Particle Heat Transfer Research Articles

The effect of intermittent mixing on particle heat transfer in an agitated dryer

Intermittent mixing, alternating agitation and no agitation, is an approach to maintain a high drying rate while minimizing particle breakage in agitated filter drying of the active pharmaceutical ingredient. In this study, the effect of intermittent mixing on heat transfer of particles was examined using DEM simulations. The agitation ratio (the fraction of time the agitator is on) and intermittent cycle number (the number of on/off cycles) represent the extent and allocation of agitation, respectively. It was observed that as the agitation ratio increases from the static bed, the rate of heat transfer and temperature uniformity initially increased sharply, and then more gradually for high agitation ratios. Additionally, the rate of heat transfer and temperature uniformity initially increased with intermittent cycle number, then reached a plateau. The results were fitted using a power law which predicted the rate of heat transfer as a function of the intermittent mixing parameters.

Computational fluid dynamics study of hydrogen production by sorption enhanced steam ethanol reforming process in fluidized bed

As a renewable resource, hydrogen plays a pivotal role in the energy transition of the current world. A promising route for hydrogen production is the sorption enhanced steam ethanol reforming (SE-SER), which is characterized by the complex multi-scale characteristics. This paper aims to explore the hydrodynamic (e.g., gas and solid flux, solid dispersion and velocity) and thermodynamic (e.g., particle temperature and heat transfer coefficient) characteristics on the micro-level together with the effect of operating parameters on the SE-SER performance. Accordingly, the reactive multiphase particle-in-cell (MP-PIC) model has been developed under the Lagrangian manner for studying the SE-SER process in the bubbling fluidized bed. In this model, it is assumed that uniform temperature appears inside the particle, and particles with similar properties are packed into a parcel to reduce computational cost. This model has been well validated with experimental data. The results indicate that along the bed height, the solid temperature decreases while the heat transfer coefficient increases. H2 and CO2 have similar distribution in the bed, mainly accumulating in the upper part of the reactor. Enlarging the ratio of H2O to C2H6O in the gas mixture promotes the yields of H2 and CO2. The relationships between key particle variables are explored. It is found that increasing the slip velocity enlarges the particle heat transfer coefficient, and large particle Reynolds number mainly appears with small solid volume fraction. The explored results provide valuable insights into deeply understanding complex multiphase flow and optimizing actual operation of the SE-SER field.

Study of biomass gasification in an industrial-scale dual circulating fluidized bed (DCFB) using the Eulerian-Lagrangian method

Dual circulating fluidized bed (DCFB) has emerged as an efficient reactor for biomass gasification due to its unique feature of high gas-solid contact efficiency and separated reactions in two reactors, yet the understanding of complex in-furnace phenomena is still lacking. In this study, biomass gasification in an industrial-scale DCFB system was numerically studied using a multiphase particle-in-cell (MP-PIC) method featuring thermochemical sub-models (e.g., heat transfer, heterogeneous reactions, and homogeneous reactions) under the Eulerian-Lagrangian framework. After model validation, the hydrodynamics and thermochemical characteristics (i.e., pressure, temperature, and species) in the DCFB are comprehensively investigated. The results show that size-/density-induced segregation makes solid fuels concentrate on the bed surface. Interphase momentum exchange leads to the continuous decrease of the gas pressure axially. In the gasifier and combustor, the lower heating value (LHV) of the gas products is 5.56 MJ/Nm3 and 0.2 MJ/Nm3 and the combustible gas concentration (CGC) is 65.5% and 1.86%, respectively. The temperature in the combustor is about 100 K higher than that in the gasifier. A higher solid concentration results in a smaller value of particle heat transfer coefficient (HTC). The HTCs range from 50 to 150 W/(m2 K) for a solid concentration larger than 0.3 in the combustor while the HTCs range from 100 to 200 W/(m2 K) in the gasifier. The Reynolds number of biomass particles is two orders of magnitude larger than that of the sand particle. The numerical results shed light on the reactor design and process optimization of biomass gasification in DCFBs.

