Thermal Conductivity Enhancement Research Articles

Phase change-related thermal property characterization and enhancement in carbon-based organic phase change composites

By utilizing the significant amount of energy absorbed and released during their phase transitions, phase change materials (PCMs) can capture and store thermal energy to fill gaps between supply and demand. Due to their many favorable properties, organic PCMs have gained attention in a wide range of applications. Nevertheless, their inherent low thermal conductivity has limited the direct use of organic PCMs in thermal energy storage (TES). Extensive research has been conducted on enhancing organic PCM thermal conductivity by incorporating high thermal conductivity materials. Owing to their high thermal conductivity and low density, carbon-based materials have been extensively used for thermal conductivity enhancement in phase change composites (PCCs). Carbon-based organic PCCs, which incorporate highly thermally conductive carbon allotropes and their direct chemical derivatives with organic PCMs, are a group of diverse PCCs with highly promising potential for TES applications. Adequate latent heat and shape stability performances are crucial to the success of the applicational performances of these PCCs. Much empirical research has pushed efforts to enhance these phase change properties, yet a logical understanding of these enhancement efforts based on the thermodynamics and intermolecular interactions of carbon-based organic PCCs has been elusive. In particular, the effect of characterization methods on the evaluation of phase change properties has been largely understudied. This review strives to provide novel physical and chemical insights into latent heat and shape stabilization evaluation processes and enhancement efforts in carbon-based organic PCCs through a detailed review and analysis of recent literature. The review provides an unprecedented comprehension of newly developed PCCs that challenge the traditional understanding that the latent heat of PCCs cannot exceed that of its base PCM. Efforts on phase change property enhancement driven by these new insights have the potential for carbon-based organic PCCs to succeed in a variety of TES applications, including solar-thermal harvesting, thermal management of batteries and electronics, thermoregulating textiles, and infrared stealth and infrared responsive materials.

Significantly Enhanced Thermal Conductivity of hBN/PTFE Composites: A Comprehensive Study of Filler Size and Dispersion.

High-temperature polymers are attractive for applications in extreme temperatures, where they maintain their mechanical flexibility and electrical insulating properties. However, their heat dissipation capability is limited due to their intrinsically low thermal conductivities. Hexagonal boron nitride (hBN) is a chemically inert, thermally stable, and electrically insulative compound with a high thermal conductivity, making it an ideal candidate as a filler within a high-temperature polymer matrix to increase the thermal conductivity. This study evaluates the effect of filler size and dispersion on thermal conductivity by producing homogeneous composite samples using a combination of solvent mixing and resonant acoustic mixing (RAM). We carefully characterized our samples, including the spread of the size distribution, and observed that the smaller sized hBN centered around 5 μm was able to integrate more seamlessly into the polytetrafluoroethylene (PTFE) matrix with particle size in the 15 μm range and hence outperformed 30 μm, in contrast to the conventional wisdom, which asserts that larger fillers universally perform better than smaller ones. Our thermal conductivity of hBN/PTFE composites at 30 wt % is 2× higher than the literature values. Notably, we reached the record-high value of 3.5 W/m K at 40 wt % with an onset of percolation at 20 wt %, attributed to optimized hBN dispersion that facilitates the formation of thermal percolation. Our findings provide general guidelines to enhance the thermal conductivity of polymer composites for thermal management, ranging from power transmission to microelectronics cooling.

Exploring the Thermal Potential of Shape Stabilized Graphene Nano Platelets Enhanced Phase Change Material for Thermal Energy Storage

Low thermal conductivity and liquid phase leakage impede the widespread adoption of phase change materials (PCMs). To enhance PCM performance and practical viability, addressing these limitations is crucial. Current study addresses low thermal conductivity and leakage issues. Enhanced thermal conductivity in PCMs is achieved by adding graphene nanoplatelets (GnPs), while expanded graphite (EG) acts as a leak‐proof barrier. The composite PCM (ss‐NePCM) composite is developed by ultra‐sonication followed by vacuum impregnation process. The samples underwent comprehensive analysis: thermal conductivity (TEMPOs), chemical composition (FTIR), photo‐transmittance (UV–Vis), and thermal stability (TGA). The results show that the composite with 0.6 wt% GnP (NePCM3) has the highest thermal conductivity enhancement of ≈112% while adding 15 wt% EG (ss‐NePCM3) diminishes leakage problem. According to the optical performance assessment, the composite exhibits a notable increase in absorbance of 116% higher than that of the base PCM. However, due to the introduction of additives, the differential scanning calorimeter (DSC) detected a minor variation from 154 to 144.76 J g−1 in the latent heat. Furthermore, the composite demonstrates chemical stability and thermal reliability following 250 heating and cooling cycles. The ss‐NePCM holds promise for thermal systems, where leakage could jeopardize system integrity.

