Solid Conductivity Research Articles

Origin of Intrinsically Low Lattice Thermal Conductivity in Solids.

Reducing lattice thermal conductivity through external modulation techniques such as defect engineering may potentially interfere with electronic transport. Materials with intrinsically low lattice thermal conductivity have the potential to decouple the control of lattice heat transport and electronic transport, which is of great significance in the field of thermoelectric energy conversion. This paper reviews the origin of intrinsically low lattice thermal conductivity, which is directly related to three physical quantities (heat capacity, phonon group velocity, and phonon relaxation time) and is ultimately reflected in the lattice structure and bonding characteristics. An understanding of the fundamental nature of low lattice thermal conductivity can aid in guiding experimental design and theoretically enabling high-throughput prediction of novel low lattice thermal conductivity materials according to the intrinsic properties.

Phonon polariton-mediated heat conduction: Perspectives from recent progress

AbstractIt has been well-accepted that heat conduction in solids is mainly mediated by electrons and phonons. Recently, there has been a strong emerging interest in the contribution of various polaritons, quasi-particles resulting from the coupling between electromagnetic waves and different excitations in solids, to heat conduction. Traditionally, the polaritonic effect on conduction has been largely neglected because of the low number density of polaritons. However, it has been recently predicted and experimentally confirmed that polaritons could play significant roles in heat conduction in polar nanostructures. Since the transport characteristics of polaritons are very different from those of electrons and phonons, polariton-mediated heat conduction provides new opportunities for manipulating heat flow in solid-state devices for more efficient heat dissipation or energy conversion. In view of the rapid growth of polariton-mediated heat conduction, especially by phonon polaritons, here we review the recent progress in this field and provide perspectives for challenges and opportunities. Graphical abstract

Refined prediction of thermal transport performance in amorphous silica

Thermal transport in amorphous silica (a-SiO2) and silica aerogel is critically important for thermal protection and microelectronics applications. However, notable disparities exist between the predicted and measured thermal conductivity of a-SiO2. Inspired by the dual-phonon theory proposed by Luo et al. [Nat. Commun. 2020, 11, 2554] for crystalline materials, this work introduces a dual-diffuson transport method for amorphous materials. The criterion based on the thermal diffusivity is employed to differentiate between normal diffusons and phonon-like diffusons. Herein, the thermal conductivity of a-SiO2 is investigated by combining a modified Allen-Feldman (AF) theory with the dual-diffuson transport method. The present method is validated well by the measurement using the transient plane source (TPS) method. In addition, the results indicate that normal diffusons primarily govern the thermal transport in a-SiO2, with only a minor contribution from phonon-like diffusons. The temperature dependence of specific heat capacity and mode linewidth contributes to the positive temperature-dependent thermal conductivity. The quantum effect of specific heat capacity is the primary influencing factor in the temperature range of 100–1000 K, while the mode linewidth becomes dominant at higher temperatures. Finally, a theoretical framework for predicting the solid thermal conductivity of silica aerogel is introduced by including the temperature effect on the inherent thermophysical properties of the backbone. This work uncovers the physical mechanisms underlying temperature-dependent thermal transport in a-SiO2 and silica aerogels.

Multi-physics simulation on transient thermal response of inductive power transfer pad

Inductive power transfer is an important technological alternative for charging infrastructure, crucial for accelerating the future adoption of electronic vehicles. The magnetic components of an inductive charging pad generate inevitable thermal losses, which, if not properly managed, can exceed the pad’s safe operating temperature. Accurate simulation of both steady-state and transient thermal responses is thus essential for evaluating the pad’s suitability for real-world applications. None of the state-of-the-art thermal prediction proposals in this field, however, are able to perform long-term transient analyses efficiently while being versatile enough to simulate generic case studies. This paper presents a multi-physics methodology that aims to address this gap. The numerical framework comprises three coupled modules: electromagnetic, fluid dynamics, and solid heat conduction. To solve the issue of time-scale discrepancies, only the latter module was solved as a transient problem, while the remaining were approximated as near steady-state physics, continuously updated at every time step. The appropriateness of the resultant hybrid transient solution was verified with a fully transient solution from an equivalent heat-conjugate problem. Finally, the prediction capability of the proposed method was validated by reproducing the thermal responses of a lab-scale charging pad energized at various excitation levels and ambient conditions, both outside of and flush-embedded inside an asphalt slab. The relative errors between the measured and simulated thermal responses were consistently within 10%, demonstrating that the multi-physics approach was able to accurately simulate the long-duration transient temperature rise and drop of the test pad.

