Thermal Isolation Research Articles

A Methodology to Qualitatively Select Upcycled Building Materials from Urban and Industrial Waste

The rising concern about climate change and other challenges faced by the planet led society to look for different design solutions and approaches towards a more balanced relationship between the built and natural environment. The circular economy is an effective alternative to the linear economic model inspired by natural metabolisms and the circular use of resources. This research explores how innovative strategies can be integrated for evaluating local urban and industrial wastes into sustainable building materials. A literature review is conducted focusing on circular design strategies, re-use, recycle, and waste transformation processes. Then, a methodology for the selection of upcycled and re-used building materials is developed based on Ashby’s method. A total of thirty-five types of partition walls, which include plastic, wood, paper, steel, aluminium, and agricultural wastes, are evaluated using a multi-criteria decision aid (M-MACBETH). Among these solutions, ten types of walls show high-performance thermal and sound isolation, fourteen types are effective for coating, and two exhibit structural reliability. Regardless of their functional limitations, the proposed solutions based on waste materials bear great potential within the construction industry.

Establishment of the basidiomycete Fomes fomentarius for the production of composite materials

BackgroundFilamentous fungi of the phylum Basidiomycota are considered as an attractive source for the biotechnological production of composite materials. The ability of many basidiomycetes to accept residual lignocellulosic plant biomass from agriculture and forestry such as straw, shives and sawdust as substrates and to bind and glue together these otherwise loose but reinforcing substrate particles into their mycelial network, makes them ideal candidates to produce biological composites to replace petroleum-based synthetic plastics and foams in the near future.ResultsHere, we describe for the first time the application potential of the tinder fungus Fomes fomentarius for lab-scale production of mycelium composites. We used fine, medium and coarse particle fractions of hemp shives and rapeseed straw to produce a set of diverse composite materials and show that the mechanical materials properties are dependent on the nature and particle size of the substrates. Compression tests and scanning electron microscopy were used to characterize composite material properties and to model their compression behaviour by numerical simulations. Their properties were compared amongst each other and with the benchmark expanded polystyrene (EPS), a petroleum-based foam used for thermal isolation in the construction industry. Our analyses uncovered that EPS shows an elastic modulus of 2.37 ± 0.17 MPa which is 4-times higher compared to the F. fomentarius composite materials whereas the compressive strength of 0.09 ± 0.003 MPa is in the range of the fungal composite material. However, when comparing the ability to take up compressive forces at higher strain values, the fungal composites performed better than EPS. Hemp-shive based composites were able to resist a compressive force of 0.2 MPa at 50% compression, rapeseed composites 0.3 MPa but EPS only 0.15 MPa.ConclusionThe data obtained in this study suggest that F. fomentarius constitutes a promising cell factory for the future production of fungal composite materials with similar mechanical behaviour as synthetic foams such as EPS. Future work will focus on designing materials characteristics through optimizing substrate properties, cultivation conditions and by modulating growth and cell wall composition of F. fomentarius, i.e. factors that contribute on the meso- and microscale level to the composite behaviour.

Development of an insulating material based on Trametes elegans mycelium and the study of its hygrothermal properties

This work presents the hygroscopic and thermal properties of a material developed from cornstalk and mycelium. The materials were produced using strains of macromycete fungi Trametes elegans as a natural binder for application as thermal isolation. The results shown are for the equilibrium moisture content on a wet basis and on a dry basis, moisture absorption in different relative humidity environments and thermal conductivity. The results obtained show that the hygrothermal properties of this material make it suitable as a thermal insulator, having a thermal conductivity value of 0.043 W/(m K) and absorbing less than 9% humidity in environments of up to 85% relative humidity.

A Simple Experimental Setup for Simultaneous Superfluid-Response and Heat-Capacity Measurements for Helium in Confined Geometries

Torsional oscillator (TO) is an experimental technique which is widely used to investigate superfluid responses in helium systems confined in porous materials or adsorbed on substrates. In these systems, heat capacity (HC) is also an important quantity to study the local thermodynamic properties. We have developed a simple method to incorporate the capability of HC measurement into an existing TO without modifying the TO itself. By inserting a rigid thermal isolation support made of alumina and a weak thermal link made of fine copper wires between a standard TO and the mixing chamber of a dilution refrigerator in parallel, we were able to carry out simultaneous TO and HC measurements on exactly the same helium sample, i.e., four atomic layers of $^4$He adsorbed on graphite, with good accuracies down to 30 mK. The data reproduced very well the previous workers' results obtained independently using setups optimized for individual measurements. This method is conveniently applicable to a variety of experiments where careful comparisons between results of TO and HC measurements are crucial. We describe how to design the thermal isolation support and the weak thermal link to manage conflicting requirements in the two techniques.

