Particle Thermal Conductivity Research Articles

Numerical study of heat transfer in process of gas adsorption in a Cu-benzene- 1, 3, 5-tricarboxylic acid particle adsorption bed

The heat transfer mechanism in the gas adsorption of a Cu-benzene- 1, 3, 5-tricarboxylic acid particle adsorption bed is investigated by a model combining the lattice Boltzmann method with the grand canonical Monte Carlo method. The effects of distribution and thermal conductivity of the adsorption particle and types of adsorbates (CO2, CH4, and H2) on gas adsorption are discussed. The results indicate that in the fluid region, the temperature peak in the particle random range, low particle thermal conductivity, and CH4 adsorption are higher than those in other cases. In the solid region, the temperature peak is independent of the particle range, whereas the temperature peak in low particle thermal conductivity and CO2 adsorption are higher than those in other cases. In the case of high thermal conductivity of the adsorbate and particle, the adsorbent with low adsorption heat is recommended to improve the adsorption performance of the adsorption bed.

A theoretical model for gas-contributed thermal conductivity in nanoporous aerogels

A theoretical model for gas-contributed thermal conductivity in aerogel is proposed by considering the coupling effects of both the local solid-gas interaction (heat crossing particles and adjacent gaseous pore) and the thermal-bridge interaction (heat crossing adjacent particles and the gas confined in the gap). The predictions of present model demonstrate a good agreement with experimental data of aerogels with different microstructures and thermophysical properties, exhibiting its good potential of application. The proposed model is then employed to investigate the influence mechanism of the above two solid-gas coupling effects in aerogels. It is shown that the coupling effect of local solid-gas interaction is in a dominant position, while the coupling effect of thermal-bridge interaction becomes noticeable and should not be neglected when the pressure exceeds about 1 atm. The effects of porosity, particle size and thermal conductivity of particles are also examined according to the present model, which could provide guidance for improving heat-insulating capacity of aerogels in engineering.

Characterisation and evaluation of a new phase change enhanced working solution for liquid desiccant cooling systems

Desiccant solutions play an essential role in desiccant cooling systems to absorb moisture from the process air. This paper presents the characterisation of a new working solution for liquid desiccant cooling systems. The new working solution was prepared through dispersion of micro-encapsulated phase change materials (MPCMs) into lithium chloride (LiCl) desiccant solutions to ensure that the dehumidification process was achieved under a low temperature condition and to improve thermal capacity and moisture removal efficiency of the mixture. The properties of the new solution, including density, enthalpy-temperature relationship, particle size distribution, thermal conductivity, and vapour pressure were characterised through either experimental tests or theoretical analysis. It was shown that the density and thermal conductivity of the new working solution slightly decreased with the increase of the mass fraction of the MPCMs in the mixture. The thermal capacity of the new working solution substantially increased in the melting temperature range of the MPCMs used. The vapour pressure of the new working solution decreased due to the existence of the MPCM particles. It is expected that the dehumidification efficiency of adiabatic dehumidifiers can be potentially improved when using this new working solution due to the decreased vapour pressure and increased thermal capacity of the phase change enhanced desiccant solution.

Relationship between Morphology of Particle Dispersion and Thermal Conductivity of TiB<sub>2</sub> Particle Dispersed Pure Al Composites

Relationship between Morphology of Particle Dispersion and Thermal Conductivity of TiB<sub>2</sub> Particle Dispersed Pure Al Composites

Flame propagation in nano-aluminum–water (nAl–H2O) mixtures: The role of thermal interface resistance

A detailed numerical analysis of flame propagation in nano-aluminum–water (nAl–H2O) mixture is performed. Emphasis is placed on investigating the role of particle thermal conductivity in the prediction of the burning properties of the mixture. Flame structure and burning characteristics are obtained by solving the energy equation using finite difference discretization and the Gauss–Seidel iteration method. Particle thermal conductivity is modeled using the temperature-dependent thermal conductivities of the aluminum core and oxide layer, as well as their interface resistance. The effective thermal conductivity of the mixture is modeled as a function of temperature, spatial coordinate, and local mixture composition, by means of the unified Maxwell–Eucken–Bruggeman model, accounting for random particle distribution and inter-particle interaction. Results indicate that the combined thermal resistance offered by the oxide layer and the interface constitute 95% of the total resistance of the particle. The calculated particle-size dependent linear burning rates show good agreement with experimental data, with only 5% error. Error in burning rate prediction increases, however, to 20% when interface resistance is excluded from the particle thermal conductivity model. It was also observed that burning rate varies as the inverse of particle size. Finally, an analysis of the sensitivity of burning rate to the individual components of the particle thermal conductivity model is also performed. Results suggest a 30% decrease in burning rate for two orders of magnitude reduction in both interface conductance and oxide thermal conductivity. The burning rate drops by only 15%, however, for a similar reduction in aluminum thermal conductivity. A heat conduction perspective on flame propagation in nanocomposites is presented, identifying the highest and the lowest conductive pathways for energy transport.

