scholarly journals Effect of density, phonon scattering and nanoporosity on the thermal conductivity of anisotropic cellulose nanocrystal foams

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Varvara Apostolopoulou-Kalkavoura ◽  
Pierre Munier ◽  
Lukasz Dlugozima ◽  
Veit-Lorenz Heuthe ◽  
Lennart Bergström
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Phonon Scattering ◽  
Cellulose Nanocrystal ◽  
Foam Density ◽  
Aqueous Dispersions ◽  
Gas Conduction ◽  
Insulation Performance ◽  
Ice Templating

AbstractAnisotropic cellulose nanocrystal (CNC) foams with densities between 25 and 130 kg m−3 (CNC25 –CNC130) were prepared by directional ice-templating of aqueous dispersions. Estimates of the solid and gas conduction contributions to the thermal conductivity of the foams using a parallel resistor model showed that the relatively small increase of the radial thermal conductivity with increasing foam density can be attributed to interfacial phonon scattering. The foam wall nanoporosity and, to a lesser extent, the orientation of the CNC particles and alignment of the columnar macropores, also influence the insulation performance of the foams. The insight on the importance of phonon scattering for the thermal insulation properties of nanocellulose foams provides useful guidelines for tailoring nanofibrillar foams for super-insulating applications.

Glass-Oxide Nanocomposites as Effective Thermal Insulation Materials

2013 ◽  
Vol 1558 ◽  
Author(s):  
Qing Hao ◽  
Minqing Li ◽  
Garrett Joseph Coleman ◽  
Qiang Li ◽  
Pierre Lucas
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Material Composition ◽  
Insulation Materials ◽  
Atomic Structures ◽  
Porous Nanocomposites ◽  
Theoretical Minimum

ABSTRACTWith extremely disordered atomic structures, a glass possesses a thermal conductivity k that approaches the theoretical minimum of its composition, known as the Einstein’s limit.1 Depending on the material composition and the extent of disorder, the thermal conductivity of some glasses can be down to 0.1-0.3 W/m∙K at room temperature,2,3 representing some of the lowest k values among existing solids. Such a low k can be further reduced by the interfacial phonon scattering within a nanocomposite that can be used for thermal insulation applications. In this work, nanocomposites hot pressed from the mixture of glass nanopowder (GeSe4 or Ge20Te70Se10) and commercial SiO2 nanoparticles, or pure glass nanopowder, are investigated for the potential k reduction. It is found that adding SiO2 nanoparticles will instead increase k if the measured k values for usually porous nanocomposites are converted into those for the corresponding solid (kSolid) with Eucken’s formula. In contrast, pure glass nano-samples always show kSolid data significantly reduced from that for the starting glass. For a pure GeSe4 nano-sample, kSolid would beat the Einstein’s limit for its composition.

Study on the Thermal Insulation Performance of PAN Pre-Oxidised Fibre Felts

2020 ◽  
Vol 28 (3(141)) ◽  
pp. 27-37
Author(s):  
Xiaoming Zhao ◽  
Yuanjun Liu ◽  
Tenglong Liang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Stability ◽  
Tensile Strength ◽  
Tensile Properties ◽  
Thermal Insulation ◽  
Silica Aerogel ◽  
Orthogonal Experiment ◽  
Excellent Thermal Stability ◽  
Coefficient Of Thermal Conductivity ◽  
Insulation Performance

In this paper, an orthogonal experiment of 3 factors and 3 levels was firstly designed to prepare PAN pre-oxidised fibre felts with good thermal insulation properties; the range method was used to analyse the result of the orthogonal experiment, and finally the tensile properties and thermal stability were tested. Finally, pre-oxidised fibre felt composites for the coating of silica aerogel were prepared using the coating process to compound silica aerogel on re-oxidised fibre felts. Firstly, the influence of the content of silica aerogel on the heat insulation performance of the coated composite materials was analysed, and then a test of the coefficient of thermal conductivity, an experiment on the back temperature, and characterisations of the tensile properties and thermal stability of the composite coating of pre-oxidised fibre felt composites of the coating of silica aerogel were carried out. Results showed that through analysis of the orthogonal experiment, we can state that the best preparation process of pre-oxidised fibre needled felts was as follows: needle number – 2, needle depth – 8 mm, and needle frequency – 140 times/min. The transverse tensile strength of PAN pre-oxidised fibre needled felts prepared by crossly webbing of PAN pre-oxidised fibres was superior to the longitudinal tensile strength; thermogravimetric analysis showed that the pre-oxidised fibre needled felts had excellent thermal stability. The coefficient of thermal conductivity of the aerogel coating of the composites firstly decreased and then increased with an increase in the content of aerogel. Coated composites had the lowest coefficient of thermal conductivity when the aerogel content was 4% wt. At temperatures of 100 °C, 150 °C and 200 °C, the heating rate of the transient-state back temperature and the steady-state average temperature were both the lowest when the aerogel content was 6% wt.

