November 6, 2013
Rachel Viger took 3rd place in the Computing, Simulation and Process Control Division Undergraduate Student Poster Competition at the 2013 AIChE Annual Meeting in San Francisco.
Her poster was titled, “Theoretical Model of a Thermochemical Metal Oxide Cycle for Hydrogen Production.” Viger works in the Weimer lab.
This work presents a three-dimensional, transient computational model for a two-step thermochemical hercynite water splitting cycle that is developed to optimize the design and operating conditions of a 4kW multiple tube solar receiver. A ray-tracing model is applied to determine the magnitude and direction of the concentrated, incident solar radiation on the aperture. The spectral and directional optical properties are applied to a Monte Carlo ray-tracing model that determines the transport of the solar radiation within the cavity. The emitted radiative transfer is calculated using a Radiosity model, which is coupled to heat transfer, species transport, and chemical reaction kinetics in a computational fluid dynamics model. The absorbing cavity contains an array of reaction tubes, each with an inner porous medium of cobalt ferrites deposited on alumina substrates that undergo a two-step water splitting redox cycle to produce hydrogen. The simulation results examine material properties, geometries, operating conditions, cycle time, and solar profile shape, and the trends in aperture size, number of tubes, and amount of reaction material are further assessed. Performance is improved with a large number of small-diameter tubes; however, the tube placement within the cavity has minimal impact. Configurations for both isothermal and temperature swing operation are analyzed, and indicate that similar time-averaged solar-to-chemical efficiencies, accounting for O2 separation and steam vaporization, of up to 14% are achievable.