Thermal Conductivity Of Gases Research Articles

Effective thermal conductivity of LaNi5 powder beds for hydrogen storage: Measurement and theoretical analysis

Accurately measuring and analyzing the effective thermal conductivity of metal hydride beds is critical to design the structure of solid-state hydrogen storage tanks. On the basis of the steady-state radial heat flow method, a measurement cell of effective thermal conductivity was manufactured. The effective thermal conductivities of nonactivated and activated LaNi5 powder beds were measured in helium, nitrogen, and argon atmospheres with the temperature changing from 20 to 60 °C and pressure from 0.1 to 4.0 MPa. Then, the effective thermal conductivities were further analyzed using the Zehner–Schlünder–Damköhler model. Results show that the effective thermal conductivities can be enhanced by increasing gas thermal conductivity, gas pressure, and bed temperature. In addition, the effective thermal conductivities can be accurately predicted using the modified Zehner–Schlünder–Damköhler model considering the Smoluchowski effect (error < ± 5 %). With the use of the modified Zehner–Schlünder–Damköhler model, the contributions of different heat transfer pathways to the entire heat transfer of LaNi5 powder beds were analyzed. Approximately 70 %–91 % of the effective thermal conductivity of LaNi5 powder beds is contributed by the conduction of the particle–gas–particle pathway.

Research on effective thermal conductivity of hollow glass microspheres under vacuum at low temperature

As insulation materials with excellent thermal insulation properties, high robustness, and low maintenance costs, hollow glass microspheres (HGM) are gradually being applied in large liquid hydrogen storage tanks. However, the low-temperature insulation mechanism of HGMs is still unknown, and the insulation effect of HGMs of different types under various conditions has been neglected in recent decades. In this study, an existing theoretical model was improved by considering the gas thermal conductivity equations under various pressure intervals, and an experimental platform was built based on the steady vertical heat flux method to measure the effective thermal conductivities of three commercially available HGM models. The effective thermal conductivities of HGM models K1, T15, and HL20 at 0.1 Pa were 10, 8.9, and 7.6 mW/(m·K), respectively. The values decreased to 2.5, 2.9, and 2.0 mW/(m·K), respectively, when the cold boundary temperature was 90 K. To analyse the effect of the HGM physical parameters and environment on the HGM insulation, the thermal conductivities were calculated using the derived theoretical model. It was found that continuing to reduce the pressure after the ambient pressure reached 10 Pa hardly improved the insulation performances of the HGMs. The radiative heat transfer was very sensitive to temperature changes and jointly dominated the heat transfer with integrated thermal conductivity in the low-temperature region. In summary, HGMs are advanced vacuum-insensitive insulation materials, which have great potential in the field of cryogenic liquid storage and transportation.

Investigation on the flow and thermal properties of fibrous insulation used in thermal batteries at alternative atmosphere and pressure gradient

The accurate prediction of behavior for insulations within thermal battery can be impeded due to the fact that the thermal properties of insulations have not been thoroughly characterized under the complex conditions in which they operate. In this study, an effective and extendible model is developed based on fractal theory and finite element method to predict the flow and thermal properties for fibrous insulations within thermal batteries. Two common fibrous insulations are tested and verified with this model under the operating gas atmosphere of thermal battery. It is found that the predictive permeability and effective thermal conductivity agree well with the existing experimental data. Verification under various gas atmosphere shows that present model can reduce the relative error of existing model by 5.21–17.2 %. The gas contributed thermal conductivity for insulations filled with high thermal conductivity gas is always significant. In addition, under the tested pressure gradients, the deviations of temperature are generally greater than 1.42 % for air, methane and carbon dioxide atmosphere, but less than 0.7 % for hydrogen atmosphere. The high porosity of material, the large or reverse pressure gradient may strongly promote the influence of the energy migration within insulations.

