Insulation Scheme Research Articles

Thermodynamic study on thermal insulation schemes for liquid helium storage tank

The temperature of liquid helium (LHe) is 4.2 K, high-performance thermal insulation schemes such as the variable density (VD) and self-evaporation vapor-cooled shield (VCS) are required for LHe tank. However, the working parameters of the VD and VCS in LHe tank have not been investigated. However, the related researches on liquid hydrogen tank neglected the heat transfer of the tank wall and the gap; The VD configuration may less than the optimal because the maximum number of spacers for each layer was pre-set artificially. Meanwhile, the recovery rate of sensible heat cannot be obtained by the existing model. In this work, these limitations are taken into account to establish the thermodynamic model of composite multilayer insulation (FMLI), VD and VCS, respectively. The results show that the correction coefficient of FMLI model is 0.1875; The layer densities of composite variable density MLI (FVD-MLI) with four segments are 3.31, 6.62, 13.23, and 19.98 layer/cm, with a 9.6% reduction in heat leakage compared to that of FMLI. The optimal position of the VCS in VCS-composited MLI (FMLI + VCS) and VCS-composited variable density MLI (FVD-MLI + VCS) is approximately 30% and 25% near the cold boundary respectively, and 36.2% and 40.7% reduction in heat leakage compared to that of FMLI and FVD-MLI respectively. The VD and VCS promote each other in improving thermal insulation performance, while the VCS plays a greater role than VD.

A new framework to select energy-efficient retrofit schemes of external walls: A case study

Abstract Retrofitting energy-inefficient external walls would improve the energy performance of building envelope by utilizing new insulation materials to decrease heat transfer. However, previous researches mainly based on environmental and economic considerations are still partial and could hardly provide a holistic perspective for the optimal selection of external walls retrofit techniques. To address this problem, this paper proposes a novel heterogeneous multi-criteria group decision-making (MCGDM) framework in which the ratings of schemes are described with real numbers and linguistic variables and the weights of criteria are unknown. Firstly, an evaluation index system is established covering criteria of thermal insulation property, technique, durability, and economic efficiency. Secondly, building information modeling (BIM) is utilized to determine multiple retrofit schemes and derive the heat transfer coefficient. Thirdly, after heterogeneous evaluation values are unified, a combined weighting approach is developed based on best worst method (BWM) and the similarity method before fuzzy VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) method is applied to rank the alternatives. Fourthly, the applicability of the proposed framework is demonstrated by a case study of the external wall retrofit scheme selection in Beijing, which reveals that extruded polystyrene (XPS) and expanded polystyrene (EPS) insulation schemes are the compromise choices with aggregating index Qk of 0.0032 and 0.0967 respectively, while rock wool insulation scheme is the last option with Qk of 0.7182. The stability of ranking results is proved with the changing weight of maximum group utility, and the effectiveness of the proposed framework is verified by a comparative analysis. This study can facilitate the implementation of building envelope retrofit by providing useful guidance for selection of external wall retrofit schemes.

Heat transfer performance of an assembled multilayer wall in a Chinese solar greenhouse considering humidity

This paper presents a new type of assembled multilayer wall suitable for Chinese solar greenhouses, and studies the heat transfer performance of the wall with three different external insulation schemes. The results show that there is coupling in the heat and moisture transfer of the assembled multilayer wall in the solar greenhouse, but it is not obvious and is not sensitive to the change in humidity outside the room, which is beneficial to the construction of thermal environments in solar greenhouses. The relative humidity of the clay filling in the wall is kept at approximately 99%, which gives the wall a stable and efficient heat storage and release capacity that can basically realize one-way heat transfer between the wall and the indoor environment. There is a lag effect in the response of the temperature field in the wall to the change in the external temperature. Increasing the thickness of the polystyrene insulation board on the outdoor side in a certain range can reduce the lag effect and increase the heat storage of the wall by 24.95%, the heat released to the room by 41.72%, and the hourly average heat released during the heat release process by 3.08 times. The wall design concept is advanced, the heat storage and release performance is good, and the wall can be quickly assembled, reused and returned to the field on site, which is suitable for large-scale application in China and in the world.