Fabrication and properties of carbon/carbon-carbon foam composites

2019 ◽  
Vol 89 (21-22) ◽  
pp. 4452-4460
Author(s):  
Bin Wang ◽  
Bugao Xu ◽  
Hejun Li
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Bonding Strength ◽  
Carbon Foam ◽  
Shear Load ◽  
Foam Composite ◽  
Final Failure ◽  
Carbon Foams ◽  
Insulation Performance

This paper was focused on the development of a new composite for high thermal insulation applications with carbon/carbon (C/C) composites, carbon foams and an interlayer of phenolic-based carbon. The microstructure, mechanical properties, fracture mechanism and thermal insulation performance of the composite was investigated. The experiment results showed that the bonding strength of the C/C-carbon foam composite was 4.31 MPa, and that the fracture occurred and propagated near the interface of the carbon foam and the phenolic-based carbon interlayer due to the relatively weak bonding. The shear load-displacement curves were characterized by alternated linear slopes and serrated plateaus before a final failure. he experiment revealed that the thermal conductivity of the C/C-carbon foam composite was 1.55 W·m−1ċK−1 in 800℃, which was 95.8% lower than that of C/C composites, proving that the thermal insulation of the new foam composite was greatly enhanced by the carbon foam with its porous hollow microstructure.

Research on the Pass Optimization Design of Sintered Shale Porous Brick

2014 ◽  
Vol 672-674 ◽  
pp. 1879-1884
Author(s):  
Jian Long Liu ◽  
Jie Nan Xie ◽  
Peng Liu ◽  
Mu Ye Huang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Optimization Design ◽  
Void Ratio ◽  
Thermal Conductivity Coefficient ◽  
Time Factors ◽  
Structure Design ◽  
3D Numerical Simulation ◽  
Equivalent Thermal Conductivity ◽  
Insulation Performance

The equivalent thermal conductivity coefficient of 10 kinds of sintered shale porous brick with different void number, void ratio, and arrangement (size: 240mm x 190mm x 90mm) are studied through 3D numerical simulation. An optimal structure design of the shale perforated brick design has been obtained. At the same time, factors such as void ratio, void number and arrangement of porous brick affected thermal insulation performance are systematically analyzed, which provides a reference to further improving the thermal insulation performance of insulation sintered shale porous brick model.

Fabrication of Infrared Opacifiers Loaded Al2O3 Aerogel-SiO2 Fiber Mat Composites with High Thermal Resistance

2020 ◽  
Vol 19 (03) ◽  
pp. 1950021
Author(s):  
Shangyan Wen ◽  
Jiayi Zhu ◽  
Qiang Yin ◽  
Yutie Bi ◽  
Hongbo Ren ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Thermal Insulation ◽  
Sol Gel ◽  
Doping Content ◽  
Low Thermal Conductivity ◽  
Sic Particles ◽  
Sol Gel Process ◽  
High Thermal Resistance ◽  
Insulation Performance

The infrared opacifiers loaded Al2O3 aerogel-SiO2 fiber mat composites were fabricated by the sol–gel process. The effects of the content of the TiO2 and SiC particles on thermal insulation performance of the Al2O3 aerogel-SiO2 fiber mat composites were studied. The results showed that the optimum doping content of TiO2 and SiC for Al2O3 aerogel-SiO2 fiber mat composites were 10[Formula: see text]mol.% and 0.5[Formula: see text]mol.%, respectively. The optimum TiO2-Al2O3 aerogel-SiO2 fiber mat composite had the low thermal conductivity of 0.021[Formula: see text]W/(m[Formula: see text][Formula: see text][Formula: see text]K) at 35∘C and 0.031[Formula: see text]W/(m[Formula: see text][Formula: see text][Formula: see text]K) at 600∘C. Meanwhile, the SiC-Al2O3 aerogel-SiO2 fiber mat composite also had the low thermal conductivity of 0.022[Formula: see text]W/(m[Formula: see text][Formula: see text][Formula: see text]K) at 35∘C and 0.025[Formula: see text]W/(m[Formula: see text][Formula: see text][Formula: see text]K) at 600∘C.

Analysis of Thermal Insulation Material on Building Exterior Wall

2017 ◽  
Vol 873 ◽  
pp. 153-157 ◽  
Author(s):  
Jia Jiu Diao ◽  
Xin Qin Liao ◽  
Can Fa Diao
Keyword(s):  
Thermal Conductivity ◽  
Flame Retardant ◽  
Thermal Insulation ◽  
Insulation Material ◽  
Low Thermal Conductivity ◽  
Insulation Materials ◽  
Existing Problems ◽  
Comprehensive Properties ◽  
First Choice ◽  
Insulation Performance