Preparation and application of chromatographic stationary phase based on two-dimensional materials

The stationary phase is the heart of chromatographic separation technology and a critical contributor to the overall separation performance of a chromatographic separation technique. However, traditional silicon-based materials designed for this purpose usually feature complex preparation processes, suboptimal permeability, pronounced mass-transfer resistance, and limited pH-range compatibility. These limitations have spurred ongoing research efforts aimed at developing new chromatographic stationary phases characterized by higher separation efficiency, adaptable selectivity, and a broader scope of applicability. In this context, the scientific community has made significant strides toward the development of new-generation materials suitable for use as chromatographic stationary phases. These materials include carbon-based nanomaterial arrays, carbon quantum dots, and two-dimensional (2D) materials. 2D-materials are characterized by nanometer-scale thicknesses, extensive specific surface areas, distinctive layered structures, and outstanding mechanical properties under standard conditions. Thus, these materials demonstrate excellent utility in various applications, such as electrical and thermal conductivity enhancements, gas storage and separation solutions, membrane separation technologies, and catalysis. Graphene, which is arguably the most popular 2D-material used for chromatographic separation, consists of a 2D-lattice of carbon atoms arranged in a single layer, with a large specific surface area and efficient adsorption properties. Its widespread adoption in research and various industries is a testament to its versatility and effectiveness. In addition to graphene, the scientific community has developed various 2D-materials that mirror the layered structures of graphene, such as boron nitride, transition-metal sulfides, and 2D porous organic frameworks, all of which offer unique advantages. 2D porous organic frameworks, in particular, have received attention because of their nanosheet morphology, one-dimensional pores, and special interlayer forces; thus, these frameworks are considered promising candidate chromatographic stationary phase materials. Such recognition is especially true for 2D-metal organic frameworks (MOFs) and 2D-covalent organic frameworks (COFs), which exhibit low densities, high porosities, and substantial specific surface areas. The modifiability of these materials, in terms of pore size, shape, functional groups, and layer-stacking arrangements allows for excellent separation selectivity, highlighting their promising potential in chromatographic separation. Compared with their three-dimensional counterparts, 2D-MOFs feature a simple pore structure that offers reduced mass-transfer resistance and enhanced column efficiency. These attributes highlight the advantages of 2D-MOF nanosheets as chromatographic stationary phases. Similarly, 2D-COFs, given their high specific surface area and porosity, not only exhibit great thermal stability and chemical tolerance but also support a wide selection of solvents and operational conditions. Therefore, their role in the preparation of chromatographic stationary phases is considered highly promising. This review discusses the latest research developments in 2D porous organic framework materials in the context of gas- and liquid-chromatographic stationary phases. It introduces the synthesis methods for these novel materials, elucidates their retention mechanisms, and describes the applications of other 2D-materials, such as graphene, its derivatives, graphitic carbon nitride, and boron nitride, in chromatography. This review aims to shed light on the promising development prospects and future directions of 2D-materials in the field of chromatographic separation, offering valuable insights into the rational design and application of new 2D-materials in chromatography.

Multi-scale investigation of heat and momentum transfer in packed-bed TES systems up to 800 K

With the rising cost of energy and the advancement of corporate social responsibility, there is a growing interest in addressing the challenge of recovering and storing high-temperature waste heat. Sensible heat storage in packed beds stands out as a cost-effective and seemingly straightforward solution for high-temperature Thermal Energy Storage (TES). Engineering models developed to design low-temperature TES systems were tentatively used to design this new generation of high-temperature systems. Delving into the physics of coupled heat and mass transfer reveals a lack of validation of this approach. This study seeks to establish a comprehensive bottom-up methodology - from the particle scale up to the system level - to provide informed and validated engineering models for the design of high-temperature TES systems. To achieve this goal, we developed a multi-scale numerical model to explore the physics of heat and momentum transfer in packed-bed TES systems. At the microscopic scale (pore/particle), we consider the flow of a compressible high-temperature gas between the particles, coupled to transient heat conduction within the particles, with particular attention given to incorporating accurate temperature-dependent viscosity for the gas phase and thermal conductivity and density for both solid and gas phases. At the macroscopic scale (engineering), we propose a high-temperature extension of state-of-the-art two-equation TES models. The governing equations considered are the volume-average conservation laws for gas-mass, gas-momentum and energy of both phases. The multi-scale strategy is applied to a randomly packed bed of spherical particles generated with the discrete element method (DEM) software LIGGGHTS. Numerical models for both scales were implemented in the Porous material Analysis Toolbox based on OpenFoam (PATO), which is made available in Open Source by NASA. Microscopic scale simulations were used to infer the effective parameters needed to inform the macroscopic model, namely, permeability, Forchheimer coefficient, effective thermal conductivities, and the heat transfer coefficient. The informed macroscopic model reproduces with excellent accuracy the average temperature fields of the physics-based microscopic model. Pore-scale analysis shows highly three-dimensional flow characterized by reverse flow and strong cross-flow in the packed bed system. Moreover, it indicates the coupling between temperature and velocity fields, where a nonuniform velocity field results in uneven temperature distributions across the fluid and the solid spheres within the packed bed, subsequently affecting the macroscopic heat transfer coefficient. The overall strategy is validated by comparison to available experimental data. This bottom-up methodology contributes to the understanding and opens new perspectives for a more precise design and monitoring of high-temperature TES systems.

