Thermal Conduction Losses Research Articles

Advanced three-dimensional textile technique for fabrication of sisal/flax hybrid fiber green biocomposite with enhanced mechanical, thermal, and sound isolation properties

Natural fibers are regarded as ideal reinforcements for fiber-reinforced composites due to their high specific strength and biodegradability. In this study, three-dimensional orthogonal woven sisal/flax yarn hybrid bio-based epoxy resin composites (3DOWSBCs) were firstly employing a novel three-dimensional orthogonal weaving technique, and their mechanical properties were experimentally examined, and compared with those of traditional lamination composites. Secondly, a finite element model (FEM) was constructed to predict and analyze the shear behaviors of 3DOWSBCs in order to elucidate the strengthening mechanisms of Z-yarns. Additionally, the thermal and acoustic properties also discussed. The results suggested that the flexural strength and shear strength of 3DOWSBCs (141.15 MPa, 22.80 MPa) were 37.9 % and 86.9 % higher than the laminates, respectively. The FEM results demonstrated a strong correlation with the experimental data and revealed that the impact of Z-yarns on the mechanical properties in out-of-plane direction was more significant than that in in-plane direction. Furthermore, 3DOWSBCs had low thermal conductivity (0.29 W/m·K) and high sound transmission loss (63 dB). The environmentally friendly and excellent-performance 3DOWSBCs are a promising semi-structural industrial composites with great potential to alleviate energy consumption and promote sustainable industry development.

Transport coefficient sensitivities in a semi-analytic model for magnetized liner inertial fusion

Performance of magnetized liner inertial fusion (MagLIF) experiments is highly dependent on transport processes including magnetized heat flows and magnetic flux losses. Magnetohydrodynamic simulations used to model these experiments require a choice of model for the transport coefficients, which are the constants of proportionality relating driving terms, such as temperature gradients and currents, to the associated heat and magnetic field transport. The coefficients have been the subject of repeated recalculation using various methods throughout the years. Using a semi-analytic MagLIF model [McBride and Slutz, Phys. Plasmas 22, 052708 (2015)], we compare models for the transport coefficients provided by Braginskii [Reviews of Plasma Physics, edited by M. A. Leontovich (Consultants Bureau, New York, 1965), Vol. 1, p. 205], Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], Ji and Held [Phys. Plasmas 20, 042114 (2013)], Davies et al. [Phys. Plasmas 28, 012305 (2021)], and Sadler et al. [Phys. Rev. Lett. 126, 075001 (2021)]. The choice of model modifies magnetic-flux losses caused by the Nernst thermoelectric effect and thermal conduction losses. We present simulated results from parameter scans conducted in order to compare the effects of the different models on parameters of interest in MagLIF. In some regions of parameter space, discrepancies of up to 38% are found in integrated quantities like the fusion yield. These results may serve as a guide for experimental validation of the various models, particularly as laser preheat energies and initial axial field strengths are increased on MagLIF experiments.

A new proposal to reduce microplastics from cigarette butts: Production of eco-friendly fired clay bricks

It is estimated that approximately 1.2 million tons of cigarette butts (CBs) are introduced into the environment annually. The aim of this work is to analyze the incorporation of shredded CBs into bricks making by extrusion, for recycling and waste recovery purposes. Samples were prepared in compositions of 0 %, 1 %, 2.5 % and 5 % w/w CBs and fired at 700 ºC, 900 ºC and 1000 ºC. Density, water absorption, apparent porosity, linear firing shrinkage, flexural strength, compressive strength, thermal conductivity, diffusivity and sound transmission loss (TL) were determined. A total of 180 samples were taken, and a Weibull statistical analysis was performed for compressive strength. The results showed a decrease in density and an increase in water absorption and apparent porosity of the clay bricks produced by mixing 1–5 % CBs compared to the control bricks. Firing shrinkage decreased with 1 % CBs and up to 2.5 %, its was lower than standard samples. Samples with CBs showed fewer cracks than standard samples. Compressive strength increased with 1 % CBs incorporation for firing temperatures of 900ºC and 1000ºC compared to standard samples. It gradually decreased with larger amounts of waste. For flexural strength, up to 2.5 % CBs, the strength increased in most cases. In addition, there was an improvement in the thermal conductivity of bricks prepared with 5 % CBs and fired at 700ºC and 900ºC (0.46–0.58 W/mK) compared to the reference samples (0.51–0.76 W/mK). All waste samples showed higher TL than the reference pieces. Above 2.5 % CBs, TL decreased, but remained larger than the reference. Thus, the results showed that the use of CBs in fired clay bricks in amounts of up to 5 % w/w is capable of forming porosity in the samples, making the part lighter, in addition to possibly reducing thermal conductivity and sound transmission, being an economical and sustainable alternative for the final disposal of CBs.

