Heat Conduction Performance Research Articles

Enhancement of thermal–mechanical performances via a selective CNTs configuration in laminated CNTs/AZ31B composite

Magnesium alloy is an excellent lightweight material. While the alloying process improves mechanical properties, it often reduces material thermal conductivity. An effective way to balance these two properties is to add CNTs. In this paper, a novel laminated CNTs/AZ31B composite was fabricated by introducing CNTs with selective configuration. First, the specific configuration of CNTs was built onto AZ31B sheets with a reticle mask using the electrophoretic deposition process. Then, the CNTs/AZ31B composite was obtained by the hot-pressing process. The effect of deposition factors on composite forming quality was studied to seek a satisfactory interlayer binding. Finally, the mechanical and thermal properties of CNTs/AZ31B composites with different CNTs content and deposition orientations were tested. The results show that the mechanical and thermal properties of CNTs/AZ31B composites were noticeably anisotropic. By adding 0.5 wt% CNTs, the tensile strength and Young’s modulus of the CNTs/AZ31B composite were effectively enhanced by 30.3 % and 10.5 %, respectively. Meanwhile, the thermal conductivity of the composites increased to 84.2 W/ (m·K) when adding 0.25 wt% CNTs, with heat conduction and dissipation performance enhanced. The studies of tensile fracture and CNT-Mg interfaces of CNTs/AZ31B composite show that CNTs can act as a shortcut of heat flow and load transfer.

Thermal transport in multilayer silicon carbide nanoribbons: reverse non-equilibrium molecular dynamics.

The heat conduction performance of materials has a crucial role in deciding their functional efficiency. For this purpose, the present study explores the structural and thermal properties of multilayer silicon carbide nanoribbons (SiCNRs). At first, we realize that the smallest values of cohesive energy correspond to the system with the largest interlayer distance due to vdW forces. The effects of stacking layers, their number, edge chirality, ribbon width, temperature (T) as well as coupling strength between the layers on the thermal conductivity, are all examined and discussed, using reverse nonequilibrium molecular dynamics. This results in an anisotropic trend of κ in terms of some parameters due to phonon scattering. By analyzing the various phonon properties, including phonon density of states, phonon dispersion relations as well as phonon mean free path, we gain critical insights into the mechanism of heat conduction in the systems. System size results reveal that thermal conductivities follow an increasing behavior with length and a decreasing trend with width as well as temperature, which is attributed to the phonon-phonon scattering rate. Furthermore, the thermal conductivities drift from the normal 1/T law and show an anomalous decreasing behavior above room temperature. Overall, these results offer a deep understating towards the thermal conductivity of n-SiCNRs and could promote their potential applications in thermoelectric and nanoelectronic devices.

Deterioration of equivalent thermal conductivity of granite subjected to heating-cooling treatment

Understanding the thermal conductivity of granite is critical for many geological and deep engineering applications. The heated granite was subjected to air-, water-, and liquid nitrogen (LN2-) coolings in this context. The transient hot-wire technique was used to determine the equivalent thermal conductivity (ETC) of the granite before and after treatment. The deterioration mechanism of ETC is analyzed from the meso-perspective. Finally, the numerical model is used to quantitatively study the impact of cooling rate on the microcrack propagation and heat conduction characteristics of granite. The results show that the ETC of granite is not only related to the heating temperature, but also affected by the cooling rate. The ETC of granite decreases nonlinearly with increasing heating temperature. A faster cooling rate causes a greater decrease in ETC at the same heating temperature. The higher the heating temperature, the stronger the influence of cooling rate on ETC. The main explanation for the decrease in ETC of granite is the increase in porosity and microcrack density produced by the formation and propagation of pore structure and microcracks during heating and cooling. Further analysis displays that the damage of granite at the heating stage is induced by the difference in thermal expansion and elastic properties of mineral particles. At the cooling stage, the faster cooling rate causes a higher temperature gradient, which in turn produces greater thermal stress. As a result, it not only causes new cracks in the granite, but also aggravates the damage at the heating stage, which induces a further decrease in the heat conduction performance of granite, and this scenario is more obvious at higher temperatures.

