CFD Techniques Research Articles

The CO2 removal of flue gas using hollow fiber membrane contactor: a comprehensive modeling and new perspectives

In this study, a novel hollow fiber membrane contactor (HFMC) under a non-wet condition was numerically explored by CFD techniques based on the finite element method to capture CO2 from the CH4/CO2 gas mixture. A new design, such as a shell and tube heat exchanger with baffles, was proposed. The MEA, DEA, and TEA, as different amines solutions, were selected as the liquid solvents. A CO2-containing gas mixture and amine solution were passed in the shell side and the tube side of the membrane contactor, respectively. The simulation findings indicated a good agreement with the reported experimental data demonstrating that such a model would evaluate the effects of different parameters during the HFMC system. Specifically, the results showed that the baffles' presence improved the separation efficiency due to the increased residence time on the shell side. The results also indicated that the MEA solution had the highest CO2 absorption. In the new design (shell and tube heat exchanger with baffles), the rising solvent inlet velocity, decreasing gas velocity, and counter-current flow pattern positively affected separation efficiency.

Rotating Microtab Implementation on a DU91W250 Airfoil Based on the Cell-Set Model

Flow control device modeling is an engaging research field for wind turbine optimization, since in recent years wind turbines have grown in proportions and weight. The purpose of the present work was to study the performance and effects generated by a rotating microtab (MT) implemented on the trailing edge of a DU91W250 airfoil through the novel cell-set (CS) model for the first time via CFD techniques. The CS method is based on the reutilization of an already calculated mesh for the addition of new geometries on it. To accomplish that objective, the required region is split from the main domain, and new boundaries are assigned to the mentioned construction. Three different MT lengths were considered: h = 1%, 1.5% and 2% of the airfoil chord length, as well as seven MT orientations (β): from 0° to −90° regarding the horizontal axis, for five angles of attack: 0°, 2°, 4°, 6° and 9°. The numerical results showed that the increases of the β rotating angle and the MT length (h) led to higher aerodynamic performance of the airfoil, CL/CD = 164.10 being the maximum ratio obtained. All the performance curves showed an asymptotic trend as the β angle reduced. Qualitatively, the model behaved as expected, proving the relationship between velocity and pressure. Taking into consideration resulting data, the cell-set method is appropriate for computational testing of trailing edge rotating microtab geometry.

Numerical Study on Interaction between Submarine Landslides and a Monopile Using CFD Techniques

Offshore installations with pile foundations in shallow water are vulnerable to submarine landslides, which cause serious damage to engineering facilities, loss of life, and loss of money. Due to a shortage of real observation data and the difficulty of reproduction, we lack insight into the interaction behavior between submarine landslides and monopiles. This study capitalized on ANSYS Fluent 20.0 to develop a three-dimensional biphasic (water and slurry) numerical model. This CFD model was used to analyze the interaction between a monopile and submarine landslides at different flow heights. The velocities of submarine landslides were from low to high values. Two modes of interactional forces acting on the monopile are proposed, which are (i) interaction force with peak value and (ii) interaction force without peak value. The influence of flow height and velocity on interaction forces was investigated. Results show that the effect of the flow heights on the interaction force is significant at low velocity stage, while the peak force representing a hazard level of the pile was non-negligible under high flow velocity and low flow height conditions, which should be considered in a future study. The related mechanisms are revealed with a hybrid model considering different components of the force.

Analysis on the lubrication performance of spiral-grooved journal bearing using CFD technique

As the main element, the lubrication characteristics of spiral-grooved journal bearing would decide the stability of mechanical systems. And, a effectivee model will represent the hydrodynamic characteristics of spiral-grooved journal bearing effectively. Based on the CFD technique, this work presents the simulation methodology for analyze the effects of spiral-grooved parameters on the lubrication performance of journal bearing. Compared with the published data, the proposed method is demonstrated effectiveness. Moreover, the influences of eccentricity ratio, groove number, spiral angle, groove width and groove depth are discussed by the orthogonal design method, which provide a reference for the optimized design of spiral-grooved journal bearing.

