Authors:Abel Gámez Rodríguez; Daniel Milian Pérez, Carlos Brayner De Oliveira Lira Abstract: Conducting three-dimensional thermohydraulic analysis of an entire nuclear reactor poses significant challenges due to the considerable geometric volume and complex internal structures involved. The top reflector is one of the internal structures found in high-temperature pebble bed Small Modular Reactors (SMR). This structure serves several critical functions, including neutron reflection, control and distribution of helium inlet into the core, neutron and thermal shielding, among others. In this kind of system, the detailed representation of the top reflector includes the representation of more than 460 channels of 2.5cm of diameter. Considering that the reactor has almost a ten of meters then dimension scales of various orders must be represented, which is a challenge. In this sense, a three-dimensional Computational Fluid Dynamics (CFD) thermohydraulic analysis of the entry pattern to the core of a High Temperature SMR using ANSYS CFX has been done. This study presents a comparison between five coolant entry patterns into the core. Initially, two prototype models of 460x2.5cm, one with vertical channels and another with inclined channels, are modeled. Additionally, two prototype models of 20x12cm of equivalent area, with vertical and inclined channels are also included. Finally, a simplified porous media model with the same equivalent area is considered. The thermohydraulic behavior of the coolant before and after passing through the top reflector was then analyzed for these five patterns. An analysis of fuel elements temperature in the core was conducted. It is important to highlight that this study is qualitative and has the goal of identifying and characterizing the impact that the coolant entry pattern into the reactor core has on the main thermohydraulic parameters in this region. The study exposes a strong correlation between the porous media model and all prototype models in terms of the maximum fuel temperature, average fuel temperature, and helium velocity. In this study, the potential applicability of the porous media models for an integral full-scale reactor simulation in the future was demonstrated. As a benefit, the porous media model reduces the mesh quantity compared to a prototypic model. PubDate: Sat, 01 Jun 2024 00:00:00 +030
Authors:Orhan Veli Kazancı; Yakup Erhan Böke Abstract: The energy required for technological advancement is primarily derived from hydrocarbon combustion, which is a key topic in thermodynamics. The stability of the flame in hydrocarbon combustion is a critical parameter that impacts both burner design and combustion efficiency. Various methods have been employed in the literature to achieve a stable flame, with swirl flow being one technique that enhances combustion performance in engineering applications. This study focuses on the numerical analysis of the SM1 flame from Sydney swirl flames. Initially, the flow incorporating the two-equation Re-Normalization Group (RNG) k-ε and Shear Stress Transport (SST) k-ω turbulence models, along with the chemical reactions of CH4 combustion using the GRI 3.0 reaction mechanism, was modeled and compared with experimental data. Subsequently, the numerical results obtained from the Shear Stress Transport k-ω turbulence model, which demonstrated the best agreement with experimental data, were compared with results from a numerical analysis in the literature using the Large Eddy Simulation (LES) turbulence model. The predictive capabilities of these two turbulence models, along with their behavior in the flow region, were evaluated. The comparison revealed that for stable flames within the Sydney swirl flame family, the Shear Stress Transport k-ω turbulence model, which provides results in a more efficient manner, is sufficient compared to the computationally expensive Large Eddy Simulation turbulence model. This choice is made possible by utilizing a solution algorithm tailored to the flow characteristics and appropriate boundary conditions. PubDate: Sat, 01 Jun 2024 00:00:00 +030
Authors:Fayza Zemmouri; Hakim Madanı, Imad Anoune, Abdelkrim Merzouguı Abstract: In this study, a novel approach employing the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) Equation of State was introduced to investigate azeotropic behavior in ternary mixtures and explore their liquid-vapor equilibria. The temperature range spans (243.15323.5) K, covering a broad spectrum of conditions relevant to industrial and chemical processes. Our analysis focuses on six different ternary mixtures: Difluoromethane (R32) + 1,1-difluoroethane (R152a) + 2,3,3,3-tetrafluoropro-1-ene (R1234yf); Isobutane (R600a) + 1,1-difluoroethane (R152a) + 1,1,2,2-tetrafluoroethane (R134); 1,1,1,2-tetrafluoroethane (R134a) + 2,3,3,3-tetrafluoropro-1-ene (R1234yf) + isobutane (R600a); 1,1,1,2-tetrafluoroethane (R134a) + 2,3,3,3-tetrafluoropro-1-ene (R1234yf) + dimethyl ether (DME); isobutene (R600a) + 1,3,3,3-tetrafluoropropene (R12345ze(E)) + trifluoroiodomethane (R13I1); and difluoromethane (R32) + fluoroethane (R161) + 1,3,3,3-tetrafluoropropene (R1234ze(E)). Among these, only three mixtures exhibit azeotropic behavior.The PC-SAFT equation of state, incorporating an expansion form tailored for Vapor-Liquid Equilibrium (VLE) calculations within ternary mixtures, determined azeotropic composition and pressure based on the Gibbs-Konovalov theorem, which characterizes azeotropic behavior under constant temperature. Our estimations of the VLE and azeotropic composition and pressure closely align with experimental data. The maximum relative error in pressure does not exceed 4.2% for the R600a + R152a + R134 mixture and remains less than 6.56% for the liquid composition of R1234ze(E) within the (R600a + R1234ze(E) + R13I1) ternary mixture. These results underscore the reliability and accuracy of the PC-SAFT equation of state in modeling azeotropes within ternary mixtures. PubDate: Sat, 01 Jun 2024 00:00:00 +030
