Role of Bouncing Potential in Molten Ash Impaction

doi:10.1080/00986445.2014.927358

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Role of Bouncing Potential in Molten Ash Impaction

Journal Article•DOI•

Role of Bouncing Potential in Molten Ash Impaction

Soundaravalli Balakrishnan¹, Rajarathinavelu Nagarajan¹•Institutions (1)

Indian Institute of Technology Madras¹

18 May 2015-Chemical Engineering Communications (Taylor & Francis)-Vol. 202, Iss: 10, pp 1360-1367

TL;DR: In this article, the authors developed a model to predict the outcome of a molten ash particle impacting a heat transfer surface, where the main driving force for a splat at maximum spread state to recoil is the difference in surface energies of the splat and its equilibrium sessile drop state.

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Abstract: The aim of the present study is to develop a model to predict the outcome of a molten ash particle impacting a heat-transfer surface. The main driving force for a splat at maximum spread state to recoil is the difference in surface energies of the splat and its equilibrium sessile drop state. If the difference in surface energies is significant, a vigorous recoiling then leads to rebounding. During the travel from splat to equilibrium state, the viscous dissipation in the rim opposes the recoiling process. By overcoming the dissipation loss, the splat reaches sessile drop state. If the drop possesses energy greater than the adhesion energy, it will detach itself from the surface; otherwise, it will deposit. A bouncing potential model based on this concept is derived and compared with models and experimental data in literature.

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Journal Article•DOI•

Modeling of ash formation and deposition processes in coal and biomass fired boilers: A comprehensive review

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Yongtie Cai¹, Kun Lin Tay¹, Zhimin Zheng¹, Wenming Yang¹, Hui Wang², Guang Zeng¹, Zhiwang Li¹, Siah Keng Boon, Prabakaran Subbaiah - Show less +5 more•Institutions (2)

National University of Singapore¹, Harbin Institute of Technology²

15 Nov 2018-Applied Energy

TL;DR: In this article, a comprehensive review on the development of the modelling of ash deposition with particle combustion, sticking, rebound and removal behaviors is presented, including the modeling of ash deposit morphomology.

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117 citations

Journal Article•DOI•

Mechanistic modeling, numerical simulation and validation of slag-layer growth in a coal-fired boiler

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Soundaravalli Balakrishnan¹, Rajarathinavelu Nagarajan¹, K. Karthick²•Institutions (2)

Indian Institute of Technology Madras¹, Bharat Heavy Electricals²

01 Mar 2015-Energy

TL;DR: In this paper, a mechanistic bouncing potential model, incorporating the phenomenon of recoiling of molten ash droplets after impaction, is employed to determine the outcome of slag-layer impaction.

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34 citations

Journal Article•DOI•

Ultrasonic coal washing to leach alkali elements from coals.

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Soundaravalli Balakrishnan¹, V. Midhun Reddy¹, Rajarathinavelu Nagarajan¹•Institutions (1)

Indian Institute of Technology Madras¹

01 Nov 2015-Ultrasonics Sonochemistry

TL;DR: Ulasonic water-washing and chemical-washing, in comparison with agitation, are studied in order to estimate the intensification of the alkali removal process by sonication.

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26 citations

Journal Article•DOI•

Mechanistic Model for Ash Deposit Formation in Biomass Suspension Firing. Part 1: Model Verification by Use of Entrained Flow Reactor Experiments

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Stine Broholm Hansen, Peter Arendt Jensen, Flemming Frandsen, Bo Sander, Peter Glarborg - Show less +1 more

16 Mar 2017-Energy & Fuels

TL;DR: In this article, two models for deposit formation in suspension firing of biomass have been developed: model #1 employs a reference viscosity in the description of the sticking probability, while model #2 combines impaction of viscoelastic particles on a solid surface with particle capture by a viscous surface.

