Linear Compressors for Clean and Specialty Gases

Size: px
Start display at page:

Download "Linear Compressors for Clean and Specialty Gases"

Transcription

1 Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1998 Linear Compressors for Clean and Specialty Gases R. L. Unger Sunpower Inc. Follow this and additional works at: Unger, R. L., "Linear Compressors for Clean and Specialty Gases" (1998). International Compressor Engineering Conference. Paper This document has been made available through Purdue e-pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu for additional information. Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at Herrick/Events/orderlit.html

2 LINEAR COMPRESSORS FOR CLEAN AND SPECIALTY GASES Reuven Z. Unger Sunpower, Inc. PO Box 2625, Athens, OH USA Phone: Fax: ABSTRACT Advancements in linear compressor technology and reliability now allow potential applications to include compression of clean and specialty gases as well as refrigeration. Configurations that use a gas bearing system and require no oil in their operation are especially appropriate for specialty gases. Such configurations overcome the life limitation and maintenance issues of the contacting piston seal designs of existing compressors. Linear compressors that combine gas bearings and oil-less operation with the ability to modulate capacity or flow rate have special potential for applications in the medical and chemical industries. Recent work is demonstrating prototypes with reliable non-lubricated (oil-less) operation and the likelihood oflong life. This report presents examples of several different linear compressor designs and their widely divergent applications. These linear compressors include machines with a compression ratio up to 26:1 in a single stage, and up to several kw in input power. With this range of compression ratios and power, it appears likely that linear compressors can meet a wide range of industrial and commercial needs. INTRODUCTION A linear compressor is a piston-type compressor in which the piston is driven directly by a linear motor, rather than by a rotary motor coupled to a conversion mechanism as in a conventional reciprocating compressor. Linear motors are simple devices in which axial forces are generated by currents in a magnetic field. Because all the driving forces in a linear compressor act along the line of motion, there is no sideways thrust on the piston, substantially reducing bearing loads and allowing the use of gas bearings or low viscosity oil. Additional background on the origin and development oflinear compressors has been presented elsewhere (Refs. 1, 2, 3, 4). COMPONENTS Gas (Fluid) Bearings: The gas bearing system is an arrangement of pneumatic passages that allow a metered amount of gas to flow into the clearance seal area. This gas acts as a cushion to prevent contact between the piston and the cylinder. The gas bearing system is fed from the high-pressure side of the process. The typical power consumption of the gas bearing system is I to 2% of the input power. Linear Motor: The linear motor is a moving magnet type and characterized by an electromagnetic coupling constant Ci (units ofvolt*secondlm or Newton/amp), inductance and resistance. The value of Ci is constant as long as the magnet remains within the boundaries of the lamination poles. (Refs.5, 6, 7). Assembly of the linear motor magnets becomes cost effective with the aid of a magnet ring support system (Ref. 8). This is a structurally sound, low loss construction for the device holding the magnets in the air gap of a linear motor. Valves: Lack of lubricant effects valve dynamics and sealing properties. In oiled machines, oil satisfies the requirements for surface lubrication, damping between moving parts, and sealing. The disadvantage of oiled valves is in the need to overcome oil-induced stiction. In any reciprocating compressor, the typical valve configuration is a single flapper type for suction and discharge. The linear compressor has an inherent simplified mechanical arrangement with easy access to the backside of the piston, pennitting the use of axial flow. The suction valve can therefore use the piston face as the valve seat. The discharge valve is mounted on the valve plate. Advantages of the arrangement include: + Reduction in heat transfer between suction and discharge. The suction gas flows from the back of the compressor through the piston into the compression space and is discharged forward through the valve plate. + Increased flow area. The piston area can be used for ports, greatly increasing the flow area and reducing flow loss. 51

