Improvement In Thermal Conductivity Research Articles

Recycling and reuse of waste banded iron formation as fine aggregate in the production of lightweight foamed concrete: Fresh-state, mechanical, thermal, microstructure and durability properties assessment

This study investigates the possibility of using BIFs as sustainable fine aggregates to produce lightweight foam concrete (LWFC) by replacing sand with 5, 10, 15, 20, and 25 % banded iron formations (BIFs). The fresh concrete properties, such as slump flow, density, and setting time, as well as its mechanical properties, including compressive strength, splitting strength, and flexural strength, were investigated. The thermal conductivity, specific heat, porosity, gas permeability, pore distribution, and sorptivity were measured to determine durability and thermal performance. Microstructural analysis of the mixes was performed using SEM, energy-dispersive X-ray spectroscopy (EDX), and mapping. The results recommended a 10 % replacement ratio to achieve an increased compressive strength ratio of 55.88 % compared to the control mix at 7 days (d). The strength at later ages increased compared to that of the control mix by 33.9 %, 30 %, 42.48 %, and 42.4 % at 14, 28, 56, and 180 d, respectively. In addition, the flexure increased by 42.7 % at 7 d, 49.6 % at 14 d, and 45.6 % at 28 d compared to the control mix. In addition, the UPV also increased gradually from 2757 to 3699 km/s with increase in BIFs content. Furthermore, the porosity decreased at 7 d, 14 d, 28 d, and 90 d. Moreover, chloride penetration decreased by 2.5 %, where an improvement in thermal conductivity was achieved with BIFs to 0.342 W/mK compared to that of the control mix. In addition, a reduction in the specific heat of the material from 1042 J/kg K to 1007 J/kg K was observed. SEM showed a better arrangement of pores when BIFs were utilized compared with that of control mix without BIFs. In conclusion, the incorporation of waste BIFs as fine aggregates in lightweight foam concrete demonstrates a promising potential for enhancing the mechanical and thermal properties of construction materials, paving the way for durable building materials in the construction industry.

Synthesis of Spherical Hexagonal Boron Nitride via Precursor Morphology Control

The growing demand for high‐performance semiconductors, driven by the advancement of emerging industries such as artificial intelligence (AI), necessitates the development of novel materials for thermal management. In this respect, hexagonal boron nitride (h‐BN) has emerged as a promising candidate due to its unique properties. However, challenges arise from its two‐dimensional layered structure, resulting in thermal transfer anisotropy and poor fluidity when mixed with polymers for thermal management. To address these challenges, researchers have attempted to fabricate h‐BN into spherical shapes. In this study, a two‐step synthesis method of spherical h‐BN (s‐BN) particles via control of the precursor morphology and a subsequent thermal reaction is proposed. Therefore, as‐fabricated s‐BN exhibits solid spherical shapes with a uniform size distribution, with a median particle size of 0.955 μm. These s‐BN particles, when integrated into epoxy resin, disperse homogeneously, forming efficient heat transfer networks that achieve a 138% improvement in thermal conductivity compared to h‐BN particles with similar diameters, even at lower viscosities. This can overcome the limitations found in the conventional particle shapes while preserving the advantages of h‐BN. Furthermore, it is anticipated that the s‐BN will be applied in thermal management systems, thereby accelerating advancements in electronic technology.

High operational functionality nanofluids from choline chloride, ethylene glycol, and multi-walled carbon nanotubes – Economical substitutes for ionanofluids

