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Analysis of the impact of flow characteristics on the separation efficiency and pressure drop of a cyclone-type oil separator
Abstract
The effects of flow structure on the separation efficiency and pressure drop in a cyclone-type oil separator were investigated via Reynolds-averaged Navier-Stokes (RANS) simulations and large eddy simulations (LES), and the results were compared with experiments. Compared with the RANS simulations, the LES results were more similar to the experimental data as they simulated the complex flow structure more realistically. Swirling flow with strong turbulent kinetic energy (TKE) at the top section hindered the flow of particles toward the separator wall. In addition, a decrease in tangential velocity along the wall at the bottom reduced the centrifugal force, resulting in a decreased separation efficiency as particles were able to flow directly toward the outlet. The LES also predicted the pressure drop slightly better than the RANS simulation did, due to increased pressure drop caused by collision of the flow with the helix and outlet tube, which led to the formation of vortical flow structures with strong TKE.
... In the case of downward axial flow, the observed increases were 6.13%, 8.63%, 8.14%, and 8.41%. These higher axial velocities contribute to an enhanced collection efficiency of cyclone separators [36]. ...
Citation: Barua, S.; Batcha, M.F.M.; Mohammed, A.N.; Saif, Y.; Al-Alimi, S.; Al-fakih, M.A.M.; Zhou, W. Abstract: Multi-inlet cyclone separators can play a vital role in industrial processes by enhancing particle separation efficiency and minimizing energy consumption. This numerical study investigates multi-inlet cyclone separators to enhance their performance using a constant flow rate with a varying inlet height and width. By systematically varying the inlet height and width, three-inlet and four-inlet cyclone separators are developed and evaluated, termed 3 inlet-a, 4 inlet-a, 3 inlet-b, and 4 inlet-b. The findings reveal that increasing the number of inlets without changing the total inlet area does not improve the separation performance. However, strategic modifications to the inlet height and width significantly enhance the separation efficiency. Notably, the 3 inlet-a and 4 inlet-a designs achieve higher separation efficiencies at a 1.22 m 3 /s flow rate without increasing the pressure drop. Meanwhile, the 3 inlet-b and 4 inlet-b models demonstrate superior performances, with a higher separation efficiency and a pressure drop only marginally higher than the two-inlet design. This study provides valuable insights into the impact of inlet variations on cyclone separator performance, guiding future efforts to enhance the separation efficiency in multi-inlet designs.
... For oil-injected screw compressor system, the installation of an efficient oil-gas separator at the discharge outlet not only ensures the purity of the discharge gas and system efficiency [1,2], but also improves the recyclability of the lubricating oil [3]. The oil-gas cyclone separator is widely employed in the chemical industry fields because of its simple design, small size and good separation effect [4,5], and is also the most commonly used primary separator of oil and gas in oil-injected compressor systems [6]. The centrifugal force and differential density between the droplets and the working fluid are used to separate the droplets. ...
The optimization of internal components in the oil-gas separator is crucial for enhancing the performance of the compressor system. In this reported study, the effects of three different oil return pipe locations on the vortex characteristics of a cylindrical cyclone separator are investigated by CFD simulation based on the omega method, and the relationship with the separation performance is analyzed. The vortex deformation and breakup near the oil return pipe are evident, with the degree following the order of C > B > A, which is conducive to reducing pressure loss. Cyclone C, with the inclined return pipe, exhibits the lowest pressure drop. The overall separation efficiency follows the sequence of A > B > C. For oil droplets of 5?m and larger, the separation efficiency is essentially the same, exceeding 97.5 %. Cyclone A exhibits the best separation effect for oil droplets smaller than 5?m. This study provides some references for optimizing the internals of oil separators.
Considerable confusion surrounds the longstanding question of what constitutes a vortex, especially in a turbulent flow. This question, frequently misunderstood as academic, has recently acquired particular significance since coherent structures (CS) in turbulent flows are now commonly regarded as vortices. An objective definition of a vortex should permit the use of vortex dynamics concepts to educe CS, to explain formation and evolutionary dynamics of CS, to explore the role of CS in turbulence phenomena, and to develop viable turbulence models and control strategies for turbulence phenomena. We propose a definition of a vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor S 2 + a 2 ; here S and 0 are respectively the symmetric and antisymmetric parts of the velocity gradient tensor Vu. This definition captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers, unlike a pressure-minimum criterion. We compare our definition with prior schemes/definitions using exact and numerical solutions of the Euler and Navier-Stokes equations for a variety of laminar and turbulent flows. In contrast to definitions based on the positive second invariant of V u or the complex eigenvalues of Vu, our definition accurately identifies the vortex core in flows where the vortex geometry is intuitively clear.