A layered aerogel composite with silica fibers, SiC nanowires, and silica aerogels ternary networks for thermal insulation at high-temperature

Due to excellent thermal insulation performance at room temperature and ultralow density, silica aerogels are candidates for thermal insulation. However, at high temperatures, the thermal insulation property of silica aerogels decreased greatly caused by transparency to heat radiation. Opacifiers introduced into silica sol can block heat radiation yet destroy the uniformity of aerogels. Herein, we designed and prepared a silica aerogel composite with oriented and layered silica fibers (SFs), SiC nanowires (SiCNWs), and silica aerogels, which were prepared by papermaking, chemical vapor infiltration (CVI), and sol-gel respectively. Firstly, oriented and layered SFs made still air a wall to block heat transfer by the solid phase. Secondly, SiCNWs were grown in situ on the surface of SFs evenly to weave into the network, and the network reduced the gaseous thermal conductivity by dividing cracks in SFs/SiCNWs/SA. Thirdly, SiCNWs weakened the heat transfer by radiation at high temperatures. Therefore, SFs/SiCNWs/SA presented remarkable thermal insulation (0.017 W (m K)–1 at 25 °C, 0.0287 W (m K)–1 at 500 °C, and 0.094 W (m K)–1 at 1000 °C). Besides, SFs/SiCNWs/SA exhibited remarkable thermal stability (no size transform after being heat treated at 1000 °C for 1800 s) and tensile strength (0.75 MPa). These integrated properties made SFs/SiCNWs/SA a promising candidate for highly efficient thermal insulators.

Cluster dynamics simulations of tritium and helium diffusion in lithium ceramics

Tritium (T) and He diffusion in LiAlO2 and LiAl5O8 phases influences the performance of tritium producing burnable absorber rods (TPBARs) by affecting the gas release, swelling and thermal conductivity of Li-bearing ceramic pellets. Frenkel pair defects and clusters created by irradiation can attract T and He interstitials and form clusters of the type HeixLi,HeixAl,HeixO,TixLi,TixAlandTixO,1≤x≤4 in a Li, Al or O vacancy site (notation denotes x He or T atoms in a 1 Li, 1 Al or 1 O vacant site). The concentration and mobility of each of these clusters collectively contribute to the diffusion of the He and T gases in LiAlO2 and LiAl5O8. In this work, free energy cluster dynamics simulations implemented in the Centipede code, are used to obtain the concentration and diffusivities of these clusters which are then used to calculate the total diffusivity of T and He gases in LiAlO2 and LiAl5O8. The results show that diffusivity of T is at least one order of magnitude higher in LiAlO2 as compared to that in LiAl5O8 whereas He diffusion is 2–13 orders of magnitude higher in LiAlO2 as compared to that in LiAl5O8. There is a higher concentration of highly diffusive species (T interstitials and Ti03Li for the case of tritium and Hei01Li, Hei02Li and Hei03Li for the case of He) in LiAlO2 than in LiAl5O8 which increase the total diffusion of T and He in LiAlO2.

Thermal Conductivity Gas Sensors for High-Temperature Applications.