Influence of structural and thermophysical parameters of insulating aggregates on the effective thermal conductivity of lightweight concrete

Understanding how structural features influence effective thermal conductivity is an essential step towards the optimization of heterogeneous materials. Generally, thermal conductivity models link the internal structure to the effective thermal conductivity, with the volume fraction as the only parameter that takes into account the internal structure. Yet, the real internal structures of materials are often too complex to be accurately characterized by the volume fraction only. In this study, the influence of three parameters - the particle size, volume fraction, and thermal conductivity ratio of the constituents - on the effective thermal conductivity of concrete is evaluated. Two-point correlation and lineal path functions are used to characterize the internal structure generated by the Random Sequential Addition (RSA) model. A finite element model is developed to evaluate the effective thermal conductivity of concrete. The results demonstrate that the internal structure of concrete is dependent on the volume fraction of the inclusions, and also of the particle size. However, for volume fractions less than 20%, the effective thermal conductivity is dependent only of the volume fraction and thermal conductivity ratio of the constituents.

Transition of p- to n-Type Conductivity in Mechanically Activated Bismuth Telluride

Bismuth telluride (Bi2Te3) exhibits a transition from p- to n-type conduction as a result of high-energy ball milling. The transition is monitored over mechanical activation through measurement of the thermoelectric properties in the temperature range of 1.9 K to 390 K. Data show a flip in polarity of the Seebeck coefficient from 225 μV K−1 for the bulk sample to − 120 μV K−1 (at 315 K) that correlates to fracturing the layered-like structure of stoichiometric Bi2Te3 into platelets and fine particles. The electronic transition is generated by fracturing the crystal 90° to the basal plane. This is the structural equivalent to inducing n-type, anti-site defects on grain boundaries. The observed phenomenon could be exploited to fabricate p- and n-type legs for thermoelectric devices from the same material. In this report, we demonstrate that the value of the Seebeck coefficient for bismuth telluride can be tuned using mechanical treatment. We also determine how mechanical activation of Bi2Te3 impacts physical properties of the system, including: particle size, crystal structure, band gap, electrical and thermal conductivity, carrier concentration and mobility, average hopping distance, and the concentration of localized charged centers.

Performance of solid particles flow thermal storage material made of desert sand

ABSTRACTIt is a safe and low-cost new heat storage method to realize sensible heat storage at medium and high temperature by using flowing inorganic inert solid particle materials. The cost and performance of granular heat storage medium are very important for this kind of heat storage technology. The yellow sand in southeast of Tenggri Desert in Ningxia is studied. By thermal shock and grinding methods, the tests of thermal shock-resistance and wear resistance were carried out, under laboratory conditions, for the unscreened raw sand and the screened sand samples with three grain sizes (40–60 mesh, 60–80 mesh, and 80–100 mesh). The particle size of the raw sand is 150–300 µm (60–100 meshes) accounts for 60% (wt %) or more and meets the requirement of heat storage material. The density, thermal conductivity, and specific heat of raw sand are higher than those of three kinds of screened sand. Thermal shock and grinding affect the particle size distribution, density, specific heat, and thermal conductivity of the particles. The degree of influence varies with the particle size. The volume ratio heat capacity is used to measure the heat storage performance of the particles. Thermal shock results in a better thermal storage performance of the screened sand than the original sand. After comprehensive analysis of the properties of three kinds of screened sand, it is found that the content of 60–80 mesh-screened sand (31.75%) is the highest in the original sand. After thermal shock and grinding, the screened sand not only has good heat storage performance (average volumetric specific heat capacity 3.232 J· K−3· K−1), but also has the smallest change of particle size (breaking rate is less than 24, and agglomeration rate is less than 6), and the thermal shock resistance and wear resistance are outstanding. It is suggested that the screened sand with the particle size range of 200-300µm (60–80 mesh), also the particles with the highest content in the original sand, should be selected as the solid particle flowing heat storage medium.

