIIVER allow for the use of heat flux sensors for measurements of insulation performance and dynamic system thermal response for future applications.

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.

Comprehensive optimization design of low temperature insulation system of regeneration cryocooler

The calculation of radiant heat leakage is a part of the design of cryogenic insulation system. The numerical radiation simulation considering geometric structure of cryogenic insulation system is established through Monte Carlo method and view factor. The difference of the multi-layer insulation outer surface temperature is about 0.5% between the simulation and experimental results. Additionally, the structure and shape of the insulation system would make radiation to redistribute between surfaces. The surface would have less heat leakage with large aspect ratio and small radius.

Vapor cooling of a structural skirt for a large-scale hydrogen tank

The demonstration of vapor cooling on a structural skirt was one of the main objectives of the Structural Heat Intercept, Insulation, and Vibration Evaluation Rig (SHIIVER) testing. SHIIVER consisted of a 4-meter diameter stainless steel tank with an aluminum forward skirt. The forward skirt was cooled by directing effluent vapor from the tank through two flow channels that each went 360 degrees around the interior of the skirt in a helical pattern. Flow rates, temperatures, and pressures in the system were measured allowing for the calculation of heat load removed via cooling stream and heat load reduction into the tank. Testing occurred at fill levels between 25% and 90% full using both liquid hydrogen and liquid nitrogen. Boil-off rate was varied independent of the skirt performance by adding multilayer insulation over the spray-on-foam insulation on the tank domes, while leaving the barrel insulated only with spray-on-foam. The results from the testing, which demonstrate vapor cooling removed heat flow from the tank flange and reduces total propellant heat load by as much as 19%, are analyzed and discussed.

Outgassing of Three Space Materials from to 25°C

Cryogenic space-science missions have been expanding in the last few years. Onboard instruments, especially detectors, but also several parts of satellites can be cooled down to cryogenic temperature during cruise, commissioning phase and in operation. In such conditions, molecular contamination may happen and affect the performance of sensitive equipment. Polymer outgassing is the main source of contaminants, and this phenomenon is commonly studied from ambient temperature to high temperature, usually . However, very few experimental data exist and there is no real evidence that tends to confirm that outgassing is negligible at temperature below . This work aimed at studying the outgassing of some representative materials such as multilayer insulation and adhesives at low temperature. A multistep temperature profile from to has been applied to the materials and deposition kinetics measured using cryogenic quartz crystal microbalance. The results showed different interesting behaviors and highlighted outgassing beginning at . Based on these results, long-term predictions have been calculated with internal simulation tool. Moreover, in situ analysis of outgassed molecules has been attempted with a residual gas analyzer.

Passive Thermal Control Design Methods, Analysis, Comparison, and Evaluation for Micro and Nanosatellites Carrying Infrared Imager

Advancements in satellite technologies are increasing the power density of electronics and payloads. When the power consumption increases within a limited volume, waste heat generation also increases and this necessitates a proper and efficient thermal management system. Mostly, micro and nanosatellites use passive thermal control methods because of the low cost, no additional power requirement, ease of implementation, and better thermal performance. Passive methods lack the ability to meet certain thermal requirements on larger and smaller satellite platforms. This work numerically studies the performance of some of the passive thermal control techniques such as thermal straps, surface coatings, multi-layer insulation (MLI), and radiators for a 6U small satellite configuration carrying a mid-wave infrared (MWIR) payload whose temperature needs to be cooled down to 100K. Infrared (IR) imagers require low temperature, and the level of cooling is entirely dependent on the infrared wavelengths. These instruments are used for various applications including Earth observations, defence, and imaging at IR wavelengths. To achieve these low temperatures on such instruments, a micro-cryocooler is considered in this study. Most of the higher heat dissipating elements in the satellite are mounted to a heat exchanger plate, which is thermally coupled to an external radiator using thermal straps and heat pipes. The effects of the radiator size, orbital inclinations, space environments, satellite attitude with respect to the sun, and surface coatings are discussed elaborately for a 6U satellite configuration.

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.