The concept of Representative Crack Elements (RCE) for phase-field fracture: transient thermo-mechanics

The phase-field formulation for fracture based on the framework of representative crack elements is extended to transient thermo-mechanics. The finite element formulation is derived starting from the variational principle of total virtual power. The intention of this manuscript is to demonstrate the potential of the framework for multi-physical fracture models and complex processes inside the crack. The present model at hand allows to predict realistic deformation kinematics and heat fluxes at cracks. At the application of fully coupled, transient thermo-elasticity to a pre-cracked plate, the opened crack yields thermal isolation between both parts of the plate. Inhomogeneous thermal strains result in a curved crack surface, inhomogeneous recontact and finally heat flow through the crack regions in contact. The novel phase-field framework further allows to study processes inside the crack, which is demonstrated by heat radiation between opened crack surfaces. Finally, numerically calculated crack paths at a disc subjected to thermal shock load are compared to experimental results from literature and a curved crack in a three-dimensional application are presented.

Engineering Properties and Applications of Air-Foamed Lightweight Soil

With the continuous development of road construction worldwide, the construction sector is trying to find a versatile material for building roads in particular areas. Air-foamed lightweight soil, which is produced using low-cost raw materials and has a lower density varying from 300 to 1800 kg/m3, adjustable strength, excellent thermal isolation, and a more straightforward construction method, has emerged as a worthy candidate. This paper reviews air-foamed lightweight soil in terms of its composition as well as physical and mechanical properties, such as its compressive strength, flexural strength, and stability. This paper also generalizes the engineering applications of air-foamed lightweight soil and provides ideas for its wide use.

500-A LaB6 Hollow cathode for high power electric thrusters

NASA continues to develop higher power ion and Hall thrusters for deep space human and robotic missions that require higher thrust and specific impulse than available in current thrusters. The NASA XR-100 nested Hall thruster successfully operated at 100 kW of power; driven by a JPL LaB6 hollow cathode that produced up to 250 A of discharge current in the thruster and 25–350A in the cathode test facility. The next generation of this LaB6 hollow cathode has been designed and built at JPL and tested at up to 500 A of discharge current. Extending the current to this high level was challenging, with iterations in the design necessary to provide adequate thermal isolation of the insert to lower the heater power required to ignite, to achieve sufficient keeper discharge current to aid in the startup, and to maintain the cathode orifice plate at acceptable temperatures during very high current operation. The 2nd generation version of the cathode successfully achieved 500 A of discharge current operation with low high-energy ion content. Discussions of the plasma instabilities observed in the plume, the plasma penetration into the insert region, and cathode life are provided.

Study on the Equivalent Average Temperature Variation of the Coal Core during the Freeze Coring Process.

In the freeze coring process, the core tube is subjected to cutting heat, frictional heat with the coal wall, and refrigerant action, which causes the temperature of the coal core to be different at different positions and at different times. The equivalent average temperature is proposed to represent the change law of the whole temperature of the coal core and to provide the temperature boundary condition for calculating gas loss. Relying on the self-developed simulation platform for the freezing response characteristics of gas-containing coal, a temperature change simulation test of the freezing core under different external heat conditions was carried out, and the freezing core heat transfer model was constructed with the help of COMSOL to analyze the coal core radial temperature changes during the freeze coring process. Because the drilling sampling time of the freeze coring process is short and there is a thermal isolation device between the drill bit and the core tube, the influence of cutting heat is ignored when the model is established, and only the coal core diameter is studied. The results show that the law of equivalent average temperature of the coal core with time is consistent with the experimental law, which is divided into three stages: rapid decline, slow decline, and relative stability. The temperature drop amplitude and rate of the equivalent average temperature of the coal core decrease with increasing external heat temperature. For example, when the external temperature is 60, 70, 80, and 90 °C, the limit temperatures of the equivalent average temperature of the coal core are −36.301, −30.358, −23.956, and −18.899 °C, respectively.

