Purdue e-pubs. Purdue University. Xiang Gao Yaopeng Zhao. Xin Yang. Yunfeng Chang. Xueyuan Peng

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1 Purdue University Purdue e-pubs International Comressor Engineering Conference School of Mechanical Engineering 01 The Research On The Performance Of Oil-gas Cyclone Searators In Oil Injected Comressor Systems With Considering The Collision And Breaku Of Oil Drolets Xiang Gao Yaoeng Zhao Xin Yang Yunfeng Chang Xueyuan Peng Follow this and additional works at: htt://docs.lib.urdue.edu/icec Gao, Xiang; Zhao, Yaoeng; Yang, Xin; Chang, Yunfeng; and Peng, Xueyuan, "The Research On The Performance Of Oil-gas Cyclone Searators In Oil Injected Comressor Systems With Considering The Collision And Breaku Of Oil Drolets" (01). International Comressor Engineering Conference. Paer 119. htt://docs.lib.urdue.edu/icec/119 This document has been made available through Purdue e-pubs, a service of the Purdue University Libraries. Please contact eubs@urdue.edu for additional information. Comlete roceedings may be acquired in rint and on CD-ROM directly from the Ray W. Herrick Laboratories at htts://engineering.urdue.edu/ Herrick/Events/orderlit.html

2 1407, Page 1 The Research on the Performance of Oil-gas Cyclone Searators in Oil Injected Comressor Systems with Considering the Breaku of Oil Drolets Xiang Gao, Yaoeng Zhao, Jianmei Feng, Yunfeng Chang, Xueyuan Peng School of Energy and Power Engineering, Xi an Jiaotong University, Xi an, Shaanxi, China Tel: , Fax: , gaoxiang.xjtu@stu.xjtu.edu.cn ABSTRACT The high-seed swirling flow field in the cyclone oil-gas searator will cause the breaku of oil drolets, thus reducing the searation efficiency. In this aer, the erformance of an oil-gas cyclone searator was investigated through both numerical simulations and exeriments with considering the breaku of oil drolets in oil-gas cyclone searators. The gas flow field was simulated using the RSM turbulence model and the trajectory of the oil drolets was calculated by the Discrete Phase Model(DPM).The breaku of oil drolets was simulated by TAB model and the wall boundary of oil drolets was treated as Reflect boundary. Meanwhile, the searation efficiency was measured and the Malvern Particle Size Analyzer was alied to get the drolets diameter distribution at the inlet and exit of the oil-gas cyclone searators to verify the simulation model. The results showed that the searation efficiency was influenced significantly by the breaku of oil drolets, esecially for the high inlet velocity. The simulation results based on the resented model were in good agreement with the exerimental data. Key Words: Oil-gas Cyclone Searator, Numerical Simulation, Discrete Phase Model, Breaku of Oil Drolets, Searation Efficiency 1. INTRODUCTION The cyclone searator has been widely used on account of its simle geometry and little maintenance. The searation efficiency of the oil-gas searator is one of the most imortant indexes in oil injected comressor systems. A considerable amount of research existed on cyclone erformance by comutational fluid dynamics (CFD). Almost all of these studies focused on the flow field in the cyclone chamber and the Reynolds Stress Modeling of turbulence (RSM) which base on the Reynolds Averaged Navier-Stokes equations (RANS) has been widely acceted. Gronald(011) comared the finite volume RANS model and two LES aroaches and ointed that unsteady RANS-based simulations on a relatively coarse grid can rovide reasonable and industrially relevant results with limited comutational effort. Slack (000) used RSM simulating the flow field in a conventional high efficiency Stairmand cyclone, and the result showed consistent agreement comared with Laser Drolet Anemometry measurements. Hoekstra and others (1999) reorted on reorted reasonable agreement with exerimental data, when International Comressor Engineering Conference at Purdue, July 16-19, 01