A closed type crankcase ventilation system has been adopted to engines to prevent emission of blow-by gas to atmosphere. In the early closed type crankcase ventilation system, blow-by gas which contains engine lubricating oil is re-circulated into the intake system. The blow-by gas containing oil mist leads to increased harmful emissions and engine problems. To reduce loss of the engine oil, a highly-efficient oil separation device is required. Principle of a cyclone oil separator is to utilize centrifugal force in the separator and, therefore, oil separator designs depend on rotational flow which causes the centrifugal force. In this paper, flow characteristics and oil separation performances for cyclone type designs are calculated with CFD methodology. In the CFD model, oil particle was injected on a inlet surface with Rosin-Rammler distribution and uniform distribution. The major design parameters considered in the analysis model are inlet area, cone length and outlet depth of the oil separator. As results, reducing inlet area and increasing cone length increase oil separation performance. Changes in outlet depth could avoid interference between rotational flow and outlet flow in the cyclone oil separator.
Considerable confusion surrounds the longstanding question of what constitutes a vortex, especially in a turbulent flow. This question, frequently misunderstood as academic, has recently acquired particular significance since coherent structures (CS) in turbulent flows are now commonly regarded as vortices. An objective definition of a vortex should permit the use of vortex dynamics concepts to educe CS, to explain formation and evolutionary dynamics of CS, to explore the role of CS in turbulence phenomena, and to develop viable turbulence models and control strategies for turbulence phenomena. We propose a definition of a vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor ; here and are respectively the symmetric and antisymmetric parts of the velocity gradient tensor . This definition captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers, unlike a pressure-minimum criterion. We compare our definition with prior schemes/definitions using exact and numerical solutions of the Euler and Navier–Stokes equations for a variety of laminar and turbulent flows. In contrast to definitions based on the positive second invariant of or the complex eigenvalues of , our definition accurately identifies the vortex core in flows where the vortex geometry is intuitively clear.
A three-dimensional Eulerian-Lagrangian fluid dynamics (CFD) model was developed to simulate the gas particulate flow inside cyclones with different sizes. Cyclones of different sizes, were used which named as cyclones I, II, and III. Cyclone I was considered as the biggest and cyclone III was considered as the smallest cyclone. The effects of cyclone size and inlet velocity on hydrodynamics behavior and performance parameters including cut-off diameter and pressure drop were investigated. The renormalization group (RNG) k-epsilon model and Reynolds stress model (RSM) were used to study the effect of turbulent modeling. Particle trajectories were calculated via discrete phase model (DPM). The velocity fluctuations were simulated with discrete random walk (DRW) model to study the turbulent dispersion of particles. The cut-off size and pressure drop were increased with increasing the cyclone size. The RSM predicted the cut-off diameter very well with the deviations of 2.3%, 3.4%, and 3.6% of the experimental data, for cyclones I, II, and III, respectively. CFD model was developed using Fluent code to simulate the gas particulate flow inside cyclone. The simulation results also confirmed the applicability of CFD modeling with RSM as a promising tool to study the cyclone size effect on performance parameters.
Numerical analysis was performed in order to design the shape of the oil separator for the cyclone-type used in the refrigeration system, which can raise the separation efficiency, and which can reduce the pressure drop. Based on the result of the existing research, the total length of the oil separator, the length of the outlet-port, and the pitch, the turn-number of the spiral structure inside the cylinder was determined. This research was performed to compare and to analyze the separation efficiency and pressure drop of the oil separator while the location of the inlet-port was changed. According to three locations in the entrance, the separation efficiency was predicted from 95.0% to 100%, and the pressure drop ranged from 2.33 to 19.8(Formula presented.)kPa. In conclusion, the shape, which was made eccentric to the edge, had the separation efficiency of 100% and the pressure drop of 2.33(Formula presented.)kPa, which could get the most excellent performance.
