Particle Thermal Conductivity Research Articles

Effects of solid particle thermal conductivity on heat storage performance of heat storage bed

The thermal properties of particles are important parameters that directly affect the heat storage performance of the solid particle heat storage bed. This paper reports the effects of solid particle thermal conductivity on heat storage performance of heat storage bed. A three-dimensional steady-state heat transfer model of heat storage bed with a single vacancy was established using ANSYS 19.0. The effects of thermal conductivity of particles were studied. With the increase in thermal conductivity of particles, the effect of the vacancy on heat storage particle bed heat transfer performance increases, the affected area size increases, so the heat storage and release performance of heat storage bed decreases. With the increase of thermal conductivity of particles from 0.5 W/ (m·K) to 50 W/ (m·K), the size of the affected region increased from 0.61 times of particle size to 1.82 times of particle size in the direction perpendicular to the heat transfer, and the size of the affected region increased from 1.61 times of particle size to 3.91 times of particle size in upstream of the direction parallel to the heat transfer. At the same time, the size of the affected region increased from 1.69 times of particle size to 3.93 times of particle size in downstream of the direction parallel to the heat transfer. It can provide a basis for improving the thermal resistance theory.

Wall-to-bed heat transfer in supercritical water fluidized bed using CFD-DEM

Supercritical water fluidized bed (SCWFB) reactors are designed to gasify biomass or coal with high efficiency. In this paper, the wall-to-bed heat transfer characteristics in SCWFB are studied using the computational fluid dynamics and discrete element method (CFD-DEM) coupled with a constant heat flux boundary. Two different methods are considered to deal with the multiphase heat flux boundary in CFD-DEM because there is currently no single widely accepted approach. Zhang’s method predicts a more accurate wall-to-bed heat transfer coefficient in SCWFB than Lattanzi’s method according to comparisons of the simulation results with an empirical correlation. The influences of temperature, pressure, velocity, and the solid phase properties, such as the particle diameter, particle heat capacity, particle thermal conductivity, and particle density, on the SCWFB wall-to-bed heat transfer characteristics are studied based on Zhang’s method. The simulation results help reveal the SCWFB heat transfer characteristics.

Effect of particle characteristic parameters on the heat transfer process of double vacancy particle bed

In order to improve the heat recovery efficiency of high-temperature solid particles, a two-dimensional heat transfer model of double vacancy particle bed was established. This paper investigated the effects of particle size and thermal conductivity on the heat transfer process of double vacancy particle bed. With the increase of the thermal conductivity from 0.4678 W/m·K to 46.78 W/m·K, in the area near the vacancy, the particle isotherm is significantly affected, the influence area of double vacancy in X direction increases from 1.5 to 4.5 times of particle size, the influence area of double vacancy in Y direction increases from 2.2 to 7.2 times of particle size, and the wall heat flux increases from 0.53 kW/m2 to 36.28 kW/m2. The particle size has little effect on the overall temperature distribution of the particle bed, the maximum influence area in the X direction is approximately the same, all are 4.5 times particle size, and the maximum influence area in the Y direction is increased from 7.1 to 7.4 times particle size, but as the particle size increases, the wall heat flux increases obviously. The results will further improve the thermal resistance network theory.

Influence of particle rotation and partial irradiation on the particle heating up process

Particle heat transfer is important for the particle heating and combustion in solid fuels combustion reactors. A 3D particle conduction model is developed to investigate the mutual interactions of the partial surface irradiation and rotation speed on the particle heat transfer. The effects of particle diameter, thermal conductivity and particle shape are investigated. The lumped parameter (0D) model is also validated to determine its accuracy. Particle temperature contours, maximum, minimum and average temperatures are presented and analyzed in detail. Partial surface irradiation leads to non-uniform temperature distribution within the particle, especially for larger particles, while particle rotation tends to decrease the non-uniformity.