Chemical and multi-physical characterization of agro-resources’ by-product as a possible raw building material

The aim of this paper is to find out the best valuation of agro-resources’ by-products as new alternative raw building materials that meet to sustainable development requirement. Five agro-resources are considered: flax, hemp, corn, rape and wheat. In the present work, the chemical characteristics of bio-aggregates are studied by FTIR, Van soest method and Phenol sulfuric method to identify their composition. The investigated physical properties are particle size distribution, density, porosity, water absorption, thermal conductivity and moisture buffer value. The studied materials differ on a chemical and a thermal point of view while they all are excellent hygric regulators. These results suggest that agro-resources can be used as a raw building materials for several types of use: as lightweight aggregates or as binder.

Particle scale study on heat transfer of gas–solid spout fluidized bed with hot gas injection

ABSTRACTIn this paper, the heat transfer characteristics of a 2D gas–solid spout fluidized bed with a hot gas jet are investigated using computational fluid dynamics-discrete element method. The initial temperature of the background gas and particles in the spouted bed was set to 300 K. The particle temperature distribution after injection of 500 K gas from the bottom, center of the bed, is presented. The simulation results indicate well heat transfer behavior in the bed. Then, statistical analysis is conducted to investigate the influence of inlet gas velocity and particle thermal conductivity on the heat transfer at particle scale in detail. The results indicate that the particle mean temperature and convective heat transfer coefficient (HTC) linearly increase with the increase in inlet gas velocity, while the conductive HTC and the uniformity of particle temperature distribution are dominated by the particle thermal conductivity. The conductive and convective heat transfer play different roles in the spout fluidized bed. These results should be useful for the further research in such flow pattern and the optimization of operating such spouted fluidized beds.

The critical particle size for enhancing thermal conductivity in metal nanoparticle-polymer composites

Polymers used as thermal interface materials are often filled with high-thermal conductivity particles to enhance the thermal performance. Here, we have combined molecular dynamics and the two-temperature model in 1D to investigate the impact of the metal filler size on the overall thermal conductivity. A critical particle size has been identified above which thermal conductivity enhancement can be achieved, caused by the interplay between high particle thermal conductivity and the added electron-phonon and phonon-phonon thermal boundary resistance brought by the particle fillers. Calculations on the SAM/Au/SAM (self-assembly-monolayer) system show a critical thickness Lc of around 10.8 nm. Based on the results, we define an effective thermal conductivity and propose a new thermal circuit analysis approach for the sandwiched metal layer that can intuitively explain simulation and experimental data. The results show that when the metal layer thickness decreases to be much smaller than the electron-phonon cooling length (or as the “thin limit”), the effective thermal conductivity is just the phonon portion, and electrons do not participate in thermal transport. As the thickness increases to the “thick limit,” the effective thermal conductivity recovers the metal bulk value. Several factors that could affect Lc are discussed, and it is discovered that the thermal conductivity, thermal boundary resistance, and the electron-phonon coupling factor are all important in controlling Lc.

Surface Modification of Graphene Nanoparticles by Acid Treatment and Grinding Process.

Surface modification is necessary to decrease graphene's (GN) stacking process and increase its advantageous properties. In this study, the effects of acid treatment and grinding processes on the structural integrity of GN have been studied. Morphological and structural characteristics of modified GN were investigated by field emission scanning electron microscopy, transmission electron microscopy, gas Pycnometer, particle size analyzer, X-ray diffractometer, UV-Vis spectroscopy and thermal conductivity measurement system which expose some strong evidences of the effects of purification and grinding process on GN nanoparticles in order to get GN based better nanofluid dispersed in water which gives 1.66% and 3.38% enhancement of thermal conductivity at 20 °C and at 40 °C respectively compared to that of DW in this experiment.