Attaining material circularity in recycled construction waste to produce sustainable concrete blocks for residential building applications

Construction waste poses a major environmental problem owing to traditional building methods, resulting in a huge global waste burden that ultimately ends up in landfills. The development of sustainable methods is necessary not only to reduce environmental problems but also to encourage material circularity and promote the effective recycling and reuse of construction waste. Yet, previous research has largely focused on using recycled construction waste as a single or double additive ingredient. However, this study aims to assess the development of sustainable concrete blocks for residential building applications with a novel blend of two or more waste ingredients, with each additive contributing to a specific characteristic. Physical properties (bulk density, porosity, water absorption, thermal conductivity, compressive strength, fire resistance, and mass loss), cost, and CO2 emissions were determined to evaluate the efficiency of the block. Subsequently, the energy savings were assessed using block samples as single-layer building envelopes within a full-scale room simulated using EnergyPlus. The results showed a reduction in density of up to 24.32 %, and thermal conductivity and heat transfer of up to 56.8 % compared to typical blocks, which satisfied the compressive strength requirements of load- and non-load-bearing walls. The sustainability assessment revealed that the developed concrete blocks could significantly lower production costs by up to 31.75 % and reduce carbon emissions by up to 27.15 % compared to typical concrete blocks. It was found that the best single-layer building envelope in a full-scale residential room improved energy efficiency by up to 9.17 % when the produced blocks were used. This enhancement could lower the cost of energy consumption from 88.34 to 80.24 kWh/m2/year. This research contributes to the utilization of circular building blocks, which reduce the need for typical raw materials while improving their functional properties and lowering the production cost, carbon emissions, and energy consumption in a single-layer residential building.

Highly Anisotropic Thermally Conductive Dielectric Polymer/Boron Nitride Nanotube Composites for Directional Heat Dissipation.

An ideal dielectric material for microelectronic devices requires a combination of high anisotropic thermal conductivity and low dielectric constant (ɛ') and loss (tan δ). Polymer composites of boron nitride nanotubes (BNNTs), which offer excellent thermal and dielectric properties, show promise for developing these dielectric polymer composites. Herein, a simple method for fabricating polymer/BNNT composites with high directional thermal conductivity and excellent dielectric properties is presented. The nanocomposites with directionally aligned BNNTs are fabricated through melt-compounding and in situ fibrillation, followed by sintering the fibrous nanocomposites. The fabricated nanocomposites show a significant enhancement in thermal properties, with an in-plane thermal conductivity (K‖) of 1.8 Wm-1K-1-a 450% increase-yielding a high anisotropy ratio (K‖/K⊥) of 36, a 1700% improvement over isotropic samples containing only 7.2 vol% BNNT. These samples exhibit a 120% faster in-plane heat dissipation compared to the through-plane within 2 s. Additionally, they display low ɛ'of ≈3.2 and extremely low tan δ of ≈0.014 at 1kHz. These results indicate that this method provides a new avenue for designing and creating polymer composites with enhanced directional heat dissipation properties along with high K‖, suitable for thermal management applications in electronic packaging, thermal interface materials, and passive cooling systems.