Effect of combining multi-jet component with axial swirl blade on evaporation in a spouted bed

To improve the fluidization behavior and the heat and mass transfer process in a spouted bed, a multi-jet–axial-swirl-blade spouted bed (MJ-ASB SB) was developed. The water evaporation process of the MJ-ASB SB was simulated and compared with those of the conventional spouted bed (CSB) and an integral multi-jet spout-fluidized bed (IMJSFB). The simulation results showed that the MJ-ASB SB combined the staged spouting action of multi-jet with the swirling action of the axial swirl blade, which promoted particle turbulence in the annulus region and ensured effective particle mixing. The swirl number of the MJ-ASB SB ranged from 0.0816 to 2.7239 with enhanced vortex intensity, thus promoting momentum and heat transfer of gas and particles in the spouted bed. The MJ-ASB SB had a higher slip velocity than the other two bed types, which indicates that the combined internal structure could improve the fluidization state of the bed and intensify the movement and mixing of phases in the spouted bed. The three-phase temperature, water evaporation rate, and gas humidity of the MJ-ASB SB were higher than those of the CSB and IMJSFB, and water evaporation occurred in an enlarged region in the MJ-ASB SB. The mass transfer intensification factors I of the MJ-ASB SB (2.62) and IMJSFB (1.92) were 91% and 161% higher than that of the CSB (1), respectively, indicating that the combined internal structure of the MJ-ASB SB significantly contributed to the water evaporation process.

Numerical Simulation of Heat Transfer and Spread of Virus Particles in the Car Interior

The epidemic caused by the coronavirus infection SARS-CoV-2 at the beginning of 2022 affected approximately 500 million people in all countries. The source of infection is the particles of the virus, which, when breathing, talking, and coughing, are released with the respiratory droplets and aerosol dust of an infected person. Actions aimed at combating and minimizing the consequences of coronavirus infection led to taking measures in scientific areas to investigate the processes of the spread of viral particles in the air, in ventilation, and air conditioning systems of premises and transport, filtration through masks, the effect of partitions, face shields, etc. The article presents a mathematical model of the spread of viral particles in technological transport. Air intake diverters and the operator’s respiratory tract are the sources of the virus. The Euler–Lagrange approach was used to simulate liquid droplets in a flow. Here, the liquid phase is considered as a continuous medium using Navier–Stokes equations, the continuity equation, the energy equation, and the diffusion equation. Accounting for diffusion makes it possible to explicitly model air humidity and is necessary to consider the evaporation of droplets (changes in the mass and size of particles containing the virus). Liquid droplets are modeled using the discrete-phase model (DPM), in which each particle is tracked in a Lagrange coordinate system. The DPM method is effective, since the volume fraction of particles is small relative to the total volume of the medium, and the interaction of particles with each other can be neglected. In this case, the discrete and continuous phases are interconnected through the source terms in the equations. The averaged RANS equations are solved numerically using the k-ω turbulence model in the Ansys Fluent package. The task was solved in a static form and in the time domain. For a non-stationary problem, the stabilization time of the variables is found. The simulation results are obtained in the form of fields of pressures, velocities, temperatures and air densities, and the field of propagation of particles containing the virus. Various regimes were studied at various free flow rates and initial velocities of droplets with viral particles. The results of trajectories and velocities of particles, and particle concentrations depending on time, size, and on the evaporability of particles are obtained.

Heat transfer in granular media consisting of particles in humid air at low confining pressure

I study the heat transfer in systems of weakly interacting particles at low confining pressure in the normal atmosphere. The particles have surface roughness with self-affine fractal properties, as expected for mineral particles produced by fracture, e.g., by crunching brittle materials in a mortar. I show that for small particles (say <10 mathrm{mu m}) with hydrophilic surfaces, at large humidity water capillary bridges dominate the heat transfer, while for big particles heat transfer via the air dominates. This differs from vacuum conditions where the propagating electromagnetic (EM) waves give the dominant heat transfer for large particles, while for small particles both the evanescent EM-waves and the phononic contribution from the area of real contact are most important.