Theoretical Investigation into the Thermal Conductivity of Particle Filled Polypropylene Composites

Theoretical models have, over the years, tried to explain the thermal conductivity of two-phased composites. This present work focuses on investigating theoretically the thermal conductivity of particle filled polypropylene composites with emphasis on micro scale irregular shaped particles. Mathematical model developed by Bruggeman, De Loor, Nan et al including the rule of mixture also known as the parallel model and the series model were used to predict the thermal conductivity of particle filled polypropylene composites. The theoretical results were validated using experimental data. It was discovered that the model proposed by Bruggeman and De Loor gave reasonable predictions of the thermal conductivity of the composites for all the particle sizes and volume content considered with the least variation of 0.10% and 0.15% recorded for 75 µm particle size inclusions, respectively. The Maxwell, Nan et al, parallel and series model showed poor predictability with increasing volume content.

Gasdynamic acceleration of microparticles and their interaction with a solid body

Based on the physicomathematical model developed before, verified by comparison results of calculations with experimental data, parameters of a gas-dispersed jet, interacting with a solid body, are numerically investigated. In a wide range of temperature and pressure values in a mixing chamber, material density, the size and mass fraction of particles, the nozzle geometry and the streamlined body form, ratio of specific heat capacities, and the Mach number of carrier gas, calculations are made, which allows one to determine the impact of specified factors on the boundary of a perfectly inelastic collision of particles with the body, accompanied by different physical processes (erosion, cold deposition, ultradeep penetration). Since temperature falls below the Debye value at high expansion of flow, the impact of a significant change of the heat capacity and thermal conductivity of particles are taken into account. Radial distributions of density and velocity of the dispersed mass are plotted, which characterize the “quality” of two-phase flow as a tool for the ground modelling of interaction of a flying vehicle with a dust-laden atmosphere (containing, for example, particles of volcanic outbursts or ice crystals) as well as in technologies of surface treatment.

Recrystallization and thermal shock fatigue resistance of nanoscale ZrC dispersion strengthened W alloys as plasma-facing components in fusion devices

Recrystallization and thermal shock fatigue resistance behavior of nanoscale ZrC dispersion strengthened bulk tungsten alloys (W-0.5 wt% ZrC, WZrC) as potential candidates for plasma-facing components were investigated. By employing heat treatments with isochronal experiments, the evolution of the tungsten grain size/orientation, second phase particle distribution, thermal conductivity and mechanical properties were systematically studied. The effects of edge-localized mode like transient heat events on the as-rolled and recrystallized WZrC were investigated carefully. Pulses from an electron beam with durations of 1 ms were used to simulate the transient heat loading in fusion devices. The cracking thresholds, cracking mechanisms and recrystallization under repetitive (100 shots) transient heat loads were investigated. Results indicate that the cracking threshold of all the WZrC samples is 220–330 MW/m2 (corresponding to a heat load parameter F = 7.0–10.4 MJ/m2s1/2) at room temperature and the heat bombardment induced recrystallization occurs at a heat parameter of 10.4 MJ/m2s1/2.

A novel liquid optical filter based on magnetic electrolyte nanofluids for hybrid photovoltaic/thermal solar collector application

Abstract Different from solid optical filters, the nanofluid filters display various optical properties and can also be easily pumped at low cost. However, finding a proper nanofluid meeting the standard of practical application is a great challenge. In the present study, we propose a novel magnetic electrolyte nanofluid (ENF) for the first time which can be potentially used as liquid optical filters for hybrid photovoltaic/thermal (PV/T) application. By dispersing optimized amount of magnetic iron oxide (Fe3O4) nanoparticles in 50% water/50% EG solutions containing methylene blue (MB) or copper sulfate (CS), we obtained two stable ENF filters satisfactorily meeting the optical absorption of two typical PV cells, Si and InGaP, respectively. Due to its magnetism, ENF can be considered as a smart liquid optical filter controllable by external magnetic field. The root-mean-square errors (RMSE) of the absorptance between the ENF filters and the corresponding ideal filters are both smaller than that of water-based nanofluid filters containing typical core/shell nanoparticles while their thickness is much smaller. The stability, particle size distribution and thermal conductivity of the optimized ENF filters were investigated. It was found that both ENF filters have good stability and higher thermal conductivities than their base fluids. Performance of ENF filters in PV/T system was evaluated based on a reported theoretical model. The results showed that the values of merit function (MF) for the two types of ENF based PV/T systems are both higher than that of typical core/shell nanoparticle nanofluid filters. Overall, our study demonstrates that ENF represents an efficient, low-cost and smart liquid optical filter for the application in PV/T system.

