Numerical Study on the Oil Pump System of Rotary Compressor

Transcription

1 Purdue University Purdue e-pubs International Comressor Engineering Conference School of Mechanical Engineering 2012 Numerical Study on the Oil Pum System of Rotary Comressor Chunhui Liu Yuanming Yuan Yanzhen Wang Follow this and additional wors at: htts://docs.lib.urdue.edu/icec Liu, Chunhui; Yuan, Yuanming; and Wang, Yanzhen, "Numerical Study on the Oil Pum System of Rotary Comressor" (2012). International Comressor Engineering Conference. Paer htts://docs.lib.urdue.edu/icec/2081 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. Herric Laboratories at htts://engineering.urdue.edu/ Herric/Events/orderlit.html

2 SIMULATION ON THE OIL PUMP SYSTEM OF ROTARY COMPRESSOR 1264 Page1 Chunhui Liu, Yuanming Yuan,Yanzhen Wang 1 Phone: , liuchh@shec.com.cn 2 Phone: , yuanyuanmingllyy@163.com,tel: Shanghai Hitachi Electrical Aliances Co.Ltd, Technology Research Det. Shanghai, China ABSTRACT Oil um lubrication system is an essential art of comressor to ensure the normal oeration. During the rocess of comressor running, lubricant system can form oil film on surface of moving arts to decrease friction and reduce abrasion and occlusion. In order to meet the lubrication requirements, we must design um oil structure reasonable. However, oil lubricating and circulating rocess is a comlex and dynamic rocess, only if through exerimental study to understand the characteristics of each comonents in oil lubrication system is very difficult. Therefore, in this article, we use commercial software CFD to research the best um structure. In order to study the um oil erformance, we adot the gas-liquid two-hase model to research the lubricating oil rising rocess and the flow of each oil hole in different seed. 1. INTRODUCTION Pum oil system of rotary comressor is comosed of oil tan, oil um, radial hole, shaft hole, the shaft undercuts, bearing on the siral tan, as well as a number of lea aths, shown in Figure 1. One end of the cranshaft is immersed in the oil. The oil rises along the cranshaft center hole, and enters into the radial hole of the cranshaft when the cranshaft rotating. This oil arrives the lubrication surface by the centrifugal force to form a film lubricated bearings, and the suerfluous lubricant oil flows bac to the oil ool. Figure 1: Pum oil sysytem 1: comressor housing 2: dust collector 3: under cylinder head 4:under cylinder 5:iston 6 :u cylinder 7:u cylinder head 8: rotating woods 9: crancase 10 oil hole

3 1264 Page2 Oil um lubrication system is an essential art of comressor to ensure the normal oeration. During the rocess of running, the lubrication system have the following function: forming the oil film on the moving arts to reduce friction, reducing wear and tear of moving arts, taing away the heat generated by friction and debris when the lubricating oil flows, imroving the woring conditions of the friction surface; The oil film can absorb the sound to reduce noise. Pum oil lubrication cycle is a comlex hysical dynamic rocess. When the comressor motor start running, the cranshaft rotating in a high seed, due to centrifugal force, lubricating oil rising along the cranshaft internal wall to overcome gravity and surface tension, and finally arriving at each hole of the bearing for lubrication. When the running is stability,the height and shae of the oil surface is affected by centrifugal force, gravity, surface tension, the interaction of decision. In order to meet the lubrication requirements, we must design the um oil reasonably. However, um oil lubrication cycle is a comlex hysical dynamic rocess. If we want to now the characteristics of each comonent, only through trial study has some difficulties. In recent years, the raid develoment of comutational fluid dynamics (CFD) rovides an imortant hole in Engineering Fluid Mechanics technology research. In 2004, Trane engineers simulated the scroll comressor um oil system by CFD, and got the detailed rocess of uming oil (Michael M. CUI.,2004). In 2008, Xi'an Jiaotong University, simulated the rotating-cylinder comressor oil system to solve ractical engineering roblems (Zhanli Zhai,2008). we aly commercial software CFD in this article to design the best um structure.we adot The gas-liquid two-hase model to study the oil um erformance and research the lubricating oil in the cran wall rising rocess and the flow of each oil hole in different seed. In order to comare the erformance the best alicable conditions of two inds of cranshaft structure, we adot the gas-liquid two-hase searation model to simulate the comressor um oil by CFD. 2.NUMERICAL SIMULATION OF COMPRESSOR PUMP OIL SYSTEM 2.1 The flow equation Lubricating oil rose along the center hole of the cranshaft, and ultimately achieve a stable surface as the cranshaft rotating, it is a free liquid surface roblems. The flow field is described by the continuity equation, the N-S equation, the energy equation and the gas equation of state. The turbulence model is RNG equation, and he oil act as a Newtonian fluid in CFD modle ( The model of the turbulent inetic energy equation as follows: µ eff ε ε 2 ui ui ( ρε ) ( ρu jε ) = Cε1 [ µ t ( P Cε 3PB ) ( µ t ρ) ] t x j σ ε x j 3 xi xi (1) Turbulent dissiation rate equation: ( ρε) t Where µ eff ( ρu jε x σ j ε ) = C x 2 C 2 ε 2 ui ui ε ui µ η (1 η η0) ρε [ µ t( P Cε 3PB ) ( µ t ρ) ] Cε 2ρ Cε 4ρε 3 3 x x x 1 βη ε1 ε j i i i 3 (2)

