Master of Engineering Science
Mechanical and Materials Engineering
Microalgae has been identified as a potential source in the production of biofuel. Photobioreactors, which are used for microalgae production, normally experience temperature variations over the diurnal cycle due to changes in ambient conditions. The thermal regulation of photobioreactors to minimize temperature variations will result in a higher yield of microalgae, which are sensitive to such variations. The present research is aimed to investigate a novel approach to thermally regulate photobioreactors using phase change materials (PCM) where the latent heat of the material is exploited as the energy storage. The present research uses a numerical approach to study the flow and thermal behaviors in a rectangular channel with PCM-filled thermal energy storage columns. An open source CFD software, OpenFOAM, is used to numerically simulate the problem. The results show that geometric parameters such as the gap and blockage ratios, column aspect ratio, column shape and column arrangement in the channel influence thermal energy storage in the PCM-filled columns. The results also show that the thermal response of the channel flow, when there is a gradual change in the flow temperature, is influenced by the flow parameters such as the mass flow rate and the rate at which the flow temperature varies.
Summary for Lay Audience
This thesis project derived its inspiration from the need to maximize microalgae growth inside photobioreactors. Microalgae are microorganisms that photosynthesize to produce biomass which can be converted to biofuel. Photobioreactors that use sunlight as the light source (required for photosynthesis in microalgae) experience temperature variations due to changes in the ambient conditions. Microalgae growth is sensitive to temperature variations, which is why temperature control inside photobioreactors is necessary to maximize microalgae yield. In this thesis, an innovative approach to thermally regulate photobioreactors using phase change materials as thermal energy storage is proposed. This thermal energy storage would store excess heat throughout the day and release the stored energy back into the photobioreactor during the night. A novel design is proposed where PCM-filled columns are placed inside the photobioreactor channel for temperature control.
The research outlined in this thesis aimed to answer three questions: (1) how does the placement of PCM-filled columns inside a rectangular channel affect the flow and heat transfer behavior in the channel and within the PCM; (2) how do the flow conditions inside the channel and the position of columns as well as the column shape and aspect ratio influence thermal energy storage; and (3) how does thermal energy storage in PCM-filled columns thermally regulate the channel fluid.
The open-source CFD software, OpenFOAM, was used to simulate flow and heat transfer inside a rectangular channel containing PCM-filled columns where the PCM undergoes phase change. The results show that the interaction of flow with the columns influenced the flow velocity and temperature. There was a change in the observed thermo-fluid behavior within the channel when the column arrangement, column shape and flow conditions in the channel were varied. Finally, energy storage in the PCM-filled columns regulated the temperature in the channel such that the higher temperature flow incoming into the channel left the channel at a relatively lower temperature.
Akber, Sameed, "Numerical Investigation of Flow and Thermal Behavior in Channels with PCM-filled Thermal Energy Storage Columns for Potential Application in Photobioreactors" (2022). Electronic Thesis and Dissertation Repository. 8832.
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