Vacuum Insulation Research Articles

Development of new vacuum insulation core panels using micronized nanocellular poly(methyl-methacrylate) (PMMA)

Development of new vacuum insulation core panels using micronized nanocellular poly(methyl-methacrylate) (PMMA)

Research on the design and thermal performance of vacuum insulation panel composite insulation materials

This study introduces a novel design methodology for composite insulation material aimed at reducing the operational energy consumption of buildings. Vacuum Insulation Panels (VIPs) are recognized for their excellent insulating properties due to their vacuum-sealed nature that minimizes thermal transmittance. However, VIPs are susceptible to damage from temperature stress and abrasion, which can compromise vacuum integrity and degrade performance over time. To mitigate this, a protective layer of rock wool board is adhered to the exterior of the VIP to create a composite insulation material. The thermal conductivity characteristics of the composite insulation materials are experimentally measured and then corroborated with simulations using ANSYS software to affirm the precision of finite element analysis methods. A composite Insulation wall model is constructed using ANSYS to analyze the impact of varying the thickness of the composite insulation materials and the pressure within the VIP on thermal performance. The findings demonstrate that the thermal transmittance coefficient of the composite insulated wall diminishes with increased insulation material thickness and rises with increased pressure within the VIP. Additionally, rock wool boards significantly enhance the durability of the composite insulation material.

Historical Evolution and Current Developments in Building Thermal Insulation Materials—A Review

The European Climate Law mandates a 55% reduction in CO2 emissions by 2030, intending to achieve climate neutrality by 2050. To meet these targets, there is a strong focus on reducing energy consumption in buildings, particularly for heating and cooling, which are the primary drivers of energy use and greenhouse gas emissions. As a result, the demand for energy-efficient and sustainable buildings is increasing, and thermal insulation plays a crucial role in minimizing energy consumption for both winter heating and summer cooling. This review explores the historical development of thermal insulation materials, beginning with natural options such as straw, wool, and clay, progressing to materials like cork, asbestos, and mineral wool, and culminating in synthetic insulators such as fiberglass and polystyrene. The review also examines innovative materials like polyurethane foam, vacuum insulation panels, and cement foams enhanced with phase change materials. Additionally, it highlights the renewed interest in environmentally friendly materials like cellulose, hemp, and sheep wool. The current challenges in developing sustainable, high-performance building solutions are discussed, including the implementation of the 6R principles for insulating materials. Finally, the review not only traces the historical evolution of insulation materials but also provides various classifications and summarizes emerging aspects in the field.

Vacuum Insulation Panel Production with Ultralow Thermal Conductivity—A Review

Vacuum Insulation Panel Production with Ultralow Thermal Conductivity—A Review

Natural fibers as promising core materials of vacuum insulation panels

To reduce energy consumption in buildings, this paper investigates the feasibility of using natural fibers as cost-effective, environmentally sustainable core materials for vacuum insulation panels (VIPs). First, a comprehensive experimental study was conducted for 10 potential natural fiber candidates. The thermal conductivities of the 10 natural fiber mats at various vacuum pressures were measured; their compression and morphology properties were quantified. In addition, an analytical model was used to explore the major factors that influence the thermal conductivity of natural fibers as a function of internal air pressure. Results show that recycled cotton, kapok, and bamboo fibers are ideal candidates for VIP core materials; at <0.05 Pa, their thermal conductivities varied between 2 and 4 mW/(m⋅K). Furthermore, for some fibers, thermal conductivity was inversely proportional to fiber density. For the selection of fiber materials for VIP cores, the ideal fiber candidate has a small fiber diameter and a low fiber mat density. Based on thermal measurements, even though the internal air pressure of 5 Pa was enough to attain the minimum thermal conductivity, obtaining internal air pressure below 5 Pa is recommended for prolonged service life, considering small leaks of VIP package barrier films and potential off-gassing from fibers. The simulation results predicting the effective thermal conductivities matched the experimental results well. These findings indicate that natural fiber–based VIPs have the potential to be a sustainable, inexpensive alternative to the current technologies in building insulation materials.