4 for the turbulent inetic energy, ε µ = µ for the turbulent dissiation rate, coefficient, η S, S 1 2 ( 2 s s ij ij ). ε For the other emirical arameters: the amendment for seed and the ε as follows: For the seed equation eff µ t, t 1264 Page3 µ turbulent viscosity U y y ln( Ey ) y > κ (3) = Where,, U = U C 1 / 4 1 / 2 µ τ / ρ w, y = 1 / 4 ρ C µ 1 / 2 y µ ;κ for von Karman coefficient, E is Smooth coefficient for the wall; τ w U is wall shear stress ; is the average seed at the oint P, for the turbulent inetic energy at oint P, y The distance to the wall for the oint P ; µ for the inematic viscosity Equation of the turbulent inetic energy for P ε is amended as follows: U P w τ w = τw 1 / 4 1 / y κρc 2 µ τ y ε 3 / 4 3 / 2 C µ = ; Without solving the ε equation. κy Use the finite volume method to control equation for discrete within collocated grids, and using SIMPLE method to solving the equations. The basic idea of SIMPLE method is bring in the concet of correction, by finding the ressure correction equation that relationshi of the ressure correction and velocity correction via continuity equation, finally solving the equation. 2.2 VOF Method VOF method is tracing of the moving interface by solving the VOF function, ( It defines a function C in the entire flow field, the function C is a ratio by the target fluid volume and the grid size in each grid. The grid have no fluid inside (C = 0) referred to "emty grid", the grid full of fluid inside (C =1) referred to "full" grid, then the grid gave some of fluid inside (0<C<1) referred to "semi-grid". At any moment, nowing that the C values of this function on each grid, we can construct a variety of free moving interface, you can calculate the free surface sloe, curvature, given a more accurate descrition of the free surface. VOF function have its own hysical meaning, it is a fluid grid in the share of the entire volume of the grid than solving equations, to maintain its hysical significance is difficult, so the equation format should be conserved. The value of each time ste function assing interface from 1 to 0 or from 0 to 1, near the moving interface to form a "ribbon", only in the "tae" within VOF function 0 <C <1. To get a clear material interface, and imrove resolution in solving hysics equations, the "tae" must not be too wide. Is to maintain the VOF function only on a grid containing interface is greater than 0 and less than 1, on the other grid must be 1 or 0.

5 1264 Page1 3. CFD SIMULATION OF OIL-PUMPING SYSYTEM 3.1 Model of um oil Using VOF method to simulate the rocess of oil rising, the grid distortion is as small as ossible, the grid size is more uniform. Also hoe the overall grid small changes to reduce the difference between the results of the calculation due to the grid changes when structure changing, (Zhang Huajun,2001)( Kamal Sharma,2010). So using "coule " method between the connection of various iing. Figure 2 oil-uming system model. The model of the fluid region contains all the lubricating oil channel excet the bearing oil film. for examle, We simulate the frequency conversion comressor for the seed of 900 rm and 2850 rm. U bearing Pull gas hole u eccentric Under eccentric Oil ool Under bearing Figure 2: Oil-uming system model 3.2 Boundary conditions are set In the Oil-uming modle, the cran-side hole, the oil surface, the siral groove are set for the ressure boundary. The value of all Boundary ressure need to simulate the exhaust chamber of the comressor rior modeling calculation, tracing the cranshaft-side hole, the oil surface, the ressure of the siral groove, the calculation model shown in Figure 3. Taing the average value of each osition in a cycle, the ressure value of the oil surface siral groove in the motor lower art is aroximately equal; while the cranshaft hole side, which is the uer art of the motor, the ressure value is less than the oil surface and siral. The greater seed the greater ressure difference of the cranshaft end hole and cross hole, the values of the boundary as shown in Figure 4 and Figure 5.

