Fibrous Insulation Research Articles

Design, formation, and property of high emissivity WSi2-Si-glass hybrid coating on fibrous ZrO2 ceramic for reusable thermal protection system

The objective of this research was to develop a high emissivity coating on the low thermal conductive insulation for reusable thermal protection system. The design principles including high emissivity, match of the coefficients of thermal expansion and excellent high temperature stability were proposed for the first time. A novel WSi2-Si-glass hybrid coating with optimized composition was successfully prepared on fibrous ZrO2 ceramic insulation by slurry dipping and subsequent high temperature rapid sintering method. The total emissivity of the as-prepared coating is up to 0.92 in wavelength of 0.3–2.5µm. After oxidation at 1673K for 100h and 1773K for 20h, the total emissivity values of the coatings are still as high as 0.89 and 0.87. A competitive mechanism between the “defects formation” caused by aging stress, the CTE mismatch stress and the volatilization of low melting point oxides and the “defects healing” resulted from self–healing phases during the different oxidizing conditions was discussed.

Effect of air leakage on the hygrothermal performance of highly insulated wood frame walls: Comparison of air leakage modelling methods

Air leakage is one of the important moisture sources that may increase the risk of moisture problems in wood frame walls. Two simplified air leakage modeling methods, i.e. air convection method and air infiltration method, can be implemented in commonly used hygrothermal models. This paper investigates the applicability of these two methods in evaluating the hygrothermal performance of three types of wood frame walls: one baseline 2 × 6 wood frame with fiberglass insulation, two highly insulated walls, i.e. deep cavity wall with I-joist framing and cellulose fiber insulation and 2 × 6 farming with exterior polyisocyanurate insulation and fiberglass stud cavity insulation. Firstly, the hygrothermal models are calibrated by comparison to measurements. Then the best matched models are used for two years' simulation to evaluate the mold growth risk of these walls at various airtightness levels. The results show that both methods can model the effect of air leakage reasonably well by adjusting the position of air layer in the air convection method and the amount of the indoor air reaching the condensation plane in the air infiltration method. The air infiltration method tends to overestimate the moisture content of OSB sheathing, while the air convection method tends to underestimate the moisture content of OSB sheathing. The baseline wall has higher mold growth risk than the I-joist wall with cellulose fiber, while the I-joist wall's mold growth risk becomes slightly higher than the baseline wall when the insulation materials are changed to fiberglass. The exterior insulated wall has no risk of condensation and mold growth.

Fiber’s hygromorphic effect on thermal conductivity of wooden fibrous insulation characterized by X-ray tomography

Fibrous-woods have very complex morphology and high heterogeneity, hence their properties are not well-known and need to be investigated, especially concerning microstructural changes due to hygro-thermal loads. The present, experimental and numerical work studies the microstructural hygro-thermal behavior of such material. The experimental procedure was performed on the microstructure level using the non-destructive method; X-ray tomography through a specifically developed processing protocol. The reconstructed volumes have a fine resolution of 7µm/voxel. The volumetric analysis illustrated a representative elementary volume of 57mm3. The geometrical microstructure properties (porosity, fiber diameter and pore, fiber orientation, etc.) were extracted from the 3D image analysis. Moreover, a successive X-ray scans of the same fibrous specimen solicited at different relative humidity levels were achieved. The evolution of both the average and the local fibers’ diameters distribution properties as a function of the water content were examined. The material’s porosity and its fibers’ thicknesses show an explicit correlation with the water content. Also, heat transfer simulation of the 3D real insulation structure was evaluated using the energy balance equation. The effective thermal conductivity is computed as a function of the relative humidity. Interlink between the porosity and the thermal conductivity was established too. The results provide enhance our understand of the wood fiber insulation’s behavior.

Mechanical Effects of the Nonuniform Current Distribution on HTS Coils for Accelerators Wound With REBCO Roebel Cable

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The EuCARD-2 WP10 Future Magnets collaboration is aiming at testing HTS-based Roebel cables in an accelerator magnet. The demonstrator should produce around 17 T, when inserted into the 100-mm aperture of Feather-M2 13-T outsert magnet. HTS Roebel cables are assembled from meander-shaped REBCO-coated conductor tapes. In comparison with fair level of uniformity of current distribution in cables made out of round Nb-Ti or Nb 3 Sn strands, current distribution within the coils wound from Roebel cables is highly nonhomogeneous. It results in nonuniform electromagnetic force distribution over the cable that could damage the very thin REBCO superconducting layer. This paper focuses on the numerical models to describe the effect of the nonhomogeneous current distribution on stress distribution in the demonstrator magnet designed for the EuCARD-2 project. Preliminary results indicate that the impregnation bonding between the cable glass fiber insulation and layer-to-layer insulation plays a significant role in the pressure distribution at the cable edges. The stress levels are safe for Roebel cables. Assuming fully bonded connection at the interface, the stresses around the edges are reduced by a large factor.