A tube heat transfer prediction model considering static friction coefficient of dense particle flow

Particulate material is an important heat transfer medium in industry. The heat transfer process of dense particle flow around tubes has important applications in industrial waste heat and solar energy conversion. However, rapid prediction of particle heat transfer processes is still worth investigating, especially when the particle flow is affected by the coefficient of friction. A heat transfer model of dense particle flow around a tube was established, the effects of particle size, density and static friction coefficient on the heat transfer characteristics were explored, and a heat transfer prediction equation considering the static friction coefficient was constructed originally. The results show that the particle size has the most significant effect on the heat transfer. As the particle size increases from 2 mm to 4 mm, the average effective heat transfer coefficient of the tube decreases from 262.35 W/(m2·K) to 217.31 W/(m2·K). The effect of particle density on the heat transfer is reflected in the difference in the heat capacity of the particles, and has little effect on the flow of the particles. The particle static friction coefficient mainly affects heat transfer by affecting the flow state of the particle flow. The average contact number decreases from 63.9 to 38.9. The relative error of the modified model is reduced from 8.9% to 3.78%.

CFD investigation of the complex multiphase flow of biomass gasification in industrial-scale dual fluidized bed reactor

In this work, the process of biomass steam-gasification via a dual fluidized bed with a thermal input of 8MWth is numerically modeled by applying the multiphase particle-in-cell method. This model is successfully validated with the experimental data. Based on the simulation, the results can be epitomized as: distinct fluidization regimes in gasifier and combustor reactors give rise to different flow pattern and dispersion coefficients of solid phase in both reactors. Large particle heat transfer coefficients mainly appear in the upper regions of both reactors due to violent reactions. In this industrial-scale apparatus, the time-averaged heat transfer coefficient of sand in the combustor is larger than that of gasifier sand for about 40 W/(m2·K). Relationships between key variables such as volume fraction, heat transfer coefficient, slip velocity, Reynolds number and temperature of solid phase are discussed. Particles with small volume fraction tend to possess large heat transfer coefficient and slip velocity. The results explored at the particle-level might be useful in the industrial operating regarding the biomass steam-gasification processes.

Numerical simulation of dust particle deposition and heat transfer in fin-plate radiators

Fin-plate radiators are actively used in cooling systems for microelectronic devices. Radiators often become dusty during operation, which leads to decrease in heat flow and heat dissipation. Consequently, the possibility of device overheating and failure increases. We carried out numerical studies to assess the influence of the radiator geometry on the deposition of dust particles and, as a consequence, the change in heat flow. We built 3D models of plate radiators with different types of fins (flat and corrugated) and the distance between them. The problem of air flow with dust particles flowing around the radiator has been solved. We revealed the dependences of the efficiency of particle deposition and changes in heat flow on the geometry of the radiator, the size of dust particles and the distance between the fins.

Study of the influence of fin-plate heat exchanger geometry on dust particle deposition and heat transfer based on numerical calculation

Cooling systems are actively used in computer technology to cool various electronic devices, for example, the central processor units (CPU). CPUs generate heat while operating, which slows down the processing speed of information, and overheating often causes the CPU to shut down or even crash. Cooling systems are designed to remove heat from the CPU. Often, during operation of the cooling system, its main element – the fin-plate heat exchanger becomes covered with a layer of dust, which significantly reduces the rate of heat transfer and can lead to CPU failure. In this work, we carried out numerical modeling of dust particles deposition on the surface of fin-plate heat exchangers of various geometries. We studied the influence of the fin shape (flat or corrugated), as well as the distance between the fins (from 1.75 to 7 mm) on the efficiency of particle deposition and the change in heat flow.

