The effect of Stefan flow on the drag coefficient of spherical particles in a gas flow

Jayawickrama, Thamali R.; Haugen, Nils Erland L.; Bäbler, Matthäus U.; Chishty, Muhammad Aqib; Umeki, Kentaro

doi:10.1016/j.ijmultiphaseflow.2019.04.022

Cited by 42 publications

(29 citation statements)

References 22 publications

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“…In previous studies about outflow particles [13][14][15]17], the Stefan flow tends to weaken the drag force. In these studies, the Stefan flow has little influence on the pressure but attenuates the friction.…”

Section: Heterogeneous Reactionsmentioning

confidence: 97%

“…This nonzero normal velocity changes the structure of the particle boundary layer. In some previous studies of particles with outflow [13,14,17,26] and porous particles [11,12,40,41], the effect of wall-normal velocity is also mentioned. As shown in Fig.…”

Section: Flow Patternmentioning

confidence: 99%

“…For this problem, a blowing correlation [16] was introduced to quantify the effect of pyrolysis when calculating the particle response time. The Stefan flow Reynolds number was also used in the drag correlation [17]. Furthermore, in Higuera's study [18], the definition of the drag force is modified.…”

Section: Introductionmentioning

confidence: 99%

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Drag force for a burning particle

Zhang

Luo

Haugen

et al. 2020

Combustion and Flame

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This study aims to study the effect of reactions and temperature on the drag force coefficient in the process of char combustion. For this purpose, two-dimensional fully resolved simulations are performed using the ghost cell immersed boundary method.Heat and mass transfer, together with the corresponding Stefan flow, is accounted for.Reactive particles with different reaction rates, temperatures and diameters are compared with a non-reactive adiabatic particle and a particle with outflow. For a char particle, results show that reactions tend to increase the drag force, which is converse to the effect observed for non-reactive particles with a pure outflow. This discrepancy is due to the fact that species and temperature distribution play an important role, and both of them can affect the property of the fluid. Hence, a reactive particle cannot be simplified as a particle with only outflow. Based on the current study, a new drag force correlation for a single reactive particle is obtained. The correlation shows a good agreement with the simulation results. A posterior analysis is also performed to verify the accuracy of the correlation.

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Section: Heterogeneous Reactionsmentioning

confidence: 97%

Section: Flow Patternmentioning

confidence: 99%

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Drag force for a burning particle

Zhang

Luo

Haugen

et al. 2020

Combustion and Flame

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“…It is worth noticing that the gas-phase velocity field exhibits a significant radial flow at the interface, due to the Stefan flow induced by the vaporization. Several authors observed that this radial flow leads to a significant reduction of the drag coefficient on the droplet [64,65],…”

Section: The Effect Of Gravitymentioning

confidence: 99%

Interface-resolved simulation of the evaporation and combustion of a fuel droplet suspended in normal gravity

Saufi,

Frassoldati,

Faravelli

et al. 2020

Preprint

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DropletSMOKE++ is a multiphase CFD framework based on OpenFOAM R , originally developed and validated for suspended droplets evaporation in a gravity field and convective conditions. In this work the solver is further extended to account for gas-phase combustion introducing: (i) an operator-splitting methodology to efficiently solve the gas-phase chemistry with large kinetic mechanisms, (ii) a model for the flame radiative heat transfer and (iii) a double vaporization model to account for possible boiling. This allows to simulate the combustion of suspended fuel droplets in normal gravity with a detailed description of the gas-phase chemistry, representing the novelty and the main objective of this work. The numerical model is applied to simulate the vaporization, ignition and combustion of a methanol droplet suspended on a quartz fiber at different oxygen concentrations. The numerical results are compared with recent experimental data, showing a satisfactory agreement in terms of diameter decay, radial temperature profiles and sensitivity to the oxygen concentration in the gas-phase. In particular, the burning rate is found to be significantly affected by thermal conduction from the fiber, due to its relatively large size and the high temperatures involved in the combustion process. On the other hand the fiber perturbs the flame itself, providing a partial quenching close to its surface. The droplet combustion behavior has been compared to the one predicted in microgravity conditions, evidencing a lower standoff ratio, a higher flame temperature and an intense internal circulation. The gas-phase chemistry has been analyzed in terms of distribution of the main species in the gas phase, showing a local accumulation of (i) intermediate oxidation products at the fiber (due to the quenching) and (ii) water at the surface, which partially condenses on the droplet surface affecting the vaporization rate.

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“…2 Pressure build-up inside the particle has a significant effect on the product distribution as the trapped gases can undergo secondary reactions. 3 Also, the convective flow of gas out of the particle affects the interaction of the particles with the environment, 4 while high pressure inside the particle can cause mechanical degradation up to the point of cracking of the particle. 3,5 Modeling of biomass pyrolysis has received considerable attention in the literature.…”

Section: ■ Introductionmentioning

confidence: 99%

1D Finite Volume Scheme for Simulating Gas–Solid Reactions in Porous Spherical Particles with Application to Biomass Pyrolysis

Sadegh-Vaziri

Winberg-Wang

Bäbler

2021

Ind. Eng. Chem. Res.

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Models for gas−solid reactions in porous particles typically consist of a set of mass and energy balances in the form of conservation equations. For spherical or close to spherical particles, these equations are formulated in 1D spherical coordinates. In the case where accumulation of gas inside the particle is significant, the balance equations contain convective terms. The present work presents a simple numerical scheme based on flux limited finite volume methods for discretizing conservation equations for convective and diffusive transport of mass and energy in radial direction in a porous sphere. The velocity is governed by Darcy's law coupled to an equation of state. The proposed scheme is applied to a series of test problems that admit full or partial analytical solutions. For the cases where only partial analytical solutions are available, a Comsol model is adopted for comparison. It is found that the scheme is able to resolve step gradients without generating oscillations and that it properly handles changes in the sign of the convective velocity. Applying the scheme for solving a common model for biomass pyrolysis reveals the importance of convective gas transport in the pyrolysis of thermally thick biomass particles.

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The effect of Stefan flow on the drag coefficient of spherical particles in a gas flow

Cited by 42 publications

References 22 publications

Drag force for a burning particle

Drag force for a burning particle

Interface-resolved simulation of the evaporation and combustion of a fuel droplet suspended in normal gravity

1D Finite Volume Scheme for Simulating Gas–Solid Reactions in Porous Spherical Particles with Application to Biomass Pyrolysis

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