Increase In Particle Temperature Research Articles

Particle temperature effect in cold spray: A study of soft particle deposition on hard substrate

In cold spray, the interactions between feedstock particles and propellant gas control deposition outcome. The particle impact temperature, along with impact velocity, governs the deposition due to its effect on the impact deformation processes. As bonding mechanisms rely primarily on the particle/substrate plastic flow upon impact, particle impact temperature holds a predominant role in process optimization.The current work studies the effect of pure aluminum particle impact temperature on deposition phenomena when propelled onto a hard steel substrate. Particle impact temperature was varied while achieving the same particle impact velocity, using low and high-pressure cold spray systems. Three different particle diameters are studied, with varying resulting inherent impact temperatures, to provide size dependent insight on deposition/adhesion.Experimental results demonstrate that at low particle impact temperature, i.e. 50 °C, coating adhesion is controlled by in-situ peening. Adhesion shifts to particle in-flight characteristics dependent bonding, i.e. η = V/Vc, as particle temperature increases. At low particle impact temperatures, the coating bond strength increases with increasing in-situ impingement intensity and frequency, i.e. decreasing deposition efficiency with increasing particle size. At higher particle impact temperatures, in-situ peening rate decreases and the adhesion strength increases with decreasing particle size. In addition to affecting the impact process (DE, Vc and adhesion), the particle impact temperature also influences the coating mechanical properties through the creation of temperature-dependent crack propagation mechanisms, i.e. deflection, bridging and acceleration, and of particle-particle structural arrangement related to deformation processes, i.e. fish scale effect and pseudo-plasticity behavior.

Simulation on flow behavior of particles and its effect on heat transfer in porous media

Mastering flow and heat transfer of fluids in porous media is significant in the development of oilfield. A three-dimensional porous model with anisotropic pore structure is developed, and flow and heat transfer behaviors of particles are simulated using CFD-DEM method incorporating with the coupled convective-conductive heat flow model. The interphase forces including drag force, lubricating force and thermophoretic force are considered comprehensively. Comparisons of the predicted results are also made and in a good agreement with the classical experimental results by Rimon. Simulation results show that the temperature in porous media rises along with the mixing and contact between particles and liquid. The migration of moving particles is restricted in pore spacing, and thus narrows the apertures of fluid channel, increases the local instantaneous liquid velocity. Moving particles are preferred to decelerate and deposit at a low porosity. The velocities of particles and frequency of collision increase while contact force and granular temperature decrease with an increase of porosity. With the increase of particle temperature, the temperature gradient around hot particles enlarges and the number of trapped particles goes up affected by thermophoretic force. The intensity of convection heat decreases at lower liquid velocity, and the heat conduction between particles is regarded as the main heat transfer mechanism.

Ignition of pine needle fuel bed by the coupled effects of a hot metal particle and thermal radiation

Spot fire and flame radiation are two important causes of Wildland-Urban interface fire. Previous studies have mainly focused on one single cause. However, the ignition of fuels by firebrands (or hot particles) coupled with flame radiation is unknown due to the lack of experimental and theoretical study. In this paper, the ignition behavior of pine needle fuel bed under the coupled action of a hot particle and thermal radiation was studied for the first time, and the critical ignition conditions were analyzed. The experimental results show that the ignition risk of a hot particle coupled with thermal radiation is much higher than that of a hot particle or thermal radiation alone. Under the coupled condition, the ignition probability increases with the increase of particle temperature and radiation heat flux, and the critical radiation heat flux required for ignition decreases with the increase of particle diameter and temperature. The ignition delay time decreases as the radiation heat flux increases for different particle diameters and temperatures. The theoretical analysis revealed that there is a good linear relationship between the critical radiation heat flux required for ignition and the parameters of the hot particle d(Tp-Tsm). This study may help provide the first step to understand the ignition mechanism of fuels by the coupled effect of firebrands and flame radiation.

Experimental and numerical investigation on thermal performance of a quartz tube solid particle solar receiver