3 1407, Page the anisotroic RSM was alied. The successful alication of the RSM turbulence model for different studies in cyclone searators has been reorted by many researches. For examle, Azadi (010) investigated the cyclone size on its erformance and the swirling field were simulated by RSM.; Khairy and Elsayed (011) studied the effect of inlet dimensions the cyclone size on its erformance and the swirling field were also simulated by RSM. Besides, there are many investigations on the article motions in the swirling flow in a cyclone searator by using the Lagrangian discrete hase model (DPM). Matsuzaki (006) studied the article motions in swirling flows in a cyclone by using a large eddy simulation(les)and redicted the erformance for article searation from the result of the article tracing. Actually, the high-seed swirling flow field in the cyclone searator will cause the break u of oil drolets that effect the erformance of the cyclone searator. But all articles mentioned above did not study the effect of the breaku of oil drolets on the erformances in the cyclone searators. In revious study, the models for the breaku of drolets in high-seed flow field have been established and these models have been used in simulation fields, for examle sray. Shan (007) used TAB drolet breaku model to solution recursor lasma sray and indicated that drolet breaku lay an imortant role in determining the final article size and velocity distribution on the substrate. In this article, a 3D model was develoed and the exerimental system was established for the urose of studying the effect of the breaku of oil drolets to the erformance of oil-gas cyclone searators. RSM was used to simulate the gas flow field and the trajectory of the oil drolets was described by DPM. The breaku of the oil drolets was calculated by TAB model.. MATHMATICAL MODELS.1 Cyclone searator Fig 1 shows the schematic view of the cyclone searator in this article. This is the familiar cyclone model in oil injected comressor systems.it has a swirl chamber with a diametric of 65mm(D=65mm)and the other arameters of the cyclone searator was showed in table 1. The oil-gas mixture enters though the to of the swirl chamber in the tangential direction and is exhausted through the central channel with a diametric of d,which is installed inside the to of swirl chamber by the deth of h. The side slitter is floating to change the deth of the swirl chamber which is signed as H. The following assumtions in this article are made in this model: 1.The flow field is stable and incomressible;.the oil drolets were regarded as a sherical articles and the deflection of them were ignored; 3.The heat transfer in this article was ignored; 4.The Magnus force which was far less than saffman force was ignored. International Comressor Engineering Conference at Purdue, July 16-19, 01

4 1407, Page 3 Fig.1 Schematic view of the cyclone searator Table 1 The geometrical dimension of the tested cyclone searators in this article Dimension Parameter(mm) Dimension/D Cyclone diameter D 65 1 Cyclone height H Cylinder diameter d Cylinder height h Inlet height a 30 Inlet width b 8 Inlet length L 60. The gas flow field In this aer, the Reynolds Stress Modeling of turbulence (RSM) was chose to describe the swirling flow in the cyclone searator. The details including governing equations and sulementary equations of this model can be found in the reference written by Safikhani (010)..3 Oil drolets The governing equation of the oil drolets in the flow field is given as follows: du dt g x ( ) FD ( u u ) Fx (1) Where u and u are the velocities of the gas and the oil drolet;ρand ρ are the densities of the gas and the oil drolet; g x is the acceleration of gravity; F D is the digestion stress of unit quality and Fχ is the additional force that are given by: F D 18 CD Re d 4 () International Comressor Engineering Conference at Purdue, July 16-19, 01

5 1407, Page 4 F x 1/ Kv dij d ( d d ) lk 1/ 4 kl ( u u ) (3) Where μ is the dynamic viscosity of the gas; d is the radii of the oil drolet; K=.594; d ij is the deformation tensor;v is the dynamical viscosity; Re r is the relative Reynolds number of the drolet and C D is the drag coefficient that are calculated as follows: d u u R er (4) C D a a3 a1 (5) Re Re r r where a1 a and a3 are constants among some secial Reynolds number range indicated by Morsi(197). The velocity of the oil drolet can be redicted by integrating equation over discrete time stes. Further integration of the velocity yields dislacement and thereby the trajectory of the oil drolet x u 1dt, y udt, z u3dt.when the trajectory equations are solved by integration over discrete time stes, the gas velocity is the mean gas-hase velocity..4 Drolet breaku The breaku of single oil drolet exists in the swirling flow field due to the effect of neumatic ressure, shear stress and turbulent disturbance. The Taylor analogy breaku(tab) develoed by O Rourke(1987) is the most widely used models on the breaku of single oil drolet. Drolet breaku in this model was considered by: d (6) x d x F kx d m dt dt Where F is the external force of drolets, x is the dislacement of the drolet equator from its sherical (undisturbed) osition. F m k m d m C F C k C d u r Where m is the mass of the drolet; r is radii of the drolet undisturbed;σis the surface tension of the drolet; μ P is the dynamic viscosity of the drolet; C F =1/3; C k =8; C d =5. If x>c b (C b =1/),the drolet will break. The energy of the large drolets is equal to the energy of all sub-drolets after the drolet breaku. The Energy of the large drolet included surface energy,vibration and torsional International Comressor Engineering Conference at Purdue, July 16-19, 01 0 r 3 r (7)