Initial development of an RIA envelope for dispersed nuclear fuel

A reactivity insertion accident (RIA) is a design basis accident in which reactivity is rapidly injected as a result of a control rod ejection or blade drop scenario. The resultant power increase can result in fuel rod failure and subsequent release of radioactive material into the reactor’s primary system. For light water reactors, failure under RIAs is typically a result of fuel melt, pellet-cladding interaction, or rod over-pressurization. Fuel melt occurs when the fuel system is unable to transport heat out of the fuel system. Pellet-cladding interaction occurs when an aggressive fuel pellet expansion pushes on an embrittled cladding beyond its strain limit. Rod over-pressurization occurs when a fuel rod exceeds the critical heat flux and departs from nucleate boiling, causing the rod internal pressure to rapidly increase, exceeding the systems pressure, and balloon until it bursts. To prevent failure, regulators have developed safety requirements that limit the injected enthalpy based on the state of the fuel system. However, dispersed fuel could enable the removal or relaxation of regulator-imposed safety criteria. Dispersed fuel embeds fuel particles in a highly conductive metal. Dispersed particles can have a particle radius of 1 µm to greater than 100 µm. Traditional fuel systems are plagued by poor thermal conductivity, especially at higher burnups, thus reducing the ability of the fuel system to respond to an RIA. However, dispersed fuel could improve the ability of the fuel system to transport injected energy away from the fissile material and into the coolant more efficiently. Additionally, dispersing the fuel particles mitigates hard contact that typically occurs in the traditional zirconium-uranium dioxide fuel system, thus removing pellet-cladding mechanical interaction as a potential failure mechanism. This paper evaluates fuel particles dispersed in a metal matrix using the BISON fuel performance code to develop an initial failure threshold based on melt temperature of the fuel particle and/or cladding material as a function of fission density for beginning-of-life and end-of-life conditions. BISON results show that (1) reducing the size of the particles allows fission density to increase as a function of time, (2) particle-to-particle proximity must be considered to evaluate the limiting conditions, and (3) improving the fuel particle thermal conductivity improves thermal performance.

Impact of a charge sheet on neoclassical transport

Perpendicular electron heating in cyclotron waves accumulates resonant particles on the low magnetic field side, where an electron charge sheet may result (Hsu et al 1984 Phys. Rev. Lett. 53 564). Electrostatic fields are produced on both sides of the charge sheet. The impact of a charge sheet on transport is investigated based on neoclassical theory. A full particle simulation is performed using the Boris algorithm. The electrostatic field in the R-direction traps circulating particles or makes trapped particles circulate depending on the field direction. Transport coefficients are rigorously derived for such an electrostatic field. The electrostatic trapping or de-trapping changes the trapped particle population, bootstrap current and thermal conductivity. The positive electrostatic field corresponding to the negative biasing reduces transport, and then a thermal barrier is produced. Therefore, a strong positive electrostatic field can improve confinement. The transport behavior qualitatively agrees with a polarity study of biasing in TEXTOR, where the particle confinement time is three times lower in positive biasing.

In-flight temperature of solid micrometric powders during cold spray additive manufacturing

During cold dynamic gas spray additive manufacturing, the thermal field within particles is generally simplified by a state of an instantaneous uniform distribution over the particle's media at any position inside and outside the De-Laval nozzle. This paper addresses critical discussions using analytical and computational analysis of the transient heat transfer within the solid particles due to the convective exchange with the flowing gas. An analytical criterion depicts conditions of instantaneous uniform temperature over the range of typical cold spray data including various particle thermal conductivity, particle size range, dragging velocities, gas nature and gas setting conditions. The analytical depiction draws the conclusion that, during cold spraying, the temperature field within particles is mostly instantaneously uniform. The notion of instantaneousness is further investigated via computational analysis of the transient thermal gradient regimes within particles. The phenomenological computations enable to characterize the duration of the transient stage prior to the state of uniform temperature. Comparisons with analytical particle's residence time using various scales of travelled distance give a more relevant notion of instantaneousness. The particle temperature is not strictly instantaneously uniform. However, such instantaneousness prevails for a covered distance unit of 1 mm which is widely enacted in the literature to compute the particles temperature during cold spraying. As conclusive remarks, issues due to this instantaneousness of the particle temperature are reviewed and suitable alternatives for efficiently heating the particles during cold spraying are reported.

Predicting the thermal conductivity enhancement of nanofluids using computational intelligence

Nanofluids, composed of nanoparticles in base liquids, have drawn increasing attention in heat transfer applications due to their anomalously increased thermal conductivity. Pertinent parameters, including the base liquid thermal conductivity, particle thermal conductivity, particle size, particle volume fraction, and temperature, have been shown to have significant but complex effects on thermal performance of nanofluids, which is commonly characterized by the thermal conductivity enhancement, E%. In this work, machine learning is used to develop the Gaussian process regression model to find statistical correlations between E% and aforementioned physical parameters among various types of nanofluids. Nearly 300 nanofluid samples, dispersions of metal and ceramic nanoparticles in water, ethylene glycol, and transformer oil, are explored for this purpose. The modeling approach demonstrates a high degree of accuracy and stability, contributing to efficient and low-cost estimations of E%.