This paper describes a fast and flexible microfabrication method for thermal conductivity gas sensors useful in high-temperature applications. The key parts of the sensor, the microheater and the package, were fabricated from glass-coated platinum wire and the combination of laser micromilling (ablation) of already-sintered monolithic ceramic materials and thick-film screen-printing technologies. The final thermal conductivity gas sensor was fabricated in the form of a complete MEMS device in a metal ceramic package, which could be used as a compact miniaturized surface-mounted device for soldering to standard PCB. Functional test results of the manufactured sensor are presented, demonstrating their full suitability for gas sensing applications and indicating that the obtained parameters are at a level comparable to those of standard industrially produced sensors. The results of the design and optimization principles of applied methods are discussed with regard to possible wider applications in thermal gas sensor prototyping in the future. The advantage of the developed sensors is their ability to operate in air environments under high temperatures of 900 °C and above. The sensor element material and package metallization were insensitive to oxidation compared with classical sensor-solution-based metal-glass packages and silicone MEMS membranes, which exhibit mechanical stress at temperatures above 700 °C.

On the Importance of MPL Structural Characteristics for PEM Fuel Cell Performance

Gas diffusions layers (GDLs) constitute vital subcomponents of proton exchange membrane fuel cells (PEMFCs) since they participate in all relevant transport processes (gases, vapor, liquid water, electricity and heat).Meanwhile, state-of-the-art GDLs are produced on commercial scale using high volume reel-to-reel (R2R) processes. In almost any case, GDLs are designed as dual-layer structures with a macro-porous carbon fiber-based substrate (backing) and a micro-porous layer (MPL) consisting of carbon particulates bonded with polytetrafluoroethylene (PTFE) binder. A body of scientific work has verified that different aspects of the MPL microstructure and the MPL/macroporous substrate interface play a substantial role in the water management of PEMFCs [1-6].A systematic study was performed based on a singular backing using different MPL types and penetration levels.A simple method to estimate the micro-porous layer penetration in gas diffusion layers based on data obtained from force-deflection behavior of backings and MPL-coated GDLs is proposed. Comparison with SEM and previously published tomographic studies shows that a good estimate for the extent of MPL intrusion into the backing is obtained.MPL loading and penetration is shown to affect different ex-situ GDL properties (in-plane gas permeability, electrical and thermal conductivity) as well as the GDL single cell performance characteristics with respect to humification and high current density operation.Keywords: Gas diffusion layers, Microporous Layer, PEMFC fuel cells Weber, and J. Newman, “Effects of microporous layers in polymer electrolyte fuel cells”, J. Electrochem. Soc. 152, A677-A688 (2005).Lee, R. Yip, P. Antonacci, N. Ge, T. Kotaka, Y. Tabuchi, and A. Bazylak, Synchrotron investigation of microporous layer thickness on liquid water distribution in a PEM fuel cell, J. Electrochem. Soc. 162, F669-F676 (2015).Zhou, S. Shukla, A. Putz, and M. Secanell, “Analysis of the role of the microporous layer in improving polymer electrolyte fuel cell performance”, Electrochim. Acta. 268, 366-382 (2018).Cho, J. Park, H. Oh, K. Min, E. Lee, and J.Y. Jyoung, “Analysis of the transient response and durability characteristics of a proton exchange membrane fuel cell with different micro-porous layer penetration thicknesses”, Appl. Energy 111, 300-309 (2013).T. Gostick, M. A. Ioannidis, M. W. Fowler, and M. D. Pritzker, “On the role of the microporous layer in PEMFC operation.”, Electrochem. Comm. 11, 576-579 (2009).P. Ramasamy, E. C. Kumbur, M. M. Mench, W. Liu, D. Moore, and M. Murthy, “Investigation of macro- and micro-porous layer interaction in polymer electrolyte fuel cells”, Int. J. Hydrogen Energy 33, 3351-3367 (2008).