6 1407, Page 5 deformation energy. The surface energy of the drolet was given by: E surf 4 r (8) and the vibration and torsional deformation energy was calculated by: Where C y r b 5 dy Eosc K r ( ) y 5 dt ;K=10/3; Therefore, the energy of the large drolet can be described as following: (9) Earent Esurf Eosc (10) The energy of the sub-drolet after collision can be calculated by: r dy E 4 r ( ) (11) 5 child r 3 6 dt Based on the conservation of energy, the average distribution of sauter distribution was given by: r r dy 1 ( ) 0 dt 3 3 8Ky r( dy/ dt) (1) Where r3 0.7rmax and r max is the of the maximum of the drolet radius distribution.the velocity of the sub-drolet was calculated as following: wherecv 1. u normal dy (13) C Cbr dt.5 Boundary Conditions At the solution cyclone searator inlet and outlet, inlet velocity, outlet ressure, drolet size distribution is determined based on the exeriment observation. During the calculation, if a drolet hits the wall, the Reflect boundary condition alies, which Means that if the drolet can not escae the searator, it is searated. If a drolet crosses the inlet and outlet, the ESCAPE boundary condition alies, which reorts that the drolet has escaed when it encounters the boundary and trajectory calculation is also terminated. 3. NUMERICAL SIMULATION 3.1 Numerical Technique Fig 3 shows the comutational grid in the cyclone searator with the mesh of cells. The whole comutational domain is meshed using hexahedral elements. The grids are fine at the zone near wall and vortex International Comressor Engineering Conference at Purdue, July 16-19, 01

7 1407, Page 6 finder while the grids are sarse at the zone away from the wall. The RSM model was emloyed to simulated the gas hase flow field and the Discrete Phase Model (DPM) was adoted to track the oil drolets trajectory together with the TAB model for considering the effect of drolets breaku. Fig.3 The comutational grid for the cyclone searator 3. Calculating Conditions The inlet velocity of the gas and the drolet are defined 9.3,10.5,1,14.1m/s while the outlet ressure of the gas are 0.6,0.7,0.8,0.9MPa. Table 3 The arameters and cases of the tested cyclone searator in this article Case A B C D Inlet velocity(m/s) Outlet ressure(mpa) Density of the gas(kg/m 3 ) Viscosity of the gas(kg/m.s).09e-06(353k) Density of the oil(kg/m 3 ) 830 The density and the viscosity of the gas are related with inlet ressure, while the density of the oil drolet is 830kg/m 3. Cases of the tested cyclone searator in this article was showed in table 3. The drolet size distribution is described by the Rosin-Rammler equation, with the mean diameter equal to mm and the sread arameter 1.45 that were obtained by the exeriment followed. The erformance for the searation of the cyclone searator is estimated by the collection rate which is calculated by the following equation: N out (1 ) 100(%) (14) N total where N out is the number of drolets which flow out from the outlet and N total is the total number of drolets mixed into the swirl chamber. 4. EXPERIMENTAL SETUP To get the searation efficiency and the drolets diameter distribution at the inlet and exit of the cyclone searator, the exerimental system was established and showed in Figure 5. The work fluid used in the exerimental investigation resented was air. From Fig.4, it can be seen that the oil gas mixture discharged out of the comressor first flows into the oil gas searator and then enters into the cyclone searator. The mixture after searated by the cyclone searator flows through the oil filter and AO/AA suerfine oil filter. To get the drolets diameter distribution International Comressor Engineering Conference at Purdue, July 16-19, 01

8 1407, Page 7 at the inlet and exit, Malvern Particle Size Analyzers were set before and after the cyclone searator. Fig.4 The exerimental system The searation efficiency was defined byεthat was calculated by the following equation. Q1 (15) Q1Q Q3 Where, Q 1,Q and Q 3 are the oil filtrated by the cyclone searator, AO and AA suerfine oil filter. The volumetric flow rate and the seed of the comressor are.5m 3 /min and 900rm. The discharge ressure ranges from 0.6MPa to 0.9MPa, whereas the inlet air temerature and ressure are 80 and 0.1MPa. 5. RESULTS AND DISCUSSION 5.1 The Trajectory of Oil Drolets in Simulation As shown in Fig. 5, the trajectories of the oil drolets were simulated with case A, B, C and D, searately.the inlet velocity was 9.3 m/s to 14m/s and the Reynolds number reached , so the flows in these cases were treated as the turbulent flow that can be indicted from the trajectories of the oil drolets. The maximum residence time reduces from to s as the inlet velocities of the oil drolet increases from 9.3 to 14.1m/s.Simulated searation efficiencies of the cases were obtained and showed in Fig Effect of Drolet Breaku In order to estimate the effect of the breaku of the oil drolets, the searator efficiencies of simulations with case A, B, C and D were comared with the values obtained by exeriment and simulations above. It can be seen that if the breaku of oil drolets were not considered in simulation, the searation efficiencies were almost 100%. But the searator efficiencies got by exeriment were 70%-85%.While TAB model was used in simulation to described the breaku of the oil drolets, the searator efficiencies were in good agreement with the exerimental data. The maximum error was less than 10% and it may be due to the low inlet velocity which reduced the collision energy. It can also be found that the searation efficiency enhanced with the velocity. 5.3 The Drolet Size Distribution Fig.7 showed the drolet size distributions at inlet and outlet of case A and C. It can been seen that the volume ercent at inlet with the diameter less than 5μm of total imorts was.6%,the diameter between 10μm and 5μ m was 51.6% and the diameter more than 5μm was 11.4%.Comared the drolet size distributions at inlets, it can be found that the drolets with the diameter more than 5μm could be searated comletely and the drolets with the diameter less than 5μm were hard to be searated. It can be indicated that the level of intensity of the breaku of oil drolets in case A was not as high as in case C and the henomenon can be exlained as the inlet velocity of case A was smaller than case C. International Comressor Engineering Conference at Purdue, July 16-19, 01