Design Considerations for High-Voltage Insulated Gate Drive Power Supply for 10-kV SiC MOSFET Applied in Medium-Voltage Converter

High-performance gate drive power supply (GDPS) plays a crucial role in ensuring the reliability and safety of the gate driver for power semiconductor devices. This article focuses on the design of a high-voltage-insulated GDPS for the 10-kV silicon carbide MOSFET in medium-voltage (MV) application. Design considerations, including insulation scheme, high-voltage-insulated transformer design, and load voltage regulation scheme, are proposed. In addition, the performance of the secondary-side-regulated (SSR) GDPS and that of the primary-side-regulated (PSR) GDPS are compared for several aspects, including interwinding capacitance, load voltage regulation rate, conversion efficiency, and hardware complexity. Finally, an SSR GDPS and a PSR GDPS, with an insulation voltage of 20 kV, are built in the lab. The test results demonstrate that the PSR GDPS is more preferable because of lower interwinding capacitance, lower load voltage regulation rate, higher conversion efficiency, and simpler control circuit.

Design and Verification of a Deep Rock Corer with Retaining the In Situ Temperature

Deep rock is always under high‐temperature conditions. However, traditional coring methods generally have no thermal insulation design, which introduces large deviations in the guidance required for resource mining. Thus, a thermal insulation design that utilizes active and passive thermal insulation was proposed for deep rock corers. The rationale behind the active thermal insulation scheme was to maintain the in situ core temperature through electric heating that was controlled by using a proportional‐integral‐derivative (PID) chip. Graphene heating material could be used as a heating material for active thermal insulation through testing. In regard to the passive thermal insulation scheme, we conducted insulation and microscopic and insulation effectiveness tests for hollow glass microsphere (HGM) composites and SiO2 aerogels. Results showed that the #1 HGM composite (C1) had an excellent thermal insulation performance (3 mm thick C1 can insulate to 82.6°C), high reflectivity (90.02%), and wide applicability. Therefore, C1 could be used as a passive insulation material in deep rock corers. Moreover, a heat transfer model that considered multiple heat dissipation surfaces was established, which can provide theoretical guidance for engineering applications. Finally, a verification test of the integrated active and passive thermal insulation system (graphene heating material and C1) was carried out. Results showed that the insulating effect could be increased by 13.3%; thus, the feasibility of the integrated thermal insulation system was verified. The abovementioned design scheme and test results provide research basis and guidance for the development of thermally insulated deep rock coring equipment.

Re-Makeable Joint With Insulation for REBCO Superconductor Cables

Composite Technology Development, Inc., in partnership with the Plasma Science and Fusion Center (PSFC) at MIT, recently developed and demonstrated a re-makeable, insulated high temperature superconductor (HTS) cable joint for a Twisted Stacked-Tape Cable. The prototype joint exhibited low tape-to-tape resistances (∼400 nΩ) with critical current through the joint for most tape pairs matching that of the as-supplied conductor tape ( I c = 142 A). The best performing insulation scheme showed dielectric withstand voltage in excess of 10 kV. Disassembly and reassembly of the joint showed no degradation in performance.

Challenges and status of the ITER IVC conductor qualification process in China

The coils inside the ITER vacuum vessel are part of the overall plasma control system that ensures and maintains stable plasma operations. Two vertical stability coils(VS)will provide fast vertical stabilization of the plasma, while an array of 27 edge localized mode (ELM) coils will create resonant magnetic perturbations to magnetically control the plasma exterior in order to suppress potentially harmful power deposition on plasma-facing components. For magnet coils operating inside of the vacuum vessel, conventional insulation schemes are not an option. After a decade of development and intensive collaboration with industry and research institutes, a copper mineral insulated conductor (MIC) in stainless steel jacket will be used as for its ability to withstand large transient electromagnetic forces, high radiation flux, and high temperature.Complex technologies have been developed by ASIPP for the series of production of IVC conductors, in terms of conductor initial dimension design, MgO block assembly and elaboration of Cu pipe insertion, compaction and winding processes. China has finished all qualification phases, especially for 100-meter unit length conductor manufacturing. The first 100-meter unit length of copper tube is successfully manufactured in China. All conductor samples required for qualification process have successfully passed the electrical tests with good performance.The challenges and status of the production of ITER IVC conductors in China are described in this paper.

