High Conductivity Materials Research Articles

Thermal performance enhancement methods of phase change materials for thermal energy storage systems – A review

Phase Change Materials (PCMs) have emerged as a promising solution for efficient thermal energy storage and utilization in various applications. This research paper presents a comprehensive overview of PCM technology, including its fundamental working principles, classification and different shapes of container used for PCM storage. The study investigates the optimal melting temperature of PCMs and explores various Thermal Energy Storage (TES) methods and their types. This paper discusses novel approaches to enhance the thermal performance of PCMs, such as incorporating high-conductivity materials, Nano-encapsulation, Composite formation, and Shape stabilization. These innovative techniques have shown great potential in enhancing efficiency of PCM-based TES systems. The information presented in this paper is an in-depth analysis of research papers published over the last five years (2019 to 2023). It is a valuable source for researchers seeking to stay current with the modern advancements in PCM technology and its applications. This research contributes to advancing sustainable and efficient thermal energy utilization by promoting a deeper understanding of PCM's capabilities and challenges.

Multifactor analysis of heat extraction performance of coaxial heat exchanger applied to hot dry rock resources exploration: A case study in matouying uplift, Tangshan, China

To obtain an excellent heat exchange effect, it is necessary to optimize the technical processes of single-well coaxial heat exchange. Based on numerical simulation and field investigation, this study shows that a high inlet temperature can significantly improve the outlet temperature while a low inlet temperature can obtain a high heat extraction power. The outlet temperature and heat extraction power show a positive correlation binomial relation with the inlet flow rate, the thermal conductivity of cement, the thermal conductivity of reservoir and the borehole diameter, which exhibit linear negative and positive correlation relationships with the thermal conductivity of inner tube and geothermal gradient. The inlet flow rate, geothermal gradient and thermal conductivity of the inner tube are the most significant factors, followed by the thermal conductivity of reservoir and the borehole diameter, while the inlet temperature and thermal conductivity of cement are the insignificant factors. It is recommended to select the reservoirs with high geothermal gradient, good thermal conductivity and wide stable distribution, develop fixing well cement with high thermal conductivity and inner pipe materials with excellent insulation performance, reduce the inlet temperature, increase the inlet flow rate of working fluid and expand the well diameter while considering costs.

Influence of the interfacial thermal resistance of a gadolinium/copper bimetal composite on solid-state magnetic refrigeration

The low heat transfer efficiency caused by a magnetocaloric material (MCM) with low thermal conductivity is the bottleneck that limits the performance of magnetic refrigeration (MR). Previous studies have shown that a bimetal composite of a high thermal conductivity material and an MCM is effective in improving the heat transfer rate. However, the bimetal composite structure causes extra interfacial thermal resistance (ITR). Therefore, this study investigates the processing of gadolinium/copper bimetal composites by fusion casting and experimentally determines the ITR. To evaluate the structural heat transfer capability, the equivalent thermal conductivity (keq) is proposed, which is calculated based on the ITR result and simulation. The influence of the ITR and keq on the cooling performance of a fully solid-state MR is carefully investigated using a validated simulation model. The results show that the smallest ITR of 3.74 × 10−5 m2 K W−1 is obtained with a copper pouring temperature of 1200 °C owing to the thinnest bonding interfacial layer. The topology-optimized structure, using the ITR obtained by fusion casting, has an keq of 159.8 W m−1K−1, with an increase of 39% compared to the structure assembled with thermal grease. As a result, the maximum specific cooling power (SCPmax) range and corresponding optimal operating range are significantly expanded to 45.6–209.3 W kg−1 and 0.23–0.61 rpm, respectively, with an average SCPmax increase of 35.5%. The combination of using topology optimization design to reduce the structural thermal resistance and using a suitable forming process to reduce the ITR can be more beneficial to the performance improvement of solid-state MR.

