Simulation and Development of Trans-critical CO2 Rolling Piston Compressor

Transcription

1 Purdue University Purdue e-pubs International Compressor Engineering Conferene Shool of Mehanial Engineering 010 Simulation and Development of Trans-ritial CO Rolling Piston Compressor Yunfeng Chang Xi'an Jiaotong University Bin He Xi'an Jiaotong University Xin Yang Xi'an Jiaotong University Younghan Ma Ingersoll Rand Climate Solutions/Thermo King Follow this and additional works at: Chang, Yunfeng; He, Bin; Yang, Xin; and Ma, Younghan, "Simulation and Development of Trans-ritial CO Rolling Piston Compressor" (010). International Compressor Engineering Conferene. Paper This doument has been made available through Purdue e-pubs, a servie of the Purdue University Libraries. Please ontat epubs@purdue.edu for additional information. Complete proeedings may be aquired in print and on CD-ROM diretly from the Ray W. Herrik Laboratories at Herrik/Events/orderlit.html

2 153, Page 1 Simulation and Development of Trans-ritial CO Rolling Piston Compressor Yunfeng Chang 1, Bin He 1, Xin Yang 1*, Younghan Ma 1 Compressor Institution, Xi an Jiaotong University, Xi an, Shaanxi, China Phone: xinyang371@gmail.om Ingersoll Rand Climate Solutions, Thermo King, Minneapolis, Minnesota, USA. Phone: ABSTRACT Environmentally speaking, of assorted widely-used refrigeration systems, the trans-ritial CO system is one of the potential ompetitors. In this researh, a horizontal semi-hermeti rolling piston ompressor is developed for trans-ritial CO yle. This paper also presents a series of mathematial simulation models to identify the main fators influening ompressor s performane. Based upon onlusions of this simulation, it puts forward several methods for improving design of trans-ritial CO rolling piston ompressor. 1. INTRODUCTION As a kind of natural refrigerants, CO, due to its environmentally benefiial, non-toxi and non-ombustible haraters as well as superior physial properties, has re-aroused extensive onerns. Trans-ritial yle using CO as refrigerant is firstly put forward by Lorentzen G (1994). The main omponents of this losed yle inludes a ompressor, a gas ooler, a regenerator, a throttle valve, an evaporator and a liquid ontainer. A two-stage hermeti CO rolling piston ompressor for heat pump appliation is developed by Masaya Tadano, et al. (000). Haruhisa Yamasaki, et al. (004), optimizes their former design by guiding 1 st stage disharge into shell of ompressor whih superiorly ools the motor. Ooi KT(007)elaborately set up mathematial models for single stage CO rolling piston ompressor, and onduts experiments and leakage analysis. In trans-ritial CO yle, disharge pressure reahes suh a high level that leakage, disharge valve and strength of ompressor omponents beome the major fators impinging its performane. In this paper, mathematial models for two-stage trans-ritial CO rolling piston ompressor are developed to simulate its working proess. With a onsideration of primitive volume variation and valve motion, effet of leakage learane and flow area of disharge valve on ompressor s performane are onluded through this simulation. Aording to the results, the optimal methods of improving design of two-stage CO rolling piston ompressor for trans-ritial yle are put forward. International Compressor Engineering Conferene at Purdue, July 1-15, 010

3 . DEVELOPMENT OF PROTOTYPE COMPRESSOR 153, Page In this researh, a trans-ritial CO rolling piston prototype ompressor is development in horizontal arrangement satisfying requirements on weight, reliability, effiieny and installation. The ompressor s struture is depited in Figure 1. In this onfiguration, CO, after ompressed in the 1 st stage, goes into ompressor shell diretly through disharge valve of 1 st stage to ool down the motor. CO goes through interooler before sution port of the nd stage to derease sution superheat of the nd stage. Finally, high-temperature and high-pressure gas after the nd stage ompression runs out of the ompressor though the nd -stage disharge valve. Figure 1: Struture of designed Trans-ritial Figure : Model of ompression hamber CO Rolling Piston Compressor 3. SIMULATION OF TRANS-CRITICAL CO ROLLING PISTON COMPRESSOR 3.1 Analysis of Physial Model For the onveniene of simulating the working proess of above ompressor, minor fators are simplified and omitted. The fundamental assumption is as follows: 1) any two points in primitive volume are of the same state- the same temperature, pressure, density, enthalpy, entropy et; ) any external effet (the exhange of mehanial energy, heat energy and mass) works on the gas point in primitive volume instantaneously; 3) the flow into and out of primitive volume is regarded as steady adiabati flow, and simulation of heat transfer proedure of ompressor will not be taken into aount; 4) gas pulse in the sution and disharge hamber is not taken into onsideration and the gas pressure and temperature in hamber are onstant, and equal to nominal disharge pressure and temperature respetively; 5) flow through sution and disharge orifie and leakage gap is adiabati steady flow, negleting the kineti and potential energy; 6) oil droplets have no phase transition and are inompressible. International Compressor Engineering Conferene at Purdue, July 1-15, 010

