Thermal Transfer Ability Research Articles

Aramid nanofiber assisted preparation of 3D-oriented graphite/silicone composite slices with high through-plane thermal conductivity and efficient electromagnetic interference shielding

High-performance electromagnetic interference (EMI) shielding materials with outstanding thermal transfer ability are urgently needed for modern electronics. Here, efficient 3D-oriented graphite/silicone EMI shielding composite slices with high through-plane thermal conductivity were prepared through the construction of 3D-oriented graphite skeletons followed by incorporation of silicone and cutting. The flaky graphite was utilized as functional fillers, and an ultra-low addition of aramid nanofibers (ANFs) was conducted to construct the supporting frameworks to maintain the structure of 3D-oriented graphite skeletons. The strategy of constructing of 3D-oriented graphite skeletons before incorporating of silicone facilitated the forming of efficient electrically conductive network and thermal transfer pathway in the prepared composite slices. The differences in thermal, electrical and EMI shielding properties that originated from the orientation of interconnected flaky graphite were systematically studied. As a result, the composite slices show significant enhancements of EMI SE of 65.28 dB in X-band, 76.62 dB in Ka-band and through-plane thermal conductivity of 10.53 W m−1 K−1 at the graphite fraction of 32.68 vol%. Additionally, the composite slices exhibit a good near-field (NF) shielding performance at the frequency range of 1–9 GHz. The composite slices reveal substantial potential for advanced EMI shielding and thermal management applications.

Reducing the impact of the sunlight in urban areas using asphalt mixtures with phase change materials: a review in Scopus in the last three years

Phase change materials (PCMs) have been incorporated into asphalt concrete pavements because they can regulate the temperature by absorbing and releasing heat during physical state changes. This effect reduces temperature gradients of pavements and, consequently, increases its service life. This work presents a systematic review of recent articles published in peer-reviewed journals (available in the Scopus database) involving asphalt mixtures with PCMs and focusing on mechanical characterization. It is observed that most of the selected papers investigated the benefits of polyethylene glycol as a PCM. The most common strategy to avoid leakage during the phase transition involved using a porous material that acts as a carrier matrix for the PCMs. Generally, asphalt pavements with PCMs are systems with favourable thermal transferability, thus demonstrating higher heat absorption and dissipation rates. Finally, the asphalt mixtures containing PCMs showed lower mechanical performance than the control mixtures. However, they still satisfy the required criteria. In any case, it is expected that with the incorporation of PCMs into asphalt pavements, the social and environmental effects (Urban Heat Island) of sunlight in urban areas can be mitigated by the thermoregulation phenomena.

Effect of jade nanoparticle content and twist of cool-touch polyester filaments on comfort performance of knitted fabrics

Cool-touch polyester knitted fabrics with excellent thermal-wet and cooling comfort ability are desired for summer and sports clothing. Jade nanoparticle content and twist of filaments have significant effects on comfort-related properties. In this work, the effects of jade content and twist level of two types of cross-section polyester filament on fabric comfort-related properties were investigated in detail. Filaments were prepared and further knitted to fabric samples. The physical performance of polyester filaments, the thermal-wet transfer properties and dynamic cooling property of their fabrics were measured and analyzed. It was found that the jade nanoparticles mainly affected thermal transfer property of fabrics, and the best thermal transfer was exhibited by fabric with 7% cool-touch PET chip. With the increase of twist level, air permeability, water spreading and drying performance improved but thermal transfer ability decreased, and lower twist level of yarns was beneficial for achieving real moisture cooling properties. These results showed a major advance in developing thermal-wet comfort knitted fabrics using cool-touch filaments with appropriate twist level.

Fundamental Properties and Thermal Transferability of Masonry Built by Autoclaved Aerated Concrete Self-Insulation Blocks.

This paper performed a detailed study on the fundamental properties and thermal conductivity of autoclaved aerated concrete (AAC) self-insulation block, and the mechanical properties and heat transfer resistance of the AAC self-insulation block masonry. Different kinds of joints and the plastering surface were used to build the masonry specimens. The distinctive feature of the blocks and mortars is the lower thermal conductivity with expected strength. Compared to those with larger thickness of insulation mortar joints, the masonry with thin-layer mortar joints had better compressive performance and lower shear strength. The compressive strength of masonry was related with the block and mortar strengths, the shear strength of masonry along mortar joints was related with the mortar strength. The stress–strain relationship of masonry in compression could be predicted by the similar expression of conventional block masonry. The tested heat transfer coefficient of AAC self-insulation block masonry with thickness of 250 mm without plastering surfaces was (0.558 ± 0.003) W/(m2·K). With the plastering surfaces, the heat transfer coefficient reduced by 4.4% to 8.9%. Good agreements in values of heat transfer coefficient existed by using the test, theoretical computation and ANSYS (ANSYS Inc. Canonsburg, PA, USA) analytical methods. Based on the extensibility analyses, the heat transfer coefficients of AAC self-insultation block masonry with different thickness are proposed. The best thickness is proposed for the outer walls of residential buildings in different cold zone to meet the design requirement of energy conservation.

