Insulation System Research Articles

A quasi-2D thermodynamic model for performance analysis and optimization of liquid hydrogen storage system with multilayer insulation and vapor-cooled shield

Liquid hydrogen (LH2) holds great potential in both aerospace and civil markets due to its high energy density. However, on account of the low boiling point and latent heat of vaporization of LH2, the high performance insulation storage system is the key to its efficient storage. One of the most efficient insulation methods for a LH2 storage system is considered to be Variable Density Multilayer Insulation (VDMLI) coupled with Vapor-Cooled Shield (VCS). This study establishes a quasi-two-dimensional (quasi-2D) thermodynamic model of liquid hydrogen storage system with VDMLI and VCS. The quasi-2D model incorporates the temperature gradient of VCS and its impact on VDMLI. The model can reveal the two-dimensional temperature and heat distribution in insulation systems, predict heat leakage and evaporation rate, and can be utilized for optimizing the design of the VCS structure. Using a NASA's tank as an example, the analysis conducted with the model indicates that the presence of VCS reduces the average temperature gradient of the inner VDMLI. The upper half of the tank exhibits a significantly smaller temperature gradient compared to the lower half, resulting in lower heat leakage. This effect becomes more pronounced as the VCS moves outward of the tank. Additionally, the VCS absorbs more heat in the inlet section than that in the outlet section, and this disparity becomes increasingly significant as the VCS moves outward of the tank. The model can also be employed to optimize the position of the VCS, resulting in a 69.73 % reduction in daily evaporation rate compared to NASA's original design. Lastly, a graphical method for the quick design of VCS structure is proposed which is based on calculated data for daily evaporation rate and apparent thermal conductivity. This method enables the retrieval of the corresponding apparent thermal conductivity based on the desired evaporation rate, facilitates the rapid determination of the range of VCS position, and allows for the quick prediction of the evaporation rate based on the VCS position. In conclusion, this research presents a new approach for the performance analysis and optimization design of liquid hydrogen storage system with VDMLI and VCS.

Topology Morphing Insulation: A Review of Technologies and Energy Performance in Dynamic Building Insulation

Topology morphing insulation enables the on-demand switching of thermal properties between insulative and conducting states through shape change. The adaptive nature of these systems allows them to regulate heat transfer by dynamically altering insulation materials or systems in response to changing conditions, including environmental factors, electrical grid dynamics, and occupant requirements. In this article, we highlight the potential of topology morphing insulation for advancing building envelope design, improving energy efficiency, and facilitating on-demand adjustments in effective thermal conductivity. We provide a comprehensive overview of topology morphing insulation, delving into its underlying principles, mechanisms, and potential applications. This review explores cutting-edge research and the potential application of insights from non-building concepts, such as nature, textiles, and origami. Additionally, it examines crucial aspects such as actuation mechanisms, effectiveness, lifecycle considerations, sustainability implications, and manufacturing feasibility. We discuss the potential benefits and challenges associated with implementing topology morphing insulation solutions. Thanks to its transformative capabilities, topology morphing insulation holds tremendous promise for advancing building envelope design, driving energy efficiency improvements, and facilitating responsive changes in effective thermal conductivity.

Electric field distribution in natural-ester retrofilled transformers under AC stress

Retrofilling a transformer with natural or synthetic esters leads to a reduction of its fire and environmental risk without making a large investment. Nowadays, most of the retrofilled transformers are medium power and voltage units, but their use in higher rated power units is rapidly expanding. Transformer retrofilling presents certain challenges due to the physico-chemical differences between mineral oil and esters. The insulation system of a transformer is designed to work with mineral oil, performing a double function as dielectric and coolant agent; when replacing mineral oil with an ester, whose relative permittivity and viscosity are different, the ability to perform these two functions must be reassessed.In this work, the electric field distribution of a retrofilled transformer has been analyzed using Finite Element Method. The study was conducted on a 280 MVA transformer which was originally designed to operate with its tank filled with mineral oil. The dielectric margins of the different parts of the insulation were calculated, and then compared with the dielectric margins of the transformer insulation before retrofilling. To improve the accuracy of the study, an experimental study was driven to obtain the permittivity values of mixtures of MO and NE in different proportions and the composition of the solid insulation in retrofilled transformers. The study also investigates the influence of the quality of the retrofilling process on the electric field distribution. The analysis shows that some parts of the insulation, such as the oil channel, operate with lower stress when the insulating liquid is changed to an ester, but other regions, such as the solid insulation in the most stressed areas of the insulation, reduce their dielectric margins significantly.