4 153, Page 3 Aording thermodynami theory of variable mass system and adopted volume ontrol analysis method, thermodynami model of the ompressor s working proess ould be set as Figure. Compression hamber is the ontrol volume in this analysis. All the fluid flowing through inlet, outlet and learane ould be reognized as mass exhange between external and ontrol volume 3. Governing Equations 3..1 Energy equations of the ompression hamber: energy equations of sution stroke, ompression stroke and disharge stroke in ompression hamber are uniformly desribed in Equation (1) and (): 1 dms dmd dml dm dq hs h h h 1 m dt dt dt dt dt dt dt h 1 p 1 p h d T T T dt T p 1 h h T T T p 1 dms dq T hs h dp d V dt dt dt h dt h T T 1 1 p p T T (1) () Figure 3: Volume variation in ompression hamber 3.. Equations of primitive volume variation: As is depited in the Figure 3, shaded part A S is the setional area of the sution volume, whih is listed in Equation (3). A 0.5R 0.5r 0.5resin s (3) Where: O1 A r OA e/ r e R l is height of ompression hamber. Sution volume is listed in Equation (4). V s Al Compression and disharge volume is listed in Equation (5). s (4) International Compressor Engineering Conferene at Purdue, July 1-15, 010

5 153, Page 4 0.5r d d 0.5R sin os 0.5esin os, r sin d d dv 0 1 d 0.5r d d 0.5R sin os 0.5esin os, 1 r sin d d (5) Where: 1 0.5aros 1 1, 1 0.5aros State equation of working fluid: To alulate the parameters of working fluid Pent-Robison equation is adopted as Equation (6). at RT p vb v vb b vb 3..4 Motion equation of disharge valve: As is shown in Figure 4, by negleting the effet of visosity and frition, a single degree of freedom motion equation is given in Equation (7) (Zhang JQ, 008). d y 1 p1a 1 pa ZKY0 y dt M (7) v (6) Figure 4: Fore analysis of disharge valve Figure 5: Leakage paths 3..5: Mass exhange equation: Oil-gas mixture flowing into the primitive volume inludes dm s through inlet and dm l1 through the leakage learane. Oil-gas mixture flowing out of the primitive volume inludes dm d through disharge and dm l through the leakage learane. Therefore, mass exhange equation in primitive volume is given in Equation (8). dm dms dmd dml dt dt dt dt (8) Where: mass flow through inlet (dm s ) and outlet (dm d ) is defined by orifie model, and leakage (dm l ) both flowing into and out of primitive volume is defined by plate model. Six leakage paths are onsidered in Figure 5: radial learane between piston and ylinder; learane between piston fae and ylinder head; learane between sliding vane and hute International Compressor Engineering Conferene at Purdue, July 1-15, 010

6 153, Page 5 (onneting disharge and hamber); learane between sliding vane and hute (onneting inlet and hamber); learane between sliding vane and ylinder fae; learane between disharge valve and piston. 4. RESULT AND COMPRESSOR ANALYSIS 4.1 Effet of Disharge Valve Outlet Flow Area on Compressor s Performane Figure 6: P-V diagram of 1 st stage before enlargemen Figure 7: The P-V diagram of nd stage before enlargement Figure 8: The P-V diagram of 1 st stage after enlargement Figure 9: The P-V diagram of nd stage after enlargement Prototype ompressor is designed where disharge pressures are 8.7MPa and 1MPa for 1 st and nd stage. However, as is revealed in Figure 6 and Figure 7, when the diameter of disharge valve s flow area is 3mm, the maximum disharge pressure is 10MPa and 14MPa, and disharge energy loss of lower and higher pressure stages are 4.5% and 37.5% of the total indiated power. This would harm both volumetri and adiabati effiienies of prototype ompressor. Aording to Figure8 and Figure 9, a 4mm diameter of disharge valve s flow area ould assure an obvious improvement. Disharge energy loss of lower and higher pressure stages are redued to 9.% and 13.3%. Indiated power of eah stage delines to 7.3% and 1.8%, and adiabati effiienies inrease from 84% and 68.4% to 91.7% and 87.8%. Therefore, the diameter of disharge valve flow area signifiantly influenes ompressor s performane. 4. Effet of Leakage Clearane on Compressor s Effiieny International Compressor Engineering Conferene at Purdue, July 1-15, 010