Effective heat conduction evaluation of lattice structures from selective laser melting printing

Lattice structures are promising for the applications as heat exchange media since additive manufacturing technology is able to prepare the parts in complex shapes. Thermal conduction performance is one of the key indicators evaluating the heat transfer capability of heat exchange media, and it is quantified by the effective thermal conductivity. The present study is to evaluate the heat conduction performance of lattice structures used as lightweight materials in industries. In order to design and fabricate lattice structures with controllable thermal conduction performance, the effects of structure design variables such as topology, porosity, specific surface area, and cross-section area on effective thermal conductivity of selective laser melting processed lattice structures are investigated systematically by experimental and numerical approaches. The results show that either decreasing the porosity or specific surface area increases the effective thermal conductivity of specific lattice structures. It is also found that the effective thermal conductivity increases up to 50.67% when the minimum cross-section area is enlarged along with the main heat conduction direction under the same porosity and specific surface area.

Multi-objective topology optimization of passive heat sinks including self-weight based on triply periodic minimal surface lattices

Advancements in additive manufacturing technology allows design of novel lightweight passive heat sink based on triply periodic minimum surfaces (TPMS) lattices. Topology optimization has been adopted to obtain efficient lightweight passive heat sink designs that maximize heat dissipation. However, in the topology optimization framework, the mechanical loads are usually not considered which limits its application under severe loading conditions. This paper presents a multi-objective topology optimization based on Solid Isotropic Method of Penalization (SIMP) approach that simultaneously optimize both thermal and structural objective functions to yield optimized structures with better heat dissipation and enhanced structural integrity. Three load cases are studied considering both the thermal and structural load scenarios. For each scenario, a weighted sum method is used to linearly combine the two objective functions in order to obtain the Pareto front. The obtained optimal configuration is further transformed to generate a TPMS-based structure employing a novel density mapping approach. Primitive (P), Diamond (D), Gyroid (G), and IWP TPMS structures are considered. To further study the effectiveness of mapping, the thermal performance of the mapped structures is measured using the effective thermal conductivity The mapped Primitive TPMS-based structures were found to possess superior heat conduction performance compared to other mapped TPMS structures. The unit cell mapping sensitivity along and perpendicular to heating direction was also investigated. It was found out that increasing number of unit cells in a direction perpendicular to heating direction enhanced the structure's effective conductivity. The structural integrity of the mapped heat sink structures were also examined measuring their strain energy density under both self weight loads and external structural loads.

Superior Thermal Conductivity of Graphene Film/Cu-Zr Alloy Composites for Thermal Management Applications.

As the power density of electronic devices continuously increases, there is a growing demand to improve the heat conduction performance of thermal management materials for addressing heat dissipation issues. Single-/few-layer graphene is a promising candidate as a filler of a metal matrix due to its extremely high thermal conductivity (k); however, the well-arranged assembly of 2D-component graphene with a high volume fraction remains challenging. Herein, we integrated a novel graphene-based macroscopic material of graphene film (GF) into a Cu matrix by infiltrating molten Zr-microalloyed Cu into a spirally folded and upright-standing GFs skeleton. The microstructure of the GF/Cu composites was regulated by an interface modification strategy. The GF/Cu composites with a spirally layered microstructure exhibit a superior k of 820 W/m K in the axial direction, much higher than that of Cu-matrix composites reinforced with graphene nanosheets (generally <500 W/m K) and twice that of Cu. The thermal transfer mechanisms were investigated by experiments and theoretical calculations. The results reveal that the excellent performance is attributed to the construction of high-heat conduction channels and a positive coordinating effect at the Zr-modified GF/Cu interface. Meanwhile, the relation between interfacial microstructure and heat transfer is established in the composites using interfacial thermal resistance as a bridge. This work yields in-depth insight into the heat conduction mechanism in highly oriented structures and provides a promising solution for the thermal management issues of high-power electronics.