Influence of envelope insulation materials on building energy consumption

In this paper, the influence of different external wall insulation materials on the energy consumption of a newly built apartment in Germany is investigated. Three types of insulation materials commonly used in Germany including mineral fiber, polyurethane, and vacuum insulation panel are chosen for the case studies. An energy analysis model is established to clarify the primary energy use for production of the insulation materials and for building space heating. The calculation results show that the energy consumption for insulation material production increases with the insulation thickness, whereas the energy use for space heating decreases with the insulation thickness. Thus, there exists an optimum thickness to get the lowest total energy consumption for each kind of insulation material. The ascending order of the total energy consumption of the three materials is mineral fiber, polyurethane, and vacuum insulation panel. However, the optimum insulation thicknesses for the three insulation materials show a verse order at a certain heat transfer coefficient of the base envelope. The energy payback time (EPT) is proposed to calculate the payback time of the primary energy use for insulation material production. Mineral fiber has the shortest time, followed by polyurethane and vacuum insulation panel. The EPTS is 10, 19 and 21 years, respectively when the heat transfer coefficient of the base envelope is 0.2 W/(m2·K). In addition, the simulated results show that the theoretical value and the simulated value are basically identical.

Effect of TaSi2 content on the structure and properties of TaSi2-MoSi2-borosilicate glass coating on fibrous insulations for enhanced surficial thermal radiation

TaSi2-MoSi2-borosilicate glass coatings with high emissivity were prepared on mullite fibrous ceramics via a slurry technique to enhance surficial thermal radiation and serve in the thermal protection systems for aircrafts. The effect of TaSi2 dosages on the coatings' structure, phase composition, emissivity, thermal shock resistance and thermal endurance were investigated. The results show that all the coatings were flat and uniform, while the surface roughness and porosity increased with TaSi2 dosages. Part of TaSi2 was oxidized into Ta2O5 during the coating preparation, and finally, the coating with TaSi2 dosage of 45wt% (C-45Ta) had the highest TaSi2 content. Emissivity of the coatings increased with TaSi2 contents. The total emissivity of C-45Ta was 0.855 in the range of 3–14.5μm at 150°C, while that of the coating without TaSi2 (C-0Ta) was 0.809. However, compared with C-0Ta, C-45Ta showed worse thermal shock resistance because of its higher CTE mismatch with the substrate and higher porosity. The thermal endurance of C-45Ta was worse due to the limited oxidation resistance of TaSi2 and the lower borosilicate glass content.

Wood Fiber vs Synthetic Thermal Insulation for Roofs Energy Retrofit: A Case Study in Turin, Italy

Abstract In this paper the thermal performance of synthetic and natural insulation materials under real applications are investigated through an experimental activity as well as numerical simulations. During the refurbishment of two houses in Turin (north western Italy) one roof was insulated with a natural material (wood fiber panels) and the other one with a business as usual synthetic material (XPS and polyurethane). An experimental activity was carried out, both during summer and winter seasons, and the results were used to validate a simplified model. During winter, as expected, the strongest influence on the global performance is related to the insulation thickness. As far as the summer season performance is regarded, for smaller roof surfaces, as for the analysed case study, no particular difference was noticed between the two solutions. A better control of the indoor air temperature was evaluated for the wood fiber insulation when applied on a large surface of the roof. In order to define the best cost-benefit retrofit solutions, ad-hoc evaluations need to be performed.

Determination of thermal diffusivity of fibrous insulating materials at high temperatures by thermal wave analysis

This work investigates the potential of measuring thermal diffusivity of materials in the high temperature range up to 1580°C by thermal wave analysis of cylindrical samples. In particular, aiming at the typical situation of fiber insulation materials, the method is evaluated for investigations on heterogeneous media with low thermal conductivity, low density and heat capacity, and significant internal radiative heat transport (participating media). Furthermore, a model for combined conductive and radiative heat transfer is introduced. The model is adapted to a commercial insulation material using experimental scattering and absorption spectra evaluated at 1000°C. The predictions of this numerical model are in accordance with the thermal diffusivity data obtained from the thermal wave analyses.