Authors:M. Faruk Karabat Abstract: In this article, we focus on the inflation dynamics of the early Universe using an inverse power law potential scalar field (V_((ϕ))=V_0 ϕ^(-n)) within the framework of Tsallis entropy. First, we derive the modified Friedmann equations from the non-additive Tsallis entropy by applying the first law of thermodynamics to the apparent horizon of the Friedmann–Robertson–Walker (FRW) Universe. We assume that the inflationary era of the Universe consists of two phases; the slow roll inflation phase and the kinetic inflation phase. We obtained the scalar spectral index n_s and tensor-to-scalar ratio r and compared our results with the latest Planck data for these phases. By choosing the appropriate values for the Tsallis parameters, which bounded by β PubDate: Sat, 01 Jun 2024 00:00:00 +030
Authors:Lindemberg De Jesus Nogueira Duarte; Gilson Medeiros, Humberto Neves Maia De Oliveira, Eduardo Lins De Barros Neto, Rayandson Raimundo Da Silva, Jessyca Bezerra Abstract: Increasing concern about climate change and the need to reduce dependence on fossil fuels have driven the search for more sustainable energy alternatives. One way to reduce emissions is by adding oxygenated compounds such as biodiesel and alcohols to diesel fuel. However, this can lead to phase separation between the fuels and have serious consequences for engine performance. In this context, the present study aimed to evaluate the effect of ethanol content on the miscibility of components in mixtures containing ethanol + biodiesel + diesel through the study of liquid-liquid equilibrium. The results from ternary phase diagrams revealed that the amount of water present in ethanol has a significant effect on the miscibility of the mixture components, with larger biphasic regions observed in systems with lower ethanol content. For the 95% ethanol diagram, the reliability of experimental data on equilibrium lines was assessed through the Othmer-Tobias and Hand correlations, which showed correlation coefficients (R²) of 0.996 and 0.995, respectively. The results obtained from the NRTL and UNIQUAC thermodynamic models demonstrated excellent agreement with the experimental data, with a deviation of only 1.78 and 0.78% for the NRTL and UNIQUAC models. PubDate: Sat, 01 Jun 2024 00:00:00 +030
Authors:Saif Ali Kadhim Abstract: The process of phasing out of medium and high global warming potential refrigerants is accelerating in all areas of refrigeration, particularly since the European F-Gas Regulation No. 517/2014 and the ensuing Kigali amendment went into effect. Hydrocarbon refrigerants are being considered as suitable alternatives due to their low global warming potential and excellent thermal properties, but due to their flammability, safety precautions must be followed. This theoretical study contributes to the evaluation of the thermal and environmental impact of hydrocarbon refrigerants as drop-in alternatives to R134a in domestic refrigerator. In order to conduct an analysis of energy, exergy, and environmental factors, R134a and all hydrocarbons refrigerants proposed by ASHRAE—R290, R600, R600a, R601, R601a, and R1270—were examined as operating fluids used in a domestic refrigerator with a cooling capacity of 157 W and constant condenser temperature of 40°C and variable evaporator temperature every 5°C between -5 and -30°C. The results revealed that all the alternative refrigerants except R601 and R601a have higher thermal and environmental performance than R134a and can be used after refrigerator compressor replacement. PubDate: Sat, 01 Jun 2024 00:00:00 +030
Authors:Amin Farzin; Saeed Mehran, Kaveh Salmalian Abstract: The present study demonstrates the successful application of the grasshopper optimization algorithm (GOA) to the thermodynamic and economic modeling and optimization of cross-flow plate-fin heat exchangers with offset strip fins. To this end, the ε-NTU method was played to determine the efficiency and pressure drop. Seven parameters, namely the exchanger length at hot and cold sides, number of hot-side layers, fin frequency, fin-strip length, fin thickness, and fin height, constitute the design parameters for the optimization of the heat exchanger. The efficiency of the heat exchanger, the entropy generation, and the total annual system cost were considered the objective functions. Accordingly, the optimization of each objective function was investigated separately. The efficiency and accuracy of the proposed algorithm were validated using two examples from the literature. Comparison between the obtained results and those in the previous studies indicates that GOA performed better in minimizing total annual cost and entropy generation and maximizing efficiency. PubDate: Sat, 01 Jun 2024 00:00:00 +030
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