The use of performance, application status and existing problems of organic and inorganic thermal insulation materials, which are commonly used in the external walls of the building, are described in detail in this paper. Organic thermal insulation materials with low thermal conductivity, good thermal insulation performance, but with the flammable, low fire rating, poor safety, then it needing for flame retardant treatment. However, Inorganic thermal insulation materials with flame retardant, high fire rating, good safety performance, but poor thermal insulation properties than the organic insulation materials, so it needs to develop a low thermal conductivity of inorganic insulation materials.In the end, we pointed out that the inorganic insulation materials with low thermal conductivity and excellent comprehensive properties are expected to be the first choice for building thermal insulation materials.

scholarly journals Enhanced Thermal Insulation of the Hollow Glass Microsphere/Glass Fiber Fabric Textile Composite Material

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 505
Author(s):  
Jintao Sun ◽  
Fei Cai ◽  
Dongzhi Tao ◽  
Qingqing Ni ◽  
Yaqin Fu
Keyword(s):  
Thermal Conductivity ◽  
Glass Fiber ◽  
Thermal Insulation ◽  
Thermal Constant ◽  
Hollow Glass Microsphere ◽  
Glass Microspheres ◽  
Textile Composite ◽  
Hollow Glass Microspheres ◽  
Hollow Glass ◽  
Insulation Performance

Glass fiber fabrics/hollow glass microspheres (HGM)–waterborne polyurethane (WPU) textile composites were prepared using glass fiber, WPU, and HGM as skeleton material, binder, and insulation filler, respectively, to study the effect of HGM on the thermal insulation performance of glass fiber fabrics. Scanning electron microscopy, Instron 3367 tensile test instrument, thermal constant analysis, and infrared thermal imaging were used to determine the cross-sectional morphology, mechanical property, thermal conductivity, and thermal insulation property, respectively, of the developed materials. The results show that the addition of HGM mixed in WPU significantly enhanced thermal insulation performance of the textile composite with the reduction of thermal conductivity of 45.2% when the volume ratio of HGM to WPU is 0.8 compared with that of material without HGM. The composite can achieve the thermal insulation effect with a temperature difference of 17.74 °C at the temperature field of 70 °C. Meanwhile, the tensile strength of the composite is improved from 14.16 to 22.14 MPa. With these results, it is confirmed that designing hollow glass microspheres (HGM) is an effective way to develop and enhance the high performance of insulation materials with an obvious lightweight of the bulk density reaching about 50%.

scholarly journals Influence of HfO2 alloying effect on microstructure and thermal conductivity of HoTaO4 ceramics

2019 ◽  
Vol 8 (4) ◽  
pp. 537-544 ◽  
Author(s):  
Lin Chen ◽  
Jing Feng
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Photoelectron Spectroscopy ◽  
Structural Transition ◽  
Atomic Weight ◽  
X Ray Diffraction ◽  
Alloying Effect ◽  
X Ray ◽  
Crystal Structural ◽  
Insulation Performance

AbstractHfO2 alloying effect has been applied to optimize thermal insulation performance of HoTaO4 ceramics. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy are employed to decide the crystal structure. Scanning electronic microscopy is utilized to detect the influence of HfO2 alloying effect on microstructure. Current paper indicates that the same numbers of Ta5+ and Ho3+ ions of HoTaO4 are substituted by Hf4+ cations, and it is defined as alloying effect. No crystal structural transition is introduced by HfO2 alloying effect, and circular pores are produced in HoTaO4. HfO2 alloying effect is efficient in decreasing thermal conductivity of HoTaO4 and it is contributed to the differences of ionic radius and atomic weight between Hf4+ ions and host cations (Ta5+ and Ho3+). The least experimental thermal conductivity is 0.8 W·K−1·m−1 at 900 °C, which is detected in 6 and 9 mol%-HfO2 HoTaO4 ceramics. The results imply that HfO2–HoTaO4 ceramics are promising thermal barrier coatings (TBCs) due to their extraordinary thermal insulation performance.

Numerical Simulation Analysis of Hole Shape Design of Self-Thermal Insulation Perforated Brick

2013 ◽  
Vol 357-360 ◽  
pp. 1089-1092
Author(s):  
Xiao Ping Feng ◽  
Yong Fu Yu ◽  
Bo Jiang ◽  
Wei Bai
Keyword(s):  
Thermal Conductivity ◽  
Numerical Simulation ◽  
Finite Element Method ◽  
Thermal Resistance ◽  
Thermal Insulation ◽  
Simulation Analysis ◽  
Shape Design ◽  
Hole Shape ◽  
Insulation Performance ◽  
Square Hole

The hole shape design of perforated brick directly affects thermal insulation performance of wall. In order to study the influence of shape, size and configuration of perforated brick on the insulation performance, six kinds of perforated brick with different hole shape were designed, and their temperature field were simulated with finite element method. The results show that the insulation performance of perforated brick with square hole is the best. Filling brick holes with thermal insulation materials can improve the insulation performance of perforated brick, Besides; The thermal conductivity of perforated brick affects its thermal resistance, so brick materials with low thermal conductivity should be developed for the achievement of energy-saving standard of wall thermal resistance.

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