7 153, Page 6 Figure 10: Mass flow of 1 st stage under different leakage learane dimensions Figure 11: Indiated power of 1 st stage under different leakage learane dimensions Figure 1: Volumetri and adiabati effiienies of 1 st stage under different leakage learane dimensions Figure 13: Mass flow of nd stage under different leakage learane dimensions Figure 14: Indiated power of nd stage under different leakage learane dimensions Figure 15: Volumetri and adiabati effiienies of nd stage under different leakage learane dimensions The leakage of CO in ompressor is diretly determined by learane dimension of leakage paths. International Compressor Engineering Conferene at Purdue, July 1-15, 010

8 153, Page 7 Under design onditions, all the leakage learane dimensions are uniformly set to be 3m, 4m, 5m, 6m, 8m and 10m for simplifying ompressor simulation. As is depited in Figure 10~Figure 15, indiated power and mass flow of eah stage of the CO ompressor obviously diminish aording with inreasing learane dimension, beause inreasing learane dimension is apable to aggravate leakage of CO and lubriating oil. However, due to the high rotational speed of motor, volumetri and adiabati effiienies of this ompressor derease slightly. Therefore, appropriately reduing learane dimension of leakage paths ould effetively improve ompressor s performane. Figure 16 and Figure 17 are the umulative leakages of 1 st and nd stage in one omplete stroke. Positive and negative leakage values respetively represent working fluid leaking into and out of ompression hamber. As is depited in Figure 16, in lower pressure stage, more mixture of CO and lubriating oil leaks into ompression hamber through 3 rd and 4 th leakage paths (learanes between sliding vane and hute) than any others. As in Figure 17, in higher pressure stage, 4 th (learane between sliding vane and hute onneting inlet and hamber) and 6 th (learane between disharge valve and piston) leakage paths are the most serious hannels through whih most working fluid leaks out of ompression hamber. Through other leakage paths, little working fluid ould leak into or out of ompression hamber and seriously derease ompressor s performane. Therefore, in order to optimize design of prototype ompressor to enhane its performane, the learane between sliding vane and hute, as well as the learane between disharge valve and piston, should be diminished. Other leakage paths should not be required to be over-preisely proessed and manufatured, as long as their tolerane and fit are guaranteed. From the analysis above, minimizing learane dimension of 3 rd, 4 th and 6 th leakage paths would be the most important method of improving ompressor s performane. Figure 16: Cumulative leakage of 1 st stage in one yle Figure 17: Cumulative leakage of nd stage in one yle 5. CONCLUSIONS This paper analyzes proedure of ompression and major fators that effet ompressor s performane. In this simulation, primitive volume variation and leakage learane dimension are onsidered aording to ompressor s working proess; a dynami model for disharge valve is developed. Therefore, newly developed model enables more preise simulating results. International Compressor Engineering Conferene at Purdue, July 1-15, 010

9 153, Page 8 Aording to the simulation of prototype ompressor, the 3 rd and 4 th leakage paths of 1 st ompression stage and 4 th and 6 th leakage paths of nd ompression stage signifiantly influene CO rolling piston ompressor s performane. Minimizing learane dimensions of these paths ould effetively inrease its apability. However, dereasing learane dimensions of other learane would ontribute little for optimization. Flow resistane of disharge valve, rather than any other fators, plays important role in augment of indiated power. Appropriate enlargement of diameter of disharge valve s outlet ould obviously improve adiabati effiieny of this trans-ritial CO rolling piston ompressor. NOMENCLATURE K spring stiffness N/m Subsripts M v mass of valve plate (g) ad isentropi proess Q heat transfer quantity (J) state in the ompression hamber T temperature (K) s sution V volume (m 3 ) d disharge Y 0 preload position of valve plate (m) l leakage Z number of spring 1 valve inlet h enthalpy (kj/kg) valve outlet m mass (g) p pressure (Pa) t time (s) v speifi volume (kg/m 3 ) y valve plate lift (m) thrust o-effiieny ad v adiabati effiieny volumetri effiieny density (kg/m 3 ) REFERENCES Lorentzen G, 1994, Revival of arbon dioxide as a refrigeran. Int. J. of Refrigeration, vol. 17, no 5: P Tadano M, Ebara T, Oda A, et al, 000, Development of the CO hermeti ompressor. Pro. ICEC, Purdue, USA. Yamasaki H, Yamanaka M, Matsumoto K, et al, 004, Introdution of Transritial Refrigeration Cyle Utilizing CO as Working Fluid. Pro. ICEC, Purdue, USA. Ooi KT, 008, Assessment of a rotary ompressor performane operating at transritial arbon dioxide yles. Applied Thermal Engineering, vol.8, no.10: p Zhang JQ, He B, Chang YF,et al. Study on high performaneinlet and disharge valves of linear mopressor. Pro. 6 th ICCR, Xi an Jiaotong University: p ACKNOWLEDGEMENT The work desribed in this paper is finanially supported by Ingersoll Rand Climate Solutions/Thermo King, Minneapolis, Minnesota, USA. International Compressor Engineering Conferene at Purdue, July 1-15, 010