Thermal Resistance Research Articles

All‐Climate Thermal Management Performance of Power Batteries Based on Double‐Layer Flexible Phase Change Materials

AbstractThermal management systems for power batteries based on phase change materials (PCM) are limited by low heat transfer efficiency, leakage issues, and high rigidity, and most of them cannot meet the needs of all‐climate thermal management. A double‐layer flexible phase change material (FPCM) sleeve structure for all‐climate thermal management is proposed in this study for the first time. Innovations in both material and design have enhanced the adaptability of the thermal management system. The outer layer FPCM achieves high thermal conductivity (4.23 W m−1 K−1) and electrical conductivity (0.95 S m−1), the inner layer FPCM achieves insulation (22.76 MΩ) and flexibility, the thermal contact resistance (TCR) between the double‐layer sleeve structure and the battery are measured to be only 0.15 °C W−1, significantly improved thermal management performance. Experimental results show that at 30 °C ambient temperature, 5 C discharge, the system reduces the maximum temperature by 14.5 °C, from 61.4 to 46.9 °C, compared to natural convection. Additionally, during heating, the system achieves heating rates of 7.0, 8.3, and 8.7 °C min−1 at −20, −10, and 0 °C, respectively, extending battery discharge duration by 32.5%, 65.9%, and 33.6%.

Study on the Oxidation Behavior of TiB2-CeO2-Modified (Nb,Mo,Cr,W)Si2 Coating on the Surface of Niobium Alloy

A novel TiB2-CeO2-modified (Nb,Mo,Cr,W)Si2 coating was prepared on a Nb-5W-2Mo-1Zr alloy substrate using two-step slurry sintering and halide-activated pack cementation to address the limitations of a single NbSi2 coating in meeting the service requirements of niobium alloys at elevated temperatures. At 1700 °C, the static oxidation life of the coating exceeded 20 h, thus indicating excellent high-temperature oxidation resistance. This was due to the formation of a TiO2-SiO2-Cr2O3 composite oxide film on the coating surface, which, due to low oxygen permeability, effectively prevented the inward infiltration of oxygen. Additionally, the dense structure of the composite coating further enhanced this protective effect. The composite coating was able to withstand over 1600 thermal shock cycles from room temperature to 1700 °C, and its excellent thermal shock performance could be attributed to the formation of MoSi2, CrSi2, and WSi2 from elements such as Mo, Cr, and W, which were added during modification. In addition to adjusting the difference in thermal expansion coefficients between the layers of composite coatings to reduce the thermal stress generated by thermal shock cycles, the formation of silicide compounds also improved the overall fracture toughness of the coating and thereby improved its thermal shock resistance.

Influence of Silicon Carbide Incorporation on Thermal and Ablation Properties of Carbon Fabric-Phenolic Resin Composites

To shield re-entry spacecraft from the extreme heat experienced during hypersonic flight through a planet's or the earth's atmosphere, thermal protection systems (TPS) were developed. This work involved the fabrication of composites using a polyacrylonitrile (PAN) based carbon fabric (Cf)-phenolic resin matrix (PR) modified with different weight percentages (wt.%) of silicon carbide (SiC), namely 0 wt.% (Cf/PR), 1wt.%, 3wt.%, and 5wt.%. The composites were prepared using the hydraulic hot press method. The manufactured composites were analyzed for their thermal conductivity and resistance to ablation using an oxyacetylene torch test. Furthermore, the ablated composites underwent X-ray diffraction (XRD), revealing a SiO2 compound layer on the ablated composite surface. The experimental results demonstrated that the Cf/PR composites modified with 3wt.% of SiC exhibited superior characteristics. The composites consist of 3wt.% Cf/PR-SiC exhibited a thermal conductivity value of 0.57 W/m K. Additionally, these composites showed a noticeable decrease in the mass ablation rate (MAR) at 0.0052 mm/sec and linear ablation rates (LAR) at 0.025061 gm/sec. This study proposed an effective way to improve the thermal and ablation characteristics of TPS materials.