Evaluation of the Impact of Bricks of Various Characteristics on Internally Insulated Masonry Walls in Cold Climate

Energy consumption in historic building stock is high compared to current energy efficiency standards. The heritage value of the façade and the limited space on the external surface in densely populated urban streets limit the application of external insulation. Internal insulation can be applied instead. However, it is considered to be a riskier technology due to moisture-related damage. In addition to mold growth and wood rot, frost damage should be considered in cold climates. This study aims to assess the impact of a vapor-open capillary-active calcium silicate internal insulation system with and without adhesive glue on the hygrothermal behavior of masonry from various historic bricks in cold climates by performing numerical simulations in the software Delphin. Test results of hygrothermal properties of 40 historic brick samples were used in numerical experiments to assess the impact of a brick type, the quality of the application of calcium silicate (with or without adhesive), and the impact of cold climate on the hygrothermal behavior. Results show that temperature behavior is similar to all wall types whereas a large difference is observed in moisture behavior. The application of adhesive glue tends to reduce moisture spikes caused by rain events when compared to the same samples without adhesive. Findings only partly correspond to other studies on factors affecting moisture behavior.

Hygrothermal Assessment of Insulation Systems for Internal Insulation of Solid Masonry Walls under Various Conditions

Energy efficiency renovation of building stock is an essential aspect of the climate change mitigation strategies in many countries. A large proportion of building stock is historical buildings. For this building stock, developing technology for safe internal insulation of external walls is crucial, preventing possible moisture damage to the building structures. Internal insulation is a risky technique as it has a high impact on the hygrothermal behavior of the wall. This study assesses the hygrothermal performance of massive masonry walls with 17 interior insulation systems exposed to different external boundary conditions, including a steady-state cycle, dynamic dry cycle, wind-driven cycle, and drying cycle. During the steady state cycle, the highest increase of moisture was observed under capillary active materials ranging from 39 to 119% increase in absolute moisture, with the exception of cellulose with an increase of only 7%. All the vapor-tight insulation systems showed no increase in absolute moisture during the steady-state cycle, with the exception being mineral wool in combination with a vapor barrier that showed a 30% increase in ablute humidity. In addition, relative moisture changes in masonry were measured. Results show that tested insulation systems exhibit similar thermal performance while having different moisture performance. Vapor-tight and vapor-open insulation systems exhibit different hygrothermal behavior under various test cycles depending on material vapor diffusion resistance. Numerical simulations are sensitive to the hygrothermal properties of materials.

Design of High Power Density MVDC Cables for Wide-Body All Electric Aircraft

Aircraft electrification yields the next generation of aircraft such as more electric aircraft (MEA) and all electric aircraft (AEA). These aircraft require high-power-density and low-system-mass electric power systems (EPS). To this end, the voltage of the system must be enhanced to reach medium voltage levels in a few kV ranges. However, using medium voltage (MV) EPS for aircraft exacerbates the challenges of designing aircraft cables such as arc and arc tracking, partial discharges (PD), and thermal management. In this paper, several novel multi-layer based insulation systems for MVDC power cables are proposed to resolve aircraft cables’ challenges while maintaining low weight and size. The proposed cables are thermally and electrically analyzed and compared to cable systems designed based on IEC60502 and AS50881 standards. We use a coupled electrical-thermal-fluid flow dynamic model, for simulations where all possible heat transfer approaches, including conduction, convection, and radiation, to transfer mainly the joule heating generated in the core conductor to ambient with a low pressure of 18.8 kPa which is the air pressure at cruising height of wide-body aircraft (12.2 km) are considered and modeled. To compare the proposed cables to the designs based on IEC 60502 and AS50881, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> is introduced, which is the product of cables’ overall mass in a unit length and diameter. The results show that besides benefiting multi-layer, multi-function insulation systems to resolve aircraft cables’ challenges, the overall diameter and weight of the designed cables are lower than single-layer insulation system designs based on AS50881 and IEC60502.