Proton Conduction via Water and Ammonia Coordinated Metal Cationic Species in MOF and MHOF Platforms.

Although metal-organic frameworks (MOFs) and metalo hydrogen-bonded organic frameworks (MHOFs) are designed as promising solid-state proton conductors by incorporating various protonic species intrinsically or extrinsically, design and development of such materials by employing the concept of proton conduction through coordinated polar protic solvent is largely unexplored. Herein, we have constructed two proton-conducting materials having different solvent coordinated metal cationic species: In-H2O-MOF, ({[In(H2O)6][In3(Pzdc)6]·15H2O}n; H2Pzdc: pyrazine-2,3-dicarboxylic acid) with coordinated water molecules from hexaaquaindium cationic species, and MHOF-4, ([{Co(NH3)6}2(2,6-NDS)2(H2O)2]n; 2,6-H2NDS: 2,6-naphthalenedisulfonic acid) with coordinated ammonia from hexaammoniacobalt cationic species. Interestingly, higher proton conductivity was achieved for In-H2O-MOF (1.5 × 10-5 S cm-1) than MHOF-4 (6.3 × 10-6 S cm-1) under the extreme conditions (80 ºC and 95% RH), which could be attributed to enhanced acidity of coordinated water molecules having much lower pKa value than that of coordinated ammonia. Greater charge polarization on hydrogen atoms of In3+-coordinated water molecules than that of Co2+-coordinated ammonia led to the high conductivity of In-H2O-MOF, as evident by quantum chemical studies. Such a comparative study on metal-coordinated protic polar solvents in achieving proton conduction in crystalline solids is yet to be made.

Understanding the impact of flow mechanisms in unsaturated layer on heat transfer near a partially submerged geothermal heat exchanger

Heat transfer near geothermal heat exchangers in the presence of groundwater flow has been extensively studied over the past years. However, previous studies often overlooked the presence of an unsaturated layer in the shallow subsurface soil, or disregarded phase change and fluid flow within this layer. In this study, a comprehensive hydro-thermal model is developed to evaluate heat transfer near a partially submerged geothermal borehole in groundwater flow while incorporating phase change and liquid and vapor flow in the unsaturated layer. The effect of unsaturated soil hydraulic analysis on heat transfer and energy efficiency of the geothermal piles is explored under varying soil permeabilities, air-entry suctions, solid thermal conductivities, and soil types. Consideration of water content variation and unsaturated fluid flow in the model enhances heat injection rate by up to 11.23 % in highly permeable soils. However, in scenarios with higher solid thermal conductivity, or lower air-entry suction values, the heat injection rate reduces by as much as 16.13 % due to unsaturated soil hydraulic analysis. Furthermore, it is found that consideration of unsaturated soil hydraulic analysis is of greater importance in Bonny silt than sandy soil, lowering the heat injection rate by 8.53 % and 2.53 %, respectively.

Effect of Strain Rate on the Structure Properties of Silica Aerogel

Silica aerogel is a versatile material used in adsorption, filtration, and thermal insulation. However, its mechanical strength is a notable weakness, making it prone to damage. This study utilized molecular dynamics simulations to investigate the mechanical properties of aerogels. We compared the simulation results with the data from the experiments. The dimensionless specific surface areas of both are nearly identical at densities below 0.7 g/cm³. We explored the impact of strain rate on aerogel properties. The compression rate had minimal effects on stress and density during uniaxial compression. The specific surface area exhibited an initial increase followed by a decrease with a rising compression rate, peaking at 2 1/ns. Furthermore, we determined the solid thermal conductivity of the aerogel, which was 0.0764 W/(m·K) without strain. The solid thermal conductivity showed little variation with compression rate but was highly sensitive to density. The stretching rate during uniaxial stretching influenced the heat transfer coefficient, density, specific surface area, and stress. However, in the low-strain region (strain < 0.3), the tensile rate had a negligible impact on these performance metrics. This investigation offers a theoretical analysis of the mechanical properties of aerogels, establishing a foundational understanding of their efficient application.

The importance of A-site cation chemistry in superionic halide solid electrolytes

Halide solid electrolytes do not currently display ionic conductivities suitable for high-power all-solid-state batteries. We explore the model system A2ZrCl6 (A = Li, Na, Cu, Ag) to understand the fundamental role that A-site chemistry plays on fast ion transport. Having synthesised the previously unknown Ag2ZrCl6 we reveal high room temperature ionic conductivities in Cu2ZrCl6 and Ag2ZrCl6 of 1 × 10−2 and 4 × 10−3 S cm−1, respectively. We introduce the concept that there are inherent limits to ionic conductivity in solids, where the energy and number of transition states play pivotal roles. Transport that involves multiple coordination changes along the pathway suffer from an intrinsic minimum activation energy. At certain lattice sizes, the energies of different coordinations can become equivalent, leading to lower barriers when a pathway involves a single coordination change. Our models provide a deeper understanding into the optimisation and design criteria for halide superionic conductors.