Solidification and heat transfer of molten steel slag particles during air quenching process

Solidification and heat transfer of molten steel slag particles during air quenching process

Compressibility and Rarefaction Effects on Particle Dynamics and Heat Transfer in Aerosol Deposition Process

The aerosol deposition (AD) method is an emerging coating technique to create a dense ceramic or metal layer on a substrate through the kinetic impaction and cumulative deposition of ultrafine solid particles under near-vacuum conditions. Prediction of the particles’ impact velocity and temperature during the AD process is crucial in enhancing the coating quality. In the present work, a two-way coupled Eulerian-Lagrangian model is developed for an AD system equipped with a converging-barrel nozzle to simulate the supersonic gas flow, particle in-flight behavior, as well as particle conditions upon impact on a flat substrate. The focus of the current study is to understand the effects of compressibility and rarefaction on particle velocity and temperature during the AD process. The effects of compressibility and rarefaction can be assessed using the Mach and Knudsen numbers. Therefore, different models for the drag coefficient and the heat transfer coefficient that take into account the Knudsen, Mach, and Reynolds number effects are implemented into the computational fluid dynamics (CFD) models. The results show that compressibility and rarefaction have significant influence on the particle temperature and velocity. As the particle size reduces, the effects of compressibility and rarefaction become more important.

Heat transfer in granular media with weakly interacting particles

We study the heat transfer in weakly interacting particle systems in vacuum. The particles have surface roughness with self-affine fractal properties, as expected for mineral particles produced by fracture, e.g., by crunching brittle materials in a mortar, or from thermal fatigue or the impact of micrometeorites on asteroids. We show that the propagating electromagnetic (EM) waves give the dominant heat transfer for large particles, while for small particles both the evanescent EM-waves and the phononic contribution from the area of real contact are important. As an application, we discuss the heat transfer in rubble pile asteroids.

Two-way coupled turbulent particle-laden boundary layer combustion over a flat plate

In the present study, turbulent particle-laden boundary layer combustion over a flat plate is investigated using direct numerical simulation (DNS). A two-way coupled Eulerian–Lagrangian point particle method is used for the solid phase. The effects of particle Stokes numbers, mass loadings and chemical reactions on the interactions between particles and boundary layer turbulence in the near-wall region are explored. It was found that particle heat transfer is dominant over wall heat transfer in the reacting case with heavy particles and large mass loadings, resulting in a lower fluid temperature. Particle accumulation due to the turbophoresis effect in the near-wall region is observed, which is more prominent in the cases with a large Stokes number. The turbophoresis effect is examined via the magnitude of streamwise vorticity $\varOmega _x$ . It is shown that $\varOmega _x$ is attenuated by heavy particles, and the attenuation increases with increasing mass loadings. Therefore, particle wall–accumulation is less prominent in the cases with large mass loadings. Compared with the non-reacting cases, the distribution of particles is more inhomogeneous for the reacting cases, where the particles move faster due to intense reactions with increasing wall-normal distance. Finally, the flow topologies and the Reynolds stress anisotropy are examined to understand turbulence modulation by combustion and particles. It was suggested that light particles augment the vortex-dominant topologies, whereas heavy particles have an opposite effect. The anisotropy mapping of the Reynolds stress shows that the flows become more one-dimensional in the near-wall region for the cases with combustion and/or large mass loadings.

An experimental study of coal particle group combustion in conventional and oxy-fuel atmospheres using multi-parameter optical diagnostics