Design of 3D-network montmorillonite nanosheet/stearic acid shape-stabilized phase change materials for solar energy storage

Phase change materials (PCMs) that have the ability to convert and store solar energy could take full advantage of clean and renewable energy. However, the large-scale commercial application of PCMs was seriously limited due to the leakage, low thermal energy storage capacity and poor thermal transfer ability. In this work, natural montmorillonite (Mt) has been exfoliated into two-dimensional montmorillonite nanosheets (MtNS) and then being self-assembled into three-dimensional network montmorillonite framework (3D-MtNS), which was applied to encapsulate stearic acid (SA) for the fabrication of composite PCMs to significantly promote solar energy conversion and storage performances. This novel 3D-MtNS framework provides super porosity and huge specific surface area to encapsulate more than 95 wt% SA without leakage, resulting in the highest latent heat capacity (198.78 J/g) among clay mineral based composite PCMs. Besides, the cross-linked MtNS throughout the PCM composites provided rapid heat transfer paths, leading to outstanding thermal transfer ability and excellent photo-thermal conversion performances. In addition, due to the protection of the 3D-MtNS framework, the composite PCMs exhibit superior form stability, thermal stability and cycling stability. Compared with previous prepared clay minerals based composite PCMs, the present 3D-network MMT/SA composite PCMs showed dramatic latent heat capacity and good heat transfer ability simultaneously, which enable the direct solar energy conversion, storage and utilization.

A trade-off study toward highly thermally conductive and mechanically robust thermoplastic composites by injection moulding

In order to achieve high thermal conductivity (TC) for graphene-reinforced thermoplastic polymer composites, many efforts have been made to reduce the interfacial thermal resistance. However, good mechanical properties may be conflicting with thermal properties due to the poor interaction bonding between matrix and fillers. In this work, graphene sheets (GSs) filled thermoplastic polypropylene (PP) composite are prepared by three different moulding methods: i) melt extrusion with subsequent injection moulding, ii) single injection moulding and iii) hot-pressing. The relationship among processing methods, microstructures and properties are systematically demonstrated in detail. It is found that single injection moulding can be used to realize a random distribution of the filler with modest size to keep good mechanical properties, and an acceptable conductive network in the matrix to improve the thermal transfer ability of the composites. As a result, high TC of 2.07 Wm−1K−1 and tensile strength of 24 MPa are simultaneously achieved for 20 wt% GSs/PP composite, realizing a tradeoff between thermal and mechanical properties. Finite element simulation is also conducted to perceive the dependence of the thermal properties on the size and distribution of GSs filler. We think that this work provides an instructive route to design thermoplastic composites with overall consideration of thermal and mechanical properties and allows a considerable step to its industrial application.

Development of 2D-Mt/SA/AgNPs microencapsulation phase change materials for solar energy storage with enhancement of thermal conductivity and latent heat capacity

Application of clay mineral based phase change materials (PCMs) on solar energy storage was limited by poor latent heat storage and thermal conductivity. In this study, two-dimensional montmorillonite/stearic acid/Ag nanoparticles (2D-Mt/SA/AgNPs) composites were prepared to enhance the latent heat capacity and thermal transfer ability. It was found that the composites possessed ultra-high latent heat storage (>187 J/g) and contained more than 90 wt% of SA. Besides, 2D-Mt/SA/AgNPs showed 229.3% increase in thermal conductivity after incorporation of AgNPs into the core of composite PCMs, compared with pure SA. In addition, 2D-Mt/SA/AgNPs exhibited remarkable thermal charging/discharging rate and outstanding light-thermal conversion ability due to the excellent heat transfer ability. Because of the excellent thermal stability and structure reliability, 2D-Mt/SA/AgNPs showed superior cycling performances in the heating/cooling tests. As a consequence, 2D-Mt/SA/AgNPs were promising sustainable energy storage materials owing to large latent heat, high thermal conductivity, outstanding thermal stability and excellent cycling performance.

