Thermal Conductivity Behavior Research Articles

Variable frequency selective structure (CFRP/Cu/CFRP) micro blind hole laser high-quality drilling method guided by acoustic emission technology

The laminated structure of carbon fiber reinforced plastic (CFRP)-Cu-CFRP is an important structure for aerospace radome. The blind holes manufacturing is core process, but there are technological challenges in achieving the exposure of a 10 μm thick copper foil at the bottom of the blind hole. The exact position of the 10 μm thick copper foil within the material’s internal space is unknown, and the uneven heat accumulation and conduction can easily cause burning and damage to the ultra-thin copper foil. To date, there is no publicly accessible literature that documents the execution of this specific process. In this paper, novel variable inner diameter spiral scanning guided by Cu-CFRP interface accurately extracted using cosine similarity (CS) algorithm is proposed to obtain a blind hole with near-zero ablation damage. The similarity of acoustic emission signals generated by laser interaction with Cu and CFRP, as well as thermal accumulation and conduction behavior under different scanning radius, are described. The high-quality blind holes have been successfully drilled, with a large area copper foil exposed at the bottom, while the surface of the copper foil remaining intact without any damage or heat affected zone. Compared with traditional drilling method, the average exposed copper foil area at the bottom of the blind holes is increased by 238.4 % (from 0.464 mm2 to 1.570 mm2). And the average taper of blind hole is reduced by 41.7 % (from 0.470 to 0.274). This method can effectively increase the area of exposed copper foil and reduces the taper of blind holes, improve the welding strength and conductivity of wires in aerospace radomes, thereby enhancing the stealth performance and operational reliability of fighter jets.

Development of fruit peel biomass cellulose and pineapple leaf fibre polyester composite: fatigue, creep, flammability, and thermal conductivity behaviour

Development of fruit peel biomass cellulose and pineapple leaf fibre polyester composite: fatigue, creep, flammability, and thermal conductivity behaviour

Combined effects of pores and cracks on the effective thermal conductivity of materials: a numerical study

Porous solids are commonplace in engineering structures and in nature. Material properties are inevitably affected by the internal inhomogeneity. The effective thermal conductivity of porous materials has been and remains to be a subject of extensive research. Less attention has been devoted to thermal conductivity impacted by internal cracks. This study is devoted to theoretical analyses of the combined effects of pores and cracks on the effective thermal conductivity. Systematic numerical simulations using the finite element method are performed based on two-dimensional models, with periodic distributions of internal pores and cracks. The parametric investigations seek to address how individual geometric layout can influence the overall thermal conduction behavior. In addition to circular pores and isolated cracks, angular pores with cracks extending from their sharp corners are also considered. It is found that both isolated cracks and cracks connected to existing pores can significantly reduce the effective thermal conductivity in porous materials. Since it is much easier to microscopically detect internal pores than thin cracks, care should be taken in using the apparent porosity from microscopic images and density measurements to estimate the overall thermal conductivity. Quantitative analyses of the detailed geometric effects are reported in this paper.

The influence of graphene oxide on the microstructure and properties of ultrafine-grained copper processed by high-pressure torsion

New metal matrix nanocomposites with enhanced thermal stability were produced in a three step process consisting of mechanical milling, spark plasma sintering and High-Pressure Torsion (HPT). The nanocomposites consisted of a copper matrix and the addition of 1 wt% Graphene Oxide (GO) as a reinforcement. A nanocrystalline microstructure, enhanced hardness and improved thermal stability were achieved. The grain size of the nanocomposites was ∼55 nm which is almost four time smaller than for Cu HPT at 210 nm. Hardnes and ultimate tensile strength of the nanocomposites reach 250 Hv and 700 MPa, respectively, which was more than three times higher than for the initial material. The most important result is that the nanocomposites remained ultrafine-grained up to 500 ⁰C whereas the Cu HPT fully recrystalized after annealing at 300 ⁰C The report also includes an investigation of the electrical conductivity of the copper-based composite which was slightly better than for copper after HPT together with the wear behaviour of this material. This is one of the first reports on copper reinforced with graphene oxide composites produced by HPT and it gives information on its thermal stability, electrical conductivity and wear behaviour together with the microstructural characteristics and mechanical properties.

