Thermal Conductivity Of Samples Research Articles

ADN Solid Propellants with High Burning Rates as Booster Material for Hypersonic Applications

AbstractRAM‐ and SCRAM‐Jet engines can not generate static thrust and only work at high speeds. This starting velocity of the motor v0 is usually generated by carrier rockets or boosters, which mostly use solid propellants based on ammonium perchlorate (AP) and hydroxyl‐terminated polybutadiene (HTPB). Modern solid propellants based on ammonium dinitramide (ADN) and Glycidyl Azide Polymer (GAP) have significant advantages in terms of environmental compatibility and thermodynamic performance. In the present work, it is shown that the already high burning rate of ADN solid propellants can be more than doubled by means of metallic fibers, which significantly increases the thrust of such engines. In order to achieve such results, 3 wt% of Al−Mg alloy fibers are added to the propellant. A formulation with 3 mm long fibres shows the highest burning rate with 84.0 mm/s at 26.5 MPa. Small scale motor tests confirm these investigations. The burning mechanism is studied by SEM/EDX investigations and by measuring the thermal conductivity. These show that the fibres remain on the burning surface and thus transfer the heat from the flame to the depth of the propellant. The thermal conductivity of samples with AlMg5 fibers is about 22 % higher than the reference.

Analysis of the Density Variation on Thermal Conductivity Wood Plastic Composite Made from Lamtoro Wood (Leucaena leucocephala) And Polypropylene Waste

The thermal conductivity of Wood Plastic Composite (WPC) made with lamtoro wood and polypropylene (PP) was studied by varying its density. The PP was obtained from 240 ml mineral plastic glasses, and the lamtoro wood particles were shieved in 6 mesh sizes. In this study, we considered the composition ratio between PP and wood particles to be 70:30, and the thermal conductivity was measured using a thermal conductivity apparatus. Based on the data analysis, we found that the density of WPC made with PP and lamtoro wood influenced its thermal conductivity. The results showed that the thermal conductivity of sample A is 0.2 W/mºC, sample B is 0.4 W/mºC, and sample C is 0.5 W/mºC, for the densities of 0.4 g/cm3, 0.5 g/cm3, 0.6 g/cm3, respectively. In conclusion, as the density increases, the thermal conductivity of WPC also increases. Thus, based on it thermal conductivity, the WPC made from PP and lamtoro wood is classified as an isolator.

Production of evaporation suppression floating covers using ultra-lightweight alkali-activated slag concrete

Evaporative losses from reservoirs exacerbate water shortage during dry spells. Notwithstanding the extensive application of self-assembling floating covers for suppressing evaporation, the cover material is often overlooked and limited to available choices such as plastics. The present study is aimed at the production of floating covers using ultra-lightweight alkali-activated slag concrete that offers a range of mechanical and chemical features. Concrete specimens were made with different percentages of ground granulated blast-furnace slag as the binder, sodium metasilicate as the alkaline activator and lightweight perlite aggregates with a density of 100–150 kg/m3. To solve the problem of fracture in the preliminary specimens, slag was partially replaced with 15, 20 and 30% lime. In addition, microsilica (10, 12 and 15%) was introduced to improve the mechanical properties of the samples. In designs without microsilica, 30% replacement of slag with lime resulted in the desirable density, strength and permeability of samples. Results showed that microsilica generally increased the density, resistance and thermal conductivity of samples by 7, 74 and 14%, respectively, while water absorption and permeability decreased by 15% and 14%, respectively. The dry density of samples was obtained between 340 and 516 kg/m3 with a compressive strength of 0.2–0.9 MPa and a conductive heat transfer coefficient of 0.067–0.093 W/mK.