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Abstract: Two models for deposit formation in suspension firing of biomass have been developed. Both models describe deposit buildup by diffusion and subsequent condensation of vapors, thermophoresis of aerosols, convective diffusion of small particles, impaction of large particles, and reaction. The models differ in the description of the sticking probability of impacted particles: model #1 employs a reference viscosity in the description of the sticking probability, while model #2 combines impaction of viscoelastic particles on a solid surface with particle capture by a viscous surface. Both models were used to describe the deposit formation rates and deposit chemistry observed in a series of entrained flow reactor (EFR) experiments using straw and wood as fuels. It was found that model #1 was not able to describe the observed influence of temperature on the deposit buildup rates, predicting a much stronger influence of this parameter. Model #2 was able to provide a reasonable description of the influence of temp...

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21 citations

Journal Article•DOI•

Influence of Chemical Leaching on Rheology and Ash Reduction of Indian Coal

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Puneet Juneja¹, Satish Kumar¹, Saroj Kumar Mohapatra¹•Institutions (1)

Thapar University¹

04 Jul 2018-International Journal of Coal Preparation and Utilization

TL;DR: The quality and calorific value of Indian coal are very low. as discussed by the authors The objective of the present study was to reduce the ash content and to produce ultraclean coal (UCC).

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Abstract: The quality and calorific value of Indian coal are very low. The objective of the present study was to reduce the ash content and to produce ultraclean coal (UCC). The low-ash-content coal was then...

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3 citations

References

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Journal Article•DOI•

Spread and rebound of liquid droplets upon impact on flat surfaces

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Ted Mao¹, David C. S. Kuhn¹, Honghi Tran¹•Institutions (1)

University of Toronto¹

01 Sep 1997-Aiche Journal

TL;DR: In this paper, a rebound model was proposed to predict the tendency of a droplet to deposit or to rebound on flat surfaces at room temperature at impact velocities, viscosities, and surface roughness.

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Abstract: The spread and rebound of droplets upon impact on flat surfaces at room temperature were studied over a wide range of impact velocities (0.5–6 m/s), viscosities (1–100 mPa.s), static contact angles (30–120°), droplet sizes (1.5–3.5 mm), and surface roughnesses using a fast-shutter-speed CCD camera. The maximum spread of a droplet upon impact depended strongly on the liquid viscosity and the impact velocity. The tendency of a droplet to deposit or to rebound is determined primarily by the liquid viscosity and the liquid/substrate static contact angle. A model more broadly applicable than existing models was developed to predict maximum spread as a function of the Reynolds number, the Weber number, and the static contact angle. Based on the conservation of energy, a rebound model is proposed that predicts the tendency to rebound as a function of maximum spread and static contact angle. The maximum-spread model prediction agrees to within 10% with more than 90% of the experimental data from different sources. In the current study, the rebound model successfully predicts the tendency of a droplet to rebound.

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561 citations

"Role of Bouncing Potential in Molte..." refers background or methods in this paper

...With this definition of BP, unlike in the Mao et al. (1997) model, the Hsiao et al. (2009) model required the threshold BP, governing the transition from sticking to bouncing, to be determined experimentally....
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...By applying the energy conservation principle during recoiling, Mao et al. (1997) framed a definition for bouncing potential (BP), a parameter with the ability to decide the outcome of the impaction of the drop....
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...…are adopted to study the maximum spread ratio, viz., energy conservation approach (Chandra and Avedisian, 1991; Gong, 2005; Hsiao et al., 2009; Mao et al., 1997; Pasandideh-Fard et al., 1996) and numerical simulation of Navier–Stokes equations (Fukai et al., 1995; Kim and Chun, 2001;…...
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...When the Mao et al. (1997) model was used to estimate the threshold contact angle for the experimental parameters of Hsiao et al. (2009), it predicted a crossover contact angle of 92 (refer Figure 5); however, experimental data revealed that it was in the range 53 to 65....
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...The BP defined by Mao et al. (1997) considered a fictitious configuration of a spherical drop of diameter equal to the diameter of the drop above the substrate before impact....
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Journal Article•DOI•

Dynamics of dewetting.

