Increase In Thermal Conductivity Research Articles

Surface modification of spherical silica micro‐powder using silane coupling agents and their application in epoxy resin‐based composite materials

AbstractIn recent years, the packaging industry has utilized electronic packaging materials with epoxy resin (EP) and high‐performance fillers, exhibiting superior mechanical properties and thermal conductivity. Spherical silica micro‐powder (SSP) is a critical thermal conductive filler but faces challenges due to its inorganic nature. Surface modification is essential to improve SSP's compatibility and dispersion in organic matrices for effective use in EP‐based composites. In this paper, the effects of the following four modification methods on SSP/EP composites were studied: (1) the processes include co‐modification with dimethyldimethoxysilane (DMDMS) and trimethylethoxysilane (MTES), (2) modification with NaOH, (3) co‐modification with DMDMS and MTES in an alkaline environment after NaOH modification, and (4) co‐modification with methyltrimethoxysilane (MTMS) and propyltrimethoxysilane (PTMOS). Through comprehensive characterization and evaluation, it is evident that modification schemes 1, 3, and 4 significantly enhance SSP's hydrophobicity, dispersibility, and compatibility with EP. This led to the improvement of thermal conductivity and stability of the composite, and modification scheme 4 showed the highest enhancement, with a 42.6% increase in thermal conductivity. Moreover, the mechanical properties of modified composite materials, such as bending strength, impact resistance, and tensile strength, surpass those of unmodified SSP/EP composite materials. The study provides valuable insights for reducing manufacturing costs and enhancing productivity in the electronic packaging sector.

Development of test methods for fire-retardant coatings of steel engineering structures during operation

Introduction. Prediction of the durability of flame-retardant coatings of steel engineering structures and preservation of their performance during operation remain important research directions. There is a lack of normative documents in the field of fire protection, regulating the process of testing of flame-retardant coatings during operation, as well as determination of their durability (service life).Aim. To develop test methods for determining the resistance of flame-retardant coatings of steel engineering structures exposed to climatic factors, preservation of their fireproof and anti-corrosion properties during operation.Materials and methods. Test specimens included 600 x 600 x 5 mm plates made of 08kp and 08ps sheet steel according to State Standard 16523-97 and State Standard 9045-93 with a flame-retardant agent applied on the front side.Results. Methods for testing thin-layer intumescent and structural flame-retardant coatings during operation are proposed. The methodology of accelerated climatic testing of specimens coated with thin-layer intumescent flame-retardant coatings (flame-retardant paints) corresponds to State Standard 9.401-2018. These coatings are inherently high-solid paint materials. A new methodology, sequence, and modes of testing are developed for structural flame-retardant coatings. The subsequent assessment of fireproof properties of coatings and their preservation is carried out by the methods of fire protection efficiency according to State Standard R 53295-99 and the methods of thermal analysis. These methods imply comparison of the characteristics of the initial flame-retardant coating and those obtained after sample aging. The preservation of fireproof properties by thin-layer intumescent and structural coatings is additionally evaluated by the intumescence coefficient and the change in thermal conductivity, respectively.Conclusions. Test methods for flame-retardant coatings of steel engineering structures during operation are developed. Threshold levels of changes in their properties are established. After accelerated climatic tests, fire protection efficiency should not decrease by no more than 20 %. For structural fire protection, an increase in thermal conductivity by no more than 5 % is permitted. For thin-layer coatings, the arithmetic mean value of the intumescence coefficient should not decrease by no more than 30 % of the initial value.Implications. The developed methods were used in the preparation of a draft national standard of the Russian Federation “Steel engineering structures with fireproof coatings. Test methods for anticorrosion properties and resistance to climatic factors during operation” to ensure regulatory fire safety requirements for these structures.

