11/07/2024
By Danielle Fretwell

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a Doctoral Dissertation defense by Ephraim Mutemwa Simasiku on: "Computational Study of Carbon Dioxide Conversion by Solar-Enhanced Microwave Plasma"

Candidate Name: Ephraim Mutemwa Simasiku
Degree: Doctoral
Defense Date: Friday, November 22, 2024
Time: 10 a.m. - Noon
Location: Southwick Hall, Room 240

Committee:
Advisor: Juan Pablo Trelles, Professor, Mechanical and Industrial Engineering, UMass Lowell

Committee Members
1. Ofer Cohen, Assoc. Professor, Physics and Applied Physics, UMass Lowell
2. John Hunter Mack, Assoc. Professor, Mechanical and Industrial Engineering, UMass Lowell
3. Noah van Dam, Asst. Professor, Mechanical and Industrial Engineering, UMass Lowell

Brief Abstract:
The use of renewable energy for the conversion of carbon dioxide (CO2) into value-added products can help meet global demands of fuel, chemicals, and materials while reducing CO2 emissions. Solar-Enhanced Microwave Plasma (SEMP) CO2 conversion aims to combine the sustainability and scalability of solar thermochemical processes with the efficiency and continuous operation of plasma-based approaches. This dissertation presents a computational study of an experimentally characterized SEMP reactor operating with 700 W of electric power, up to 525 W of concentrated solar radiation, at atmospheric pressure conditions, and with Ar or Ar˗CO2 as the feedstock gas. Two computational models, providing two-dimensional (2D) and three-dimensional (3D) descriptions of the SEMP reactor, are created and used for the analysis. The models integrate fluid flow, energy conservation for free-electrons and for heavy-species, species transport and chemical kinetics, electrostatics, and microwave field propagation, together with radiation transport. The 2D model employed geometry-based scaling of the microwave and solar power inputs to compensate for the model’s geometric approximations. Modeling results showed that adding solar power increases temperatures across the reactor, leading to improved CO2 conversion, with model predictions closely matching experimental data. Nevertheless, the need for empirical power scaling underscores the need for 3D modeling to accurately describe plasma-microwave power coupling and improve the predictive capabilities of the model. The 3D model accurately describes the geometry and coupling of the cylindrical discharge chamber with the rectangular waveguide. Simulation results from the 3D model reveal the strong coupling between incident microwave energy and plasma generation and show that radiative transport within the discharge tube leads to more uniform temperature distribution. Overall, results from the 2D and 3D models reveal that the integration of solar power enhances CO2 conversion by increasing the power density of the plasma, circumventing skin-depth absorption limitations often encountered in microwave plasma reactors operating at high power levels. This dissertation’s methods and findings contribute to the understanding and advancement of SEMP reactor technology and contribute broadly to the field of solar thermochemical and plasma-assisted CO2 conversion.