Topology optimization for near-junction thermal spreading of electronics in ballistic-diffusive regime

Hotspots in electronic devices can cause overheating and reduce performance. Enhancing the thermal spreading ability is critical for reducing device temperature to improve the reliability. However, as devices shrink, phonon ballistic effects can increase thermal resistance, making conventional optimization methods less effective. This paper presents a topology optimization method that combines the phonon Boltzmann transport equation with solid isotropic material with penalization method to optimize high thermal conductivity (HTC) material distributions for thermal spreading problems. Results show that the contraction-expansion structure can effectively reduce thermal resistance. Optimal distributions differ from that based on Fourier's heat conduction law, and only the trunk structure appears in optimized layouts due to the size effect. Additionally, HTC material with longer mean free paths tends to be filled around the heat source with a gap in a ballistic-diffusive regime. This work deepens understanding of thermal spreading and aids in thermal optimization of microelectronic chips.

Sulfonate-Functionalized Polyoxovanadate-Based Metal-Organic Polyhedra for Enhanced Proton Conduction via the Synergy of Linker and Metal Cluster Vertex

Metal-organic polyhedra (MOPs) have emerged as novel porous platforms for proton conduction, however, the concerted employment of both linker and metal cluster vertex is rarely applied for the fabrication of MOPs-based high conducting materials. Herein we report the synthesis of sulfonate-functionalized polyoxovanadate-based MOPs for enhanced proton conduction via the synergistic effect from linker and metal cluster node. MOPs 1 and 2 exhibit octahedral cage configuration constructed from {V5O9Cl} vertex and 5-sulfoisophthalate linker. Owing to the ordered packing of octahedral cages along three axes, 3D interpenetrated open channels that are lined with high-density sulfonates are thus formed within 2. Coupled with the proton-conductive {V5O9Cl} vertexs as well as protonated counterions, an extensive H-bonded network is therefore generated for facile proton transfer. 2 exhibits high proton conductivity of 3.02×10−2 S cm−1 at 65 °C under 90% RH, recording the highest value for MOPs pellet sample. This value is enhanced ~1 order of magnitude compared with that of carboxylate-functionalized analogue 3, clearly illustrating the advantage of combining linker and metal cluster node for enhanced proton conduction. This work will further promote the exploitation of high proton conductive MOPs-based materials by the synergy design strategy.

Picosecond magneto-optic thermometry measurements of nanoscale thermal transport in AlN thin films

The thermal conductivity Λ of wide bandgap semiconductor thin films, such as AlN, affects the performance of high-frequency devices, power devices, and optoelectronics. However, accurate measurements of Λ in thin films with sub-micrometer thicknesses and Λ > 100 W m−1 K−1 is challenging. Widely used pump/probe metrologies, such as time–domain thermoreflectance (TDTR) and frequency–domain thermoreflectance, lack the spatiotemporal resolution necessary to accurately quantify thermal properties of sub-micrometer thin films with high Λ. In this work, we use a combination of magneto-optic thermometry and TiN interfacial layers to significantly enhance the spatiotemporal resolution of pump/probe thermal transport measurements. We use our approach to measure Λ of 100, 400, and 1000 nm AlN thin films. We coat AlN thin films with a ferromagnetic thin-film transducer with the geometry of (1 nm-Pt/0.4 nm-Co)x3/(2 nm-TiN). This PtCo/TiN transducer has a fast thermal response time of <50 ps, which allows us to differentiate between the thermal response of the transducer, AlN thin film, and substrate. For the 100, 400, and 1000 nm thick AlN films, we determine Λ to be 200 ± 80, 165 ± 35, and 300 ± 70 W m−1 K−1, respectively. We conclude with an uncertainty analysis that quantifies the errors associated with pump/probe measurements of thermal conductivity, as a function of transducer type, thin-film thermal conductivity, and thin-film thickness. Time resolved magneto-optic Kerr effect experiments can measure films that are three to five times thinner than is possible with standard pump/probe metrologies, such as TDTR. This advance in metrology will enable better characterization of nanoscale heat transfer in high thermal conductivity material systems like wide bandgap semiconductor heterostructures and devices.