Photothermal Infrared Radiometry and Thermoreflectance—Unique Strategy for Thermal Transport Characterization of Nanolayers

Thermal transport properties for the isotropic and anisotropic characterization of nanolayers have been a significant gap in the research over the last decade. Multiple studies have been close to determining the thermal conductivity, diffusivity, and boundary resistance between the layers. The methods detailed in this work involve non-contact frequency domain pump-probe thermoreflectance (FDTR) and photothermal radiometry (PTR) methods for the ultraprecise determination of in-plane and cross-plane thermal transport properties. The motivation of one of the works is the advantage of the use of amplitude (TR signal) as one of the input parameters along with the phase for the determination of thermal parameters. In this article, we present a unique strategy for measuring the thermal transport parameters of thin films, including cross-plane thermal diffusivity, in-plane thermal conductivity, and thermal boundary resistance as a comprehensively reviewed article. The results obtained for organic and inorganic thin films are presented. Precise ranges for the thermal conductivity can be across confidence intervals for material measurements between 0.5 and 60 W/m-K for multiple nanolayers. The presented strategy is based on frequency-resolved methods, which, in contrast to time-resolved methods, make it possible to measure volumetric-specific heat. It is worth adding that the presented strategy allows for accurate (the signal in both methods depends on cross-plane thermal conductivity and thermal boundary resistance) and precise measurement.

Thermal modelling and layout optimization of GaN half-bridge IC with integrated drivers and power HEMTs

The paper presents the results of thermal modeling of a half-bridge monolithic integrated circuit (IC) with integrated drivers and enhanced mode power high electron mobility transistors, based on a GaN-on-SOI heterostructure. It had been established that the main heat sources in the IC were the half-bridge GaN HEMTs. The heat from the half-bridge GaN HEMTs propagates in the chip and leads to heating of the logic block and gate drivers. Heating of half-bridge GaN HEMTs leads to increased channel resistance and IC output current drop. Heating of the gate drivers reduces driving current, as a result, increases the switching time of the half-bridge GaN HEMTs. Heating of the logic block increases the rise and fall times of the generated control signals, which worsens the dynamic characteristics of the IC. A comparative analysis of heat propagation for IC dies based on GaN-on-SOI and GaN-on-Si heterostructures showed that GaN-on-SOI structure has a 40% greater junction-to-backside thermal resistivity compared to GaN-on-Si structure. In this case, the specific thermal resistance in the direction of heat propagation from the hotspot of the transistor to the backside of the die for the GaN-on-SOI structure is almost two orders of magnitude greater than in the direction of its propagation to the frontside of the chip. The results obtained were used for IC layout optimization. The rearrangement of GaN-on-SOI IC functional blocks, as well as to introduction of additional heat-spreading elements on the frontside of chip were carried out during the optimization.

Ultrahigh Energy Storage of Twisted Structures in Supramolecular Polymers.

Polymer dielectrics possess outstanding advantages for high-power energy storage applications such as high breakdown strength (Eb) and efficiency (η), while both of them decrease rapidly at elevated temperatures. Although several strategies have been evaluated to enhance Eb and heat resistance, the discharged energy density (Ud) is still limited by the planar conjugated structure. In this study, a novel approach to manipulate polymer morphology is introduced, thereby influencing dielectric properties. A range of polyurea (PU)-based polymers are predicted from different structural unit combinations by machine learning and synthesized two representative polymers with high dielectric constants (K) and thermal stability. These polymers are combined with PI to form a twisted polymer via hydrogen bonding interactions (HNP). Both experimental results and computational simulations demonstrate the twisted structure disrupts the conjugated structure to widen the bandgap and increase dipole moment through the twisting of polar groups, leading to simultaneous improvements in both K and Eb. Consequently, HNP-20% achieves an ultrahigh Ud of 6.42 Jcm-3 with an efficiency exceeding 90% at 200 °C. This work opens a new avenue to scalable high Ud all-polymer dielectric for high-temperature applications.