Rapid preparation of Si3N4 ceramics with high thermal conductivity and low dielectric loss by fast hot-pressing (FHP) sintering

A series of Si3N4 ceramics with MgO and Y2O3 as sintering additives were successfully prepared by fast hot-pressing (FHP) sintering at the sintering temperature of 1700 °C, with the hold time of only 10 min and the whole sintering process of 36 min. The sintering behavior, densification process, microstructure, crystalline phase composition, bond composition, thermal conductivity and dielectric properties were systematically investigated. FHP reduces the sintering temperature and sintering time of Si3N4 ceramic compared to traditional solid-state method. The results of a series of tests have shown that the densification of Si3N4 ceramics and the phase transition from α-Si3N4 to β-Si3N4 can be facilitated by appropriate levels of additives, resulting in a dense, homogeneous and non-porous microstructure. Additionally, based on test results in this work, Si3N4 -4 wt.% Y2O3 -2 wt.% MgO exhibit the highest thermal conductivity of 78.16 W/mK, the dielectric constant of 8.50 and the dielectric loss of 5.52 × 10−4. The Si3N4 ceramics investigated in this work exhibit excellent properties for use of power semiconductor device packages, microwave devices, and power electronics. And also demonstrate the potential of FHP in laying the foundation for the further preparation of higher performance Si3N4 ceramics.

High thermal conductivity and low dielectric loss of three-dimensional boron nitride nanosheets/epoxy composites

Electronic power devices are moving towards high frequency, high integration, and high power, which urgently needs to develop high thermal conductive encapsulating insulation materials to improve the heat dissipation of electronic devices. Herein, we propose to modify the commercialized encapsulating materials of epoxy resin (EP) by incorporating three-dimensional hydroxylated boron nitride nanosheets (3D-BNNSs). The cryogel and vacuum freeze-drying techniques are employed to prepare the 3D-BNNSs using agarose. The results show that the constructed high thermal conductive structure of 3D-BNNSs can effectively enhance the thermal conductivity of EP and reduce the interfacial thermal resistance between BNNSs fillers. The thermal conductivity of 3D-BNNSs/EP composites with 33.03 wt% BNNSs reach 2.54 W/(m·K), which is 13.11 times higher than that of EP (0.18 W/(m·K)). Meanwhile, the resultant composites remain outstanding electrical insulation and dielectric properties. Because agarose contains numerous hydroxyl groups that can form hydrogen bonds with the hydroxyl groups on the surface-functionalized BNNSs, hydrogen bonding can lead to strong intermolecular interactions, which is conductive to accelarate phonon transport. Additionally, agarose can cross-link with the molecular chains of epoxy, impeding the movement of molecular chain segments and resulting in composites with low dielectric loss at high frequencies. This study demonstrates that the 3D-BNNSs/EP composites have great potential for application in thermal management of electronic components.

Thermal conductivity loss in WC-Co hard metal due to high-temperature cyclic loading damage as a function of microstructure and temperature

Many structures made of WC-Co hard metal are subject to thermo-mechanical loading and have to conduct heat in order to function properly in industrial application. The current work provides results on a significant drop in thermal conductivity of WC-Co hard metals as a function of material volume damage that accumulates during cyclic high-temperature loading of the materials depending on material microstructure. Average WC grain size and Co binder metal content of the investigated grades ranged from submicron to medium and from 10 to 12 wt%, respectively. The hard metals were subjected to uniaxial cyclic loading in a vacuum for different numbers of load cycles at 700 °C and 800 °C. Damage features accumulated in the material volume were documented by means of scanning electron microscopy. Thermal conductivity properties of virgin and damaged materials were determined via laser flash analysis. The results indicated a significant decrease depending on the materials' microstructure, i.e. the defects' predominant location within the microstructure. The damage features that occurred mainly between WC grains in the coarser-grained grade led to larger drops in thermal conductivity with rising temperature compared to damage features that occurred within the Co binder metal in the finer-grained grade. The presented results are of high relevance to the thermo-mechanical load situation of e.g. milling tools since the heat conduction away from their cutting edges is hindered by the documented effect and deemed to lead to a self-acceleration of the damage accumulation.

