Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7051873 | Experimental Thermal and Fluid Science | 2018 | 12 Pages |
Abstract
The injection of urea-water-solution sprays in the exhaust pipe of modern diesel engines eliminates NOx emissions in a very great extent. However, as water evaporates from the solution, urea is crystallized and causes wall-deposit formations hindering the performance of selective-catalytic-reaction. In this study, the crystallization of urea from an evaporative aqueous solution droplet placed on a heated wall is experimentally investigated, aiming to understand macroscopically the morphology of crystal growth at various conditions. Using optical and thermal imaging, urea crystallization patterns are examined at sub-boiling temperatures and substrates with different wettability. In all cases, the macroscopic initiation of crystal growth starts at the solid-liquid interface when urea concentration has reached supersaturated conditions. The experiments indicate two different crystallization modes depending on surface temperature and wettability as well as a significant heat release at the solidification front due the exothermic character of the process.
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Fluid Flow and Transfer Processes
Authors
J. Schmid, I. Zarikos, A. Terzis, N. Roth, B. Weigand,