Development and validation of a local thermal non-equilibrium model for high-temperature thermal energy storage in packed beds

High-temperature thermal energy storage (TES) in packed beds is gaining interest for industrial energy recovery. The wide range of temperature distributions causes significant variations in thermophysical properties of the fluid and solid phases, leading to inaccuracies of classical TES models and heat transfer correlations. The objective of this work is to develop and validate a detailed but pragmatic model accounting for high-temperature effects. Based on a literature survey spanning over several communities interested in high-temperature porous media, we propose a generic local thermal non-equilibrium model for granulate porous media accounting for conservation of mass, momentum and energy (two-equation temperature model). The effective parameters needed to inform the model are the effective thermal conductivities of the different phases and the heat transfer coefficient. An experimental-numerical inverse analysis method is employed to determine these parameters. A dedicated experimental facility has been designed and built to study a model granulate made of glass bead of 16 mm diameter. Experiments are conducted using the Transient Single-Blow Technique (TSBT) by passing hot air (ranging from 293 K to 630 K) through cold particles at various mass flow rates, covering a Reynolds number range of 58 to 252. The new model was implemented in the Porous material Analysis Toolbox based on OpenFoam (PATO) used to compute the transient temperature fields. Two optimization algorithms were employed to determine the parameters by minimizing the error between experimental and simulated temperatures: a Latin Hypercube Sampling (LHS) method, and a local optimization method Adaptive nonlinear least-squares algorithm (NL2SOL). The results indicate that the value of heat transfer coefficient hv in the two-equation model falls in the range of 1.0 × 104∼1.93× 104 W/(m3 K) under the given conditions. The axial dispersion gas thermal conductivity was found to be around 5.9 and 67.1 times higher than the gas thermal conductivity at Peclet numbers of around 55 and 165, respectively. Furthermore, two improved correlations of Nusselt number (Nu=2+1.54Re(T)0.6Pr(T)1/3) and of axial dispersion gas thermal conductivity (kdis,∥=0.00053Re(T)2.21Pr(T)⋅kg) are proposed and validated for a range of Reynolds number from 58 to 252. The overall approach is therefore validated for the model granulate of the study, opening new perspectives towards more precise design and monitoring of high-temperature TES systems.

Using infrared opacifiers to reduce the thermal conductivity of micro and nanocellular polymethylmethacrylate

Nanometric cells in cellular polymers leads to a reduced gaseous thermal conductivity but a relatively high heat transfer by radiation, which counteracts the previous reduction. In this work, the impact of the inclusion of graphene nanoplatelets (GnPs), in the thermal conductivity of micro and nanocellular polymethylmethacrylate is evaluated.Production parameters are optimized to produce materials with the desired cellular structure and good macroscopic quality. Nanocellular and microcellular materials containing a 2 wt% of GnPs with similar cellular structures to those obtained with the original PMMA resin are produced.Minimum thermal conductivity of 36 mW/(m·K) is obtained with the microcellular composite containing Nano 307 GnP. The inclusion of GnP block infrared radiation reducing the radiation term up to 60 %. In addition, particles modify the structural factor, leading to a reduction up to 22 % in the solid thermal conductivity. The keys to further reduce the thermal conductivity are also discussed.

Thermal conductivity analysis of natural fiber-derived porous thermal insulation materials

Natural fibers, derived from plants such as wood, hemp, straw and cotton, have been explored for the fabrication of porous structures for thermal insulation applications due to their widespread availability, sustainability, and cost-effectiveness. Understanding the fundamental heat transfer mechanisms within natural fiber-derived porous structures is crucial for both optimized geometric design and real-world insulation applications. Herein, we developed a theoretical framework considering geometric parameters, including pore size, fiber diameter and porosity (i.e., density), to examine the contribution of various heat transfer modes (i.e., conduction, convection, and radiation) on the effective thermal conductivity of porous structures derived from natural fibers. Our results indicate that thermal radiation is largely responsible for the rapid increase in effective thermal conductivity of the natural fiber-derived porous insulations in low-density regions (< 50 kg/m3) and that natural convection rarely occurs within these materials. The insulation materials derived from natural fibers with diameters in the micron range (5–50 μm) can achieve their minimum thermal conductivity at an optimal density of 50–90 kg/m³. Effective strategies to lower the effective thermal conductivity of natural fiber-derived porous materials include increasing porosity to curtail solid conduction, incorporating nanoscale pores by using nanosize fibers to diminish gaseous thermal conductivity. This research offers valuable insights into the heat transfer mechanisms in natural fiber-derived materials and should guide the structural design and optimization process toward developing super-thermal insulation materials derived from natural fibers.

