Proton exchange membrane fuel cells (PEMFCs) are efficient and emission free electrochemical generators, making them an attractive alternative power source. However, PEMFCs are yet to reach widespread commercial adopt...
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Proton exchange membrane fuel cells (PEMFCs) are efficient and emission free electrochemical generators, making them an attractive alternative power source. However, PEMFCs are yet to reach widespread commercial adoption, warranting further research. 3D computationalfluids dynamics (CFD) models of PEMFCs are a powerful research and design tool due to their ability to predict internal reactant, temperature, and current distributions. However, these models can be challenging to design and use due to the complex electrochemistry, the large parity in the length scale of different components and experimentally unknown input parameters. This work reviews the literature regarding these inherent challenges to PEMFC CFD models, examining numerical methods, computational mesh, assumptions and simplifications, input parameters and validation methods. Recommendations are made based on current literature findings and research gaps are identified, both with the goal of aiding and improving future PEMFC CFD research.(c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://***/ licenses/by/4.0/).
Drying is an important process found in different industries including spray dry scrubbing as used in flue gas desulphurization. Understanding the fundamental processes in drying requires accurate description of turbu...
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Drying is an important process found in different industries including spray dry scrubbing as used in flue gas desulphurization. Understanding the fundamental processes in drying requires accurate description of turbulence and drying models, which is important in the design and optimization of new processes. Available research in spray dry scrubbing generally picks a single model to describe drying with the key assumption that it is relevant to the case being studied. This work does not make such an assumption but investigated the applicability of three drying models and three turbulence models in analyzing the drying process in a laboratory spray dry scrubber. computational fluid dynamics was used to model the process employing the Euler-Lagrangian framework. The results from validated models showed that the investigated hindered drying mechanistic model is superior to the often used d 2 law and perfect shrinkage models and should therefore be used preferentially in drying applications.
This study presents numerical simulations and their validation for flow boiling of liquid nitrogen (LN2) in a vertical upflow orientation, with a primary aim to understand the complex two-phase flow and heat transfer ...
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This study presents numerical simulations and their validation for flow boiling of liquid nitrogen (LN2) in a vertical upflow orientation, with a primary aim to understand the complex two-phase flow and heat transfer phenomena important to space applications. The computational fluid dynamics (CFD) model utilized the coupled level set volume of fluid (CLSVOF) method, incorporating additional source terms for bubble collision dispersion force and shear lift force in the momentum conservation equation to enhance simulation accuracy. The simulations were conducted for two mass velocities (G = 526 and 804 kg/m(2)s) and three different heat flux levels (approximately 10%, 30%, and 70% of critical heat flux (CHF) under Earth gravity. The model was validated against measured wall temperature data acquired from the authors' previous experimental studies, demonstrating average deviations of less than 2.8 K across all operating conditions. The simulated two-phase flow contours illustrated various flow patterns, including bubbly, slug, churn, and annular. Both mass velocity and heat flux were observed to impact the onset of nucleate boiling (ONB), bubble nucleation, growth, and coalescence, and overall vapor structure. The simulations also offered insight into axial and radial void fraction and velocity profiles, revealing local flow acceleration trends synchronized with void fraction development. A comparison between predicted and measured bulk fluid temperature profiles showed excellent agreement, further validating the CFD model's accuracy and practical usefulness for two-phase cryogenic flow boiling simulations in space applications.
Ammonia is emerging as a potential marine fuel, yet its toxicity and risk of accidental leaks pose significant safety challenges compared to other alternatives. This study focuses on the critical ship-to-ship bunkerin...