Research on NaCl-KCl High-Temperature Thermal Storage Composite Phase Change Material Based on Modified Blast Furnace Slag

The high-temperature composite phase change materials (HCPCMs) were prepared from solid waste blast furnace slag (BFS) and NaCl-KCl binary eutectic salt to achieve efficient and cost-effective utilization. To ensure good chemical compatibility with chlorine salt, modifier fly ash (FA) was incorporated and subjected to high-temperature treatment for the processing of industrial solid waste BFS, which possesses a complex chemical composition. The HCPCMs were synthesized through a three-step process involving static melting, solid waste modification, and mixing–cold pressing–sintering. Then, the influence of the modification method and the amount of SiC thermal conductivity reinforced material on chemical compatibility and thermodynamic performance was explored. The results demonstrate that the predominant phase of the modified solid waste is Ca2Al2SiO7, which exhibits excellent chemical compatibility with chlorine salt. HCPCMs containing less than 50 wt.% chloride content exhibit good morphological stability without any cracks, with a melting temperature of 661.76 °C and an enthalpy value of 108.73 J/g. Even after undergoing 60 thermal cycles, they maintain good chemical compatibility, with leakage rates for melting and solidification enthalpies being only 6.3% and 0.23%, respectively. The equilibrium was achieved when 40 wt.% of chloride salt was encapsulated upon the addition of 10% of SiC, and the incorporation of SiC resulted in an enhancement of thermal conductivity for HCPCMs to 2.959 W/(m·K) at room temperature and 2.400 W/(m·K) at 200 °C, with an average increase of about 2 times. The cost of the prepared HCPCMs experienced a significant reduction of 81.3%, demonstrating favorable economic performance and promising prospects for application. The research findings presented in this article can offer significant insights into the efficient utilization of solid waste.

Influence on solar PV performance integrated with heat sinks and nano-enhanced phase change material

The inevitable advancement of solar photovoltaic (PV) system performance highly relies on temperature control, which enhances electrical efficiency. The objective of this study is to enhance electrical efficiency by incorporating phase change material of HS36 (PCM) and nano enhanced PCM (NePM). The thermal properties of PCM were improved by adding graphene flakes (GF) into PCM to enhance the thermal transfer rate between the PV panel and PCM. The phase change properties and thermal conductivity of PCM with different concentrations of GF were assessed. The results indicated that the 0.9 wt.% NePCM exhibited the highest thermal conductivity enhancement of 47% in solid states and a significant reduction in latent heat by 9.4% during freezing compared to pure PCM. The effect of cooling on PV performance was studied using a reference panel, integrated with a heat sink containing PCM (PV/PCM) and NePCM (PV/NePCM). Outdoor experiments were conducted using a 10 W panel, and the results for the use of PCM showed a reduction in temperature and an improvement in efficiency. The findings revealed that attaching a heat sink and integrating the PV panel with pure PCM and NePCM reduced the temperature by 8.65°C and 10.04°C, respectively, and improved efficiency by 11.65% and 12.15%, respectively. It can be concluded that the proposed thermal management method for PV systems offers a viable solution for increasing daily average electrical generation with maximum efficiency.

Expanded Graphite (EG) Stabilization of Stearic and Palmitic Acid Mixture for Thermal Management of Photovoltaic Cells

