Analysis of Novel Compression Concepts for Heat Pumping, Air Conditioning and Refrigeration Applications

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1 Oklahoma State University Seminar Presentation Analysis of Novel Compression Concepts for Heat Pumping, Air Conditioning and Refrigeration Applications Dr.-Ing. Eckhard A. Groll Reilly Professor of Mechanical Engineering Director of the Office of Professional Practice Purdue University Ray W. Herrick Laboratories West Lafayette, Indiana 47907, USA Phone: ; Fax: Slide 1

2 Contents Introduction Modeling of Compressors Rotating Spool Compressor S-RAM Compressor Bowtie Compressor Z-Compressor Linear Compressor Slide 2

3 Introduction Overview of Refrigeration Compressors Compressor Types Positive Displacement Compressors Dynamic Compressors Reciprocating Compressors Rotary (Rotational Piston) Compressors Orbital Compressors Axial Flow Machines Radial Flow Machines Rolling Piston Compressor Rotary (Sliding) Vane Compressor Screw Compressor Scroll Compressor Trochoidal Compressor Single Shaft: Single-Screw Compressor Double Shaft: Twin-Screw Compressor Slide 3

4 Introduction Range of Applications of Compressors Cooling Capacity Domestic Refrigerators & Freezers Automotive Air Cond g Room Air Conditioners Unitary Air Conditioners & Heat Pumps Commercial Air Cond g & Refrigeration Large Air Conditioning Fractional Reciprocating 200 kw (50 tons) Fractional Rotary 10 kw (3 tons) 5 kw (1.5 tons) 70 kw (20 tons) Scroll 150 kw (40 tons) 1500 kw (400 tons) Screw 350 kw (100 tons) and up Centrifugal Slide 4

5 Introduction Motivation for New Compression Concepts Political and economic concerns» Global warming» Ozone depletion» Increased competition Technological advances» New working fluids» New design and manufacturing capabilities» New applications Slide 5

6 Introduction Overview of Refrigeration Compressors Compressor Types Positive Displacement Compressors Dynamic Compressors Reciprocating Compressors Rotary (Rotational Piston) Compressors Orbital Compressors Axial Flow Machines Radial Flow Machines Rolling Piston Compressor Rotary (Sliding) Vane Compressor Screw Compressor Scroll Compressor Trochoidal Compressor Single Shaft: Single-Screw Compressor Double Shaft: Twin-Screw Compressor Slide 6

7 Contents Introduction Modeling of Compressors Rotating Spool Compressor S-RAM Compressor Bowtie Compressor Z-Compressor Linear Compressor Slide 7

8 Modeling of Compressors: Underlying Principles Compressor modeling relies on many engineering disciplines:» Thermodynamics e.g.: Changes in refrigerant properties» Fluid mechanics e.g.: Flow of refrigerant in chambers and flow passages» Solid mechanics e.g.: Forces acting on valves and the resulting deformations» Electrical engineering e.g.: Conversion of electrical energy to mechanical energy in a motor» Chemical engineering e.g.: Unwanted decomposition of refrigerant and oil Slide 8

9 Modeling of Compressors: Process Dynamics Compressor modeling relies on understanding of various time scales inside the compressor Motor current and voltage Motor angular velocity Load on shaft Valve movement Refrigerant pressure Ambient temperature Temperature of suction gas Component temperature Valve opening & closing ns s ms s ks Time scale Slide 9

10 Modeling of Compressors: Model Flow Chart Slide 10

11 Modeling of Compressors: Compression Process Equations Conservation of Mass and Energy» Combined mass and energy balance can be solved in series for dρ/dθ and dt/dθ: (properties) (leakage) (geometry) (heat transfer) d 1 dv 1 min d V d m out dt d dv u 1 h uv V Q m h d m h u V T in in out out Slide 11

12 Modeling of Compressors: Modeling Approach Schematic of energy flows inside a hermetic compressor Q rad,dis,shell T suc T evap T super T gas T cyl,in Q rad,wall,shell T cyl,out Tdis Given values T amb Q shell,amb Q rad,shell,amb T shell T wall Q wall,gas Q gas,shell Q friction loss T gas Q motor loss Q oil,shell W comp mech W shaft Q oil,gas motor T oil Q dis,gas : friction model : motor map W elec RPM Slide 12