The present work reports an experimental study of particle group combustion of pulverized bituminous coal in laminar flow conditions using advanced multi-parameter optical diagnostics. Simultaneously conducted high-speed scanning OH-LIF, diffuse backlight-illumination (DBI), and Mie scattering measurements enable analyses of three-dimensional volatile flame structures and soot formation in conventional (i.e., N2/O2) and oxy-fuel (i.e., CO2/O2) atmospheres with increasing O2 enrichment. Particle-flame interaction is assessed by calculating instantaneous particle number density (PND), whose uncertainties are estimated by generating synthetic particles in DBI image simulations. Time-resolved particle sequences allow the evaluation of the particle velocity, which indicates a PND dependency and interactions between particles and volatile flames. 3D flame structure reconstruction and soot formation detection are first demonstrated in single-shot visualizations and then extended to analyze effects of O2 concentration, PND, and inert gas composition statistically. The increasing O2 concentration significantly reduces local flame extinction and suppresses soot formation in N2 and CO2 atmospheres. Volatile flames reveal higher intensities and lower lift-off heights as O2 concentration increases. In contrast to that, an increased PND leads to earlier flame extinction and stronger soot formation due to the local gas temperature reduction and oxygen depletion. The lift-off height reduces with increasing PND, which is explained by the complex interaction between particle dynamics, heat transfer, and volatile reactions. Slightly stronger soot formation and delayed ignition are observed in CO2 atmospheres, whereas CO2 replacement reveals insignificant influences on the flame extinction behavior. Finally, non-flammability is quantified for particle group combustion at varying PNDs in different atmospheres.

Simulation of mass and heat transfer of Quercus leaf particles during hydrothermal extraction

AbstractMass and heat transfer models of Quercus leaf particles during hydrothermal extraction were developed in COMSOL Multiphysics. The main physical properties used in the model were measured. The results showed that the average particle size was 116.7 μm, and after soaking in water for 24 h, the average particle size increased to 127.3 μm. However, the average particle size increased from 116.7 to 132.8 μm after soaking in a 60% (v/v) ethanol solution for 40 min, and decreased to 127.3 μm after 60 min. The Quercus leaf particles have a higher ability to absorb ethanol solution than water. The simulations showed that it took 3.2 s for the ethanol concentration and 0.5 s for the temperature in the particles to tend stably after soaking in a 60% (v/v) ethanol solution at 40°C. From the edge of the particle to the centre, the increasing rates of ethanol concentration and temperature gradually slowed down, while the changing rates of the centre accelerated with the increase in solution concentration and temperature, respectively. When the particles soaked at the lowest concentration, the central concentration first reached stability, and at the lowest temperature, the centre temperature first stabilized.

Discrete Phase Analysis of Self Heating Particles Over an Immersion Liquid Cooled High Power Blue Light-Emitting Diode With Suspended Phosphor Particles

Abstract In recent years, the interaction of unrestricted particles with dispersed multiphase flows has been linked to a number of important engineering applications. Among these applications, the novel idea of immersion-cooled phosphor particles, which has the potential of significantly increasing the thermal limits of phosphor converted white light-emitting diode (LEDs) (Pc-WLEDs), has yet to be thoroughly investigated. With this objective, this research utilizes the discrete phase modeling (DPM) technique for the characterization of phosphor location and movements within a buoyancy-driven flow, which is the determining factor in the optical behavior of the newly proposed Pc-WLED configuration. Two-phase flow analysis is conducted to characterize particle movement. Heat transfer, flow, and energy paths of self-heating phosphor particles are extracted, and the influence of particle sizes is analyzed in detail. The results show that with immersion liquid cooling, the highest phosphor particle temperature is recorded to be under 420 K, while larger size particles introduce higher heat transfer rates to the Pc-WLED package for the same number of particles. Moreover, depending on the particle size and position, individual phosphor particles can follow a different trajectory that can affect the probability of obtaining white light emission.

Particle Distribution and Heat Transfer of SiO2/Water Nanofluid in the Turbulent Tube Flow.

