Fixed bed reactors are among the most important equipment in chemical industries as these are used in chemical processes. An accurate insight into the fluid flow in these reactors is necessary for their modeling. The pressure drop and heat transfer coefficient have been studied for the fixed bed reactor with tube to particle diameter ratio (N) of 4.6 and comprising 130 spherical particles using computational fluid dynamics (CFD). The simulations were carried out in a wide range of Reynolds number: 3.85≤Re≤611.79. The RNG k-ε turbulence model was used in the turbulent regime. The CFD results were compared with empirical correlations in the literature. The predicted pressure drop values in laminar flow were overestimated compared with the Ergun's [27] correlation and underestimated in the turbulent regime due to the wall friction and the flow channeling in the bed, respectively. It was observed that the CFD results of the pressure drop are in good agreement with the correlations of Zhavoronkov et al. [28] and Reichelt [29] because the wall effects have been taken into account in these correlations. Values of the predicted dimensionless heat transfer coefficient showed better agreement with the Dixon and Labua's [32] correlation. This is explained by the fact that this correlation is a function of the particle size and shape in the bed.
Optimization of energy production equipment due to significant production cost of each unit of energy is one of the most significant factors for economic development and countries progress. The aim of this work is to improve the efficiency of the parabolic trough collector (PTC) by reducing the heat losses from it. Therefore, it was utilized a PTC with a receiver tube in the focal center of the concentrator that was applied a phase change material (PCM) inside it to store better energy. In the present work, by adding a new section called transparent cover to envelope the PTC, waste of thermal energy from the receiver tube was prevented. The numerical solutions were performed for both summer and winter days. By using of existing formulas, energy and exergy efficiency of the PTC system with different geometrical shapes and heights were obtained and their performance were compared. The results showed that by reducing the height of the covers (i.e. reduction of the space), energy and exergy efficiencies were increased and by providing the triangular cover shape, the system performed better than two others elliptical and rectangular shapes.
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