Effect of AlN nanoparticle doping on thermophysical properties of nitrate via mechanical milling: Experimental studies and microscopic mechanisms

A compounding method based on ball milling was used to incorporate AlN into LiNO3 to effectively improve its thermal conductivity. The optimal doping ratio was determined to be 2 wt% with an increase in thermal conductivity of 112.09 % integrating the enthalpy decrease. From the perspective of molecular dynamics simulations, it is demonstrated that AlN achieves a better matching of vibrations with LiNO3 by changing its vibrational modes at the doping ratio of 2 wt% with the support of vibration density of states, overlapping energy and phonon participation ratio. When 2 wt% AlN was added, non-local vibrational modes of LiNO3 increased, which microscopically illustrated the intrinsic mechanism of 2 wt% as the optimal doping ratio. The radial distribution function was used to explain the microscopic mechanism behind the changes in the specific heat of LiNO3 concerning temperature. The reason why the enthalpy of LiNO3 would decrease after AlN added is that AlN can bind LiNO3 molecules on the surface, and LiNO3 is confined by stronger intermolecular forces, leading to a blockage of its phase change behavior. This study proposed a doping method that can uniformly disperse AlN and avoid crystallized water. It also provides a strategy for selecting the appropriate nanoaddictives for compositing in molten salts to enhance energy storage efficiency.

Thermal properties of a raw earth-flax fibers building material

The aim of this paper is to investigate the thermal behavior of composite building materials comprised of silt and flax fibers, considering various initial conditions. The experiments were conducted on flax fibers alone, examining factors such as moisture content variation, fibers arrangement, and density. Subsequently, the thermal properties of the earth-flax fiber composite were studied, taking into account the influence of water content and fibers mass content. The thermal properties of both flax fibers and raw earth-flax fibers composite specimens were determined using the experimental unsteady-state method. The results indicate that the thermal conductivity and heat capacity of flax fibers increase with density, temperature, and moisture content. Regardless of fibers density and arrangement of fibers, linear relationships have been established for both thermal conductivity and heat capacity as functions of temperature. Additionally, it was demonstrated that the heat capacity and the thermal conductivity increase with water content, regardless of the percentage of added fibers. Moreover, mixing randomly flax fibers with compacted raw earth material has improved the thermal properties of the composite. This improvement pertains to its insulating capacity, ability to store heat, and, subsequently, its contribution to the thermal comfort provided by such earth composite material when used as a building material.

Anomalous thermal conductivity in 2D silica nanocages of immobilizing noble gas atom

Noble gas atoms such as Kr and Xe are byproducts of nuclear fission in nuclear plants. How to trap and confine these volatile even radioactive gases is particularly challenging. Recent studies have shown that they can be trapped in nanocages of ultrathin silica. Here, we exhibit with self-consistent phonon theory and four-phonon (4ph) scattering where the adsorption of noble gases results in an anomalous increase in lattice thermal conductivity (κL), while the presence of Cu atoms doping leads to a reduction in κL. We trace this behavior in host–guest 2D silica to an interplay of tensile strain, rattling phonon modes, and redistribution of electrons. We also find that 4ph scatterings play indispensable roles in κL of 2D silica. Our work illustrates the microscopic heat transfer mechanism in 2D silica nanocages with the immobilization of noble gas atoms and inspires further exploring materials with the kagome and glasslike κL.

Influence of various surfactants on the stability and solidification characteristics of DI water-based CuO NFPCM for cool thermal energy storage system

The current study goals to investigate the stability and solidification characteristics of deionized water (DI water) based copper oxide (CuO) nanofluid phase change materials (NFPCMs) with a nucleating agent, different types of surfactants (SBDS, CTAB, and GA) and different weight concentration of surfactant for cool thermal energy storage systems (CTES). The stability of NFPCMs was assessed through average particle size distribution, zeta potential, and UV–vis absorbance. Among all NFPCMs, 0.1 wt% SDBS - CuO NFPCM showed prolonged stability with −42.7 mV and 212.6 nm of zeta potential and average particle size value. The heat transfer properties of NFPCMs were studied with differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA) and thermal conductivity measurements. The introduction of 0.05 wt% SDBS to NFPCM resulted in a notable 17.84 % and 7.64 % increase in thermal conductivity in solid and liquid states, with a slight decrease in latent heat by 5.2 % and 6.01 % during melting and crystallization as compared to DI water. The solidification experiments of NFPCMs were investigated in a spherical encapsulation at a surrounding bath temperature of −8 °C and − 10 °C. Comparing various surfactants in NFPCMs, the SDBS–CuO NFPCM was the most efficient in reducing the solidification time by 26.3 % and 28.4 % at −8 °C and − 10 °C respectively, compared to the nucleating agent PCM (NAPCM). Further, the different concentrations of SDBS in NFPCM demonstrated that 0.05 wt% SDBS–CuO NFPCM displayed the greatest reduction in solidification time, achieving 29.4 % and 27.7 % at −10 °C and − 8 °C, respectively, compared to the NAPCM.