Preparation of low‐temperature self‐crosslinking acrylic resin and its performance research

AbstractAcrylic resin, as a common coating and adhesive, possesses excellent heat resistance, weather resistance, and is inexpensive, making it widely used in industries related to automotive, construction, electronics, fabrics, and other sectors essential to our daily life. Traditional acrylic resin not only pollutes the environment but also poses certain health risks. Therefore, we studied the synthesis of a low‐temperature self‐crosslinking acrylic emulsions were synthesized by free radical solution polymerization using methyl methacrylate (MMA), butyl acrylate (BA), acrylic acid (AA), diacetone acrylamide (DAAM), hydroxypropyl acrylate (HPA), epoxy resin (E‐51) as the monomers, vinyltriethoxysilane (A‐51) as the coupling agent, and adipic dihydrazide (ADH) as the cross‐linking agent. This water‐based acrylic resin undergoes a crosslinking reaction between the carbonyl group of DAAM and the hydrazide group of ADH, substantially improved the drying speed and adhesion compared to unmodified versions, and also improved the thermal stability. The contact angle of the film increased from 72.8° to 86.9° with the increase of the degree of cross‐linking, and the mechanical properties were improved by 60%. This study provides a suitable formulation for preparing water‐based acrylic resins with superior performance.

Poly(l-lactide)/poly(d-lactide)/bamboo fiber (BF) bio-composites with enhanced heat resistance, mechanical and rheological performance

Poly(l-lactide)/poly(d-lactide)/bamboo fiber (BF) bio-composites with enhanced heat resistance, mechanical and rheological performance

Effect of interfacial thermal resistance on the near-field photoacoustic signal from gold nanorod in water: a numerical study.

The near-field photoacoustics of gold nanoparticle in water has received much attention for its biomedical applications and is strongly affected by the gold-water interfacial thermal resistance. However, the effect of interfacial thermal resistance on near-field photoacoustics has been very little studied. Here we present the numerical simulations of near-field photoacoustic signal generation from a single gold nanorod in water by considering different thermal resistances at the gold-water interface. It is shown that, different from the reported reduction of far-field photoacoustic signals by interfacial thermal resistance, enhancement of near-field photoacoustic signals is obtained with the typical gold-water interfacial thermal resistance. Further analysis reveals that the higher rate of net heat transfer to the surrounding water at the typical interfacial thermal resistance, which corresponds to faster thermal expansion of the surrounding water, accounts for such enhancement of near-field photoacoustic signal and that the enhancement of near-field photoacoustic amplitude is mainly present at a distance within thermal diffusion length.

Improvement of curing efficiency and heat resistance of CFRP by the growth of SiCNWs on CF

Carbon fiber-reinforced polymer composites are widely used in modern industry. However, poor heat transfer between layers of carbon fiber cloth during the curing process leading to poor curing of the substrate, long curing cycles, and excessive heat accumulation has become an urgent problem to be solved. A common approach is dispersing highly thermally conductive fillers in the polymer matrix to improve the curing efficiency of the composites. Different from adding fillers, we report a novel method of in situ growth of SiC nanowires (SiCNWs) on the surface of carbon fiber (CF) by the chemical vapor deposition (CVD) method and study the effects of CVD deposition time on curing efficiency and thermal stability of the composites. The results indicate that the nano bridge effect of SiCNWs significantly improves the curing efficiency of the composites. Compared with pure CF/epoxy composites, the curing efficiency can be increased by 38.72%. The cross-linking point between SiCNWs and the resin matrix enhances the thermal stability of the composites and increases the heat resistance index ( T HRI) by 8.4°C.

