Effects of Initial Droplet Diameter on Interference between Flame Propagating in Combustible Mixtures and a Single Fuel Droplet

The paper describes the physical and mathematical model of the ignition of a liquid fuel droplet suddenly immersed in a hot oxidizing medium. The model was solved numerically by the finite element method. The ignition lags in terms of ambient temperature, oxygen concentration and initial droplet diameter were computed.

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Droplet Characteristics of Rotating Packed Bed in H2S Absorption: A Computational Fluid Dynamics Analysis

Processes ◽

10.3390/pr7100724 ◽

2019 ◽

Vol 7 (10) ◽

pp. 724

Author(s):

Wang ◽

Wu ◽

Yang ◽

Wang ◽

Liu ◽

...

Keyword(s):

Residence Time ◽

Droplet Diameter ◽

Packed Bed ◽

Droplet Velocity ◽

Radial Position ◽

Selective Absorption ◽

Rotating Speed ◽

Initial Droplet ◽

Rotating Packed Bed ◽

Computational Fluid Dynamics Analysis

Rotating packed bed (RPB) has been demonstrated as a significant and emerging technology to be applied in natural gas desulfurization. However, droplet characteristics and principle in H2S selective absorption with N-methyldiethanolamine (MDEA) solution have seldom been fully investigated by experimental method. Therefore, a 3D Eulerian–Lagrangian approach has been established to investigate the droplet characteristics. The discrete phase model (DPM) is implemented to track the behavior of droplets, meanwhile the collision model and breakup model are employed to describe the coalescence and breakup of droplets. The simulation results indicate that rotating speed and radial position have a dominant impact on droplet velocity, average residence time and average diameter rather than initial droplet velocity. A short residence time of 0.039–0.085 s is credited in this study for faster mass transfer and reaction rate in RPB. The average droplet diameter decreases when the initial droplet velocity and rotating speed enhances. Restriction of minimum droplet diameter for it to be broken and an appropriate rotating speed have also been elaborated. Additional correlations on droplet velocity and diameter have been obtained mainly considering the rotating speed and radial position in RPB. This proposed formula leads to a much better understanding of droplet characteristics in RPB.

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The Combustion of a Liquid Fuel Droplet during Forced Convection

Journal of Fire Sciences ◽

10.1177/073490419401200103 ◽

1994 ◽

Vol 12 (1) ◽

pp. 44-61

Author(s):

Andrzej Teodorczyk ◽

Stanislaw Wójcicki

Keyword(s):

Reynolds Number ◽

Forced Convection ◽

Droplet Diameter ◽

Fuel Droplet ◽

Combus Tion ◽

Air Stream ◽

Freely Suspended ◽

High Reynolds ◽

Additional Support ◽

Physical And Mathematical Models

A new experimental technique was used to investigate single fuel droplet combustion during forced convection: the burning droplet was freely suspended in the controlled air stream, without any additional support. Based on the photo-records of the burning process, the characteristics of the change of square of droplet diameter with time were made and the actual values of burning constants were determined for four hydrocarbon fuels: ben zene, n-heptane, iso-octane and toluene. The experiments were also carried out under micro-gravity and free convection conditions for the same set of fuels. The investigations have allowed the comparison of the burning mechanism of a single droplet for the three different external conditions and have compared quantitatively the burning constants. On the basis of the color pictures of the droplet burning under forced convection conditions and the temperature and gas concentration measurements within the flame, the mechanism of combus tion of fuel droplet was explained. The physical and mathematical models of the process have been proposed which included the aerodynamics of the droplet located in the high Reynolds number air stream, the energy balance of the evaporating droplet and the chemical reaction in the flow. The models have made it possible to determine the quantitative dependence of the burning con stant of different kinds of fuels on Reynolds number, the flow field parameters and the physical and chemical parameters of the liquid and its close surround ings. The calculated values of the parameters describing the burning pro cess have been compared to the experimental data and to the results reported by other investigators. The model has revealed the importance of the feed back mechanism between physical processes involved during droplet combus tion.

