Cho, N. K.

Lee, B. C.

Min, M. K.

Youn, Y.

English

Purdue E-Pubs

Purdue UniversityPurdue e-PubsInternational Compressor Engineering Conference School of Mechanical Engineering2000The Characteristics of Tip Leakage in ScrollCompressors for Air ConditionersY. YounKorea UniversityN. K. ChoKorea UniversityB. C. LeeL. G. ElectronicsM. K. MinKorea UniversityFollow this and additional works at: https://docs.lib.purdue.edu/icecThis document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu foradditional information.Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at https://engineering.purdue.edu/Herrick/Events/orderlit.htmlYoun, Y.; Cho, N. K.; Lee, B. C.; and Min, M. K., "The Characteristics of Tip Leakage in Scroll Compressors for Air Conditioners"(2000). International Compressor Engineering Conference. Paper 1465.https://docs.lib.purdue.edu/icec/1465The Characteristics of Tip Leakage in Scroll Compressors for Air Conditioners Young Youn1, Nam-Kyu Cho1, Byung-Chul Lee2, and Man-Ki Min3 1 HV AC & Refrigeration Laboratol)', Graduate School of Korea University 2 Digital Appliance Laboratory, LG Electronics Co. Ltd. 3 Department of Mechanical Engineering, Korea University Abstract This Paper describes the characteristics of tangential and radial leakage which is occurring at micro tip clearance in a scroll compressor for an air conditioner (R22) under actual operating condition. It is well known that leakage phenomena have a large effect on the performance of a scroll compressor. But the leakage phenomena of a scroll compressor under actual operating condition were not clear because of a complex sealing mechanism and two phase flow. To define complex tip leakage phenomena under actual operating condition, experimental research was executed by using indirect flow rate measuring method. And analysis model of tip leakage was made for analyzing tangential and radial leakage occurring at grooves and contact points of a tip seal. In case of no oil, it was also validated as theoretical result was compared with experimental result. Therefore the quantity of tip leakage with pressure ratio, orbiting angle, discharge pressure, tip clearance, and leakage point was found out. Also it was known that tip leakage at tip part occurs somewhat although a tip seal has sealing effect for radial leakage. Nomenclature A A tsb A tsbs A Iss Awl Atstc.t A tssc.t A tstc.r At=·.r a c k Lt.in L !.out : Leakage area Tip seal bottom area Tip seal bottom side area Tip seal side area Wrap tip area Tip seal top contact area, tangential Tip seal side contact area, tangential Tip seal top contact area, radial Tip seal side contact area, radial : Base circle radius Flow coefficient Tip seal height : Specific heat ratio Inner leakage length Outer leakage length Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 R Wts Wwt r/Ja e (5 tstc m L tst : Up stream pressure : Down stream pressure : Gas constant of refrigerant : Up stream temperature : Tip seal width : Wrap tip width : Involute starting angle : Orbiting angle Tip seal bottom clearance Tip seal side clearance Tip seal top contact clearance Tip clearance Tip seal side contact clearance : Leakage mass flow rate : Tip seal leakage length 797 Introduction Scroll compressors have be widely built in room and packaged air-conditioners because higher performance, lower noise, and lower vibration. In a scroll compressor, a sealing mechanism is needed for preventing flank and tip leakage between pockets during compression process. For example, the back pressure or the tip seal mechanism is generally adopted for preventing tip leakage at tip(axial) clearance. And the variable radius crank mechanism is widely used for reducing flank leakage at flank(radial) clearance. Studies on sealing mechanisms for reduction of leakage loss have been made.(l)-(3) But studies on leakage phenomena under actual operating condition and sealing effect of the tip seal mechanism are very insufficient because of complex structure of compression part, complicated mechanism of tip seal, and two phase flow of working fluid. In this study, the quantity of tip leakage was measured in . actual operating condition by experimental apparatus using indirect flow rate measuring method. And analysis model of tip leakage was made for analyzing tangential and radial leakage occurring at grooves and contact points of a tip seal. Experiment Experiment was performed to find out the characteristics of the tip leakage between pockets under actual operating condition of a scroll