Mechanical and thermal properties of lateritic soil mixed with cement and polymers as a non-bearing masonry unit

Masonry units are self-insulation wall blocks that are among the most common construction materials, owing to their fast and straightforward wall construction, high strength, and low cost. However, the high thermal conductivity of masonry units results in increased energy consumption. The current research investigated polymers, namely polyvinyl pyrrolidone, polyvinyl alcohol, and polyethylene glycol, as alternative insulation materials in building walls. The effect of variables, including cement (C) content, liquid (L) type, liquid content, and curing time, on the mechanical and thermal properties of lateritic soil (LS) mixed with C and L was investigated via the unconfined compressive strength (UCS), indirect tensile strength (ITS), and thermal conductivity. The results indicated that the UCSs and ITSs of LS-C samples mixed with polymer were higher than those mixed with water. The specimen with the optimal liquid content and 3 wt% C content performed best for all L types. Furthermore, the thermal conductivity of the LS-C with polymers was lower than that of the sample with water for all C contents. The equations for estimating dry unit weight, UCS, ITS, and thermal conductivity of samples were proposed.

Effect of carbon nanotubes addition on thermoelectric properties of Ca3Co4O9 ceramics

Increasing the phonon scattering center by adding nanoparticles to thermoelectric materials is an effective method of regulating the thermal conductivity. In this study, a series of Ca3Co4O9/x wt.% CNTs (x = 0, 3, 5, 7, 10) polycrystalline ceramic thermoelectric materials by adding carbon nanotubes (CNTs) were prepared with sol-gel method and cold-pressing sintering technology. The results of x-ray diffraction and field emission scanning electron microscopy show that the materials have a single-phase structure with high orientation and sheet like microstructure. The effect of adding carbon nanotubes to the thermoelectric properties of Ca3Co4O9 was systematically measured. The test results of thermoelectric properties show that the addition of carbon nanotubes reduces the electrical conductivity and Seebeck coefficient of the material. Nevertheless, the thermal conductivity of the samples with carbon nanotubes addition is lower than that of the samples without carbon nanotubes. At 625 K, the thermal conductivity of Ca3Co4O9/10 wt.% CNTs sample is reduced to 0.408 W⋅m−1⋅K−1, which is about 73% lower than that of the original sample. When the three parameters are coupled, the figure of merit of Ca3Co4O9/3 wt.% CNTs sample reaches 0.052, which is 29% higher than that of the original sample. This shows that an appropriate amount of carbon nanotubes addition can reduce the thermal conductivity of Ca3Co4O9 ceramic samples and improve their thermoelectric properties.

Numerical simulation on photo-thermal properties of double glazing unit filled with TiN-Al2O3 binary nanoparticles enhanced phase change material

Due to the importance role in building energy saving and poor thermal resistance of window unit, considering the widely application in energy storage of phase change material (PCM) and the superior enhancement on photo-thermal properties by binary nanoparticles, Al2O3-TiN binary nanoparticles are suspended into paraffin to consist enhanced phase changes material (NePCM) as the filler for double glazing unit to improve it photo-thermal performance. A numerical simulation method is built for investigating the effect of nanoparticles from binary NePCM on the photo-thermal performance of window unit including the volume fraction, particle size and mixing ratio of Al2O3-TiN nanoparticles. The results show that, ignoring the influences of fillers optical properties, the mainly affection for window unit is the thermal conductivity of samples. The influences of Al2O3: TiN ratios are slightly, however, the effect of nanoparticles concentration and diameter are obviously in comparison, under the same condition, the sample with 0.01% nanoparticles volume fraction gives the largest energy consumption Δq of 0.23% by the comparison with 10% concentration and the sample with 5 nm diameter gives the largest Δq of 0.73% compared with 10 nm. Thus, the Al2O3-TiN binary NePCM with 1% concentration, 5 nm particle size and 9:1 of Al2O3: TiN is the most suitable configuration scheme as the filler for improving photo-thermal performance of double glazing unit.

Effects of Black Scoria on Mechanical Properties and Thermal Insulation Properties of Building Materials

The effect of fine black scoria on the mechanical properties and thermal conductivity of building materials was investigated in this study. Black scoria was used to replace cement in concrete with various percentages. Four concrete samples containing 0%, 10%, 20%, and 30% black scoria were prepared. Characterization black scoria was performed via X-ray powder diffraction, X-ray fluorescence, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry analysis. Then, the compressive strength of the samples was investigated after 14, 21, 28, and 91 days of curing at room temperature. Finally, the thermal conductivities of the samples were measured after 28 days. Based on the experimental results, the highest compressive strength among the samples was 45.3 MPa, obtained from the mixture containing 10% black scoria after 91 days of curing. It was also observed that the average thermal conductivity of the concrete samples decreased with an increase in the fine black scoria content from 1.8 to 0.193 W m−1 K−1. Thus, black scoria is an appropriate substitute for commercial admixtures in cement composites in thermally insulating building materials due to its low density, excellent compressive strength, and good heat insulation properties.