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The evaporation and combustion of levitated arrays of two, three and five droplets at a hot surface

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1988.0089 ◽

1988 ◽

Vol 418 (1855) ◽

pp. 365-382 ◽

Cited By ~ 3

Keyword(s):

Droplet Diameter ◽

Flame Height ◽

Linear Arrays ◽

Initial Droplet ◽

Surface Temperatures ◽

Droplet Array ◽

Burning Rates ◽

Hot Surface

The interactions between droplets in several geometrical arrays in Leidenfrost evaporation and combustion on a hot surface were studied. Comparisons between evaporation and burning times of isolated droplets, two- and three-droplet linear arrays, and a five-droplet array (a centre droplet surrounded by four droplets) were made. The liquids studied were water, n -heptane, and n -hexadecane at 0.101 MPa and at surface temperatures above their respective Leidenfrost values. A range of centre distance to initial droplet diameter ratios, L / d 0 , were studied (2 < L / d 0 < ∞). The evaporation or burning rates of droplets in binary arrays were found to be identical to those of isolated droplets ( L / d 0 → ∞). The flames around each droplet, however, merged as the droplets were brought closer together. In three- and five-droplet arrays more significant interactions were observed, with the edge droplets in the arrays burning faster than the centre droplets. The results are explained on the basis of flame-height measurements for the arrays. In pure evaporation, though, the droplets evaporated without regard for their neighbours.

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The effect of initial diameter in spherically symmetric droplet combustion of sooting fuels

Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences ◽

10.1098/rspa.1994.0103 ◽

1994 ◽

Vol 446 (1927) ◽

pp. 255-276 ◽

Cited By ~ 55

Keyword(s):

Burning Rate ◽

Rate Constants ◽

Soot Formation ◽

Droplet Diameter ◽

Droplet Surface ◽

Spherically Symmetric ◽

Low Gravity ◽

Initial Droplet ◽

Initial Diameter ◽

Burning Rates

The effect of initial droplet diameter on the burning rate of sooting fuels – n-heptane and 1-chloro-octane – was examined experimentally at low gravity. A 1.2s drop tower provided a low gravity environment to minimize buoyancy and achieve spherically symmetric flames for stationary droplets. Free-floating and fibre-supported droplets were burned, and both techniques gave matching results for droplets of similar initial diameter. Burning rate constants for both fuels were measured for a large number of droplets ranging from 0.4 to 1.1 mm in initial diameter. Results showed that burning rate constants decreased monotonically as the initial droplet diameter was increased above 0.6 mm for both fuels. This decrease was considered to be due to the observed increase in soot formation and accumulation in a shell-like structure inside the flame of the larger droplets. The increased collection of soot inside the larger droplet flames reduced the proportional heat release from the flame and may have acted as a barrier to heat transfer from the flame to the droplet. Flame-to-droplet diameter ratio increased monotonically with time, thus suggesting that quasi-steady combustion was not achieved. The flames and soot shells for 1-chloro-octane droplets with their lower burning rates remained closer to the droplet surface than similarly sized n-heptane droplets.

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Droplet Burning and Evaporation Times for Distillate and Residual Fuel Oils

Volume 1A: General ◽

10.1115/80-gt-59 ◽

1980 ◽

Cited By ~ 1

Author(s):

P. C. T. de Boer

Keyword(s):

Gas Turbine ◽

Constant Velocity ◽

Droplet Diameter ◽

Diffusion Constant ◽

Gas Mixture ◽

Residual Oil ◽

Gas Turbine Combustor ◽

Initial Droplet ◽

Fuel Oils ◽

Industrial Gas Turbine

Estimates are given of the burning and evaporation times of No. 2 distillate and No. 6 residual oil droplets, under conditions typical of industrial gas turbine combustors. Account is taken of the temperature dependence of the specific heat, the diffusion constant, and the thermal conductivity of the gas mixture surrounding the droplet. Detailed calculations are presented of the factor by which the droplet lifetime is reduced as a result of convection, for the case that the droplet is released in a gas moving at constant velocity. This factor is on the order of four for the conditions of interest. Using estimates of initial droplet diameter based on data reported by Jasuja, it is found that the ratio of characteristic droplet burning time to characteristic droplet residence time in a typical industrial gas turbine combustor is much smaller than 1 for distillate oil, but may be on the order of 1 for residual oil.