EXPERIMENTAL AND CFD- SIMULATION OF POLLUTANT TRANSPORT IN POROUS MEDIA

Efforts were made in this search to design a physical and computer model using the CFD techniques to simulate the problem of transporting pollutants through a porous media in unsteady state case. A physical model was built to measure the transmission of a copper nitrate pollutant at an initial concentration of 25 mg/l in a medium consists of (sand + gravel) and study the movement of the pollutant through. Then the results of the pollutant transport through used in the physical model were entered as entry data to the CFD simulated model using COMSOL 5.4. Software. The results of the CFD simulated model showed that the change in the inlet velocity to more than 20% of the initial velocity increases the pollutant concentration and reduces the time wanted to reach the highest value of the pollutant, while reducing the inlet velocity to less than 20% of the initial velocity, cause to decrease the concentration and increase the time to reach the highest pollutant value. When changing the porosity by (30%, -15%) of the initial porosity, it was noticed that increasing the porosity value reduces the pollutant concentration and increases the time required to reach the highest value of the pollutant. while when the porosity decreases to 15% of the initial porosity, the concentration increases the time decreases to reach the highest value of the pollutant at all control points. The adsorption factor has a noticeable effect on the emergence of the pollutant, while the temperature change was almost imperceptible for all degrees. However, the results of laboratory work were compared with the results of the CFD simulated model, which showed a good match between them.

CFD Investigation of Different Flow Field Designs for Efficient PEMFC Performance

Proton exchange membrane (PEM) fuel cell performance depends substantially on the geometry, configuration of the flow channels, and size. A right gas flow field pattern requires a homogeneous reactant distribution, low-pressure drop, and good water management. This paper outlines a numerical study, investigated the influence of the U-type, Z-type, and serpentine flow field configuration on the steady-state cell performance using the CFD technique ANSYS FLUENT PEMFC module. The main goal of this study focuses on a novel perspective for enhancing the design of the PEMFC resulting in better performance. The results indicate that the PEMFC with serpentine flow field configuration yields a significantly higher power density compared to the other designs.

Numerical investigation on effect of various pump rotational speeds on performance of centrifugal pump based on CFD analysis technique

In this study, the flow structure and effect of different pump rotational speeds on a centrifugal pump’s performance are experimentally and numerically investigated. The internal flow field pattern within the pump has been analyzed and discussed using the CFD technique. The numerical results are compared with experimental data under a wide range of operating conditions. The comparison results between them have indicated a considerable agreement. The pressure variations are gradually increasing from inlet to outlet impeller of the pump. The results note that when the impeller rotates near the tongue region, the pressure in this region was higher than in other parts. Also, the interaction between the impeller and volute tongue region is actually according to the impeller blades’ relative position concerning the tongue region. Furthermore, the pressure and velocity variations within a centrifugal pump increase with rotational impeller speed.

Multi-Scale Simulation on the Wind Field for Complex Terrain Based on Coupled WRF and CFD Techniques

Multi-Scale Simulation on the Wind Field for Complex Terrain Based on Coupled WRF and CFD Techniques

Computational fluid dynamics study of the impact of surface roughness on cyclone performance and erosion

In this study, the effect of roughness of cyclone wall on the rate of erosion and cyclone performance was studied using the CFD technique with the aid of the Ansys-Fluent 19.2 software. The Reynolds stress transport model was used to simulate the airflow turbulence in the rotating flows in the cyclone. The validated computational model was used, and the variations of axial velocity, tangential velocity, collection efficiency, cyclone pressure drop, and rate of erosion for different wall roughness were evaluated. For simulating surface erosion, the Oka model was used. The result of this study revealed that the wall roughness significantly affected airflow behavior in the cyclone and the resulting cyclone performance. In addition, when the wall roughness increased, the wear rate decreased. It was also found that the solid loading and inlet gas velocity significantly affect the erosion rate and even more than that of particle size.