In this work, passive cooling systems for the revamping of existent silicon photovoltaic (PV) cells were developed and analysed in order to mitigate the efficiency loss caused by temperature rise in the hot season. For this purpose, expanded graphite (EG) was used to stabilize a phase change material (PCM) with a melting temperature close to 53 °C in order to realize thermal management systems (TMSs) able to store heat at constant temperature during melting and releasing it in crystallization. In particular, stearic and palmitic acid mixture (PA-SA) was shape-stabilized in EG at different concentrations (10, 12 and 14 part per hundred ratio) under vacuum into a rotary evaporation apparatus followed by cold compaction; PA-SA leakage was reduced due to its intercalation between the graphite lamellae, and the thermal conductivity necessary to maximize the heat transfer to a bulk TMS was improved via powder cold compaction, which minimizes voids and creates preferential thermal conductive patterns. The composite materials, stable till 150 °C, were tested by differential scanning calorimetry (DSC) at 1 °C/min to precisely determine the phase transition temperatures and the enthalpic content, which was only slightly reduced from 196 J/g of the neat PCM to 169 J/g due to the very low EG fraction necessary for the stabilization. Despite only the 14:100 EG-to-PA-SA ratio, the system’s thermal conductivity was enhanced 40 times with respect to the neat PCM (from 0.2 to 8.3 W/(m K), value never reached in works present in the literature), with a good convergence of the values evaluated through hot disk tests and laser flash analysis (LFA), finding correlation with both graphitic content and density. In order to completely avoid leaking with the consequent dispersion of PCM in the environment during the final application, all the samples were encapsulated in a PE-made film. The mechanical properties were evaluated with compression tests at 30 °C and 80 °C simulating a possible compressive stress deriving from the contact needed to maintain the TMS position on the rear of the PV cells. Finally, the material response was simulated by imposing thermal cycles into a climatic chamber and reproducing the three hottest and coldest days of summer 2022 of two Italian locations, Verona (Veneto, 45° N, 11° E) and Gela (Sicily, 37° N, 14° E), thus highlighting the thermal management effects with delays in temperature increase and daily peak temperature smoothing. The role of EG is strategic for the processing and the properties of the resulting composites in order to realize a proper compromise between the melting enthalpy of PCM and the thermal conductivity enhancement given by EG.

Performance enhancement of porous clay cooler for BIPV applications using hollowed clay structures and metallic extended fins as evaporation and thermal conductivity enhancers

This paper investigates the employing of a passive evaporative cooling approach to mitigate the temperature rise of PV panels within building-integrated photovoltaic (BIPV) systems. The investigation explores enhancing the heat transfer capabilities of composite clay layers by incorporating thermal conductive materials such as iron-oxide and zinc-oxide. This enhancement aimed to improve the overall thermal properties of the composite clay structures, thereby boosting heat transfer rates. Additionally, two distinct designs were evaluated as well: one integrating hollowed clay layer and the other featuring a clay layer with extended fins to enhance both heat and mass transfer rates within the evaporative porous clay structure. A series of experiments conducted under real conditions using prototyped building rooms to simulate real BIPV systems to assess the cooling performance of the presented scenarios. The results revealed that the hollowed clay layer achieved the most substantial decrease in PV panel temperature, with a reduction of 16.5 % compared to the findings with a solid clay layer. In contrast, the composite Iron-oxide/clay layer demonstrated the smallest decrease in PV temperature at 11 %. Moreover, utilizing the hollowed clay structure led to a 6.3 % increase in average PV output power, as well as around 4.5 % enhancement in average photovoltaic’s efficiency compared to the outcomes observed with the solid clay layer. Moreover, incorporating the hollowed clay layer resulted in the most significant decrease in the building's annual load, achieving a reduction of 79.6 %. This signifies approximately a 2 % higher enhancement in cooling capabilities compared to utilizing solid clay layer. Further, the cost of electricity production decreased by 7.7 % (from 0.104 $/kWh to 0.096 $/kWh) following the incorporation of the hollowed clay layer, while the payback time was reduced by roughly 0.8 years compared to utilizing the solid clay layer and by 1.7 years in comparison to the non-cooled BIPV system.

Theoretical study of the effect of ionization effect on the thermal conductivity of stannous oxide

Effectively modulating the thermal conductivity of materials is critical for meeting the various requirements of thermal-management devices. In this work, the influence of ionization on the phonon-transport properties of stannous oxide (SnO) was systematically investigated using first-principles calculations combined with the Boltzmann transport equation. The results show that ionization has a positive effect on the thermal conductivity of SnO, and this phenomenon can be further enhanced with increased ionization magnitude. Specifically, it was found that the thermal conductivities of SnO along the x (y) and z directions could be increased by 35%/200% and 65%/300% after the removal of four and eight electrons, respectively, from neutral SnO. The phonon mode information implies that the enhancement of thermal conductivity mainly originates from the suppression of anharmonicity in the ionized SnO. This behavior was further demonstrated by analyzing the root mean square displacement and potential-well structure. More in-depth examination suggested that the enhancement of the thermal conductivity of SnO does not originate from the ionization itself, but from the internal strain in the lattice caused by the ionization. The findings presented in this work elucidate how ionization can impact thermal conductivity, providing theoretical guidance for modulating thermal conductivity at the electron level.