Ultra-low dielectric loss and high thermal conductivity of PTFE composites improved by schistose and globular alumina

Polytetrafluoroethylene (PTFE) based microwave dielectric composite has been widely used because of its adjustable dielectric constant and low dielectric loss, but its low thermal conductivity can not meet the heat dissipation requirements of high-power microwave devices. Therefore, it is of great significance to develop microwave dielectric composites with high thermal conductivity and low loss. In order to obtain microwave composite materials with high thermal conductivity and low losses, schistose Al2O3/PTFE (S-A/PTFE) composites and globular Al2O3/PTFE (G-A/PTFE) composites were successfully prepared. It is compared whether S-A can combine with PTFE more fully than G-A, which can promote the dielectric properties and thermal conductivity of Al2O3/PTFE composites. Surprisingly, the S-A/PTFE composites demonstrate higher thermal conductivity, lower thermal expansion and hygroscopic properties. The S-A/PTFE composites can deliver a high thermal conductivity of 0.986 W/m K. Composite substrates with 53 wt% S-A filler exhibits excellent performance, which specifically show credible dielectric constant (εr = 4.01) and admissible dielectric loss (tanδ = 0.0014 at 10 GHz). Furthermore, the composite substrate shows a similar thermal expansion coefficient to copper, and lower water absorption rate (0.05 %). The relationship between dielectric constant of composite and filler was predicted by different theoretical modeling methods.

Flexible Janus Black Silicon Photothermal Conversion Membranes for Highly Efficient Solar-Driven Interfacial Water Purification.

Photothermal conversion materials are critical in the development of solar-driven interfacial evaporation techniques; however, achieving a high energy conversion efficiency remains challenging owing to the high cost and instability of light-absorbing materials, in addition to the difficulties of simultaneously improving light absorption while suppressing heat loss. A black silicon (Si) powder with a porous structure was prepared by chemical etching of a low-cost commercial micron-sized Al-Si alloy, and a flexible Janus black Si photothermal conversion membrane was constructed. The partially broken spherical particles and porous structure obtained after etching enhanced the refraction of light from the Si powder, imparting the prepared membrane with an average light absorption rate of 95.95% over the solar spectrum. Evaporation from the membrane increased the intermediate water content and reduced the equivalent evaporation enthalpy. The thermal conduction loss was inhibited through a one-dimensional water transport structure, and the membrane achieved a water evaporation rate of 2.17 kg m-2 h-1 and a photothermal efficiency of 94.95% under 1 sun illumination. Benefiting from the broadband absorption and high photothermal efficiency of black Si powder, surface modification of hydrophobic polydimethylsiloxane, and directional salt-out structure design, the evaporation rate of the Janus black Si membrane-based system in a 10% NaCl solution was maintained >2.10 kg m-2 h-1 after 7 days of continuous evaporation cycles. The removal rate of metal ions from simulated seawater and from practical wastewater containing complex heavy metals reached >99.9%, indicating the promising potential of black Si membrane for application in solar-driven interfacial water purification.

In-situ exfoliation of hexagonal boron nitride during the forced flow of highly elastic polylactide to fabricate electrospun fibrous film with high thermal conductivity and low dielectric loss

Boron nitride nanosheets (BNNS) have promising applications in thermal management materials, due to their high thermal conductivity and low dielectric loss. However, it is still challenging to fabricate BNNS with large lateral size and structural integrity via solvent-free methods. Here, we report a novel processing method for in-situ exfoliation of hexagonal boron nitride (h-BN) to fabricate BNNS with an average lateral size of 1.45 μm, average thickness of 4.88 nm and few lattice defects during the forced flow of polylactide (PLA) in a highly elastic state. We further fabricate flexible and bio-degradable PLA/BNNS electrospun fibrous film for electronic devices to replace petroleum-based composites. The PLA/BNNS fibrous film exhibits an in-plane thermal conductivity of 4.9 W/(m·K) at the BNNS loading of 20 wt%. Moreover, the fibrous film also has a low dielectric loss (0.007 at 1 kHz) and good electrical insulation. The in-situ exfoliation strategy is simple, economical and environmentally friendly, providing an effective route to design thermal management materials with high thermal conductivity and low dielectric loss in the future of electronic devices.

