•A 2D CFD model is built using a fine grid to resolve the liquid flow in an RPB.•The model predictions are in reasonable agreement with observations.•On increasing the MEA concentration, the degree ...of liquid dispersion decreases.•High rotational speed decreases the holdup and increases the liquid dispersion.•At a high contact angle, more liquid droplets are formed but holdup decreases.
Rotating packed beds (RPBs) have been proposed as an emerging technology to be used for post-combustion CO2 capture (PCC) from the flue gas. However, due to the complex structure of the packing in RPBs, characteristics of the liquid flow within RPBs are very difficult to be fully investigated by experimental methods. Therefore, in this paper, a two-dimensional (2D) CFD model has been built for analysing the characteristics of liquid flow within an RPB. The volume of fluid (VOF) multiphase flow model is implemented to calculate the flow field and capture the interface between the gas and liquid phases in the RPB. The simulation results show good agreement with the experimental data. The distinct liquid flow patterns in different regions of an RPB are clearly observed. The simulation results indicate that increasing the rotational speed dramatically decreases the liquid holdup and increases the degree of the liquid dispersion. The increasing liquid jet velocity decreases the liquid residence time but slightly increases the liquid holdup. In addition, the liquid holdup increases and the degree of the liquid dispersion decreases with increasing MEA concentration, but the effects are weaker at a higher rotational speed. With the increasing of the contact angle, both the liquid holdup and the degree of the liquid dispersion are reduced. This proposed model leads to a much better understanding of the liquid flow characteristics within RPBs.
This paper presents a 2D computational investigation on the dynamic stall phenomenon associated with unsteady flow around the NACA0012 airfoil at low Reynolds number (
Re
c
≈
10
5). Two sets of ...oscillating patterns with different frequencies, mean oscillating angles and amplitudes are numerically simulated using Computational Fluid Dynamics (CFD), and the results obtained are validated against the corresponding published experimental data. It is concluded that the CFD prediction captures well the vortex-shedding predominated flow structure which is experimentally obtained and the results quantitatively agree well with the experimental data, except when the blade is at a very high angle of attack.
The estimation of the thermochemical radius is very important because most of the properties of the electrolyte solutions are, to some extent, linked to this property. Also, these thermochemical ...radii can be used to estimate lattice energies, which can be a very important parameter to be evaluated when assessing the possibility of synthesizing new inorganic materials. This study presents a formulation for estimating the thermochemical radii of complex ions. More specifically, these thermochemical radii are estimated using a weighted sum based on the radii of the contributing cations and anions. Also, the influence of the ionic charge on these thermochemical radii is assessed and discussed. Finally, the parameters obtained from the estimation of the thermochemical radii of complex cations are used to estimate cation volumes, and this estimation is then validated through comparison with literature values. As a result, the equations developed for thermochemical radii of complex ions produce predictions that are accurate to within 15% in general, whereas the equation developed to estimate cation volumes produces predictions that are accurate to within 20% considering cation volumes greater than 70 Å3.
The development of a compact mechanism has made a great contribution to work on the combustion of hydrocarbon species and facilitates the investigations on chemical kinetics and computational fluid ...dynamics (CFD) studies. N-propylcyclohexane (NPCH) is one of the important components for jet, diesel, and gasoline fuels which needs a reliable compact reaction kinetics mechanism. This study aims to investigate the construction of a well-validated mechanism for NPCH with a simplified chemical kinetics model that delivers a good prediction ability for the key combustion parameters in a wide range of conditions (temperatures, pressures, and equivalence rates). The NPCH reaction kinetic mechanism was constructed with the aid of a coupling process, simplification process, rate modification, and a combination of standard reduction methods. The model includes a simplified sub-mechanism with 16 species and 58 reactions and a semi-detailed core mechanism with 56 species and 390 reactions. Two key parameters including ignition delay time and laminar flame speed are simulated by the use of ANSYS Chemkin-Pro. The simulation results for these parameters are validated against the available data in the literature, and the results show a good agreement compared to the experimental data over a wide range of conditions covering low to high temperatures at different pressures and equivalence ratios.
Concentrated solar power (CSP) has gained traction for generating electricity at high capacity and meeting base-load energy demands in the energy mix market in a cost-effective manner. The linear ...Fresnel reflector (LFR) is valued for its cost-effectiveness, reduced capital and operational expenses, and limited land impact compared to alternatives such as the parabolic trough collector (PTC). To this end, the aim of this study is to optimize the operational parameters, such as the solar multiple (SM), thermal energy storage (TES), and fossil fuel (FF) backup system, in LFR power plants using molten salt as a heat transfer fluid (HTF). A 50 MW LFR power plant in Duba, Saudi Arabia, serves as a case study, with a Direct Normal Irradiance (DNI) above 2500 kWh/m2. About 600 SM-TES configurations are analyzed with the aim of minimizing the levelized cost of electricity (LCOE). The analysis shows that a solar-only plant can achieve a low LCOE of 11.92 ¢/kWh with a capacity factor (CF) up to 36%, generating around 131 GWh/y. By utilizing a TES system, the SM of 3.5 and a 15 h duration TES provides the optimum integration by increasing the annual energy generation (AEG) to 337 GWh, lowering the LCOE to 9.24 ¢/kWh, and boosting the CF to 86%. The techno-economic optimization reveals the superiority of the LFR with substantial TES over solar-only systems, exhibiting a 300% increase in annual energy output and a 20% reduction in LCOE. Additionally, employing the FF backup system at 64% of the turbine’s rated capacity boosts AEG by 17%, accompanied by a 5% LCOE reduction. However, this enhancement comes with a trade-off, involving burning a substantial amount of natural gas (503,429 MMBtu), leading to greenhouse gas emissions totaling 14,185 tonnes CO₂ eq. This comprehensive analysis is a first-of-a-kind study and provides insights into the optimal designs of LFR power plants and addresses thermal, economic, and environmental considerations of utilizing molten salt with a large TES system as well as employing natural gas backup. The outcomes of the research address a wide audience including academics, operators, and policy makers.