Moisture Transfer Characteristics in Silicone Oil–Silicone Rubber Insulation System Considering Swelling Effect

Moisture Transfer Characteristics in Silicone Oil–Silicone Rubber Insulation System Considering Swelling Effect

Investigation of Insulation Layers on Additive Manufactured Electrical Steel Laminations in Electric Motors

In this paper, the insulation properties of printed electrical steel laminations for high-efficiency electric machines are investigated. In contrast to conventionally produced electrical steel laminations made from rolled coil material, additive manufacturing from powder material allows extremely thin and complex near-net-shape geometries with no scrap material. At the same time, the printed electrical steel laminations offer the advantage that no additional cutting steps are required and specific material characteristics are adjustable which enables special machine modifications. To avoid global eddy current paths between the single sheet layers after the stacking process, the laminations must be insulated from each other in order to keep losses low, especially at high operating frequencies. This requires a sufficiently high surface insulation resistance on the sheets. Since the insulation coating cannot be applied continuously during rolling, as in conventional production, alternative approaches for application are required. The investigations characterize and evaluate potential insulation systems for additive manufactured laminations. The printed sheets are analyzed geometrically, electrically and metallurgically at first and characterized for the next process steps. Afterwards, potential insulation systems are analyzed and investigated in practical tests. The coating systems are characterized in terms of application, thickness, electrical and mechanical insulation properties, and options for further processing. This is crucial as the coating needs a sufficient level of adhesion to the substrate and allows successive bonding.

Dynamic moisture diffusion in transformer winding insulation

Wind power production is intermittent due to varying wind conditions. This leads to frequent temperature changes in the wind farm transformers, which in turn affects the lifetime of the transformer winding insulation. To extend the lifetime through prediction of effects from dynamic loading, new models for degradation of insulation systems are needed. This article is laying the foundations of a model for dynamic moisture migration in the winding insulation of wind farm transformers. Relevant equations and approximations are presented and an experimental setup for laboratory testing of transformer insulation ageing related moisture migration under dynamic loading is described. The demonstration experiment clearly shows moisture migration through paper layers in a simple physical winding insulation model. As the ageing of cellulose is very moisture-dependent, the migration should clearly be included in models of ageing under dynamic load.

Amorphous/Nanocrystalline, Lightweight, Wave-Transparent Boron Nitride Nanobelt Aerogel for Thermal Insulation.

At present, the new generation of aircraft is developing in the direction of high speed, long endurance, high mobility, and repeatability. Some studies have shown that the surface temperature of the radome can reach even 1800 °C as the flight speed of the aircraft increases. However, the antenna inside the radome cannot serve at this temperature. Consequently, a thermal insulation system with electromagnetic wave-transparent ability and high-temperature resistance is urgently needed to protect the antenna from working normally. An aerogel material is known as "solid smoke," with the lowest density currently. Because of its high porosity (>90%) and the characteristics of nanopore size, its application in the field of thermal insulation always draws the attention of researchers. In this work, a novel amorphous/nanocrystalline boron nitride (BN) nanobelt aerogel was synthesized successfully. The BN aerogel shows lightweight (18 mg/cm3), good thermal stability (1400 °C under an inert atmosphere and 750 °C under an air atmosphere), wideband wave-transparent performance (dielectric constant of 1.03 and dielectric loss of 0.016 at 4-18 GHz), and thermal insulation property (43 mW/(m·K) at room temperature and 73 mW/(m·K) at 600 °C). The BN aerogel is a suitable candidate as an electromagnetic wave-transparent thermal insulator and fire-resistant material. What is more, the structural stability of the BN aerogel is good (Young's modulus remains basically constant during the fatigue tests), and the energy loss coefficient (∼0.56) is high; it also has the potential to be a mechanical energy dissipative material. The study on the amorphous/nanocrystalline BN nanobelt aerogel provides a new idea for structure design and performance optimization of a high-temperature electromagnetic functional insulation material.

