Characterization Of Thermal Conductivity Research Articles

Realizing the Accurate Measurements of Thermal Conductivity over a Wide Range by Scanning Thermal Microscopy Combined with Quantitative Prediction of Thermal Contact Resistance.

Quantitative thermal performance measurements and thermal management at the micro-/nano scale are becoming increasingly important as the size of electronic components shrinks. Scanning thermal microscopy (SThM) is an emerging method with high spatial resolution that accurately reflects changes in local thermal signals based on a thermally sensitive probe. However, because of the unclear thermal resistance at the probe-sample interface, quantitative characterization of thermal conductivity for different kinds of materials still remains limited. In this paper, the heat transfer process considering the thermal contact resistance between the probe and sample surface is analyzed using finite element simulation and thermal resistance network model. On this basis, a mathematical empirical function is developed applicable to a variety of material systems, which depicts the relationship between the thermal conductivity of the sample and the probe temperature. The proposed model is verified by measuring ten materials with a wide thermal conductivity range, and then further validated by two materials with unknown thermal conductivity. In conclusion, this work provides the prospect of achieving quantitative characterization of thermal conductivity over a wide range and further enables the mapping of local thermal conductivity to microstructures or phases of materials.

Reply to “Discussion on characterization of thermal conductivity of seasonally frozen turfy soil from Northeastern China by He et al. Bulletin of Engineering Geology and the Environment, 81, 481”

Reply to “Discussion on characterization of thermal conductivity of seasonally frozen turfy soil from Northeastern China by He et al. Bulletin of Engineering Geology and the Environment, 81, 481”

Discussion on characterization of thermal conductivity of seasonally frozen turfy soil from Northeastern China by He et al. Bulletin of Engineering Geology and the Environment, 81, 481

Discussion on characterization of thermal conductivity of seasonally frozen turfy soil from Northeastern China by He et al. Bulletin of Engineering Geology and the Environment, 81, 481

Effects of Carbonization Temperature on Mechanical and Thermal Insulation Properties of Carbon Aerogel Composites using Phenolic Fibers as Reinforcement

A series of carbon fiber-reinforced carbon aerogel composites (C/CAs) were prepared via carbonizing phenolic fibers impregnated organic aerogel at temperatures ranging from 1,000 to 1,600°C. Phenolic fiber as soft reinforcement shrinks synchronously with the aerogel matrix during the preparation process, which effectively avoided microcracks and achieved an excellent reinforcement effect. The effects of carbonization temperatures on the mechanical and thermal insulation properties of the C/CAs were investigated via pore structural and morphological analysis, as well as the characterization of mechanical strength and thermal conductivity. The results show that the compressive strength of C/CA is 1.26–2.14 MPa in xy-direction and 0.55–1.20 MPa in z-direction. The obtained bending strength range from 1.92 to 3.62 MPa with the carbonization temperature increase from 1,000 to 1,600°C. The thermal conductivity of C/CA-1000 at 1,800°C is 0.1637 W·m−1·K−1 while that of reached 0.2713 W·m−1·K−1 of C/CA-1600. Further study found that the change of porosity and pore size caused by the closure of micropores at high temperatures should be responsible for performance evolution.

Simulation and Property Characterization of Nanoparticle Thermal Conductivity for a Microscale Selective Laser Sintering System

Abstract Current additive manufacturing (AM) technologies are typically limited by the minimum feature sizes of the parts they can produce. This issue is addressed by the microscale selective laser sintering system (μ-SLS), which is capable of building parts with single micrometer resolutions. Despite the resolution of the system, the minimum feature sizes producible using the μ-SLS tool are limited by unwanted heat dissipation through the particle bed during the sintering process. To address this unwanted heat flow, a particle scale thermal model is needed to characterize the thermal conductivity of the nanoparticle bed during sintering and facilitate the prediction of heat affected zones. This would allow for the optimization of process parameters and a reduction in error for the final part. This paper presents a method for the determination of the effective thermal conductivity of copper nanoparticle beds in a μ-SLS system using finite element simulations performed in ansys. A phase field model (PFM) is used to track the geometric evolution of the particle groups within the particle bed during sintering. Computer aided design (CAD) models are extracted from the PFM output data at various time-steps, and steady-state thermal simulations are performed on each particle group. The full simulation developed in this work is scalable to particle groups with variable sizes and geometric arrangements. The particle thermal model results from this work are used to calculate the thermal conductivity of the copper nanoparticles as a function of the density of the particle group.

