Investigation of droplet collisions for solutions with different solids content

Kuschel, Matthias; Sommerfeld, Martin

doi:10.1007/s00348-012-1440-z

Cited by 47 publications

(58 citation statements)

References 12 publications

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“…However, this is not in accordance with the studies of Tang et al (2012) where  = 0.4 results in a shift to Wec ~ 40. A shift of this boundary line to the right was also observed by Kuschel and Sommerfeld (2013) and Sommerfeld and Kuschel (2016) when increasing the dynamic viscosity of the liquid, similar to the work of Gotaas et al (2007). This shift of the critical Weber number could be quite well correlated in dependence of the Ohnesorge number as well as the capillary number (Sommerfeld and Kuschel 2016).…”

Section: Theoretical Boundary Linessupporting

confidence: 72%

“…Hence the non-linear correlation proposed by Gotaas et al (2007) fits the high-viscosity data reasonably well (Figure 7 a) including silicon oils, MEG and DEG and a VOF (volume of fluid) simulation of Xia and Hu (2015) for 10 µm liquid aluminium droplets (Oh = 0.115). The critical Weber-number for mixtures of Diesel/Biodiesel and Diesel/water emulsions (Chen et al 2016) are however remarkably over-predicted by this correlation, similar to solution droplets of Kuschel and Sommerfeld (2013). Now we turn to the low Oh-regime wherefore numerous data are available (Figure 7 b).…”

Section: Characteristic Points In the Collision Mapsmentioning

confidence: 85%

“…An exception is water where this line extends to B = 1 at We = 0 separating bouncing and coalescence (see e.g. Kuschel and Sommerfeld 2013). This matching procedure was successfully achieved with the Jiang et al (1997) model which accounts for the effect of viscous dissipation (Sommerfeld 2016).…”

Section: Characteristic Points In the Collision Mapsmentioning

confidence: 87%

“…In the droplet collision studies of Kuschel and Sommerfeld (2013) several solutions were used as liquid with viscosities between 1 and 50 mPas, yielding up to Oh = 0.37. However, since here the maximum We-number was about 100, not for all cases the critical Weber-number could be identified.…”

Section: Characteristic Points In the Collision Mapsmentioning

confidence: 99%

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Numerical analysis of sprays with an advanced collision model

Sommerfeld

Laı́n

2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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Modelling of collisions between liquid droplets in the frame of a Lagrangian spray simulation has still many open issues, especially when considering higher viscous droplets and if colliding droplets have a large size difference. A generalisation of the collision maps is attempted based on the behaviour of characteristic points, namely the triple point where bouncing, coalescence and stretching separation coincide and the critical Weber-number where reflexive separation first occurs in head-on collisions. This is done by correlating experimental data with respect to the Capillary number with the Ohnesorge-number for the triple point and the critical Weber-number is also well described by a correlation the Ohnesorge-number. Based on these results the boundary line between stretching separation and coalescence is found by adapting the Jiang et al. (1992) correlation. For the upper boundary of reflexive separation the shifted Ashgriz and Poo (1990) correlation is used. It was however so far not possible to predict the lower bouncing boundary through the Estrade et al. (1999) boundary line correctly. The proposed boundary-line models were validated for various liquid, however still considering only a size ratio of one. With the developed three-line boundary model Euler/Lagrange numerical calculations for a simple spray system were conducted and the droplet collisions were analysed with respect to their occurrence. Droplet collision modelling is performed on the basis of the stochastic droplet collision model, also considering the influence of impact efficiency, which so far was neglected for most spray simulations. The comparison with measurements showed reasonable good agreement for all properties. KeywordsDroplet collisions, stochastic collision model, impact efficiency, collision outcomes, Euler/Lagrange calculations, spray simulations. IntroductionIn numerous technical and industrial spraying systems higher viscous liquids, suspensions or solutions are being atomised. Examples are liquid fuels (including bio-fluids) in combustion systems, liquid melts or other mineral melts in the field of materiel science and spray drying of foodstuff or pharmaceutical materials. Therefore, in a numerical calculation of such spraying systems, mostly done with an Euler/Lagrange approach, the resulting different liquid properties have to be accounted for. Here the focus is related to droplet collision modelling. Hence, established droplet collision models have to be generalized regarding liquid properties, mainly viscosity and surface tension. Since colliding droplets may have considerable different size also the droplet size ratio is an important parameter to be considered in droplet collision modelling. In order to model droplet collisions in the frame of the Lagrangian droplet parcel concept, where only pointmasses are tracked, applied to spraying systems several elementary processes have to be considered (Sommerfeld and Kuschel 2016). The first step is the detection of possible collisions between two droplets. In orde...