compressor. Fig.l is a schematic diagram of experimental apparatus. The experimental apparatus is consisted of three parts; a modified test compressor part, an modified air conditioner part, a multi flow rate measuring device part. Fig.2 is a sectional view of the modified test compressor. And Fig.3 represents positions of bypass holes at the top of a fixed scroll. The modified test compressor has the same structure as a real scroll compressor except a driving motor removed. The modified air conditioner is device to supply high pressure refrigerant to the modified test compressor continuously. The multi flow rate measuring device was made for measuring flow rate at several points with a mass flow meter. It is impossible that the tip leakage only is measured due to rotation of a orbiting scroll. The leakage mass flow rate of tip and flank at an orbiting angle for an sample can be totally measured. Therefore the leakage mass flow rate of tip is obtained by subtracting that of flank from that of flank and tip. Theoretical analysis Fig.4 represents tangential and radial leakage of tip occurring at tip clearance between a fixed and a orbiting scroll. And Fig.5 represents tangential and radial leakage model of a tip seal. 'The tangential leakage occurs at surrounding clearance of a tip seal; top, bottom, left side, right side, and bottom left side clearance of a tip seal, clearance between tip of a wrap and plat of a scroll. And the radial leakage occurs at top contact and side contact clearance of a tip seal. The leakage lengths of tip between 720 o and 990 o of orbiting angle can be expressed as ( P a-1[- B) L /,in= 7rX aX 2 Ltout=7fXaX( cpa+l.57f-e) And leakage areas of tip can be defined as Atsb= WtsX Otsb Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 (1) (2) (3) 798 Atsbs= otssx Otsb Atss= otssx( hts+ Otste) Awr= WwtX Ot A tstc, t= W ts X 0 tstc (4) (5) (6) (7) A /sse, 1= 0 tsse X h wg (8) A lstc,r= L /siX 0 Isle (9) A /sse, r= L lsi X 0 /sse (1 0) The tangential and radial leakage mass flow rate of tip can be theoretically obtained by usmg the flow coefficient equation of steady state one-dimensional compressible fluid, assuming leakage flow as single phase and isentropic nozzle flow. m= J k+l k 2 k-1 CAPup RT"" ( k+ 1) ( P dn ) ( 2 ) k~I Pup ( k+l (11) The analysis model of tip leakage was made by usmg above equations, flow coefficient, and tip seal contact clearance on condition of no oil. Results and Discussion The Condition of pressure, Tip Clearance, and Tip Leakage Length with Orbiting Angle Fig.6 shows the upstream and downstream pressure condition of a leakage part with orbiting angle at different suction and discharge pressure. As known from Fig.6, downstream pressure condition with orbiting angle is constant because the discharge pressure has no effect on it. On the other hand, upstream pressure condition is constant at 720 o and 765 °, but variable at 900 o and 990 o due to the connection between a compression pocket and a discharge pocket. Fig. 7 represents tip clearance condition with orbiting angle at different tip clearance. Every tip clearance has constant clearance with orbiting angle. Fig.S shows variation of tip leakage length with orbiting angle. The tip leakage length is linearly reduced with increase of orbiting angle. Therefore it is know that the tip leakage area decreases _ as orbiting angle increases in case of constant tip clearance. Oil Concentration Fig.9 represents the variation of oil concentration of mixture with measuring number at the inlet of a test compressor. Although the value of oil concentration measured by an oil sampler has some fluctuation, it is about 0.5%. Therefore it is known that oil has little effect on leakage of tip between pockets in this experiment. Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 799 Effect of Pressure Ratio Fig. I 0 shows the comparison of tip leakage with pressure ratio between experimental and theoretical value. In that case, the pressure ratio is defined as the pressure ratio of upstream to downstream. In experimental result, the leakage mass flow rate of tip is obtained by subtracting that of flank from that of flank and tip on condition of the same clearance and temperature. On the other hand, the theoretical value of tip leakage is directly calculated by analysis model of tip leakage using flow coefficient and tip seal contact clearance. As known from Fig. I 0, the theoretical result of analysis model of tip leakage has a good agreement with experimental