The thermal performance of a quartz tube solid particle solar receiver (SPSR) with the gravity driven packed particles moving down in a semi-annular particle flow channel has been experimentally and numerically investigated, and the particle flow channel in the quartz tube was shaped by a ceramic fiber insert. The SPSR was heated by a solar simulator with 7 Xenon lamps at 130A electric current which generated a mean irradiant flux of 276 kW/m2 on the 0.26 m irradiated length, grey ceramsite sand with the solar weighted absorptivity of 72.34% was used in the study. The experimental results with a 6 mm particle layer thickness indicated the particle temperature increase of 164 K and the thermal efficiency of 50.25%. A thinner particle layer thickness was shown to improve the thermal performance of the SPSR as verified both in the experiments and simulations. Although the particle temperature increase in a single pass was not high enough in the experiments, compared with other types of SPSR, this design obtained an advantageous particle temperature increase in per unit irradiation length. Moreover, the particle temperature increase in a single pass can be promoted by a longer irradiated length, and therefore the requirement for continuous recirculation of the solid particles will be decreased which can greatly reduce the required parasitic power. Besides, according to the numerical model, the thermal efficiency can be further improved by various means such as improving the solar weighted absorptivity of the solid particles, reducing the particle layer thickness, increasing particle mass flow rate and so on. A sensitive analysis illustrated that the mean particle diameter had the minimal impact on the thermal performance among the various influencing factors, but a value of greater than 700 μm was recommended based on the simulation results.

Numerical Study on Performance of Flat Tube with Water Based Copper Oxide Nanofluids

Abstract The aim of the present study is to perform numerical analysis on the performance of a flat tube with copper oxide nanofluids. The nanofluid was passed through a virtual 3D model of a flat tube. Advantages of using nanofluids instead of pure base fluid were evaluated. The thermophysical properties of the nanofluid were calculated using correlations (function of temperature and volumetric concentration nanoparticles) developed from experimental work. It was observed that the heat transfer performance of a flat tube increased with increase in particle concentration, temperature and Reynolds number. The pressure drop across flat tube increased with increasing volumetric concentration of nanoparticle and Reynolds number

Modeling the microwave emission of a moist granular medium

Based on the Mie Scattering Theory and the Dense Medium Radiative Transfer (DMRT) Theory, this paper analyze the electromagnetic scattering properties of particles under different humidity and temperature, and discusse the polarization brightness temperature of moist granular layer. The numerical calculation results show that when the particle temperature is over 273 K, the particle humidity has more obviously influence on the electromagnetic scattering properties of sand particles than its temperature. When the temperature is below 273 K, the optical properties of particles are mainly affected by the humidity of particles, and with the increase of humidity, the extinction efficiency of particle shows a trend of increasing initially and decreasing afterwards, and the maximum value appears when the humidity of the wet ice is 0.2. In addition, with the increase of particle temperature and humidity, the microwave brightness temperature of particle layer significantly increases, and its vertical polarization brightness temperature is greater than the horizontal polarization brightness temperature, the maximum difference appears near the observation angle of 55°. However, it is more sensitive to the thickness of sand layer when the observation angle is below 30° and the thickness does not exceed 30 cm.

Parameter optimization of a motorized spindle lubrication system using biogeography-based optimization

Using response surface methodology, two-target parameter mathematical models for a 100MD60Y4 motorized spindle are established using biogeography-based optimization. Air supply pressure, fuel supply rate, and oil supply interval are the independent variables, while the spindle temperature increase and oil mist PM2.5cumulative volume distribution percentage are the response variables. Biogeography-based optimization is used to find a set of optimal lubrication system parameters with the constraint of a small temperature increase in the motorized spindle at 30,000 r/min while considering the influence of oil mist particle size on environmental quality. After lubrication system parameter optimization, comparing the particle size distribution density and temperature increase between the biogeography-based optimization model’s calculated values and the experimental test results, the errors were 1.8% and 1.17%, respectively.

Experimental studies on two dimensional particle swarm gasification of different coal chars and petroleum coke at high temperature

In this study, the effects of particle concentration on particle temperature and gasifying agent concentration was analyzed based on the gasification experiments. The gasification processes of different coal chars and petcoke were divided into fast reaction process (gasification of lignite and bituminous char) and slow reaction process (gasification of anthracite char and petcoke). The reactivity index of fast reactions was extremely higher than that of slow reactions. The reaction rate of sparse particle swarms also differed from that of dense particle swarms for the same sample. For fast reactions, the effects of particle concentration on gasification reactivity was limited. It was illustrated that the evident increase of particle temperature and the decrease of gasifying agent played a contrary effect on reactivity for fast-reaction samples. Nevertheless, the slight decrease of particle temperature and evident decrease of gasifying agent concentration led to the decrease of reaction rate with particle concentration for slow-reaction samples.