Thermodynamic analysis and comparison of four insulation schemes for liquid hydrogen storage tank

Hydrogen has more energy per unit mass (141.8 MJ/kg) than any other fuel but also has the lowest gaseous density (0.084 kg/m3), and liquid hydrogen (LH2) storage is a solution with high energy density. However, LH2 storage has the characteristics of low temperature (20 K) and easy evaporation, putting forward higher requirements for insulation system. At present, the improvement and optimization of insulation system consisting of spray on foam insulation (SOFI), multilayer insulation (MLI) and variable density MLI (VDMLI) is a hot topic. Considering the considerable sensible heat of hydrogen, this paper introduces self-evaporation vapor cooled shield (VCS) into the above-mentioned insulation systems to fully recover its sensible heat to improve insulation performance. A thermodynamic model has been established to study the insulation properties of composite insulation system for LH2 tank, and the results have good agreement with test data. Coupling effects among them are analyzed and the optimization strategies of MLI, VDMLI and VCS are quantitatively explained to obtain better insulation performance. The heat flux and temperature profile of four insulation structures (MLI, VDMLI, MLI + VCS and VDMLI + VCS) have also been quantitatively analyzed, which can provide guidance for insulation system optimization. The insulation performance of composite insulation system under different vacuum conditions have also been compared.

Thermal design optimization and analysis on heating load of rural buildings in northern China

The envelope of rural buildings has been lack of effective and reasonable thermal insulation method and therefore its energy consumption has always been high. In order to address this problem, this paper aims to optimize the thermal design of building envelope. The simulation using DesignBuilder software for modeling and analyzing, using the orthogonal experimental design method to study the effects of external wall, external window and roof on heating load, and optimal thermal insulation scheme was obtained, which was 100mm PUF (external wall), 6mm+12mm+6mm low-E glass (external window) and 100mm PUF (roof). Results revealed that the addition of sunspace can significantly reduce the heating load and thus the selection of window thermal insulation material is very important. Compared with the condition of highest heating load, the energy-efficient rate of optimal scheme reached to 21.4%. The results of this study will serve as the idea for optimal design of rural buildings envelope.

Сравнение эффективности схем утепления в системах навесных вентилируемых фасадов

В статье рассмотрены проблемы, связанные с качеством монтажа утепления навесных вентилируемых фасадов, и, в первую очередь, связанные с зазорами между теплоизоляци­онными плитами. В соответствии с СТО НОСТРОЙ 2.14.67-2012 «Навесные фасадные системы с воздушным зазором. Работы по устройству. Общие требования к производству и контролю работ» допустимая величина незаполненного шва составля­ет 2 мм. В реальности добиться требуемой ширины зазора между плитами просто невозможно, а на однослойных схемах утепления возникают дополнительные повышенные теплопо­тери. Произведена оценка влияния зазоров между плитами теплоизоляции на приведённое сопротивление теплопере­даче наружной стены с системой навесного вентилируемого фасада с использованием российской и европейской методик расчёта. Расчёты проведены согласно СП 50.13330.2012, СП 230.1325800.2015 и EN ISO 6946. Для анализа приняты две конструкции наружной стены - из монолитного железобетона и кладки из газобетонных блоков - и три варианта утепления: однослойное и два двухслойных. Предложены оптимальные варианты теплоизоляции и типы оснований для крепления теплоизоляции. Рассмотрены три типа воздушных прослоек согласно EN ISO 6946 и взят в расчёты третий тип - сильно вентилируемая прослойка. Представлены результаты рас­чётов двухмерных температурных полей, линейных коэффи­циентов теплопередачи, коэффициентов теплотехнической однородности и приведённых сопротивлений теплопере­дачи для 16 вариантов сочетаний зазоров в теплоизоляции и оснований.