Given that refrigerant demand is set to rapidly increase, long term solutions for leakage prevention are required to affect change in the industry. This paper presents the results of a project which investigated refrigerant leakage within two of the UK's major supermarket chains. Leakage data from 1464 maintenance records were analyzed. The analysis categorized the type, location of each leak and volume of refrigerant replaced during repair. Over 82% of the recorded leaks were from R404A refrigeration systems, and mainly consisted of pipe or joint failures or a leaking seal/gland/core located in the compressor pack and the high pressure liquid line. It is recommended that the industry focuses on improving design, installation and maintenance of pipework and valves, at the components that most often develop faults to minimize refrigerant leakage.
The efficiency and pressure drop in the oil separator of a multi heat pump system were experimentally investigated. R410A and polyvinylether (PVE) oil were used as the refrigerant and lubricant of the system, respectively. The refrigerant mass flow rate and the liquid circulation ratio were varied between 30 and 150 g s⁻¹ and between 1.5% and 4.5%, respectively. Five different oil separators were considered, and the measured efficiencies and pressure drops were analyzed with respect to the height and diameter of the oil separators. The analytical results were used to develop empirical equations for predicting the efficiency and pressure drop of the oil separator. The mean absolute percentage errors between the predicted and measured efficiencies and pressure drops for the oil separators were 0.4% and 11.7%, respectively.
In order to improve a refrigeration system’s energy efficiency, the separation efficiency of its oil separator should be improved. To do so, we turned to nature for inspiration. A Namib Desert beetle collects water in fog by using its skin, which combines hydrophilic and hydrophobic surfaces. Inspired by nature’s design, we applied a surface with oleophilic and oleophobic patterns to an oil separator used in a refrigeration system. In order to make the oil separator, an appropriate design was established using computational fluid dynamics. A cyclone-type oil separator was produced with an oleophobic-treated surface on its lower cup. The efficiency of the treated surface of this oil separator was tested with an open-type experimental setup using an oil mist generator. To obtain conditions similar to those of a refrigeration system in the open-type experimental setup, the oil particle diameter and working fluid pressure were set to yield a Stokes number similar to that of oil particles in the oil separator of the refrigeration system. The oil separator with the treated oleophilic–oleophobic surface improved its oil separation efficiency by 1.67% and its pressure drop by 2.48% compared to a conventional cyclone-type oil separator. © 2015, Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.
The development of a simple and feasible fluid–solid separation device is critical to further advancement in the use of micro-technology. The mini-hydrocyclone, which possesses a concise geometry and simple operational process, has been proposed as a promising solution to bridge this gap since the cut-size decreases with decreasing hydrocyclone diameter. In this work, we investigated the fluid flow and particle separation ability of a 5 mm diameter mini-hydrocyclone through computational fluid dynamics (CFD) modelling. Direct numerical simulation (DNS) results with CFD have shown that the flow transition and subsequent unsteady state behaviour occurred in the mini-hydrocyclone at a low Reynolds number (Rein = 300) because of the onset of centrifugal instability. The centrifugal instability offered an insight into the flow transition and the development of turbulent flow in hydrocyclones which have not been studied. The centrifugal instability in the mini-hydrocyclone begins as Görtler vortices developing in the boundary layer and they subsequently affect the flow field. Particle motion tracing showed that improved separation with finer cut size, d50, and steeper separation sharpness were obtained as the inlet velocity was increased. The improvement can be explained by the flow characteristics when the flow transits to turbulent flow.
The mixing of refrigeration oil with refrigerant in a refrigeration cycle has great influence on cycle performance. A sampling method is the most general way to measure the mixing ratio of refrigerant and refrigeration oil. Since the sampling method is time-consuming and reduces the amount of refrigerant and oil in the cycle, a real-time measurement is desirable. In this study, a refractive index measurement was applied to measure the mixing ratio of refrigerant/oil mixture. A laser displacement sensor was used to detect any change in optical path which results from changes of the refractive index of refrigerant/oil mixture. For the practical application of real-time measurement of the oil circulation ratio (OCR) in the refrigeration cycle, a correlation between the refractive index and the mixing ratio was developed. In addition, the changes of the refractive index in a range of a few percentages of the oil concentration and under subcooled conditions were measured. Finally, a transient measurement of the OCR in a practically operating refrigeration cycle was carried out successfully.