Preparation and Properties of High‐Temperature‐Resistant and Low‐Dielectric Constant Silicon‐Containing Arylacetylene Resin/SiO2 Syntactic Foams

A silicon‐containing arylacetylene resin (PSA)/SiO2 syntactic foam was prepared through a chemical foaming approach, with PSA serving as the matrix, quartz sand (QS) and nanosilica (nSiO2) acting as fillers, and their structures and properties were characterized. The results show that the incorporation of appropriate amounts of QS and nSiO2 can reduce the cell size and apparent density of the syntactic foam, and improve its heat resistance, dielectric properties and wave transmission properties. The addition of QS can increase the compressive strength of the syntactic foam, while the addition of nSiO2 decreases the compressive strength. The apparent densities of the PSA/9QS and PSA/9nSiO2 syntactic foams with 9% filler addition are 0.242 g cm−3 and 0.157 g cm−3, respectively, and the temperatures at 5% weight loss (Td5) under a nitrogen atmosphere were 692 °C and 658 °C, respectively. The dielectric constants were 1.59 and 1.25, respectively. The wave transmittance within the frequency range of 8.2–12.4 GHz was 98.5% and 96.8%, respectively. PSA/SiO2 syntactic foam can be used as a lightweight and high‐temperature‐resistant wave‐transmission material in aerospace and other fields.

Thermal–Hydraulic Performance Analysis of Combined Heat Sink with Open Microchannels and Embedded Pin Fins

An open type of microchannel with diamond pin fins (OM-DPFs) is introduced for the cooling of high-performance electronic chips. For a Reynolds number (Re) of 247~1173, a three-dimensional model is established to explore the hydrothermal properties of the OM-DPF and compare it to traditional heat sinks with closed rectangular microchannels (RMs), heat sinks with open microchannels (OMs), and the results in the existing research. Firstly, the synergy between tip clearance and pin fins on the hydrothermal properties is discussed. Secondly, the entropy production principle is adopted to analyze the irreversible losses for different heat sinks. Lastly, the total efficiencies of different heat sinks are assessed. The RMs present the worst heat transfer with the lowest friction loss. For the OMs, the temperature and pressure drop are decreased slightly compared to those of the RMs, and the irreversible loss is reduced by 4% at Re = 1173 because of the small tip clearance. But the total efficiency is lower than that of the RMs because the pressure drop advantage is offset by the weak heat transfer. For the OM-DPF, the combined structure has a noticeable impact on the multiple physical fields and hydrothermal characteristics, which present the best thermal performance at the cost of the highest friction loss. The irreversible loss of heat transfer in the OM-DPF is reduced obviously, but the friction irreversible loss significantly increases at high Re values. At Re = 429, the total entropy production of the OM-DPF is reduced by 47.57% compared with the RM. Compared to the OM and the single-pin fin structure in the literature, the total efficiency of the OM-DPF is increased by 14.56% and 40.32% at Re = 614. For a pump power of 0.1 W, the total thermal resistance (Rth) of the OM-DPF is dropped by 23.77% and 21.19% compared to the RM and OM. For a similar Rth, the pump power of the combined structure is 63.64% and 42.86% lower than that of the RM and OM. Thus, the novel combined heat sink can achieve efficient heat removal while controlling the energy consumption of liquid cooling systems, which has bright application prospects.

Correlating Catalyst Growth with Liquid Water Distribution in Polymer Electrolyte Fuel Cells.

This study investigates the impact of liquid water distribution in a polymer electrolyte fuel cell (PEFC) on the spatially heterogeneous platinum (Pt) catalyst degradation. The membrane electrode assemblies (MEAs) are aged using accelerated stress tests (ASTs) in varied cathode gas environments (N2 and air) to instigate Pt catalyst degradation. The study employs high-resolution neutron imaging and synchrotron micro-X-ray diffraction (micro-XRD) to map liquid water distribution and Pt particle size, respectively. Neutron radiographs reveal liquid water accumulation primarily within the diffusion media, especially under flow field lands, due to thermal resistance differences between channels and lands. Aged MEAs exhibit increased water retention, likely due to increased hydrophilicity of the diffusion media with aging. Synchrotron micro-XRD maps unveil significant heterogeneity in Pt particle size distribution in the aged MEAs, correlated with preferential liquid water accumulation under flow field lands. This study highlights the critical role of flow field design and water distribution in catalyst degradation, underscoring the need for innovative strategies to enhance fuel cell durability and performance.