Probing the thermophysical property mechanism of Mg2+-doped high-entropy oxide ceramics

To create thermal barrier coatings (TBCs) with superior thermal characteristics and high-temperature stability, understanding the microscopic process of heat transfer in high-entropy solid solutions is crucial. In this study, novel (Zr0.2(1-x)Ce0.2(1-x)Pr0.2(1-x)Y0.2(1-x)Ho0.2(1-x)Mgx)O2-δ single-phase high-entropy fluorite-structured oxides with varying Mg elemental contents were successfully synthesized at 1600 °C. Given the unique ionic radius and valence nature of Mg2+, the effects of varying the Mg doping amount on the thermophysical properties and microstructures were explored. Furthermore, the mechanism influencing high-temperature thermal conductivity was studied at the microscopic scale using first-principles calculations to clarify the nature of the thermal conductivity behavior. On one hand, an increase in oxygen vacancies leads to an enhancement of the lattice distortion degree and phonon scattering level. On the other hand, divalent Mg2+ activates the lattice via unequal substitutions, thereby reducing the thermal conductivity. The experimental and simulation results revealed that as Mg doping increases, the content of oxygen vacancies significantly increases, the degree of lattice distortion increases, phonon scattering is enhanced (19.54–21.37 THz), high-temperature thermal conductivity progressively decreases (1.91-1.20 w·m−1·K−1), and the coefficient of thermal expansion progressively increases (11.70 × 10−6-12.31 × 10−6 K−1). These results offer a novel approach for designing doped high-entropy strategies that can satisfy the performance requirements of TBCs.

Compositing thermal conductivity behavior to enhance thermoelectric properties of honeycomb-like porous Ca3Co4O9 ceramics

Microstructures and thermoelectric properties of porous Ca3Co4O9 ceramics were investigated, which were prepared by tert-butanol alcohol (TBA)-based freeze casting method. The honeycomb-like porous Ca3Co4O9 ceramic presented an average pore diameter of 2.5 μm and the porosity of 65 %. The excellent low total thermal conductivity of 0.354 W (m K)−1 was obtained along the parallel channel direction, which was attributed to the oriented pores and isolated pores dispersed in ceramics matrix. The compositing thermal conductivity behavior of porous Ca3Co4O9 ceramics was jointly regulated by the parallel and Maxwell-Eucken (ME-1) models. The ZT value reached 0.37 at 1073 K. This work provides an effective strategy to improve thermoelectric properties of oxides thermoelectric ceramics, which can complete the decoupling of electrical and thermal properties.

Fabrication and Characterization of Graphene-Mesoporous Carbon-Nickel-Poly(Vinyl Alcohol)-Coated Mandrel-Coiled TCPFLNR Artificial Muscle.

This study investigates the performance enhancement of mandrel-coiled twisted and coiled polymer fibers with a nichrome heater (TCPFLNR) by coating with a solution of graphene-mesoporous carbon-nickel-polyvinyl alcohol. The coating process involved a one-pot synthesis utilizing graphene powder, Ni nanoparticles, mesoporous carbon, and PVA as a binding agent. The coating was performed by manually shaking the TCPFLNR and the subsequent annealing process, which results in improved thermal conductivity and actuation behavior of the TCPFLNR. Experimental results on a 60 mm long actuator demonstrated significant enhancements in actuation displacement and actuation strain (20% to 42%) under various loads with an input current of 0.27 A/power 2.16 W. The blocked stress is ~10 MPa under this 2.16 W power input and the maximum strain is 48% at optimum load of 1.4 MPa. The observed actuation strain correlated directly with the input power. The coated TCPFLNR exhibited better thermal contacts, facilitating enhanced heat transfer, and reducing power consumption by 6% to 9% compared to non-coated actuators. It was found that the nanomaterial coating helps the TCP actuator to be reliable for more than 75,000 actuation cycles at 0.1 Hz in air due to improved thermal conductivity. These findings highlight the potential for further research to optimize electrothermally operated TCP actuators and unlock advancements in this field.