Development and preparation of novel nano-enhanced organic eutectic phase change materials for low-temperature solar thermal applications

ABSTRACT Thermally reliable and stable eco-friendly Phase change materials are of significant aid in thermal energy storage technology, leading to improved energy utilization and reliability of the system. This study develops two novel organic eutectic PCM of Lauric acid – Margaric acid (LM) and Myristic acid – Margaric acid (MM), which are chemically stable and thermally compatible for latent heat energy storage. LM eutectic mixture had a melting temperature of 52.66°C with a latent heat of 163.68 J/g, and MM eutectic mixture had its melting temperature at 44.79°C and a latent heat of 197.31 J/g. The phase change temperatures were favorable for low temperature solar thermal applications with good latent heat capacity. The thermal characteristics of these eutectic mixtures are further enhanced with the dispersion of highly conductive Multi walled carbon nanotubes (MWCNT) at three different mass fractions (.5%, 1% and 1.5% by weight). Nano enhancement could achieve exceptional thermal conductivity enhancement in MM eutectic mixture by 110.6% and 83.73% in LM eutectic mixture. Thermogravimetric analysis and Fourier-transform infrared spectroscopy analysis ensured the thermal and chemical stability of the eutectic mixtures. The optical absorption characteristics were extensively enhanced with nano particle addition, which is highly preferable in solar thermal applications.

Laser flash technique as an efficacious assessment approach for thermal conductivity of tungsten disulphide nanofluids

Two-dimensional tungsten disulphide (WS2) dispersed oil-based nanofluids are prepared by a two-step process and their stability and thermal properties are assessed. UV–visible spectrophotometry reveals marginal loss in relative absorbance over 15 days ensuring dispersion stability of the nano-additives. Thermal diffusivity of nanofluids is measured using the laser flash analyzer while specific heat capacity is studied by differential scanning calorimetry. The thermal diffusivity coupled with the specific heat capacity of the nanofluids provides an estimate of the thermal conductivity of the prepared nanofluids. Specific heat of the nanofluids is observed to increase with temperature and reduce with an increase in the concentration of the nano-additives. A statistical model is developed to predict the influence of density and temperature on the specific heat of the nanofluids. Higher thermal conductivity in comparison to the base fluid is observed which further enhances with an increment in concentration of the nano-additive. The parameters such as concentration of dispersoid and temperature reveal the effect on the thermal conductivity at elevated temperatures. Enhancement in thermal conductivity is observed between 3–12 % which is validated with an analytical model for thermal conductivity of composite nanofluids.

Eutectic phase change composites with MXene nanoparticles for enhanced photothermal absorption and conversion capacity

Phase change composite materials with uniform nanomaterial dispersion are potential solutions for improving thermophysical properties and enhancing latent heat capacity applicable in thermal management. In this study, various transitional carbide-based MXene samples were synthesised via acid etching to augment the heat transfer capacity and efficiency of the solar thermal energy storage (TES). These samples were then uniformly dispersed in a eutectic mixture (1:1) of paraffin wax (PW) and polyethylene glycol (PEG-6000), resulting in the formation of a MePCM composite. The controllable porous structure and hydrogen interactions with the external layer of MXene and long-chain PCM benefitted in the well impregnation of PCM and compatibility impregnated into the composite. An exceptionally higher mass fraction of 1 wt % Ti3C2Tx MXene-based phase change composite unveiled a higher phase change enthalpy of 138.66 J/g in the melting phase and 139.54 J/g in the solidification phase with 89.82 % energy storage efficiency. In contrast to pure eutectic PCM (0.2593 W/mK), the thermal conductivity of MePCM composite is relatively higher and provides a thermal conductivity of 0.9209 W/mK for Ti3C2Tx MXene-based composite. The enhancement of thermal conductivity is ascribed to the increased heat conduction pathway facilitated by the MXene arrangement. The utilisation of spatially constrained eutectic phase change material (PCM) assembly resulted in the development of MePCM, which exhibited enhanced thermal conductivity, chemical and physical stability, and thermal consistency across 500 melting-solidification cycles. Benefitting from the thermal conduction path, the MePCM exhibits an excellent photothermal conversion efficiency of 98.53 %. The thermal responsive tests of Ti3C2Tx and V2CTx MXene composite samples provide better thermal response than eutectic PCM without thermal reduction. With a higher thermal storage capacity and higher heat transfer property, thermally reliable MePCM composites exhibited tremendous potential for photothermal applications.