Numerical investigation of effect of mechanical compression on the transport properties of fuel cell microporous layer using a pore-scale model

The microporous layer (MPL) plays an important role in water and thermal management of proton exchange membrane fuel cells (PEMFCs). An in-depth investigation of the mechanical compression effect on transport properties in the MPL can help optimize cell performance. In this work, the microstructure of the MPL is numerically reconstructed and the finite element method is applied to simulate mechanical behavior. Besides, the distribution of stress-strain, porosity, and pore size in the MPL under ten different levels of mechanical compression strains are studied. Lastly, the pore-scale model is employed to investigate the effective transport properties of the MPL as a function of compression strain. The analysis reveals that as the MPL strain increases from 0% to 40%, there is a 29% decrease in porosity, a 50% reduction in average pore diameter, a 60% decrease in effective gas diffusivity, a 100% increase in tortuosity, and an 80% increase in electrical and thermal conductivity. With the escalation of mechanical compression, both the magnitude and uniformity of stress-strain-displacement concurrently rise. Mechanical compression strains below 20% exhibit a lesser impact on transport properties. Beyond this threshold, exceeding the 20% compression strain point, mechanical stress assumes a critical role in influencing MPL transport properties.

Optimizing the performance of the thermal transistor based on negative differential thermal resistance

Thermal transistors have significant potential in thermal management due to their ability to precisely control the heat fluxes. However, the current design has a limited working temperature range and cannot meet the demand for heat control. In this work, we optimize the performance of a thermal transistor based on negative differential thermal resistance using a modified Lorentz gas model, focusing on the effects of gate control and thermal conductance. We find that the control of the gate has an asymmetrical property, and the sufficient control can expand the working region by more than 1.5 times. In addition, the switching and amplifying functions of the thermal transistor are inversely dependent on thermal conductance, and an increase in thermal conductance can lead to a 27 times amplification in heat flux. The synergistic regulation of the two factors results in the optimal performance of a 44% working region and a 33 times amplification in heat flux. These findings refresh the understanding of the performance limits of thermal transistors, promoting efficient thermal management and addressing heat dissipation issues.

Enhanced phonon transport in sI-type methane hydrate under uniaxial compression strain: Unveiling the opening of an advantageous channel

Unveiling the thermal transport mechanisms of natural gas hydrate under strain conditions is fundamental to the heat transfer of the hydrate reservoir during drilling and production. This work investigated the structural stability and phonon transport mechanisms of methane hydrate using equilibrium molecular dynamics simulations subjected to uniaxial compression strain. The results indicate that the stability of large cages within methane hydrates weakens under strain. However, the presence of methane molecules effectively stabilizes the cage structure, enabling it to remain intact even under significant deformation. Furthermore, the thermal conductivity of methane hydrate demonstrates non-linear behavior, characterized by an initial increase followed by a subsequent decrease with increasing uniaxial compression strain. Particularly, the thermal conductivity of methane hydrate attains a maximum value of 0.87±0.018 W⋅m−1⋅K−1 at a strain of -0.04. The results suggest that the elevated spectral energy density and the prolonged phonon lifetime contribute to the enhanced thermal conductivity of methane hydrate. Interestingly, it was observed that the overlapping of phonon vibration modes between water and methane molecules results in the suppression of the peaks and valleys when the strain reaches -0.04. This overlap eliminates the gap and opens up an advantageous channel for phonon transport, thereby enhancing the heat transport capability of methane hydrate. The opening of an advantageous channel for phonon transport results in an extended phonon lifetime and a subsequent increase in thermal conductivity. This study presents a novel perspective for comprehending the unusual thermal conductivity of methane hydrate under strain conditions.