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C. Redon¹, Françoise Brochard-Wyart¹, F. Rondelez¹•Institutions (1)

Pierre-and-Marie-Curie University¹

11 Feb 1991-Physical Review Letters

TL;DR: In this paper, a dry spot at the center of a silicone wafer was nucleated and the rate of growth was observed to be independent of R, independent of the film thickness, inversely proportional to the oil viscosity, and very sensitive to the value of the equilibrium contact angle between oil and wafer.

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Abstract: Films of silicone oils (or alkanes) deposited on low-energy surfaces (grafted silicone wafers) are metastable. We nucleate a dry spot at the center of the wafer and observe the rate of growth V=dR/dt of the dry patch of radius R. We find that V is (a) independent of R, (b) independent of the film thickness, (c) inversely proportional to the oil viscosity, and (d) very sensitive to the value of ${\mathrm{\ensuremath{\theta}}}_{\mathit{e}}$, the equilibrium contact angle between oil and wafer. At small ${\mathrm{\ensuremath{\theta}}}_{\mathit{e}}$, V\ensuremath{\approxeq}${\mathrm{\ensuremath{\theta}}}_{\mathit{e}}^{3}$. All these features are in agreement with a recent hydrodynamic theory.

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512 citations

"Role of Bouncing Potential in Molte..." refers background in this paper

...With detailed experimental studies, and theoretical understanding, Redon et al. (1991) have derived a relation between dewetting contact angle (hd) and equilibrium contact angle (he) as: hd¼ he=p 2....
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...In various dewetting experiments, it has been confirmed that when the film= lamella thickness is less than the critical thickness, the film is in a meta-stable state (Mourougou-Candoni et al., 1999; Redon et al., 1991)....
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Journal Article•DOI•

Wetting effects on the spreading of a liquid droplet colliding with a flat surface: Experiment and modeling

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Jun Fukai, Y. Shiiba¹, T. Yamamoto¹, Osamu Miyatake¹, Dimos Poulikakos², Constantine M. Megaridis², Z. Zhao² - Show less +3 more•Institutions (2)

Kyushu University¹, University of Illinois at Chicago²

01 Feb 1995-Physics of Fluids

TL;DR: In this article, an experimental and theoretical study of the deformation of a spherical liquid droplet colliding with a flat surface is presented, which accounts for the presence of inertia, viscous, gravitation, surface tension, and wetting effects, including the phenomenon of contact angle hysteresis.

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Abstract: In this paper an experimental and theoretical study of the deformation of a spherical liquid droplet colliding with a flat surface is presented. The theoretical model accounts for the presence of inertia, viscous, gravitation, surface tension, and wetting effects, including the phenomenon of contact‐angle hysteresis. Experiments with impingement surfaces of different wettability were performed. The study showed that the maximum splat radius decreased as the value of the advancing contact angle increased. The effect of impact velocity on droplet spreading was more pronounced when the wetting was limited. The experimental results were compared to the numerical predictions in terms of droplet deformation, splat radius, and splat height. The theoretical model predicted well the deformation of the impacting droplet, not only in the spreading phase, but also during recoiling and oscillation. The wettability of the substrate upon which the droplet impinges was found to affect significantly all phases of the spre...

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480 citations

"Role of Bouncing Potential in Molte..." refers background or methods in this paper

...…the maximum spread ratio, viz., energy conservation approach (Chandra and Avedisian, 1991; Gong, 2005; Hsiao et al., 2009; Mao et al., 1997; Pasandideh-Fard et al., 1996) and numerical simulation of Navier–Stokes equations (Fukai et al., 1995; Kim and Chun, 2001; Pasandideh-Fard et al., 1996)....
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..., 1996) and numerical simulation of Navier–Stokes equations (Fukai et al., 1995; Kim and Chun, 2001; Pasandideh-Fard et al., 1996)....
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Journal Article•DOI•

The Dynamics of Thin Sheets of Fluid. III. Disintegration of Fluid Sheets

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Geoffrey Ingram Taylor

15 Dec 1959-Proceedings of The Royal Society A: Mathematical, Physical and Engineering Sciences

TL;DR: In this paper, it was shown that the free edge of a sheet of uniform thickness moves into an expanding sheet at the same speed as antisymmetrical waves, sweeping the fluid into roughly cylindrical borders.