Correlations among Thermal Conductivity, Porosity, and Permeability of Mesozoic Sandstones and Siltstones from the Southern Regions of the West Siberian Plate

Abstract —We consider results of measurements of thermal conductivity, porosity, and permeability for 780 samples of Mesozoic sandstones and siltstones from the cores of 50 wells drilled in three southern regions of the West Siberian Plate (Novosibirsk and Tomsk regions, Surgut region of the Khanty-Mansi Autonomous Area). The thermal conductivity of the samples was measured twice: in dry and in water-saturated states. It has been established that the thermal conductivity of water-saturated rocks is on average 20–40% higher. The thermal conductivities of dry and water-saturated samples show stable correlations between each other and with the sample porosity and permeability. These correlations can be used for the approximate estimation of the thermal conductivity of water-saturated rocks from the measured thermal conductivity of dry samples or even from the porosity values. The relationship between thermal conductivity and porosity can be used for the rapid assessment of rock porosity from the measured thermal conductivity of the core.

Effects of AlN Content and Sintering Atmospheres on the Thermal Conductivity of Hot-Pressed SiC Ceramics

In pursuit of high thermal conductivity of SiC ceramics, this article reports the effects of AlN and sintering atmospheres on the thermal properties and microstructure evolution of SiC ceramics. Dense SiC ceramics with different contents of AlN additive were fabricated through hot-press sintering at 1950°C in Ar/N2 atmosphere under a pressure of 40 MPa for 3 h. The results showed that the thermal conductivity of samples without AlN addition was 53.5 W.m−1.K−1 when sintered in Ar and 50.3 W.m−1.K−1 when sintered in N2. The SiC ceramics with 4 wt% AlN sintered in Ar showed abnormally large grains and exhibited the highest thermal conductivity of 121.7 W.m−1.K−1 among all the samples. The sample with 2 wt% AlN sintered in N2 exhibited a thermal conductivity of 108.6 W.m−1.K−1; the thermal conductivity deceased with the increasing AlN content afterwards. Such a decreasing trend of thermal conductivity was attributed to the ascending 2Hss content and smaller grains of ceramics. There existed an optimal content of AlN and a proper sintering atmosphere for perfecting the microstructure and the thermal conductivity of SiC ceramics.

Experimental investigation of heat conduction characteristics of density-layered stone wool materials

This work presents an experimental study to investigate the heat conduction coefficient of the density-layered stone wool plates insulation materials used in heat insulation applications. The stone wools, which have 70, 100, and 150 kg/m3 of densities, have been combined in different thicknesses to 60 mm. The aim of this layer combination is to benefit from lower heat conductivity and lightness of the lower density stone wools and the better strength of higher density stone wools. First, the single-layer stone wools with 60 mm of thickness, which is in the insulation market, have been tested. Then, they have been combined in different thicknesses, with a total thickness of 60 mm. A total of 18 samples have been produced, and the thermal conductivity of samples has been measured experimentally. Consequently, the heat conduction coefficient of density-layered stone wools and their weights have been compared experimentally. At the end of the present study, it is observed that density-layered stone wool plates play a critical role in improving the heat conductivity and lowering the weight of high-density plates. When combining 10 mm thick 150 kg/m3 density stone wool with 50 mm thick 70 kg/m3 density stone wool, the heat conductivity has been improved by 3.52% and the weight of the 1 m2 plate has reduced by 4 kg (44%) according to the stone wool with 150 kg/m3 of density.