In order to clarify the effect of particle coagulation on the heat transfer properties, the governing equations of nanofluid together with the equation for nanoparticles in the SiO2/water nanofluid flowing through a turbulent tube are solved numerically in the range of Reynolds number 3000 ≤ Re ≤ 16,000 and particle volume fraction 0.005 ≤ φ ≤ 0.04. Some results are validated by comparing with the experimental results. The effect of particle convection, diffusion, and coagulation on the pressure drop ∆P, particle distribution, and heat transfer of nanofluid are analyzed. The main innovation is that it gives the effect of particle coagulation on the pressure drop, particle distribution, and heat transfer. The results showed that ∆P increases with the increase in Re and φ. When inlet velocity is small, the increase in ∆P caused by adding particles is relatively large, and ∆P increases most obviously compared with the case of pure water when the inlet velocity is 0.589 m/s and φ is 0.004. Particle number concentration M0 decreases along the flow direction, and M0 near the wall is decreased to the original 2% and decreased by about 90% in the central area. M0 increases with increasing Re but with decreasing φ, and basically presents a uniform distribution in the core area of the tube. The geometric mean diameter of particle GMD increases with increasing φ, but with decreasing Re. GMD is the minimum in the inlet area, and gradually increases along the flow direction. The geometric standard deviation of particle diameter GSD increases sharply at the inlet and decreases in the inlet area, remains almost unchanged in the whole tube, and finally decreases rapidly again at the outlet. The effects of Re and φ on the variation in GSD along the flow direction are insignificant. The values of convective heat transfer coefficient h and Nusselt number Nu are larger for nanofluids than that for pure water. h and Nu increase with the increase in Re and φ. Interestingly, the variation in φ from 0.005 to 0.04 has little effect on h and Nu.

MP-PIC investigation of glycerol steam reforming in bubbling fluidized bed for high-quality hydrogen production

A reactive multiphase particle-in-cell approach is adopted to numerically investigate the physical and thermochemical characteristics of glycerol steam reforming process in a three-dimensional bubbling fluidized bed. Via the model verification, the simulated results are in acceptable agreement with the experimental measurements. The gas-solid flow hydrodynamics and the particle thermochemical properties are explored. In addition, the effects of different operating parameters (reaction temperature, particle diameter, steam/glycerol ratio, operating pressure) on the performance of the glycerol steam reforming system are discussed. The results reveal the significantly non-uniform spatial distribution of particle temperature and heat transfer coefficient (HTC) due to the intense endothermic reactions and nonlinear hydrodynamics. Comparatively large HTC of solid particles appears in the lower part of the bed. Enlarging the reaction temperature and operating pressure give rise to a larger particle HTC. The back-mixing and internal circulation behavior of particles highly influence the spatial distribution of particle velocity inside the bed. The slip velocity of particle accumulated around the gas feeding port is obviously large. The slip velocity and HTC of particle are almost positively correlated. Decreasing the steam/glycerol ratio enhances the particle thermochemical properties. Moreover, elevating the reaction temperature significantly promotes the yields of H2 and CO while the formation of CH4 is suppressed.

Influence of internal heat transfer on reactive force applied to powder particles in laser cladding

Formation of two-phase powder-gas flows is the key factor determining the quality of materials synthesized by laser cladding and similar laser processes. Currently, the influence of the processing laser beam on such flows is insufficiently studied. Recent experiments on high-speed imaging show that the laser beam can considerably accelerate and deviate the exposed powder particles. This phenomenon is commonly explained by the reactive force arising at laser evaporation of particles. It seems that the existing theoretical approaches considerably overestimate the reactive force because they ignore internal heat transfer in the particle. The aim of the present work is to analyze theoretically the combined conductive-convective heat transfer in the particle exposed to laser radiation and the related evaporation and formation of the resultant reactive force. Computational Fluid Dynamic (CFD) simulation has shown that the internal heat transfer can reduce the temperature gradient in the particle, thus considerably reducing the resultant reactive force in the typical conditions of laser cladding. The CFD indicates that in such conditions, the influence of convection on the reactive force is low. An analytic model of conductive heat transfer and evaporation of a spherical particle is developed. The CFD validates this model and indicates that the confidence interval of the estimated resultant reactive force is within 1%. This model can be useful for analyzing experimental data and simulation of gas-powder flows exposed to laser radiation.