Tripled critical current in racetrack coils made of Bi-2212 Rutherford cables with overpressure processing and leakage control

We fabricated three racetrack coils (RC1, RC2, and RC3) from Bi-2212 Rutherford cables (17-strand, thickness × width = 1.44 mm × 7.8 mm, strand diameter = 0.8 mm) and applied overpressure processing heat treatment (OPHT). The quench currents of RC1 and RC2 reached 5268 A and 5781 A, respectively, despite them still, surprisingly, exhibiting some Bi-2212 leakage to the surface. After removing most of the leakages using a simple-to-implement insulation scheme, the quench current of RC3 improved to 6485 A, which is about three times the average quench current of a dozen racetrack coils that had been fabricated and reacted using the conventional 1 bar heat treatment. The results confirm the effectiveness of the OPHT technology and the new leakage control scheme for coils made from Bi-2212 Rutherford cables. Coils exhibited an increased quench current with increasing the current ramp rate from 5 to 200 A s−1; they were quite stable against point and transient disturbances, and were capable of adsorbing persistent Joule heating at ∼80 mW for >15 s before quenching. These behaviors are different from Nb–Ti and Nb3Sn accelerator magnets. Overall, our results provide a critical evaluation and verification of Bi-2212 wire and magnet technologies (wire, insulation, heat treatment, coil fabrication, and coil operation), reveal crucial new stability features of Bi-2212 magnets, and demonstrate technological options for it to become a practical high-field magnet technology.

Does Retrofitted Insulation Reduce Household Energy Use? Theory and Practice

We analyze the household energy use impacts of a large-scale, universally available, subsidized retrofit insulation and clean heat scheme. Theory shows that the energy-saving effects of such schemes are ambiguous. Our difference-in-differ-ence model of energy impacts resulting from each of insulation and clean heat treatment uses a sample of more than 12,000 treated houses. Retrofitted insulation treatment under the Warm Up New Zealand: Heat Smart program resulted in a statistically significant reduction in metered household energy consumption of almost 2%. Clean heat (heat pump) treatment resulted in increased electricity use but little change in total metered energy use other than at warmer temperatures, when heat pumps may have been used as air conditioners. Actual energy savings from insulation are approximately one-third of the modeled energy savings predicted by an engineering model.

Performance test of a 6 L liquid hydrogen fuel tank for unmanned aerial vehicles

A 6 L liquid hydrogen fuel tank has been designed, fabricated and tested to optimize boil-off rate and minimize weight for a 200 W light weight fuel cell in an unmanned aerial vehicle (UAV). The 200 W fuel cell required a maximum flow rate of 2.3 SLPM or less liquid hydrogen boil-off from the fuel tank. After looking at several different insulation schemes, the system was optimized as two concentric lightweight aluminum cylinders with high vacuum and multi-layer insulation in between. MLI thickness and support structures were designed to minimize the tank weight. For support, filling and feed gas to a fuel-cell, the system was designed with two G-10 CR tubes which connected the inner vessel to the outer shell. A secondary G10-CR support structure was also added to ensure stability and durability during a flight. After fabrication the fuel tank was filled with liquid hydrogen. A series of boil-off tests were performed in various operating conditions to confirm thermal performance of the fuel tank for a 200 W fuel cell.