Modelling the effective thermal conductivity and porosity of an open-cell material using an image-based technique coupled with machine learning

Effective thermal conductivity is considered one of the most important parameters in the characterization of insulating materials. The effective thermal conductivity of open-cell porous materials is influenced by both their microstructure and the types of solid and fluid phases present. Currently, many analytical models are available for predicting the final performance based on material porosity, as well as the thermal conductivity of the solid and fluid phases. However, these procedures have two main drawbacks: difficulty in selecting the correct prediction model and challenges in accurately determining porosity. Moreover, when attempting to measure effective thermal conductivity, strict procedural conditions and defined sample geometries are required, necessitating multiple samples due to variations in porosity from specimen to specimen. The procedure proposed here aims to address these challenges. Utilizing microtomography coupled with 3D virtualization and finite element method simulation, this procedure provides validated results which are then used as a dataset to train a machine-learning model capable of predicting thermal conductivity across a comprehensive range of porosities, solid thermal conductivities and fluid thermal conductivities. Comparative analysis has demonstrated that this procedure is significantly more accurate than conventional analytical models or measurement procedures and it has the potential to be applied to any material.

Transient Shutdown Cooling Simulation of a Gas Turbine Test Rig Configuration Under Ventilated Natural Convection

Abstract A transient simulation of shutdown cooling for a gas turbine test rig configuration under ventilated natural convection has been successfully demonstrated using a coupled aero-thermal approach. Large eddy simulation (LES) and finite element analysis (FEA) were employed for fluid domain computational fluid dynamics (CFD) and solid component thermal conduction simulation, respectively. Coupling between LES and FEA was achieved through a plugin communicator. The buoyancy-induced chimney effect under the axially ventilated natural convection is correctly reproduced. The hotter turbulent flow in the upper part of the annular path and the colder laminar-type air movement in the lower part of the annulus are appropriately captured. The heat transfer features in the annular passage are also faithfully replicated, with heat flux of the inner cylinder reaching its maximum and minimum at the bottom dead centre (BDC) and the top dead centre (TDC), respectively. Agreement with experimental measurements is good in terms of both temperature and heat flux, and the result of the transient simulation for the shutdown cooling is encouraging too. In addition, radiation is simulated in the FEA model based on the usual grey body assumptions and Lambert?s law for the coupled computation. It has been shown that at the high power (HP) condition, the radiation for the inner cylinder is approximately 11% of its convective heat flux counterpart. The importance of radiation is thus clearly revealed even for the present rig test case with a scaled-down temperature setup.

Theoretical analysis of entropy generation in multilayer insulations: A case study of performance optimization of variable density multilayer insulations for liquid hydrogen storage systems

Liquid hydrogen (LH2) is a promising and economical clean energy for achieving global carbon neutrality. Multi-layer insulation (MLI) with high performance is essential for the safe storage and operation of LH2. To perform a better optimization of MLI, the second law of thermodynamics becomes a complement to the first law of thermodynamics. However, very few studies have carried out the optimization of MLI performance through the second law of thermodynamics. For the sake of achieving more efficient optimization of MLI as well as revealing the fundamental indicators limiting the performance of MLI, this paper analyzes the characteristics of entropy generation produced by the solid heat conduction, thermal radiation, and residual gas conduction distributed in the MLI schemes by a validated layer-by-layer model.For a 40-layer MLI arranged with a constant layer density of 20 layers/cm, the first 15 layers near the cold boundary occupy more than 98% of the total entropy generation, providing an effective range of layers for thermodynamic optimization. Besides, an optimization of variable-density MLI (VDMLI) separated into two segments based on the entropy generation minimization is conducted. The optimal VDMLI has substantially lowered the entropy generation from the solid heat conduction but at the cost of increasing the entropy generation from radiation and residual gas conduction. This study provides a reliable optimization method of MLI, which allows the safe storage of clean energy with a low boiling temperature.

Modular MPS3-Based Frameworks for Superionic Conduction of Monovalent and Multivalent Ions.