Enhancing thermal conductivity of sinterized bronze (Cu89/Sn11) by 3D printing and thermal post-treatment: Energy efficiency and environmental sustainability

Enhancing the thermal conductivity of bronze is essential to enhance the efficiency of heat transfer and reduce energy consumption in systems such as heating, cooling, and heat exchangers systems. This study investigates the feasibility of producing sinterized bronze (Cu89/Sn11) using low-cost 3D printing Fused Deposition Modeling (FDM) technology and thermal post-treatment processes. The intention is to identify optimal printing parameters and sintering temperatures to maximize thermal conductivity, while focusing on minimizing energy consumption, raw material usage, and environmental impact. The thermal conductivity of twenty-seven samples was evaluated according to the ASTM E1530:2019 standard. A statistical analysis revealed significant effects of nozzle diameter and flow rate on thermal conductivity and density. The optimal results were obtained with a sintering temperature of 845 °C, a 1.0 mm nozzle diameter, and a 110 % flow rate. These conditions yield the highest thermal conductivity (87.61 W/m·K) and density (7.52 g/cm3). The lowest values were observed at a sintering temperature of 865 °C, a 0.6 mm nozzle diameter, and a 100 % flow rate. A Life Cycle Assessment (LCA) using the ReCiPe Endpoint (E) methodology was employed to compare the environmental impact of the resulting thermal conductivities. The results suggest that sintered bronze produced by FDM and thermal post-treatment provide superior performance and a smaller environmental impact than conventional methods. This study underscores the potential for more efficient and sustainable manufacturing practices in the production of sintered bronze.

Synthesis of novel Stachytarpheta jamaicensis flower liked hexagonal boron nitride nanoribbons (SJF-BNNBs) to efficiently improve the thermal/mechanical/electrical properties of flexible polyimide films

Heat dissipation has become a bottleneck restricting large-scale integration and flexible electronic technologies. This study reports a novel fabrication strategy to prepare flexible stachytarpheta jamaicensis flower-like hexagonal boron nitride nanoribbons (SJF-BNNBs) and their composite films with polyimide (PI). The effect of synthesis conditions on the morphology of SJF-BNNBs was investigated, and the growth mechanism was proposed. The in-plane and through plane thermal conductivities of the 4 wt% SJF-BNNBs/PI composite film reach 5.98 W m−1 K−1 and 0.79 W m−1 K−1, which are 3047 % and 316 % higher than those of the pure PI film, respectively. The in-plane and through plane thermal conduction enhancement efficiencies reach 761.8 % and 78.9 %, respectively. The tensile strength of the composite film is 61.7 % higher than that of pure PI, and maintains excellent electrical insulating and thermal stability properties. Infrared imaging tests verified the excellent heat dissipation performance of the composite film as a thermal interface material and a flexible copper clad laminate substrate, where the operating temperature of device could be reduced by 17.3 °C. To the best of our knowledge, SJF-BNNBs outperform the most efficient thermally conductive electrically insulating filler and are to break the overcome of polymer composites in heat dissipation applications.

Construction of three-dimensional network using boron nitride microspheres and the thermal conductivity/stability of epoxy resin composites

Efficient heat dissipation has become the focus of electronic packaging materials, constructing three-dimensional thermally conductive filler networks to prepare composites can realize efficient heat transfer. However, there are few studies comparing the effects of different ways of constructing three-dimensional networks on the thermal conductivity enhancement of polymers. In this study, BNMS self-assembled from BNNSs was used as a thermally conductive filler, and the three-dimensional skeleton was constructed by both the powder mixing pressing method and the ice template method, and scanned to analyze the morphological and structural characteristics. At the same time, the epoxy composites were prepared, and the advantages and disadvantages of the thermal conductivity of the composites prepared in different ways were analyzed by combining the SEM structures. In the powder mixing pressing method, the in-plane and through-plane thermal conductivity of the epoxy composites with the BNMS additive amount of 53.92 wt% reached 10.961 W·m−1·K−1 and 9.955 W·m−1·K−1, respectively, which was increased by 58 and 52 times. The thermal stability has been improved significantly that the T60 was in creased by 60.89°C compared to pure epoxy. Using the ice template method with 7.67 wt% of BNMS addition, the through-plane thermal conductivity of the epoxy composites reaches 0.977 W·m−1·K−1, which is an improvement of 428.1 % compared with pure EP. In addition, both composites maintain low dielectric constants and dielectric losses. It is instructive for the preparation method of subsequent construction of three-dimensional thermally conductive filler networks.

