scholarly journals Grid convergence study of a cyclone separator using different mesh structures

2017 ◽  
Vol 23 (3) ◽  
pp. 311-320 ◽  
Author(s):  
R.A.F. Oliveira ◽  
G.H. Justi ◽  
G.C. Lopes
Keyword(s):  
Pressure Drop ◽  
Collection Efficiency ◽  
Fluid Dynamic ◽  
Two Phase ◽  
Mesh Structure ◽  
Pressure Drops ◽  
Regular Elements ◽  
Grid Convergence ◽  
Grid Convergence Index ◽  
Mesh Structures

In a cyclone design, pressure drop and collection efficiency are two important performance parameters to estimate its implementation viability. The optimum design provides higher efficiencies and lower pressure drops. In this paper, a grid independence study was performed to determine the most appropriate mesh to simulate the two-phase flow in a Stairmand cyclone. Computational fluid dynamic (CFD) tools were used to simulate the flow in an Eulerian-Lagrangian approach. Two different mesh structure, one with wall-refinement and the other with regular elements, and several mesh sizes were tested. The grid convergence index (GCI) method was applied to evaluate the result independence. The CFD model results were compared with empirical correlations from bibliography, showing good agreement. The wall-refined mesh with 287 thousand elements obtained errors of 9.8% for collection efficiency and 14.2% for pressure drop, while the same mesh, with regular elements, obtained errors of 8.7% for collection efficiency and 0.01% for pressure drop.

Uncertainty Analysis in the Numerical Simulation of the Air-Water Droplet Motion Through Drift Eliminators

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Blas Zamora ◽  
Antonio S. Kaisere ◽  
Ulrich Kling ◽  
Manuel Lucas ◽  
Javier Ruíz
Keyword(s):  
Numerical Simulation ◽  
Pressure Drop ◽  
Uncertainty Analysis ◽  
Water Droplet ◽  
Collection Efficiency ◽  
Droplet Motion ◽  
Scaled Distance ◽  
Fine Mesh ◽  
Grid Convergence ◽  
Grid Convergence Index

This work presents an uncertainty study in the numerical simulation of the air-water droplet motion through three types of drift eliminators using the grid convergence index (GCI) method. The analysis of independence of the results with respect to the fineness of mesh is developed with special emphasis on the influence of the nondimensional sub-layer scaled distance. The coefficient of pressure drop and the droplet collection efficiency are numerically calculated. It may be concluded that using the GCI method leads to reliable numerical results, but it is also necessary to establish a sufficiently fine mesh near the walls.

scholarly journals Numerical and experimental studies of gas–liquid flow and pressure drop in multiphase pump valves

2020 ◽  
Vol 103 (3) ◽  
pp. 003685042094088
Author(s):  
Yi Ma ◽  
Minjia Zhang ◽  
Huashuai Luo
Keyword(s):  
Pressure Drop ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Test System ◽  
Ball Valve ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Disk Valve ◽  
Predicted Values

A numerical and experimental study was carried out to investigate the two-phase flow fields of the typical three valves used in the multiphase pumps. Under the gas volume fraction conditions in the range of 0%–100%, the three-dimensional steady and dynamic two-phase flow characteristics, pressure drops, and their multipliers of the ball valve, cone valve, and disk valve were studied, respectively, using Eulerian–Eulerian approach and dynamic grid technique in ANSYS FLUENT. In addition, a valve test system was built to verify the simulated results by the particle image velocimetry and pressure test. The flow coefficient CQ (about 0.989) of the disk valve is greater than those of the other valves (about 0.864) under the steady flow with a high Reynolds number. The two-phase pressure drops of the three valves fluctuate in different forms with the vibration of the cores during the dynamic opening. The two-phase multipliers of the fully opened ball valve are consistent with the predicted values of the Morris model, while those of the cone valve and disk valve had the smallest differences with the predicted values of the Chisholm model. Through the comprehensive analysis of the flow performance, pressure drop, and dynamic stability of the three pump valves, the disk valve is found to be more suitable for the multiphase pumps due to its smaller axial space, resistance loss, and better flow capacity.