Study on the effect of structural parameters of a thermal liner on its thermal protective performance under radiant heat exposure

To comprehend the impact of elementary construction parameters of nonwoven thermal liners on their thermal protective performance, the current research primarily emphasizes on studying the effect of needle penetration depth and needle punch density of the thermal liner. Nonwoven fabrics with three different punch densities and three needling depths were prepared. The air permeability and thermal resistance of the thermal liner were investigated through regression analysis to determine the influence of needle penetration depth and needle punch density. It was observed that both factors had a notable impact on the air permeability and thermal resistance of the thermal liner. An increase in needle penetration depth and needle punch density resulted in a decrease in the air permeability and thermal resistance of the thermal liner. An experiment was carried out utilizing the 33 Box-Behnken designing approach; the factors employed were the radiant heat flux intensity, needle punch density, and needle penetration depth of the thermal liner. The thermal protective performance of thermal liners was measured at three discrete intensities of radiant heat exposures. To investigate the effect of the test and construction parameters and their interaction, an analysis of variance study was carried out. It was observed that protection time rises with the decrease in needling depth and needle punch density at every level of heat flux. With the rise in incident radiant heat flux, protection time declines, irrespective of needle penetration depth and punch density levels.

Visualization Study on Oil Return Characteristics of Vapor Compression Heat Pump System

Vapor compression heat pump technology is a widely utilized method for energy conversion. Lubricating oil plays a crucial role in the heat pump system cycle by effectively reducing wear on the compressor’s moving parts and preventing refrigerant leakage. However, it can also create an oil film in the heat exchange equipment, which increases thermal resistance and diminishes heat transfer efficiency. This study utilizes a vapor compression heat pump system test bench to investigate factors influencing the system’s oil circulation rate, the two-phase flow patterns of refrigerant and lubricating oil, and the impact of oil circulation on system performance. The findings reveal that as the compressor speed increases, the oil circulation rate initially decreases before increasing again. Additionally, a decrease in the evaporator’s heat load leads to a reduction in oil circulation at high temperatures, while it increases at low temperatures. Furthermore, increasing the opening of the electronic expansion valve results in a gradual decrease in the oil circulation rate, whereas an increase in the refrigerant charge correlates with a rise in the oil circulation rate. The oil return flow pattern can primarily be categorized into three states: slow oil return, oil film flow, and high-speed oil return. These patterns are closely related to the degree of superheat, with lower superheat levels intensifying oil return.

Compressive Mechanical and Heat Conduction Properties of AlSi10Mg Gradient Metamaterials Fabricated via Laser Powder Bed Fusion

Metamaterials are defined as artificially designed micro-architectures with unusual physical properties, including optical, electromagnetic, mechanical, and thermal characteristics. This study investigates the compressive mechanical and heat transfer properties of AlSi10Mg gradient metamaterials fabricated by Laser Powder Bed Fusion (LPBF). The morphology of the AlSi10Mg metamaterials was examined using an ultrahigh-resolution microscope. Quasi-static uniaxial compression tests were conducted at room temperature, with deformation behavior captured through camera recordings. The findings indicate that the proposed gradient metamaterial exhibits superior compressive strength properties and energy absorption capacity. The Gradient-SplitP structure demonstrated better compressive performance compared to other strut-based structures, including Gradient-Gyroid and Gradient-Lidinoid structures. With an apparent density of 0.796, the Gradient-SplitP structure exhibited an outstanding energy absorption capacity, reaching an impressive 23.57 MJ/m3. In addition, heat conductivity tests were performed to assess the thermal resistance of these structures with different cell configurations. The gradient metamaterials exhibited higher thermal resistance and lower thermal conductivity. Consequently, the designed gradient metamaterials can be considered valuable in various applications, such as thermal management, load-bearing, and energy absorption components.