3 + The backside of the piston can be used as a muffler to reduce the sound generated by the suction process. We have not experienced degradation in performance due to valve-seat wear problems during performance and life testing. Extensive life tests will determine long-term stability and resistance to wear. Compliance: A compliant member is combined with fluid bearings and planar springs in a unique combination. The arrangement uses planar springs to resonate the piston at or near the operating frequency and to position the piston at the approximate center of the cylinder. The compliant member is located between the piston and an axially compliant spring. The anti-friction fluid bearings fme-tune the position of the piston by applying lateral centering forces such that the piston reciprocates linearly, virtually without friction. The combination of features permits easily achievable machining tolerances, simple assembly, and little or no wear on moving and adjacent components. (Ref. 9) OPERATION Dynamics: The free piston linear compressor provides the designer a great deal of flexibility for a wide range of working conditions. Because of the non-linear behavior of the gas spring, there is more than one dynamic mode of operation. This is particularly true for high compression ratio machines. In practice, to minimize the force required from the motor, the moving mass is resonated through a mass-spring combination, and designed such that the natural frequency will be close to the operating frequency. Part of that spring is the gas spring created by compression expansion processes. The gas spring is non-linear and subject to change as the cycle conditions vary; this in turn moves the natural frequency away from the initial conditions. To minimize those effects, mechanical springs are added along with an additional reciprocating mass. The result is a more stable but heavier machine, which produces stronger vibrations. The designer, of course, has to optimize these spring-mass trade-offs Controls: Varying both the stroke amplitude and mean position of the piston creates tight requirements for the controls. When the application calls for a low compression ratio, re-expansion volume (dead volume) has a small effect on flow rate and efficiency. In this case, the compressor can be designed and constructed with sufficient clearance at top dead center (TDC) for operation without collisions. With high compression ratios, clearances at TDC must be minimized, and the gas spring is highly non-linear over each operating cycle. This combination imposes severe requirements on the compressor control system. Different methods have been developed and implemented, using a dedicated position sensor (Ref. 10), or using the motor as sensor either for position or stroke control (Refs. II, I2). Some of these techniques are described in Ref. 7. Heat Management: Lack of oil introduces a difficulty in heat removal if the compressor is mounted through soft springs into the pressure vessel. Adequate heat removal is crucial when permanent magnets are part of the motor. One potential solution is a dedicated cooling loop. In this configuration, a secondary liquid is directed into the pressure vessel compressor assembly to absorb the heat from the compressor and transport and reject it outside. Another option is a "tight shell configuration," in which the compressor is hard-mounted to the pressure vessel. Heat flows from the compressor to the pressure vessel, and then to ambient air. The overall configmation can be smaller since there is no need for space between the compressor and the pressure vessel. The "tight shell configuration" does tend to increase noise and vibration levels. APPLICATIONS Below we present four separate linear compressors and their applications. The basic linear compressor technology as outlined above is used throughout all designs. Efficiencies, therefore, fall in similar ranges. The nature of the application, power level and system requirements influence the arrangement of the different components for any single compressor design. Differences in valve design and placement cause differences in flow management. Two of these compressors have been produced as hardware and used for extensive qualification and testing. Clean Air Compressor: in hardware The clean air compressor was designed to work at relatively low compression ratios and can be used in laboratory, medical, or chemical applications. Qualifications particularly relevant to these needs are the fact that it is oil-less, 52

4 ----'-, _,_IV-/A--, modulatable and highly efficient. Several variants of this application have been designed, constructed and tested. Some of these prototypes have demonstrated high reliability and life tests of over 24,000 hours with no degradation in performance. Figures 1 and 2 present the performance of the linear air compressor and a comparison between the linear and two production compressors A and B. The comparison is presented in a normalized flow ofliters per :Limn' Air Corq:ressor ~P-~--~--~--~--~--~~! I I I I 3~~--~~,--~~~~==~~--~~ --~~--~~~~ I 'i I ~~= f---1 2~ I : I I / 200 ~ I~ ,, - 1! L : I~~ I I /--,--"' ! ---+,--+--~---1 ~ ,...""-_..-/T----::!:---:±' :------':::-' ----±1----:::: ~ ~ ,:, :---+i i',1_-1 i I 1 0~ ~ Pressure (p;ig) Fig. 1. Input power of linear (free-piston) compressor over a range of pressure requirements I " 1.0,...---,...--~-~-~ ' ~...-' '-----~ -+--I..inear 0.7 t----'------'1± h... ~A! '----'---" ;_-~1 - '1\-. O:np' B = 0.5 t t:: ,-----f ~ " "i: 0.4 t-----i "'., ~ ::::i 0.3 t----'---..,.~..,-,< '----f : ~~--~ t ~ :..-..: IS Pressure (rsig) Fig. 2. Efficiency oflinear (free-piston) and two conventional, commercially available compressors minute per Watt of input power, vs. pressure. Flow rate can be maintained at a constant rate over a range of pressures (5 to 30 psig) (Figure 1). Efficiency exceeds that of conventional compressors throughout this range, and is notably higher in the lower pressure ranges (Figure 2). Fig. 3. Clean Air Compressor (back cover removed, two views). 53