Enhancement of thermal conductivity in PDMS/CFP composites using a dredging-plugging thermal network

In the preparation of thermally conductive polymer composites (TCPC), it is necessary to incorporate a filler network in the polymer matrix. Further enhancement of the thermal conductivity (TC) of TCPCs is challenging due to the exceptional heat absorption of the polymer matrix, which results in heat flow losses in the network. To address this issue, a novel procedure, termed thermal network dredging-plugging, has been proposed. In this study, polydimethylsiloxane (PDMS) composites with a carbon fiber powder (CFP) network and a CFP/glass ball (GB) network enhanced by dredging-plugging were prepared by a coating method. The TC of the PDMS/CFP system increased with an increase in CFP loading from 0 to 12 wt% and a decrease in sample thickness from 0.4 to 0.2 mm. At a 12 wt% CFP loading, the PDMS/CFP composites exhibited a maximum TC of 4.687 W/(mK). With the addition of GBs ranging from 0 to 2 wt%, the dredging-plugging CFP/GB network increased the maximum TC by a factor of 1.26 relative to the dredged CFP network. In conjunction with the thermal resistance method, a mathematical model that considers both the plugging and dilution effects of GBs was constructed. The calculated TCs were validated by using the prepared PDMS/CFP/GB composites, with average absolute relative errors ranging from 0.5 % to 4.19 %. In addition to TC enhancement, the mechanical properties and thermal management of the PDMS composites were evaluated.

Covalent vs. Non covalent chemical modification of multiwalled carbon nanotubes based-nanofluids: Stability and thermal conductivity steadiness over temperature

Thermal conductivity enhancement coupled to nanoparticle dispersion stability over time are the two main conflicting requirements to overcome to develop carbon nanomaterial-based nanofluids. Both covalent and non-covalent approaches, having their own advantages and disadvantages, are commonly used for carbon nanotube based nanofluids development. However, they are rarely compared regarding their impact on stability and thermal conductivity performances for the same kind of nanofluid. In this work, multiwalled carbon nanotubes have been chemically modified by both covalent and non-covalent functionalization. For the covalent functionalization, a simple oxidation method is applied. It consists of refluxing the powdered MWCNTs in H2SO4/HNO3 at 5 M concentration. For the non-covalent approach, both an anionic (sodium dodecyl sulfate) and a non-ionic (Pluronic P123, comprising poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) in an alternating linear fashion, PEO-PPO-PEO) surfactants were employed at a concentration of 1 wt%. Nanofluids were prepared with multiwalled carbon nanotubes at a fixed concentration of 0.2 wt% for both chemical modification approaches. The oxidation reaction occurs without significant structure damaging as shown by transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. UV–visible spectrophotometry analysis shows a remarkable stability with temperature in the 293.15–303.15 K range over one-week and for a longer period of 49 days for all the three types of nanofluids. Their thermal conductivity has been investigated in the same temperature range. For all the three nanofluid series prepared with a fixed concentration of carbon nanomaterials, a thermal conductivity enhancement compared to that of the base fluid has been observed. The thermal conductivity evolution with temperature is different for each type of nanofluid. The covalently oxidized multiwalled carbon nanotube based nanofluids showed the better thermal conductivity enhancement steadiness (around 7 %) with temperature. The discussion on the surfactant-based nanofluid behavior proposes the possible involved mechanisms as temperature increases for each surfactant.

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.