Moisture and Temperature Response of Structural and Lithology based Thermophysical and Energy Saving Traits of Limestone using Experimental and Least-Square Fitting Methods

Thermophysical analysis of the crustal rocks is important for heat transfer determination and insulation purposes to save energy in buildings. In the presented work, thermophysical properties of four limestones were investigated in dry and moist state under ambient conditions by using a transient plane source method. A thermal constant analyzer was used to raise the sample temperature and to measure the thermal properties in the temperature range of 300 K to 433 K. Thermal conductivity and diffusivity were measured by developing a linear relationship between temperature response of TPS (transient plane source) sensor and dimensionless time function through least-square fitting method. The experimental observations and predicted thermal conductivity of samples have shown that in-situ observations are important to determine the thermal properties accurately. The effect of temperature on thermal properties of limestone was defined by considering the chemical composition of the samples and associated heat transfer mechanism. Both thermal conductivity and diffusivity of limestone decreased while specific heat capacity increased with a rise in temperature. The overall findings indicate that the spinoff of this research is useful in studying the reliance of thermophysical properties of rocks on their structures and lithology.

Thermal conductivity of coconut shell particle epoxy resin composite

Coconut shell is one of the agricultural wastes that are widely available in Indonesia and other tropical countries. Unfortunately, the coconut shell waste has not been used optimally for new materials, especially for thermal insulation material. In this work, the composite from coconut shell particles using epoxy resin adhesives has been prepared. The particle sizes of coconut shells for composite samples were 60, 80, 100, and 120 mesh. The compositions of samples for each particle size (ratio between coconut shell and epoxy resin) were 70/30, 75/25, 80/20, and 85/15 (vol %). The thermal conductivity of each composite sample has been examined by using a single-plate method. The density of each sample has also been measured. The results showed that the thermal conductivity of composite sample for 60 mesh of particle size with 70/30 vol.% composition was 0.071 W/m K. As the composition of coconut shell was increased to 85 vol.%, the value of thermal conductivity decreased to 0.062 W/m K. It was found that the thermal conductivity of composite sample decreased as the composition of coconut shell was increased. For the composition of 70/30 vol.%, the thermal conductivity increased to 0.078 W/m K for 120 mesh of particle size. This behavior was also the same for other compositions, where the value of thermal conductivity of composite increased as the coconut shell particle size decreased. The density of the composite was found in the range of 0.799 – 0.938 g/cm3. As the particle size of the coconut shell was reduced, the density of the composite increased. This study revealed that both thermal conductivity and density of coconut shell epoxy composite are dependent on the particle size of the coconut shell. The thermal conductivity of all samples was less than 0.1 W/m K indicating that the coconut shell epoxy composite is quite potential for thermal insulation.

Experimental study on thermo physical properties of biodegradable borassus fruit fiber-reinforced polyester composites

Abstract The Biodegradable fiber- reinforced composites are increasingly developed for energy saving applications in automobile and construction industries with significant ecological advantage. The aim of this study is to explore thermal conductivity, specific heat capacity, and thermal diffusivity of Borassus fruit fiber (BFF) reinforced polyester composites. Biodegradable composites were fabricated with the incorporation of Borassus fruit fiber (BFF) in the polyester resin via hand lay-up technique. The thermal conductivity of samples was measured using a guarded heat flow meter as per ASTM E1530 standards. The results revealed that higher content of BFF can contribute to improve the thermal insulation capability of composite. As fiber content increases, the insulation capability of composites increased. The reduction in thermal conductivity of composite at maximum volume fraction was 23.5% compared to unfilled polyester. The thermal conductivity of composites increased with the increase of temperature. Thermal conductivity, heat capacity and diffusivity of composite at maximum fiber content, were 0.186 w/(m.K), 1.64 (kJ/kg.K) and 1.04e-07 mm2/s, respectively. The results propose that the BFF/polyester composites can be a feasible candidate for energy saving applications that require good thermal insulation properties.