5 Compressor Motor Motor Piston Seal Dnving Bearing Type Type efficiency Mechanism System Recip' Induction 70-80% Rings I Crank Shaft Oil/Grease Diaphragm Connecting Rod lubricated Linear Permanent Magnet 90% Clearance Direct Coupling Gas-Bearings Table 1. Characteristics of conventional (reciprocating, rotary) and linear compressor Specialty Gas Compressor: in hardware For some applications, compressed gas produced by lubricated refrigeration-type compressors can be adequately cleansed of oil residues. However, for systems with delicate gas passages or in cryogenic applications, the system can become blocked or contaminated by residues of oil, with performance degradation or system failure. The linear, oil-free specialty gas compressor should be able to provide the required compression and avoid the introduction of contaminants entirely. To meet this need, an oil-less compressor with a 26:1 compression ratio was constructed and tested. This compressor delivers a special mixture of gases from a low side of above atmospheric pressure and discharges it at higher then 28 bar. The single piston configuration required special attention to seal properties, thermal expansion, and material compatibility. Also, special consideration was needed in dealing with the highly non-linear gas spring and sophisticated piston control. The system has performed successfully in reliability tests, is currently in beta testing, and is being prepared for production. The machine (Figure 3) operates at We input level and is mounted inside the pressure vessel on soft springs. This mounting arrangement is very similar to those in conventional refrigeration compressors, and provides sufficient vibration isolation, but complicates heat removal from the compressor to the outside. Fig. 4. Special Gas Compressor (without pressure vessel), 26:1 Compression Natural Gas Compressor: in design stage With the deregulation of utilities, there will be a significant market for distributed power generation ( kw) that can supply electricity and heat directly to end-users. One such distributed power generation system is a micro- 54

6 turbine using natural gas as fuel. Full development and market use of micro-turbines has been limited by past regulatory practice. An essential element of a natural gas-flred micro-turbine system is a gas compressor, which needs to be clean, efficient, and exhibit very low vibration. Figure 5 shows a two piston opposed unit, one means of obtaining the required level of vibration control This machine would be appropriate for use with micro-turbines in the 50 to 75 kw 0 range. 1-S t Suction Dis:cho.rge Suction Fig kw Natural Gas Compressor Valveless compressor (pressure wave generator): in design sta2:e A different use of the oil-less free piston compressor is in the form of pressure generator. In these applications the valves are removed from the compressor. This allows the unit to be coupled into an arrangement such as a pulse tube cooler, a Stirling machine, or any other system requiring a pressure wave generator. These machines typically operate at very low compression ratios (less then 2:1). With the absence of suction and discharge processes, the dynamics approach the ideal of sinusoidal behavior. CONCLUSIONS There is a wide range of possible non-refrigeration applications for the linear compressor. Two applications have been proven in hardware and are moving towards commercialization. Other applications are demonstrated at the design stage. Any of these machines may find applications beyond those suggested here, and numerous other specific designs are feasible. The linear compressor is now proven in a variety of hardware. Its efficiency, modulation, oil-free option, and precise control are features that should make it compete successfully with conventional compressors over a wide range of applications. 55