Through Plane Networked Graphene Oxide/Polyester Hybrid Thermal Interface Material for Heat Management Applications

ABSTRACT The role of electronic devices in our lives is increasing rapidly, with more research focusing on miniaturization, creating more demand for thermal interface materials (TIM). Grease-based TIM presently available have good thermal conductivity values, but issues such as contamination, pump-out, and an additional curing step are observed. Fibrous textile substrates are soft and flexible, making them suitable for occupying the asperities between the heat sink and heat-producing devices. However, they are insulating in nature and can be made conductive using conductive fillers such as graphene oxide (GO). In this article, a networked through-plane thermally conductive TIM using the cutting waste of polyester and GO was fabricated. The methodology involved functionalizing the PET substrate and studying its interaction with GO. A networked GO/PET, (N-GOPET) hybrid TIM was fabricated from waste PET with good through-plane heat conduction performance, softness, and cuttability as a promising replacement for grease-based TIM.

Annealing treatment on waterborne polyurethane film-forming and structural features induced heat conduction performance in conductive adhesive

Thermal annealing treatment (60, 80, 100, 120 and 150 °C) on waterborne polyurethane (WPU) film-forming and further the structural features induced heat conduction behavior was investigated. It was found that the WPU films annealed at 100 °C or 120 °C showed a higher thermal conductivity than others, which was attributed to more ordered structural sequences as shown by x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Combined with Fourier transform infra-red spectroscopy (FTIR), atomic force microscopy (AFM) and dynamic mechanical analysis (DMA), it is concluded that appropriate annealing can facilitate the creeping of polymer chains and further occurring rearrangement for forming ordered structural sequences. As concluded, annealing is an easy way of regulating morphological structures and further boosting microphase separation in engineering applications. Also for practical application in heat management domains, it is a good sign to see the WPU materials, such as conductive adhesive, with more ordered structural sequences (or high crystallinity) display a good heat transfer performance.

Multiphysics Field Topology Optimization Design of Main Support Structure of High-Temperature Superconducting Magnets

The high-temperature superconducting magnet (HTS) is one of the core technologies of a superconducting maglev. The effects of multiphysics fields including electromagnetic, mechanical, and thermal should be taken into consideration in design. Traditional design methods rely on the initial configuration and the engineer's experience and only consider the design for the heat conduction performance or the structure strength, which often significantly increases the weight. To solve the above problems, based on COMSOL Multiphysics software, the mathematical model of topology optimization of the main support was established with electromagnetic force and thermal stress as the input loads. The objective functions were assigned to total strain energy and heat leakage, combined with stress value and volume fraction constraint conditions. The solid isotropic material with penalization (SIMP) method was used to carry out the topological analysis of multiphysics. Finally, the innovative structure of main support is obtained. Through finite element analysis of multiphysics fields, the heat leakage, the max Von-Mises stress, and weight were taken as evaluation indexes to compare the optimal structure performance. The results show that the method adopted in this paper can reduce the heat leakage by 61.7% while reducing the weight of the main support by 85%, and the max Von-Mises stress does not exceed the yield limit of the material. The work of this paper provides a theoretical foundation for the engineering design of the heat conduction structure of a HTS magnet.

Investigation on Silver Modification of Different Shaped Filler on the Heat Conduction Performance Improvement for Silicone Elastomer

The continuous miniaturization and multi-function of electronic devices have put forward high requirements for the effective removal of the heat generated in the system. Developing thermally conductive polymer composite-based thermal interface materials is becoming the research hotspot. In addition to the usually concerned intrinsic thermal conductivity of the filler itself, surface modification is one of the important ways to form an effective heat conduction pathway and improve the overall thermal conductivity of materials. In this work, we used silicon rubber as the polymer matrix and achieved the thermal conductivity increment via various fillers with different shapes. The adopted fillers are spherical aluminum oxide (Al2O3), linear carbon fiber and boron nitride sheets, which can be considered as zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) fillers respectively. We also prepared the silver-modified fillers and investigated the influence on the formation of heat conduction pathways and interfacial thermal resistance of different shaped fillers. An obvious increment in thermal conductivity of the composite with silver-modified fillers was observed compared to the composite with pristine fillers. Furthermore, through the practical thermal management performance investigation, we found the thermal conductivity increment did improve the actual heat transfer performance of composite elastomers functioning as thermal interface materials

A thermal conductivity prediction model of cement-based grouts for ground source heat pump