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Ammonia is emerging as a potential marine fuel, yet its toxicity and risk of accidental leaks pose significant safety challenges compared to other alternatives. This study focuses on the critical ship-to-ship bunkering process using computational fluid dynamics (CFD) simulations to analyse diverse ammonia leakage scenarios considering various leak orientations relative to the wind and the ships. The numerical setup was initially validated against controlled experiments, demonstrating satisfactory agreement. Results indicate that atmospheric ammonia dispersion is significantly influenced by obstacles like the superstructure and hull in the near field, with diminishing effect in the far field. Conventional Gaussian plume models are inadequate within the first few hundred metres from the release source due to the complex near-field flow patterns and increased turbulence generated by the wakes of the hull and superstructure. These findings underscore the necessity for improved ship-scale dispersion models to accurately evaluate the impact of obstacles on ammonia dispersion. The consequence analysis reveals that upward leaks create larger risk zones with potential for irreversible health effects, while horizontal leaks may expose personnel to life-threatening concentrations. Vertical leaks in crosswind configurations generate lethal zones covering tens of metres on deck. These results highlight the importance of considering the exact location of the transfer hose relative to the ship and all potential wind orientations in risk assessments. Given the extensive range of potential dispersion patterns and the inadequacy of conventional Gaussian dispersion models in this context, we strongly recommend vessel-specific CFD simulations before certifying ammonia bunkering operations as safe. This approach is crucial for accurate risk assessment at the ship scale, where complex geometries and multi-directional flows invalidate the assumptions of traditional point-source, uni-direc
A computational fluid dynamics method has been developed to describe the hydrodynamics of different stirring devices, which are commonly used in the development stage of protein crystallization. The experimental setup...
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A computational fluid dynamics method has been developed to describe the hydrodynamics of different stirring devices, which are commonly used in the development stage of protein crystallization. The experimental setup consisted of minicrystallizers in which the crystallization cocktail was stirred using a magnetic stirrer, mechanical agitator, shaker, or rotating mixer at different rotational frequencies. The hydrodynamics of the setups was determined with respect to local and average values of flow velocity, turbulent dissipation rate (epsilon), turbulent kinetic energy (k), and shear rate ((gamma)over dot). The calculations were performed by using the ANSYS Fluent software, in which the k-epsilon RNG turbulence model was implemented. The model was used to determine the probability density functions (PDFs) of the hydrodynamic parameters, which were correlated with the morphology of the protein crystalline phase obtained in the crystallization experiments. Lysozyme was used as a model protein, which was crystallized from sodium chloride solutions. For the shaker and rotating mixer, the dependence of the crystal size distribution on the k-PDF or (gamma)over dot-PDF distributions followed a similar pattern. For the mechanical agitator, a minor discrepancy was observed from that pattern at higher rotational frequencies. The correlation could not be validated for the magnetic stirrer, in which no crystalline phase was obtained under the crystallization conditions used. This was attributed to the pulverization of the solid phase caused by the magnetic bar.
This study developed a numerical model to efficiently treat solid waste magnesium nitrate hydrate through multi-step chemical *** model simulates two-phase flow,heat,and mass transfer processes in a pyrolysis furnace ...
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This study developed a numerical model to efficiently treat solid waste magnesium nitrate hydrate through multi-step chemical *** model simulates two-phase flow,heat,and mass transfer processes in a pyrolysis furnace to improve the decomposition rate of magnesium *** performance of multi-nozzle and single-nozzle injection methods was evaluated,and the effects of primary and secondary nozzle flow ratios,velocity ratios,and secondary nozzle inclination angles on the decomposition rate were *** indicate that multi-nozzle injection has a higher conversion efficiency and decomposition rate than single-nozzle injection,with a 10.3%higher conversion rate under the design *** decomposition rate is primarily dependent on the average residence time of particles,which can be increased by decreasing flow rate and velocity ratios and increasing the inclination angle of secondary *** optimal parameters are injection flow ratio of 40%,injection velocity ratio of 0.6,and secondary nozzle inclination of 30°,corresponding to a maximum decomposition rate of 99.33%.
Introduction In major hepatobiliopancreatic surgery, an accurate preoperative planning is essential. Postoperative impaired blood supply due to arterial disease or variants can cause postoperative complications. Compu...