7 ACKNOWLEDGMENTS The author wishes to express his sincere appreciation for the valuable contributions of Nicholas R. Vander Walt in the development ofsunpower's linear compressors. REFERENCES I. Vander Walt, N.R. and Unger, R. "The Simulation and Design of a High Efficiency, Lubricant Free, Linear Compressor for a Domestic Refrigerator." International Compressor Engineering Conference, July 14-17, Purdue University, West Lafayette, Indiana, USA. 2. Berchowitz, D.M. "Free-Piston Rankine Compression and Stirling Cycle Machines for Domestic Refrigeration." Greenpeace Ozone Safe Conference, October 18-19, Washington, DC. 3. Vander Walt, N.R. and Unger, R. "Linear Compressors- A Maturing Technology." International Appliance Technical Conference, May 9-11, University of Wisconsin. Madison, Wisconsin. 4. Unger, R.Z. and van der Walt, N.R. "Linear Compressors for Non-CFC Refrigeration." International Appliance Technical Conference, May 13-15, Purdue University, West Lafayette, Indiana, USA. Available at 5. U.S. Patent 4,602,174. Issued Electromechanical Transducer Particularly Suitable for a Linear Alternator Driven by a Free-Piston Stirling Engine.. Also patented in Germany, UK, Japan. 6. Redlich, R. "A Summary of Twenty Years Experience with Linear Motors and Alternators." Distributed at Linear Drives for Industry Applications, May 31 - June 2, 1995, Nagasaki, Japan. Available at 7. Redlich, R., Unger, R., and van der Walt, N. "Linear Compressors: Motor Configuration, Modulation and Systems." International Compressor Engineering Conference, July 23-26, Purdue University, West Lafayette, Indiana, USA.. Available at 8. U.S. Patent 5,642,088. Issued Magnet Ring Support. Patents pending in Australia, Brazil, EPO, Japan, South Korea, Mexico, New Zealand, Singapore. 9. U.S. Patent 5,525,845. Issued Fluid Bearing with Compliant Linkage for Centering Reciprocating Bodies. Also patented in Taiwan, Australia. Patents pending in India, Canada, EPO, Japan, South Korea, Mexico, New Zealand. 10. U.S. Patent 5,592,073. Issued Triac control circuit. Patents pending in Australia, Brazil, EPO, Japan, South Korea, Mexico, New Zealand, Singapore. 11. U.S. Patent 5,342, 176. Issued Method and Apparatus for Measuring Piston Position in a Free Piston Compressor. Also patented in New Zealand, Australia, EPO. Patents pending in Japan, Korea. 12. U.S. Patent 5,496,153. Issued Method and Apparatus for Measuring Piston Position in a Free Piston Compressor. 56

A HIGH PERFORMANCE LINEAR COMPRESSOR FOR CPU COOLING

A HIGH PERFORMANCE LINEAR COMPRESSOR FOR CPU COOLING Presented at the 16 th International Compressor Engineering Conference at Purdue. C23-3 A HIGH PERFORMANCE LINEAR COMPRESSOR FOR CPU COOLING Reuven Unger Shlomo Novotny Sunpower, Inc. Sun Microsystems

More information

New Capacity Modulation Algorithm for Linear Compressor

New Capacity Modulation Algorithm for Linear Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 010 New Capacity Modulation Algorithm for Linear Compressor Jaeyoo Yoo Sungho Park Hyuk

More information

The Simulation and Design of a High Efficiency, Lubricant Free, Linear Compressor for a Domestic Refrigerator

The Simulation and Design of a High Efficiency, Lubricant Free, Linear Compressor for a Domestic Refrigerator Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1992 The Simulation and Design of a High Efficiency, Lubricant Free, Linear Compressor for

More information

Research of the Effectiveness of Use of New Mechanism in Reciprocating Compressors

Research of the Effectiveness of Use of New Mechanism in Reciprocating Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2000 Research of the Effectiveness of Use of New Mechanism in Reciprocating Compressors

More information

Small Oil Free Piston Type Compressor For CO2

Small Oil Free Piston Type Compressor For CO2 Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2002 Small Oil Free Piston Type Compressor For CO2 H. Baumann Baumann Engineering M. Conzett

More information

Comparing FEM Transfer Matrix Simulated Compressor Plenum Pressure Pulsations to Measured Pressure Pulsations and to CFD Results

Comparing FEM Transfer Matrix Simulated Compressor Plenum Pressure Pulsations to Measured Pressure Pulsations and to CFD Results Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2012 Comparing FEM Transfer Matrix Simulated Compressor Plenum Pressure Pulsations to Measured

More information

The Digital Simulation Of The Vibration Of Compressor And Pipe System

The Digital Simulation Of The Vibration Of Compressor And Pipe System Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2002 The Digital Simulation Of The Vibration Of Compressor And Pipe System J. Ling Shanghai

More information

Infinitely Variable Capacity Control

Infinitely Variable Capacity Control Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1972 Infinitely Variable Capacity Control K. H. White Ingersoll-Rand Company Follow this

More information

Characteristic of a Miniature Linear Compressor

Characteristic of a Miniature Linear Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2010 Characteristic of a Miniature Linear Compressor Wen Wang Shanghai Jiao Tong University

More information

Structural Analysis Of Reciprocating Compressor Manifold

Structural Analysis Of Reciprocating Compressor Manifold Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2016 Structural Analysis Of Reciprocating Compressor Manifold Marcos Giovani Dropa Bortoli