Deep eutectic solvents (DESs) are an emerging class of green, easy-to-synthesize, and inexpensive solvents with designable properties widely used in nanotechnology applications. The optimization of such working fluids for energy transfer purposes requires the simultaneous maximization of their thermal/electrical conductivities and thermal/shelf-life stabilities, as well as minimization of their viscosity and overall material/maintenance costs. In this work, there is provided a comprehensive analysis of physicochemical properties, including, first-ever measurements of electrical conductivity and refractive index, of new highly-concentrated DES-based nanofluids composed of choline chloride/ethylene glycol (ChCl/EG) with molar ratios of 1:15, 1:5, 1:3, and 0.25–1 wt% of originally 860-µm-long multi-walled carbon nanotubes (MWCNTs), cut upon sonication to 14.0–16.9 µm. The study deepens the understanding of the mechanisms occurring at the molecular level during heat and electricity transfer in DES-based nanofluids and provides new empirical transport-property correlations. The analyzed nanodispersions are highly viscous (150–840 mPa·s at 25 °C, 9.3 s–‍1) non-Newtonian fluids (flow behavior index 0.49 ≤ m ≤ 0.66), though their viscosity can be notably reduced by elevated temperature and shear rate (28.3–120 mPa·s at 40 °C, 186 s−1). Importantly, DES-based nanofluids exhibit significant improvement in thermal conductivity (λ = 0.307 W·m−1·K−1), AC electrical conductivity (σ = 42.6 mS·cm−1), and decomposition temperature (T50%=255 °C) for ChCl/EG 1:3 + 1 wt% MWCNTs at 25 °C, thus, they can potentially become an interesting alternative to ionanofluids with up to 83 times lower raw material costs and at least 30-month shelf-life stability.

Enhancing Radiator Cooling with CuO Nanofluid Microchannels

The study explores in employing copper oxide (CuO) nanofluid as a cooling medium in the vehicle radiators. To simulate the heat transfer process, the microchannel is constructed using elec-tron discharge machining (EDM) and a computational fluid dynamics (CFD) modeling is em-ployed. UV-visible spectroscopy, scanning electron microscopy (SEM), and dynamic light scat-tering (DLS) are used to characterize the CuO nanofluid. CuO nanofluid surpasses water in the heat transfer capabilities, with a 40% improvement in thermal conductivity. The average size of CuO nanoparticles was determined via DLS to be 485.1 nm. The heat transfer coefficient of CuO nanofluid is 5366 W/m2K, which is 116% larger than that of water. The increased heat transfer capabilities of CuO nanofluid microchannel flow indicate to its potential as a viable replacement for conventional radiators in the automotive applications. Lower engine tempera-tures, increased fuel efficiency, and longer engine lifespan may result from improved cooling performance. Due of the small size of microchannels, more efficient and space-saving radiators for automobiles are conceivable. More research is needed to improve the microchannel design as well as to realize the practical benefits of CuO nanofluids in car cooling systems.

Constructing phonon transport bridges via low-temperature sintering in Diamond@Ag/EP composite to achieve efficient 3D networks structure

The rapid advancement of integrated circuits and electronic devices presents challenges to traditional epoxy molding compound (EMC), necessitating the demand for highly thermally conductive yet electrically insulating composites to address the “hotspot issues” in high-power chips. Here, a low-temperature sintering technology based on metal–organic decomposition is developed to fabricate a three-dimensional interconnected networks structure composite (3D-Diamond@Ag/EP). The in-situ decomposition of the silver amine complex on the surface of the Diamond@Ag hybrid filler forms nano-silver bridges, which facilitate the successful construction of the three-dimensional networks structure. When the Ag reaches 4.0 vol%, the thermal conductivity of the composite (reaches 6.42 W/m·K) breaks out of the low numerical blockade of the epoxy resin (0.18 W/m·K), while maintaining excellent insulation performance. It is noteworthy that the great improvement of thermal conductivity is achieved by the synergistic effect of sufficient thermal pathways and minimizing interfacial thermal resistance along these paths. Moreover, this work obtained composite exhibits other excellent thermal characteristics. It provided a practical route to produce high thermal conductivity polymer-based composites with electrical insulation for heat management in modern electronic devices.

Achieving Long‐Range Arbitrary Uniform Alignment of Nanostructures in Magnetic Fields