Effects of Y doping on phase structure, mechanical properties and sintering behavior of (Yb1-xYx)2SiO5 environmental barrier coating materials

Yb2SiO5 is one of the most widely studied environmental barrier coating materials due to its excellent high-temperature phase stability and resistance to water oxygen corrosion. In this paper, a series of (Yb1-xYx)2SiO5 (x = 0, 0.1, 0.2, 0.3, 0.4) ceramics were fabricated by high-temperature solid state sintering at 1550 °C. The effects of Y doping concentration on phase composition, mechanical properties, thermal conductivity and high-temperature sintering behavior of Yb2SiO5 ceramics were investigated in detail. The results show that all the (Yb1-xYx)2SiO5 ceramic specimens are composed of single X2-Yb2SiO5 phase with relative high compactness. The introduction of Y gives rise to the reduction of the thermal conductivity of Yb2SiO5 and the value of cell parameters and volume of (Yb1-xYx)2SiO5 is proportional to the Y3+ doping concentration. Among the five (Yb1-xYx)2SiO5 ceramics, (Yb0.9Y0.1)2SiO5 possesses the lowest brittleness index and its average fracture toughness is 2.85 MPa m1/2, which is about 10 % higher than pure Yb2SiO5. In addition, (Yb0.9Y0.1)2SiO5 has good high temperature phase stability from room temperature to 1450 °C and the grain size of (Yb0.9Y0.1)2SiO5 is basically unchanged after sintering at 1400 °C for 100 h. We believe that (Yb0.9Y0.1)2SiO5 is one of the most promising candidate materials for environmental barrier coatings.

Multi-scale Modeling and Finite Element Analyses of Thermal Conductivity of 3D C/SiC Composites Fabricating by Flexible-Oriented Woven Process

Thermal conductivity is one of the most significant criterion of three-dimensional carbon fiber-reinforced SiC matrix composites (3D C/SiC). Represent volume element (RVE) models of microscale, void/matrix and mesoscale proposed in this work are used to simulate the thermal conductivity behaviors of the 3D C/SiC composites. An entirely new process is introduced to weave the preform with three-dimensional orthogonal architecture. The 3D steady-state analysis step is created for assessing the thermal conductivity behaviors of the composites by applying periodic temperature boundary conditions. Three RVE models of cuboid, hexagonal and fiber random distribution are respectively developed to comparatively study the influence of fiber package pattern on the thermal conductivities at the microscale. Besides, the effect of void morphology on the thermal conductivity of the matrix is analyzed by the void/matrix models. The prediction results at the mesoscale correspond closely to the experimental values. The effect of the porosities and fiber volume fractions on the thermal conductivities is also taken into consideration. The multi-scale models mentioned in this paper can be used to predict the thermal conductivity behaviors of other composites with complex structures.

Thermal comfort and mechanical analysis of vigorous diamond and diaper weaves; warp, weft and balanced float fabrics with equal thread densities

Diamond (pointed twill) and diaper (herringbone twill) woven assemblies are considered ideal for applications where thermal insulation, heat retention, wrinkle resistance, strength, softness, and breathability attributes are crucial. Limited research has been found on the optimization of thermal comfort and mechanical performance of warp face, weft face and balanced float diaper and diamond woven assemblies. In this work six different woven assemblies have been engineered using cotton (cellulosic yarn) on a dobby machine, having warp face (4/2) weft face (2/4) and balanced float (3/3) based diamond and diaper weave designs with equal number of thread densities. Thermal comfort (dry fluid transmission, thermal resistance, stiffness, and overall wet fluid management capability) and mechanical (tensile, puncture and tear strength) tests were performed for developed woven fabrics. The results of diamond warp face sample showed the highest dry fluid transmission and volume porosity. Diamond weft face specimens showed the highest thermal conductivity behavior and diaper weft face exhibited the highest overall wet fluid management capability behavior. Stiffness was the highest in diamond balanced float. Diamond warp faced fabric showed the highest tearing durability and diaper weft face showed the highest tensile resilience in mechanical performance attributes.