Regulating surface energy and establishing covalent bonds to enhance interface interaction between m‐BN and polyphenylene oxide for 5G applications

AbstractIncorporation of boron nitride (BN) into polymers is a promising method to obtain composites with high thermal conductivity, low dielectric constant (Dk), and dielectric loss (Df), while the practical applications are limited by the poor interface between BN and polymer because of surface energy mismatch and absence of covalent bond connection between them. Herein, polydopamine (PDA) with good adhesion is deposited onto the BN. Then, a different amount of silane coupling agent containing vinyl reactive groups is grafted onto PDA‐coated BN. In this way, the surface energy of modified BN (m‐BN) can be adjusted to ensure BN contacts well with polymers. Moreover, reactive groups were introduced on BN for further reaction. Subsequently, covalent bonds between the m‐BN and the polyphenylene oxide (PPO) were established in situ during the curing process. The effects of the m‐BN surface energy on interface quality and thermal conductivity of composites are investigated. The m‐BN/PPO composite achieves a through‐plane thermal conductivity of 5.87 W/m·K and a low Df value of 1.53 × 10−3, as well as a low coefficient of thermal expansion (CTE) value (7.8 ppm/K) when the m‐BN loading is 32.6 vol%. This research provides a simple and efficient strategy for fabricating high‐performance composites for high‐frequency applications.Highlights Hexagonal boron nitride was modified successfully by combining non‐covalent and covalent modifications. Regulating surface energy and establishing covalent bonds enhances interface interaction between BN and polyphenylene oxide. Modified BN/polyphenylene oxide composites display improvements in thermal conductivity and dimensional stability as well as dielectric loss. Provides a feasible strategy for designing polymer composites with high thermal conductivity, dimensional stability, and low dielectric loss for 5G applications.

Acoustical, vibrational, and thermal investigations of pyrolytic carbon black reinforced natural rubber composites

The present study aims to utilize the carbonaceous filler (pyrolytic carbon black (PCB)) obtained from tire waste to fabricate composites for thermal, vibrational, and acoustical applications. Four composites were fabricated by increasing the PCB content (0, 10, 20, and 30 parts per hundred rubber (phr)) in the natural rubber (NR) matrix following ASTM D3182-21a standard. The optimum curing time was determined using a Moving Die Rheometer based on the ASTM D2084-19 standard. The physical, functional, microstructural, wettability, thermal, and mechanical properties of fabricated NR/PCB composites were comprehensively examined. Further, from an application standpoint, the study influence of increasing PCB content in a polymer matrix on thermal conductivity (TC), vibration damping, and sound transmission loss (STL) of the fabricated NR/PCB composites was investigated following ASTM E1530-19, ASTM E756-05, and ASTM E2611-17 standards, respectively. The study results indicate significant enhancement in the properties of the composites with increased PCB content. Specifically, the reinforcement of 30 phr of PCB in the polymer matrix led to a notable increase in TC (at 40 °C) by approximately 21.16% compared to NR/PCB0 composite. Also, the configuration mild steel (MS) + NR/PCB30 achieved the highest damping ratio, measuring 6.56 at the third vibration mode. Moreover, the average STL value of the NR/PCB30 composite showed a notable improvement of approximately 17.19% when compared to the NR/PCB0 composite, underscoring the effectiveness of PCB in enhancing the desired properties of the NR-based composites.

Parâmetros térmicos do UHPC em situação de incêndio: uma abordagem à norma brasileira ABNT NBR 15200

Abstract Ultra-high-performance concrete (UHPC) has exceptional mechanical properties at room temperature. However, there are no standardized thermal procedures proposed by ABNT NBR 15200 to characterize UHPC at high temperatures, such as in the case of fire. This is due to the lack of research on the subject, leaving gaps for experimental and numerical investigations. Based on experimental analyzes on standardized, small-scale specimens, this research collects a set of parametric data for UHPC at high temperatures. Thermal diffusivity, thermal conductivity, thermal expansion and specific heat as thermal parameters were defined for different temperature ranges. The results were compared with other structural concretes proposed in the literature (NSC, HSC and UHSC). The UHPC exhibited a particular fire behavior. Compared to NSC, HSC and UHSC, the thermal expansion and mechanical parameters of UHPC are less affected at high temperatures, but its thermal conductivity and mass loss are higher. UHPC also has the highest specific heat compared to other concretes. The thermal field of UHPC tends to be higher compared to the other concretes.