Characterization of thermal conductivity of seasonally frozen turfy soil from Northeastern China

Characterization of thermal conductivity of seasonally frozen turfy soil from Northeastern China

Thermal Conductivity and Mechanical Characterization of Bamboo Fiber and Rice Husk/MWCNT Filler Epoxy Hybrid Composite

Recent trends utilizing recycled materials from around the world aim to improve a wide range of industrial and domestic applications. The natural fiber/filler matrix is used to evaluate the mechanical qualities of the hybrid nanocomposites. The specific concentration is dealing with a bidirectional bamboo fiber mat/rice husk particle/MWCNT blend with epoxy composite. The experimental work plan to execute with the three different proportional composites was as follows: bamboo fiber mat constant loading for all the specimens, but the filler particle ratio will be varied, prominently rice husk particle concentrated for all the three specimens: 5%, 10%, and 15%, and additionally, MWCNT drawn two specific specimens (2 and 3): 0.5% and 1% based on the fiber/filler concentration balanced the epoxy resin. The research presented here is hybrid nanocomposite experimented with thermal, mechanical, and morphological characterization. Thermal conductivity measured by Lee’s disc method is observed at 0.2577 W/mK for specimen 3. The tensile and flexural properties are higher for 0.5% MWCNT concentration (specimen 2): 42.66 MPa and 54.72 MPa, respectively. The maximum impact strength is reached at 1% MWCNT concentration (specimen 3). Bamboo fiber and rice husk filler matrix composite (specimen 1) reached extremities shore-Dhardness 84. Scanning electron microscopy was performed to examine the morphological characteristics of the tensile fractography specimen and analyzed the dispersion of the fiber/filler matrix adhesion of the surface. The bamboo fiber mat/rice husk/MWCNT (specimen 3) filler had better binding and observed fewer fiber pull-out, fiber fracture, fiber extension, and voids. In the graphic comparison, 0.5% MWCNT achieved more mechanical properties than the other two combinations.

Thermal Conductivity Evaluation and Road Performance Test of Steel Slag Asphalt Mixture

Substituting steel slag for mineral materials in road construction has potential economic and environmental benefits. Due to the excellent thermal conductivity of steel slag, it is often used in functional pavements. However, there are few studies on the thermal conductivity characterization of steel slag asphalt mixture (SSAM). For this reason, the thermal conductivity of SSAM was first qualitatively evaluated by microscopic characterizations. The thermal conductivity was the quantitatively evaluated by the heating wire method. Theoretical calculations were used to verify the reliability of the quantitative characterization. Finally, the effects of steel slag on the volume indices and the road performance of SSAM were studied. Results showed that active minerals such as iron oxides make the steel slag thermally conductive, while a large number of protrusions and micropores on the surface of the steel slag may be detrimental to thermal conductivity. The thermal conductivity first increases and then decreases with the steel slag content. The asphalt mixture with 60% steel slag replacing aggregate of 3–5 mm (6.6% of the mixture) had the highest thermal coefficient of 1.746 W/(m·°C), which is only 4.78% different from the theoretical value. The porosity and water absorption of SSAM gradually increased with the content of steel slag. The road performance test indicated that steel slag increased the high-temperature performance of the asphalt mixture to a certain extent, but weakened the low-temperature performance and moisture resistance. After comprehensive consideration of the thermal conductivity and road performance, it is recommended that the optimum content of steel slag is not more than 60%.