AbstractFor magnetic field orientation of nonstructures to become a viable method to create high performance multifunctional nanocomposites, it is of paramount importance to develop a method that is easy to implement and that can induce long‐range uniform nanostructural alignment. To overcome this challenge, inspired by low field nuclear magnetic resonance (NMR) technology, a highly uniform, high field strength, and compact magnetic‐field nanostructure orientation methodology is presented for polymeric nanocomposites using a Halbach array, for the first time. Potential new advances are showcased for applications of graphene polymer composites by considering their electro‐thermal and antibacterial properties in highly oriented orthogonal morphologies. The high level of anisotropy induced in the graphene nanocomposites studied stands out through: 1) up to four decades higher electrical conductivities recorded in comparison to their randomly oriented counterparts, at concentrations where the latter show minimal improvements compared to the unfilled polymer; 2) over 1200% improvement in thermal conductivity, 3) antibacterial surfaces at field benchmark levels with lower filler content and with the added versatility of arbitrary orientation of the nanofillers. Overall, the new method and variations thereof can open up new horizons for tailoring nanostructure and performance for virtually all major nanocomposite applications based on graphene and other types of fillers.

Preparation and Evaluation of Epoxy Based Material for High Performance Electronic Packaging through the Surface Modification of Fillers

The continuous integration and refinement of electronic equipment results in the more stringent requirements for epoxy resin (EP) based materials, such as excellent heat dissipation and low coefficient of thermal expansion (CTE). In order to improve the dispersion of silica powder (SP) in EP and thus expand the application of EP in the field of electronic packaging, our research described in this paper adopted the KH-550 coupling agent to modify the surface of SP (m-SP). The effects of KH-550 coupling agent on the characteristics of the composites were investigated in terms of thermal, rheological, electrical insulation and mechanical properties. The results showed that when the content of KH-550 was 2 wt% of the fillers, the best modification effect was achieved, and the surface properties of the fillers were changed accordingly. In particular, the materials filled with m-SP exhibited lower viscosity end, better mechanical and electrical insulation properties. It was also found that the adding of the KH-550 had different effects on the thermal degradation, dynamic thermo-mechanical properties and the thermal deformation behavior of the materials. According to our study, the thermal conductivity and the CTE of m-SP/EP filled with 70 wt% of modified fillers were 0.787 W/m.K and 28.3 ppm/°C respectively, corresponding to a significant thermal conductivity improvement and low CTE.

Green synthesis, characterization and thermophysical properties of diverse molar Ag decorated GO hybrid nanofluids

The present work critically analyses the thermal characteristics of diverse molar (0.03, 0.06, and 0.09 M) Ag decorated GO hybrid nanofluids at constant 0.05 wt.%. The study broadly encompassed the synthesis, characterization, stability, thermophysical properties, reactivity, and contact angle measurements on copper substrates using varied molar Ag-GO hybrid nanofluids. The thermal impact of these hybrid nanofluids was evaluated across a temperature range of 293–333 K, encompassing thermal conductivity, specific heat, viscosity, surface tension, and density. The results illustrate that increasing the molarity of Ag over GO significantly influenced the thermal properties of the hybrid nanofluids. Notably, the most substantial improvements in thermal conductivity are observed at 333 K, reaching 30.12, 22.63, and 17.13% for 0.09, 0.06, and 0.03 M Ag-GO, respectively, compared to the base fluid. Furthermore, central composite design approach (CCD) was employed to establish correlations between the experimental and predicted thermal conductivity enhancement ratio (K-ratio) results. In conclusion, these studies underscore a promising insight that the optimizing of Ag molarity in GO hybrid nanofluids holds substantial potential for enhancing heat transfer performance across diverse heat transfer applications.

Effect of surface modification on the thermophysical properties of ethylene glycol dispersed with Al2O3 nanoparticles for solar thermal applications

This study focuses on investigating the effects of surface modification on the stability and thermal conductivity of ethylene glycol dispersed with aluminium oxide (Al2O3) nanoparticles. Aluminium oxide (Al2O3) nanoparticles were dispersed in ethylene glycol after surface modification with the surfactant Cetrimonium bromide (CTAB) at concentrations of 1, 0.5, 0.25 and 0.125 mass percent. The thermal conductivity and dynamic viscosity at various concentrations were evaluated in the temperature range from 20°C to 170°C, in contrast to prior studies in which the properties were determined in the range from 20°C to 60°C. The stability of the suspension dispersed with CTAB proved to be excellent, and the nanofluids remained stable for one month due to its excellent electrostatic interaction with the surface of Al2O3 nanoparticles. The addition of Al2O3 nanoparticles to ethylene glycol led to a significant improvement in thermal conductivity, which is between 15% and 25%. The influence of the surfactant is clear from the results, and it shows that CTAB is the most suitable surfactant for metal oxide nanoparticles. The experimental data are compared with the data available in the literature in the temperature range from 30°C to 60°C and are found to be in good agreement.