Reduction of temperature fluctuation in a South African shack house using phase change material insulation

The majority of South African informal settlements are made from corrugated profile galvanized metal sheets. These informal settlements are prone to temperature fluctuations due to high thermal conductivity of the metal sheet and its low thermal resistance to heat transfer between the exterior and the interior of the shack. Families have resorted to using fuels such as paraffin during cold days, which has resulted in fire outbreaks that ravage surrounding shacks. This study experimentally investigated the temperature fluctuations around a shack fitted with plank chipboard and one without. Energy plus 22.2.0 software was then used to simulate the temperature fluctuations effects after integrating a Phase Change Material (PCM) layer on the shack walls. From the experiments, the internal temperature fluctuations on the shack without the insulations reached close to +50 °C during the day, and −5 °C during the night. While the shack with insulation reached +25 °C during the day and 7 °C during the night. The temperature distribution inside the shack was observed to be uneven, with the top section of the shack at higher temperatures than the bottom section. The region and the location of the shack largely contributed to the temperature fluctuations. Simulations revealed that by integrating a PCM layer in the shack walls, temperature fluctuations were greatly reduced. A lower phase change temperature yielded greater results as the atmospheric air allowed the PCM to fully solidify and melt, thus releasing the latent heat energy. A phase change temperature between 17 and 19 °C was selected based on the average atmospheric yearly temperature range. A 30 mm thick PCM reduced the temperature fluctuations to between +14 °C and +16 °C. However, materials with high thermal conductivity are not well supported by the Conduction Finite Difference used to simulate the performance of a phase change material in energy plus, it is proposed to remove such thin and high conductive materials in the model.

Ultrafine Fe2VO4 nanoparticles anchored on Ti3C2Tx nanosheets (Fe2VO4@Ti3C2Tx) as high-energy anode for lithium-ion storage

Recently, as a new breakthrough for lithium-ion storage anode materials, transition metal vanadates, such as Fe2VO4, have attracted much attention, which, however, still suffer from slow electrochemical kinetics and substantial volume expansion. Hybrid with high conductivity materials is an effective route to deal with these issues. Herein, in situ synthesis of Fe2VO4@Ti3C2Tx composites with porous sandwich structure by co-precipitation-calcination process was reported. Ultrafine Fe2VO4 nanoparticles (10–15 nm) in situ grew and was anchored on Ti3C2Tx nanosheets, which effectively inhibits both the grain growth for Fe2VO4 and stacking for Ti3C2Tx, thus facilitating the electrochemical kinetics and alleviating the volume change of Fe2VO4 to maintain the integrated structure during the cycling process. As a result, Fe2VO4@Ti3C2Tx anode shows high Li+ diffusion coefficient (2.72 × 10−11 cm2 s−1) and pseudocapacitive charge storage mechanism (capacitive charge storage contribution 70.85–84.80 % at 0.2–1.0 mV s−1), which guarantee rapid charging and discharging capability. Consequently, outstanding rate performance (1012–595 mAh g−1 at 0.2–3.0 A g−1) and superior cycling capability (663 and 416 mAh g−1 at 1.0 A g−1 for 200 cycles and 2.0 A g−1 for 500 cycles, with the average capacity attrition rate of 0.059 % and 0.053 %, respectively), were achieved, which render Fe2VO4@Ti3C2Tx composites important potential for lithium-ion storage.

Study of the hot-pressing sintering process of diamond/copper composites and their thermal conductivity

Diamond/copper composites have been widely studied as high thermal conductivity (TC) materials for heat dissipation in electronic integrated devices. In this study, diamond/copper composites with fin structures were prepared by hot-pressing sintering. The relative density and TC of the composites were analyzed for different diamond particle sizes, diamond volume fractions, sintering temperatures and sintering pressures. The relative density of the composites decreases significantly with increasing diamond particle size and volume fraction. The TC of the composite was found to be a maximum of 564.2 W/m·K at 1400 N sintering pressure and 900 °C sintering temperature when the diamond particle size was 230 µm and the volume fraction was 60%. In addition, the coefficient of thermal expansion (CTE) of the diamond/copper composite was 7.01 × 10−6 K−1 at 1400 N sintering pressure and 900 °C sintering temperature, which meets the packaging requirements for electronic integrated devices. The heat dissipation experiment of the diamond/Cu microchannel heat sink (MCHS) showed that the surface temperature of the heat source can be controlled at 59.9 °C when the inlet velocity was 0.4 m/s, achieving a cooling of 40.1 °C.

Self-Stacked 3D Anisotropic BNNS Network Guided by Para-Aramid Nanofibers for Highly Thermal Conductive Dielectric Nanocomposites.