Experimental evaluation of vitrified waste as solid fillers used in thermocline thermal energy storage with parametric analysis

This work presents the first use of Cofalit® (vitrified asbestos-containing waste) as a solid filler in pilot-scale thermocline thermal energy storage (TES). The thermocline size is 4 m³ connected to the MicroSol-R installation at the PROMES research facility in Odeillo, France. The study compares the thermal performance of the thermocline filled with Cofalit® to the reference case of alumina spheres for typical charge and discharge operations. It evaluates the actual thermal behavior of thermocline considering three leading performance indicators: process duration, thermocline thickness, and process efficiency. The investigation shows a 22% shorter charge duration in Cofalit® compared to alumina and 16% shorter discharge duration. Cofalit® exhibits about 16% lower thermocline thickness during both charge and discharge compared to alumina. The charge efficiency is slightly better in Cofalit® than alumina with an efficiency of 82% and 78%, respectively. Also, Cofalit® has a better discharge efficiency, 90% with respect to 84% for alumina. These results confim a good thermal performance of Cofalit® as filler material in thermocline TES. Considering the cost-saving and positive environmental impact of using Cofalit® as well as the good thermal performance of the thermocline filled with it, Cofalit® appears a very good filler material in TES. The obtained temperatures from radial positions indicate no significant variation during charge and discharge, and this confirms the one-dimensional thermal behavior of this setup. A parametric analysis is performed using a 1D continuous solid (C-S) model to investigate the influence of particle diameter, porosity, thermal conductivity, and volumetric heat capacity on the thermal performance of the thermocline. The analysis confirms the experimental findings, and it indicates that about a 10.9% longer process duration is associated with a 10% larger volumetric heat capacity and less affected with other parameters. Thermocline thickness is mainly affected by the diameter as well as the volumetric heat capacity of the solid filler; it grows 2.2% for each 10% diameter increase and around 3.23% for doubling the volumetric heat capacity. Charge efficiency demonstrates independency from evaluated properties. While discharge efficiency increases sharply at a tiny particle diameter before an optimum diameter value is reached, then it starts to decrease by 1.4% to each 10% bigger diameter.

Thermal conductivity of flake-shaped iron particles based magnetorheological suspension: Influence of nano-magnetic particle concentration

The non-spherical shape (flake-shape) iron particles based magnetorheological (MR) fluid thermal conductivity is experimentally investigated using the hot-wire method. Under the magnetic field, thermal conductivity is enhanced by 20% compared to spherical shape commercial MR fluid having nearly 20% higher volume fraction of iron particles. This enhancement attributes to the larger contact area of the flake-shape particle (when they form a chain), which helps to transport heat quickly. The magnetic nanoparticles of size 6.5 nm were added to this MR fluid for varying magnetic weight fraction and studied its influence on thermal conductivity. The increase of magnetic nanoparticle concentration enhances the thermal conductivity and increases field reversibility. The observed increase in thermal conductivity and low hysteresis losses is attributed to the friction reduction in flake-shaped iron particles in the presence of nanoparticles.

2D modeling of fusion ignition conditions for a multilayer plasma liner magneto-inertial fusion target in a cylindrical configuration

A set of 2D time dependent simulations of an imploding cylindrical target and liner is presented. These simulations were performed using an ideal magnetohydrodynamic methodology that augmented the energy equation to account for fusion alpha particle deposition, thermal conduction, and Bremsstrahlung radiation. A reference case of a deuterium and tritium (DT) target compressed by a multilayer liner consisting of an inner layer of DT and an outer layer of argon was evaluated. The reference case was chosen to be within the region of positive fusion heating predicted by the Lindl–Widner power balance model. Analysis of the reference case determined fusion gains of three or greater can be achieved. A sensitivity analysis of four parameters was performed. These parameters were the target: radius, density, temperature, and inner/outer liner thickness ratio. It was found that the Lindl–Widner parameter space accurately predicts regions of positive fusion heating, but over-predicts the effects of mechanical work done by a plasma liner. It was determined that a plasma liner could be used as a confinement mechanism to contain a thermally conditioned target and allow it to ignite and burn. Thermal conduction from the hot fusing target was capable of heating the inner liner layer to fusion ignition conditions and increasing the fusion yield.