Insulation system for high temperature superconductor cables

Large-scale superconductor applications, like fusion magnets, require high-current capacity conductors to limit system inductance and peak operating voltage. Several cabling methods using high temperature superconductor (HTS) tapes are presently under development so that the unique high-field, high-current-density, high operating temperature characteristics of 2nd generation REBCO coated conductors can be utilized in next generation fusion devices. Large-scale magnets are generally epoxy impregnated to support and distribute electromagnetic stresses through the magnet volume. However, the present generation of REBCO coated conductors are prone to delamination when tensile stresses are applied to the broad surface of REBCO tapes; this can occur during epoxy cure, cooldown, or magnet energization. We present the development of an insulation system which effectively insulates HTS cabled conductors at high withstand voltage while simultaneously preventing the intrusion of the epoxy impregnant into the cable, eliminating degradation due to conductor delamination. We also describe a small-scale coil test program to demonstrate the cable insulation scheme and present preliminary test results.

Experimental research on thermal insulation performance of lightweight ceramic material in oxidation environment up to 1700 °C

Because hypersonic vehicles face environments with extremely high temperatures in which the vehicles׳ outer shells experience single-sided heating and the temperature varies nonlinearly over time, a self-designed radiation and one-sided heating test apparatus is established in this paper, which can perform the thermal insulation performance test for lightweight ceramic thermal protection materials of hypersonic aircraft in extremely high-temperature/oxidation environments up to 1700°C. Meanwhile, experimental research on thermal insulation performance of a lightweight ceramic material specimen and a novel ceramic-nanomaterial hybrid structure in high-temperature/oxidation environments up to 1700°C was carried out. Different materials alone and in combination were analyzed and compared to select the most effective insulation scheme. It is found that the thermal insulation performance of the ceramic-nanomaterial hybrid thermal protection structure can be increased approximately 50% compared with that of the lightweight ceramic material specimen. Additionally, non-linear time-varying thermal environments with extremely high temperatures were generated and the thermal insulation performance tests were performed in this paper. The present work provides an important test method for the thermal protection design of hypersonic aircraft through the establishment and application of an extreme high-temperature/oxidation test system which can create one-sided heating, time-varying thermal environments.

HTS coil with enhanced thermal stability in over-current operation for fast response magnet power application

This paper examines the effect of improved winding geometry on high-temperature superconducting (HTS) coils for use in superconducting power applications. One of the most important functions in such a superconducting magnetic energy storage system is to charge–discharge the superconducting coils as fast as possible to secure sufficient power demand. The HTS coils are vulnerable to the thermal instability caused by cyclic and/or unexpected charge–discharge variation. Therefore, it is necessary to enhance the safety of the HTS coils under fast response operation at the request of varying loads. In this study, improved thermal stability in over-current operation is demonstrated by implementing the proposed insulation scheme. The performance of the HTS coil with the proposed winding geometry was experimentally evaluated in comparison with a conventional insulation (CI) coil. Cryo-stability characteristics of the proposed coil are verified with a circuit analysis under a charge–discharge operation scenario. The results of this study show the usefulness of the proposed winding coil as a replacement for CI coils, which have drawbacks related to thermal recovery rate in over-current operation.

Design of a Superconducting 28 GHz Ion Source Magnet for FRIB Using a Shell-Based Support Structure

The Superconducting Magnet Program at the Lawrence Berkeley National Laboratory (LBNL) is completing the design of a 28 GHz NbTi ion source magnet for the Facility for Rare Isotope Beams (FRIB). The design parameters are based on the parameters of the ECR ion source VENUS in operation at LBNL since 2002 featuring a sextupole-in-solenoids configuration. Whereas most of the magnet components (such as conductor, magnetic design, protection scheme) remain very similar to the VENUS magnet components, the support structure of the FRIB ion source uses a different concept. A shell-based support structure using bladders and keys is implemented in the design allowing fine tuning of the sextupole preload and reversibility of the magnet assembly process. As part of the design work, conductor insulation scheme, coil fabrication processes and assembly procedures are also explored to optimize performance. We present the main features of the design emphasizing the integrated design approach used at LBNL to achieve this result.