Solving transient coupled conductive and radiative transfers in porous media with a Monte Carlo Method: Characterization of thermal conductivity of foams using a numerical Flash Method

This paper presents a single Monte-Carlo algorithm used to solve transient conductive and radiative heat transfers in three-dimensional porous media. The complete methodology presented step by step herein enables practical and efficient study of geometrical and multiphysical complexities. The code was validated against results obtained by commercial software, analytical and semi-analytical solutions. Computation times were found to be greatly reduced when radiative transfer is predominant compared with those obtained using a deterministic solver. This kind of approach allows a probe calculation in the frame of linear thermal transfers and is well suited for the numerical characterization of heterogeneous media. In this work a numerical flash method was reproduced and enabled us to evaluate the effective total conductivity of the equivalent homogenized medium. The influence of various parameters such as porosity, size of the unit cell, bulk conductivity of the solid phase, reference temperature and emissivity was studied for a stack of Kelvin cells. This tool enables the parametric investigation of geometric and thermal properties. The results are in good agreement with those of the literature.

Near-field radiation analysis and thermal contact radius determination in the thermal conductivity measurement based on SThM open-loop system

With the rapid development of materials science, plenty of materials with micro-nano structures are emerging in various fields due to their outstanding physical properties. In order to fulfill the needs of micro-nano-scale thermal measurement, a series of thermophysical characterization methods have been evolving. In this article, a measurement method based on the Scanning Thermal Microscopy open-loop system is proposed to realize nano-scale thermal conductivity characterization. Both forward and backward thermal contact radius are measured. The heat transfer tunnel raised by the near-field radiation is calculated to be 1.73 × 10−14 W/K as the upper limit, which can be neglected compared to the total value. The total thermal conductance between tip and sample was calibrated as 1.8 × 10−6 W/K by several standard bulk samples, and thermal conductivity varies from 0.28 to 237 Wm−1 K−1.

Measurements of the thermal conductivity of reference liquids using a modified transient hot-wire needle probe

Many power generation processes feature some type of working fluid that plays a critical role in the transfer of heat throughout the system. To optimize thermal efficiencies, an accurate characterization of the temperature-dependent thermal conductivity of the fluid is needed. This study develops a time-domain Modified Transient Hot-wire Needle Probe to overcome phenomena that have impaired traditional measurement techniques when the fluid is both corrosive and at an elevated temperature. First, the physical design of the instrument is presented to demonstrate features that limit interference from corrosion, electrical conduction, and convective and radiative heat transfer. Next, a governing equation for 1D (radial) heat conduction is fully developed using the thermal quadrupoles technique. A finite-element study is performed for validation. A sensitivity analysis is done to assess the time-dependent influence of critical parameters in the governing equation for several samples. Finally, thermal conductivity measurements are presented for seven different liquid substances by fitting the thermal model to experimental data across a range of temperatures. Reference correlations are included for comparison. The sample thermal conductivity and ambient temperature of the experimental conditions range from 0.125–16.5WmK and 10–400∘C, respectively. The total uncertainty, comprised of both the experimental design and fitting process, of all measurements is quantified.

Methods for Measuring Thermal Conductivity of Two-Dimensional Materials: A Review.

Two-dimensional (2D) materials are widely used in microelectronic devices due to their excellent optical, electrical, and mechanical properties. The performance and reliability of microelectronic devices based 2D materials are affected by heat dissipation performance, which can be evaluated by studying the thermal conductivity of 2D materials. Currently, many theoretical and experimental methods have been developed to characterize the thermal conductivity of 2D materials. In this paper, firstly, typical theoretical methods, such as molecular dynamics, phonon Boltzmann transport equation, and atomic Green’s function method, are introduced and compared. Then, experimental methods, such as suspended micro-bridge, 3ω, time-domain thermal reflectance and Raman methods, are systematically and critically reviewed. In addition, the physical factors affecting the thermal conductivity of 2D materials are discussed. At last, future prospects for both theoretical and experimental thermal conductivity characterization of 2D materials is given. This paper provides an in-depth understanding of the existing thermal conductivity measurement methods of 2D materials, which has guiding significance for the application of 2D materials in micro/nanodevices.

