Fluid Dynamics of a Transverse Jet Reactor for Zinc Aerosol Hydrolysis

Abstract

A new concept for control of the flow field, and thus particle yield, in an aerosol reactor designed for the hydrolysis of Zn in the two-step Zn/ZnO solar thermochemical cycle for hydrogen production is described and evaluated. For the hydrolysis step, much attention has been given to Zn nanoscale reacting aerosols for their potential to increase conversion to ZnO and because they enable a continuous, controllable process. The success of this continuous process depends on achieving high particle yields in the reactor. A key challenge is to control the flow field in aerosol reactors to keep the particles entrained in the flow without deposition on the reactor wall. The ability of a new reactor concept based on transverse jet fluid dynamics to control the flow field and rapidly cool the Zn vapor is investigated. In the transverse jet reactor, evaporated Zn entrained in an Ar carrier gas issues vertically into the horizontal tubular reactor through which cooler H2O and Ar flow. Particles are formed in the presence of steam at ~450 K. The trajectory of the jet is controlled via the effective velocity ratio, R, which is the square root of the ratio of the kinetic energy of the jet to that of the cross-flow. A computational fluid dynamics (CFD) model indicates that the trajectory of the jet can be controlled so that the majority of the Zn mass is directed down the center of the reactor, not near the reactor walls for R = 4.25 to R = 4.5. Experimentally, maximum particle yields of 93% of the mass entering the reactor are obtained at R = 4.5.