Gradient structure high emissivity MoSi2-SiO2-SiOC coating for thermal protective application

This study presents a one-pot preparation of gradient porous high emissivity coatings on ceramic fibrous insulations. MoSi2-SiO2-SiOC coatings have been prepared on mullite fibrous substrates with polysiloxane-derived SiOC glass as low-temperature adhesive, SiO2 as high-temperature ceramic aggregate, MoSi2 as emission agent and polydimethylsiloxane (PDMS) as pore former by slurry-spraying, drying and sintering. Scanning electron microscopy shows the MoSi2-SiO2-SiOC coating gradually changes from a porous structure into a dense structure with obviously decreasing porosity from substrate to surface. The pore size and porosity of the bonding-layer increase with the PDMS content and the density of the surface-layer increases with the sintering temperature suggesting the gradient porous structure is formed by two-steps of “low-temperature decomposition pore-forming” and “high-temperature sintering pore-sealing” during sintering. Firstly, the pores come into formation after decomposition of PDMS and the organic-to-inorganic transformation of the SiOC glass at lower temperature (<1000 °C). Secondly, the formed pores are partly sealed accompanied by carbothermal reduction of the SiOC glass and carburization reaction of the MoSi2 at higher temperature (>1400 °C). The gradient MoSi2-SiO2-SiOC coating increases the bonding strength between the coating and substrate up to 0.6 MPa, which is nearly twice as high as that of dense MoSi2-SiO2 coating. The MoSi2-SiO2-SiOC coating exhibits high spectral emissivity (0.90 at 700 °C), excellent thermal shock resistance (90 cycles without cracking at 25–1500 °C) and oxidation resistance up to 1500 °C, all of which can meet requirements of high temperature application.

Effects of Ceramic Fibre Insulation Thickness on Skin Formation and Nodule Characteristics of Thin Wall Ductile Iron Casting

Skin formation has become one of the problems in the thin wall ductile iron casting because it will reduce the mechanical properties of the materials. One of the solutions to reduce this skin formation is by using heat insulator to control the cooling rate. One of the insulators used for this purpose is ceramic fibre. In this research, the thickness of the ceramic fibre heat insulator used in the mould was varied, i.e. 50 mm on one side and 37.5 mm on the other side (A), no heat insulator (B), and 37.5 mm on both sides (C). After the casting process, the results were characterized in terms of metallography by using scanning electron microscope (SEM) and tensile test for mechanical properties. The results showed that the skin thickness formed in A is 34.21 μm, 23.38 μm in B, and 27.78 μm in C. The nodule count in A is 541.98 nodule/mm2 (84.7%) with an average diameter of 15.14 μm, 590 nodule/mm2 (86.7%) with an average diameter of 13.18 μm in B, and 549.73 nodule/mm2 (87.2%) with an average diameter of 13.95 μm in C. The average ultimate tensile strength for A was 399 MPa, B was 314 MPa, and C was 415 MPa. Microstructural examination under SEM showed that the materials have a ductile fracture with matrix full of ferrite.

Tomography based analysis of conduction anisotropy in fibrous insulation

The anisotropic conductivity of high porosity fibrous glasswool insulation is characterized using tomographic reconstruction data. Direction dependent effective conductivity values are obtained by solving the 3D heat equation over a sample with temperature drops applied along multiple directions. A piece of glasswool is inserted into a square syringe and incrementally compressed to simulate variation in porosity occurring in application cases. The conductivity tensor is obtained using directional conductivities within the conductivity ellipsoid formulation for solid to fluid conductivity ratios, (ks/kf), increasing from 10 to 400, at each porosity. Principal effective conductivity values in 3D are obtained from the tensor. These are compared with experimental measurements: the ratio of effective conductivity to the conductivity of air keff/kf from laboratory measurements varies between 1.19 and 1.28 while the same ratio obtained from simulation using a sample of similar porosity varies between 1.05 and 1.30 depending on the direction of heat flow. Simulation results are compared with various effective conductivity models for high porosity fibrous media. The Halpin-Tsai model predicts the minimum conductivity, which occurs transverse to the fiber plane, within an error of 2.1% over the entire range of conductivity ratios and sample porosities simulated. The Miller Upper Bound model for needle-like inclusions best predicts the maximum conductivity, which occurs in the fiber plane, with a root mean square error of 3.9%. The degree of anisotropy, i.e., ratio of maximum to minimum principal values, is also examined across the porosity range: anisotropy increases with decreasing porosity and with increasing ks/kf. The paper demonstrates, that anisotropic behavior of fibrous insulation materials can be readily explained by their micro geometry and in particular, by a layered fiber arrangement.