Cement-based material is frequently used in many aspects. For example, it is used as a sort of grout in a ground source heat pump system, whose heat conduction performance directly affects the heat change efficiency of the vertical ground heat exchanger. However, there are few thermal conductivity models applicable to cement-based grout materials, and the accuracy of published models needs to be improved. Therefore, a thermal conductivity prediction model for cement-based materials was performed according to the structure and heat conduction equation, which can predict the influence of many factors on thermal conductivity, such as aggregate content (sand-cement ratio), porosity and saturation degree. The overall accuracy is high, with 39 sets of data (75% of the data volume) whose errors are less than ±10%, meeting engineering applications, while the error using existing models mostly exceeds ±20%. This model can also predict a large proportioning range with the water-cement ratio from 0.3 to 0.7, the sand-cement ratio from 0.5 to 3.0, and the saturation degree from 0 to 1. Based on the model prediction results, the variation maps of different sand-cement ratios and porosity under dry and saturated conditions were proposed, and the simplified fitting formula for a range of common values was given.

Mussels-inspired design a carbon nanotube based underwater superoleophobic/hydrophobic Janus membrane with robust anti-oil-fouling for direct contact membrane distillation

Membrane distillation is an emerging technique effective in desalination and other membrane separation processes. However, hydrophobic membrane fouling caused by non-polar foulants limits the practical oily wastewater application. In this study, an underwater-super-oleophobic/hydrophobic Janus membrane with flux enhancement and robust anti-oil-fouling property was fabricated through formation of a carbon nanotube/PDA/PEI hydrophilic surface coating on a PVDF membrane. The process comprised construction of carbon nanotube layer and bioinspired-adhesive polydopamine/Polyethyleneimine (PDA/PEI) which enhanced hydrophilicity and stability of the membrane. Integration of the hydrophilic property of PDA/PEI and the multiscale structures of CNT endowed the membrane with air-hydrophilicity, underwater superoleophobicity and anti-oil-fouling properties. Introduction of CNT increased the mass and heat conduction performance of the membrane, which was attributed to increased flux. Use of PDA/PEI firmly fixed the carbon nanotube layer on the membrane surface and effectively increased hydrophilicity of the membrane surface. Increase in hydrophilicity resulted in improved underwater-superoleophobicity of the modified membrane. The anti-oil-fouling properties of the Janus membrane were explored by treatment with saline feed containing 1000 mg L−1 mineral oil. The Janus membrane showed an excellent enhanced flux and oil repellent during the test. Our study provides an ideal strategy to tailor Janus membrane with excellent surface wettability for oily wastewater treatment.

A novel polymer composite coating with high thermal conductivity and unique anti-corrosion performance

Corrosion prevention and heat conduction are the key issues of numerous industrial equipment. Unfortunately, they are generally mutually exclusive properties for various heat exchangers-improving one capability usually causes decreased capability in another. Herein, a novel highly thermally conductive and anticorrosive coating for heat exchanger protection is reported, in which L-phenylalanine (Phe) modified boron nitride (BN) and graphene (G) sheets not only form heat conduction pathways, but also have unique multiple barrier effects. And the modified fillers exhibit improved interfacial compatibility with epoxy (EP). These factors confer the BN/G/Phe/zinc phosphate (ZP)/EP coating with a high thermal conductivity of 1.63 W/(m·K), which enhances 641% than that of EP coating (0.22 W/(m·K)), and could significantly reduce the heat transfer coefficient loss of the coated heat exchanger from 9.47% (when EP coating is coated) to 1.39% according to the theoretical calculations. Moreover, further combined with the corrosion-inhibiting film formed by ZP, the impedance modulus at 0.01 Hz of the BN/G/Phe/ZP/EP coating always maintains above 1011ohm·cm2 during 150 days of immersion in 3.5 wt% NaCl solution. The mechanism of the enhanced heat conduction and anti-corrosion performance of the coating are vividly discussed in detail. This work is of great significance to the development of new functional coatings with both high heat conduction and unique corrosion prevention capabilities.

