HIGEE (High Gravity Rotary Device) rotating oil purifier which consists of two parts: hydrocyclone separator and rotating packed bed (abbr. RPB) is considered to be capable of removing the solid particle contaminant, moisture and gas simultaneously. As the major unit of HIGEE, the RPB uses centrifugal force to intensify mass transfer. Because of the special structure of RPB, the hydraulic characteristics of the RPB are very important. In this study, the multiphase flow model in porous media of the RPB is presented, and the dynamical oil-water separation in the RPB is simulated using a commercial computational fluid dynamics code. The operating conditions and configuration on the hydraulic performance of the RPB are investigated. The results have indicated that the separation efficiency of HIGEE rotating oil purifier is predominantly affected by operating conditions and the configurations. The best inlet pressure is 0.002 MPa. When the liquid inlet is placed in the outside of the lower surface of RPB; oil outlet is placed in the upper surface, where it is near the rotation axis; and water outlet is placed in the middle of the RPB, where it is far away from the oil outlet, the separating efficiency is the best.
The pollution of hydraulic engineering equipment is the mainly responsible for the trouble of hydraulic system, and it is the key of maintenance. Contaminant particles can bring about a number of detrimental effects on the hydraulic system components as well as the fluid itself. One of the key problems of hydraulic contamination control is to design and maintain system reasonably reducing the contamination level of key point as low as possible. There are various kinds of purification technologies to improve the contamination control level of fluid power system (FPS), such as oil filter, electrostatic oil cleaner, oil vacuum cleaning, magnetic field pulse filtration, and other coalescence methods [
3D plot of HIGEE rotating oil purifier.
Rotating packed beds (RPBs) intensify mass transfer by using centrifugal force to realize separation, which has been applied to distillation, absorption, striping, polymer devolatilization, bio-oxidation, and so on [
The hydraulic characteristics of the RPB have been reported in many studies, such as the liquid holdup, the pressure drop, flooding, residence time distribution, and visualized liquid flow [
Many studies have been investigated by theory or experiment. However, many physical experiments are very expensive and time-consuming, and there are no precise experimental data about the flow in RPBs. Hence, using mathematical models as design tools can contribute to a better understand of the hydraulic characteristics of the RPB with the fast development of the computer technology. Computational fluid dynamics (CFD) is a good design and analysis tool to simulate the flow of mass and momentum throughout a fluid continuum. It is an advantage method to study the hydraulics characteristics of RPB. Numerical simulation by using FLUENT software will be conducted in this research. The multiphase flow in porous media of RPB will be numerically studied. The effects of operating conditions and configuration on the hydraulic performance of RPB are investigated to increase the separation efficiency of HIGEE rotating oil purifier.
According to the introduction of HIGEE rotating oil purifier (Figure
Sectional drawing of HIGEE rotating oil purifier. 1: connecting motor shaft; 2: the hydraulic oil outlet; 3: packing; 4: vortex finder; 5: underflow outlet; 6: shell; 7: tangential nozzle; 8: contaminated oil inlet; 9: parting face.
The 3D model (Figure
3D model of the RPB.
In this research, the Eulerian multiphase model is applied. The phases are water and oil. The description of multiphase flow as interpenetrating continua incorporates the concept of phasic volume fractions which is defined by
The volume of phase
In this paper, the Ergun equation is used to derive porous media input for a packed bed, and the laminar flow through the porous media is simulated, which is similar to a packed bed in this paper and easy to simulate on existing computers. The permeability and inertial loss coefficients in each component direction could be identified as
To solve the governing equations, appropriate grid generation and boundary conditions are specified at all external boundaries based on the following. The 3D model (Figure
Material properties of the model.
Parameter | Unit | Water | Oil |
---|---|---|---|
Volume fraction | — | 5% | 95% |
Density |
|
1000 | 780 |
Viscosity |
|
0.001003 | 0.0024 |
Boundary conditions of the model.
Description | Type |
---|---|
Porosity of porous medium | 0.5 |
Mean particle diameter of porous medium | 0.05 mm |
Flow condition of the oil-water mixture | Turbulence |
Viscous model |
|
Inlet of the oil-water mixture | Pressure inlet |
Outlet of oil or water | Pressure inlet |
Mesh generation of the 3D model.
The material properties and boundary conditions are selected reasonably. The standard
The multiphase flow in porous media of RPB will be numerical simulated. The effects of operating conditions and configuration on the hydraulic performance of the RPB are investigated to increase the separation efficiency of HIGEE rotating oil purifier.
To understand the feature distribution of inner hydrocyclone separator more clearly, the outlet pressure of hydrocyclone separator is 0.002 MPa which is considered a reference. The static pressure is firstly to be simulated as shown. This example is identified as follows: the configuration of the RPB is certain. The oil-water mixture inlet is set near to the middle of the lower surface of the RPB, whose diameter is 15 mm. The outlet for water and oil is set in the upper surface, where the oil outlet is in the middle, while the water outlet is in the edge. The diameter of outlets is 10 mm. The rotation speed is 1500 rpm. The other conditions are constant. This research investigated the separation efficiency of HIGEE rotating oil purifier by changing the inlet pressure. The sectional drawings are extracted. Contour plot and graph of the outlet volume fraction of oil in the outlet with different pressures are shown in Figures
Contours of the outlet volume fraction of oil in the outlet with different pressures.