value. Thus the analysis model of tip leakage is validated through that comparison. And the leakage mass flow rate of tip in case of tip clearance 37 f1lli is linearly proportional to pressure ratio in condition of the same temperature. Fig.ll shows the comparison of tip leakage with pressure ratio defmed as the pressure ratio of downstream to upstream at different tip clearance between experimental and theoretical value. The theoretical result of tip leal<.age has a good agreement with experimental value of tip leakage. Thus it is known that the analysis model of tip leakage has validity and tip leakage with pressure ratio at any clearance reveals typical choking phenomenon of compressible fluid. Also it is clear that oil of mixture has little effect on tip leakage from this analysis. Tip Seal Contact Clearance Fig.l2 represents the variation of tip seal contact clearance with pressure ratio at top and side of a tip seal. The value of tip seal contact clearance is theoretically obtained by comparing theoretical value with experimental value of tip leakage in Fig.lO. In case of tip clearance 37 fJ,m, it is found out that the value of tip seal contact clearance at top and side of a tip seal is nearly constant and about 2.5fJ,m as known from Fig. 12. Effect of Orbit!ng Angle Fig.l3 and Fig.14 show experimental result of tip leakage with orbiting angle at tip clearance 37 and 52fJ,m respectively in case of discharge pressure 21. The tip leakage is nearly constant between 720 o and 765 o because increase of upstream pressure has effect of increase to it, but decrease of tip leakage length has effect of decrease to it. And the tip leakage sharply increases between 765 o and 900 o due to sharp increase of upstream pressure in spite of decrease of tip leakage length. Also the tip leakage a little decreases between 900 o and 990 o due to reduction of pressure difference between pockets and tip leakage length. Tip leakage in case of tip clearance 52pm reveals the same trend as that in case of tip clearance 37 pm. Effect of Discharge Pressure Fig.15 shows the comparison of tip leakage with orbiting angle at different discharge pressure between experimental and theoretical value. Tip leakage with discharge pressure is constant at 720 o and 765 o because of the same pressure and area condition. On the other hand, tip leakage with increase of discharge pressure reveals linear increase at 765 o and 900 o due to increase of upstream pressure as shown in Fig.6. Although there is some deviation, theoretical result has a good agreement with experimental result. Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 800 Effect of Tip Clearance Fig.l5 represents shows the comparison of tip leakage with orbiting angle at different tip clearance between experimental and theoretical value. Tip leakage with increase of tip clearance linearly increases with over all angle. It reveals that total leakage area of tip is linearly proportional to tip clearance. Therefore it is clear that in spite of sealing effect of a tip seal, the more tip clearance increases, the more tip leakage increases. Conclusions In this study, the tip leakage of a scroll compressor was measured by using experimental apparatus under actual operating condition. And leakage of tip and contact clearance of a tip seal were theoretically analyzed by analysis model of tip leakage. Finally, the following conclusions were obtained from above research. (1) The analysis model of tip leakage in case of oil was validated by comparing theoretical result with experimental result of tip leakage. (2) The tip leakage with pressure ratio at any tip clearance reveals typical choking phenomenon of compressible fluid. (3) The value of tip seal contact clearance at top and side of a tip seal has no variation with pressure condition and orbiting angle, and is about 2.5,um at tip clearance 37 flill. ( 4) At any tip clearance and discharge pressure, the tip leakage is nearly constant between 720 o and 765 o , sharply increases between 765 o and 900 o , a little decreases between 900 o and 990 °. ( 5) Tip leakage with increase of discharge pressure is constant at 720 o and 765 o , reveals linear increase at 765 o and 900 o • ( 6) Although a tip seal has sealing effect for radial leakage, tip leakage with increase of tip clearance linearly increases with over all angle. Acknowledgement We would like to express our great thanks to LG electronics Co. Ltd., for their financial and technical support in carrying out this research. References (1) .Jean-Luc Caillat, Shimao Ni, Michael Daniels, 1988, "A computer model for scroll compessors," Proc. of Int. Compressor Engineering Conf. at Purdue, pp.47-55 (2) Tsutomu Inaba, Masahiro Sugihara, Toshyuki Nakamura, Tadashi Kimura, Etsuo Morishita, 1986, "A scroll compressor with sealing means and low pressure side shell," Proc. of Int. Compressor Engineering Conf. at Purdue, pp.887 -900 (3) Noriaki Ishii, Kenichi Bird, Kiyoshi Sano, Mamoru Oono, Shinji lwamura, Takayuki Otokura, 1996, "Refrigerant leakage flow evaluation for scroll compressor," Proc. of Int. Compressor Engineering Conf. at Purdue, pp.633 -638 (4) M. K Min, Y. Yom1, N. K Cho, 1999, "A Study on the Characteristics of Leakage in Scroll Compressors for Alternative Refrigerants", Research Report, Korea. University (5) B. C. Lee, "Analysis Model of Internal Leakage in Refrigerant Compressors for Air Conditioners", Internal Report, LG Electronics Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 801 Condenser Expansion valve Evaporator compressor L -I l l Figures Mass flow l I -----------------------------L--------------------------------------------------1 Fig.l Schematic of experimental apparatus Flow in l l lBy-pass Flow out Howou'i Fig. 2 Test compressor Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 y Fig. 3 Bypass. holes X 802 \ / / Inner / Fig. 4 Tip leakage of a scroll compressor Fixed Scroll Orbiting Scroll Fig. 5 Leakage mode\ of a tip sea\ Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 ot i j I rbtc hts 0 tsb hw Outer 803 i9 "'E ~ Ol ~ ~ ::;, UJ UJ Q) 0:: E .s J:: 0, c Q) --' Q) Ol "' -"'. "' Q) --' Q_ F "2 fn 6 Q) n; ~ Q LL UJ (f) ro 2 30 25 =~~;~ • -A-Pup21 ... 20 -+-Pup24 • • 15 ·------10 _________ ... ____________ ... 5 ______ ... ... 0 720 810 900 990 Orbiting Angle ( o ) Fig. 6 Pressure condition 100 80 ·~ -~ 60 ·~ 40 • 20 0 720 810 900 990 Orbiting Angle ( o ) Fig. 8 Tip leakage length condition 0.25 0.20 0.15 0.10 0.05 0.00 1.0 -L>-Cf60E 6=720" -o-Ct37E Pdn=5 -<>-C6037E Tup=90 /~ -A-Cf60S -•-Ct37S /~/ -•-C6037S . ~· !~~ -----· ... . --===~~ . ...---------1.5 2.0 2.5 3.0 Pressure Ratio 100 80 A-A A---A :;: 60 !'l ·-· ·---· c [!! "' 40 (I) ·-· ·---· u Q_ -•-CI37 F 20 -e-Ct52 -A-C!73 0 630 720 810 900 990 1080 Orbiting Angle ( o ) Fig. 7 Tip clearance condition 1.0 coil.avr = 0.470/o 0.8 ~ <= 0.6 0 ~ c Q) 0.4 0 c 0 0 0 0.2 0.0 2 3 Measuring Number Fig. 9 Measured oil concentration 0.8 I -o-CfAE 'i'=~---•-etAS 0.6 -L>-CtAE : y~ "2 -A-etAS .E --o--CtBE 0, •~•r~~ 6 -·-CtBS Q) 0.4 ··'\/- CtCE ~ ·- jk~"\ ;;: - ... -ctCS 0 iL UJ 0.2 9=1080" UJ ro Pu=21 2 Tu=OO 3.5 0.0 0.0 0.2 0.4 I 0.6 0.8 1.0 Pressure Ratio Fig. 11 Theoretical and experimetal resu It of tip Fig. 10 Theoretical and experimental result of tip leakage with pressure ratio leakage with pressure ratio at each tip clearance Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 804 5 ::;;;: 4 Ol 0 c ro rn 3 Ol u 0 ro 2 c 0 ·-·~-~·-· 0 ro <ll Cf) a. i= 0 1.0 1.5 2.0 2.5 3.0 3.5 Pressure Ratio Fig. 12 Tip seal contact clearance at tip clearance 37f1.m 0.10 . b Ct37E 0.08 ---+-Ct37S c ] 0.06 Q) ·"-······ ~ Ol 1§ 3: 0.04 0 u:: en en ro 0.02 2 0.00 720 810 900 990 Orbiting Angle ( o ) Fig. 13 Experimental result of tip leakage with orbiting angle at tip clearance 37 fl.rn c E a, ~ 2 e? ~ u:: en en ro 2 0.10 .-----------------, -o-Pd18E -6-Pd21E 0.08 -<>-Pd24E -m-Pd18S -.to- Pd21S @I 6 -~-Pd24~~4o~jlt ~~~91~ 0.06 0.04 0.02 720 810 900 990 Orbiting Angle ( o ) Fig. 15 Theoretical and experimental result of tip leakage with discharge pressure at 37 fl.rn 0.20 .------------------, 8.· Ct52E -w-Ct52S 0.00 '---L---~-..1--~---L-~-----'--_J 720 810 900 990 Orbiting Angle ( o ) Fig. 14 Experimental result of tip leakage with orbiting angle at tip clearance 52J1.m c: ] <J) ~ <ll 1§ ~ u:; en en ro 2 0.20 .-------------------, -o-Ct37E -6-Cl52E 0.15 -O-Ct73E -m-Ct37S 0.10 -t!>-Cl52S ~ -~-Ct73S~~ ~--~~ 0---<> ~·-----------6 4>--~------ .to 0.05 Iii 0 !B---t!j~-1!1 0.00 '---'---'---'---~-'---'----'-----' 720 810 900 990 Orbiting Angle ( o ) Fig. 16 Theoretical and experimental result of tip leakage with tip clearance at Pd 21 Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 805 Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USA- July 25-28, 2000 806 

The Characteristics of Tip Leakage in Scroll Compressors for Air Conditioners

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The Characteristics of Tip Leakage in Scroll Compressors for Air Conditioners

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