An effective model for the thermal conductivity of nanoparticle composites/polymers

In this study, an effective model is proposed to predict the effect of nanoparticle agglomeration on the thermal conductivity of three-phase nanocomposites/polymers. In order to better describe this effect, the concept of agglomeration degree is introduced. The effect of particle volume fraction on thermal conductivity of composites is also studied by considering the interphase and agglomeration degree of particles. First, the relationship between agglomeration degree and particle volume fraction is discussed. Then, the effects of particle volume fraction, agglomeration degree and interphase thickness on thermal conductivity of composites are studied. The obtained results show that the agglomeration degree increases with increasing particle volume fraction. The thermal conductivity of composites increases first and then decreases with increasing particle agglomeration degree, and is also affected by the different thermal conductivity of particles and matrix, and the thickness of interphase.

A finite element simulation of transition-edge sensor for measuring kinetic energy of fission fragments

It is necessary to accurately measure the kinetic energy of fission fragments when using the Time-Of-Flight method to determine the mass of fission fragments. The ionization chamber and the Au-Si surface barrier detector are conventional kinetic-energy detectors, but their energy resolution is not sufficient to achieve a mass resolution of 1 amu. The Transition-Edge Sensor (TES) is a cryogenic calorimeter that can be used to measure the kinetic energy by measuring the temperature variation induced by the energy of the incident particle, with a typical resolution of 0.02% of TES detector can be achieved[1]. In this article, we designed a TES to measure the kinetic energy of fission fragments, and the signals of this TES with different incident particle positions, kinetic energy, and thermal conductivity were simulated using ANSYS. Therefore, we verified the feasibility of the TES and improved the count rate of the TES to 100cps.

Influence of different parameters on the tube-to-bed heat transfer coefficient in a gas-solid fluidized bed heat exchanger

In this paper a combined use of CFD techniques and Design of Experiments is proposed in order to study the significance of different variables on the heat transfer coefficient in a gas-solid fluidized bed heat exchanger. Initially a computational model was developed using Ansys Fluent and validated in order to represent the system under study. Then, this model was used to complete the runs of a 25−1 fractional factorial design, in which the response variable was the heat transfer coefficient and factors were: particle diameter, particle thermal conductivity, gas velocity, diameter of the heat transfer tubes and distance between tubes. The results of 16 simulation were used to create different models in which the significance of each coefficient was analyzed. Particle diameter proved to be the parameter that influenced the most the response variable, while gas velocity and solid thermal conductivity showed little effect on the heat transfer coefficient.

Capric acid phase change microcapsules modified with graphene oxide for energy storage

To improve the efficiency of energy, phase change microcapsules with capric acid as core material and urea–formaldehyde resin modified by graphene oxide (GO) as shell material were synthesized by in situ polymerization. The particle characteristics, chemical structure, thermal conductivity and thermal stability of capric acid phase change microcapsules were studied by environmental scanning electron microscopy, laser particle size analyzer, Fourier transform infrared spectroscopy, thermal conductivity meter and differential scanning calorimeter. The results showed that the surfaces of MEPCMs–0.3%GO, MEPCMs–0.6%GO and MEPCMs–0.9%GO are relatively smooth compared with MEPCMs, but the surface smoothness of capric acid phase change microcapsules will decrease with the increase in graphene oxide dosage. The inflection point of encapsulation ratio of capric acid phase change microcapsules occurs in the 0.6% dosage of graphene oxide. Compared with MEPCMs, thermal conductivity of MEPCMs–0.9%GO increased by 75.1%, 64.2% and 73.6% at 20 °C, 30 °C and 40 °C, respectively. In the thermal cycle experiment, capric acid phase change microcapsules possess the better heat stability. Because graphene oxide can be stably buried or embedded in the shell material of urea–formaldehyde resin and forms heat transfer channels on the surface and inside of urea–formaldehyde resin, the thermal properties of capric acid phase change microcapsules can be improved.