Reset transition in HfO2-Based memristors using a constant power signal

Memristors, also known as resistive switching devices, have great potential for applications in memory and neuromorphic systems. Understanding the switching mechanisms is crucial since ReRAM memories need to operate at high frequencies. It is known the reset transition is dominated by the conductive filament Joule heating. We have studied the reset transition in TiN/Ti/HfO2/W metal–insulator–metal memristors by applying constant power signals to different initial filament thicknesses, which were obtained using different initial low resistance states. The results show that power value controls the reset times, decreasing when the power is increased. On the other hand, larger resistances lead to faster reset transitions. These measurements have allowed us to obtain a value of the thermal resistance of the conductive filament. Moreover, we have observed the reset times as a function of the initial resistance and the power lies on a common plane, which allows us to estimate the transition time by fixing an initial resistance and a power value.

Facilitating the Production of 3D-Printed Spare Parts in the Design of Plastic Parts: A Design Requirement Review

Using additive manufacturing for spare part production can ensure that spare parts are available for a long time. However, spare parts are currently not designed for additive manufacturing. This study aimed to find how the production of 3D-printed spare parts can be facilitated in the design of plastic parts. We used a literature review and illustrative case to find how the design requirements for standard injection moulded plastic parts relate to the manufacturing capabilities of additive manufacturing for spare parts. The design requirements were defined by assigning corresponding structural and material properties. These requirements were then used to construct and evaluate the capabilities of additive manufacturing compared to injection moulding. It was found that additive manufacturing is especially suitable for requirements like Accuracy, Heat resistance, and Chemical resistance. However, to fully enable 3D-printed spare parts, certain design challenges still need to be tackled. Designers should pay careful attention to the synergies and trade-offs between design requirements and the challenges that might arise from the combination of certain requirements. Also, designers should ensure products are easily reparable before considering 3D-printed spare parts. If we target these challenges in the design phase, we can facilitate 3D-printed spare parts that enable product repairability.

Heat transfer of mid-deep ground source heat pump for crude oil gathering and transportation

Wax precipitation in crude oil gathering and transportation (COG&T) causes substantial decrease in oil flowability and thus blockages of pipelines, presenting high safety risks and dramatic economic loss. Conventional oil/gas blending and low-temperature transport are inefficient and energy-intensive. Geothermal energy released from abandoned oil wells may be used as renewable heat source, but remains unexplored. This study focused on feasibility of utilizing geothermal energy from abandoned oil wells by mid-deep ground source heat pump (MD-GSHP), so as to alleviate wax precipitation for short-distance COG&T. Numerical models of ground heat exchanger (GHE) were established by using finite difference method (FDM) based on validation of engineered examples. The results demonstrated that, to enhance geothermal extraction, it was essential to increase fluid flow rate, lower inlet temperature, use materials with high thermal resistance, and optimize the pipe dimensions. Additionally, the impacts of operational parameters of GHE and COG&T subsystems on MD-GSHP system performances were also analyzed. Increasing inlet temperature by 8 °C resulted in 39.5 % reduction in system load and 89.4 % increase in coefficient of performance (COP). This study provides a proof-in-concept demonstration for extracting geothermal energy from abandoned wells by MD-GSHP to mitigate wax precipitation in COG&T project.

Effects of yeast β-glucan on gelatinization, structure and digestibility of potato starch.

Potato starch (PS) is widely used in food, but its application is limited because of its poor heat resistance and easy aging. Therefore, it is necessary to adopt some modification methods to improve its performance and expand its application range. To improve these shortcomings of PS, the effect of yeast β-glucan (YG) at different concentrations (0%, 1%, 2% and 3%, w/v) on the gelatinization, structure and in vitro digestive properties of PS were investigated. The interaction of YG with PS was different because of different molecular weights. The addition of YG reduced the peak viscosity and increased the final viscosity of PS. YG made the texture of PS gel softer, and the effect of low molecular weight YG was more obvious. YG enhanced the thermal stability of PS. Fourier transform infrared spectroscopy showed that YG and PS interacted through hydrogen bonds. In addition, YG reduced the digestibility of PS in vitro. Collectively, the addition of β-glucan to PS can serve as a new approach to enhance the technological properties of PS in food applications. These results will provide theoretical basis for PS to develop into functional food. © 2024 Society of Chemical Industry.