Determination of Kinetic Parameters of Coal Pyrolysis to Simulate the Process of Underground Coal Gasification (UCG)

Purpose The aim of the research presented in this paper was to determine the values of the kinetic parameters of coal pyrolysis from two areas of the planned experiment, UCG, i.e. the Barbara Experimental Mine of the Central Mining Institute and the Wieczorek Mine. Methods The thermal decomposition of coal analysis used the thermogravimetric technique. The test was carried out in a temperature range of 298–1173 K in a nitrogen atmosphere for three fixed heating rates, β − 5, 10, and 15 K/min. A selection of sample heating rates of coal and reaction environments were designed to reflect the conditions seen during the process of underground coal gasification. The kinetic parameters were determined by using modified Coats-Redfern, Kissinger and Mianowski-Radko methods. Results The values of the activation energy, E, and the pre-exponential factor, A, were determined for a given model of the first order decomposition reaction of coal. The study successfully compared kinetic parameters of the tested coals. Practical implications Designated kinetic parameters may be used to model the process of pyrolysis and – as preliminary data – for installation design of pilot underground coal gasification. Originality/value The devolatilization of a homogenous lump of coal is a complex issue. Currently, the CFD technique (Computational Fluid Dynamics) is commonly used for the multi-dimensional and multiphase phenomena modelling. The mathematical models, describing the kinetics of the decomposition of coal, proposed in the article can, therefore, be an integral part of models based on numerical fluid mechanics.

A comparison between the presence and absence of virtual viscosity in the behaviour of the two phase flow interface

In this paper, a numerical study is performed in order to investigate the effect of the virtual viscosity on simulation of separated two-phase flow of gas-liquid. The governing equations solved by shock capturing method which can provide predicting the interface without the flow field solving. In this work, in order to calculate the numerical flux term, first-order centered scheme (Force scheme) was applied cause of its accuracy and appropriate validation. Analysis approves that the obtained stability range of this research is consistent with the classic Kelvin- Helmholtz instability equation only for the long wavelength with small amplitude. Results reveal that when the wavelengths are reduced, the specified range is not consistent and wavelength effects on instability range and it is overpredicted. An algorithm for water faucet problem was developed in FORTRAN language. Short wavelength perturbations induce unbounded growth rates and make it impossible to achieve converging solutions. The approach taken in this article has been to adding virtual viscosity as a CFD technique, is used to remedy this deficiency.

Performance analysis of a solar chimney power plant system in two Algeria regions

In this paper, we have investigated the possibility of implementation of three solar chimney systems in the two Algeria regions (Constantine, Tamanrasset). Numerical simulations were performed for the prototype geometry in Manzanares, Spain. Usage of CFD techniques (Computational Fluid Dynamics); we have simulated a two-dimensional axisymmetric model of an SCPP with the RNG k–ε turbulence. Using a band radiation model to solve the equation of radiation transfer by implementing the model of discrete ordinate radiation. Our results show that the secondary and tertiary collector roof system is able to achieve the highest electricity generation. The obtained results show the solar chimney power plant systems can be produced from 51 to 79 kW of electricity over the year and the highest hourly electricity produced in June is around 47 to –80 kW. The highest electricity generation has been recorded in the Tamanrasset region.