13 Contents Introduction Modeling of Compressors Rotating Spool Compressor S-RAM Compressor Bowtie Compressor Z-Compressor Linear Compressor Slide 13

Rotating Spool Compressor: Design Motivation: Achieve competitive compressor performance at significantly reduced manufacturing costs Introduced by

14 Rotating Spool Compressor: Design Motivation: Achieve competitive compressor performance at significantly reduced manufacturing costs Introduced by Kemp et al. (2008, 2010) Performance data presented by Orosz et al. (2012) Model(s) presented by Bradshaw et al. (2013) and Bradshaw, C.R. (2013) Slide 14

15 Rotating Spool Compressor: Design Slide 15

Rotating Spool Compressor: Features Four major components with simple geometry for reduced manufacturing cost Leakage Paths Spool face motion nearly

16 Rotating Spool Compressor: Features Four major components with simple geometry for reduced manufacturing cost Leakage Paths Spool face motion nearly eliminates frictional and leakage losses between the vane and face Active sealing elements allow for creative solutions to minimize leakage and friction Slide 16

17 Rotating Spool Compressor: Geometry Slide 17

18 Rotating Spool Compressor: Model Validation Volumetric Efficiency Power Consumption Slide 18

19 Rotating Spool Compressor: Design Optimization Volumetric Efficiency Discharge Temperature Slide 19

20 Rotating Spool Compressor: Performance of 6 th Gen. Prototype Volumetric Efficiency Overall Isentropic Efficiency Data of Latest Prototype Spool Compressor, 141 kw (40 ton) Orosz, J., Bradshaw, C.R., Kemp, G., and Groll, E.A., Updated Performance and Operating Characteristics of a Novel Rotating Spool Compressor, Proc. 23 rd Int l Compr. Eng. Conf. at Purdue, Paper 1377, Purdue Univ., W. Lafayette, IN, July 11-14, 2016 Slide 20

21 Rotating Spool Compressor: Summary Latest generation prototype achieves competitive volumetric and energy efficiencies Manufacturing cost much lower than scroll compressors Size range comparable to reciprocating compressors Commercialization interaction with multiple compressor manufacturers Concept shows good performance as an expander in ORC applications Slide 21

22 Contents Introduction Modeling of Compressors Rotating Spool Compressor S-RAM Compressor Bowtie Compressor Z-Compressor Linear Compressor Slide 22

23 S-RAM Compressor: Overview High-efficiency mechanism to convert rotary shaft motion into piston reciprocating motion Can mechanically change displacement independent of speed No VFD 35+ patents issued since the first patent in 2000 ( Slide 23

(CO 2 at 0 o C) Advantages» Oil free» Less frictional power loss» Variable

24 S-RAM Compressor: CO 2 Compressor Specifications Characteristics» Suction Volume: 345 cm 3» Nominal Flow Rate: ~30 m 3 /hr at 1500 rpm» Nominal Capacity: 100 kw (CO 2 at 0 o C) Advantages» Oil free» Less frictional power loss» Variable capacity control (25% to 100%) (constant clearance volume above the piston top!) Slide 24

25 S-RAM Compressor: Kinematics Model Piston Displacement/Velocity/Acceleration Slide 25

26 S-RAM Compressor: In-Cylinder Process Model Effect of discharge pressure P-V diagram In-cylinder refrigerant temperature Slide 26

27 S-RAM Compressor: In-Cylinder Process Model Valve Models Slide 27

28 S-RAM Compressor: In-Cylinder Process Model Effect of stroke-to-bore ratio Instantaneous refrigerant leakage through clearance between piston assembly and cylinder wall Instantaneous heat transfer between in-cylinder refrigerant and cylinder wall Slide 28

29 S-RAM Compressor: Predicted Efficiencies Effect of stroke-to-bore ratio Volumetric Efficiency: vol m V Nn suc 0 Compressor displacement volume Number of cylinders Compressor speed Yang, B., Kurtulus, O., and Groll, E.A., An Integrated Model for an Oil Free Carbon Dioxide Compressor Using Sanderson-Rocker Arm Motion (S-RAM) Mechanism, Proc. 23 rd Int l Compr. Eng. Conf. at Purdue, Paper 1336, Purdue Univ., W. Lafayette, IN, July 11-14, 2016 Slide 29