The enhancement of the heat-dissipation property of polymer-based composites is of great practical interest in modern electronics. Recently, the construction of a three-dimensional (3D) thermal pathway network structure for composites has become an attractive way. However, for most reported high thermal conductive composites, excellent properties are achieved at a high filler loading and the building of a 3D network structure usually requires complex steps, which greatly restrict the large-scale preparation and application of high thermal conductive polymer-based materials. Herein, utilizing the framework-forming characteristic of polymerization-induced para-aramid nanofibers (PANF) and the high thermal conductivity of hexagonal boron nitride nanosheets (BNNS), a 3D-laminated PANF-supported BNNS aerogel was successfully prepared via a simple vacuum-assisted self-stacking method, which could be used as a thermal conductive skeleton for epoxy resin (EP). The obtained PANF-BNNS/EP nanocomposite exhibits a high thermal conductivity of 3.66 W m-1 K-1 at only 13.2 vol % BNNS loading. The effectiveness of the heat conduction path was proved by finite element analysis. The PANF-BNNS/EP nanocomposite shows outstanding practical thermal management capability, excellent thermal stability, low dielectric constant, and dielectric loss, making it a reliable material for electronic packaging applications. This work also offers a potential and promotable strategy for the easy manufacture of 3D anisotropic high-efficiency thermal conductive network structures.

Validation of a Skin Calorimeter to Determine the Heat Capacity and the Thermal Resistance of the Skin.

In vivo determination of the skin's thermal properties is of growing interest. Several types of sensors are being designed and tested. In this field, we have developed a skin calorimeter for the determination of the heat flow, the heat capacity and the thermal resistance of the skin. The calorimeter calibration consists of the determination of the parameters of the model we have chosen to represent the behavior of the device. This model considers the heat capacity and the thermal resistance of the skin, which depend on the case (body zone, subject, physical state, etc.) and also have a strong time dependence. Therefore, this work includes a validation study with reference materials. Finally, it is concluded that the heat capacity determined is a function of the thermal penetration depth of the measurement characteristics. In the case of high thermal conductivity materials in which the thermal penetration is nearly total, the heat capacity obtained coincides with that of the reference material sample.

Blended Conjugated Host and Unconjugated Dopant Polymers Towards N-type All-Polymer Conductors and High-ZT Thermoelectrics.

N-Type thermoelectrics typically consist of small molecule dopant+polymer host. Only a few polymer dopant+polymer host systems have been reported, and these have lower thermoelectric parameters. N-type polymers with high crystallinity and order are generally used for high-conductivity ( ) organic conductors. Few n-type polymers with only short-range lamellar stacking for high-conductivity materials have been reported. Here, we describe an n-type short-range lamellar-stacked all-polymer thermoelectric system with highest of 78 S-1 , power factor (PF) of 163 μW m-1 K-2 , and maximum Figure of merit (ZT) of 0.53 at room temperature with a dopant/host ratio of 75 wt%. The minor effect of polymer dopant on the molecular arrangement of conjugated polymer PDPIN at high ratios, high doping capability, high Seebeck coefficient (S) absolute values relative to , and atypical decreased thermal conductivity ( ) with increased doping ratio contribute to the promising performance.

Metal Hydride Composite Structures for Improved Heat Transfer and Stability for Hydrogen Storage and Compression Applications

Metal alloys and intermetallic compounds offer an attractive method for safely storing hydrogen (H2). The metal alloys absorb H2 into their structure, often swelling and fracturing as a result of phase transformation during hydride formation/decomposition cycles. The absorption of H2 is an exothermic process, requiring the effective and efficient removal of heat. This can be challenging as heat transfer to/from powdered beds is notoriously difficult, and often limited by poor thermal conductivity. Hence, the observed reaction kinetics for absorption and desorption of H2 is dominated by heat flow. The most common method for improving the thermal conductivity of the alloy powders is to prepare them into composite structures with other high thermal conductivity materials, such as carbons and expanded natural graphite. Such composite structures, some also combined with polymers/resins, can also mitigate safety issues related to swelling and improve cyclic durability. This paper reviews the methods that have been used to prepare such composite structures and evaluates the observed impact on thermal conductivity.