An Experimental Study on the Effect of Nanofluids on the Thermal Conductivity and Rheological Properties of a Coolant for Liquids

Thermal conductivity and viscosity are important properties for nanofluids as they significantly affect the flow and heat transfer process. To date, the rheological properties of water-based nanofluids have been well studied, while the results are scarce for non-aqueous nanofluids. In this study, the thermal conductivity and rheological properties of two different kinds of oxide nanofluids (CuO and Al2O3) in a typical commercial data center focusing on liquid coolants were systematically investigated at different mass fractions and temperatures. The results showed that the addition of nanoparticles can significantly improve the heat conduction capacity of mineral oil coolants. There is an average increase in thermal conductivity of up to 20–25%. The shear rate–shear stress and shear rate–viscosity curves all showed that mineral oil coolant-based oxide nanofluids behaved as Newtonian fluids and that nanoparticles did not cause the increment in viscosity. The effect of temperature on rheological properties was also studied, and the result showed that high temperatures resulted in low viscosity and shear stress. Finally, the effect of particle type was investigated, and it was found that no matter what kind of nanoparticles were added, their effects on the rheological behaviors were the same.

Numerical study of the volume fraction and thermophysical properties of nanofluids in a porous medium

PurposeThe purpose of the paper is to conduct a numerical and experimental investigation into the properties of nanofluids containing spherical nanoparticles of random sizes flowing through a porous medium. The study aims to understand how the thermophysical properties of the nanofluid are affected by factors such as nanoparticle volume fraction, permeability of the porous medium, and pore size. The paper provides insights into the behavior of nanofluids in complex environments and explores the impact of varying conditions on key properties such as thermal conductivity, density, viscosity, and specific heat. Ultimately, the research contributes to the broader understanding of nanofluid dynamics and has potential implications for engineering and industrial applications in porous media.Design/methodology/approachThis paper investigates nanofluids with spherical nanoparticles in a porous medium, exploring thermal conductivity, density, specific heat, and dynamic viscosity. Studying three compositions, the analysis employs the classical Maxwell model and Koo and Kleinstreuer’s approach for thermal conductivity, considering particle shape and temperature effects. Density and specific heat are defined based on mass and volume ratios. Dynamic viscosity models, including Brinkman’s and Gherasim et al.'s, are discussed. Numerical simulations, implemented in Python using the Langevin model, yield results processed in Origin Pro. This research enhances understanding of nanofluid behavior, contributing valuable insights to porous media applications.FindingsThis study involves a numerical examination of nanofluid properties, featuring spherical nanoparticles of varying sizes suspended in a base fluid with known density, flowing through a porous medium. Experimental findings reveal a notable increase in thermal conductivity, density, and viscosity as the volume fraction of particles rises. Conversely, specific heat experiences a decrease with higher particle volume concentration.xD; xA; The influence of permeability and pore size on particle volume fraction variation is a key focus. Interestingly, while the permeability of the medium has a significant effect, it is observed that it increases with permeability. This underscores the role of the medium’s nature in altering the thermophysical properties of nanofluids.Originality/valueThis paper presents a novel numerical study on nanofluids with randomly sized spherical nanoparticles flowing in a porous medium. It explores the impact of porous medium properties on nanofluid thermophysical characteristics, emphasizing the significance of permeability and pore size. The inclusion of random nanoparticle sizes adds practical relevance. Contrasting trends are observed, where thermal conductivity, density, and viscosity increase with particle volume fraction, while specific heat decreases. These findings offer valuable insights for engineering applications, providing a deeper understanding of nanofluid behavior in porous environments and guiding the design of efficient systems in various industrial contexts.

Thermal Conductivity of a Fluid-Filled Nanoporous Material: Underlying Molecular Mechanisms and the Rattle Effect.