9 1407, Page 8 A B C D Fig.5 The trajectory of the oil drolets in simulation Fig.6 Comared of the searation efficiencies by exeriment and simulation Fig.7 The drolet size distribution at inlet and outlet 5.3 Conclusions A numerical simulation taking the drolets breaku into account of oil gas cyclone searator and exerimental investigation were carried out in this aer. By simulating and testing the searator efficiency of the searator, the International Comressor Engineering Conference at Purdue, July 16-19, 01

10 1407, Page 9 influence of the breaku of oil drolets on searation erformance was analysed. Both the exerimental data and simulation results showed that the breaku of oil drolets which influenced the searator efficiency existed in cyclone searators due to the high seed swirling flow field. The simulation results based on model considering the breaku of the oil drolets were in good agreement with the exerimental data. The velocity at inlet of searator layed an imortant role in the searator efficiency, because it determined the tangential velocity and then caused the breaku of the oil drolets, articularly at high inlet velocity. Further investigation on different structures of cyclone searator and what about the mechanism of the oil drolet breaku are required to understand how best to design the searator. ACKNOWLEDGMENTS The research was suorted by the National Natural Science Foundation of China (Research Project /E06050). NOMENCLATURE a inlet height (mm) b inlet width (mm) C D drag coefficient D cyclone diameter (mm) d cylinder diameter (mm) d ij deformation tensor d P oil drolet radii (m) E surf oil drolet surface energy (J) E osc vibration and torsional deformation energy (J) E arent large drolet energy (J) E child sub-drolet energy (J) F χ additional force (N) F D digestion stress of unit quality (N) g x gravity acceleration (m/s - ) H cyclone height (mm) h cylinder height (mm) L inlet length (mm) m oil drolet mass (kg) R gyration radii of the drolet (m) Re gas Reynolds number Re oil drolet Reynolds number Re r relative Reynolds number r oil drolet radii (m) u gas velocity (m/s) u P oil drolet velocity (m/s) u normal sub-drolet velocity (m/s) ρ gas density (kg/m 3 ) ρ P oil drolet density (kg/m 3 ) ε searation efficiency v dynamical viscosity (m /s) μ gas viscosity (a s) μ P oil drolet viscosity (a s) REFERENCES Gronald G, Derksen J J,011,Simulating turbulent swirling flow in a gas cyclone: A comarison of Varous modeling aroaches, Powder technology, no 05: Slack M D, Prasad R O, Bakker A, Boysan F, Advances in cyclone modeling using unstructured grids, Trans IChemE, vol78,part A International Comressor Engineering Conference at Purdue, July 16-19, 01

11 1407, Page 10 Hoekstra A J, Derksen J J, Van Den Akker,1999,An exerimental and numerical study of turbulent swirling flow in gas cyclones, Chemical Engineering Science, no 54: Azadi M, Azadi M, A Mohebbi,010,A CFD study of the effect of cyclone size on its erformance arameters, Journal of Hazardous Materials,vol18: Elsayed K, Lacor C,011,The effect of cyclone inlet dimensions on the flow attern and erformance. Alied Mathematical Modeling,no 35: Matsuzaki K, Ushijima H, Munekata M,006,Numerical study on article motions in swirling flows in a cyclone searator. J. of Thermal Science,vol.15,no. Shan Y, Coyle T W, Mostaghimi J,007,Numerical simulation of drolet breaku and collision in the solution recursor lasma sraying, Journal of Thermal Sray Technology, vol 16: Safikhani H, Akhavan-Behabadi M,Shams M, Rahimyan M H,010,Numerical Simulation of Flow Field in Three Tyed of Standard Cyclone Searators, Advanced Powder Technology, no 1: Morsi S, Alexander A.,197,An investigation of article trajectories in two-hase flow systems, Journal of Fluid Mechanics, no 55 : O Rourke P J,.Amsden A A,1987,The Tab Method for Numerical Calculation of Sray Drolet Breaku, SAE Technical Paer International Comressor Engineering Conference at Purdue, July 16-19, 01