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Coalescence of Binary Droplets in the Transformer Oil Based on Small Amounts of Polymer: Effects of Initial Droplet Diameter and Collision Parameter

Polymers ◽

10.3390/polym12092054 ◽

2020 ◽

Vol 12 (9) ◽

pp. 2054

Author(s):

Yiting Wang ◽

Lijuan Qian ◽

Zhongli Chen ◽

Fang Zhou

Keyword(s):

Kinetic Energy ◽

Droplet Diameter ◽

Transformer Oil ◽

Water Droplets ◽

Droplet Deformation ◽

Oil Separation ◽

Coalescence Time ◽

Maximum Deformation ◽

Initial Droplet ◽

Central Collisions

In engineering applications, the coalescence of droplets in the oil phase dominates the efficiency of water-oil separation. To improve the efficiency of water-oil separation, many studies have been devoted to exploring the process of water droplets colliding in the oil phase. In this paper, the volume of fluid (VOF) method is employed to simulate the coalescence of water droplets in the transformer oil based on small amounts of polymer. The influences of the initial diameter and collision parameter of two equal droplets on droplet deformation and coalescence time are investigated. The time evolution curves of the dimensionless maximum deformation diameter of the droplets indicate that the larger the droplet diameter, the more obvious the deformation from central collisions. As the collision parameter increases, the contact area of the two droplets, as well as the kinetic energy that is converted into surface energy, decreases, resulting in an increase in droplet deformation. Furthermore, the effects of the initial droplet diameter and collision parameter on coalescence time are also investigated and discussed. The results reveal that as the initial droplet diameter and collision parameter increase, the droplet coalescence time increases.

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Heat and Mass Transfer of Droplet Vacuum Freezing Process Based on Dynamic Mesh

Mathematical Problems in Engineering ◽

10.1155/2014/798040 ◽

2014 ◽

Vol 2014 ◽

pp. 1-6 ◽

Cited By ~ 5

Author(s):

Lili Zhao ◽

Yuekai Zhang ◽

Zhijun Zhang ◽

Xun Li ◽

Wenhui Zhang

Keyword(s):

Mass Transfer ◽

Heat And Mass Transfer ◽

Droplet Diameter ◽

Dynamic Mesh ◽

Freezing Process ◽

Freezing Time ◽

Droplet Temperature ◽

Obvious Effect ◽

Initial Droplet ◽

Vacuum Freezing

A numerical simulation using dynamic mesh method by COMSOL has been developed to model heat and mass transfer during vacuum freezing by evaporation of a single droplet. The initial droplet diameter, initial droplet temperature, and vacuum chamber pressure effect are studied. The surface and center temperature curve was predicted to show the effect. The mass transfer rate and radius displacement were also calculated. The results show the dynamic mesh shows well the freezing process with the radius reduction of droplet. The initial droplet diameter, initial droplet temperature, and vacuum pressure have obvious effect on freezing process. The total freezing time is about 200 s, 300 s, and 400 s for droplet diameter 7.5 mm, 10.5 mm, and 12.5 mm, respectively. The vacuum pressure less than 200 Pa is enough for the less time to freezing the droplet, that is, the key point in freezing time. The initial droplet temperature has obvious effect on freezing but little effect on freezing temperature.

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An Experimental Study of the Vaporization Characteristics of Diesel-Benzyl Azides Blend Droplets

Volume 2: Fuels; Numerical Simulation; Engine Design, Lubrication, and Applications ◽

10.1115/icef2013-19072 ◽

2013 ◽

Cited By ~ 1

Author(s):

Kai Han ◽

Geng Fu ◽

Changlu Zhao ◽

Bolan Liu ◽

Shibo Ma

Keyword(s):

Experimental Study ◽

Ambient Temperature ◽

Atmospheric Pressure ◽

High Speed ◽

Droplet Diameter ◽

Video Camera ◽

Initial Droplet ◽

High Speed Video Camera ◽

Combustion Duration ◽

Suspended Droplet

An experimental study of diesel-benzyl azides blend droplets vaporization characteristics was carried out to study the reasons of diesel-benzyl azides blend shortened combustion duration using suspended droplet device and a high-speed video camera. Experiments were performed at atmospheric pressure, ambient temperature range 480–933 K, and initial droplet diameter of 0.98, 1.42, 1.88 mm. The results show a shorten in diesel-benzyl azides blend droplet lifetime by 10% compared to diesel droplet at 1.42 mm initial droplet diameter and 933 K ambient temperature companion to puffing. The above results support the original idea of designing diesel-benzyl azides blend where the energy released by the decomposition of azides improves the vaporization and the release of nitrogen leads to the breakup of the droplet. In addition, it is observed that the blend lifetime decrease with increasing ambient temperature compared to diesel droplet lifetime. More nitrogen is released and the expansion of bubbles is more violent with increasing initial droplet diameter.

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