Study of thermally conductive polyurethane/boron nitride composite fibers: Fabrication, characterization, properties and textile applications

AbstractPolyurethane resin (PU) and boron nitride (BN) are used to develop a series of boron nitride/polyurethane (BN/PU) composite fibers by a wet‐spinning method. The thermal conductivity of the composite fibers was improved by blending modified thermally conductive particles with polymer. The improvement of thermal conductivity depends largely on the interfacial effect between them. The results show that PU composite fabric filled with BN functionalized with polyethylenimine and glutaraldehyde (GPBN/PUF) has a high thermal conductivity, revealing an increase of 226% compared to the PU fabric. The GPBN/PUF fabric can reduce the simulated skin temperature by 2.3°C compared with conventional cotton fabric. Additionally, the as‐prepared GPBN/PUF fabric possesses good mechanical stability and washability. This work provides a strategy for developing flexible heat‐conducting fabric.Highlights The stability of the PEI coating formed on the BN surface was significantly improved by GA cross‐linking. The composite fiber fabric has improved thermal conductivity and good mechanical properties. The composite fiber fabric can dissipate heat quickly in practical applications.

Ternary particle composite synergistically enhances the fluidity and dielectric properties of filled thermal conductive epoxy resin

Abstract Particle-packed epoxy materials are widely used to improve the thermal conductivity of insulation materials. However, the addition of fillers increases the viscosity of the composite which reduces its operability, and is not conducive to the packaging of power electronic equipment such as electric transformers and reactors. Multi-scale particle compounding is one of the effective methods to enhance the co-processing performance of materials by reducing the friction between particles and epoxy matrix while forming an effective thermal conductivity network. Three types of spherical alumina sized around 4 μm, 38 μm, and 125 μm were used as fillers to study the fluidity, thermal conductivity, and dielectric properties of single-filled and ternary compounds. The results showed that the ternary particle composite reduced the viscosity of the precursor by up to 68.8%, achieving a synergistic improvement in operability, thermal conductivity, and electrical performance.

Additive manufacturing of functional corundum-mullite refractory with acid-corrosion resistance and heat insulating by direct ink writing

The low thermal conductivity and high chemical stability of corundum-mullite refractories have garnered attention for high-temperature insulation and acid-corrosion-resistant applications. A 3D extrusion-based method (direct ink writing) utilizing clay-alumina-silica fume foaming inks was employed to create corundum-mullite refractories with controllable structures (non-porous surface, porous interior). The rheology and printing ability of the inks were modified by adjusting the additives (dispersant and foaming agent) content. Printing parameters, specifically pressure and nozzle moving speed, were adjusted to enhance the precision of the printed construction. The impact of extrusion pressure in the ink on the surface structure of printed products was also investigated. The properties of the corundum-mullite refractory were evaluated by heating it from 1200 °C to 1500 °C, resulting in improvements in acid corrosion rate (from 1.9 % to 14.7 %), thermal conductivity (from 0.35 to 1.65 W/m·K), and compressive strength (from 20.1 to 45.5 MPa), respectively. The Ashby-Glicksman model (closed pore) was employed to forecast the thermal conductivity of the porous refractory with complex pore structures, proving to be a beneficial choice. After acid corrosion for 12 h, there were minimal microcracks and pores on the surface of the refractory prepared at 1500 °C, and the acid corrosion rates were less than 3.4 %. This study illustrates the effectiveness of optimizing printing parameters to adjust pore structure and enhance refractory properties.