Experimental investigation on strengthening of Zea mays root fibres for biodegradable composite materials using potassium permanganate treatment

Humans are the only species who generate waste materials that cannot be broken down by natural processes. The ideal solution to this waste problem would be to employ only compostable materials. Biodegradable materials play a key role in creating a safer and greener world. Biodegradability is the gift that keeps on giving, in the sense of creating an Earth worth living. The future is thus best served by green energy, sustainability, and renewable resources. To realize such goals, waste should be considered as a valuable resource. In this context, Zea mays (Zm) root fibres, which are normally considered as agricultural waste, can be used as reinforcing substances in polymer matrices to produce structural composite materials. Before being used in composites, such fibres must be analysed for their physical properties. Chemical treatments can be employed to improve the structural quality of fibres, and the changes due to such modification can be analysed. Therefore, the current work examines the effect of permanganate treatment on the surface properties of Zm fibres. The raw and potassium permanganate-treated samples were assayed for various properties. Physical analysis of the fibre samples yielded details concerning the physical aspects of the fibres. The thermal conductivity and moisture absorption behaviour of the samples were analysed. Chemical analysis was employed to characterize the composition of both treated and untreated samples. p-XRD was employed to examine the crystalline nature of the Zm fibres. Numerous functional groups present in each sample were analysed by FTIR. Thermogravimetric analysis was used to determine the thermal stability of Zm fibres. Elemental analysis (CHNS and EDS) was used to determine the elemental concentrations of both raw and treated samples. The surface alterations of Zm fibres brought on by treatment were described using SEM analysis. The characteristics of Zm roots and the changes in quality due to treatment were reviewed, and there were noticeable effects due to the treatment. Both samples would have applications in various fields, and each could be used as a potential reinforcing material in the production of efficient bio-composites.

Effects of Hydroxyethyl Cellulose Protection on Sizes and Thermal Conduction Behaviors of Boron Nitride Nanosheets Exfoliated from Ball-Milling and Homogenization

Effects of Hydroxyethyl Cellulose Protection on Sizes and Thermal Conduction Behaviors of Boron Nitride Nanosheets Exfoliated from Ball-Milling and Homogenization

Two-phase Hybrid Thermal Interface Alkali-treated E-Glass Fiber/MWCNT/Graphene/Copper Oxide Nanocomposites for Electronic Gadgets.

Two-phase hybrid mode thermal interface materials were created and characterized for mechanical properties, thermal conductivity, and wear behaviour. Therefore, the ultimate goal of this current research was to use alkali-treated glass fibre and other allotropes to produce high-performance two-phase thermal interface materials. Three different polymer composites were prepared to contain 20 vol.% alkalies [NaOH] treated e-glass fibre [E] and epoxy as a matrix with varying proportions of multi-walled carbon nanotube [MWCNT], graphene [G], copper oxide [C]. The one-phase material contained epoxy+20%e-glass+1%MWCNT [EMGC1], the two-phase hybrid composite contained epoxy+20%e-glass+1%MWCNT+1%graphene+1%CuO [EMGC2], and two-phase material contained epoxy+20%e-glass+1%graphene+1%CuO [EMGC3]. Vacuum bagging method was used for fabricating the composites. The higher thermal conductivity observed was 0.3466 W/mK for EMGC2, the alkali-treated glass fibre/hybrid mode nanofillers epoxy matrix composite was mechanically tougher than the other two composites [EMGC1 & EMGC3]. Scanning electron microscopy analysis revealed the fine filler dispersion and homogenous interaction with the glass fibre/epoxy resin composite of the upper and lower zone, which also revealed the defective zone, fibre elongation, fibre/filler breakages, and filler leached surfaces. Finally, it was concluded that the hybrid mode two-phased structure EMGC2 epoxy matrix composite replicated the maximum thermal conductivity, mechanical properties, and wear properties of the other two specimens.