Thermal conductivity characterization of Ni60A/WC composites with different copper dilutions

To improve the accuracy of heat transfer analysis of coating, the influence of the dilution ratio on the thermal-physical parameters of coating was considered for the first time. Ni60A/WC composites with different copper content were prepared by smelting to simulate the Ni60A/WC coatings with different dilution ratios. The thermal conductivity of composites at different temperatures was systematically characterized. As the increase of copper content and temperature, the thermal conductivity shows an upward trend. The composites with 30% copper content at 600 °C shows a higher thermal conductivity of 26.8 W/(m·K). A fourth-order polynomial function between thermal conductivity and copper content was created for the first time by non-linear fitting. As a result, the value of thermal conductivity of the Ni60A/WC composite coating with different copper dilutions can be approximately predicted.

A comprehensive experimental study regarding size dependence on thermal conductivity of graphene oxide nanosheet

Graphene-based materials have great application prospects in the thermal management field due to their high intrinsic thermal conductivity. Understanding the factors affecting the thermal conductivity of graphene and graphene-based materials is essential for further application of the materials. This study aims to explore the effect of graphene oxide (GO) nanosheet size on its intrinsic thermal conductivity experimentally. By simultaneously characterizing the morphology and thermal conductivity of the nanosheet, an obvious size dependence of thermal conductivity is observed: larger-sized GO nanosheets are preferred to have higher thermal conductivity values. Further detailed morphology and structural analysis identify that this dependence is caused by morphological defects. In addition, whether this dependence at the microscale still exists in practical GO-based materials is also studied. The characterization of thermal conductivity and thermal management performance for macroscopic materials confirms this inheritability. This work clarifies the dependence and its generation principle of thermal conductivity on the GO nanosheet size, meanwhile, it also proves that this dependence still exists when microscopic nanosheets are integrated into macroscopic systems.

Impact of roughness on heat conduction involving nanocontacts

The impact of surface roughness on conductive heat transfer across nanoscale contacts is investigated by means of scanning thermal microscopy. Silicon surfaces with the out-of-plane rms roughness of ∼0, 0.5, 4, 7, and 11 nm are scanned both under air and vacuum conditions. Three types of resistive SThM probes spanning curvature radii over orders of magnitude are used. A correlation between thermal conductance and adhesion force is highlighted. In comparison with a flat surface, the contact thermal conductance can decrease as much as 90% for a microprobe and by about 50% for probes with a curvature radius lower than 50 nm. The effects of multi-contact and ballistic heat conduction are discussed. Limits of contact techniques for thermal conductivity characterization are also discussed.

Understanding bipolar thermal conductivity in terms of concentration ratio of minority to majority carriers

Bi2Te3 is a good candidate to be used in thermoelectric generators. For a higher efficiency of the generators, shifting the temperature at which Bi2Te3 performs best to higher temperatures is required. Bipolar thermal conductivity suppression is the most effective approach to improve high-temperature thermoelectric performance. However, characterization of the bipolar thermal conductivity is challenging because it is related to individual contribution to Seebeck coefficient and electrical conductivity from the majority and minority carriers. Two-band model calculations are performed using reported band parameters of n-type Bi2Te3 to estimate the effects of band gap and minority to majority carrier concentration ratio in the bipolar thermal conductivity suppression. Individual Seebeck coefficient, electrical conductivity, and carrier concentrations from the majority and minority carriers are evaluated while varying chemical potential with a different band gap. It was demonstrated that increasing the band gap and chemical potential increased the individual Seebeck coefficient from minority carriers while decreasing the individual electrical conductivity and concentration from minority carriers. As a result, it was shown that the band gap increase and especially the magnitude of the minority to majority carrier concentration ratio decrease was effective in the bipolar thermal conductivity suppression.

Thermal Conductivity Characterization of Epoxy Based Composites Reinforced with Date Palm Waste Particles

Natural additives are largely available and have good environmental properties, therefore it mostly added as reinforcing material in a large number of polymeric materials. The intention of this study is to prepared green composite products to utilize as an insulating material and also in internal components of automobiles and the shipbuilding industry. For that reason, six composites were prepared that using particles from the date palm waste (palm mesh, seed of fruit, and trunk) as reinforcing fillers at (10, 20, and 30) wt.% loading as well as a hybrid of each three fillers in an epoxy matrix. The result included that the variation of thermal properties with the filler volume fraction and also with the type of fillers. At maximum volume fractions (30%), the seed date palm attained the lowest values of thermal properties of 0.138W/m.K, 720 m2/s, and 0.0201 J/kg.K for the thermal conductivity, specific heat, and thermal diffusivity respectively. Epoxy hybrid composites have the lowest thermal conductivity than other composite materials, making them more suitable for thermal insulation materials.