More information

Influence of Cylinder Bore Volume on Pressure Pulsations in a Hermetic Reciprocating Compressor

Influence of Cylinder Bore Volume on Pressure Pulsations in a Hermetic Reciprocating Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2014 Influence of Cylinder Bore Volume on Pressure Pulsations in a Hermetic Reciprocating

More information

Elimination of Instability in Modulating Capacity Reciprocating Compressor

Elimination of Instability in Modulating Capacity Reciprocating Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2000 Elimination of Instability in Modulating Capacity Reciprocating Compressor P. Wagner

More information

Development of Highly Efficient Compressor Series Driven by IPM Motors

Development of Highly Efficient Compressor Series Driven by IPM Motors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2 Development of Highly Efficient Compressor Series Driven by IPM Motors T. Obitani Daikin

More information

Investigation of Torque-Fluctuation Reducer Made of Permanent-Magnets for Screw Compressors

Investigation of Torque-Fluctuation Reducer Made of Permanent-Magnets for Screw Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1996 Investigation of Torque-Fluctuation Reducer Made of Permanent-Magnets for Screw Compressors

More information

Development of Scroll Compressor for 16HP VRF System

Development of Scroll Compressor for 16HP VRF System Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2014 Development of Scroll Compressor for 16HP VRF System Fumikazu Nagaoka Mitsubishi Electric

More information

Research And Development Of Variable-Speed Scroll Compressor

Research And Development Of Variable-Speed Scroll Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2002 Research And Development Of Variable-Speed Scroll Compressor H. Li Beijing Polytechnic

More information

A Prototype Oil-Less Compressor for the International Space Station Refrigerated Centrifuge

A Prototype Oil-Less Compressor for the International Space Station Refrigerated Centrifuge Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2000 A Prototype Oil-Less Compressor for the International Space Station Refrigerated Centrifuge

More information

A Two Stage-Double Acting Scroll Air Compressor

A Two Stage-Double Acting Scroll Air Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1994 A Two Stage-Double Acting Scroll Air Compressor Y. Chang X. Ju D. Wang M. Wang Follow

More information

Development of High Efficiency Swing Compressor for R32 Refrigerant

Development of High Efficiency Swing Compressor for R32 Refrigerant Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2014 Development of High Efficiency Swing Compressor for Refrigerant Yuuichi Yamamoto DAIKIN

More information

A New Device to Measure Instantaneous Swept Volume of Reciprocating Machines/Compressors

A New Device to Measure Instantaneous Swept Volume of Reciprocating Machines/Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2004 A New Device to Measure Instantaneous Swept Volume of Reciprocating Machines/Compressors

More information

The Characteristics of LGE Linear Oscillating Motor

The Characteristics of LGE Linear Oscillating Motor urdue University urdue e-ubs International Compressor Engineering Conference School of Mechanical Engineering 010 The Characteristics of LGE Linear Oscillating Motor Sangsub Jeong Wonsik Oh Hyuk Lee Sungman

More information

The Reduction of the Noise/Vibration Generated by the Discharge Valve System in Hermetic Compressor for Refrigerator

The Reduction of the Noise/Vibration Generated by the Discharge Valve System in Hermetic Compressor for Refrigerator Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2000 The Reduction of the Noise/Vibration Generated by the Discharge Valve System in Hermetic

More information

Study of a Novel Compliant Suspension Mechanism in Low Side Type Scroll Compressor

Study of a Novel Compliant Suspension Mechanism in Low Side Type Scroll Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2008 Study of a Novel Compliant Suspension Mechanism in Low Side Type Scroll Compressor

More information

The Design Aspects of Metal- Polymer Bushings in Compressor Applications

The Design Aspects of Metal- Polymer Bushings in Compressor Applications Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2006 The Design Aspects of Metal- Polymer Bushings in Compressor Applications Christopher

More information

Development of DC Inverter Scroll Compressor used for Marine Container Refrigeration Unit

Development of DC Inverter Scroll Compressor used for Marine Container Refrigeration Unit Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2012 Development of DC Inverter Scroll Compressor used for Marine Container Refrigeration

More information

Transient Thermal Analysis of Screw Compressors, Part III: Transient Thermal Analysis of a Screw Compressor to Determine Rotor-to-Rotor Clearances