Design of MtNS/SA microencapsulated phase change materials for enhancement of thermal energy storage performances: Effect of shell thickness

Clay minerals are excellent supporting materials to synthesize shape-stabilized phase change materials (ssPCMs) because of outstanding pore structure, excellent thermal stability, perfect organic compatibility and eco-friendly features. However, previous clay-based ssPCMs show very low thermal energy storage capacity due to little loading of working PCMs (<65 wt%). In this work, stearic acid (SA) encapsulated by two-dimensional montmorillonite nanosheets (MtNS) has been designed in order to form core-shell structural MtNS/SA composite PCMs with ultra-high core mass fraction and dramatic latent heat capacity. This study mainly investigates the effect of MtNS shell thickness on thermal energy storage performances, including latent heat, thermal transfer ability, shape stability and cycling performances. Self-assembly mechanism of MtNS/SA was attributed to that the positively charged MtNS strongly attached on the surface of negatively charged SA latex particles and formed a core-shell structure mainly through electrostatic interaction. The MtNS/SA composite showed very large latent heat capacity (184.88 J/g) due to encapsulation of massive SA (>85 wt%). Besides, the composite PCMs also displayed improved thermal transfer ability due to the combination of MtNS, which leads to outstanding thermal charging/discharging rate and excellent photo-thermal conversion efficiency. It was also found that the thinner the MtNS, the better the thermal conductivity and latent heat storage capacity. In addition, the MtNS/SA composites show thermal and structural stability, no leakage occurred even under the encapsulation of the thinnest MtNS shell. Also, the cycling performances of this composite PCMs are very outstanding owing to the effective protection of MtNS shell. Hence, this non-leaking and green MtNS/SA composite PCMs with high-performance heat storage properties can be applied in sustainable energy field.

Research on Influencing Factors of the Thermal Contact Resistance in Thin-Wall Injection Molding

Abstract Thermal contact resistance, a parameter that describes the thermal transferability of the interface between the melt and the metallic wall, exercises a significant influence on the surface quality of the resulting part, especially in thin wall injection molding. In this study, temperature data of the melt was quantitatively measured with only 2 micro thermocouples, and TCR of specimens with 4 kinds of thickness was calculated after data processing with a new mathematical model. It was demonstrated that TCR was deeply affected by mold temperature. When the mold temperature increased from 90 °C to 130 °C, the rate of TCR decline was 56.72 %. Melt cooling simulation was performed with different values of TCR, which played the dominant role of TCR in calculating the temperature distribution in thin-wall injection molding. It showed that TCR exercises a significant influence on the simulation of the cooling rate, and the influence cannot be ignored, especially in thin-wall injection molding.

Influence of Substrate Properties on the Formation of Suspension Plasma Sprayed Coatings

In this study, YSZ coatings were deposited on different substrate materials (stainless steel and aluminum) using suspension plasma spray technique. The effects of substrate properties (material, surface topology, temperature, and thickness) on the formation of coatings were investigated. The results showed that, with the identical spray parameters, the porosity is higher for the coatings deposited on aluminum than that on stainless steel due to the high thermal transfer ability of the former substrate material. The SEM results revealed that the microstructure of as-prepared coatings could be tailored from the vertical cracked structure to the columnar structure by increasing the substrate surface roughness and their formation mechanisms were discussed. The substrate preheating temperature has an influence on the microstructure of the coatings, especially in the interfacial region. Increasing the substrate temperature is an effective means for reducing the interface defects and for improving the adhesion of the coatings. With the increase in the substrate thickness, the quantity of the vertical cracks in the coatings is reduced and their width becomes narrower.

Graphene for Water-Based Nanofluid Preparation: Effect of Chemical Modifications on Dispersion and Stability

Graphene, whatever its number of layers, is recognized for heat and thermal transfer ability. As it is widely known to be highly hydrophobic, its use in water-based nanofluid development requires first to improve both their dispersion and stability properties. Here, we have investigated several ways to chemically modify the surface properties of multi-layer graphene in order to increase their hydrophilic character. Chemical reactivity of graphene was deeply analyzed based on a multi-scale characterization using TEM, Raman spectroscopy and TGA-MS coupled technique. By optimizing and combining both covalent and non-covalent functionalization, stable graphene-based nanofluids under static conditions could be prepared with a straightforward approach. Moreover, we have investigated their flowing behavior. Contrary to graphene nanosheets strongly attacked by HNO3, under a gentler oxidation treatment using KMnO4, stability is well preserved under flowing conditions. Such high-stability nanofluids could help toward the practical use of graphene-based dispersions as heat transfer fluid in flowing systems.

Modeling heat transport in nanofluids with stagnation point flow using fractional calculus

This paper studies the flow and heat transfer of power-law type nanofluids with stagnation point flow past a porous sheet. The governing equation of temperature involving spatial fractional derivative is used to investigate the anomalous heat diffusion of nanofluids. Four types of nanoparticles are considered with the carboxymethyl cellulose and water miscible liquids as the heat transfer fluid. By suitable similarity transformations, the governing partial differential equations are reduced to a system of ordinary differential equations, which are discussed thoroughly. It is found that the thermal transfer ability of nanofluids shows inverse correlation with the order of fractional derivative. Effects of the other physical parameters on flow and heat transfer are analyzed in detail.

Thermal Conductance of Cu and Carbon Nanotube Interface Enhanced by a Graphene Layer**Supported by the National Science Foundation of China under Grant No 61131004, and the Fundamental Research Funds for the Central Universities under Grant No DUT14LAB11.

