Master of Engineering Science
Mechanical and Materials Engineering
Environment and Sustainability
Straatman, Anthony G
Fossil fuel usage is resulting in climate change. There is a need to switch to renewable energies, but existing technologies lack the efficiency for wide-scale adoption. Concentrating solar energy to a receiver using a parabolic reflector is an efficient method of converting sunlight into thermal energy at a high efficiency. Current receivers suffer efficiency challenges due to significant re-radiation losses as they reach a high temperature at the front surface. This project is focused on the creation of a computational model to simulate the radiation heat transfer in porous geometries, which can be used to optimize the geometric properties of the concentrated solar receiver and improve the efficiency. Two different computational fluid dynamics (CFD) software were considered, and their capabilities were assessed. A parametric study was conducted that involved changing the input radiation flux, porous material, porosity, pore size, and porosity gradient of the block. Results showed that of the geometries and materials tested, a graphite block with 70% porosity had the highest output flux from the system.
Summary for Lay Audience
Fossil fuel usage is resulting in climate change due to the emission of greenhouse gases. There is a need to switch to renewable energies, but existing technologies lack the efficiency for wide-scale adoption. Solar energy is the most abundant source of renewable energy; however, commercially available solar energy technologies typically have low efficiencies, making them less competitive compared to conventional fossil-based systems. Concentrated solar power (CSP) is promising approach to convert sunlight into thermal energy at very high efficiency. Among CSP systems, the parabolic-dish CSP system is considered the most efficient. In this system, a parabolic dish directs sunlight to a single focal point where it is concentrated and converted into thermal energy through absorption into a thermal receiver. A challenge with current designs is that the surface of the thermal receiver reaches a high temperature and does not efficiently transfer the heat due to radiation losses. Porous media can reduce these losses because they have a large internal surface area which allows for absorption of radiation at many internal surfaces. However, the radiation exchange process in the porous medium requires better understanding, which is crucial to design high-efficiency concentrated solar receivers.
This project is focused on the creation of a computational model which can be used to design a solar thermal receiver that reduces the front surface temperature and improves the heat transfer within the receiver. To create this computational model, a simple experimental study was conducted, and computationally replicated. Then, the initial stages of a parametric study were conducted with more complex porous models. This study involved changing multiple parameters and measuring the heat output from the system. The parameters that changed were the value of incoming radiation, the porous material, the porosity of the block, the pore diameter of the block, and the porosity gradient of the block. Results from this study showed that of the geometries tested, a graphite block with 70% porosity had the highest output heat flux from the system, however the author notes that more geometries need to be tested to further optimize the receiver’s design.
Blokker, Elizabeth, "An Investigation of Porous Materials for the Capture of Concentrated Solar Energy" (2022). Electronic Thesis and Dissertation Repository. 8362.
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