0.01 MPa
0.005 MPa
0.002 MPa
0.001 MPa
Graphs of the outlet volume fraction of oil in the outlet with different pressures.
0.01 MPa
0.005 MPa
0.002 MPa
0.001 MPa
Figure
Figure
It can be seen from the simulation results that the inlet pressure has a big effect on the separation efficiency of HIGEE rotating oil purifier. The separation efficiency of HIGEE rotating oil purifier improves with the decreasing of inlet pressure; in particular when the inlet pressure is 0.002 MPa, the separation efficiency is the best. The volume fraction of oil in the oil outlet can be up to 100%, and it is entirely 100%, and the fraction of oil in the water outlet can also be about less than 96%, which is better than other inlet pressures.
In order to investigate the effect of the configuration, the example is identified as follows. The rotation speed is 1500 rpm. The inlet pressure is 0.002 MPa with the other boundary conditions unchanged. This research investigated the separation effect of HIGEE rotating oil purifier by changing the configuration, such as the location of the oil-water mixture inlet, oil outlet, and water outlet in the RPB.
Based on previous theoretical and experimental results, fluids of different densities will concentrate on different places accordingly under rotation speed. The fluid of high density concentrates close to the rotation axis, while the fluid of low density concentrates away from the rotation axis. Therefore, four different configurations are investigated in this research.
Contours of the volume fraction of oil in the outlet with different configurations.
Configuration A
Configuration B
Configuration C
Configuration D
Graphs of the volume fraction of oil in the outlet with different configurations.
Configuration A
Configuration B
Configuration C
Configuration D
Figure
Figure
Simulation results show that the simulation results indicate that the separating efficiency of HIGEE rotating oil purifier is greatly affected by the configuration; Configuration D is the best configuration. In Configuration D, the volume fraction of oil in the oil outlet can be up to 100%, and it is entirely 100%, but the fraction of oil in the water outlet can also be about less than 95%.
Simulation results show that because of different densities, when the oil from preliminary purification goes through the HIGEE field, the oil-which has a low density outflows from the oil outlet in the middle, where it is near the rotation axis, while water which has a high density outflows from the water outlet is in the edge, where it is far away from the oil outlet.
Applying the inlet pressure is for applying an inlet velocity to the oil from preliminary purification. When the inlet pressure is small, which can increase the residence time of the oil-water mixture, therefore, the fluid from preliminary purification can make a good contact with hydrophilic material in the RPB to get better separation efficiency. The separation efficiency of HIGEE rotating oil purifier increases with the decreasing of inlet pressure; in particular when the inlet pressure is 0.002 MPa, the separation efficiency is the best. However, a small pressure is not the best choice for the inlet pressure. The working hours will last long when the inlet velocity is very small.
The separating efficiency of HIGEE rotating oil purifier is greatly affected by the configurations. Configuration D is the best configuration. The layout of liquid inlet, oil outlet, and water outlet of the RPB significantly affected the separating efficiency. When the liquid inlet is placed in the outside of the lower surface of RPB; oil outlet is placed in the upper surface, where it is near the rotation axis; and water outlet is placed in the middle of the side of the RPB, where it is far away from the oil outlet, the corresponding separating efficiency was the best. In Configuration D the volume fraction of oil in the oil outlet can be up to 100%, and it is entirely 100%, but the fraction of oil in the water outlet can also be about less than 95%, which is better than other configurations.
Unlike previous experimental research, numerical simulation is employed in this paper to analyze the flow characteristics inside the RPB, and related conclusions are got. The oil-water two-phase flow is simulated based on the 3D model of the RPB which is established in Gambit. The operating conditions on the hydraulic performance of the RPB are investigated. Inlet pressure has big effect on the separation efficiency of HIGEE rotating oil purifier. The separation efficiency of HIGEE rotating oil purifier increases with the decreasing of inlet pressure; in particular when the inlet pressure is 0.002 MPa, the separation efficiency is the best. Simulation results also show that the separating efficiency of HIGEE rotating oil purifier is greatly affected by the configuration, especially the layout of liquid inlet, oil outlet, and water outlet in the RPB. When the liquid inlet is placed in the outside of the lower surface of RPB; oil outlet is placed in the upper surface, where it is near to the rotation axis; and water outlet is placed in the middle of the side of the RPB, which it is far away from the oil outlet, the corresponding separating efficiency is the best.
Compared with theoretical analysis and experimental research, numerical simulation has provided an easy and effective method to design and optimize the HIGEE rotating oil purifier and other mechanical devices, which was widely used in resources and environmental systems. In order to certificate the numerical results, corresponding experiments need to be investigated in the future work.
This research was funded by the Natural Science Foundations of China (no. 51075007), National High-tech R&D (863) Program (no. 2012AA091103), and The Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions (CIT&TCD 20130316).