Thermal performance of a single-layer packed metal pebble-bed exposed to high energy fluxes

It is difficult to accurately measure the temperature of the falling particle receiver since thermocouples may directly be exposed to the solar flux. This study analyzes the thermal performance of a packed bed receiver using large metal spheres to minimize the measurement error of particle temperature with the sphere temperature reaching more than 700°C in experiments in a solar furnace and a solar simulator. The numerical models of a single sphere and multiple spheres are verified by the experiments. The multiple spheres model includes calculations of the external incidence, view factors, and heat transfer. The effects of parameters on the temperature variations of the spheres, the transient thermal efficiency, and the temperature uniformity are investigated, such as the ambient temperature, particle thermal conductivity, energy flux, sphere diameter, and sphere emissivity. When the convection is not considered, the results show that the sphere emissivity has a significant influence on the transient thermal efficiency and that the temperature uniformity is strongly affected by the energy flux, sphere diameter, and sphere emissivity. As the emissivity increases from 0.5 to 0.9, the transient thermal efficiency and the average temperature variance increase from 53.5% to 75.7% and from 14.3% to 27.1% at 3.9 min, respectively. The average temperature variance decreases from 29.7% to 9.3% at 2.2 min with the sphere diameter increasing from 28.57 mm to 50 mm. As the dimensionless energy flux increases from 0.8 to 1.2, the average temperature variance increases from 13.4% to 26.6% at 3.4 min.

A theory of angel hair: Analytic prediction of frictional heating of particulates in pneumatic transport

An analytic prediction of the frictional temperature rise of materials in pneumatic transfer systems is developed, with the aim of anticipating from first principles the onset of problematic formation of melt structures such as ‘angel hair’. Specifically, particulates of size d passing at velocity V through a 90° bend of radius R experience a maximum surface temperature rise ΔT = μdV2(Vρ/kcR)0.5, where μ,ρ,k,c are the particle friction coefficient, density, thermal conductivity and heat capacity respectively. Limits of applicability of this idealized (but conservative) model are discussed, and simple corrections for the mitigating effects of pipe texture and gas cooling are discussed. The expression predicts temperature increments of many tens of Kelvin for 5 mm polyethylene granules at speeds of >40 m/s, but only a few K for 1 mm organic grains at 30 m/s in a planned pneumatic sampling system for a planetary exploration mission.

Numerical approach to predicting the effective thermal conductivity of a packed bed of binary particles

Thermal analysis of a packed bed of two types of particles is conducted using the homogenization method. Using a thermal radiation coefficient, sigmoidal curves are obtained as functions of the Nusselt number in the same way as for a unary bed, even when the two types of particle have different emissivities and thermal conductivities. The emissivities are contributing terms to the Nusselt number, and the parameters that express the shape of the sigmoidal curve are determined mainly by the ratios of particle number and thermal conductivity between the two types of particle. The data show that thermal radiation analysis in more complex packed beds could be simplified, and the present technique is expected to contribute to reductions in computational costs.

Study on thermal conductivity of cement with thermal conductive materials in geothermal well

In the exploitation of geothermal resources, geothermal single-well heat extraction technology can realize geothermal development without extracting water, which has a wide application prospect. The single-well heat extraction relies on heat conduction between wellbore and reservoir, and heat convection between wellbore and reservoir water. Therefore, the thermal resistance between wellbore and reservoir is an important factor affecting performance of heat extraction. Employing cement with thermal conductive materials in the thermal recovery section of geothermal reservoir is an effective method to enhance heat extraction performance. The study presents a method of producing thermal conductive cement by mixing oil well cement with thermal conductive materials, including graphite, ferrum and copper. Then thermal conductivity and compressive strength tests are carried out, and the influence of thermal conductive material exerted on the thermal conductivity of cement paste is studied. Moreover, relations between porosity and thermal conductivity of cement paste, and relations between particle continuity and thermal conductivity of cement paste are studied by porosity test and SEM scanning. The study demonstrates that with graphite increases, the porosity of cement paste decreases firstly and then increases, and the thermal conductivity of cement paste increases firstly and then decreases; With ferrum increases, the porosity of cement paste decreases, and the thermal conductivity of cement paste increases; With copper increases, the porosity of cement paste decreases, and the thermal conductivity of cement paste increases; As the temperature rises, the thermal conductivity of cement paste decreases gradually; Thermal conductive materials can enhance thermal conduction in cement, and pore would provide thermal insulation; On the condition of improve thermal conductivity, cement with 0.05-0.15 graphite, cement with 0.05-0.20 ferrum and cement with 0.05-0.20 copper can meet requirements. The results of this study provide theoretical guidance for improving the thermal conductivity of cement in geothermal well.

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.