A study on the reduction of high-temperature in the high-pressure piping system of civil aircraft

Abstract For the study of the bleed air flow process in high-pressure pipelines, theoretical analysis and numerical simulation were used to investigate the temperature drop problem in the pipelines. The effect of bleed air and ambient temperatures on the performance of temperature drop in high-pressure pipelines was discussed in detail. The performance of pipeline insulation before and after applying the insulation layer was also discussed. The results show that the higher bleed air temperature and lower ambient temperature obviously cause a greater drop in the bleed air temperature drop. The entrance section of the pipeline is approximately five times the l/d range. Applying the insulation layer can effectively reduce the drop in pipeline temperature. Generally, the air insulation layer can reduce the temperature drop of high-pressure pipeline gas by 25%. If further reduction is required, the vacuum insulation layer can be applied.

Research on thermal insulation performance and application simulation of high-temperature vacuum insulation panel

Research on thermal insulation performance and application simulation of high-temperature vacuum insulation panel

Methodology for Testing Selected Parameters of Low-Current Vacuum Electric Arc

This article presents the author’s methodology for testing selected parameters of a low-current vacuum arc, implemented using an innovative test stand based on a vacuum discharge chamber with a contact system mounted inside. In order to verify the validity of the adopted research methodology, as well as the correctness of the operation of the developed laboratory bench, measurements and calculations were made, among other things, of the energy and burning time of the vacuum arc, depending on selected factors, such as pressure and the delay time of the contact opening, calculated from the “passage through zero” of the sinusoid of the current flowing through the system. The tests were performed at 230 V and a current of 5 A for two pressure values: p1 = 1.00 × 105 Pa (atmospheric pressure) and p2 = 4.00 × 10−3 Pa (high vacuum environment). It was found that the vacuum insulation technique allows a significant reduction in the value of the arc energy and the burning time of the arc. It was also observed that in the case of a high vacuum environment, the ignition of the vacuum arc occurs after a time equal to about 3 ms from the “passage through zero” of the current flowing through the system. Below this value, the phenomenon did not occur. The results obtained provide an opportunity for the design and manufacturing of vacuum switchgear, where there is the prospect of reducing the negative effects associated with the arc burning process in the contact gap.

Acoustical properties of the new sandwich structures for aircraft cabin interiors with integrated vacuum insulation

AbstractAny modern passenger aircraft must provide a high level of comfort for passengers who spend considerable time inside the cabin. The cabin's climate and interior noise levels contribute to this comfort. Vacuum insulation panels (VIP) have been explored as insulation materials to improve these factors due to their extremely low thermal conductivity. When integrating VIPs into the aircraft cabin's interior, it was discovered that the thermal conductivity of the entire sandwich structure was 3–6 times lower than conventional structures. This finding has generated much interest in using VIPs for aircraft cabin insulation. This article delves into the acoustic properties of these new structures featuring integrated VIPs. Tests were carried out to analyze the sound insulation capabilities of these structures. The results showed that the new interior structures exhibited promising acoustic properties.

The Inclusion Characteristics and Mechanical Properties of M2 High-Speed Steel Treated with a Vacuum Carbon Deoxidation Process

The oxygen content of M2 high-speed steel has not been intentionally controlled in industrial production through secondary refinement in vacuum furnaces. However, a lower oxygen content has a significant effect on the cleanliness, toughness, and addition of rare-earth elements to M2 high-speed steel. The changes in total oxygen content controlled by vacuum carbon deoxidation (VCD) treatment and inclusion evolution were investigated in M2 high-speed steel to understand the effects of carbon on dissolved oxygen and oxides in the carbon–oxygen (C-O) reaction process. Furthermore, the microstructure and properties of M2 high-speed steel caused by vacuum insulation and the role of reducing oxygen content in rare-earth alloying were briefly demonstrated. The results showed that the [O%] decreased from 30 ppm to 3 ppm in a vacuum at holding times above 25 min through the C-O reaction, leading to an inclusion reduction of approximately 70%. In the case of [O%] = 3 ppm in M2 high-speed steel, the addition of rare-earth elements has a greater effect on the inclusion characteristics. Lowering the oxygen content of M2 high-speed steel improves cleanliness and plays a significant role in rare-earth alloying.