Thermal conductances between Cu and graphene covered carbon nanotubes (gCNTs) are calculated by molecular dynamics simulations. The results show that the thermal conductance is about ten times larger than that of Cu-CNT interface. The enhanced thermal conductance is due to the larger contact area introduced by the graphene layer and the stronger thermal transfer ability of the Cu-gCNT interface. From the linear increasing thermal conductance with the increasing total contact area, an effective contact area of such an interface can be defined.

Evaluation of heat transfer coefficient between polymer and cavity wall for improving cooling and crystallinity results in injection molding simulation

Heat transfer coefficient (HTC), as a parameter that describes the thermal transfer ability of the interface between the polymer melt and the metallic wall, has a dominant role in calculating temperature distribution. This research focuses on evaluating the HTC between the polymer and the cavity wall for improving the cooling and crystallinity simulation. A mathematical model for evaluating HTC was presented. Injection molding experiments were carried out to obtain temperature data near the cavity wall; HTC was calculated after data processing. Injection molding simulation was performed with different values of HTC, which represented various processing conditions. Finally, relative crystallinity from the simulation were obtained and compared with the result acquired by differential scanning calorimetry analysis. This research showed that HTC significantly influences the simulation of cooling rate and crystallinity. Comprehension of heat conduction phenomenon across the interface can promote the accuracy of injection molding simulation to predict mechanical behavior and dimensional precision.

Thermal conductivity of UO2 and PuO2 from first-principles

Based on our previously calculated phonon spectra from first-principles, in the present work, we have applied the Slack relation to obtain the thermal conductivity of UO2, PuO2, (Th, Pu) O2, and (U, Pu) O2 in temperature range of 300–1500K. Also, the mode Grüneisen parameters of PuO2 and UO2 were presented to analyze the anharmonic properties. Rapid decrease of the thermal conductivity for UO2 at low-temperature zone was observed. As for PuO2, its larger phonon group velocity results in better thermal transfer ability than ThO2, UO2, and AmO2 at high-temperature zone.

An Effective Approach for the Development of Reliable YBCO Bulk Cryomagnets with High Trapped Field Performances

Widespread use of YBa2Cu3O7‐δ (Y123) bulk superconductors as source of strong magnetic fields requires development of high‐performance materials sufficiently reliable with improved thermal transfer ability. An effective approach based primarily on the growth of bulk Y123 single domains comprising a holes‐network to diminish the oxygen diffusion paths is reported here, as well as their progressive annealing at high temperature under oxygen pressure to reduce undue stresses and processing time. Finely, it aims to stimulate the thermal exchange inside the superconductor and compensate for induced magnetic stresses during the field‐trapping process. The approach brings considerable time and energy savings, and turns out to knock down barriers having stymied hitherto the use of Y123 bulk superconductors for engineering applications. Indeed, it enables the achievement of a pore‐free and crack‐free microstructure yielding marked fracture toughness and promoting large size persistent current loops, thereby boosting the trapped field performances. The fostering of the internal thermal exchange leads the maximum trapped field Bmax to shift to higher temperatures by up to 14 K. A value Bmax of 6.34 T is attained at 17 K on ≈16 mm‐diameter reinforced pellet (disk area s = 1.99 cm2), resulting in an outstanding field density Bmax/s=3.19 Tcm−2.

Parametrization of the Gay–Berne potential for conjugated oligomer with a high aspect ratio

The Gay-Berne (GB) potential has been a popular semiempirical model for describing the short-range intermolecular forces for a wide variety of aspherical molecules, including liquid crystals and anisotropic colloids, with generally small molecular dimensions and low aspect ratios (<5). This study evaluates the parametrization of the GB potential for a high-aspect-ratio (=10) oligomer belonging to a model conjugated polymer. We elaborate that the semiflexibility associated with a large oligomer species demands a variant umbrella-sampling scheme in establishing the potentials of mean force (PMFs) for four pair ellipsoid arrangements typically utilized to parametrize the GB potential. The model ellipsoid so constructed is shown to capture the PMFs of essential intermediate arrangements as well, and, according to the results of simplex optimizations, recommendations are given for the minimum set of parameters to be included in the optimization of a large oligomer or particulate species. To further attest the parametrized GB potential, the coarse-grained (CG) Monte Carlo simulations employing the GB potential and the back-mapped, full-atom atomistic molecular dynamics (AMD) simulations were performed for a dense oligomer system at two representative system temperatures. The results indicated that the CG simulations can capture, with exceptional computational efficiency, the AMD predictions with good thermal transferability. In future perspectives, we remark on potential applications to construct efficient, parameter-free CG models for capturing fundamental material properties of large oligomer/particulate species as well as long-chain conjugated polymers.