Articles | Volume 10, issue 3
Research article
09 Mar 2017
Research article |  | 09 Mar 2017

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

Yuanlong Huang, Matthew M. Coggon, Ran Zhao, Hanna Lignell, Michael U. Bauer, Richard C. Flagan, and John H. Seinfeld

Abstract. 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 (O3) 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 (OHexp) ranging from ∼ 109 to ∼ 1012 molecules cm−3 s can be achieved from photolysis of H2O2. A method to calculate OHexp with a consideration for the axial dispersion in the present photochemical system is developed.

Short summary
We report on the development of a new laminar flow tube reactor for the study of gas-phase atmospheric chemistry and secondary organic aerosol formation. The present paper is devoted to the design and fluid dynamical characterization of the reactor. The results of gas and particle residence time distribution experiments in the reactor, together with an evaluation of the effect of non-isothermal conditions, are reported.