Temperature dependence of sorption isotherm of hygroscopic building materials. Part 1: Experimental evidence and modeling

The knowledge of sorption isotherm is of high importance when evaluating the performance and the durability of building envelope. Whereas the influence of hysteresis was often investigated, less attention has been paid to the influence of temperature. In the present paper, a specific experimental protocol is defined to investigate the influence of temperature on relative humidity variations within three building materials (Autoclaved Aerated Concrete, wood fiber insulation and hemp concrete). The measurements are analyzed in terms of a hygrometric coefficient κ [%r.h./°C], defined as the maximal relative humidity amplitude against the maximal temperature amplitude, and are compared to three modeling approaches: temperature dependent sorption model, Kelvin equation and Clausius-Clapeyron equation. Discussions show that the third approach is relevant and that it can be used to evaluate effortless the isosteric heat of sorption and the temperature dependence of the sorption isotherm.

Micro-tomography based analysis of thermal conductivity, diffusivity and oxidation behavior of rigid and flexible fibrous insulators

Material properties and oxidation behavior of low-density felts used as substrates for conformal carbon/phenolic ablators were compared with those of a rigid carbon fiber preform used to manufacture heritage lightweight ablators. Synchrotron X-ray micro-tomography measurements were performed to characterize the materials’ microstructure at the scale of the fibers. Using the tomography voxels as computational grids, tortuosity in the continuum regime, and room temperature conductivity were computed. Micro-scale simulations of the oxidation of carbon fibers were carried out using a random walk model for oxygen diffusion and a sticking probability law to model surface reactions. The study shows that, due to a higher porosity and lower connectivity, the felt materials have lower thermal conductivity but a faster recession rate than that of the rigid preform. Challenges associated with computations based on micro-tomography are also discussed.

The Possibilities of Modification of Crop-based Insulation Materials Applicable in Civil Engineering in Low-energy and Passive Houses

Currently in Europe there is a growing trend towards low energy and passive houses where natural materials are often used. These materials are very promising in terms of environmental protection. The use of green thermal insulation materials brings a significant reduction of energy requirements of buildings which is their major benefit. Previous research shows that crop-based thermal insulating materials exhibit very good thermal insulation and acoustic properties. However, their structure is different from conventional insulation materials (EPS, XPS, PUR, and MW) and their hygrothermal behaviour is much different. This article focuses on studying the behaviour of fibrous green insulations under humidity and moisture load. The test samples of the materials were treated with different types of hydrophobic agents before testing. The goal of the experiments was to reduce the sensitivity of the insulation to humidity and moisture (i.e. reduce their hygroscopicity). The chemical treatment of the fibres should improve the practical properties of the thermal insulation materials and extend their service life after they have been incorporated in a structure and attacked by moisture.

Hygric characterization of wood fiber insulation under uncertainty with dynamic measurements and Markov Chain Monte-Carlo algorithm

The present work is the hygric characterization of wood fibre insulation boards, using dynamic measurements of relative humidity and sample weight, analyzed in the frame of Bayesian inference for parameter identification under uncertainty. It is an attempt at identifying detailed profiles of moisture-dependent properties, and thus a relatively high number of parameters. Because of this ambition, some caution should be exercised once the outcome of the inversion algorithm is available: in addition to confidence intervals of parameters provided by the Bayesian framework, a simplified form of identifiability analysis is performed by analysing a posteriori parameter correlations and likelihood-based confidence intervals.The characterization methodology does not require for the model structure to have a differentiable analytical formulation, or for material samples to reach mass equilibrium between each RH step of the experimental process. Two separate experimental designs were used for material characterization and for validation, respectively. Results show a clear relation between available information (experimental data) and inference (confidence intervals of parameters). A single relative humidity step is not informative enough for a precise inference of moisture-dependent properties such as vapour permeability and moisture capacity. A two-step experiment however holds enough information to significantly reduce parameter uncertainty.

A rapid screening method to determine the susceptibility of bio-based construction and insulation products to mould growth

Mathematical models have been developed to evaluate materials' durability and susceptibility to biodeterioration by moulds, however models are material and mould species specific. Ultimately the best way to determine a materials’ susceptibility is to expose the material to microorganisms. This study attempted to develop a quick, reliable screening method to evaluate a number of different materials for their susceptibility to moulds at optimal and limiting conditions. This test method was based on modified versions of ASTM 4445-91 and BSEN 846. The water absorption coefficient and Dynamic Vapour Sorption tests were also conducted to determine any correlation between the materials hygric properties and mould growth. The materials used to validate the novel screening method were: MDF, laminated MDF, Chipboard, Laminated chipboard, Wool, Hemp, Wood fibre insulation and pine. It was found chipboard was the most susceptible to mould growth and wool the least when in direct and indirect contact with agar. Primary colonisers (A. niger) easily colonised the materials, regardless of the environmental conditions, whereas secondary (A. alternate) and tertiary (T, virens) colonisers were absent on materials under limiting conditions.

