Single droplet impingement of urea water solution on heated porous surfaces

Kuhn, C.; Schweigert, David; Kuntz, Christian; Börnhorst, Marion

doi:10.1016/j.ijheatmasstransfer.2021.121836

Cited by 11 publications

(8 citation statements)

References 39 publications

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“…Both values for smooth surfaces were closer to the temperature found by Kuhn for a rough one, which might have been caused by the significantly larger droplets than in [8,24]. It also cannot be neglected that the rougher impingement targets were also porous in [11].…”

Section: Influence Of Surface Roughness On Droplet Impingementsupporting

confidence: 76%

“…The term 'splash' is an excellent example of an often-used name in impingement classification that can be linked to very different behaviors. It ranges from a small fraction of tiny secondary droplets at the rim of a spreading lamella to the complete disintegration of the droplet on impact [3,10,11]. Additionally, many of the resulting impingement maps show sharp threshold values separating one regime from another; for example, a certain temperature [2][3][4].…”

Section: Impingement Characterizationmentioning

confidence: 99%

“…On a rough surface, the temperature necessary for a droplet rebound can be increased significantly, which can be explained by the vapor mass escaping via the valleys of the surface topography [24]. The kinetic rebound-splash threshold was also reported to change with increasing roughness [11]. A change in surface roughness was associated with the change in contact angle and wettability [25,26].…”

Section: Influence Of Surface Roughness On Droplet Impingementmentioning

confidence: 99%

“…For UWS, Steinbach (80 µmdroplets) showed an increase of the LFP from around 300 °C for a smooth surface to 400 °C for R z = 35 µm [24]. Kuhn (3 mm droplets) found an LFP of 220 °C for R z = 4.5 µm, with the temperature values also increasing significantly for rougher surfaces (330 °C on R z = 98.4 µm) [11]. For a smooth surface, this is much lower than the values found by Steinbach [24] or in earlier experimental investigations by the current authors [8].…”

Section: Influence Of Surface Roughness On Droplet Impingementmentioning

confidence: 99%

“…Several methods have been described previously for studying the impingement of droplets [11,14,30,31]. Experiments were carried out using a droplet chain generator (DCG), to achieve droplet sizes comparable to those in SCR injectors.…”

Section: Test Bench Setupmentioning

confidence: 99%

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Impact of Surface Roughness on the Impingement of Urea–Water Solution Droplets

Quissek

Lauer

2023

Fluids

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The understanding of impingement processes is crucial for optimizing automotive selective catalytic reduction (SCR) systems. An accurate description of this behavior helps design exhaust systems and increases the validity of modeling approaches. A component test bench was set up, featuring a droplet chain generator for producing droplet sizes typically found in the urea–water solution sprays of SCR systems. A heatable impingement plate with an interchangeable surface enabled investigation of the influence of surface roughness. Data were acquired using a high-speed camera and image postprocessing. The droplet–wall interaction could be described using different regimes. An approach to characterizing impingement behavior based on weighted-regime superposition enabled gradual transitions between regimes, instead of step-like changes. It was observed that the surface roughness increased the droplet–solid contact area and generated thermal-induced secondary droplets at lower temperatures. A region of enhanced mechanical disintegration of the droplet was found, caused by peaks of the surface shearing off parts of the droplet. The probability of a droplet rebounding from the wall was reduced on a rough surface, due to the interference of the surface spikes with the droplet’s spreading and contracting motion. Additionally, the influence of surface topography was investigated using a shot-peened surface. Caused by this surface’s reduced root mean square slope, the aforementioned enhancement of mechanical disintegration was not observed.

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Section: Influence Of Surface Roughness On Droplet Impingementsupporting

confidence: 76%

Section: Impingement Characterizationmentioning

confidence: 99%

Section: Influence Of Surface Roughness On Droplet Impingementmentioning

confidence: 99%

Section: Influence Of Surface Roughness On Droplet Impingementmentioning

confidence: 99%

Section: Test Bench Setupmentioning

confidence: 99%

See 3 more Smart Citations

Impact of Surface Roughness on the Impingement of Urea–Water Solution Droplets

Quissek

Lauer

2023

Fluids

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Coupling of Liquid and Surface Chemistry in Urea SCR Systems

Kuntz

Jägerfeld

Mmbaga

et al. 2023

Emiss. Control Sci. Technol.

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Close-coupled selective catalytic reduction (SCR) systems are one method to deal with tightening emission legislation for NOx in internal combustion engines. Due to smaller mixing sections and at unfavourable boundary conditions, however, urea-water solution (UWS) droplets can impact on the SCR catalyst itself. To investigate this phenomenon further, this work develops a modeling capability of this process. Established mechanism for NH3-SCR and HNCO hydrolysis from literature is integrated into DETCHEMCHANNEL and a 2D COMSOL model to simulate the influence in the SCR Channel. Simulations are validated against end-of-pipe experiments from literature and spatially resolved concentration profiles from a hot gas test rig with very good agreement. Finally, a channel simulation is coupled with a model to describe the catalytic decomposition of an urea droplet. The coupled simulation is able to simulate the influence of UWS droplet impact onto a catalyst channel. Fast droplet decomposition causes a peak in NH3 and HNCO in the single channel and thus increases NOx conversion. However, the overall uniformity and efficiency are decreased, which is why droplet impact on the catalyst should be strictly avoided.

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