Articles
Renewable Energy (09601481)256
This study presents the development of a mathematical model to accurately predict the dynamics of salt and water transport in a batch electrodialysis system used for either NaCl desalination or LiCl brine concentration. The primary aim of the model is to simulate the desalination of high-salinity water under specified current density conditions. The governing equations for the electrodialysis stack and associated tanks were formulated and solved using numerical methods. Model predictions were validated against experimental data, demonstrating high accuracy: the deviation between measured and predicted tank concentrations was within ±2 % for both NaCl and LiCl systems. In addition, the study investigated how initial salt concentration, current density, and flow rate influence system performance. The results show that system efficiency is significantly affected by the initial brine concentration. Increasing the salt concentration from 5 wt% to 10 wt% and 20 wt% reduced desalination efficiencies by approximately 67 % and 93 %, respectively. Moreover, salt flux improved with higher current density, with a 71 % increase in desalination observed when current density was raised from 100 A/m2 to 400 A/m2. © 2025 Elsevier Ltd
Chemical Engineering Journal (13858947)510
The most cost-effective way to produce hydrogen is by steam reforming of methane. Traditionally, conventional fired burners were used for this purpose, despite their drawback of large volumes. The present study modeled an industrial convection reformer integrated into a bayonet tube used for methane steam reforming. The key feature of this compact design is that the furnace and reactor tube remain separate and do not make direct contact with each other. This type of reactor has many complexities from various aspects, including multilayer structure, heat transfer mechanisms, and reactions. A multi-scale one-dimensional model is developed to model the reactor, considering the effects of radiative heat transfer based on fundamental principles. A creative approach is employed to calculate the radiation view factor. A hybrid approach is employed to solve the equations, combining the shooting method with the method of lines to optimize CPU time and ensure equation convergence. The results agree well with plant data across various capacities and operating conditions, achieving 86 % methane conversion while maintaining the fixed bed temperature below 830 °C. Notably, neglecting radiation effects can lead to a 16.2 % error in methane conversion predictions and a 6.5 % error in the estimated reformed gas outlet temperature. Sensitivity analysis reveals that increasing flue temperature from 950 °C to 1300 °C increases methane conversion from 55 % to 95 %, while raising feedstock temperature from 380 °C to 500 °C has a smaller effect, increasing conversion from 83 % to 86 %. These findings highlight the model's potential for accurately predicting the performance of an industrial-scale convective reformer. © 2025 Elsevier B.V.
This study explores the experimental and mathematical modeling of energy recovery from hot exhaust gases using a finned tube heat exchanger filled with paraffin. The experimental setup employs air as the heating fluid, water as the cooling fluid, and paraffin with a melting point of 68°C as the phase change material. Key parameters investigated include inlet air temperature, air mass flux during heating, and water mass during cooling. The system's thermal behavior is modeled mathematically by assuming heat accumulation in the paraffin-filled finned tubes. Numerical solutions of the equations are compared with experimental data, and dimensionless parameters are used to evaluate system performance under varying conditions. The model also examines the effects of structural features, such as fin height and the number of fins per unit tube length. The results show that increasing inlet air temperature and reducing air mass flux improve the heating and cooling efficiencies and overall system performance. Enhancing fin height from 0 to 1.5 cm and the number of fins from 0 to 20 within a 10 cm tube length leads to heating efficiency gains of 10.88% and 15%, respectively. © 2025 Wiley Periodicals LLC.
Chemical Engineering Research and Design (17443563)212pp. 121-133
Catalytic dehydrogenation of long-chain normal paraffins is the most attractive route for producing of linear alkyl benzene. To make this happen, the radial-flow packed-bed reactors are employed as one of the most efficient currently available technologies. Simplifying assumptions that are sometimes imposed on reactor models to reduce the computational cost may also significantly decrease the accuracy of simulations. Here, it is decided to shed light on this matter by assessing the effect of typical model-simplifying assumptions on simulation results. To this end, one- and two-dimensional semi-homogeneous models are used to simulate an industrial-scale radial-flow packed-bed dehydrogenation reactor under isothermal and adiabatic conditions. Simulations are designed in four 1D isothermal, 1D adiabatic, 2D isothermal, and 2D adiabatic modes to compare different modeling strategies and investigate the effect of flow distribution on the reactor performance. An appropriate LHHW kinetics model is considered for paraffin dehydrogenation and the main associated side reactions over a commercial Pt-Sn-K-Mg/γ-Al2O3 catalyst. The model equations are solved numerically using the finite element method by COMSOL Multiphysics CFD software. The results show a 1–3 % discrepancy between the predictions of one- and two-dimensional models for feed conversion under isothermal and adiabatic conditions. In contrast, the comparison of isothermal and adiabatic results for each one- and two-dimensional models indicate a discrepancy of 33–36 %. Furthermore, the two-dimensional model shows a low non-uniformity in flow distribution under reaction conditions (∼ 0.175), which has a trivial negative effect on paraffin conversion. © 2024 Institution of Chemical Engineers
Madadi avargani, V.,
Zendehboudi, S.,
Rahimi, A.,
Soltani, S. Applied Thermal Engineering (13594311)203
Although obstacles on the absorber surface of a solar air heater (SAH) can increase the thermal efficiency by creating turbulent conditions, they might reduce the system's exergy efficiency due to an increase in the pressure drop. In the present work, a 3-dimensional computational fluid dynamics (3D CFD) model is first developed to simulate conical obstacles, and the developed model is then validated using the available experimental data. To find optimal design features, obstacles with various shapes/geometries such as cylindrical, spherical, hemispherical, pyramidal, and cubical are investigated. To attain this goal, a comprehensive study is conducted by including energy, exergy, enviro-exergy, and thermo-hydraulic analyses. The results reveal that vertical cylindrical obstacles have better performance than other geometries as well as a flat absorber without obstacles. The average daily thermal efficiency of the system is increased by 69.16%, and the exergy efficiency of the system is increased by 103.16%. The relative CO2 reduction potential (RCDRP) for a SAH with vertical cylinders is improved up to 168.7%. In addition, the vertical cylinder with a daily average thermo-hydraulic performance parameter of 1.2 shows the greatest thermo-hydraulic performance parameter (THPP) among other geometries, and the pyramidal obstacle with the THPP of 0.66 has the minimum performance. © 2021 Elsevier Ltd
