Boundary layer flow with radiation heat transfer and a hydrolysis reaction during the Cu-Cl cycle of hydrogen production

Rimal, Samita (2024) Boundary layer flow with radiation heat transfer and a hydrolysis reaction during the Cu-Cl cycle of hydrogen production. Masters thesis, Memorial University of Newfoundland.

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Abstract

With the realization of Earth’s depleting fossil fuel reserves, the environment-friendly technologies and renewable energy sources has been witnessing a growing demand for. As an energy carrier, hydrogen has emerged as a promising solution aimed at addressing clean energy demands while limiting carbon emissions. Current usage of hydrogen as the carrier of energy is primarily obtained from fossil fuel reformation while releasing CO₂ into the atmosphere. Replacement of hydrocarbon fuels by hydrogen produced from sustainable and cost-effective thermochemical water splitting is a promising technology. The Copper-Chlorine (Cu-Cl) cycle offers a proven and environmentally advantageous method for hydrogen production. This process distinguishes itself through its relatively low heat requirement in comparison to other hydrogen production methods. However, complex solid-gas reactions and heat transfer present challenges that need to be addressed for industrial-scale implementation. The conversion from cupric chloride (CuCl2) to copper oxychloride (Cu₂OCl₂) in the hydrolysis stage of the Cu-Cl cycle determines the reaction extent, chemical kinetics of each process and hence the hydrolysis reactor efficiency for industrial scale-up. Numerous investigations have focused on the heat and mass transfer of hydrolysis reactions, aiming to understand their respective roles and enhance the overall cycle efficiency. However, few or no prior research has explored the impact of radiation on the process. This thesis focuses on radiation heat transfer incorporating thermophysical property variation in the hydrolysis step of the cycle to better understand the heat transfer processes inside the reactor. The primary contribution of this thesis lies in the development of a semi-analytical model that integrates radiative heat transfer and chemical reactions in a gas-solid system, employing a similarity solution and numerical methods. A similarity transformation is used to solve the governing equations utilizing a fourth-order Runge-Kutta method and a Rosseland approximation is employed to study the impact of thermal radiation. It is recognized that thermal radiation has a significant role in the boundary layer flow problem in a hydrolysis reaction. The thickness of the thermal boundary layer was observed to increase with the change of radiation parameters. The presence of the chemical reaction thickens the thermal boundary layer and the effect of the endothermic chemical reaction on the thermal boundary layer thickness is found to be decreasing with an increase in the radiation parameter. The solid particle presence enhances the heat and mass transfer and affects the concentration profile. It is also known that the combined influence of thermal radiation and varying thermophysical properties is crucial and reveals a decrease in the concentration of chemical species near the wall surface. This could be due to enhanced mass transfer, an increase in the reaction rate, or changes in fluid properties with temperature in promoting faster diffusion of species away from the boundary. The result of this study provides valuable insight into the effects of radiation and chemical reactions on the boundary layer behaviour. A better comprehension of the thermal radiation effects in the flow in the hydrolysis reaction will be beneficial to improve the reactor design in the thermochemical cycle of hydrogen production while improving the overall Cu-Cl cycle efficiency. Overall, this research presented a detailed boundary layer study with hydrolysis along a flat surface and highlighted the effects of thermal radiation and thermophysical property variations.

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