Synthesis, characterization and evaluation of tunable thermal diffusivity of phosphorus-doped carbon nanodot

Present study focusses to report the tunable thermal properties of phosphorus-doped carbon nanodot (PCND) using dual-beam mode matched thermal lens spectroscopic technique. The morphological, structural, and optical characterization of prepared carbon nanodot was probed by transmission electron microscopic technique (TEM), X-ray photoelectron spectroscopic technique (XPS), UV–visible absorption spectroscopic technique and photoluminescence spectroscopic technique. The average size of PCND was found to be 4.02 ± 0.13 nm. To date, there have been a few reports the thermal diffusivity and thermal conductivity of carbon dot by Dual-beam mode matched thermal lens spectroscopic technique. Among them, the present system has high value of thermal diffusivity (9.1139 ± 1.8644)*10−8 m2/s) and thermal conductivity (0.3807 ± 0.0778 W/mK). The variation in thermal diffusivity and thermal conductivity of sample with different concentration was also recorded.The variation in thermal diffusivity values ranging from (9.1139 ± 1.8644)*10−8 m2/s to (2.9532 ± 0.8547)*10−8 m2/s indicates the tuning in heat transfer property of the present system by altering their concentration.These extend their application potential in microelectronic cooling as well as thermal insulation.

A novel thermal insulation composite fabricated with industrial solid wastes and expanded polystyrene beads by compression method

Building energy consumption and industrial solid wastes have attracted great concerns in recent years. A novel thermal insulation composite (NTIC) is prepared by combining industrial solid wastes with expanded polystyrene (EPS) beads for non-structural applications of building energy conservation. Industrial solid waste containing flue gas desulfurization (FGD) gypsum improves the fire resistance of NTIC samples and reduces the carbon footprint of the material as compared with similar insulation composites based on portland cement. In order to substantially reduce the density and thermal conductivity of NTIC samples, the proportion of industrial solid wastes should be decreased. However, significant quantities of large voids appear in the samples which leads to the difficulty of the shaping and sharp decrease of mechanical properties. Compression method was used to solve the above problem in this paper. The morphological characterization, physico-mechanical properties, water absorption, thermal conductivity and fire behavior of the NTIC samples with different compression ratios were studied. The results showed that density, mechanical properties, water absorption and thermal conductivity of the NTIC samples gradually decreased with the increase of EPS beads content. The samples with a compression ratio of 1.8 possessed preferable mechanical properties and lower water absorption than those with a compression ratio of 1.4 in the case of approximately same density due to many voids inside the latter. The thermal conductivity of samples was mainly determined by their density. There is no fire combustion for all the samples under the flame, which illustrated the NTICs in this paper possessed superior fire safety.

Preparation and characterization of polymer matrix passive cooling materials with thermal insulation and solar reflection properties based on porous structure

Porous polymer materials achieve thermal insulation and solar reflection property at the same time because of their own porous structure, which makes the passive cooling property more superior so as to reduce the indoor temperature more effectively and achieve the purpose of energy saving. In this study, the pore structure was constructed in polyvinyl chloride (PVC) matrix by chemical etching with calcium carbonate (CaCO3) particles as pore template. The effects of porosity on the structure and properties of PVC porous films were studied. The thermal insulation performance of PVC porous films improves with the increase of porosity, which is better than that of PVC films and PVC/CaCO3 composite films. The thermal conductivity of sample with the porosity of 67 v% is 0.0868 Wm−1K−1. The total solar reflectance of sample 67 v% is 96.34%, which is 454.9% higher than that of PVC films. Although the thermal emissivity from 3 to 5 μm of PVC porous films is decreased, it still remains at a high level about 0.83 in the whole infrared region. In temperature test, the final temperature of sample with the porosity of about 67 v% is only 25.2 °C, 23.8 °C lower than that of PVC films, and 1.2 °C higher than the room temperature. The cooling property of PVC/titanium dioxide (TiO2) composite films with 10 v% TiO2 was also measured for comparation, and the final temperature is 29.1 °C, which is between that of samples with porosity of about 20 v% and 33 v%. The PVC porous material prepared in this study has the advantages of low thermal conductivity, good solar reflectance and simple preparation, which has potential application prospects in the field of passive cooling materials.