Experimental and comparative analysis between nitrile rubber foam insulated and vacuum insulated fiber reinforced plastic tank used in a low temperature sensible heat storage system for building space cooling applications

AbstractThermal energy storage devices are gaining importance and momentum in the building space cooling and renewable energy applications. Retaining the stored energy for long hours through proper insulation is crucial in achieving economic benefits. In the present research, a novel composite material (FRP) is introduced for the development of cool storage tank along with two different methods of insulation (nitrile rubber foam insulation and vacuum insulation) to assess the performance of cool energy retention. The results show that the effect of vacuum insulation is lower compared with nitrile rubber foam insulation. This is due to the low specific heat capacity of the FRP material compared with air that increases the surface temperature of the tank than the ambient air during the day time in the case of vacuum insulation. Hence the study concludes that the additional layer of insulation material with high specific heat capacity than the ambient air to be added on the surface to avoid the overheating of the wall surface. The results are useful in designing the insulation for thermal storage tanks and managing the heat loss.

A novel approach to thermal insulation modelling in soft and medium vacuum insulation systems

The accuracy of vacuum-dependent models for predicting thermal performance of Multi-Layer Insulation (MLI) and other layered insulation systems is critical for the development of novel solutions in the aerospace and energy sectors, particularly long distance superconductors and cryogenic transfer lines. This paper presents a review of the current state of the art in cryogenic vacuum insulation systems and their associated modelling techniques and test methods. Current modelling techniques, namely the Lockheed and McIntosh MLI models, are compared to cryogenic, boil-off calorimeter test data for 3 types of MLI from the current literature. Both current models provide acceptable accuracy at high vacuum pressures but deviate from the test data when gas conduction becomes the dominant heat transfer mechanism (Kn≤1). Neither of the current models follow the characteristic S-curve observed by researchers during insulation tests. This paper presents the introduction of a novel modelling approach for layered insulation systems though changes to the current state of the art, specifically at soft (pvac≤7.5×105 mTorr) and medium vacuum (pvac≤7.5×102 mTorr) pressures, by substituting the gas conduction term in both equations with alternative terms based on the system Knudsen number (Kn) and molecule mean free path (l). This results in a stronger pressure dependence across the vacuum regime. Both modified models exhibited the characteristic S-curve with significantly reduced errors over the entire range.

Revelation of the high surface insulation performance of the electron-delocalized group through molecule self-assembly on alumina insulator

Surface modification of vacuum insulators is a promising way to improve their surface insulation performance but commonly used surface modification technologies in surface insulation area such as fluorination and plasmas treatment are unable to control the surface chemical components at the molecular level, which makes it hard to explore molecular groups with high surface insulation performance. In this paper, molecule self-assembly is introduced to control the surface molecular structure precisely and vacuum surface insulation performance of a special molecular structure electron-delocalized group is studied. Hexagonal phenyl group containing delocalized electrons and cyclohexyl group with the same hexagonal molecular structure but without delocalized electrons are grafted onto the surface of alumina insulators through molecule self-assembly. Secondary electron emission yield test shows that phenyl group endows alumina insulators lower SEY than cyclohexyl group. Correspondingly, phenyl group grafted alumina insulators show higher surface insulation performance than cyclohexyl group. The results indicate that group containing delocalized electrons can endow insulators higher surface insulation characteristics.

Silane modified Cr2O3/polyimide nanocomposite films with excellent surface insulation performance for space applications

The exploration of deep space significantly increases the probability of spacecraft failures due to surface electrostatic discharge, which imposes higher vacuum insulation protection requirements on polyimide (PI), the external insulation material of spacecrafts. To address this challenge, this study proposes using silane coupling agent KH550 for organic grafting treatment of Cr2O3nanoparticles, which are then used to dope and modify PI to enhance the vacuum surface insulation of PI films. The KH550 grafting improves the interface strength between the fillers and the matrix, allowing the fillers to be uniformly dispersed in the matrix. Compared to pure PI films, the prepared PI-Cr2O3@KH550 composite films exhibit significantly enhanced vacuum surface flashover voltage, improved surface/volume resistivity, and dielectric properties. The results demonstrate that PI composite films with 0.8% by mass of Cr2O3@KH550 show the most notable performance improvement, with the DC flashover voltage and impulse flashover voltage in vacuum increasing by 20.7% and 27.8%, respectively. The doping of chromium oxide nanoparticles introduces more deep traps into the PI films and reduce the surface resistivity. The higher deep trap density inhibits charge migration, thereby alleviating secondary electron emission and surface electric field distortion. Simultaneously, the lower surface resistivity facilitates dissipating surface charges and improves the surface insulation. These findings are of significant reference value for promoting the enhancement of aerospace insulation performance.