High thermal conductive and anti-leakage composite phase change material with halloysite nanotube for battery thermal management system

The thermal safety of battery module is demonstrated as the main bottleneck to hinder wider adoption of electric vehicles (EVs). It is vital to explore efficient thermal management system to satisfy the rapidly increasing need for EVs. Composite change materials (CPCMs) as passive cooling system has greatly potential application in battery packs. However, the inherent leakage and low thermal conductivity are restricted its widely utilized in practical applications. In this study, the high thermal conductivity CPCM with PEG/EG/HNT@AP has successfully prepared through a synergistic method of in situ chemical reduction and physical blending technology. Polyethylene glycol (PEG) as the phase change matrix and halloysite nanotube (HNT) as the support material can provide cross-linked network to prevent its leakage. Especially, the expanded graphite (EG) and silver nanoparticles (AgNPs) assembled into HNT (HNT@AP) play a synergistic role to construct an interconnected thermal network. The results indicates that the thermal conductivity is increased to 1.15 W·m−1·K−1 and the latent heat of phase change can maintain to 103.65 J·g−1, when the content of HNT@AP is 40 %. In addition, the battery module with PEG/EG/HNT@AP and PEG/EG/ER are designed and measured during charge and discharge cycling process, respectively. It reveals that battery module with PEG/EG/HNT@AP can exhibit excellent thermal management effect, which temperature was controlled below 60 °C at 3C discharge rate even under 35 °C ambient temperature. Therefore, this work sheds light on rational design of high thermal conductive composite material to improve thermal safety of battery pack in the EVs.

Preparation and Properties of Boron Nitride or Aluminum Nitride Reinforced Glass Fiber/Modified Polyphenylene Sulfide Composites

In this work, polyphenylene sulfide (PPS) containing carboxyl group was synthesized and used to prepare PPS-2COOH/LGF/AlN and composites with high-temperature resistance, corrosion resistance, low dielectric constant, and low dielectric loss were prepared with boron nitride/aluminum nitride (BN/AlN) and glass fiber (LGF). The results showed that the introduction of carboxyl groups did not affect the structure and thermal properties of PPS. The composites exhibited good mechanical properties with a tensile strength of 65 MPa~97 MPa and flexural strength of 112 MPa~154 MPa. The TGA results showed that the composites had good thermal stability, and the T5% of PPS-2COOH/LGF/AlN (20) and PPS-2COOH/LGF/BN (20) reached up to 511.6°C and 506.3°C, respectively. They were insoluble in some organic solvents, such as NMP and DMF at room temperature, and they exhibited excellent chemical resistance. The dielectric performance results showed that with the increase of frequency, the dielectric constant and dielectric loss gradually decreased, the dielectric constant of PPS-2COOH/LGF/BN (15) was 3.9, and the dielectric loss of PPS-2COOH/LGF/BN (15) was 0.01. From the above results, it can be concluded that the composite materials PPS-2COOH/LGF/AlN and PPS-2COOH/LGF/BN have potential application prospects in the field of 5G high thermal conductivity materials.

Reorganization Energy Predictions with Graph Neural Networks Informed by Low-Cost Conformers.

A critical bottleneck for the design of high-conductivity organic materials is finding molecules with low reorganization energy. To enable high-throughput virtual screening campaigns for many types of organic electronic materials, a fast reorganization energy prediction method compared to density functional theory is needed. However, the development of low-cost machine-learning-based models for calculating the reorganization energy has proven to be challenging. In this paper, we combine a 3D graph-based neural network (GNN) recently benchmarked for drug design applications, ChIRo, with low-cost conformational features for reorganization energy predictions. By comparing the performance of ChIRo to another 3D GNN, SchNet, we find evidence that the bond-invariant property of ChIRo enables the model to learn from low-cost conformational features more efficiently. Through an ablation study with a 2D GNN, we find that using low-cost conformational features on top of 2D features informs the model for making more accurate predictions. Our results demonstrate the feasibility of reorganization energy predictions on the benchmark QM9 data set without needing DFT-optimized geometries and demonstrate the types of features needed for robust models that work on diverse chemical spaces. Furthermore, we show that ChIRo informed with low-cost conformational features achieves comparable performance with the previously reported structure-based model on π-conjugated hydrocarbon molecules. We expect this class of methods can be applied to the high-throughput screening of high-conductivity organic electronics candidates.