Multifunctional TPU composite foams with embedded biomass-derived carbon networks for electromagnetic interference shielding

Although flexible and lightweight electromagnetic interference (EMI) shielding materials have drawn a host of interest in recent years, it is still an issue to design multifunctional polymer composite foams reinforced with biomass-derived 3D carbon skeletons for integrating outstanding performances in EMI shielding, thermal isolation and joule heating. Herein, lightweight and flexible thermoplastic polyurethane (TPU) composite foams with the combination of highly conductive cotton-derived 3D carbon networks and microporous elastic TPU skeleton have been manufactured by facile freeze-drying method, and they could not only show high shielding effectiveness up to ∼68 dB at low thickness and density (∼0.2 g/cm3), but also possess satisfactory thermal-insulation performance and excellent low-voltage driven joule-heating capability with good recyclability and long-term durability. The multifunctionality of such foams could provide the ability to minimize the influence of external temperature on the working performance of protected electronic equipments during EMI shielding, suggesting the availability and effectiveness of biomass-derived 3D carbon skeletons for preparing flexible and multifunctional CPC foams.

Effect of ceramic coating thickness on fracture behaviour of coating structure under thermal shock cycles

Ceramic coatings are commonly used to fulfil some form of protection function, such as thermal protection, electric isolation, or corrosion resistance. However, coating failure caused by mechanical mechanisms can reduce the effectiveness of these functions. In this study, the effect of the coating thickness of thermal barrier coatings on fracture behaviour was investigated to understand its importance and the related mechanical mechanisms. Thermal shock cycling experiments were conducted with a corresponding stress analysis based on the finite element method. The results indicate that coatings thicker than 300 μm are more likely to fail after a low number of cycles, the number of cycles at the failure of 500 μm coatings is only 16.6% of that of 100 μm coatings, and the underlying mechanism can be explained as the larger compressive stress influence of thicker coatings. The residual compressive stress increased to 125 MPa only after ten cycles for 300 μm coatings.

Second-Scale 9 Be + Spin Coherence in a Compact Penning Trap

We report microwave spectroscopy of co-trapped $^9\text{Be}^+$ and $^{40}\text{Ca}^+$ within a compact permanent-magnet-based Penning ion trap. The trap is constructed with a reconfigurable array of NdFeB rings providing a 0.654 T magnetic field that is near the 0.6774-T magnetic-field-insensitive hyperfine transition in $^9\text{Be}^+$. Performing Ramsey spectroscopy on this hyperfine transition, we demonstrate nuclear spin coherence with a contrast decay time of >1 s. The $^9\text{Be}^+$ is sympathetically cooled by a Coulomb crystal of $^{40}\text{Ca}^+$, which minimizes $^9\text{Be}^+$ illumination and thus mitigates reactive loss. Introducing a unique high-magnetic-field optical detection scheme for $^{40}\text{Ca}^+$, we perform spin state readout without a 729~nm shelving laser. We record a fractional trap magnetic field instability below 20 ppb (<13 nT) at 43 s of averaging time with no magnetic shielding and only passive thermal isolation. We discuss potential applications of this compact, reconfigurable Penning trap.

Integration of Bio-based Insulation Materials as a Contribution to the Biological Transformation of Production Technology

In the context of a circular economy, the adoption of biological principles and materials play a decisive role in the transformation to a more sustainable production technology. Ecologically harmful materials such as polystyrene (so-called Styrofoam), for example, has properties for thermal and acoustic isolation. This material has therefore been used in production machinery to control thermal issues and improve product quality. Here, the use of renewable and biodegradable materials can ensure these measures have a minimal environmental footprint while maintaining the intended functionality.This paper serves to open-up opportunities and define requirements for the integration of bio-based isolation materials in production machines. For both thermal and acoustic issues, the place of implementation and the choice of insulation material, as well as its shape and composition, determine the ability to isolate over the required temperature range. In addition, coatings and surface functionalization offer possibilities for using bio-based materials even under demanding process conditions. Concluding, the experimental approach on the effectiveness of bio-based insulation materials within a machine tool is presented. The technologies presented in this work have been developed by the participating Fraunhofer institutes.