Silent Room: A (non)sensory interactive art installation

Simon Heijdens, a London-based Dutch artist, was commissioned by South by Southwest (SXSW), an annual film, media, and music festival in Austin, TX, to create an installation artwork to premiere at SXSW in March 2016. In reaction to the sensory overload of the festival, he created Silent Room. Students and professors from the University of Texas at Austin worked alongside Mr. Heijdens to design a portable, self-sufficient, reusable space providing sound isolation and absorption from outside and inside the chamber, respectively. Housing the space in a shipping container, Silent Room was successfully built and showcased at SXSW in downtown Austin to hundreds of visitors, achieving a minimum sound reduction of 27 dBA at 40 Hz and a maximum reduction of 55 dBA at 1.45 kHz. These results were achieved using a suspended floor and decoupled wall/ceiling construction of Auralex rubber U-Boats, 2” x 4” wood studs, mineral fiber insulation, plywood, Auralex SheetBlok vinyl, and acoustically treated gypsum board. After initial acoustical measurements, more U-Boats were added, decoupling the container underside from the street and isolating it from ground-borne vibration. However, the room performance worsened after this change, possibly due to exposure to a new air-borne path for noise ingress.

Study on the Principle Mechanisms of Heat Transfer for Cryogenic Insulations: Especially Accounting for the Temperature-Dependent Deposition–Evacuation of the Filling Gas (Self-Evacuating Systems)

This study concentrates on the principles of heat transfer within cryogenic insulation systems, especially accounting for self-evacuating systems (deposition–evacuation of the filling gas). These principles allow the extrapolation to other temperatures, gases and other materials with the input of only a few experimentally derived or carefully estimated material properties. The type of gas (e.g. air or \(\hbox {CO}_{2}\)) within the porous insulation material dominates the behaviour of the effective thermal conductivity during the cooldown of the cryogenic application. This is due to the specific temperature-dependent saturation gas pressure which determines the contribution of the gas conductivity. The selected material classes include powders, fibrous insulations, foams, aerogels and multilayer insulations in the temperature range of 20 K to 300 K. Novel within this study is an analytical function for the total and the mean thermal conductivity with respect to the temperature, type of gas, external pressure and material class of the insulation. Furthermore, the integral mean value of the thermal conductivity, the so-called mean thermal conductivity, is calculated for a mechanically evacuated insulation material and an insulation material evacuated by deposition–evacuation of the filling gas, respectively. This enables a comparison of the total thermal conductivity of cryogenic insulation materials and their applicability for a self-evacuating cryogenic insulation system.

Hydrophobic treatment of wood fibrous thermal insulator by octadecyltrichlorosilane and its influence on hygric properties and resistance against moulds

Abstract The natural fibrous materials are widely used as thermal insulator for building application. The thermal insulating performance of natural fibrous material are affecting by the high humidity and temperature. Due to high moisture in natural fibrous insulators, they are very susceptible for microorganisms attack as well as the reduction in the thermal insulating properties. In this work, hydrophobic surface treatment was given to the wood fibrous insulator using octadecyltrichlorosilane (OTS). The deposition of OTS monolayers on wood fibers surface was confirmed by X-ray photoelectron microscopy (XPS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and water contact angle of wood fibers measured by sessile drop method. The influence of hydrophobic treatment on hygric properties of wood fibrous insulator was characterized using especially designed double-climatic set-up. The effectiveness of hydrophobic treated wood fibers towards mould fungi growth was also examined. The hydrophobic treatment improved the hygric properties and effectiveness towards mould significantly.

Behavior of Wooden Based Insulations at High Temperatures

Insulation materials may give a different contribution to the fire resistance of timber frame assemblies. At present, Eurocode 5 Part 1-2 [1] provides a model for fire design of the load bearing function of timber frame assemblies with cavities completely filled with stone wool. The extension of this model for glass wool for post protection phase has been published in the European technical guideline Fire Safety in Timber Buildings [2]. Very little is known about the protection of bio-based insulation materials. Eight model scale furnace tests of floor specimens were carried out. Two different design tools to calculate the charring rate of timber frame assemblies insulated with wooden based insulations are provided. The first one is a design model for timber frame assemblies insulated with batt-type and loose fill cellulose fiber insulations. The second tool includes the functions of conductivity, specific heat and loss in mass against the temperature calibrated on the standard fire curve to implement advanced heat transfer calculations. The purpose is to give the designers two design procedures with a different level of complexity and accuracy.