Experimental Study on a Liquid Hydrogen Tank for Unmanned Aerial Vehicle Applications

A lightweight, 12 L liquid hydrogen fuel tank has been designed, fabricated, and tested with the aim of optimizing boil-off rates while minimizing the weight of a complete propulsion system intended to be integrated into an unmanned aerial vehicle. After looking at several different insulation schemes, the system was optimized as two concentric, lightweight titanium cylinders with high vacuum and multilayer insulation in between. The thickness of the multilayer insulation and the design of support structures were optimized to reduce the overall weight of the tank. This paper focuses on characterizing the boil-off rate of a small liquid hydrogen tank in relation to ambient temperature and fuel level. Additionally, it addresses the analysis of the instrumented transfer line between the reservoir and the operating fuel cell, presenting pressure and temperature measurements for each component of the transfer line. The efficiency of the heat exchanger under natural and forced convection is also discussed. The key contribution of the experimental campaign lies in demonstrating an average boil-off rate of 19.5 g/h over 45 h. This significantly surpasses the limits of ultra-long-range flight achievable with alternative electric energy sources. Furthermore, the paper highlights the importance of the variable boil-off with time and its impact on aircraft performance.

Double envelope vacuum insulation panel to contribute to the long-term thermal insulation performance

Vacuum insulation panels (VIPs) have a potential to be used for retrofitting thermal insulation to existing buildings from the viewpoint of low thermal conductivity, small thickness, and light weight. However, in order to realize vacuum insulation panels applicable to building thermal insulation, it is necessary to overcome the challenge of maintaining the low pressure at which high thermal insulation performance can be achieved for several decades. The authors propose double envelope VIPs to maintain this long-term high thermal insulation performance. The double envelope VIP is fabricated by creating a single envelope VIP, wrapping the VIP with core materials, and then inserting it into the envelope for vacuum sealing. By applying the double envelope VIPs, the pressure difference and the permeation of gas in the inner VIP can be drastically reduced, resulting in a longer VIP lifetime. In this paper, the gas permeabilities of the gas barrier envelopes are experimentally estimated. Then, the pressure ageing in the double envelope VIP is calculated. The inner pressure of double envelope VIP after 50 years is 5.4 Pa for the envelope of aluminium composite film, indicating that low pressure can be maintained long-term. Next, the authors carry out accelerated test, in which the double envelope VIPs are placed in a chamber at 80oC and removed every two weeks to measure the effective thermal conductivity. Even after 141 weeks, one sample with a getter agent on the inside and a desiccant agent on the outside indicates only 10.5 % decrease in the thermal resistance. From this result, the long-term high thermal insulation performance can be obtained by fabricating double envelope VIPs.

New robust multi-criteria decision-making framework for thermal insulation of buildings under conflicting stakeholder interests

The choice of thermal insulation technology for existing building retrofit can be a complex multi-criteria decision-making (MCDM) problem characterized by multiple stakeholders with conflicting interests. The conflicting interests of the building owners and the policymakers could negatively influence the adoption of low-carbon energy retrofit measures by building possessors, slowing down the progress toward sustainable development. The investigation of this issue is, therefore, crucial to support more informed decisions and offer policymakers useful insights to develop future economic incentives for energy refurbishment of buildings. Most of the existing MCDM studies on the subject do not emphasize the differences among different stakeholders nor consider the outcomes' robustness. To overcome this gap, this paper integrates multi-stakeholder analyses and robustness assessments to provide broad-spectrum and reliable results. An innovative robust MCDM framework for building thermal insulation under conflicting stakeholder interests is proposed and tested on a real case study building (located in Southern Italy) using building dynamic energy simulation. Several alternatives of thermal insulation are evaluated under environmental, energy, and economic key performance indicators (KPIs). The Analytic Hierarchy Process is used to define criteria weights for conflicting decision-makers representing collectivity (policymakers) and private interests. TOPSIS, VIKOR, WASPAS, and MULTIMOORA methods are integrated to perform initial rankings of the alternatives. A rank similarity analysis is performed to evaluate the consensus between MCDM methods, and an ensemble ranking is obtained for each decision-maker using an approach based on the half-quadratic theory. A Confidence Index and a Trust Level are used to evaluate the agreement among the MCDM approaches, verifying the reliability of the final ensemble ranking. The robustness of the framework is attained by complying with well-established literature guidance. The hybrid MCDM analysis showed that porous materials like expanded clay and expanded perlite lead to better results under the KPIs investigated. The worst performances are attained by vacuum insulation panels and aerogel, mainly due to high values of embodied CO2 emissions and long payback periods. Insights upon the performance of different thermal insulating alternatives are also highlighted by the study and a stakeholder comparative analysis demonstrates that global rankings obtained for the different decision-makers show some similarities, but also important deviations, and a full compromise solution is not achieved.