A new three-dimensional numerical model of a polymer electrolyte fuel cell (PEFC) with a single straight channel was developed to primarily investigate the important impact of the double-sided ...microporous layer (MPL) coating on the overall performance of the fuel cell and the distribution of the current and the oxygen concentration within the cathode gas diffusion layers (GDLs). Realistic experimentally estimated interfacial contact resistance values between the gas diffusion layer and each of the bipolar plates and the catalyst layer values were incorporated into the model, and parametric studies were performed. The results showed that the double-sided MPL coating could significantly improve the fuel cell performance by up to 30%. Additionally, it was shown that the neglect of the contact resistance between the MPL and the catalyst layer could overestimate the fuel cell performance by up to 6%. In addition, the results showed that the fuel cell performance and the distribution of the current and oxygen are more sensitive to the porosity of the MPL facing the bipolar plate than the porosity of the MPL facing the catalyst layer. All the above results are presented and critically discussed in detail.
The Vertical Axis Wind Turbines (VAWTs) have an increasing global market and this emphasis the need for to improve the performance of VAWTs, especially at relatively low wind speed. This paper ...utilises the Response Surface methodology to optimise the performance of a VAWT. A three bladed VAWT configuration was considered with a NACA0015 profile. Three significant input parameters were selected including the tip speed ratio, the turbine solidity, and the pitch angle. An extended range of each input parameter was chosen in order to gain a good insight into how these input parameters affect the performance of the VAWT. The high-fidelity Computational Fluid Dynamics (CFD) simulations were carried out for the modelling of the turbine. The use of the Response Surface Optimisation based on Multi-Objective Genetic Algorithm (MOGA) along with the CFD simulations is found to be useful in the selection of the optimal design of VAWT. Moreover, the 3D aspects of the VAWT geometry are investigated and these include the turbine aspect ratio and the effect of the blade tip geometry. The implementation of an optimised winglet at the tip of the turbine blades is found to provide a significant enhancement of the cycle averaged power coefficient, especially at low aspect ratios.
The through-plane gas permeability and morphology of PEFC gas diffusion media (GDM) is investigated for different microporous layer (MPL) ink homogenisation techniques (bath sonication and magnetic ...stirring) for low- (Vulcan XC-72R) and high (Ketjenblack EC-300J)-surface-area carbon powders. The MPL composition is held constant at 80 wt.% carbon powder and 20 wt.% PTFE for a carbon loading of 1.0 mg cm−2. The MPL ink homogenisation time is held constant at two hours for both techniques and increased by one hour for bath sonication to compare with previous investigations. The results show that the through-plane gas permeability of the GDM is approximately doubled using magnetic stirring when compared with bath sonication for MPLs composed of Vulcan XC-72R, with a negligible change in surface morphology between the structures produced from either homogenisation technique. The variation in through-plane gas permeability is almost negligible for MPLs composed of Ketjenblack EC-300J compared with Vulcan XC-72R; however, MPL surface morphology changes considerably with bath sonication, producing smoother, less cracked surfaces compared to the large cracks produced via magnetic stirring for a large-surface-area carbon powder. An MPL ink sonication time of three hours results in a percentage reduction in through-plane gas permeability from the GDL substrate permeability by ~72% for Ketjenblack EC-300J compared to ~47% for two hours.
The expansion of neutral particles in a plasma arc jet is crucial for the distribution of the ions and electrons, especially in an unsteady rarefied plasma arc jet with chemical reactions. A 3-D ...unsteady investigation of neutral particles in a rarefied flow with chemical combination and dissociation reactions is numerically simulated based on an in-house direct simulation Monte Carlo (DSMC) code. The evolution of the neutral particles flow in vacuum cylinders is presented, and the influence of the chemical reactions has been investigated for the neutral particles. The predicted results imply that the dissociation reaction plays a key role in the expansion of the neutral particles process. In order to study the expansion of the neutral particles in an electric field, an electrostatic particle-in-cell (PIC) and DSMC are combined to simulate the axisymmetric rarefied plasma flows with chemical reactions. Two sets of grids are employed for the DSMC/PIC method by considering the different requirements of both the methods based on the molecule mean free path and the Debye length. The properties of both the flow and electric fields are analyzed in detail. It is found that the electric potential increases if the initial velocity of the ions from the inlet is sufficiently large, and accordingly, the number density of the ions in the flow field increases further.
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