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Introduction In major hepatobiliopancreatic surgery, an accurate preoperative planning is essential. Postoperative impaired blood supply due to arterial disease or variants can cause postoperative complications. computational fluid dynamics has previously been successful in revealing distinct features of haemodynamic disturbances. The purpose of our study is to describe the feasibility of a computational fluid dynamics model to predict hepatic artery flow and its variations following gastroduodenal (GDA) or common hepatic (CHA) artery ligation. Material and methods This is a pilot study including 20 patients undergoing robotic pancreaticoduodenectomy at a single centre. Preoperative images and intraoperative vascular flows were used to the computational model. Three scenarios of the hepatic artery were analysed: (1) without any clamps, (2) clamped GDA and (3) clamped CHA. Patients 1 to 15 were used to develop the model, and patients 15 to 20 were used for model validation. Finally, the model was tested in 3 abnormal cases: celiac trunk stenosis (2) and replaced right hepatic artery (1). Results The selected methodology proved to be reproducible, with the CFD model demonstrating 100% accuracy in predicting blood flow redistribution after gastroduodenal artery (GDA) clamping and 80% accuracy following common hepatic artery (CHA) clamping. The model accurately simulated reversed GDA flow in cases of celiac trunk stenosis and displayed independent flow distribution in patients with anatomical variations, even without prior specific model training. Conclusion The developed computational model accurately predicts flow variations in the proper hepatic artery in case of gastroduodenal artery and common hepatic artery clamping. Further studies are needed to validate this methodology.
The primary objective of this numerical study is to analyse the 2D flow across a circular cylindrical tube under various laminar as well as turbulent flow regimes. In this study, the implicit finite volume scheme was ...
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The primary objective of this numerical study is to analyse the 2D flow across a circular cylindrical tube under various laminar as well as turbulent flow regimes. In this study, the implicit finite volume scheme was employed to compute incompressible flow with time precision using convective flux discretization schemes of the second order. The computational results were validated by comparing the simulation results with empirical data of mean surface pressure, wake characteristics in both constant and transient flow regimes, and the Strouhal frequency associated with vortex scattering. In addition, the present simulation model adequately captures the intricate 2D flow structure of the cylinder wake.
In this paper, the numerical simulation was done for a cylindrical tee by establishing a steady-state simulation to examine the mixing performance. The temperature of the fluid at the hot inlet was chosen as 36 degree...
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In this paper, the numerical simulation was done for a cylindrical tee by establishing a steady-state simulation to examine the mixing performance. The temperature of the fluid at the hot inlet was chosen as 36 degrees C and 19 degrees C for the cold inlet. The numerical simulation was done for a short tee of 192 mm and a long mixing tee of 262 mm at a variety of momentum ratios. The geometry was meshed in FLUENT before solving the domain. For the meshing, the faces were initially named hot inlet, cold inlet, outlet, and walls. The triangular method was chosen to generate a mesh for the flow domain. The size of the cell in meshing was taken as 0.1 m. In this work, the SST k-omega models were selected to perform the computations. The analytical values of temperature were used to validate the numerical results. Results show that the thermal mixing was done effectively using the CFD ANSYS software package. Results show that the size of the mixing area is the same hence there is not much of a difference between the long tee and the short tee in that particular sector. The thermal mixing was found better when the velocity at the vertical inlet (y-axis) becomes greater and the average temperature is lower. Also, the increase in the pipe's length causes the average temperature to drop since the fluid mixes better the farther along it travels, while also slightly increasing the velocity.
This study utilized computational fluid dynamics (CFD) simulations to investigate the impact of operational variables on the performance of a two-dimensional Vacuum Membrane Distillation (VMD) module. The analysis foc...
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This study utilized computational fluid dynamics (CFD) simulations to investigate the impact of operational variables on the performance of a two-dimensional Vacuum Membrane Distillation (VMD) module. The analysis focused on various feed flow rates and temperatures. Within the feed channel, mixing promoters of three diameters (0.5 h, 0.3 h, and 0.1 h, where 'h' represents channel height) were employed to assess the effects of nettype spacers on reducing concentration and temperature polarizations while enhancing vapor flux. The findings revealed that higher feed water temperatures significantly increased vapor flux, concurrently reducing the temperature polarization coefficient (TPC) and raising the concentration polarization coefficient (CPC). This increase in vapor flux notably influenced CPC by exacerbating salt accumulation on the membrane surface. The incorporation of spacers consistently led to a decrease in both concentration and temperature polarizations throughout the module, with larger spacer diameters contributing to improved system performance. Notably, the use of spacers with a diameter of 0.5 h resulted in a 53 % increase in overall vapor flux.
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