30 S-RAM Compressor: Summary Oil-free compression provides large application range Variable capacity control while keeping clearance volume constant gives high performance at different operating conditions Competitive compressor performance at different pressure ratios Future Work:» Frictional power loss analysis» Global energy balance analysis» Validation of model predictions Slide 30

31 Contents Introduction Modeling of Compressors Rotating Spool Compressor S-RAM Compressor Bowtie Compressor Z-Compressor Linear Compressor Slide 31

Bowtie Compressor: Overview Motivation: Provide mechanical capacity control without changing clearance volume» Avoid re-expansion losses associated with the increased clearance volumes

32 Bowtie Compressor: Overview Motivation: Provide mechanical capacity control without changing clearance volume» Avoid re-expansion losses associated with the increased clearance volumes in many capacity control solutions» Based on Beard-Pennock variable-stroke compressor» Blade reciprocates axially instead of linearly» Cylinder can move in direction of springs Slide 32

33 Bowtie Compressor: Basic Geometry Slide 33

34 Bowtie Compressor: Prototype Design Leakage passages:» Through the radial clearance» Over the vane» Between the side vane and the journal shaft» Between the journal bearing and the journal shaft» Between the top vane and the journal shaft 3 mleak,03 4 mleak,04 5 mleak,05 2 mleak,02 1 mleak,01 Slide 34

35 Mass Flow Rate (lbm/hr) Bowtie Compressor: Model Validation Power Input (W) Mass Flow Rate Power Consumption T cond =43.3 o C,Map T cond =43.3 o C,Model T cond =48.9 o C,Map T cond =48.9 o C,Model T cond =54.4 o C,Map T cond =54.4 o C,Model T cond =43.4 o C,Map T cond =43.4 o C,Model T cond =48.9 o C,Map T cond =48.9 o C,Model T cond =54.4 o C,Map T cond =54.4 o C,Model Evaporating Temperature ( o C) Evaporating Temperature ( o C) Slide 35

36 Overall Isentropic Compressor Efficiency (%) Bowtie Compressor: Design Optimization Compressor Mass Flow Rate (g/sec) Overall Isentropic Compressor Efficiency (%) Use model to optimize clearance dimensions and ratio of vane radius to height Friction losses dominate Leakage losses dominate Clearance ( m) Mass Flow Rate, Swept Angle = o Mass Flow Rate, Swept Angle = o o.s.c, Swept Angle = o o.s.c, Swept Angle = o Maximum performance Ratio of Vane Radius and Height Slide 36

37 Mass Flow Rate (g/sec) Bowtie Compressor: Performance Results Overall Isentropic Compressor Efficiency(%) Motor Efficiency (%) Modeled results for compressor at 54.4ºC condensing, -23.3ºC evaporating and 32.2ºC suction temperature: % -9.2% -20.6% -52.0% -42.8% -4.3% -31.4% Mass Flow Rate o.s.c -17.5% Tecumseh Compressor Recipro. Compressor Motor Model Map (TP1390) Swept Volume (cm 3 ) Shaft Power (W) Slide 37

38 Bowtie Compressor: Summary Overall isentropic efficiency only drops from 60 to 50% when suction volume is reduced from 4.70 cm 3 to 3.04 cm 3 (almost 50% decrease) Change in overall isentropic efficiency could be significantly less if appropriate electric motor is used Feasible, lower-cost alternative to electronic variable speed compressor for domestic refrigerator/freezer Current interest by German Company in electronic cabinet cooling using reversed Brayton cycle. Slide 38

39 Contents Introduction Modeling of Compressors Rotating Spool Compressor S-RAM Compressor Bowtie Compressor Z-Compressor Linear Compressor Slide 39

Z-Compressor: Motivation Motivation: Reduce noise and vibration by developing a rotary compressor without an eccentric» Simultaneously compresses two pockets of gas separated by a Z-blade» Z-blade

40 Z-Compressor: Motivation Motivation: Reduce noise and vibration by developing a rotary compressor without an eccentric» Simultaneously compresses two pockets of gas separated by a Z-blade» Z-blade provides continuous variation in chamber volume without eccentric» Cylindrical vane separates suction and compression chambers on each level Upper compression chamber Blade Lower compression chamber Upper suction chamber Lower suction Vane chamber Slide 40