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Section: Theoretical Boundary Linessupporting

confidence: 72%

Section: Characteristic Points In the Collision Mapsmentioning

confidence: 85%

Section: Characteristic Points In the Collision Mapsmentioning

confidence: 87%

Section: Characteristic Points In the Collision Mapsmentioning

confidence: 99%

See 2 more Smart Citations

Numerical analysis of sprays with an advanced collision model

Sommerfeld

Laı́n

2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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“…3) and setting the other involved constant Cb = 1. The data from the experiments by Kuschel and Sommerfeld [6] were obtained only from ~ 380 µm mono-sized droplets. To validate the 3rd order polynomial fit of Ca and Ohnesorge number, it was necessary to run experiments with variation of the droplet size properties.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of size effects in colliding droplet

Pasternak¹,

Sommerfeld²

2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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The present work focuses on the size effect of binary collisions of PVP droplets (viscosity 5.5 mPas). The aim was the identification of the boundaries between bouncing, coalescence, stretching and reflexive separation. These boundaries are necessary for numerical simulations of droplet collisions in spray drying processes. Therefore, droplet chains were generated by droplet generators with oscillating membrane and directed towards each other at different angles for producing binary collisions. In the experiments two droplet properties (i.e. droplet size and size ratio) were varied. Two synchronised high-speed cameras were used to observe the collision process and outcome perpendicularly and parallelly to the collision plane. The variation of the impact parameter B was performed by a frequency offset for one droplet generator. The relative velocity (i. e. 0.5 to 4.7 m/s) was set by changing the collision angle. Keywords droplet collision, droplet size ratio, modelling separation IntroductionSpray drying processes constitute a very complex multiphase system due to the different elementary processes involved, i.e. atomization, drying, collision of droplets and formation of agglomerates. After atomization, droplet collisions with the different possible collision outcomes result in a modification on the product particle size distribution. Typical results of a collision of two droplets may be bouncing, coalescence and separation and were plotted in the well-known collision maps (see Figure 1). In these maps the non-dimensional impact parameter B (see Eq. 1) is plotted against collision Weber number (see Eq. 2). However, the collision map depends on droplet parameters, i.e. liquid and size properties of the droplets. For Euler/Lagrange calculation of sprays it is necessary to know the pattern of the collision map without running experiments.

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The role of wall deposition and re‐entrainment in swirl spray dryers

et al. 2015

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A new experimental method is outlined to study fouling in spray dryers and similar devices. In essence, it makes the deposits traceable so that one can quantify the material that comes off the walls, how long it remains there and how the deposits agglomerate with particles in the air. This paper investigates a countercurrent swirl spray dryer of detergent and provides sound evidence that fouling is a dynamic process: clusters form and break at the walls renewing an active layer of deposits. Remarkably, the wall generates >20% of the product and most of the large granules, and increases drastically the residence time of the powder. The assumptions of current numerical models are clearly invalid (i.e. particles rebound at the wall or deposit indefinitely). Several re-entrainment mechanisms and their times scales are identified in this work, and accordingly, a new general framework to describe fouling in spray dryers is proposed.

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Investigation of droplet collisions for solutions with different solids content

Cited by 47 publications

References 12 publications

Numerical analysis of sprays with an advanced collision model

Numerical analysis of sprays with an advanced collision model

Experimental investigation of size effects in colliding droplet

The role of wall deposition and re‐entrainment in swirl spray dryers

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