Effects of flake graphite on property optimisation in thermal conductive composites based on polyamide 66

ABSTRACTIn this study, in order to improve the thermal conductivity of polyamide 66(PA66), PA66 composites filled with flake graphite (FG) were prepared by twin-screw extruder. Effects of filler content, particle size and particle size mixing on thermal conductivity, mechanical and rheological properties of the composites were investigated. The results showed that as FG content increased from 0 to 50 wt-%, thermal conductivity of the composites filled with 100 μm FG gradually increased, whereas mechanical properties and rheological properties decreased. At 50 wt-% loading, thermal conductivity reached 3.07 W/(m K). With the increase of particle size, thermal conductivity and rheological properties of the composites improved, but mechanical properties increased first and then decreased. The composite filled with 100 μm FG had relatively optimal mechanical properties. Particle size mixing can improve thermal conductivity and the maximum value was achieved in the 1:2 mass ratio of 20 and 100 μm particles.

Influence of surface topography, crystallinity, and thermal conductivity on reflectance and color of metallic‐effect high‐density polyethylene parts filled with aluminum pigments

Metallic effect in injection molded parts is created using composites of high‐density polyethylene (HDPE) filled with high‐sparkle aluminum (Al) pigments (HDPE/Al). The mechanism of micro shrinkage induced by the leafing phenomenon influences the surface topography and roughness, and has been studied with SEM and AFM. Reflectance, whiteness index (WI), and luminance (L*) of the surface were assessed in relation to the surface roughness, the particle sizes, the crystallinity and thermal conductivity of composites. The results show that the leafing induces the micro shrinkage and causes micro caverns, which increased surface roughness. Besides, the length of micro caverns and surface roughness increased as the particle size increased. These morphologies were not benefit for improving reflectance, WI, and L* values, therefore the reflectance, WI, and L* values decreased proportionally with the surface roughness and particle sizes increased. High‐sparkle Al pigments improved the crystallinity and thermal conductivity of the composites. A higher reflectance, WI, and L* were associated with a higher crystallinity and a higher thermal conductivity. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Recommendation of the RILEM TC 236-BBM: characterisation testing of hemp shiv to determine the initial water content, water absorption, dry density, particle size distribution and thermal conductivity

This recommendation is the outcome of research conducted by a working group within the RILEM Technical Committee 236-BBM ‘Bio-aggregate-based building Materials’. The work of the group related to the study of construction materials made from plant particles. The major raw material utilised being renewable, recyclable and easily available plant particles. These particles are obtained from the processing of hemp, flax, miscanthus, pine, maize, sunflower, bamboo and other plants. In this report, the outcome of the Round Robin Testing is centred on hemp because hemp shiv is the bio-aggregate that is the most widely used in building materials and the most studied in the literature. The first round robin test of the TC-BBM published in the State of The Art Report of Technical Committee 236-BBM ‘Bio-aggregate-based building Materials’ was carried out to compare the protocols in use by the different laboratories (labs) to measure initial water content, bulk density, water absorption, particle grading and thermal conductivity. The aim was to define a standardised characterisation protocol developed from those used by the different labs. The different methodologies used by 7 labs constitute a set of statistically representative data which have been analysed to develop this recommendation for the characterisation of hemp shiv.

Synthesis and characterization of Zn-Al layered double hydroxide nanofluid and its application as a coolant in metal quenching

The current study comprises of the synthesis and characterization of Zn-Al layered double hydroxide (LDH) nanofluid for use as a potential coolant in the steel industry. Coprecipitation method was used in the preparation of Zn-Al LDH nanoparticles by using the nitrate salts of Zn, Al and Na, in the ratio of 2:1:2. The nanofluids were characterized based on their particle size, stability, surface tension, thermal conductivity and viscosity. TEM analysis revealed that the nanoparticles were needle-shaped with an average particle size of 45.61nm and aspect ratio of 7.3. Different concentrations of the nanofluid, from 40ppm to 240ppm, were used to analyze the effect of particle concentration on the enhancement in thermal conductivity and viscosity. Stability analysis of the nanofluid exhibited good results, even without any stabilizer. An optimum cooling rate of 125°C/s was obtained for a nanofluid concentration of 160ppm, which is 1.29 times when compared to water.