6 1264 Page2 Figure 3: Boundary ressure value model Figure 4 :Each boundary ressure curve (900RPM) Figure 5: Boundary ressure curve (2850RPM) 4. CALCULATION RESULTS 4.1 Flow characteristics of oil-uming system When Cranshaft s seed is 900 rm, we calculate 70 cycles, it means that cran turned 70 revolutions to stabilize. While Cranshaft seed at 2850rm, the cran turned 50 rm to achieve stability. The flow characteristics of the oil-uming system and rocess in different seed is basically the same, namely, the oil um through the dust collector, it first to reach the cranshaft out of the hole the oil, to lubricate the lower bearing, and then reach the hole in the cranshaft oil then to rise reach the eccentric bearing and then divided into two-way,inside and outside, inside to reach the bearings and outside to reach siral groove on bearing lubrication. Comare with 900 rm and 2850rm, the seed is higher, the lubricants climb faster, oil-uming system to achieve stability in the shorter time, the shorter time the corresonding dry friction in the comressor starts. Figure 6 is the lubricant distribution ma at seed 900rm when cran turned 1.2s, 2s, 2.8s, 3.6s, we can see that the basic rocess of the cranshaft um oil.

7 1264 Page3 1.2s 2s 2.8s 3.6s Figure 6:Lubricating oil at different times mas 4.2 Oil quantity comarison The erformance of um oil is decided by two factors: the centrifugation by rotating and the ressure difference of the cranshaft-side hole from the oil surface. Due to there is ressure difference in motor u and down, so the ressure in cranshaft end hole is smaller than the ressure of the oil surface of the ool, is favorable for uming oil. The centrifugal force and the side hole with the oil surface ressure difference in different seeds.the greater the seed, the greater centrifugal force, he greater the ressure difference, the greater the force, and the stronger the corresonding oil-uming caacity. Moreover, the ressure of the straight hole and the siral groove and the oil surface of the ool is ulsation, so the flux of each hole is not a stable value. For the four oil hole, the flux of under eccentric is the biggest, and the uer bearing second, the under bearing and the under eccentric is less in different seeds, showed as Figure 7, Figure 8. Figure 7: Out of hole flow with the angle change/900rpm Figure 8:Out of hole flow with the angle change/2850rpm

8 1264 Page1 5. CONCLUSION (1)The oil is umed through the dust collector, then it first to reach the under cranshaft oil hole to lubricate the bearing, and then lubricant oil in the internal cranshaft wall continues to rise to reach the eccentric bearing and then divided into two channel, and external, internal to reach the bearings and external to reach siral groove on bearing lubrication. (2)The erformance of um oil is decided by two factors: the centrifugation by rotating and the ressure difference of the cranshaft-side hole from the oil surface. Due to there is ressure difference in motor u and down, so the ressure in cranshaft end hole is smaller than the ressure of the oil surface of the ool, is favorable for uming oil. (3)Moreover, the ressure of the straight hole and the siral groove and the oil surface of the ool is ulsation, so the flux of each hole is not a stable value. (4) For the four oil hole, the flux of under eccentric is the biggest, and the uer bearing second, the under bearing and the under eccentric is less in different seeds. NOMENCLATURE Physics Terms Subscrit t temerature K i vector,orientation X incoordinate ressure Pa j vector,orientation Y incoordinate ρ density g/m^3 ε 1 exeriential coefficient 1;often1.44 turbulent inetic energy -- ε 2 exeriential coefficient 2, often1.92 ε turbulent dissiation rate -- ε 3 exeriential coefficient 3, often0,or 1 µ viscosity m^2/s ε 4 exeriential coefficient 4,often1.44 τ shear stress N/m^2 w wall y distance in Y incoordinate m C exeriential coefficient -- β exand coefficient -- REFERENCES Michael M. CUI.,2004,Investigation on the oil suly system of a scroll comressor,purdue,c093, Page 1~8 Zhanli Zhai, Jianhua Wu and Ruihong Ma, 2008,The Analysis of Oil Suly System for Twin-Cylinder Rotary Comressor, Purdue C1426,age1~7 Zhang Huajun, Wang Jun, Li Hongjun and so on, 2001, Rolling rotor comressor lubrication system calculation, low temerature and secial gas,vol 19 no.5. 1~5 Kamal Sharma, etc. 2010, July 12-15,CFD Analysis of Discharge Gas flow in Rotary Comressor for OCR Reduction, International Comressor Engineering Conference at Purdue, c8,1224,age:1~8, Transient flow analysis of an air conditioning comressor, htt:// ACKNOWLEDGEMENT An acnowledgement can be located at the end of the text to indicate the sonsor of the study resented and/or to acnowledge additional contributors to the aer.