Next-generation batteries based on more sustainable working ions could offer improved performance, safety, and capacity over lithium-ion batteries while also decreasing the cost. Development of next-generation battery technology using "beyond-Li" mobile ions, especially multivalent ions, is limited due to a lack of understanding of solid state conduction of these ions. Here, we introduce ligand-coordinated ions in MPS3-based (M = Mn, Cd) solid host crystals to simultaneously increase the size of the interlayer spacing, through which the ions can migrate, and screen the charge-dense ions. The ligand-assisted conduction mechanism enables ambient temperature superionic conductivity of various next-generation mobile ions in the electronically insulating MPS3-based solid. Without the coordinating ligands, all of the compounds show little to no ionic conductivity. Pulsed-field gradient nuclear magnetic resonance spectroscopy suggests that the ionic conduction occurs through a hopping mechanism, where the cations are moving between H2O molecules, instead of a vehicular mechanism which has been observed in other hydrated layered solids. This modular system not only facilitates tailoring to different potential applications but also enables us to probe the effect of different host structures, mobile ions, and coordinating ligands on the ionic conductivity. This research highlights the influence of cation charge density, diffusion channel size, and effective charge screening on ligand-assisted solid state ionic conductivity. The insights gained can be applied in the design of other ligand-assisted solid state ionic conductors, which will be especially impactful in realizing solid state multivalent ionic conductors. Additionally, the ion-intercalated MPS3-based frameworks could potentially serve as a universal solid state electrolyte for various next-generation battery chemistries.

Effects of viscous dissipation, temperature dependent thermal conductivity, and local thermal non‐equilibrium on the heat transfer in a porous channel to Casson fluid

AbstractThe current paper deals with viscous dissipation effects in a permeable (or porous) channel filled with non‐Newtonian Casson fluid by considering the local thermal non‐equilibrium (LTNE) model. The dependency of the effective thermal conductivities of the solid and fluid phases on the respective temperatures has been studied along with the spatially varying Biot number. The Brinkman number Casson fluid parameter , thermal conductivity variation parameter , porosity Darcy number , and the ratio of fluid and solid phase thermal conductivities are the main governing parameters. The Darcy–Brinkman model is employed to govern the fluid flow in permeable media and the velocity profile has been obtained analytically. Moreover, the energy equations for both phases along with suitable boundary conditions are derived and solved with the fourth order boundary value solver. The findings of the current study depict that the Nusselt number increases with the increment in Casson fluid parameter and decreases with the increment in Brinkman number and thermal conductivity variation parameter. Overall, the heat transmission between the solid and fluid phases increases with the decrement in Brinkman number and thermal conductivity variation parameter. On the other hand, the heat transmission between both the phases magnifies by increasing the value of Casson fluid parameter.

A Novel Approach to Continuum FE Multiphysics Simulation of Batteries via Heterogeneous Homogenization

Advancements in modern technology necessitate batteries that can be safely charged and discharged at high rates with minimal aging. A promising strategy to achieve these ends is through optimization of porous microstructures of existing electrode materials to promote better electrical and ionic transport without compromising energy density, as has been shown experimentally by introducing laser ablation channels to the electrodes. The present work proposes a microstructure up-scaling methodology that efficiently accounts for material heterogeneity by assigning a porosity field to a continuum scale finite element mesh, effectively homogenizing materials while maintaining the heterogeneous porosity distribution inherent to the original microstructure. Constitutive relationships relating solid electric conductivity and pore tortuosity to local porosity are directly computed from fully resolved anode, cathode, and separator microstructure 3D models and assigned in the continuum as material properties of a finite element mesh. This allows for utilization of the computationally efficient, homogenized Newman model while maintaining dependency on the heterogeneous local porosity. Then, coupled electrochemical-thermal-mechanical-pore pressure finite element simulations are performed on the battery cell model with this heterogeneous porosity field, and associated local variations on transport properties are prescribed as material properties by the precomputed constitutive relationships. Performance metrics and lithium plating potential are compared to the results of simulations of the fully homogenized cell with the same constitutive relationships and to the base case of a fully homogenous cell with typical modelling assumptions applied to porosity dependent constitutive relationships. These comparisons are made both as a means of validating the methodology and to demonstrate the vast differences that arise when simplifying assumptions are used instead of the constitutive relationships of the actual material microstructure. Finally, the methodology is used in its intended optimization application to compare the performance of a typical battery microstructure to a similar porous microstructure with micro holes added via laser ablation. The results indicate that differences in the microstructure of materials with identical average porosities and similar constitutive relationships can have significant differences in both cell performance and aging that would typically be impossible to detect using fully homogeneous continuum modeling. Figure 1

