CFD Thermal Energy Storage Enhancement of PCM Filling a Cylindrical Cavity Equipped with Submerged Heating Sources

International audienceIn this paper, two-dimensional CFD simulations were performed to simulate the melting process of a phase change material (PCM) filling a cylindrical cavity which includes heating sources. A CFD model based on the physical enthalpy-porosity formulation was used to simulate the phase change of the solid Gallium and to optimize the geometry of the heating sources according to the operating conditions in terms of the applied temperatures. The geometric effect of the heating sources, as well as the boundary conditions on the heat transfer characteristics are investigated in detail. In fact, the evolution of the temperature, liquid fraction and streamlines contours for the studied configurations, namely the cylindrical heating sources and the heating source with fins for two applied temperatures (Th = 40 °C) and (Th = 45 °C) were carried out. Temperature and liquid fraction measurement were assessed numerically for some specific points located inside the studied configurations for determining the redesign effect of the heating sources. Finally yet importantly, the heat transfer coefficient at the heating sources has been defined as indicator of performance to measure the contribution of the fins in the improvement of the melting time within the cylindrical cavity. It has been found that the cylindrical cavity where four fins are integrated at each heating source have enhanced the heat transfer in the PCM and improved its melting time from 18.35 min to 13.35 min while applying a hot temperature (Th = 40 °C). Furthermore, the configuration with fins enhanced the heat transfer and improved the melting time of the PCM. \textcopyright 201

Numerical Modeling and Optimization of Thermal Stratification in Solar Hot Water Storage Tanks for Domestic Applications: CFD Study

International audienceThis study aims to assess the thermal stratification inside a standard hot water storage tank such an important device of solar water heaters. A number of flat plates with different titled positions are integrated inside a vertical tank prototype. The purpose of this investigation is to numerically study the impact of the flat plate positions within a vertical storage tank, which operates during the charging mode, on the thermal stratification and to conduct the possible performance enhancements to achieve. CFD numerical comparison between two configurations was carried out and performance parameters such as temperature evolution, Richardson number and stratification number were calculated. It was shown that thermal stratification inside the storage tank is depending on the flat plate's positions. Thus, increasing flat plates in different positions inside the storage tank does not establish a suitable thermal stratification. Therefore, a superior thermal performance was achieved for the flat plate which is maintained at the middle height of the storage tank. Also, it was found that flat plate's integration at different angles improves the thermocline structure development

A Critical Review of CFD Modeling Approaches for Darrieus Turbines: Assessing Discrepancies in Power Coefficient Estimation and Wake Vortex Development

This critical review delves into the impact of Computational Fluid Dynamics (CFD) modeling techniques, specifically 2D, 2.5D, and 3D simulations, on the performance and vortex dynamics of Darrieus turbines. The central aim is to dissect the disparities apparent in numerical outcomes derived from these simulation methodologies when assessing the power coefficient ((Formula presented.)) within a defined velocity ratio ((Formula presented.)) range. The examination delves into the prevalent turbulence models shaping (Formula presented.) values, and offers insightful visual aids to expound upon their influence. Furthermore, the review underscores the predominant rationale behind the adoption of 2D CFD modeling, attributed to its computationally efficient nature vis-à-vis the more intricate 2.5D or 3D approaches, particularly when gauging the turbine’s performance within the designated (Formula presented.) realm. Moreover, the study meticulously curates a compendium of findings from an expansive collection of over 250 published articles. These findings encapsulate the evolution of pivotal parameters, including (Formula presented.), moment coefficient ((Formula presented.)), lift coefficient ((Formula presented.)), and drag coefficient ((Formula presented.)), as well as the intricate portrayal of velocity contours, pressure distributions, vorticity patterns, turbulent kinetic energy dynamics, streamlines, and Q-criterion analyses of vorticity. An additional focal point of the review revolves around the discernment of executing 2D parametric investigations to optimize Darrieus turbine efficacy. This practice persists despite the emergence of turbulent flow structures induced by geometric modifications. Notably, the limitations inherent to the 2D methodology are vividly exemplified through compelling CFD contour representations interspersed throughout the review. Vitally, the review underscores that gauging the accuracy and validation of CFD models based solely on the comparison of (Formula presented.) values against experimental data falls short. Instead, the validation of CFD models rests on time-averaged (Formula presented.) values, thereby underscoring the need to account for the intricate vortex patterns in the turbine’s wake—a facet that diverges significantly between 2D and 3D simulations. In a bid to showcase the extant disparities in CFD modeling of Darrieus turbine behavior and facilitate the selection of the most judicious CFD modeling approach, the review diligently presents and appraises outcomes from diverse research endeavors published across esteemed scientific journals

3D CFD modeling for the limits’ identification of 2D flow pattern’s effects on the aerodynamic performance of a reference H-Darrieus prototype

Abstract: The comparative assessment carried out in this paper aims to investigate the results driven from our 2D and 3D CFD modeling of H-Darrieus, based on the URANS approach. It describes the aerodynamic operation of H-Darrieus that has been used for several numerical investigations since 2010. The k- ω SST has been used to reproduce the flow structures developing in the wake. The maximal 2D and 3D power coefficients that have been achieved are Cp= 0.4016 and Cp= 0.5734 , respectively for λ= 3.0976 . The maximal 2D and 3D absolute error, which is corresponding to the power coefficient assessment were equal respectively to 14.9714% and 29.1582%. They were calculated at λ= 2.5183 and λ= 3.0976 . Our parametric study showed that the increase range of the power coefficient, while taking into account the 3D aerodynamic effects becomes larger than that obtained by 2D calculations. This range is defined in 3D modeling between λ= 1.85 and λ= 3.10 , while it is defined in 2D modeling by the interval having the bounds λ= 2.05 and λ= 3.10 . The necessary contours to conduct our confrontation between the 2D and 3D approach and to describe the flow structures developing around H-Darrieus were constructed and discussed. Graphical abstract: [Figure not available: see fulltext.]