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Published March 9, 2017 | Published
Journal Article Open

The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization


Flow tube reactors are widely employed to study gas-phase atmospheric chemistry and secondary organic aerosol (SOA) formation. The development of a new laminar-flow tube reactor, the Caltech Photooxidation Flow Tube (CPOT), intended for the study of gas-phase atmospheric chemistry and SOA formation, is reported here. The present work addresses the reactor design based on fluid dynamical characterization and the fundamental behavior of vapor molecules and particles in the reactor. The design of the inlet to the reactor, based on computational fluid dynamics (CFD) simulations, comprises a static mixer and a conical diffuser to facilitate development of a characteristic laminar flow profile. To assess the extent to which the actual performance adheres to the theoretical CFD model, residence time distribution (RTD) experiments are reported with vapor molecules (O_3) and submicrometer ammonium sulfate particles. As confirmed by the CFD prediction, the presence of a slight deviation from strictly isothermal conditions leads to secondary flows in the reactor that produce deviations from the ideal parabolic laminar flow. The characterization experiments, in conjunction with theory, provide a basis for interpretation of atmospheric chemistry and SOA studies to follow. A 1-D photochemical model within an axially dispersed plug flow reactor (AD-PFR) framework is formulated to evaluate the oxidation level in the reactor. The simulation indicates that the OH concentration is uniform along the reactor, and an OH exposure (OH_(exp)) ranging from ∼ 10^9 to ∼ 10^(12) molecules cm^(−3) s can be achieved from photolysis of H_2O_2. A method to calculate OH_(exp) with a consideration for the axial dispersion in the present photochemical system is developed.

Additional Information

© Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 29 Aug 2016 – Discussion started: 22 Sep 2016. Revised: 07 Feb 2017 – Accepted: 24 Feb 2017 – Published: 09 Mar 2017. We gratefully acknowledge a generous gift by Christine and Dwight Landis to support the construction of this reactor. We also thank Paul Wennberg for useful discussions and for offering laboratory supplies. This work was supported by National Science Foundation grant AGS-1523500. Ran Zhao was supported by the Natural Science and Engineering Research Council of Canada. Data availability. Data presented in this work are available from the authors. Edited by: H. Harder. Reviewed by: A. Lambe and four anonymous referees. The authors declare that they have no conflict of interest.

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