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Abstract: The free edge of a sheet of uniform thickness moves into it at the same speed, (2 T /ρ t ) ½ , as antisymmetrical waves, sweeping the fluid into roughly cylindrical borders. Here T , ρ and t are surface tension, density and thickness of the sheet. In a radially expanding sheet t decreases with increasing radius and beyond a radius R where (2 T /ρ t ) ½ is greater than u the radial velocity of the sheet, the edge moves inwards faster than it is convected outwards. Photographs show that the edge of an expanding sheet establishes itself near but inside the radius R . The sheet produced by a swirl atomizer expands as a cone but photographs show that its thickness fluctuates very greatly at the point where it emerges from the orifice. The edge of a conical sheet of varying thickness establishes itself at a point well inside the radius at which (2 T /ρ t ) ½ = u , t being the mean thickness. A moving sheet of uniform thickness can be bounded by a stationary free edge at angle sin -1 ( W ½ ) to the direction of motion. Here W , the Weber number, is 2 T /ρ tu 2 . Photographs show free edges at this angle and therefore parallel to antisymmetrical waves. If this remained true in an expanding sheet the edges would coincide with the cardioids discussed in part II, but reasons are given to show that this is not the case. A small obstacle can divide an expanding sheet forming two edges which lie at the same angle to one another as the two cardioids, namely, 2 sin -1 ( W ½ ) but photographs show that these edges do not subsequently lie on cardioids.

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473 citations

"Role of Bouncing Potential in Molte..." refers background in this paper

...This will lead to a receding phase, with the retraction velocity being constant throughout the dewetting process, as in rupturing of a soap film (Culick, 1960; Redon et al., 1994; Taylor, 1959)....
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Journal Article•DOI•

Comments on a Ruptured Soap Film

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Fred E. C. Culick

01 Jun 1960-Journal of Applied Physics

TL;DR: In this paper, a more detailed analysis of the motion of the edge gives this result; the neglected contribution arises from inelastic acceleration of the undisturbed fluid up to the velocity of the edges.

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Abstract: Subsequent to puncturing at a point, a horizontal soap film develops a hole whose edge, owing to surface tension, propagates outward from the point of puncture at apparently constant velocity. Measurements by Ranz [1] yielded results roughly 10% lower than those calculated on the basis of a simple energy conservation suggested by Rayleigh [2]. The discrepancy was attributed to an additional retarding viscous stress not included in the analysis. It appears, however, that the energy balance quoted [1] neglects an important contribution, indeed related to th viscous effect noted by Ranz, but which reduces the calculated values to 20% below those measured. A more detailed analysis of the motion of the edge gives this result; the neglected contribution arises from inelastic acceleration of the undisturbed fluid up to the velocity of the edge. The concomitant loss in mechanical energy may be identified with viscous dissipation which is estimated to be confined to a relatively thin region. Lack of agreement between calculated and measured values of the edge velocity seems to be causes by a second-order effect in the method used [1] to determine the thickness of the film.

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462 citations

"Role of Bouncing Potential in Molte..." refers background in this paper

...This will lead to a receding phase, with the retraction velocity being constant throughout the dewetting process, as in rupturing of a soap film (Culick, 1960; Redon et al., 1994; Taylor, 1959)....
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...…(3) reduces to: Vr ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi clv 1 cos hdð Þ qhf s ð4Þ The velocity at which the rim retracts may be calculated from Equation (4) and is conceptually similar to the dewetting velocity described by Culick (1960)....
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...The velocity at which the rim retracts may be calculated from Equation (4) and is conceptually similar to the dewetting velocity described by Culick (1960). The inference from Equation (4) is that the retraction velocity depends on material properties and on film thickness....
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