Nanoporous materials are central to the energy and environmental crisis, with key applications in adsorption, separation, and catalysis. While confinement and surface effects on fluids severely confined in their porosity are well documented, the thermal behavior of nanoporous solids subjected to fluid adsorption remains puzzling in many aspects. With striking phenomena such as the so-called rattle effect, through which fluid/solid collisions decrease the overall thermal conductivity, the solid thermal conductivity and, more generally, heat transfer and dispersion in these complex systems challenge classical approaches (e.g., mixing rules including effective medium approaches fail to capture such effects as shown here). In particular, a robust molecular framework to describe the crossover between the decrease in thermal conductivity through the rattle effect in very narrow pores and the increase in thermal conductivity when replacing vacuum with a fluid phase in larger pores is still missing. Here, using a prototypical model of fluid-filled nanoporous materials (a Lennard-Jones phase confined in an all-silica zeolite), we perform a molecular simulation study to shed light on the parameters that govern the rattle effect in nanoporous solids. First, by varying the fluid/fluid, fluid/solid, and solid/solid interaction strengths as well as the fluid number density and mass density, we unravel the ingredients that lead to the essential coupling between fluid adsorption and phonon transport. Second, despite this complex interplay, inspired by pioneering molecular approaches on the rattle effect, we show that all data obey a simple statistical physics model that relies on the change in the speed of sound due to the fluid adsorbed density and the decrease in phonon lifetime due to scattering by fluid molecules. This framework, which provides a simple formalism to rationalize the thermal behavior of this class of solid/fluid composites, points to a decrease in thermal conductivity upon fluid confinement (up to 30% in some cases). Such an effect paves the way for the design of novel applications involving fluids in interaction with nanoporous materials.

Effect of seawater aging on mechanical, buckling, structural, and thermal properties of nano Al2O3 and TiO2‐doped glass‐epoxy nanocomposites

AbstractEnsuring the stability of composite structures in the marine environment is crucial. The harsh and corrosive nature of marine conditions presents unique challenges, making maintenance a top priority. In this study, the impact of seawater aging on the mechanical, buckling, structural, and thermal properties of glass fiber‐reinforced polymer nanocomposites was investigated. Composites were produced using the VARTM method with 2% nano Al2O3 and 2% nano TiO2. Aging was conducted in a seawater environment at room temperature for 120, 240, and 360 days. Mechanical properties, including tensile, compressive, flexural, impact, and buckling tests, were performed, and water absorption was determined. Structural analysis was carried out using SEM images. The experimental results indicated that the presence of nanoparticles minimized the effect of seawater. TiO2 preserved tensile strength by 10.33%, impact energy by 6.8%, and critical buckling load by 3.06% compared to the pure composite. Al2O3 reduced water absorption to 0.594% and preserved tensile strength by 6.67%, impact energy by 4.02%, and critical buckling load by 2%. Thermal test revealed an increase in thermal conductivity with aging, with the TiO2‐doped composite exhibiting the smallest increase (14.66%). The significance of the obtained results was confirmed through ANOVA analysis.Highlights Glass fiber‐reinforced nanocomposite was produced with nano Al2O3 and TiO2. The effect of seawater aging was investigated. It showed that TiO2 nanoparticles are a good candidate against seawater aging. The experimental results showed statistical significance.

Experimental investigation of conductive heat transfer and fire protection in a polymer-based plate heat exchanger

Polymer-based heat exchangers offer several attractive features for thermal management applications such as low-cost, lightweight, antifouling, and anti-corrosion characteristics. However, their thermal performance is compromised primarily by the low thermal conductivity and high-flammability. This work consists of developing new polymer-based plate heat exchangers, which are made from epoxy resin reinforced by banana fibres and manufactured using the vacuum bag resin transfer moulding technique. The aim of this research is to improve both the heat transfer efficiency and thermal protection. The proposed approach involves incorporating silicon carbide powder as charge into samples to increase their thermal conductivity, and applying an intumescent fire-retardant coating to improve their capacity to withstand heat and flames. To determine the efficacy of this approach, a cone calorimetry test was performed to examine the thermal distribution within the plate heat exchanger samples and to assess fire reaction parameters during a fire scenario. The results revealed a notable increase in thermal conductivity, due to the addition of silicon carbide powder. Furthermore, the intumescent fire-retardant coating substantially improved the samples’ thermal resistance. This result has been verified by thermogravimetric analysis conducted during this work. These findings suggest that using banana fibres-reinforced epoxy resin, combined with silicon carbide powder and intumescent fire-retardant coating, has the potential to enhance the overall thermal performances of plate heat exchangers. The addition of silicon carbide powder increases the thermal conductivity by 36%. This demonstrates the feasibility of utilizing sustainable and biodegradable materials to manufacture heat exchangers that are more efficient and eco-friendly.