A novel approach for thermal conductivity improvement of metal oxide nanofluids

A novel approach for thermal conductivity improvement of metal oxide nanofluids

The preparation and selection process for a new form stable phase change material (FSPCM) intended for use as thermal storage in applications at intermediate temperatures

There is a greater focus on solar energy since the food processing business requires a lot of thermal energy to remove moisture from agricultural products. This study thoroughly explains how to choose Phase Change Materials (PCMs) within a specific temperature range. The best PCM is selected from the Multiple Criteria Decision Making (MCDM) procedures based on a few characteristics. Based on the results of the MCDM method, the eutectic of paraffin and palmitic acid is chosen. PCM is bound, and FSPCM is formed using clay. The method of preparation of Clay-based FSPCM is described in detail. The amount of clay materials and different clay percentage combinations are chosen from the leakage experiment. Kaolin has the least amount of leakage out of all the clay materials tested. Kaolin-based FSPCM Exhibits improvement in thermal conductivity compared to Pure PCM.

Sintering and toughening of self-reinforced AlN with integrated AlN whiskers via spark plasma sintering

Aluminum nitride (AlN), prized for its high thermal conductivity and electronic insulating properties, finds widespread use in electronic applications, particularly as a substrate material. However, its relatively low fracture toughness limits its application. In this study, to enhance both the thermal and mechanical properties of AlN ceramics, we thoroughly investigate the microstructure, thermal, and mechanical properties of self-reinforced AlN ceramics fabricated by spark plasma sintering, with self-reinforcement achieved through the integration of AlN whiskers within the AlN matrix. Unlike previous studies utilizing conventional pressureless sintering with limited sintering conditions, this work employs spark plasma sintering with a wide range of temperatures (1600–1900°C) and holding times (10–30 min), providing a comprehensive understanding of the sintering behavior. Microstructural features, observed through optical and scanning electron microscopy, reveal distinct toughening mechanisms via crack deflection and branching, with a maximum 20% enhancement. The self-reinforced AlN ceramics exhibit remarkable improvements in thermal conductivity, reaching up to 150Wm−1K−1, surpassing reported values for spark plasma-sintered AlN ceramics. Adding AlN whiskers enhances the thermal and mechanical properties of AlN simultaneously, particularly at 1800°C for 10 min with controlled grain size and nicely integrated AlN whiskers. This work not only contributes valuable insights into the complex relationship between processing parameters, microstructure, and resulting thermal and mechanical properties but also highlights the enhanced thermal and mechanical properties of self-reinforced AlN ceramics.

Novel Approach to Augment Thermal Conductivity of Dihybrid Nanofluids

In this experimental study, the copper oxide (CuO) nano–particle (NP) was mixed with a water/ethylene glycol hybrid base fluid to form a hybrid nano–fluid (HNF). Further, this HNF was mixed with a MgO nano–particle and also separately with a TiO2 nano–particle to form two different dihybrid nano–fluids (DHNFs). For the preparation of nano–fluids, two-step procedure was used. In all three cases, the volume fraction of the NP was 0.25, 0.5, 0.75, 1.0, and 1.25%. The thermal conductivity (TC) of HNF was measured with KD2 pro and compared with the DHNFs' at temperatures 26, 28, 30, and 32°C. It was inferred that the CuO/TiO2 nano–particle addition in the water/ethylene glycol hybrid base fluid resulted in an average of 0.8% rise in thermal conductivity at chosen temperatures and volume fraction. Also, the agglomeration due to the presence of CuO/MgO was a critical issue at higher volume fractions such as 0.75, 1, and 1.25%. The MgO nano–particle addition in the CuO nano–particle also resulted in a 0.6% increase in thermal conductivity at 0.25 and 0.5% volume fraction. The result was that in the CuO/MgO - water-ethylene glycol nano–fluid combination the TC was enhanced by 29.57% compared with CuO/water/ethylene glycol at a volume fraction increase of 0.5%. Also, it was noted that the nano–particles volume fraction has little effect on thermal conductivity improvement at higher proportion.