Mechanisms for thermal conduction in molten salt-based nanofluid

The addition of nanoparticles to molten salt can enhance its utility as a thermal energy storage material for concentrating solar power plants. The heat transfer property of solar salt loaded with Al2O3 nanoparticle is investigated by molecular dynamics simulations. The results show that the introduction of Al2O3 nanoparticles improves the thermal conductivity of solar salt, but its enhancement effect is not as significant as SiO2 nanoparticles. The increased thermal conductivity cannot be explained by the previously proposed hypothesis, such as the Brownian motion of nanoparticles, microconvection of base liquid, ordered layer of base liquid and coulombic potential energy. New insights into heat conduction performance of molten salt based nanofluid are given from the perspectives of material components and heat flux fluctuation modes. It is found that the nanofluid thermal conductivity is mainly contributed by the atom motions and interactions between atoms in Al2O3 nanoparticle, rather than in base fluid. The heat flux is concentrated in nanoparticle, which promotes the heat transfer. Furthermore, the collision involving the work done by the interatomic forces or the virial interaction dominates the heat conduction in nanofluid with lower mass fraction (< 6%), while the potential energy and collision both contribute to the nanofluid with higher mass fraction (> 6%). These new findings make a step forward in understanding the heat conduction mechanisms of molten salt based nanofluid.

금속 입자 기둥 고분자 복합소재 TIM의 열전도 특성

Special pariticle column and silicone composite thermal interface material were designed and proposed to assure reliability via CTE matching owing to the rise in the quantity of heat produced per unit area of electronic devices. Using nickel columns, a total of nine thermal interface materials (TIMs) were developed based on the mixing ratio and pattern of thermal TIMs. As a result, an experiment was carried out on thermal performance as a function of load variation. Thermal resistance reduced as load rose in all TIMs, heater power increased, and then thermal resistance was slightly raised or not altered after exhibiting the lowest value at 15W. The 10:7 mixing ratio of Silicon-Nickel produced the best thermal performance. The heat conduction performance of TP107 with a mixing ratio of 10:7 was 7 to 8% better than TP109 and 14 to 16 percent greater than TP105. Furthermore, as compared to pads with higher nickel hardness, pads with reduced nickel hardness enhanced heat transfer performance by 12-14 percent. It can be expected that there is an ideal mixing ratio for TIM via the metal pillar, and that by lowering metal hardness, contact thermal resistance between metal particles may be lowered.

Numerical study on the thermal enhancement of horizontal latent heat storage units with hierarchical fins

The poor thermal performance of shell and tube latent heat storage (LHS) units using phase change materials restricts large-scale renewable energy utilisation. To address this issue, an innovative hierarchical fin is designed here to improve the charging performance of horizontal LHS units. The charging characteristics of innovative LHS units are explored and compared with available LHS units by a numerical model using the enthalpy-porosity scheme. Moreover, the response surface method (RSM) is applied to optimise the hierarchical fin by maximising its charging rate. The results indicate that hierarchical fins significantly improve the charging rate and temperature uniformity of horizontal LHS units. Except for the early heat conduction stage, melting convection develops as the dominant mode in the middle stage but decays in the later stage. Compared to tree-shaped fins, the hierarchical fin dramatically enhances heat conduction performance in the late melting stage, leading to a maximum reduction of 41.1% in the whole melting time of horizontal LHS units. To maximise the charging performance, the RSM results suggest the thickness gradient of the primary bifurcation, thickness fractal dimension, and length ratio of hierarchical fins should be 3.98, 1.34, and 1.11, respectively, providing constructive guidance for engineering applications of horizontal LHS units.

Fast calculation method of directly buried cables ampacity

Accurate calculation of the ampacity of underground cables is an important prerequisite for ensuring the safe and economical operation of cables, the realization of this goal mainly depends on the accuracy of the calculation of the external thermal resistance of the cable. The accuracy of numerical method is high but slow calculation speed, the analytical algorithm (IEC standard supply) is fast, but the calculation error is large when dealing with the non-uniform soil problems with poor heat conduction performance backfill soil. In this paper, the external thermal resistance of cable is calculated by finite volume method and equivalent thermal circuit method, substitutes the calculation result into the analytical calculation formula, which can quickly and accurately calculate the ampacity of the cable group. This method is faster than the pure numerical method, and which is more accurate than the analytical algorithm. The superiority of this method is proved by comparing with analytical algorithm, coordinate combination method and field-circuit combination method in uniform and non-uniform soils.