Driving sustainable energy storage: A multi-scale investigation of methane hydrate formation with green promoters and innovative reactor design

Synthetic Gas hydrates are promising materials for safe and compact energy storage but their wide-scale application is hindered by slow formation kinetics. We investigated the effect of green kinetic promoters of H-SSZ-13 zeolite, L-tryptophan, L-leucine, and L-methionine in a novel reactor design to accelerate hydrate formation at 6 MPa. In (NSR), H-SSZ-13 and L-tryptophan showed superior performance over L-leucine and L-methionine. While H-SSZ-13 showed the lowest average (t90) of 286 mins and the highest volumetric capacity of 115 V/V at 283 K, its kinetic performance, along with other promoters, dropped significantly at 293 K. We introduced a new (FBR) equipped with light (MFP) to increase gas diffusion and thermal conductivity. The combined effect of (FBR)-(MFP) reactor with zeolite significantly improved the kinetics overcoming (NSR) drawbacks. At 293.15 K, H-SSZ-13 zeolite promoter showed superior performance reducing the induction time and (t90) to 3 and 154 mins, respectively. Furthermore, it exploited 88.6%, and 96% of the sII clathrates volumetric storage capacity at 293 K and 283 K, respectively. Finally, we showed that the synthesized hydrates can be stored at atmospheric pressure for 4 months without significant methane loss. This multi-scale approach is paving the way for scaling up green and economical gas hydrate technology.

A coupled model of finite element method and Mie theory for heat transfer inside expanded perlite vacuum insulation panels (VIPs) at high temperatures

The present study introduces the first coupled model of the finite element method and Mie theory that predicts the heat transfer mechanism inside the expanded perlite vacuum insulation panels at a temperature range of 300–800 K. The finite element method is applied to discretise the governing equation of the steady state heat transfer and the three-dimensional Fourier's law is used. COMSOL Multiphysics is the finite element numerical solver which predicts solid and gaseous thermal conductivity inside the VIPs. Moreover, Mie theory predicts the radiative conductivity. Heat transfer radiation is superimposed on the heat transfer through conduction. The model is capable of predicting total thermal conductivity of VIPs at high temperatures ≥ 500 K, which makes it a unique model with clear advantage over previously developed numerical models. The numerical predictions of the developed coupled model are validated experimentally. The predictions of the coupled model are in good agreement with the experimental measurements, which indicate the capability of the developed model to predict the mechanisms of heat transfer at high temperatures. For instance, the values of total thermal conductivity for numerical prediction and experimental measurement, at 557 K, are 14.6 and 14.7±1.2 mW/m/K, respectively, excellently agreeing within ± 8.9 %.

Thermal insulation of phenolic resin modified fly ash geopolymer

Phenolic resin has been widely used owing to its excellent thermal insulation performance. However, the application of phenolic resin in the field of geopolymer remains unexplored. Here, the foamed fly ash geopolymer samples with high porosity were prepared using phenolic resin for the purpose of foaming materials. The thermal insulation properties of these samples were evaluated by Transient Plane Source Method, and the effect of phenolic resin on pore characteristics was investigated by Mercury Intrusion Porosimetry (MIP), aim to explore how phenolic resin affects the thermal conductivity by changing the pore characteristics of geopolymer. In addition, considering that the internal gas thermal conductivity of pores with different pore sizes is also different (Knudsen effect), in order to predict the thermal conductivity more accurately, this research proposes an iterative calculation method to establish a thermal conductivity model. The results show that phenolic resin can improve the thermal insulation effect of geopolymer, and the minimum thermal conductivity of the sample is 0.17 W/m·K. In addition, according to the test results of MIP, it can be found that phenolic resin mainly promotes the porosity of micron pores (>1 μm) whereas there is slight inhibition on nano pores (<1 μm), but the beneficial effect of the increase of micron-sized pores (>1 μm) on the thermal insulation performance of geopolymer is greater than the negative influence effect of the disappearance of nano pores. Moreover, according to the results of MIP, phenolic resin can narrow the throat in the pore of the ink bottle, limit the thermal convection of the gas between the pores, and reduce the thermal conductivity. Finally, the newly modified Russell model considering the Knudsen effect can effectively predict the thermal conductivity by using the experimental data. This study provides a new method to improve thermal insulation performance of geopolymers and offers a new building insulation product.