Power Sensor Characterization From 110 to 170 GHz Using a Waveguide Calorimeter

This article proposes a new calorimetry-based measurement method to measure absolute microwave power obtained through dc substituted power from 110 to 170 GHz (WG 29, WR 6/7, or D-band) using a custom-designed thin-film microwave power sensor. This method complements traditional microcalorimetry techniques used to provide traceability for microwave power in this band while diversifying the potential applications and accessibility to such traceability. The thermopile of the measurement system was characterized using a known dc power with the microwave sensor and the thermopile coefficient obtained. Absolute microwave power on the microwave sensor was calculated using the thermopile coefficient and was used to remove the effect of a thermal isolation section (TIS) and calorimeter unbalance effect. To transfer the power traceability from the calorimeter to microwave power measurement applications, the effective efficiency of a device under test (DUT), consisting of a power sensor/meter combination, was defined using the calorimeter’s absolute microwave power and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters of the measurement system and the DUT. The effective efficiency (EE) of the DUT was obtained between 0.9386 and 0.9815 for the whole frequency band.

Design of a flexible surface/interlayer for packaging.

Impact resistance and thermal insulation are important factors to be considered in the fields of encapsulation and drug transportation. In this study, a classic circular sleeve structure is designed by integrating the multi-level surface topography of the sleeve and a hollow sandwich in the wall, which effectively improves the energy absorption efficiency and thermal insulation effect. With the increase of the levels of surface structure, the stiffness of the whole structure and the stress on the topmost structure decreases, which is conducive to protecting the structure. In addition, the thermal conduction efficiency can be limited and the heat preservation ability would be improved as the reduction of the contacting area of packages with internal objects is attributed to such specific topography. Moreover, the synergistic effect of the hollow sandwich further enhances the advantages of mechanics and heat insulation. Based on the findings of this study, this novel design has potential applications in fields such as thermal insulation, packaging, and pharmaceuticals.

Magnetic-electric composite coating with oriented segregated structure for enhanced electromagnetic shielding

Manipulation of the internal architecture is essential for electromagnetic interference (EMI) shielding performance of metal-based coatings, which can address the electromagnetic pollution in large-size, complex geometries, and harsh environments. In this work, oriented segregated structure with conductive networks embedded in magnetic matrix was achieved in Fe-based amorphous coatings via Ni–Cu–P functionalization of (Fe0.76Si0.09B0.1P0.05)99Nb1 amorphous powder precursors and then thermal spraying them onto aluminum (Al) substrate. Benefiting from the unique magnetic-electric structure, the [email protected] composite delivered prominent EMI shielding performance. The EMI shielding effectiveness (SE) of modified [email protected] composite is ~41 dB at 8–12 GHz, doubling the value of Al substrate and is 15 dB greater than that of Ni–Cu–P-free [email protected] composite. Microstructure analysis showed that the introduced Ni−Cu−P insertions forcefully suppress the serious oxidation of the magnetic precursors during thermal spraying and form a dense conductive network in the magnetic matrix. Electron holography observation and electromagnetism simulation clarified that the modified coating can effectively trap and attenuate the incident radiations because of the electric loss from Ni−Cu−P conductive network, magnetic loss from Fe-based amorphous coating, and the electromagnetic interactions in the oriented segregated architectures. Moreover, the optimized thermal isolation and mechanical properties brought by structural improvement enable the coating to shield complex parts in thermal shock and mechanical loading environments. Our work gives an insight on the design strategies for metal-based EMI shielding materials and enriches the fundamental understanding of EMI shielding mechanisms.

A Study to Explore the Dew Condensation Potential of Cars

The metal surfaces of a car exhibit favorable properties for the passive condensation of atmospheric water. Under certain nocturnal climatic conditions (high relative humidity, weak windspeed, and total nebulosity), dew is often observed on cars, and it is appropriate to ask the question of using a vehicle as a standard condenser for estimating the dew yield. In order to see whether cars can be used as reference dew condensers, we report a detailed study of radiative cooling and dew formation on cars in the presence of radiating obstacles and for various windspeeds. Measurements of temperature and condensed dew mass on different car parts (rooftop, front and back hoods, windshield, lateral and back windows, inside and outside air) are compared with the same data obtained on a horizontal, thermally isolated planar film. The paper concludes that heat transfer coefficients, evaluated from temperature and dew yield measurements, are found nearly independent of windspeed and tilt angles. Moreover, this work describes the relation between cooling and dew condensation with the presence or not of thermal isolation. This dependence varies with the surface tilt angle according to the angular dependence of the atmosphere radiation. This work also confirms that cars can be used to estimate the dew yields in a given site. A visual observation scale h = Kn, with h the dew yield (mm) and n = 0, 1 2, 3 an index, which depends whether dew forms or not on rooftop, windshield, and lateral windows, is successfully tested with 8 different cars in 5 sites with three different climates, using K = (0.067 ± 0.0036) mm·day−1.