Study on heat conduction and adsorption/desorption characteristic of MIL-101/few layer graphene composite

Aiming at the poor heat conduction performance of porous MIL-101 applied in adsorption cooling process, few layer graphene (FLG) was selected as a promising thermal conductive additive to enhance thermal conductivity of MIL-101. The factors which influencing thermal conductivity of MIL-101/FLG composites were investigated. Thermal conductive mechanism of FLG for MIL-101 was discussed. Adsorption/desorption characteristics of water on the MIL-101/FLG composites were determined. Results show a two-dimensional structure of FLG with no defects and high degree of order is beneficial to the improvement of thermal conductivity for MIL-101/FLG composites. At 30 °C and bulk density of 0.55 g/cm3, thermal conductivity of MIL-101/20%FLG and MIL-101/25%FLG composite is 6.5 and 11.3 times higher than that of MIL-101. Thermal conductivity of MIL-101/FLG composites is related to the alignment direction of FLG and test direction of heat flow, and the interfacial thermal resistance between MIL-101 and FLG. Adding FLG in the MIL-101/FLG composites does not affect adsorption/desorption mechanism of water on the MIL-101. The addition of FLG can strengthen mass transfer and thermal diffusion process on the surface of MIL-101. Adsorption rate constant of water on the MIL-101/25%FLG composite is 2.05 times higher than that of MIL-101. The desorption temperatures and desorption activation energies of water on MIL-101/20%FLG and MIL-101/25%FLG composites are lower than those of MIL-101. It can provide basic research for the development of new adsorption water chiller working pair (MIL-101/FLG–water) with high efficiency.

Exceptional in-plane and interfacial thermal transport in graphene/2D-SiC van der Waals heterostructures

Graphene based van der Waals heterostructures (vdWHs) have gained substantial interest recently due to their unique electrical and optical characteristics as well as unprecedented opportunities to explore new physics and revolutionary design of nanodevices. However, the heat conduction performance of these vdWHs holds a crucial role in deciding their functional efficiency. In-plane and out-of-plane thermal conduction phenomena in graphene/2D-SiC vdWHs were studied using reverse non-equilibrium molecular dynamics simulations and the transient pump-probe technique, respectively. At room temperature, we determined an in-plane thermal conductivity of ~ 1452 W/m-K for an infinite length graphene/2D-SiC vdWH, which is superior to any graphene based vdWHs reported yet. The out-of-plane thermal resistance of graphene → 2D-SiC and 2D-SiC → graphene was estimated to be 2.71 × 10−7 km2/W and 2.65 × 10−7 km2/W, respectively, implying the absence of the thermal rectification effect in the heterobilayer. The phonon-mediated both in-plane and out-of-plane heat transfer is clarified for this prospective heterobilayer. This study furthermore explored the impact of various interatomic potentials on the thermal conductivity of the heterobilayer. These findings are useful in explaining the heat conduction at the interfaces in graphene/2D-SiC vdWH and may provide a guideline for efficient design and regulation of their thermal characteristics.

Constructal Design of an Arrow-Shaped High Thermal Conductivity Channel in a Square Heat Generation Body.

A heat conduction model with an arrow-shaped high thermal conductivity channel (ASHTCC) in a square heat generation body (SHGB) is established in this paper. By taking the minimum maximum temperature difference (MMTD) as the optimization goal, constructal designs of the ASHTCC are conducted based on single, two, and three degrees of freedom optimizations under the condition of fixed ASHTCC material. The outcomes illustrate that the heat conduction performance (HCP) of the SHGB is better when the structure of the ASHTCC tends to be flat. Increasing the thermal conductivity ratio and area fraction of the ASHTCC material can improve the HCP of the SHGB. In the discussed numerical examples, the MMTD obtained by three degrees of freedom optimization are reduced by 8.42% and 4.40%, respectively, compared with those obtained by single and two degrees of freedom optimizations. Therefore, three degrees of freedom optimization can further improve the HCP of the SHGB. Compared the HCPs of the SHGBs with ASHTCC and the T-shaped one, the MMTD of the former is reduced by 13.0%. Thus, the structure of the ASHTCC is proven to be superior to that of the T-shaped one. The optimization results gained in this paper have reference values for the optimal structure designs for the heat dissipations of various electronic devices.