41 Z-Compressor: Basic Geometry Modeling Assumption:» Upper and lower chambers identical, but separated by 180º rotation» Frictional and electric losses rejected to high pressure gas in shell» Shell exchanges heat with ambient» Constant pressure suction Slide 41

42 m model [kg/h] Z-Compressor: Model Validation W model [W] Mass flow rate % -7 % Power input % % m experimental [kg/h] W experimental [W] Slide 42

Z-Compressor: Performance Results m L [kg/h] Lower volumetric efficiency than currently available rolling piston compressors due to increased leakage paths» Between suction

43 Z-Compressor: Performance Results m L [kg/h] Lower volumetric efficiency than currently available rolling piston compressors due to increased leakage paths» Between suction and compression chambers on same level» Between levels» Between chambers and shell Leakage losses (h/d) Paths L6-L9 Paths L4-L5 Slide 43

44 Z-Compressor: Design Optimization W loss [W] Improve volumetric efficiency by reducing mass flow through the most significant leakage path, which is between the Z-blade and cylinder wall» Reduce clearance between z-blade and cylinder Frictional losses increase» Reduce diameter of Z-blade If cylinder height is increased to maintain same chamber volume, leakage around vane increases Average frictional losses Thrust bearing Journal bearing Blade-cylinder Flat region of the blade Comparison of friction losses Contactat various contacts Slide 44

45 Z-Compressor: Design Optimization, cont d Impact of blade-cylinder clearance change on compressor efficiencies Volumetric efficiency Overall isentropic efficiency Piston ring Piston ring v s Reference Reference Blade-cylinder clearance [ m] Blade-cylinder clearance [ m] Slide 45

46 Z-Compressor: Summary Compared to current rotary compressors:» Lower noise and vibration» But also, lower volumetric efficiency Dimensions can be optimized to balance leakage and friction losses for maximum isentropic efficiency Feasible alternative to rolling piston compressor for room and small unitary air conditioners, but higher manufacturing costs Current interest by Canadian company for small-scale air compression application Slide 46

47 Contents Introduction Modeling of Compressors Rotating Spool Compressor S-RAM Compressor Bowtie Compressor Z-Compressor Linear Compressor Slide 47

48 Linear Compressor: Control Volumes Slide 48

49 Linear Compressor: FBD of Piston with EOM Note: both forces act through centroid xk p gas k ( x ) mech p M, p J CG F drive xc p eff x M x c x ( k k ) x k F p p eff p gas mech p mech drive J k k x 2 CG mech mech p (Inertial) (Damping) (Stiffness) (Coupling) Slide 49

50 Linear Compressor: Stroke Control/Friction Factor Impact of dead volume and dry friction factor on efficiencies Volumetric Efficiency Overall Isentropic Efficiency Slide 50

51 Linear Compressor: Capacity Control Variable stroke can be utilized to generate variable capacity By assuming 10 C subcooling at the condenser outlet, a cycle can be simulated A linear compressor provides high performance over wide capacity ranges System COP and 2 nd Law Effectiveness Slide 51

52 Linear Compressor: Comparison to Reciprocating Compr. All else constant, vary net dead volume by increasing x dead Simulates a variable stroke compressor As dead volume increases the recoverable energy increases The mechanical springs act as capacitance, allowing energy to be recaptured that would otherwise be lost Overall Isentropic Efficiency Slide 52

Linear Compressor: Final Design 200 W cooling capacity Replaced compression springs with planar springs Moved location of mechanical springs New linear bearing

53 Linear Compressor: Final Design 200 W cooling capacity Replaced compression springs with planar springs Moved location of mechanical springs New linear bearing selection Key Compressor Dimensions and Predicted Performance k mech f g V d f res x/d vol o,is N/m - m cm cm 3 Hz Slide 53

54 Linear Compressor: Summary Linear compressors are the highest performing compressors on the market Only two commercial products available» Embraco and LG» Both are for refrigerator-freezer application Research interest focuses on scaling to larger capacities Slide 54

55 Thank you! Slide 55

Updated Performance and Operating Characteristics of a Novel Rotating Spool Compressor

Updated Performance and Operating Characteristics of a Novel Rotating Spool Compressor Joe Orosz Torad Engineering Cumming, Georgia Greg Kemp Torad Engineering LLC Cumming, Georgia Craig R. Bradshaw, PhD