Estimating Al2O3–CO2 nanofluid viscosity: a molecular dynamics approach

High-viscosity CO2 is of interest to the oil and gas industry in enhanced oil recovery and well-fracturing applications. Dispersing nanoparticles in CO2 is one way of achieving increased viscosity. However, parametric studies on viscosity estimation of CO2 nanofluids is not found in the open literature. A comparison of various interatomic potentials for their accuracy in predicting viscosity is also missing. In this work, we studied Al2O3 nanoparticles in CO2 base fluid. We screened the inter-molecular interaction potential models available for CO2–CO2 interactions and found that the TraPPE-flexible model (with MORSE potential) to be most suitable for conditions used in this work. We estimated the CO2–Al2O3 interaction potential using quantum mechanical simulations. Using this combination for CO2–CO2 and CO2–Al2O3 interactions, we explored the effects of temperature and nanoparticle size on viscosity using molecular dynamics simulations (MD). We predicted that the viscosity would increase with increase in temperature and particle size. We also calculated the base fluid self-diffusion coefficient to investigate the effect of Brownian motion and its contribution to changes in viscosity. We found that it decreases with increase in particle size and temperature, thereby indicating that Brownian motion does not contribute to the increased viscosity. Further, the nanolayer formed at the Al2O3–CO2 interface is studied through density distributions around the nanoparticle; the thickness of this nanolayer is found to increase with nanoparticle diameter. Finally, we examined the structures of CO2 fluid in presence of nanoparticles at different thermodynamic states through radial distribution functions. The current work sheds light on the viscosity enhancement by the addition of nanoparticles; it is hoped that such studies will lead to tools that help tailor fluid properties to specific requirements.

Stored electromagnetic energy and radiated power by spherical thermal micro/nano-emitters: Radiation Q-factor

We examine theoretically (based on fluctuational electrodynamics) the stored electromagnetic energy and radiated power by a spherical thermal emitter. Moreover, we propose a measure for the radiation quality Q-factor for a polychromatic source such as a thermal emitter. We consider that the thermal emitter is made of tungsten and silicon carbide and we study in detail how the aforementioned radiative quantities depend on size and temperature of the antenna. Particularly, we obtain the emissivity (ratio of spectral radiated power by emitter and that by an ideal blackbody), and the spectral density of stored electromagnetic energy normalized with respect to that of a blackbody. For a SiC-emitter, the emissivity and the normalized spectral stored density energy exhibit multiple narrow peaks associated with surface phonon-polariton and whispering gallery mode resonances; while for a W-antenna, high ohmic losses yield broad spectra of the aforementioned quantities (only an interband resonance appears). These spectra depend strongly on particle size; the corresponding unnormalized spectra are perturbed by the temperature. There is an optimal size of the antenna for which the emissivity is maximal; the aforementioned materials yield an emissivity larger than one. The radiation Q-factor decreases as particle radius and temperature increase, implying that the radiation efficiency of a thermal emitter increases as these parameters grow. The Q-factor for a W-antenna is smaller than that for a SiC-antenna (same size and temperature) for nano-scale particles, whereas, for micrometric particles, the opposite happens over a certain temperature range. Our work might have implications for infrared sources and thermophotovoltaics.

Modeling and simulations of nanofluids using classical molecular dynamics: Particle size and temperature effects on thermal conductivity

We use molecular dynamics simulations to investigate the thermal conductivity of argon-based nanofluid with copper nanoparticles through the Green-Kubo formalism. To describe the interaction between argon-argon atoms, we used the well-known Lennard-Jones (L-J) potential, while the copper–copper interactions are modeled using the embedded atom method (EAM) potential that takes the metallic bonding into account. The thermal conductivity of the pure argon liquid obtained in the present simulation agreed with available experimental results. In the case of nanofluid, our simulation predicted thermal conductivity values larger than those found by the existing analytical models, but in a good accordance with experimental results. This implies that our simulation is more adequate, to describe the thermal conductivity of nanofluids than the previous analytical models. The efficiency of nanofluids is improved and the thermal conductivity enhancement is appeared when the particle size and temperature increase.

New correlations for slip flow and heat transfer over a micro spherical particle in gaseous fluid

In this work, a numerical model was established to simulate the gas flow and heat transfer over a micro spherical particle in the slip regime, in which the gas rarefaction effects (slip phenomena and gas compressibility) and temperature-dependent properties were considered. The Navier-Stokes equations and energy equation were adopted to govern the gas flow and heat transfer in the continuum region, for which the velocity slip and temperature jump boundary conditions were implemented at the gas-particle interface to predict the slip phenomena. The influences of the gas compressibility and temperature-dependent properties on the gas flow and heat transfer characteristics were investigated based on the numerical predictions. It shows that the drag force and heat transfer rate on the particle surface decrease due to the gas velocity slip and temperature jump, respectively. The drag force acting on the particle surface increases with the increase of particle temperature, which is caused by the increasing viscosity of the gas around the particle. The heat transfer coefficient decreases as the particle temperature increases, which is caused by the increasing thermal resistance due to the increase of temperature jump. Finally, the novel correlations for drag coefficient and Nusselt number of the rarefied gas flow over a micro spherical particle were proposed, which consider the influences of the gas rarefaction effects and temperature-dependent properties.