Numerical Simulation of Microchannel Deformation in Enhanced Insulation for Nb–Ti Superconducting Accelerator Magnets

A new insulation scheme for the Nb-Ti superconducting magnets to better extract heat from the coil was proposed in 2007, and several experiments were done to validate this novel concept, including the construction of a large aperture quadrupole. An essential parameter of this scheme is the size of the microchannels provided by a new topology of the insulation wrapping, allowing a direct helium path from the helium bath to the strands. The main question is whether these channels are still open under the large pressures induced during assembly and by electromagnetic forces. In this paper, one shows that a thermal model of the insulation scheme can be used to interpret the experimental data. The model suggests that the microchannels are significantly reduced with respect to their nominal values but are still well open. To validate this result, a finite-element model of the insulation and strands under pressure is done, and the behavior of this complex topology is estimated. The mechanical model confirms that the microchannels are open even under pressures of 100 MPa, with a cross-sectional reduction on the order of 50%. A parametric analysis of the microchannel deformation versus pressure is carried out, showing a good agreement with the experiments.

Fire behaviour of thermally insulated RC beams strengthened with NSM-CFRP strips: Experimental study

This paper presents the results of fire resistance tests on reinforced concrete (RC) beams flexurally strengthened with carbon fibre reinforced polymer (CFRP) strips installed according to the near surface mounted (NSM) technique using two different adhesives. The beams were simultaneously subjected to a service load and the ISO 834 standard fire. Different fire protection schemes were studied, comprising a thinner insulation layer along the bottom soffit of the beams and a thicker one at the CFRP anchorage zones. The main objectives of this paper were (i) to understand in further depth the fire behaviour of NSM-strengthened RC beams, in particular the structural effectiveness of the strengthening system during fire, (ii) to evaluate the efficiency of the above-mentioned fire protection strategy in extending the CFRP mechanical contribution during fire, and (iii) to compare the fire performance of the NSM-strengthening system with that of the alternative externally bonded reinforcement (EBR) technique, recently investigated under similar test conditions. The results obtained showed that using the adopted insulation schemes (i.e., thicker insulation at the anchorage zone and thinner insulation in the current zone), even after the CFRP-concrete bond is highly damaged in the central zone of the beams, the strengthening system is able to retain its structural effectiveness through a cable mechanism: for insulation thicknesses of 25 mm (current zone) and 50 mm (anchorage zones), the fire resistance of the strengthening system was extended up to 114 min. The loss of effectiveness of the CFRP system occurred when the average temperature in the adhesive at the CFRP anchorage zones attained values ranging from 2.2 to 5.6 times its glass transition temperature (Tg). The comparison with the EBR-strengthened beams confirmed the much better performance of the NSM strengthening.

A Study of the Composite Insulation Breakdown Properties for Wrapping Cables in Liquid Nitrogen

To optimize the insulation design of high-temperature superconductivity (HTS) cable, the multilayer wrapping cable insulation properties in the liquid nitrogen should be studied. In this paper, we investigated the breakdown properties of multilayer wrapping of cable insulation in liquid nitrogen. AC and dc breakdown tests of a minimodel cable with an insulation floor composed of polypropylene laminate paper (PPLP), PPLP/100HN (DuPont polyimide film), PPLP/100CR (DuPont polyimide film), and PPLP/150FCR019 (DuPont polyimide film) and of singer-layer sheets, including PPLP, 100HN, 100CR, and 150FCR019, respectively, were performed in liquid nitrogen. The breakdown characteristics of the sheets and model cable insulation consisting of PPLP and composite insulation schemes according to the arrangement of PPLP/HN, PPLP/100CR, and PPLP/150FCR019 were compared. For the sheets, the ac breakdown strength of 100HN is greater than that of 100CR; this may be because there are large amounts of organic-inorganic interface in 100CR. The dc breakdown strength of 100CR is greater than that of 100HN, which may be because the space charge of 100CR homogenizes the electric field. For the minimodel cable insulation, the dc and ac breakdown strengths of the composite insulation in which the third layer of wrapping tape insulation material was composed of three layers of 100HN, which is overlapped completely, are greater than those of the insulation consisting of PPLP and other composite insulations.