Structural optimization for the thermal conductivity and thermal cycling behavior in thermal barrier coatings and analysis of thermomechanical properties by computational investigation

The microstructure affects the service life and performance in thermal barrier coatings (TBCs). A series of yttria-stabilized zirconia (YSZ) coatings with embedded micro-agglomerated particles (EMAP) are prepared using plasma co-spraying technology. The thermal conductivity and thermal cycling behavior between EMAP coatings with various transfer speeds and traditional YSZ coating are explored. Experimental and finite element simulations are conducted to explore the effect of pore structure characteristics on the thermomechanical properties of coatings. Results show that the thermal conductivity of EMAP coatings is lower than that of traditional YSZ coating, with EMAP coating deposited at 200 mm/s transfer speed having the lowest thermal conductivity. The thermal cycling life of EMAP coatings at transfer speeds of 600 mm/s and 800 mm/s is improved by 20.00 % and 58.33 % compared to traditional YSZ coating. This paper suggests the mechanism of excellent thermal insulation and service life of porous coatings.

Mechanical, wear, thermal conductivity and hydrophobicity behavior of Kevlar fiber-epoxy structural composites reinforced with onion peel carbon quantum dot and commercial carbon nanotubes: a comparative study

Mechanical, wear, thermal conductivity and hydrophobicity behavior of Kevlar fiber-epoxy structural composites reinforced with onion peel carbon quantum dot and commercial carbon nanotubes: a comparative study

Temperature dependences of thermal conductivity of solid heterogeneous crystalline and amorphous materials: An empirical approach to the description in the high-temperature region

This paper presents a detailed analysis of the thermal conductivity behaviors exhibited by a diverse array of nanostructured materials, ranging from multilayer graphene nanocomposites to semiconductor-based nanostructures such as Bi0.5Sb1.5Te3 and In0.53Ga0.47As composites. The investigation extends to superlattices, nanowires, and hybrid nanostructures, encompassing materials like hexagonal boron nitride flakes, iron oxide nanoporous films, and organic-inorganic hybrid materials. The thermal conductivity of these materials is characterized by distinct trends, with some showcasing crystal-like behavior and others demonstrating glass-like characteristics. The analysis employs empirical expressions to discern the contributions of phonons and diffusons in crystal-like materials and incorporates Peierls contributions and Arrhenius-type terms for glass-like behavior. Noteworthy observations include deviations in fitting certain materials at lower temperatures and the identification of negative diffuson contributions in specific cases. These findings contribute to a nuanced understanding of thermal transport in nanostructured materials and have implications for applications in advanced thermal management systems and thermoelectric devices. The extracted parameters provide valuable insights for researchers exploring the thermal conductivity of diverse nanostructured materials.

A comparative study on the effects of multi-walled carbon nanotubes and graphene nanoplates incorporated for improved thermal conductivity and dielectric properties of polyvinyl chloride

In the present work, the improvement in the thermal conductivity and dielectric behavior in the frequency range of 0.025–5 MHz of polyvinyl chloride (PVC) films incorporated with graphene nanoplates (GNs) and multi-walled carbon nanotubes (CNTs) were investigated. The neat PVC and PVC composites consisting of different filler ratios of 0.25, 0.5, 0.75, and 1 wt% were synthesized using the casting technique. The increase in the concentration of GNs or CNTs up to 0.75 wt% enhanced the dielectric constant, ac conductivity, q-factor, F-factor, thermal conductivity, and total impedance of PVC composites. The values of the investigated parameters are slightly higher for PVC-CNTs composites compared to PVC-GNs composites. A further increase in concentration to 1 wt% reduces these parameters, but still more than PVC consisting of 0.5 wt% fillers. The mechanism of correlated barrier hopping (CBH) could be successfully used to describe the AC electrical conductivity of both PVC-GNs and PVC-CNTs composites thin films. Furthermore, the glass transition and decomposition temperatures were determined and found to be dependent on the filler ratio and type, and the thermal stability was increased after adding the GNs or CNTs nanofillers. These findings have drawn special attention to developing PVC composites that can be used in various industrial fields including flexible and wearable technologies, power devices, supercapacitors, electric vehicle battery systems, and aerospace components.