Non-isothermal slip flow over micro spherical particle at low Reynolds numbers

In present work, a numerical study was carried out to investigate the non-isothermal slip flow over a micro spherical particle at low Reynolds numbers. The slip boundary conditions (non-equilibrium momentum exchange and heat transfer) were adopted in the numerical model to predict the discontinuity phenomena at the gas-particle interface. It shows that the drag force acting on the particle and the average Nusselt number on the particle surface both decrease as the Knudsen number increases, which are caused by the effects of velocity slip and temperature jump on the gas-particle interface, respectively. As the particle temperature increases, the drag coefficient increases due to the increasing gas viscosity and the average Nusselt number decreases as the heat conduction becomes dominant at low Reynolds numbers. The influence of gas compressibility on the flow and heat transfer processes were studied based on the numerical predictions, which should be considered for the non-isothermal gaseous flow in the slip regime even if the Mach number is smaller than 0.3. And the effect of gas variable properties cannot be neglected as the temperature difference exists between the particle and gaseous fluid.

Modeling of torrefaction of small biomass particles

ABSTRACTA simple single-step kinetic model consisting of two parallel reactions is proposed for torrefaction of small biomass particles. The model is validated against experimental data on torrefaction of poplar wood fines. Comparison of experimental data and model prediction shows that the results predicted by the proposed simplified model are as accurate as those from the models of Di Blasi and Lanzetta (1997) and Rousset et al. (2006) which involve larger numbers of model parameters – eight and sixteen, respectively – compared to four in the proposed model. This makes it suitable for incorporation into the overall reactor model. At 493 and 553 K, the relative mean errors are found to be 0.056, 0.080, 0.051 and 0.050, 0.100, 0.048 for the proposed model, Rousset et al.’s (2006) model and Blasi and Lanzetta's (1997) model, respectively. The effect of particle size, temperature and residence time on torrefaction of biomass is investigated. A transformation of rate-controlling regime from kinetic to heat transfer is identified with an increase in particle size and temperature. Sensitivity analysis shows that the dimensionless groups such as pyrolysis number, dimensionless heat of reaction and dimensionless activation energy have significant influence on the particle temperature and torrefaction behaviour.

Supercritical CO2 extraction of candlenut oil: process optimization using Taguchi orthogonal array and physicochemical properties of the oil.

A series of experiments was conducted to determine optimum conditions for supercritical carbon dioxide extraction of candlenut oil. A Taguchi experimental design with L9 orthogonal array (four factors in three levels) was employed to evaluate the effects of pressure of 25-35MPa, temperature of 40-60°C, CO2 flow rate of 10-20g/min and particle size of 0.3-0.8mm on oil solubility. The obtained results showed that increase in particle size, pressure and temperature improved the oil solubility. The supercritical carbon dioxide extraction at optimized parameters resulted in oil yield extraction of 61.4% at solubility of 9.6g oil/kg CO2. The obtained candlenut oil from supercritical carbon dioxide extraction has better oil quality than oil which was extracted by Soxhlet extraction using n-hexane. The oil contains high unsaturated oil (linoleic acid and linolenic acid), which have many beneficial effects on human health.

Experimental investigation of the effect of nanoparticle size on thermal conductivity of in-situ prepared silica–ethanol nanofluid

In this study the effects of particle size, temperature and volume fraction of SiO2 nanoparticles on thermal conductivity of nanofluid were investigated. Silica nanoparticles were prepared by the Stöber method. The results of experiments showed that with the increase of particle size, temperature and volume fraction the thermal conductivity of silica–ethanol nanofluid increased. Effect of particle size on thermal conductivity of nanofluid was attributed to high surface hydrophilicity of silica nanoparticles resulting decrease in interfacial thermal resistance with the increase of particle size. Also an empirical equation incorporating particle size, volume fraction and temperature was proposed for estimation of thermal conductivity of nanofluid. Comparison between this correlation and measurements showed that the deviation of calculated data from experimental results is within −9.5% to 5.4%. The literature results agree well with the predictions by correlation proposed.