Centrifugal Extraction-Assisted Fiber-Enhanced Raman Spectroscopy for Online Detection of Trace Furfural in Oil Power Equipment.

Oil-paper insulated equipment is integral in power conversion and supports low-loss electricity transport. As a characteristic byproduct of the oil-paper insulation system, the realization of efficient detection of furfural in oil is crucial to the safe operation of the power grid. We proposed a novel approach using dual-enhanced Raman spectroscopy for sensing trace liquid components. This method employs a centrifugal extractor to separate and enrich the targeted components, achieving selective enhancement. The optimal phase ratio was determined to be 30:1. A liquid-core fiber was used to optimize the laser transmission efficiency and Raman signal collection efficiency, resulting in a nonselective signal enhancement of 44.86. It also investigated the impact of intermolecular interactions on the shift of Raman spectra, identifying the reasons for the differences in Raman signals between pure furfural, furfural in oil, and furfural in water. A batch of samples with furfural dissolved in insulation oil was measured using this system and achieved a limit of detection of 0.091 mg/L. The stability of the dual-enhanced Raman platform was experimentally verified with a spectral intensity fluctuation of 0.68%. This method is fast, stable, adaptable, and suitable for the detection of a wide range of liquid ingredients.

The energy saving performance of the thermal diode composite wall in different climate regions

The effective management of energy consumption during building operations continues to be of utmost importance. The role of a building's envelope in regulating energy consumption is critical. However, traditional building insulation systems often struggle to maintain optimal indoor temperatures in the face of fluctuating external temperatures. Solar energy, for instance, can easily penetrate a room through windows during the cooling season, leading to increased energy consumption. Similarly, heat dissipates easily during the heating season. To address these challenges, thermal diode composite walls with unidirectional heat transfer offer a groundbreaking approach to simplifying the design of thermal management systems. The thermal diode composite wall effectively controls heat conduction, convection, and radiation through the implementation of different functional layers. By regulating the heat flux through the building envelope, this technology significantly reduces energy consumption during building operations while maintaining a stable indoor temperature. To evaluate the performance of an adaptable thermal diode composite wall, we designed, implemented, and conducted tests on a thermal diode composite wall building. The results of the study demonstrate substantial energy savings, ranging from 3.5% to 69.3% for annual operation in various regions, with better performance observed in colder regions. In the forward heat conduction mode, the temperature difference between the inside and outside wall surfaces reached a maximum of 20.99 K, while in the reverse mode, it reached −35.67 K. These findings highlight the remarkable potential of thermal diode composite walls in significantly improving the energy efficiency and comfort of buildings. Consequently, the adoption of thermal diode composite walls presents numerous opportunities for the development of low-carbon buildings.

Evolution Law of Structural Form and Heat Transfer Performance of Thermal Insulation System.