Numerical and Mechanistic Modelling of Two-Phase Liquid-Gas Flow’s Pressure Drop Across Sharp-Edged Orifices

2019 ◽  
Author(s):  
Zurwa Khan ◽  
Reza Tafreshi ◽  
Matthew Franchek ◽  
Karolos Grigoriadis
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Relative Error ◽  
Two Phase Flow ◽  
Mechanistic Model ◽  
Gas Mixture ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Phase Liquid

Abstract Pressure drop estimation across orifices for two-phase liquid-gas flow is essential to size valves and pipelines and decrease the probability of unsafe consequences or high costs in petroleum, chemical, and nuclear industries. While numerically modeling flow across orifices is a complex task, it can assess the effect of numerous orifice designs and operation parameters. In this paper, two-phase flow across orifices has been numerically modeled to investigate the effect of different fluid combinations and orifice geometries on pressure drop. The orifice is assumed to be located in a pipe with fully-developed upstream and downstream flow. Two liquid-gas fluid combinations, namely water-air, and gasoil liquid-gas mixture were investigated for different orifice to pipe area ratios ranging from 0.01 to 1 for the superficial velocity of 10 m/s. Volume of Fluid multiphase flow model along with k-epsilon turbulence model were used to estimate the pressure distribution of liquid-gas mixture along the pipe. The numerical model was validated for water-air with mean relative error less than 10.5%. As expected, a decrease in orifice to pipe area ratio resulted in larger pressure drops due to an increase in the contraction coefficients of the orifice assembly. It was also found that water-air had larger pressure drops relative to gasoil mixture due to larger vortex formation downstream of orifices. In parallel, a mechanistic model to directly estimate the local two-phase pressure drop across orifices was developed. The gas void fraction was predicted using a correlation by Woldesemayat and Ghajar, and applied to separated two-phase flow undergoing contraction and expansion due to an orifice. The model results were validated for different orifices and velocities, with the overall relative error of less than 40%, which is acceptable due to the uncertainties associated with measuring experimental pressure drop. Comparison of the developed numerical and mechanistic model showed that the numerical model is able to achieve a higher accuracy, while the mechanistic model requires minimal computation.

Numerical Evaluation of Pressure Drop Across Orifices for Different Gas-Liquid Mixtures

2018 ◽  
Author(s):  
Zurwa Khan ◽  
Reza Tafreshi ◽  
Matthew Franchek ◽  
Karolos Grigoriadis
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Water Flow ◽  
Fuel Oil ◽  
Phase Flow ◽  
Empirical Correlations ◽  
Local Pressure ◽  
Two Phase ◽  
Pressure Drops ◽  
Mass Fractions

Modeling two-phase flow across orifices is critical in optimizing orifice design and fluid’s operation in countless architectures and machineries. While flow across different orifice geometries has been extensively studied for air-water flow, simulations and experiments on other two-phase flow combinations are limited. Since every fluid mixture has its own physical properties, such as densities, viscosities and surface tensions, the effect of these properties on the local pressure drops across the orifices may differ. This study aims to investigate the effect of different fluid combinations on the pressure drop across sharp-edged orifices with varying gas mass fractions, orifice thicknesses, and area ratios. A numerical model was developed and validated using experimental data for air-water flow. Then, the model was extended to include various gas-liquid flows including gasoil, argon-diesel and fuel oil. The local pressure drops were then estimated and compared with the existing empirical correlations. The developed model presents a unified approach to measure pressure drop across orifices for different fluid mixtures with different geometries and gas-liquid compositions, unlike existing empirical correlations which are applicable for specific orifice geometries. The results showed that Morris correlation, Simpson correlation, and Chisholm correlation are more appropriate for gasoil, argon-diesel and fuel oil mixtures, respectively. They also yielded that for all fluid combinations, increasing orifice thickness and area ratio led to a decrease in local pressure drop, while increasing gas mass fraction led to an increase in local pressure drop. This revealed that, despite having similar responses to changes in orifice geometries and gas fractions, unlike the assumption made by previous works on air-water flow, no empirical correlation is able to predict pressure drops for all flow mixtures, while the presented numerical model can efficiently determine the local pressure drop for all combinations of flow mixtures, orifice geometries and gas mass fractions.

