| dc.description.abstract | Many environmental problems are related to the production, transformation and use
of energy. Some of the concerns include, but are not limited to, acid rain, ozone depletion
and climate change. Therefore, “greener” alternatives for energy production are sought.
The hydrogen economy is one potential avenue to a clean energy system, and a promising
option for hydrogen production is the thermochemical Cu-Cl cycle for water
decomposition.
When hydrogen or oxygen is produced from water splitting by electrolysis,
thermochemical cycles or solar-based photocatalytic methods in water, bubble flow and
vapour transfer into the gas phase occur during phase transition. This undesirable vapour
transfer requires the use of more energy input to compensate for the evaporation heat
requirement as well as for subsequent gas purification in the downstream unit. This work
examines the thermodynamics and kinetics of vapour diffusion and entrainment for
ascending bubbles in a vertical column through experimental studies for various gas
production rates. Vapour entrainment is interpreted in terms of the phase transition rate
and its dependence on various operating parameters such as gas bubble size, liquid depth,
temperature and concentration is examined analytically and experimentally. A phase
transition correlation is obtained to analyze these parameters and predict the amount of
water carried to the surface of the liquid. It was determined that mass transfer is a
function of Reynolds number (characterizes the flow regime), Eotvos number
(characterizes bubbles’ shape) and distance the bubbles travel through liquid.
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Additionally, this work presents experimental studies of particle dynamics,
dissolution and transport processes for hydrogen production via thermochemical water
decomposition. The processes involve multiple steps, some consisting of multiphase
reaction systems. It examines the importance of design optimization of liquid-solid phase
systems and process integration of a thermochemical copper-chlorine cycle for hydrogen
production. The dissolution of cuprous chloride particles in hydrochloric acid is examined
in order to provide a predictive modeling method for more complex multiphase reacting
systems that determine the thermodynamic equilibrium, which regulates the final state
that the transport processes can approach. A ternary system consisting of cuprous chloride
(CuCl), hydrochloric acid (HCl) and water exists in different variations of the Cu-Cl
cycle, and the modeling of the solubility for the ternary system is essential to providing
the mathematical boundary conditions for the transport processes occurring in the system.
This work examines the transport processes involving the ternary system and the
constituent solubilities. A semi-mechanistic model is obtained that formulates the
solubility of the ternary system. It was found that the reaction kinetics is accelerated when
the solution is turbulent and when the concentration of HCl is increased, until the
thermodynamic limit is achieved. These findings are of importance in the integration of
the electrolysis with other reactors of the Cu-Cl cycle. | en |