The Montreal Protocol on Substances that Deplete the Ozone Layer1 is an agreement to reduce production and emissions of chlorofluorocarbons (CFCs) motivated primarily by the need to protect the Earth's ozone layer. The possible effects of CFCs on global climate were noted as an additional cause for concern. Here, the effect of the protocol on future concentrations of CFC-11 (CFCl3) and CFC-12 (CF2Cl2) is examined, and the greenhouse-effect implications are evaluated. The protocol reduces the 1986–2030 warming commitment attributable to CFCs by a factor of three to seven, but high CFC concentrations (up to four times present levels for CFC-12) would still occur eventually unless further restrictions are imposed.
A study, comparing the effect of blowing agent selection on energy consumption and the life cycle climate performance (LCCP) of a typical European refrigerator is discussed. Energy consumption of prototype European-style refrigerators made with a foam formulation with HFC-245fa as the blowing agent was measured and compared with energy consumption of the same model as currently produced (using a foam with a pentane blend for the blowing agent). Results were used in a LCCP study, considering both direct and indirect climate impacts due to blowing agent emissions and energy consumption in manufacturing processes and over the life cycle of the refrigerator. An assumption is made that the refrigerator is built and used in the European market.
The separation efficiency and the flow field of a dynamic cyclone were studied experimentally and simulated using commercial CFD software (FLUENT 6.0). The experimental results show that the rotational classifier position and the ratio of the classifier opening area to the inlet area have significant impact on the separation efficiency of the dynamic cyclone. The separation efficiency can be significantly improved as the classifier rotates at a speed beyond its natural swirling frequency. The RSM model was used to simulate the 3-D gas flow field, and the simulation predictions were validated by the experimental results measured by a five-hole pressure probe. The tangential velocity distribution in the dynamic cyclone body can be divided into three zones: inlet, separation, and bottom. Each zone has its own tangential velocity distribution curve. The effects of operating conditions and geometric parameters of the classifier on the tangential velocity distribution were also studied.
A lubrication agent is necessary in almost all the refrigeration vapour compression systems, particularly for the correct operation of the compressor. However, a certain portion of the oil always circulates with the refrigerant through the cycle. This circulation is at the origin of a deviation from the theoretical behaviour (i.e. based on pure refrigerant) of the components. This article aims at reviewing the oil-related researches in the field of refrigeration. Previous reviews in the literature focused on the thermo-hydraulic consequences of the presence of oil; we will analyse here its thermodynamical consequences. In a first part, a brief literature review will give an overview of current scientific and technological issues concerning the impact of oil on components or on whole refrigeration systems. The typical approaches and methods employed to address this problem will be described. These researches require sound tools for the evaluation of thermodynamic properties of refrigerant-oil mixtures. The second part of this article is hence a critical review of these tools, and focuses particularly on liquid-vapour equilibrium, absorption-diffusion, and mixture enthalpy calculation.
The infrared bands of chlorofluorocarbons and chlorocarbons enhance the atmospheric greenhouse effect. This enhancement may lead to an appreciable increase in the global surface temperature if the atmospheric concentrations of these compounds reach values of the order of 2 parts per billion.
This article aims at the gas flow into the dustbin of conventional cyclones, the prolonged cyclone (attaching a vertical tube at the bottom of the dust outlet) is proposed by some researchers, which can make flow with dust enter into the tube and separate further. The Reynolds stress transport model (RSTM) has been employed to predict the gas flow fields of the conventional and prolonged cyclones. The tangential velocity, axial velocity profiles and turbulent kinetic energy profiles are presented, and the downward flow rates into the dustbin of the three cyclones are compared. The separation performances of these three cyclones are tested. The result indicates that the tangential velocity, axial velocity and turbulent kinetic energy in the dustbin reduce greatly when the prolonged vertical tube attaching into the dust outlet, which can avoid the re-entrainment of already separated dust effectively. Furthermore, the prolonged vertical tube increases the separation space of dusts. The downward flow rate into the dustbin of the prolonged cyclone decreases compared with the conventional cyclone. The experimental results show that the prolonged vertical tube can improve the separation efficiency by a slightly increased pressure drop. However, for an even longer tube, the separation efficiency is slightly reduced. Thus, there is an optimal tube length for a given cyclone.