Experimental investigations on heat transfer enhancement in a double pipe heat exchanger using hybrid nanofluids

Abstract Heat exchanger (HE) is an instrument that facilitates the operation of HE between two fluids that are at various temperatures. Double-pipe HEs are used in many organizations because of their low installation, design, maintenance costs, flexibility, and their suitability for high pressure applications. Heat transfer (HT) augmentation techniques (passive, active or compound techniques) are used in heat exchangers to reduce the HT surface area, to increase HT capacity and to reduce pumping power. Passive augmentation techniques are much cheaper and do not involve any external power input. They aim to improve the effective surface area, the residence time of the HT fluid and its thermal conductivity by the usage of nanofluids. Nanofluids are used for cooling applications in organizations, transportation, nuclear reactors, electrical and electronic devices and for biomedical applications. Hybrid nanofluids have higher thermal conductivity, low PD and frictional losses and pumping power as compared to the mono nanofluids. In this present work, experiments are conducted in a double pipe HE using TiO2, and SiC-water nanofluids by varying the volume concentration and cold fluid mass flow rate ranging from 17.5 to 34.5 lpm by making constant hot fluid mass flow rate. Further, experiments are conducted using TiO2–SiC/water hybrid nanofluids. Influence of nano and hybrid nanofluids on the overall HTC and friction factor are experimentally investigated. From the experiments, TiO2–SiC/water hybrid nanofluid with nanoparticle ratio TiO2:SiC = 1:2 is found to be optimum as the heat transfer enhancement is more with less improvement in friction factor. The overall heat transfer, and friction factor enhancement is 22.92 %, and 11.20 % higher respectively when compared with base fluid for TiO2:SiC = 1:2.

Preparation and properties of branch‐leaf‐like polyimide composite films with high thermal conductivity and low dielectric loss

AbstractPolyimide (PI) is widely used in the communication field benefited from its low dielectric properties and good electrical insulating properties, however, its low thermal conductivity simultaneously limits its application in electronic packaging. Delayed heat dissipation can exacerbate the thermal stress generated by device operation to damage electronic structures, thereby affecting work efficiency. As a result, it is necessary to improve the thermal conductivity of polyimide and maintain excellent dielectric performance. Here, we demonstrate the polyimide (BPDA‐ODA) composites with ordered structure are prepared by filling commercial polyimides with aramid nanofibers connection nitrides greatly improve thermal conductivity and maintain the low dielectric loss. When the filling amount of SBN@CN is 30 wt%, the thermal conductivity increases to 1.162 W/mK, which is 8 times higher than that of pure PI (0.0147 W/mK). Moreover, thermal stability and mechanical properties are maintained, realizing that the dielectric constant is about 3.81 and the dielectric loss is as low as 0.0034 at 100 MHz, which endows a new insight for the application of polyimide in electronic packaging.

Isotope dependence of transport in ST40 hot ion mode plasmas

The ST40 compact, high-field spherical tokamak, operating at 2.1 T and with 1.8 MW of neutral beam heating, achieved central carbon impurity ion temperatures in excess of 10 keV, surpassing their business milestone of 100 M ∘C (8.6 keV). The high temperature discharges were in the hot ion mode, with , and they were achieved in both hydrogen and deuterium plasmas with deuterium neutral beam injection. In order to achieve the high temperature scenarios, careful wall conditioning and scenario optimization was carried out in , , and finally in plasmas. The TRANSP transport code was employed to study the dependence of confinement and transport on isotopic mass, and the conditions that led to the high measured central ion temperatures in the and plasmas. The kinetic profiles input into TRANSP were inferred from line-of-sight and limited radial measurements as well as consistency with a number of other experimental constraints. The TRANSP results first showed that the main species central ion temperature was only 0.5–1 keV lower than the measured carbon impurity temperature, and thus in the high performance plasmas also surpassed the 100 M ∘C level. TRANSP also showed that while the electron thermal conduction loss was dominant, reductions in central ion transport, and an effective decoupling of the ions from the electrons, led to an increase in central ion temperatures with increasing plasma mass. In fact, the associated confinement times exhibited a strong dependence on the isotopic mass of the thermal plasma. These preliminary results are foundations for dedicated experiments with full kinetic profile measurements on ST40 in the next run campaign.