High entropy alloys (FeCoNi)0.75Cr0.25-xCux – thermal stability and physical properties

The paper reports on the phase stability of the (FeCoNi)0.75Cr0.25-xCux HEA system with equimolar ratio of Fe, Co and Ni by differential scanning calorimetry (DSC) and measurements of physicochemical properties: density, electrical resistivity, Seebeck coefficient, thermal conductivity, and magnetic behaviour in a broad temperature region as well as hardness and elastic modulus at room temperature as a function of the gradual substitution of chromium by copper in a series of (FeCoNi)0.75Cr0.25-xCux alloys with different mole fraction of Cu (x = 0, 0.05, 0.1, 0.15 and 0.2). DSC measurements showed that all alloys are thermally stable. Increasing content of Cu was found (i) to increase the formation of a fcc Cu-rich phase, (ii) to strengthen ferromagnetic interactions, resulting in rising ordered magnetic moments, as well as in growing ferromagnetic transition temperatures, and (iii) to distinctly change physical properties like electrical resistivity, thermal expansion, and mechanical properties. Experimental data regarding the phase stability are supported by CALPHAD calculations.

On the Influence of Humidity on a Thermal Conductivity Sensor for the Detection of Hydrogen.

Thermal conductivity sensors face an omnipresent cross-influence through varying humidity levels in real-life applications. We present the results of investigations on the influence of humidity on a hydrogen thermal conductivity sensor and approaches for predicting the behavior of thermal conductivity towards humidity. A literature search and comparison of different mixing equations for binary gas mixtures were carried out. The theoretical results were compared with experimental results from three different thermal conductivity sensors with mixtures of water vapor in nitrogen. The mixing equations show a large discrepancy between each other. Some of the models predict a continuously decreasing thermal conductivity and some predict an increasing thermal conductivity for increasing levels of humidity. Our measurements indicate an increase in thermal conductivity followed by a decrease after reaching a peak value. It is shown that the measured behavior is reproducible with different sensors. Depending on the sensor, this corresponds to an error up to 2 vol.% in the measured hydrogen value. The measured behavior is consistent with only one of the three models. Compared to this model, our own sensor shows a maximum deviation of 1.4%. Mixing equations for gas mixtures must be chosen carefully, taking into consideration whether mixing partners include polar or non-polar molecules. Some simplified mixing equations cannot be used to calculate the thermal conductivity of water vapor in air or nitrogen.

Magnetohydrodynamic influence on fractional nanofluid convection in infinite vertical porous media with constant heat flux

This study investigates the complex dynamics governing free convection flow in nanofluids under Magnetohydrodynamics (MHD) within a porous medium along an infinite vertical surface. We specifically focus on scenarios involving constant and uniform heat flux as well as heat sources. The governing equations, incorporating the Boussinesq approximation, continuity, and momentum equations, are formulated and solved using Caputo-Fabrizio derivatives and Laplace transforms. This comprehensive approach integrates the Boussinesq approximation and Caputo-Fabrizio fractional derivatives, while the use of Laplace transforms enables precise analytical solutions. Additionally, our investigation highlights the significant impact of nanometer-sized copper particles on fluid properties, transforming the behavior from Newtonian (water-like) to non-Newtonian. This transformation profoundly affects thermal conductivity and velocity behavior within the system. Overall, this research establishes a robust foundation for future studies and provides a framework for exploring non-Newtonian nanofluid systems in the context of MHD-driven free convection flow.