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Volume 18, issue 4
Atmos. Chem. Phys., 18, 2669–2686, 2018
https://doi.org/10.5194/acp-18-2669-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 18, 2669–2686, 2018
https://doi.org/10.5194/acp-18-2669-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Technical note 23 Feb 2018

Technical note | 23 Feb 2018

Technical note: Influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies

Guo Li1,4, Hang Su2,1, Uwe Kuhn1, Hannah Meusel1, Markus Ammann3, Min Shao2,4, Ulrich Pöschl1, and Yafang Cheng1,2 Guo Li et al.
  • 1Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
  • 2Institute for Environmental and Climate Research, Jinan University, Guangzhou, China
  • 3Laboratory of Environmental Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • 4College of Environmental Sciences and Engineering, Peking University, Beijing, China

Abstract. Coated-wall flow tube reactors are frequently used to investigate gas uptake and heterogeneous or multiphase reaction kinetics under laminar flow conditions. Coating surface roughness may potentially distort the laminar flow pattern, induce turbulence and introduce uncertainties in the calculated uptake coefficient based on molecular diffusion assumptions (e.g., Brown/Cooney–Kim–Davis (CKD)/Knopf–Pöschl–Shiraiwa (KPS) methods), which has not been fully resolved in earlier studies. Here, we investigate the influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies. According to laminar boundary theory and considering the specific flow conditions in a coated-wall flow tube, we derive and propose a critical height δc to evaluate turbulence effects in the design and analysis of coated-wall flow tube experiments. If a geometric coating thickness δg is larger than δc, the roughness elements of the coating may cause local turbulence and result in overestimation of the real uptake coefficient (γ). We further develop modified CKD/KPS methods (i.e., CKD-LT/KPS-LT) to account for roughness-induced local turbulence effects. By combination of the original methods and their modified versions, the maximum error range of γCKD (derived with the CKD method) or γKPS (derived with the KPS method) can be quantified and finally γ can be constrained. When turbulence is generated, γCKD or γKPS can bear large difference compared to γ. Their difference becomes smaller for gas reactants with lower uptake (i.e., smaller γ) and/or for a smaller ratio of the geometric coating thickness to the flow tube radius (δg ∕ R0). On the other hand, the critical height δc can also be adjusted by optimizing flow tube configurations and operating conditions (i.e., tube diameter, length, and flow velocity), to ensure not only unaffected laminar flow patterns but also other specific requirements for an individual flow tube experiment. We use coating thickness values from previous coated-wall flow tube studies to assess potential roughness effects using the δc criterion. In most studies, the coating thickness was sufficiently small to avoid complications, but some may have been influenced by surface roughness and local turbulence effects.

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Coated-wall flow tube reactors are frequently used to investigate gas uptake and heterogeneous or multiphase reaction kinetics under laminar flow conditions. In previous applications, the effects of coating surface roughness on flow conditions were not well quantified. In this study, a criterion is proposed to eliminate/minimize the potential effects of coating surface roughness on laminar flow in coated-wall flow tube experiments and validate the applications of diffusion correction methods.
Coated-wall flow tube reactors are frequently used to investigate gas uptake and heterogeneous...
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