Browsing by Author "Hassan, EBE"

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    Flow and heat transfer in packed beds of rock.
    (Stellenbosch : Stellenbosch University, 2023-11) Hassan, EBE; Hoffmann, JE; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Utilizing thermal energy storage systems in a solarized Brayton cycle increases the capacity factor of the power plant by using waste heat. The waste heat can be used to power a Rankine cycle to produce additional energy after sunset or during periods of high demand. Packed beds of crushed rock have been proposed as a promising storage solution since it is readily available, inexpensive, and able to withstand high temperatures. Dolerite is one of the rock types selected as the optimal choice for storing high temperatures. Nevertheless, predicting the pressure drop over a packed bed is a crucial parameter for estimating the pumping power of the system. There are various parameters that influence the pressure drop through the bed, such as the shapes and sizes of the crushed rocks, which affect the packing density and particle orientation. In this study, the investigation of the pressure drop through the packed bed of crushed rock depending on the flow direction was conducted. The crushed rock was represented by an ellipsoidal shape with the same volume and aspect ratio as the average of randomly collected crushed rock samples. This is because the aspect ratio is considered one of the particle characteristics that enables one to capture the flow directional effect. Simulation models were developed to assist in deriving a pressure drop correlation as well as the effect of particle orientation on pressure drop. For simulation, a discrete element model (DEM) was used to generate the particles and computational fluid dynamics (CFD) to simulate the flow at pore scale over the particles. Firstly, a packed bed of ellipsoidal particles was developed using a DEM-CFD method. Afterward, an experimental model was developed to validate the DEM-CFD model. Following the validation, the DEM-CFD model was compared with a crushed rock packed bed to examine how well the ellipsoid particles represent the crushed rocks. The findings reveal that the model successfully captured the flow direction effect across the crushed rock bed. However, it underestimated the pressure drop through the crushed rock by 5 % in horizontal flow and overestimated it by 20 % in vertical flow. The wall has a direct effect on the particles' alignment, where at the bottom of the container the particles are aligned with their flat faces. The wall effect is high for the particles close to it; however, it does not extend deep into the bed. Additionally, it depends on the bed-to-particle diameter ratio. For a large rock bed where it is a free packing bed, the wall has an insignificant effect on the particles' alignment. Therefore, the wall effect was then eliminated from the DEM-CFD model, and a correlation was proposed to predict the pressure drop through a crushed rock packed bed using the porous media approach. The proposed correlation was used to predict the pressure drop across a packed bed of 10 MWth. The findings were compared with the isotropic Ergun model. After investigation of the outcomes, it was found that the proposed correlation captured the directional effect. Also, it was predicted that the pressure drop across a porous bed would be about 22 % lower than that predicted by the Ergun equation in the vertical direction.