Emission Control Science and Technology

, Volume 3, Issue 4, pp 289–301 | Cite as

CFD Simulation of Liquid Back Suction and Gas Bubble Formation in a Circular Tube with Sudden or Gradual Expansion

  • Xuan CaiEmail author
  • Martin Wörner
  • Holger Marschall
  • Olaf Deutschmann


To avoid potential damage of the dosing unit in selective catalytic reduction by freezing urea-water-solution, the liquid is usually drained from the delivery line when the vehicle is out of operation. When liquid is sucked back counter to the normal delivery direction, the urea-water-solution is replaced by gas with the risk of air being sucked in. In this paper, we study the liquid back suction process and bubble formation numerically by interface-resolving simulations with a phase field method for a generic simplified geometry. We consider two connected circular tubes with sudden or gradual change of the diameter and provide guidelines for proper numerical setup of such flow problems in order to ensure physically reliable results. We study the influence of the geometry on the liquid draining process through variations of inner and outer tube diameters as well as transition inclination angle. The present numerical results indicate that geometrical modification is an effective means to control liquid draining in expanding pipes while preventing gas bubble formation.


Urea-water-solution SCR Draining of delivery line CFD simulation Phase field method 



X.C. and O.D. acknowledge the support by the Deutsche Forschungsgemeinschaft through SFB/Transregio 150 project B05. H.M. acknowledges the support by the Deutsche Forschungsgemeinschaft through SFB 1194 project B02.

Compliance with Ethical Standards

Conflict of Interest

The authors declare that they have no competing interests.


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Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.Institute for Chemical Technology and Polymer ChemistryKarlsruhe Institute of Technology (KIT)KarlsruheGermany
  2. 2.Institute of Catalysis Research and TechnologyKarlsruhe Institute of Technology (KIT)KarlsruheGermany
  3. 3.Mathematical Modeling and Analysis, Department of MathematicsTechnische Universität DarmstadtDarmstadtGermany

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