Papers by Keyword: CFD

Abstract: The expansion of the urban population has contributed to the formation of urban agglomerates; whose spatial morphology favors the formation of heat islands. The installation of Green Roofs (GR) is a strategy that can be applied to mitigate the effects of this phenomenon, especially in regions lacking vegetation cover. The objective of this paper is to evaluate, through Computational Fluid Dynamics (CFD), the potential to reduce the internal temperature of a building located in the city of Rio de Janeiro, Brazil. The temperatures of the inner surface of the roof were measured in two buildings, one with GR and one without GR. This information was used as input data into Solidworks software to simulate the heat distribution inside the building. Results indicated that the temperature was reduced by about 2°C in the building with GR, proving the technology's effectiveness, notably in the hottest months of the year.

Abstract: In this study, Computational Fluid Dynamics (CFD), applied to a non-Newtonian fluid, was developed to characterize gas-liquid interaction and mixing process in a 15 m³ (working volume) bioreactor. The bioreactor was equipped with four arrangements of standard Rushton, Pitch-blade and Scaba® impellers. Gas-liquid hydrodynamics was estimated based on CFD results. The chosen operating conditions were defined by the settings used for production of xanthan gum via fermentation route by Xanthomonas campestris. The mixing process was simulated by using the k-epsilon turbulence model, Multiple Reference Frame and Population Balance Model approaches. The simulation results have been compared and analyzed by isosurfaces, volume fractions, velocity graphs, torques and flow analysis calculations. Obtained results revealed that for the Pitched-Pitched-Pitched arrangement to avoid the constraint-imposed overload torque limitations impeller diameter size should be reduced by 10%. The use of Rushton-Rushton-Rushton impeller arrangement was discouraged for non-Newtonian pseudoplastic fluid mixing, whereas Pitched-Rushton-Scaba and Scaba-Rushton-Pitched impeller arrangements were both acceptable.

Abstract: Elbow pipes are important pipeline components in hydrocarbon transportation systems, and they were prone to erosive wear by the impact of abrasive particles. A discrete phase modeling (DPM) and numerical simulation of the liquid-sand transportation process was carried out focused on the investigation into the influence of carrier fluid viscosity on erosion distribution of carbon steel 90° elbows. The accuracy of the predicted results was validated by comparison with experimental data. CFD simulations have been carried out by combining DPM to predict the erosion rate and particle impaction regions in carbon steel 90° elbow with a diameter of 50.8 mm. The fluid viscosity is set for 1cP, 5cP, and 15 cP with an inlet velocity of 8 m/s, and the size of sand particles is 200 μm. While the maximum erosion rates enhance with an increase in fluid viscosity, the location of maximum particle impaction has been specified to be adjacent to the outlet for 1 cP and 5 cP carrier fluid viscosity. It is also found that increasing the viscosity does not considerably alter the average erosion rate. Moreover, the increase in carrier fluid viscosity with the same flow velocity influences maximum erosion rate and yields 1.45 times higher erosion rates at 15 cP compared to 5cP and 1cP. This is mainly due to severe sand impaction at the side of the elbow wall.

Abstract: The polymer electrolyte membrane (PEM) fuel cells flow fields channels serve the same roles as nutrient and reactant circulation systems in plants and animals, so bio-inspired flow field channels with a similar could improve reactant uniform transport efficiency and boost fuel cell performance. In this analysis, the lung channel configuration of a humane lung and a tree leaf bio-inspired flow field channels are used as an anode and cathode bipolar plate. A channel model is developed for three new flow field patterns designs: leaf design, lung design and triple-serpentine. It has been observed that the performance improvement in terms of power in the bio-inspired flow field is 13.32% more than the triple serpentine. This indicates the bio-inspired design has good performance than other flow field design. Further a parametric steady is carried out experimentally to study the effect of cell operating temperature, anode and cathode humidity, hydrogen and oxygen flow rate on the cell performance.

Abstract: Boiler is one of the critical parts and plays an important role in Steam Generation Power Plant. It transforms the chemical energy of fuel into heat or thermal energy. During plant operations, some problems occurred in the boiler and Superheater leakage is the heaviest problem that interfered the whole operations, and the units needed to stopped for maintenaces outages. Failure analysis is necessary to determine the cause of failure. Root Caused Failure Analysis methods was through mechanical tests in the laboratory, which is Visual Observation included Macrofractography Structure examination, Metallographic or Microstructure Examination, Hardness Test. The metallographic examination result shows that the microstructure of the base metal is ferrite pearlite, and there is no indication of microstructure changes in tube as effect from high operation temperature. Likewise, microstructure in the weld region is in normal conditions, no weld failure phenomenon. Hardness value for base metal, weld and HAZ area are still in a good condition. Macrofractrography structure examination shows that the fracture is in mechanical fatigue condition. Based on those results the source of the tube leak is not caused by operating errors, inside or outside deposit nor weld failure. Superheater tube failures caused by mechanical factors, namely due to cyclic tensile stress as result in vibration by gas flow coupled with an increase in the local area due to the welding heat, therefore, increases the rate of crack propagation. To verified the data from mechanical test, CFD simulation will be used. CFD can detect the direction of the gas flow around the Superheater tube. The simulation result shows the possibility of turbulence flow around the tube, which creates the vibrations on the tube due to gas flow velocity. Thus, the superheater tube leakage mostly because vibration that create cyclic tensile stress.