A novel candidate shape-stabilized phase change material for building energy conservation based on lauric acid/roasted iron tailings-expanded graphite

This study presents the fabrication of a novel shape-stabilized phase change material (SSPCM) characterized by high thermal capacity and heat transfer efficiency. The material was composed of lauric acid (LA) embedded in roasted iron tailings (RIT) and expanded graphite (EG), utilizing a straightforward, low-cost, and direct impregnation method. The as-prepared LA/RIT-EG SSPCM underwent a comprehensive analysis of leakage tests, surface morphology, chemical compatibility, phase change properties, thermal stability, and reliability. Furthermore, the heat transfer efficiency and thermal conductivity were measured through cooling tests and a laser thermal conductivity analyzer, respectively. The LA/RIT-EG formulation demonstrated an ability to absorb 61.57 wt% LA without leakage, maintaining excellent form-stability with a mass fraction proportion of 29:9.43 for RIT and EG. DSC results revealed phase temperatures and latent heats of 42.49–46.31 °C and 108.1–113.1 J/g, respectively. Compared to pure LA, LA/RIT-EG exhibited a 489.7 % increase in thermal conductivity. Additionally, heat storage and release rates were improved by 81.25 % and 88.24 %, respectively. The study elucidated the mechanism behind the enhancement in encapsulation capacity and thermal conductivity by RIT-EG, validated through specific surface area and wettability tests. Overall, the results suggest that LA/RIT-EG, characterized by high thermal capacity and heat transfer efficiency, holds promise as a potential candidate for thermal energy storage, particularly in the context of energy conservation in buildings.

Layer-by-layer assembly of boron arsenide and copper nanoflake-based aramid nanofibers for thermoconductive electromagnetic interference shielding materials with superior mechanical flexibility and flame retardancy

Flexible and wearable electronics represent an emerging frontier, but realizing their potential requires addressing challenges like electromagnetic interference (EMI) shielding, electrical insulating thermal management, and mechanical flexibility. Layer-by-layer structure with alternating conductive and insulating layers offers a promising solution. In this work, we fabricated layer-by-layer structured papers combining boron arsenide (BA) as insulating layers and two-dimensional copper nanoflake (CuF) as conductive layers based on aramid nanofiber (ANF) film via alternating vacuum filtration. The resultant paper (BA4/CuF3) consists of 3 layers of CuF (50 wt%) based ANF (CuF@ANF) conductive layers sandwiched between 4 layers of BA (50 wt%) based ANF (BA/ANF) insulating layers providing exceptional EMI shielding effectiveness (SE) up to 52 dB in the X-band frequency, and in-plane thermal conductivity up to 32.8 W/mK. Meanwhile, the composite papers also demonstrate excellent mechanical flexibility, with the BA4/CuF3 papers exhibiting a tensile strength of 92.38 MPa and EMI SE above 50 dB. Moreover, the composites impart thermal stability up to 500 °C and reduce flammability. The concurrent enhancement of EMI shielding, thermal conductivity, and mechanical properties confirms the potential of layer-by-layer BA/CuF papers for next-generation flexible electronics demanding electromagnetic protection and thermal management.

In situ three-roll mill exfoliation approach for fabricating asphalt/graphite nanoplatelet composites as thermal interface materials

Thermal interface materials (TIMs) are vital to dissipate excess heat generated by electronic components with ever-growing power density to ensure their reliability and performance. However, the limited dispersibility of nano-sized thermal conductive fillers hinders further enhancement of thermal conductivity in TIMs. It remains challenging to manufacture high-performance TIMs with simultaneous high thermal conductivity, low cost, and capability of large-scale production. Herein, a solvent-free and scalable approach was adopted to fabricate asphalt/graphite nanoplatelets (GNPs) composites by in situ exfoliating graphite in asphalt melt using a three-roll mill. During exfoliation, asphalt was adsorbed onto the surface of GNPs via π-π interaction and improved their dispersibility. Hence, GNPs formed integrated thermal conductive pathways with reduced interfacial thermal resistance, which significantly improved the thermal conductivity of asphalt/GNP composites. At 25 vol% loading, the asphalt/GNP composite displayed a thermal conductivity of 1.95 W m−1 K−1, showing a 114 % increase compared to the asphalt/commercial GNP (c-GNP) composite prepared by conventional mechanical mixing. Moreover, the heat-resistant and mechanical properties of the asphalt/GNP composites were also enhanced due to the improved filler dispersion and filler-matrix interactions. Thus, the asphalt/GNP composites fabricated by in situ three-roll milling possessed remarkable advantages as TIMs compared with asphalt/c-GNP composites and commercial silicone rubber thermal pads.