Building thermal insulation and energy conservation have become urgent problems in the field of civil engineering because they are important for achieving the goal of carbon neutralization. Thermal conductivity is an important index for evaluating the thermal insulation of materials. To study the influence of different porosity levels on the thermal conductivity of materials, this paper established a random distribution model using MATLAB and conducted a comparative analysis using COMSOL finite element software and classical theoretical numerical calculation formulas. The thermal conductivity of composite materials was determined based on a theoretical calculation formula and COMSOL software simulations, and the theoretical calculation results and simulation results were compared with the measured thermal conductivity of the composites. Furthermore, the influence of the width of the gaps between the materials on the heat transfer process was simulated in the fabricated roof structure. The results showed the following: (1) The thermal conductivity values calculated using the Zimmerman model were quite different from those calculated using the Campbell-Allen model and those calculated using the COMSOL software; (2) The thermal conductivity values calculated using the theoretical calculation formula were lower than the measured data, and the maximum relative error was more than 29%. The COMSOL simulation results were in good agreement with the measured data, and the relative error was less than 5%; (3) When the gap width was less than 60 mm, it increased linearly with the heat transfer coefficient. The heat transfer coefficient increased slowly when the gap width was greater than 60 mm. This was mainly due to the thermal bridge effect inside the insulation system. Based on these research results, a thermal insulation system was prepared in a factory.

High thermal conductivity electrical insulation composite EP/h‐BN obtained by DC electric field induction

AbstractEpoxy resin, as an adhesive for the main insulation system of large generators, has excellent insulation properties. But its poor thermal conductivity limits the capacity enhancement of large generators. Forming thermally conductive pathways by using electric field to induce high thermal conductivity fillers in the polymer can effectively improve the thermal conductivity of the composite at low loading condition. In this article, a DC electric field is used in epoxy resin (EP) to induce two‐dimensional inorganic fillers h‐BN deflection and head‐to‐tail lap, which can make the heat flow transfer along the in‐plane of the particles and contribute to the more efficient thermal conductivity network. A high thermal conductivity of 0.544 W/(m K) was achieved at a low load of 10 wt%, which has an improvement of 289% compared to pure EP (0.14 W/[m K]) and 130% compared to the randomly dispersed composite with the same load. The composites have excellent thermal conductivity as well as insulating properties, among which volume resistivity is 1.46 × 1012 Ω/cm, increasing by 61.4% compared to pure EP. This method is easy to be carried out in engineering and has great possibilities for the main insulation of large generators and even for other applications with high thermal conductivity electrical insulation.Highlights The structure of composites was adjusted by direct current electric field. The high in‐plane thermal conductivity of h‐BN is fully exploited. The relationship between deflection angle of BN and thermal conductivity of composites was built.

Solving Separation Distances from Flammable Surfaces of Exterior Walls by Central-European Standards

The paper deals with the topic of determining the density of heat flow from combustible surface treatments of exterior walls, such as combustible insulation systems, combustible cladding of facades and from all-wood constructions of exterior walls. Heat flow density is an important indicator in determining the fire resistance rating of exterior walls and in determining safe separation distances. The article describes the ways in which exterior walls can be classified in terms of fire resistance. One of these methods is a numerical calculation (of the surface amount of released heat and heat flow density), which will be applied to various types of combustible surfaces of the perimeter walls of wooden buildings. The results showed that the numerical calculation is a suitable method for determining the classification of fire resistance rating of exterior walls with combustible coating. The Czech legislation defines the criteria for this classification better.

Development of a perioperative thermal insulation system: Testing comfort properties for different textile sets.

The poorly physical and psychological conditions of the patients make the body thermal protection crucial in the perioperative context, due to the risk of hypothermia. The lack of evidence regarding the effectiveness of textile coverings in protecting patients in the operating room, underscores the recommendation of the forced warming system using non-woven fabric for ensuring the best thermal protection in the perioperative context. This study is part of a development process of a three-layered thermal insulation system, a blanket for use in the perioperative context. After previous selection of two fabrics for the mid and outer layers, in this study three fabric samples for the inner layer with same soft tactile sensation and different textile compositions were tested to find its effect on increasing the thermal insulation of the whole set, using a thermal manikin. The serial method was used to calculate the thermal insulation properties of the sets. The best thermal insulation and thermal comfort performance was obtained by the set using an inner layer composed of polypropylene, polyamide, and elastane whose results were the highest thermal conductivity and thickness and the lowest maximum stationary heat flow density. The results indicated that this fabric influenced positively the values of the whole set once increased its thermal protection effectiveness when compared to the other tested sets. This set is more suitable for future testing in patients during their stay in the perioperative setting.