Thermal conductivity of a Jurkat cell measured by a transient laser point heating method

To understand and quantify the thermal energy transfer in a biological cell, the measurement of thermal properties at a cellular level is emerging as great importance. We report herein a unique technique that utilizes a laser point heat source for temporal temperature rise in a micro-pipette thermal sensor; this technique characterizes heat conduction of a measured sample, the Jurkat cell, thus measuring the sample's thermal conductivity (TC). To this end, we incorporated the computational model in COMSOL to solve for the transient temperature and used the multi-parameter fitting of the experimental data using MATLAB. To address the influence of a Jurkat cell's chemical composition on TC, we compared three structural models for prediction of effective thermal conductivity in heterogeneous materials thereby determining the weight percentage of the Jurkat cell. When considering water and protein as the major constituents, we found that a combination of Maxwell-Euken and Effective Medium Theory modeling provides the closest approximation to published weight percent data and, therefore, is recommended for prediction of the cell composition. We validate the accuracy of the measurement technique, itself, by measuring polyethylene microspheres and observed 1% deviation from published data. The unique technique was determined to be mechanically non-invasive, capable of maintaining viable cells, and capable of measuring the thermal conductivity of a Jurkat cell, which was demonstrated to be 0.538 W/(m⋅K) ± 1%.

Monolithically fabricated sample for the calibration of the tip-sample thermal conductance in scanning thermal microscopy

A novel device consisting of a set of membranes with nine different geometries and metallizations monolithically fabricated on a single die is proposed as a possible calibration sample for characterizing thermal conductance between the tip and the sample with “active” resistive scanning thermal microscope (SThM) probes. Such probes, in which the tip is significantly heated by the current used to measure their temperature-dependent resistance, are often used in investigations of the thermal conductivity of samples. Thermally grown silicon dioxide was chosen as a membrane material for all devices due to its low thermal and electrical conductivity, and gold structures were used to vary the thermal conduction to mimic a range of materials. The result showed a range of samples with thermal conductance of 15–85 times the thermal conductance quantum at room temperature, which would be typical for SThM measurements of thermal conductance resulting from contact of the tip with bulk materials having thermal conductivities ranging from those of poly methyl methacrylate to bulk silicon.

Effects of modified materials prepared from wastes on the performance of flue gas desulfurization gypsum-based composite wall materials

The utilisation of industrial wastes and straw fibre to prepare building materials is a green alternative that saves natural resources and protects the environment. This study investigates the effect of cement, inorganic wastes, and straw fibre on the properties of flue gas desulfurization (FGD) gypsum. Response surface methodology was adapted to study the mechanical and water resistance properties of the samples. The results indicate that the properties of gypsum-based composites improved upon addition of cement and wastes due to the synergistic effect between them, which resulted in formation of calcium silicate hydrates (C-S-H) and ettringite (AFt). The addition of 3 wt% of sorghum straw fibre (SSF) significantly improved the flexural strength, decreased the apparent density and thermal conductivity of samples at a length to diameter ratio (LDR) of 7.5. The SSF successively treated with alkali, enzyme, and waterproofing agent removed the non-toughening compounds of the fibre, resulting in better mechanical properties and thermal conductivity. This outcome occurred because the non-toughening compounds of SSF, especially protein, pectin, and hemicellulose, negatively impact the studied properties. This work provides a theoretical basis to improve the overall properties and prepare a lightweight high-strength thermal insulation FGD gypsum-based composite for wall materials.

The effect of nitrogen on the compressibility and conductivity of iron at high pressure

Although nitrogen in the Earth’s interior has attracted significant attention recently, it remains the most enigmatic of the light elements in the Earth’s core. In this work, synchrotron X-ray diffraction (XRD) and electrical conductivity experiments were conducted on iron nitrides (Fe2N and Fe4N) in diamond anvil cells (DACs) up to about 70 ​GPa ​at ambient temperature. These results show that iron nitrides are stable up to at least 70 ​GPa. From the equation of state (EOS) parameters, iron nitrides are more compressible than iron carbides. Moreover, using the van der Pauw method and Wiedemann-Franz law, the electrical and thermal conductivity of samples were determined to be much lower than that of iron carbides. The conductivities of Fe2N and Fe4N were similar at 20–70 ​GPa, suggesting no evident effects by varying the N stoichiometries in iron nitrides. Iron nitrides are less dense and conductive but more compressible than carbides at 0–70 ​GPa. This study indicates that less nitrogen than carbon can explain geophysical phenomena in the deep Earth, such as the density deficit.