Design of a Mass Air Flow Sensor Employing Additive Manufacturing and Standard Airfoil Geometry

This work concerns the design, fabrication, and preliminary characterization of a novel sensor for determining the air intake of low and medium power internal combustion engines employed at various applications in the marine industry. The novelty of the presented sensor focuses on the fabrication process, which is based on additive manufacturing combined with PCB technology, and the design of the sensing elements housing geometry, which is derived through suitable CFD simulations and is based on standard airfoil geometry. The proposed process enables low-cost, fast fabrication, effective thermal isolation, and facile electrical interconnection to the corresponding circuitry of the sensor. For initial characterization purposes, the prototype device was integrated into a DIESEL engine testbed while a commercially available mass air flow sensor was employed as a reference; the proper functionality of the developed prototype has been validated. Key features of the proposed device are low-cost, fast on-site manufacturing of the device, robustness, and simplicity, suggesting numerous potential applications in marine engineering.

Field-dependent nonelectronic contributions to thermal conductivity in a metallic ferromagnet with low Gilbert damping

Heat conduction in metals is typically dominated by electron transport since electrons carry both charge and heat. In magnetic metals magnons, or spin waves, excitations of the magnetic order can be used to transport information. Heat conduction via magnons has been previously shown mostly for insulating magnets with low Gilbert damping and resulting long spin-wave lifetimes where conduction electrons cannot contribute. Here we show that thin films of properly optimized metallic ferromagnetic (FM) alloys show significant nonelectronic contributions to heat conduction, which furthermore depend on the direction of an applied magnetic field. These measurements are enabled by micromachined thermal isolation platforms optimized for thermal conductivity measurements of thin-film systems. Electrical conductivity measurements on exactly the same samples allow application of the Wiedemann-Franz relation, which shows large nonelectronic contributions to thermal conductivity for the cobalt-iron alloy with $25%$ Co. This composition has been shown to have exceptionally low damping for a metallic FM. The thermal conductivity of a 75-nm-thick film of the $25%$ Co alloy changes by more than $20%$ at some temperatures, while a reference sample with $50%$ cobalt that has much higher damping shows no field-direction dependence. Our measurements indicate that applied magnetic fields alter the magnon lifetimes in these films and that these magnons contribute to thermal conductivity in this metallic magnetic alloy with low Gilbert damping.

Integrating Design of Flexible Surface and Gradient Porosity Interlayer for Improving Impact Resistance and Thermal Isolation

A flexible porous interlayer is vital for stress transfer and energy storage; thus, it is widely used in the packaging field. The pomelo peel as a representative gradient porous topography is necessary for the protection of the seed and pulp. On subjecting the surface to an external force, the gradient porous interlayer of the pomelo peel not only generates a large deformation inside the peel for decreasing the stress on the pulp, but also decreases the deformation and stress at the upper surface for enhancing the stability of the surface topography. Combined with the surface structure design of the lotus leaf and gradient porosity interlayer of the pomelo peel, a sample with flexible multilevel topography surface and gradient porosity interlayer is successfully prepared herein for improving the impact resistance and extending the superhydrophobic/icephobic functions. This novel binary design has potential applications in rapid energy absorption, packaging, and thermal isolation.

Thermal insulation of autoclaved materials

The construction industry relies on the production of building materials, which are created as a result of particular actions of binding materials widely used in construction, and directly condition the quality of life of a society. Following these thesis, one should create possibilities of conscious choice and use of building materials not only among scientists and constructors, but among the whole society. Two types of additives are used in building materials: additives with a crystalline structure (SiO2) and additives with an amorphous structure (fly ash), which affects the properties and durability of materials. In the last decade industry is also moved on the fight against global warming and overproduction of materials. In May 2019, the level of CO2 concentration in the atmosphere exceeded 415ppm, which was the highest result in the last 50 years. Overproduction is, in turn, associated with the excessive use of natural resources (SiO2) and since 2010 there has been talk of the “sand deficit”. One way to combat overproduction is to use and promote recycling to avoid excess waste. The article describes the method of managing recycled glass sand in autoclaved materials and checking their thermal properties. This study describes the relationship between the physical (thermal isolation), mechanical and microstructural properties of autoclaved materials which undergone hydrothermal treatment and consist of lime (7%) and were modified through the introduction of glass components (up to 90%). For this modification, a certain amount of crystalline SiO2 was replaced with amorphous glass sand. Hydrated calcium silicates are formed in building materials (CaO-SiO2-H2O).