Experimental and Numerical Analysis of Cavity/Mean-Flow Interaction in Low Pressure Axial Flow Turbines

The increasing performance of modern aeroengines led the research towards the optimization of machine components not deeply analyzed in the past. In this context, the mechanisms driving the interaction process between the secondary flows evolving at the hub of low-pressure turbines with the rotor-stator cavity systems have been poorly investigated in the literature. In this work, an experimental and numerical analysis of the interaction between the endwall near wall flow and the leakage flow of a real cavity system is presented. The experimental results were carried out in the annular low-pressure axial flow turbine of the University of Genova. Experimental blade loading and pressure distributions into the cavity, as well as the measured total pressure loss coefficient, have been used for a proper validation of CFD results. Both steady and unsteady calculations were carried out through the commercial solver Numeca. Particularly, several numerical approaches have been tested into this work: RANS, Non Linear Harmonic (NLH), and URANS. The most promising CFD techniques have been firstly identified by comparison with experimental results and then systematically employed to extend the analysis of secondary flow-cavity flow interaction to positions and quantities not available from the experiments. Losses characterizing the mean flow-cavity flow interaction process will be shown to cover a great amount of the overall stage losses and should be properly accounted for the design of future optimized cavity configurations.

Numerical prediction of ship motion and slamming load characteristics in cross wave

When waves from two weather systems converge at a certain sea area, cross waves can be produced. It is important to have a better understanding of the motion characteristics of ship in cross sea to ensure its navigation safety. In this paper, the motion responses of a S175 container ship hull in cross sea is first analyzed based on CFD technique using RANS method. VOF method is used to model and capture the free surface and overset grid technique is adopted to simulate ship motions in waves. Verifications on ship motion by the numerical method have been conducted for time step- and grid-independent studies. According to the motion results by numerical simulation, typical conditions are chosen for further investigation of slamming pressure on bow area and green water on deck. It is found that vertical motion responses of ship induced by cross waves can be quite large and the ship experienced obvious roll–pitch-coupled motion. Severe bow slamming and green water under cross sea state are also observed. The bow flare slamming pressure on the baseline can be quite large in symmetric cross wave. Asymmetrical slamming impacts occurred when the ship sails in an asymmetric cross wave field.

CFD based thermal efficiency of square shape protruded roughened absorber plate for solar air heater

ABSTRACT In present paper, CFD technique is used to investigate the thermal efficiency of square shape protruded roughened absorber plate used in solar air heater. A 3-D CFD model of solar air heater with sixteen geometrical arrangements of roughness is analyzed under varying Reynolds number from 4000 to 20000 by using RNG k-epsilon method under transient conditions. The dimensionless geometrical parameters (P/e and e/D) having values vary from 38.8 to 61.1 and 0.016 to 0.036, respectively. The simulated results from the present study is further used to calculate the thermal efficiency of actual solar air heater with the help of computer program. Maximum enhancement in the value of performance parameters like, thermal efficiency, Nusselt number and friction factor are at minimum value of geometrical parameters (P/e) of 38.8 and at higher e/D value of 0.036. Design plot has been also proposed in order to design square shape protruded roughened solar air heater.

Simulation of flow around a permeable dike using physical and 3D-CFD models

ABSTRACT In this research, complementary numerical and experimental physical models were conducted to investigate flow parameters around an isolated permeable spur dike using ANSYS FLUENT ver. 16.1 software. The volume of fluid method VOF with the help of CFD technique and the turbulence model was used to simulate the complex free-surface flow by applying a geometric reconstruction scheme. Two different mediums with different porosities were used, namely, gravel and glass beads. It was found that, for low flow rate values, there are no significant changes in the water profiles in both longitudinal and lateral directions for both media. Although for high flow rate values, the differences tend to be clearer. Results showed that there is a slight effect of the medium's properties if the dike width is less than 1/3 of width of the channel, in particular with low flow rate values. Good agreement was observed between the computational and the measured results for the water surface profiles. Also, there is an exact match between the lateral velocity distribution of gravels and glass beads. Downstream the dike, the lateral velocity profiles exhibit an S shape curve due to high velocity in the free flow and small flow velocity behind the porous dike. The results show good agreement between the CFD results and the experimental observations of the water surface profiles and velocity distribution according to the statistical analysis using some standard indexes error.