Frequency Analysis of the Loire River water Total Suspended Solid and Electrical Conductivity (Orléans, France)

Frequency Analysis of the Loire River water Total Suspended Solid and Electrical Conductivity (Orléans, France)

Electrocoagulation efficiency probed using electrochemical impedance spectroscopy

Electrocoagulation efficiency probed using electrochemical impedance spectroscopy

Effect of Speed of Rotation and Catheter Shape on Rotation Response of Solid Core Conduction System Pacing Lead

Effect of Speed of Rotation and Catheter Shape on Rotation Response of Solid Core Conduction System Pacing Lead

Transient thermal management of laser systems using Plate-Fin phase change heat Exchangers: Experimental and computational study

To mitigate transient thermal shocks in lasers and reduce thermal stresses caused by temperature fluctuations, the use of phase change materials (PCMs) in thermal management systems is a viable solution. This study proposes an innovative two-dimensional transient heat transfer model specifically designed for plate-fin phase change heat exchangers (PFPCHEs). The model meticulously simulates the complex heat transfer phenomena within the heat exchanger, including fluid convection, solid thermal conduction, and the phase change processes of PCM. The convective heat transfer coefficient between fluid and plate is calculated using the Wieting correlation. An advanced pulse-mode experimental test platform was constructed to validate the model, dynamically monitoring and recording outlet temperatures and heat exchange performance for stringent experimental comparison. The research explores the impact of key operating parameters such as initial temperature, flow rate, and inlet temperature of the cooling cycle on the performance of the heat exchanger, providing valuable design and control strategies for transient thermal management of laser systems. The experimental results confirm that the model accurately predicts the dynamic response characteristics and temperature distribution of PFPCHEs under multi-cycle pulse loads, with 96% of the predictions within a 10% error margin. A significant finding is that the initial temperature has negligible influence on the heat transfer characteristics when it is below the solid phase temperature of the PCM. Moreover, by meticulously adjusting the flow rate and inlet temperature of cooling cycle, it is possible to effectively maintain the stability of the outlet temperature throughout the entire pulse cycle. This is crucial for minimizing temperature fluctuations within the thermal management system and extending the service life of electronic components.

Correcting force error-induced underestimation of lattice thermal conductivity in machine learning molecular dynamics

Machine learned potentials (MLPs) have been widely employed in molecular dynamics simulations to study thermal transport. However, the literature results indicate that MLPs generally underestimate the lattice thermal conductivity (LTC) of typical solids. Here, we quantitatively analyze this underestimation in the context of the neuroevolution potential (NEP), which is a representative MLP that balances efficiency and accuracy. Taking crystalline silicon, gallium arsenide, graphene, and lead telluride as examples, we reveal that the fitting errors in the machine-learned forces against the reference ones are responsible for the underestimated LTC as they constitute external perturbations to the interatomic forces. Since the force errors of a NEP model and the random forces in the Langevin thermostat both follow a Gaussian distribution, we propose an approach to correcting the LTC by intentionally introducing different levels of force noises via the Langevin thermostat and then extrapolating to the limit of zero force error. Excellent agreement with experiments is obtained by using this correction for all the prototypical materials over a wide range of temperatures. Based on spectral analyses, we find that the LTC underestimation mainly arises from increased phonon scatterings in the low-frequency region caused by the random force errors.

Towards the Optimization of Polyurethane Aerogel Properties by Densification: Exploring the Structure–Properties Relationship

The aerogel performance for industrial uses can be tailored using several chemical and physical strategies. The effects of a controlled densification on polyurethane aerogels are herein studied by analyzing their textural, mechanical, sound, optical, and thermal insulating properties. The produced aerogels are uniaxially compressed to different strains (30%–80%) analyzing the consequent changes in the structures and, therefore, final properties. As expected, their mechanical stiffness can be significantly increased by compression (until 55‐fold higher elastic modulus for 80%‐strain), while the light transmittance does not noticeably worsen until it is compressed more than 60%. Additionally, the modifications produced in the heat transfer contributions are analyzed, obtaining the optimum balance between density increase and pore size reduction. The minimum thermal conductivity (14.5%‐reduction) is obtained by compressing the aerogel to 50%‐strain, where the increment in the solid conduction is surpassed by the reduction of the radiative and gas contributions. This strategy avoids tedious chemical modifications in the synthesis procedure to control the final structure of the aerogels, leading to the possibility of carefully adapting their structure and properties through a simple method such as densification. Thus, it allows to obtain aerogels for current and on‐demand applications, which is one of the main challenges in the field.