Consumption of advanced engineering composite materials to check the electro-magnetic properties of concrete

Electrically Conductive Concrete is a cement-based composite that contains electrically conductive components, resulting in a long-lasting, high-conductivity material. It can be used to melt snow from parking lots, road walkways, highway bridges, automobile entries, and airport runways, as well as for electrical grounding. Concrete has existed in numerous forms throughout history, yet it is one of the few materials with tremendous future potential. Many unsuccessful experiments have been conducted over the years to develop a concrete that can be blended with the electrical conductivity properties of standard concrete mixtures. Using conductive concrete, this paper was able to accomplish this difficult task. It is possible to measure the characteristics of conductive concrete mixes made using sand, coarse particles, and cement. The findings calculated using scanning electronic microscope and X-ray diffraction are explained under the physical importance. To create electrically conductive concrete, the interaction between steel fibre and graphite is enhanced. The maximum strength, which is 9.69% greater than the strength attained by the controlled sample, is acquired after a continual increase in strength up to 4%.

A novel attempt to enhance the heat transfer rate of thermal energy storage using multitemperature phase change materials through experimental and numerical modelling

This work aims to develop the numerical model for the three-stage phase transition of multi-level phase change materials (PCMs) and present the comparative performance analysis between single PCM and multi-temperature PCM thermal energy storage (TES) systems. The performance of the thermal energy storage system was conducted by the implementation of multiple phase change materials (PCMs) which are arranged following the temperature profile of the heat transfer fluid. The proposed TES system has two models; the first is fully packed with single PCM – Erythritol TES, and the second is packed with multi-temperature PCMs, namely acetanilide in the first half of the tank and 1-Naphthol in the second half of the tank. The experiments are conducted to validate the numerical model values and observed that the results are in close agreement with each other and the percentage variation is within 3–5%. The results show that using multi-temperature PCMs provides better performance than single-PCM systems. Based on the results, the performance of the TES system can be enhanced with multi-level PCMs rather than choosing high-conductivity materials in the system, which lead to considerable potential in saving energy loss and an economical way of designing the efficient TES system.

Design and optimization of composite phase change material for cylindrical thermal energy storage

Phase change materials store thermal energy in the form of latent heat, and are often integrated with high thermal conductivity metals to make composites that have both high power density and large energy storage capacity. In this study, we provide a theoretical framework to design and optimize cylindrical composites with three figures of merit – minimization of temperature rise, maximization of the effective volumetric heat capacity and maximization of the effective heat capacity based on mass. We validate the figures of merit experimentally by 3D printing AlSi12 alloy and using octadecane as phase change material for a heat flux of 13.3 Wcm−2 and heating time of 10 s. The metal component volume fractions in the printed structures vary from 15% to 70% for straight fin structures, 10% to 70% for the SC lattice structures, and 20% to 70% for branching fin structures. When minimizing temperature rise, the optimum volume fraction of thermally conductive material is 0.5–0.7. When maximizing the effective volumetric heat capacity, the optimum volume fraction for the high conductivity material is 0.3–0.5. Finally, when maximizing the effective heat capacity by mass in cylindrical composites, the optimum volume fraction for the high conductivity material is 0.2–0.3. Importantly, the optimum values depend on the applied thermal load, which is not captured in existing figures of merit for thermal storage systems. The volumetric and mass based heat capacity values of the optimized composites identified in this study are at least 10x higher when compared to single component PCMs that are widely used for volumetric and mass based thermal storage systems. The figures of merit developed here can assess the performance of most composite PCM systems and help to design future cylindrical composites while accounting for the thermal loads specific to the thermal storage application.

Application of New Materials in Aerospace Thermal Management

This paper summarizes the mission, scheme and main technology of spacecraft thermal management. The development requirements of new thermal control technologies, especially new thermal control materials, for future spacecraft are analysed. The research progress of new high thermal conductivity materials, new interface filler materials and intelligent thermal control coatings at home and abroad and their applications in the thermal control field of spacecraft are reviewed.