Aerodynamic Torque Acting on a Butterfly Valve. Comparison and Choice of a Torque Coefficient

1999 ◽  
Vol 121 (4) ◽  
pp. 914-917 ◽  
Author(s):  
C. Solliec ◽  
F. Danbon
Keyword(s):  
Pressure Drop ◽  
Static Pressure ◽  
Fluid Dynamic ◽  
Dynamic Pressure ◽  
Low Cost ◽  
Normalization Method ◽  
Pressure Drops ◽  
Torque Coefficient ◽  
Aerodynamic Torque ◽  
Valve Pressure

Most technological devices use butterfly valves to check the flow rate and speed, through piping. Their main advantages are their low cost, their mechanical suitability for fast operation, and their small pressure drops when they are fully open. The fluid dynamic torque about the axis of large valves has to be considered as the actuator could be overstrained. This torque is generally defined using a nondimensional coefficient KT, in which the static pressure drop created by the valve is used for normalization. When the valve is closed downstream of an elbow, the valve pressure drop is not well defined. Thus, the classic normalization method gives many ambiguities. To avoid the use of the pressure drop, we define another torque coefficient CT in which the dynamic pressure of the flow is the normalization factor instead of the pressure drop. Advantages and drawbacks of each normalization method are described in the following.

Prediction of Pressure Drop of Various Refrigerants During Condensation in Horizontal Smooth and Micro-Fin Tubes by Means of Artificial Neural Networks

2012 ◽  
Author(s):  
Muhammet Balcilar ◽  
Ahmet Selim Dalkiliç ◽  
Şevket Özgür Atayılmaz ◽  
Hakan Demir ◽  
Somchai Wongwises
Keyword(s):  
Neural Networks ◽  
Artificial Neural Networks ◽  
Pressure Drop ◽  
Tube Length ◽  
Two Phase ◽  
Pressure Drops ◽  
Data Points ◽  
Artificial Neural ◽  
Fin Tubes ◽  
Liquid And Vapor Phases

The predictions of condensation pressure drops of R12, R22, R32, R125, R410A, R134a, R22, R502 and R507a flowing inside various horizontal smooth and micro-fin tubes are made using the numerical techniques of Artificial Neural Networks (ANNs) and non-linear least squares (NLS). The National Institute of Standards and Technology’s (NIST) experimental data and, Eckels’ and Pate’s experimental data, as presented in Choi et al.’s study provided by NIST, are used in our analyses. In their experimental setups, the horizontal test sections have 1.587 m, 3.78 m, 3.81 m and 3.97 m long countercurrent flow double tube heat exchangers with refrigerant flowing in the inner smooth (8 mm, 8.01 mm and 11.1 mm i.d.) and micro-fin (5.45 mm and 7.43 mm i.d.) copper tubes as cooling water flows in the annulus. Their test runs cover a wide range of saturation pressures from 0.9 MPa to 2.9 MPa, inlet vapor qualities range from 0.19 to 1.0 and mass fluxes are from 8 kg m−2s−1 to 791 kg m−2s−1. The condensation pressure drops are predicted using 673 measured data points, together with numerical analyses of artificial neural networks and non-linear least squares. The input of the ANNs for the best correlation are the measured and the values of the test sections are calculated, such as mass flux, tube length, inlet and outlet vapor qualities, critical pressure, latent heat of condensation, mass fraction of liquid and vapor phases, dynamic viscosities of liquid and vapor phases, hydraulic diameter, two-phase density, and the outputs of the ANNs as the experimental total pressure drops in the condensation data from independent laboratories. The total pressure drops of in-tube condensation tests are modeled using the artificial neural networks (ANNs) method of multi-layer perceptron (MLP) with a 12-40-1 architecture. The average error rate is 7.085%, considering the cross validation tests of the 867 condensation data points. A detailed model of f(MLP) is given for direct use in MATLAB. This explanation will enable users to predict the two-phase pressure drop with high accuracy. As a result of the dependency analyses, dependency of the output of the ANNs from 12 sets of input values is shown in detail, and the pressure drops of condensation in smooth and micro-fin tubes are found to be highly dependent on mass flux, all liquid Reynolds numbers, the latent heat of condensation, outlet vapor quality, critical pressure of the refrigerant, liquid dynamic viscosity, and tube length. New ANNs based empirical pressure drop correlations are developed separately for the conditions of condensation in smooth and micro-fin tubes as a result of the analyses.

scholarly journals Evaluation of Mixture Viscosity Models in the Prediction of Two-phase Flow Pressure Drops

2012 ◽  
Vol 29 (2) ◽  
pp. 115 ◽  
Author(s):  
N.Z Aung ◽  
T Yuwono
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Viscosity Models ◽  
Oil Water ◽  
Mixture Viscosity ◽  
Gas Liquid Flow

Nine existing mixture viscosity models were tested for predicting a two-phase pressure drop for oil-water flow and refrigerant (R.134a) flow. The predicted data calculated by using these mixture viscosity models were compared with experimental data. Predicted data from using one group of mixture viscosity models had a good agreement with the experimental data for oil-water two-phase flow. Another group of viscosity models was preferable for gas-liquid flow, but these models gave underestimated values with an error of about 50%. A new and more reliable mixture viscosity model was proposed for use in the prediction of pressure drop in gas-liquid two-phase flow.