Preparation and thermal performance study of a novel hydrated salt composite PCM for space heating

In order to effectively address the mismatch between thermal energy supply and demand in buildings, latent heat storage (LHS) based on phase change material (PCM) stands out as a key technology. While hydrated salt has emerged as a promising PCM, it encounters common issues such as substantial supercooling, phase separation, and low thermal conductivity, hindering its development. To mitigate these limitations, this study focused on modifying Ba(OH)2·8H2O by incorporating various nucleating agents and thickening agents to reduce supercooling, enhancing the composite PCM's thermal properties by introducing expanded graphite (EG) to elevate thermal conductivity. Subsequently, the thermal stability of the PCM was evaluated through accelerated thermal cycling tests, encompassing the assessment of critical thermal parameters, including supercooling degree, enthalpy, and thermal conductivity of the composite PCM. Experimental findings unveiled the effectiveness of incorporating 2 wt% BaCl2·2H2O and 1 wt% CMC to Ba(OH)2·8H2O, effectively diminishing the supercooling degree from 14 °C to 1.42 °C. Further integration of 3.5 wt% EG led to a substantial decrease in the supercooling degree to 0.24 °C. Simultaneously, the addition of EG resulted in an improvement in thermal conductivity, elevating it from 0.62 W/(m·K) to 1.03 W/(m·K), while the enthalpy decreased from 283.68 J/g to 252.81 J/g. Notably, the composite PCM exhibited notable thermal reliability with a latent heat drop of 15.9 % following 1000 accelerated cycles of testing. Moreover, the composite PCM demonstrated superior thermal storage density, measuring at 2.36 times that of traditional paraffin wax, yet with a thermal storage cost merely a quarter of paraffin wax, rendering it more favorable for extensive deployment in building energy systems.

Enhancing high-speed CNC milling performance of Ti6Al4V alloy through the application of ZnO-Ag hybrid nanofluids

Abstract This research investigates the performance of high-speed CNC milling operations on Ti6Al4V alloy by employing a novel ZnO-Ag hybrid nanofluid. The study involves the preparation and characterization of nanofluids with varying concentrations of nanoparticles, focusing on thermal conductivity and stability. The machining experiments encompass four critical input parameters: Minimum Quantity Lubrication (MQL) flow rate, cutting speed, nanofluid concentration, and feed rate. Performance evaluation is based on average surface roughness (Ra) and cutting temperature. Key findings include a remarkable 21.05% improvement in thermal conductivity for the ZnO-Ag-based sunflower oil at 0.2% volume concentration compared to 0.05% concentration. The prepared nanofluids exhibit good stability. Moreover, cutting speed and MQL flow rate emerge as significant contributors to Ra, accounting for 35.62% and 34.82%, respectively. Interestingly, MQL flow rate is identified as the most influential factor, surpassing even cutting speed. SEM images for tool wear reveals that the ZnO-Ag based sunflower oil reduced tool wear significantly. In conclusion, the proposed ZnO-Ag-based sunflower oil at 0.2% concentration emerges as the good option for sustainable high-speed machining of Ti6Al4V alloy, showcasing

Techniques for Enhancing Thermal Conductivity and Heat Transfer in Phase Change Materials in Hybrid Phase Change Material–Water Storage Tanks

In recent years, extensive research has been dedicated to enhancing energy efficiency and promoting environmental sustainability in heating and cooling systems. Among the promising solutions, phase change materials (PCM) technology stands out as a key area of exploration. This study focuses on improving the thermal performance of PCM–water hybrid tanks by investigating methods to enhance thermal conductivity and heat transfer. Through experimental testing using techniques such as copper matrices, steel twisted matrices, and copper spirals, this study demonstrates significant improvements in thermal conductivity, particularly with the use of copper matrices. The integration of a copper matrix placed in the PCM reservoir increased the heat transfer coefficient and thermal conductivity of the PCM, and thus, the total phase transformation time for solidification was reduced by 79.19% and for melting by 54.7%. Our experimental results demonstrate that the integration of a copper matrix can increase latent heat transfer from 55,677.6 J up to 125,274.6 J, marking a 125% enhancement over the experiment with pure PCM. Additionally, comparisons of the energy storage potentials for different PCMs underscore the benefits of integrating PCMs into hybrid storage tanks. These findings highlight the immense potential of PCM technology to increase energy storage efficiency in heating and cooling applications.

Temperature dependency of electric field treatment for improvement of effective thermal conductivity of functional carbon/silicone rubber composite sheets

Temperature dependency of electric field treatment for improvement of effective thermal conductivity of functional carbon/silicone rubber composite sheets