폐냉장고의 진공단열재 재제조 사례연구와 탄소 감축 잠재량 산정

This study investigates the current processes and technologies for remanufacturing vacuum insulation panels (VIPs) recovered from end-of-life refrigerators, with a focus on making them reusable. The potential industrial applications of these re-VIPs in the building and cold chain sectors are also explored. Based on the above remanufacturing process information, the carbon reduction potential through the reuse of VIPs was assessed using Life Cycle Assessment (LCA). The study concluded that VIPs intended for reuse are most suitable for the cold chain sector. Additionally, it was estimated that assuming 15,600 VIP refrigerators are processed annually at one recycling centers, approximately 32 tons of VIPs can be reused, potentially reducing carbon emissions by −94,282 kg CO2-eq.

Functionalising kapok fibre with lignin to enhance the structural and thermal performance of vacuum insulation panels

Kapok fibre has the advantage of low density, low porosity and low thermal conductivity, which make it an excellent substitute for fumed silica and environmentally-unfriendly synthetic polymers as core material of vacuum insulation panels (VIP). However, kapok fibre is hydrophobic, consequently, kapok fibre core materials made by conventional wet forming with weakly-bound fibres and large voids that shorten their service life. Lignin is a natural and sustainable material that has good hydrophilicity and small particle size to form nano-porous networks. Therefore, we herein present the incorporation of lignin in kapok fibre to generate a composite core material with hierarchical porous structure. Lignin functionalises the kapok fibre surface to make it hydrophilic and dispersible in water. Simultaneously, lignin enhances the mechanical properties and service life of core material by transforming its internal microstructure. The effective thermal conductivity of prepared VIP is below 6.00 mW/(m∙K), and after 28 days of accelerated ageing test without desiccant or getter, the effective thermal conductivity increases less than 5.00 mW/(m∙K). Interestingly, the addition of lignin also reduces radiative heat transfer in the VIP. So, lignin addition enables high-performance VIP to be produced. Moreover, as a natural material, kapok fibre is low-cost, environmentally-friendly, sustainable, and energy-efficient.

Experimental and theoretical thermal performance analysis of additively manufactured polymer vacuum insulation panels

Vacuum Insulation Panels (VIPs) are characterized by low thermal conductivity, which makes them attractive for applications in buildings, refrigerators, and cold chain logistics. The study of new technologies to manufacture VIPs has grown considerably in recent years. This work presents a feasibility analysis of additive manufacturing technique to manufacture polymer VIPs. The 3D printable multilayered VIPs, in which several interlayers are utilized to suppress gas conduction and thermal radiation, are designed and then manufactured using a commercial fused deposition modeling 3D printer. The effective thermal conductivity of the 3D printed VIPs is evaluated at various vacuum levels (1 atm, 10,000 Pa, 1000 Pa, 100 Pa and 10 Pa) using the standard test method (ASTM C518). Additionally, an analytical model and numerical simulation are performed to analyze heat transfer in these 3D printed VIPs and optimize the VIP design. The experimental results show that an effective thermal conductivity of 0.0155 W/m/K is achieved for the 3D printed VIP with 8 solid interlayers at 10 Pa, which is about 60 % of the thermal conductivity of air at 1 atm pressure. It is also found that there exists an optimal number of interlayers in the multilayered VIPs when its pressure is >1000 Pa. At lower pressures, the effective thermal conductivity of the multilayered VIPs decreases monotonically with increasing number of interlayers. This work is the first one to employ 3D printing techniques to manufacture polymer VIPs, and it is expected to offer a pathway for wider adoptions of VIPs due to its advantage low cost and high manufacturing flexibility.