Euler–Euler model for CO2-MEA reactive absorption on a sieve-tray

CFD studies dedicated to Carbon Capture and Storage are still limited to simple geometries or mass transfer models. In this work, the CO2-MEA system is studied through a three-dimensional, transient, Eulerian–Eulerian model. A sieve-tray is chosen as case study and a global mass transfer coefficient model is implemented. A preliminary validation study in an air-water system is made to assess which drag force correlation provides better results for local clear liquid height, and therefore experimental measures for local clear liquid heights are also taken. Relative errors of about 20% are obtained for total clear-liquid height measures, and the numerical results are qualitatively validated. For the reactive absorption cases, CO2 is fully absorbed and consumed in the liquid phase, while with disabled chemical reaction less than 90% is absorbed. The implemented model physical consistency reinforces the potential of using CFD techniques for process intensification scale-up and design.

Measurements and predictions of harmful releases of the gathering station over the mountainous terrain

Having a risk analysis of harmful releases over mountainous terrains through wind tunnel experiment is a frontier problem in China. In this paper, a straight-flow wind tunnel is applied to simulate the atmospheric boundary layer and research the motion of high-sulfur gas released to atmosphere when accidental releases occur in a gathering station over the mountainous terrain. After an analysis of hourly concentration in the field accident for eight wind directions, experimental results reveal that nearby concentration fields are dominated by wind and far-field concentration distribution is dominated by topography, which leads to complete levels of consequence impact for the personnel risk inside and around the gathering station. Based on CFD techniques, a three-dimensional modelling was established in comparison with the wind tunnel experiment, which suggests that CFD prediction had underestimated the near-field gas concentration and the performance could not precisely match actual risks the gathering station causes to the mountainous terrain, which leads to a modified equation for numerical prediction. Instead of proposing a lower personnel risk evaluation obtained through the use of CFD techniques, the wind tunnel experiment offers a new choice for the consequence impact analysis for the petrochemical industry in China.

Predicting the effect of the rib pitch on thermal performance factor of small channels plate heat exchangers fitted with Y and C shapes obstacles

This study presents a numerical analysis of a laminar counter flow inside small channels plate heat exchanger fitted with Y and C shape obstacles. Using the Computational Fluid Dynamics CFD, an advanced and modern simulation technique, the influence of the geometrical parameters (such as geometry, rib pitch) on the flow characteristics, the thermal and the hydrodynamics performance of the PHE (plate heat exchanger) is investigated numerically. The main goal of this work is to increase the flow turbulence, enhance the heat transfer and the thermal efficiency by inserting new obstacles forms. The computational domain is a conjugate model which is developed by the Computer Aided Design CAD software Solidworks. The results, obtained with Ansys Fluent, show that the presence of the shaped ribs provides enhancement in heat transfer and fluid turbulence. The CFD analysis is validated with the previous study. The non-dimensional factors such as the Nusselt number Nu, the skin friction factor Cf and the thermo-hydraulic performance parameter THPP are predicted with a Reynolds number Re range of 200–800. The temperature and the velocity distribution are presented and analyzed. The Y ribs and the C ribs offer as maximum THPP values respectively about 1.44 and 2.6 times of a smooth duct.

CFD Simulation of Air Pollution Distribution and Its Effect on Patients in Hospital Operating Rooms

This paper uses the CFD technique to simulate the internal environment of a hospital operating room, including the surgical area that includes the patientand the surgical team. Moreover, this work provides mathematical simulation of many models to be placed in the air entry and air exit areas in the operating room to obtainthe optimal model of air distribution within the operating room. The results obtained matched well with experimental data from approved literature and standards. These results found that airflow and air velocity significantly affect the patient’s thermal comfort in the operating room.Besides, it is observed that some recirculation zone is formed, and this is a result of the heat generated by the surgical team and the accelerated air. This region is considered a source for the survival of the polluted air in the room.
 Keywords: CFD, Operating room, Numerical analysis.