Numerical Simulation of Geotechnical Isolation of Building Subjected to Earthquake Using Rubber Sand Mixtures

The use of recycled rubber in various civil engineering applications has seen a considerable rise in recent years. The rubber-soil mixture can exhibit a higher energy absorption capacity than soil alone, which would reduce the energy applied to structures, the stresses, and shocks they undergo. Base isolation is the process of isolating the base of a structure to limit the effects of earthquakes, so that the seismic forces applied to the base of the bedrock cannot move with the same intensity towards the super structure.In this work, the beneficial effects of rubber mixtures (RSM) in mitigating earthquakes when these mixtures are inserted as layers in the soil profile are highlighted; the approach is based on a method of using worn tires for seismic protection applications for infrastructures subjected to seismic loads. It involves mixing particles from used tires with soil materials and placing the mixtures under the foundation of the building as geotechnical insulation systems for vibration absorption.The foundation of a four-storey building is implanted in a soil profile in which a layer of rubber-sand mixture (RSM) has been inserted; to perform the role of seismic isolation when subjected to seismic excitation.The investigation is focused on the variation in the thickness of the layer on the one hand (between 1m and 4m), and on the other hand on the position of this layer in the soil mass (top, middle and bottom of the profile).The peaks of horizontal accelerations recorded at the base and top of the structure show that the sand-rubber mixture has adequate and promising potential for their application as seismic isolation materials for low-rise buildings. Moreover, the thickness of the layer and its location are two very determining parameters in the improvement of the performances of these RSM mixtures, especially in terms of reduction of the acceleration peak recorded.

Tracking Resistance in Polymeric Insulation Materials for High-Voltage Electrical Mobility Applications Evaluated by Existing Test Methods: Identified Research Needs.

With the increasing electrification of the transportation and mobility sectors, polymer insulation materials are inevitably exposed to harsher environments, including exposure to contamination, wide temperature ranges, operation at higher voltages and switching frequencies, and low-pressure environments. This paper reviews the tests to characterize the polymeric materials used in insulation systems for electric mobility applications, focusing on resistance to tracking. This paper also reports on the limitations of existing standard test methods and identifies the challenges and research needs to meet the increasing demands of the electric mobility industry. To this end, an evaluation of the scientific and technological state of the art is carried out through the analysis of theses, research articles, technical reports, manufacturers' datasheets, international standards, and white papers.

Failure Analysis of Transformers under Impulse Test

Transformers are the most critical and costly components in AC power systems. Insulation is the weakest link in transformers, and the design and quality of a transformer's insulation system shall be confirmed by performingdielectric tests according to National or International standards. The impulse test is more critical among the dielectric tests, as it verifies the integrity of the whole insulation system of the transformer. However, concluding the impulse test result is difficult when minor discrepancies exist in the earth's current waveforms. This paper presents two such case studieswith distribution class transformers.

Characterization of a Wall System with Dynamic Thermal Insulation—Experimental Campaign and Numerical Simulation

Dynamic thermal insulation systems (DTISs) can adapt to external environment conditions and help to reduce energy consumption and increase occupants’ thermal comfort, contributing towards the mitigation of overheating. DTISs adjust their configuration to optimize heat transfer through the façade. In this study, the performance of a DTIS was assessed through laboratory tests and numerical simulation. The DTIS is based on the ventilation of an air gap that facilitates the heat exchanges between the exterior and the interior. To extend the results of the experimental campaign, a set of scenarios was assessed based on numerical simulation. The results of the laboratory tests showed that the R-value obtained when the mechanical ventilation of the air gap is off (insulation state) is 3.89 m2.°C/W. In comparison, when it is on (conductive state), the R-value is 1.56 m2.°C/W, which corresponds to a reduction of approximately 60%. The results of the simulations showed that, when the shading system was on, the higher U-value was useful more than 50% of the time with discomfort, increasing to 75% when the shading system was off.