Thermophysical properties of ethylene glycol-water mixture containing silver nanoparticles

In the present work, we report the thermophysical properties of ethylene glycol and water mixture based silver nanofluids. The thermo physical properties such as thermal conductivity, viscosity, density and specific heat are measured using KD2 Pro thermal properties analyser, capillary viscometer, electronic weighing balance and differential scanning calorimeter respectively. The thermal conductivity increases with the increase in particle concentration and temperature. The maximum enhancement of thermal conductivity observed is approximately ~12% for 0.15 vol% at 50°C. The higher thermal conductivity of the particle, Brownian motion and clustering of the particles could be the possible reason for the improvement in thermal conductivity of the nanofluid which is consistent with the published literature. The viscosity and density increases with increase in particle concentration and decreases with increase in temperature. The specific heat decreases with increase in particle concentration and increases with increase in temperature.

Investigation of particle characteristics, composition and microstructure of LaxCe1−xO2−x/2 thermal barrier coatings during supersonic atmospheric plasma spray using Box–Behnken design

Abstract In this work, Box–Behnken design was used for investigating the influence of the main operating parameters (Argon flow rate: Ar , hydrogen flow rate: H 2 and arc current: I ) on velocity and temperature of La 2 Ce 2 O 7 in-flight particle characteristics (i.e., mean velocity and temperature) during supersonic atmospheric plasma spraying (SAPS). The relationship between the particle characteristics and the composition and the microstructure of LC coating was investigated eventually. During spraying, the particle temperature and velocity were monitored by on-line diagnosis system. The results indicated that the particle velocity linearly increased with the increase of Ar , H 2 and I . I and the interaction between I and Ar and/or H 2 were the most important parameters which influenced the particle temperature. The content of Ce 4 + in the as-sprayed coating rapidly decreased when the particle temperature increased from 2923 to 3036 °C, and then slowly decreased in the range of 3127–3218 °C. When the particle velocity fluctuation was less than 5%, the porosity of as-sprayed coatings decreased with the increase of particle temperature, however, it increased with the increase of particle velocity.

Mechanisms of heat and mass transfer during drying of mate (Ilex paraguariensis) twigs

ABSTRACTExperimental results of surface temperature and moisture content of twigs of mate were obtained in a conveyor-belt dryer operated batchwise. The first response was determined with an infrared sensor, while the second was by conventional gravimetry. A set of 0.04-m-long cylindrical twigs classified manually into three different subgroups on the basis of their diameters (3.5 × 10−3, 6.5 × 10−3, and 10 × 10−3 m) were used in the experiments. Drying always took place in a chamber fed with a thin single layer of material 0.5 m in length and 0.05 m wide. The fresh twigs without leaves at ambient temperature (≈27.2 ± 2.6°C) and with an initial moisture content close to 0.8 ± 0.1 were dried at three different average air temperatures (65.5, 80.2, and 83.8°C) for 7200 s. A full set of nine (31 × 31) drying experiments were performed by varying the examined factors (particle diameter and drying temperature) at three levels. The low estimated Biot numbers (<0.55) indicate that convection plays a much more important role than conduction in heat transfer. Because of this and since heating was much faster than drying, the Newton’s law of cooling alone was successfully applied to describe the increase of particle temperature with time. From a similar analysis involving a convective mass transfer coefficient calculated with the Chilton-Colburn analogy emerged high-mass-transfer Biot numbers (≈5.37 × 103 − 3.65 × 105) that reveal drying of twigs is governed by diffusion. In fact, the equation that represents the Fick’s second law of diffusion in a long cylinder (one-dimensional transfer), solved analytically and coupled to the model of heat transfer, was able to describe the kinetics of drying of mate twigs.

Thermophysical properties of Single Wall Carbon Nanotubes and its effect on exergy efficiency of a flat plate solar collector

In order to enhance thermal efficiency of a flat plate solar collector, the effects of thermo-physical properties of short Single Wall Carbon Nanotubes (SWCNTs) suspended in water was investigated in this study. Sodium dodecyl sulphate was used as a dispersant for preparing a stable nanofluid. Subsequently, the nanofluid was comprehensively characterized by particle size measurement and spectroscopic technique. Specific heat with the increase of particle loading and temperature was investigated. Thermal conductivity increment also showed a linear dependence on particle concentration and temperature. Viscosity of the nanofluids and water reduced with the increase of temperature and increased with the particle loading. Using improved thermo-physical properties of the nanofluid, the maximum energy and exergy efficiency of flat plate collector was enhanced up to 95.12% and 26.25% compared to water which was 42.07% and 8.77%, respectively. This low exergy efficiency shows that flat plate collectors still require substantial enhancement. To the authors’ knowledge, SWCNTs–H2O was used as the functioning fluid for the first time to investigate both the thermos-physical properties as well as the increase in thermal efficiency of a flat plate solar collector.