Proposition of parametric data for UHPC at high temperatures

Ultra-high-performance concrete (UHPC) has exceptional mechanical properties at room temperature. However, its fire behavior is not well known. There are no standardized procedures for characterizing UHPC at high temperatures. This is due to the lack of research on the subject and leaves gaps for experimental and numerical investigations. This study collects a set of parametric data of UHPC at high temperatures. Thermal diffusivity, thermal conductivity and specific heat as thermal parameters, compressive strength and elastic modulus as mechanical and thermal strain and density as physical parameters were defined for different temperature ranges. The results were compared with other structural concretes (NSC, HSC and UHSC) proposed in the literature. The UHPC exhibited a particular fire behavior. Compared to NSC, HSC and UHSC, the thermal expansion and mechanical parameters of UHPC are less affected in fire, but its thermal conductivity and mass loss are higher. UHPC also has the highest specific heat compared to other concretes. When compared to the others, UHPC has a higher thermal field. A FEA-numerical analysis was made using Abaqus software to compare the thermal fields of UHPC and NSC cross-sections in order to demonstrate and apply the equations supplied in this research.

Analysis of heat transfer characteristics of a sandwich cylindrical shell with a metal-rubber core

This work aims to analyze the heat transfer characteristics of a sandwich cylindrical shell with a metal-rubber core (SCS-MR) using both finite element analysis and experimental techniques. The SCS-MR is a lightweight and high-temperature resistant material that is suitable for construction in environments with varying conditions, such as rocket launchers, aircraft injectors and ships. The heat transfer, heat flux, and thermal convection loss were first analyzed using thermal resistance and Fourier law. Subsequently, a representative volume element of the SCS-MR was established to simulate thermal transfer, followed by a series of comparative experiments that measured the temperature gradients, the boundary conditions, and the density of the SCS-MR. Additionally, three types of metal spirals were examined using differential scanning calorimeter (DSC). The convective thermal conductivity, heat flux, and heat convection loss of the SCS-MR were analyzed experimentally, revealing that the metal spiral exhibited an exothermic peak in the DSC. Furthermore, the heat transfer rate of the SCS-MR was faster than that of the solid cylindrical shell (CS) when the set temperature was reached. The insulation cover was capable of providing boundary conditions to minimize the impact of natural convection. In the high-temperature environment, the thermal conductivity decreased with increasing density of the scaled model SCS-MR.

Ultrafast microwave heated form-stable thermal package providing operating temperature for PEO all-solid-state batteries

All-solid-state batteries (ASSBs) have been regarded as satisfying future energy storage devices owing to the advantages of notably high energy density and outstanding safety. However, their attainable energy density, especially in poly(ethylene oxide) (PEO)-based ASSBs, is limited by low operating ambient temperature due to sluggish lithium-ion transport of solid electrolyte. Herein, a functional anti-leakage skeleton (alumina ceramic and boron nitride) with efficient graphene-modified phase change material (GPCM) and microwave thermal energy storage system is proposed for providing the operating temperature of ASSBs. The composite, prepared by alumina ceramic fiber, boron nitride, and GPCM, presenting excellent thermal properties such as great enhancement of thermal conductivity (64.6%) and low enthalpy loss (11.27%). The superior thermal effect is confirmed by experiments and simulations of microwave absorption. Through microwave irradiating the ASSBs wrapped with the composite, ASSBs can realize cold-starting in 1 min from room temperature in a fast, safe and low-power heating pathway. Significantly, the combination of multi-scale characteristics in graphene increases the thermal energy generated by the composite during microwave processing. Furthermore, the composite material (GPBC), used as portable auxiliary heating equipment, enables the ASSB to exhibit 92% capacity of those ASSBs placed in 55 °C ovens at 1C. This work provides a distinctive route to achieve efficient and extensive applications of ASSBs through external preheating.