Investigating arc and molten metal transport phenomena in gas metal arc welding with Ar–CO2 gas mixtures using a numerical method

This paper presents a numerical investigation of the transient transport phenomena of the arc and molten metal during gas metal arc welding (GMAW) using shielding gas mixtures ranging from 100% Ar + 0% CO2 to 80% Ar + 20% CO2. The thermophysical parameters of the Ar–CO2 mixtures, considering the presence of metal vapor, were calculated as a function for a temperature range of 1000–30 000 K. The influence of metal vapor content and CO2 proportion on the thermophysical properties of the mixed gas was discussed in detail. As the CO2 content increased from 0 to 20%, the shape of the arc changed from a bell to a cone due to the increase in mass density, specific heat, and thermal conductivity. The maximum arc temperature and velocity decreased with increasing CO2 content, resulting in larger droplets and a lower droplet transfer frequency. Although the change in electrical conductivity did not affect the arc shape, it did influence the arc temperature by altering the distribution of current density. Experiments of droplet transfer and arc behavior were carried out, and the results showed that the simulated droplet size, transfer frequency, and arc temperature distribution agreed well with the experimental values. These findings could serve as a theoretical tool for better understanding the underlying physical mechanisms of the GMAW process using different shielding gases, ultimately aiming to achieve high weld quality.

Core-shell PCM encapsulation model for thermoregulation of asphalt pavements

The implementation of cooler pavements plays an important role in alleviating the urban heat island (UHI) effect and extending the lifespan of pavements. One potential approach to develop cool pavements involves the incorporation of phase change materials (PCMs). In this study, a numerical investigation is conducted to evaluate the effectiveness of incorporating core–shell encapsulated PCMs within asphalt pavements. To facilitate this analysis, an enthalpy-porosity-based heat transfer model is developed, and its accuracy is validated through experimental data obtained in-house. For this study, commercially available PCMs, namely Organic Mixture 35 (OM 35) and Organic Mixture 42 (OM 42), encapsulated within hollow steel balls are used. The outcomes of the investigation reveal that the inclusion of core–shell encapsulated PCMs is a viable method for reducing the temperature of asphalt pavements. Further, it is found that as the thermal conductivity of asphalt pavements increases from 1.21 to 2.41 W/mK, there is corresponding proportional increase in the temperature reduction achieved by integrating the PCMs with the pavements. The proportional temperature reduction with increase in thermal conductivity of asphalt pavements are found to be 3.55 °C using OM 35 and 3.37 °C using OM 42 respectively. It is worth noting that while the thermal characteristics of the steel balls exhibit a limited influence on temperature reduction, their physical attributes should be given careful consideration during the design phase of asphalt pavements.

Effect of Morphological Characteristics of Aggregates on Thermal Properties of Molten Salt Nanofluids

Molten salt-based nanofluid is a thermal storage and heat transfer medium for concentrated solar thermal power plants formed by adding nanoparticles to molten salt, which can enhance the thermal performance of molten salt. However, the nanoparticles tend to aggregate in nanofluids, causing changes in thermal properties. In this work, molecular dynamics simulations were used to study the effect of morphological characteristics of aggregates on the thermal conductivity and specific heat capacity of molten salt-based nanofluids. The results show that the aggregated nanoparticles cause a greater increase in thermal conductivity and specific heat capacity than dispersed nanoparticles. Additionally, the increase in fractal dimension leads to thermal conductivity reduction, while there is no clear correlation between the fractal dimension and specific heat capacity. New insights into the thermal properties of aggregated nanofluids are provided by analyzing the contribution of material components, heat flux fluctuation modes, and energy compositions. It is found that the thermal conductivity of aggregated nanofluids is mainly dominated by the base liquid and collision term. However, the specific heat is not related to the variation in the contribution of different energy compositions. Moreover, compared to the dispersed nanofluid, the increased specific heat capacity of aggregated nanofluids is attributed to the thicker semi-solid layer. This study provides guidance for the design and control of the thermal properties of molten salt-based nanofluids.