Characterization of 3D microstructure, thermal conductivity, and heat flow of cement-based foam using imaging technique

Characterization of 3D microstructure, thermal conductivity, and heat flow of cement-based foam using imaging technique

Characterization of high thermal conductivity fuel surrogates before and after ion irradiation

• Thermal conductivity of UO 2 surrogates was enhanced during sintering using aluminum oxide and silicon carbide additives. • Compositions were stable up to 5 dpa and 700 °C while a decrease in their mechanical properties was observed at 15 dpa. • Microcrack formation due to anisotropic swelling of the additives was not observed. High thermal conductivity nuclear fuels offer important potential advantages over traditional oxide-based fuels such as higher burnup, reduction in fission gas release, and better overall safety of the system. One proposed approach to high thermal conductivity fuels utilizes high thermal conductivity nonfissile additives with UO 2 fuel to lower the fuel operating temperature and thereby take advantage of the highly favorable radiation resistance of UO 2 at lower operating temperatures. However, differential swelling in the matrix and high conductivity additive phases during high dose irradiation could lead to internal cracking and poor performance. In the current study, ceria (CeO 2 ) and zirconia (ZrO 2 ) surrogate matrices were used to model UO 2 behavior. Additives of 10 vol. % Al 2 O 3 or SiC in the form of short fibers or platelets were used for the high conductivity second phase. The nuclear fuel surrogates were sintered to achieve densities greater than 93% of the ideal values. Scanning electron microscopy (SEM) imaging and X-ray diffraction confirmed the uniform distribution of the second phase and that no intermetallic second phase was formed during sintering. The thermal conductivity of the sintered samples was measured from 50 °C to 900 °C and confirmed the desirable increase compared to pure CeO 2 /ZrO 2 pellets. Samples were irradiated with 20 MeV Ni 6+ ions at midrange doses ranging from 1 to 15 displacements per atom (dpa) and temperatures from 300 °C to 700 °C. Post irradiation characterization revealed a good stability of the samples at low to medium doses with matrix lattice parameter swelling of < 0.14 % but showed a significant microstructural deterioration and decrease of the mechanical properties at 15 dpa.

Evaluation of the effects of heat conducting enhancement measures on MOFs hydrogen storage system for ship's propulsion plant

Experiments were conducted for developing an on board MOFs hydrogen storage system by cryo-adsorption in terms of adsorption equilibrium and charge/discharge characteristic of the adsorbent bed. MIL-101 was synthesized by hydrothermal method, the expanded natural graphite (ENG) and a honeycomb heat exchanging device were then introduced for monolith and heat conducting enhancement. Structural characterization and measurement of thermal conductivity were performed on the MIL-101 and its composites synthesized by mixing ENG with different mass ratios. Adsorption equilibrium data of hydrogen on the MIL-101 and MEI-01 (composite formed by adding ENG with a mass ratio 0.1) were measured at a temperature-pressure range from 77.15K to 87.15 K and 0–6 MPa. Accuracies of results predicted by Langmuirian equations were compared, Toth equation and Henry law were then employed to calculate the isosteric heat of hydrogen adsorption. Charge and discharge tests were conducted under the flow rate 20 L·min−1 on a 3.2 L conformable vessel respectively filled MIL-101, MIL-101+honeycomb heat exchanging device and MEI-01. It shows that the isosteric heats on two samples are similar and are about 3.1kJ·mol−1−7.4kJ·mol−1; the honeycomb heat exchanging device is better on weakening the thermal effect of the adsorbent bed than adding the ENG. It suggests that employing a conformable shape vessel equipped with a honeycomb heat exchanging device is a feasible solution to an on board MOFs hydrogen storage system.