On the Importance of MPL Structural Characteristics for PEM Fuel Cell Performance

A systematic study was performed with GDLs based on a singular backing using different MPL types and penetration levels. A simple method to estimate the micro-porous layer penetration in gas diffusion layers based on data obtained from force-deflection behavior of backings and MPL-coated GDLs is proposed. Comparison with SEM and previously published tomographic studies shows that a good estimate for the extent of MPL intrusion into the backing is obtained. MPL loading and penetration is shown to affect different ex-situ GDL properties (in-plane gas permeability, electrical and thermal conductivity) as well as the GDL single cell performance characteristics with respect to humification and high current density operation. Similar effects are reported for MPLs differing with respect to the presence of mud-cracks.

Guarded Parallel-Plate Instrument for the Determination of the Thermal Conductivity of Gases, Liquids, Solids, and Heterogeneous Systems

In the present study, a new version of a guarded parallel-plate instrument (GPPI) for the absolute determination of the thermal conductivity under steady-state conditions is presented. It is based on an existing concept of an automated instrument and includes several modifications with the aim of further improving the achievable accuracy and experimental uncertainty while reducing the measurement time. These modifications mainly include improvements to the guard system in the upper hot part, which lead to a further suppression of parasitic heat fluxes, and the integration of flow circulation systems for the active temperature control in the periphery of the instrument. By using relatively large values for the temperature difference between the heating and cooling plates and for the sample thickness, expanded (k = 2) measurement uncertainties between (2 and 3)% could typically be achieved for the thermal conductivity. For mean temperatures from (283 to 358) K and atmospheric pressure, the measurement results agree well with reference data for liquid water, toluene, and ethylene glycol as well as air, polytetrafluorethylene (PTFE), and stainless steel 316. In addition, the applicability of the new GPPI for the determination of the effective thermal conductivity of heterogeneous systems was demonstrated using water-based nanofluids containing dispersed silicon dioxide, titanium dioxide, or copper oxide nanoparticles.

Modeling the rarefied gas thermal conductivity in nanochannels

Modeling the rarefied gas thermal conductivity in nanochannels

Internal temperature distribution in lithium-ion battery cell and module based on a 3D electrothermal model: An investigation of real geometry, entropy change and thermal process

The temperature of lithium-ion cell and module has a significant impact on performance and ageing. Therefore, it is crucial predicting the temperature distribution and evolution of lithium-ion batteries. However, most of the electrothermal models consider a simplified cell geometry. In this work, a 3D electrothermal model of prismatic cells is developed based on the internal geometry reconstructed from tomography. The numerical results for one single cell and a module of 12 cells in series (12S) are compared to experimental measurements for charge and discharge at different current-rates (C-rates). This study shows a cooling process due to entropy change at low C-rate while at higher C-rate the Joule effect is predominant. The real cell geometry highlights the non-uniform temperature distribution induced by the inert gas and anisotropic thermal conductivity of the jelly roll. Finally, higher internal temperatures are observed in the module because of its architecture.

Sensors for anaerobic hydrogen measurement: A comparative study between a resistive PdAu based sensor and a commercial thermal conductivity sensor

Hydrogen sensors able to perform measurements in real time in anaerobic environment such as natural gas (NG) will greatly help the development of power to gas technology. For now, thermal conductivity (TC) gas sensors and Pd thin film based sensors have demonstrated their capability to measure H2 in air and N2 but there is still lack of testing in natural gas environment. In this study, the sensing performances (response, hysteresis, response time and selectivity) of two sensors were assessed in three anaerobic environments: N2, CH4, and NG. The first one is a homemade resistive sensor based on a PdAu thin film and the second one is a commercial thermal conductivity sensor. While most performances are equivalent for both technologies, only the PdAu sensor is able to detect selectively H2, without any interfering effect with NG components. Thus, Pd based thin film sensors are promising for H2 detection in anaerobic environments.