Thermal performance enhancement of lauric acid using nanomaterials as composite phase change material.

In the present work, lauric acid was taken as a phase change material (PCM), and different nanoparticles (NPs) such as SiO2, TiO2, CuO, and ZnO were taken as the supporting materials. CuO NPs were prepared through the co-precipitation technique; SiO2, TiO2, and ZnO NPs were synthesized via the sol-gel technique. These NPs with different weight fractions were dispersed into molten lauric acid, individually. The variations in thermal properties (phase change temperature and latent heat for solid and liquid) of the prepared composite PCMs due to the dispersion of NPs were observed by DSC analyses. An increase in thermal conductivity of the composite PCMs was observed with the increasing weight fraction of NPs. In order to ascertain the long-term utility, a thermal reliability test was conducted on the composite PCMs with repeated heating and cooling cycles. Also, the specific heats of the pure PCM and the composite PCMs were determined as a function of temperature. Further, the experimental investigation was performed on the pure PCM and the prepared composite PCMs to assess their phase change behavior, and the test results clearly proved that the time required for the complete melting and freezing process of the composite PCMs was less when compared to pure PCM. By considering the above facts, the newly prepared composite PCMs can be recommended as a potential candidate for low-temperature solar heating applications.

Preparation, Microstructure and Thermal Properties of Aligned Mesophase Pitch-Based Carbon Fiber Interface Materials by an Electrostatic Flocking Method.

The mesophase pitch-based carbon fiber interface material (TIM) with a vertical array was prepared by using mesophase pitch-based short-cut fibers (MPCFs) and 3016 epoxy resin as raw materials and carbon nanotubes (CNTs) as additives through electrostatic flocking and resin pouring molding process. The microstructure and thermal properties of the interface were analyzed by using a scanning electron microscope (SEM), laser thermal conductivity and thermal infrared imaging methods. The results indicate that the plate spacing and fusing voltage have a significant impact on the orientation of the arrays formed by mesophase pitch-based carbon fibers. While the orientation of the carbon fiber array has a minimal impact on the shore hardness of TIM, it does have a direct influence on its thermal conductivity. At a flocking voltage of 20 kV and plate spacing of 12 cm, the interface material exhibited an optimal thermal conductivity of 24.47 W/(m·K), shore hardness of 42 A and carbon fiber filling rate of 6.30 wt%. By incorporating 2% carbon nanotubes (CNTs) into the epoxy matrix, the interface material achieves a thermal conductivity of 28.97 W/(m·K) at a flocking voltage of 30 kV and plate spacing of 10 cm. This represents a 52.1% increase in thermal conductivity compared to the material without TIM. The material achieves temperature uniformity within 10 s at the same heat source temperatures, which indicates a good application prospect in IC packaging and electronic heat dissipation.

Dimensionless Analysis of the Spatial–Temporal Coupling Characteristics of the Surrounding Rock Temperature Field in High Geothermal Roadway Realized by Gauss–Newton Iteration Method

Understanding the time–space coupling characteristics of the surrounding rock temperature field in high geothermal roadways is essential for controlling heat damage in mines. However, current research primarily focuses on individually analyzing the temperature changes in the surrounding rock of roadways, either over time or space. Therefore, the Gauss–Newton iteration method is employed to model the coupling relationship between temperature, time, and space. The results demonstrate that the dual coupling function describing the temperature field of the surrounding rock in both time and space provides a more comprehensive characterization of the temperature variations. Over time, as ventilation duration increases, the fitting degree of the characteristic curve steadily rises, and the characteristic curve descends overall. In the spatial dimension, the fitting degree of the characteristic curve gradually decreases with the rise of the dimensionless radius, and the characteristic curve ascends overall. Additionally, as thermal conductivity increases, the fitting degree of the characteristic curve steadily rises.