Abstract: In this paper a NACA 6412 regulated shape will be inverted to understand the behaviour of the air flow around the shape, this with the intention of convert the lifting effect to a downforce and braking effect changing the shape of the wing, displacing the trailing edge approximately 100mm over the first stage position. Using analysis as Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) to depicts the operational parameters of the two stages of the inverted NACA 6412 air foil. To reach this displacement, the main idea is using a flexure hinge designed as a M-Shape beam, this flexure hinge works as a spring to allows to the morphing wing moves around the 100mm of trailing edge displacement and the spring-beam effect creates an inverse force, when the wing moves close to the110mm and does not exceed the yield strength of the Acrylonitrile butadiene styrene (ABS) of 74Mpa. As a result of this motion parameters, we could integrate a flexure hinge to an inverted air foil regulated to reach braking and downforce forces in order to slow down vehicles or aerodynamic devices.

Abstract: The water temperature distribution and spatio-temporal variation law of the reservoir have a great influence on the water quality and ecological environment of the reservoir, and it is also an important temperature boundary condition for the design of concrete dam of hydropower station project, which is of great significance for the optimal design and operation of the reservoir. There are many factors affecting the water temperature of the reservoir, and it is difficult to predict the water temperature distribution accurately because of the lack of data and experience. In this paper, a numerical analysis model is established for the reservoir of a hydropower station on the Nam Ngum in Laos, and the water temperature of the reservoir is calculated and predicted, and the water temperature distribution in the reservoir and the water temperature distribution in front of the dam are analyzed and discussed. The results show that the solar shortwave radiation is the main factor affecting the temperature stratification of the reservoir. The stable low temperature layer of the reservoir is not obvious, but there is a tendency to form stratification. The research results can provide water temperature value for the design of concrete dam of the hydropower station and provide reference for the prediction of the water temperature of other similar reservoirs.

Abstract: The continuing depletion of light oil supplies and the rapidly growing demand for energy are forcing oil and gas companies to explore unconventional oil extraction techniques. The structure and flow rate implies an impact on the trapping and mobilization of oil in the reservoir. This article studies the effect of pore geometry and dynamics on water-oil displacement as a two-phase flow system. The pore geometries of sandstone were extracted using the non-destructive 3D micro computational tomography (micro-CT) technique. Two-phase flow simulations were performed using COMSOL Multiphysics on the micro-CT images to show the effect of the capillary number and the flow pattern. Velocity and relative permeability of the non-wetting phase at different points of the porous structure was computed. The effect of viscosity of wetting fluid on the pore structure was also studied to evaluate the parameters affecting enhanced oil recovery (EOR).

Abstract: Several parameters affect the properties of Portland cement and one of these parameters is the cooling rate of the clinker. If the effectiveness of the cooling method of the clinker increases, a good enhancement in the properties of Portland cement will be found. Depending on the new cooling method suggestion by Nasr et. al. [20], the counter pattern of air clinker flow was studied using (FLUENT 6.3.26). The dimensions of the cooling room in grate cooler, the constant mass flow rate of both clinker and air, different height ratios, and different clinker porosity were considered in this numerical work. The results show that the heat transfers in the first half of the cooling room (0 < X < 0.9 m) is larger than that in the second half (0.9 < X < 1.8 m), and this leads to an increase in the temperature of outlet air so can benefits from it in the heating of furnace. When the clinker and air are flowing in the counter direction, the cooling method is more beneficial when compared with that of parallel flow because the exiting clinker has a great rate of cooler and the air exits from the grate cooler is loaded with large thermal energy. Finally, it can design the best length of gate according to the required clinker temperature at the outlet side, and this results to reduce the cost of the cooling process according to the temperature distribution results at (0 < X > 1.8m) for different porosity and H.R values.

Abstract: In the present report, a two dimensional (2D) model was developed to describe the fluid dynamics, heat and mass transfer of a Chemical Vapor Deposition activated by a Hot Filament (HFCVD) reactor, as well as the chemical generation of the precursor species which are present in the growth of non-stoichiometric silicon rich oxide (SRO) films. The SRO is known for have excellent photo luminescent properties which are useful in optoelectronic applications. This material can be obtained by the HFCVD technique which offers important advantages such as the easily to obtain thin films with diverse structural, compositional and optical characteristics. During deposition is a priority to control key parameters as inlet flow, substrate temperature and pressure so it compels to know previous theoretical information about these parameters which can be obtained by computational simulation. Therefore, by means of commercial Computational Fluid Dynamics (CFD) were solved the continuity, momentum and energy equations in steady state. Also, a thermodynamic equilibrium study of the SiO₂(s) + H₂ (g) reaction was carried out with the Factsage software. The thermodynamic equilibrium results provide the main chemical species which are present during the deposit process of the SRO films. The 2D model was used to simulate the temperature and velocity distribution of the hydrogen in the deposit process. The theoretical calculated temperatures were compared with those obtained experimentally by thermocouple measurements. From the simulation results, the temperature and gas velocity profiles were obtained at different hydrogen flow levels (50, 75, 100 sccm) and temperature source-substrate distances (5, 6 and 7mm) for a 50 sccm level. SEM micrographs and profilometry measurements disclose that the outlet configuration affects substantially both the thickness and surface uniformity of the SRO films. This parameter was modified to obtain a better quality (thickness and uniformity) and a large deposit area.