Evaporation Heat Transfer and Pressure Drop in Horizontal Tubes With Strip-Type Inserts Using Refrigerant 600a

1999 ◽  
Vol 122 (2) ◽  
pp. 387-391 ◽  
Author(s):  
S.-S. Hsieh ◽  
K.-J. Jang ◽  
Y.-C. Tsai
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Pressure Drops ◽  
Horizontal Tubes ◽  
Evaporation Heat

Results of a study on saturated boiling heat transfer of refrigerant R-600a in horizontal tubes (ID=10.6 mm) with strip-type inserts (longitudinal strip LS with/without perforated holes and cross-strip CS inserts) are reported. Local heat transfer coefficients are measured for a range of heat flux (9.1∼31.2 kW/m2), mass velocity (8.23∼603.3 kg/m2s), and equilibrium mass quality (⩽0.8) and the influences were studied. The data were compared with the performance of the corresponding smooth tubes. Enhancement factors are presented and discussed. Pressure drop measurement was also conducted and it is found that both single-phase and two-phase pressure drops increase with increasing heat flux levels and mass velocities. [S0022-1481(00)00302-9]

Effect of Inclination on the Air-Water Flow in 4-Inch Pipe

2014 ◽  
Author(s):  
Mehaboob Basha ◽  
S. M. Shaahid ◽  
M. Mudasar Imam ◽  
Aftab Ahmad ◽  
Luai M. Al-Hadhrami
Keyword(s):  
Pressure Drop ◽  
Two Phase Flow ◽  
Petroleum Industry ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Increase With Increase ◽  
Inclination Angles ◽  
Reference Pressure ◽  
Velocity Pressure

Air-water two-phase flow in a pipeline often occurs in petroleum industry. It is important to study behavior of such flows in order to characterize two-phase flow in upstream production pipelines. This paper presents pressure drop measurements of air-water two-phase flow in a horizontal and inclined 4 inch diameter stainless steel pipe at different flow conditions. Experiments were carried out for different inclination angles including; 0°, 15°, 30° (upward and downward flows) and for different water-to-air volume fractions. Inlet superficial water velocities were varied from 0.3 to 3 m/s and reference pressure was set at 1 and 2 bars. For a given superficial air velocity, pressure drop has been found to increase with increase in superficial water velocity. Pressure drop was also affected by the inclination of pipe. Upward flows were associated with high pressure drops as compared to downward flows. Measured pressure drops were compared with existing empirical relations and good agreement was found.

scholarly journals Case Studies of Air Filtration at Microscales: Micro- and Nanofiber Media

2008 ◽  
Vol 3 (2) ◽  
pp. 155892500800300 ◽  
Author(s):  
Benoît Mazé ◽  
Hooman V. Tafreshi ◽  
Behnam Pourdeyhimi
Keyword(s):  
Pressure Drop ◽  
Fiber Diameter ◽  
Collection Efficiency ◽  
Particle Diameter ◽  
Molecular Flow ◽  
Air Filtration ◽  
Gas Temperature ◽  
Pressure Drops ◽  
Continuum Flow ◽  
The Media

In this work, 3–D fibrous geometries are developed to resemble the microstructure of spun-bonded and electrospun filters media and used here to simulate their filtration efficiency and pressure drop. For the sake of simplicity, a continuum flow theory was considered to prevail for the case of spun-bonded media (microfiber media) whereas our electrospun media (nanofiber media) were assumed to be in a free molecular flow regime. Our simulations results are in good general agreement with the experimental data. Especially, in predicting media's pressure drop, our results show better predictions when compared to some of the existing models. We also quantitatively demonstrated that by decreasing the fiber diameter, the minimum collection efficiency of the media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies – the most penetrating particle diameter. Studying the influence of the gas temperature, we showed that filter's efficiency increases as the gas temperature increases. Conversely, the filter's pressure drop decreases by increasing the gas temperature.

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