Transient Thermal Analysis of Screw Compressors, Part III: Transient Thermal Analysis of a Screw Compressor to Determine Rotor-to-Rotor Clearances Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 26 Transient Thermal Analysis of Screw Compressors, Part III: Transient Thermal Analysis

More information

Extending the Operation Range of Dry Screw Compressors by Cooling Their Rotors

Extending the Operation Range of Dry Screw Compressors by Cooling Their Rotors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2004 Extending the Operation Range of Dry Screw Compressors by Cooling Their Rotors Nikola

More information

Noise Reduction of Accumulators for R410A Rotary Compressors

Noise Reduction of Accumulators for R410A Rotary Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2008 Noise Reduction of Accumulators for R410A Rotary Compressors Ling Li Guangdong Meizhi

More information

Theoretical and Experimental Investigation of Compression Loads in Twin Screw Compressor

Theoretical and Experimental Investigation of Compression Loads in Twin Screw Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2004 Theoretical and Experimental Investigation of Compression Loads in Twin Screw Compressor

More information

The Performance Optimization of Rolling Piston Compressors Based on CFD Simulation

The Performance Optimization of Rolling Piston Compressors Based on CFD Simulation Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2004 The Performance Optimization of Rolling Piston Compressors Based on CFD Simulation

More information

Comparison Between Different Arrangements of Bypass Valves in Scroll Compressors

Comparison Between Different Arrangements of Bypass Valves in Scroll Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2008 Comparison Between Different Arrangements of Bypass Valves in Scroll Compressors Yangguang

More information

Abstract. Introduction

Abstract. Introduction Abstract Preliminary Design of a 7 kw e Free-Piston Stirling Engine with Rotary Generator Output James G. Wood, Neill W. Lane and William T. Beale Sunpower, Inc. Athens, Ohio, USA www.sunpower.com A preliminary

More information

Development of High Performance 3D Scroll Compressor

Development of High Performance 3D Scroll Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2006 Development of High Performance 3D Scroll Compressor Taichi Tateishi Mitsubishi Heavy

More information

Linear Compressor Without Position Controller

Linear Compressor Without Position Controller Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 24 Linear Compressor Without Position Controller Kyeong Bae Park LG Electronics Eun Pyo

More information

Spool Seal Design and Testing for the Spool Compressor

Spool Seal Design and Testing for the Spool Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2012 Spool Seal Design and Testing for the Spool Compressor Greg Kemp greg.kemp@toradengineering.com

More information

Reduction of Oil Discharge for Rolling Piston Compressor Using CO2 Refrigerant

Reduction of Oil Discharge for Rolling Piston Compressor Using CO2 Refrigerant Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2006 Reduction of Oil Discharge for Rolling Piston Compressor Using CO2 Refrigerant Takeshi

More information

Twin-Screw Compressor Performance and Suitable Lubricants with HFC-134a

Twin-Screw Compressor Performance and Suitable Lubricants with HFC-134a Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1990 Twin-Screw Compressor Performance and Suitable Lubricants with HFC-134a L. J. Sjoholm

More information

Oil Circulation Rate in Rotary Compressor: Its Measurement and Factors Affecting the Rate

Oil Circulation Rate in Rotary Compressor: Its Measurement and Factors Affecting the Rate Purdue University Purdue e-pubs nternational Compressor Engineering Conference School of Mechanical Engineering 2 Oil Circulation Rate in Rotary Compressor: ts Measurement and Factors Affecting the Rate

More information

Development of a New Type Cylinder Head for Piston Compressors

Development of a New Type Cylinder Head for Piston Compressors Purdue University Purdue e-pubs nternational Compressor Engineering Conference School of Mechanical Engineering 2 Development of a New Type Cylinder Head for Piston Compressors E. Ayder nstanbul Technical

More information

Compressor Noise Control

Compressor Noise Control Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1972 Compressor Noise Control G. M. Diehl Ingersoll-Rand Research Follow this and additional

More information

Development of a Low Noise Rotary Compressor

Development of a Low Noise Rotary Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1996 Development of a Low Noise Rotary Compressor Y. Adachi Toshiba Corporation I. Onoda

More information

CFD Analysis of Oil Discharge Rate in Rotary Compressor

CFD Analysis of Oil Discharge Rate in Rotary Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering CFD Analysis of Oil Discharge Rate in Rotary Compressor Liying Deng haitunsai@.com Shebing

More information

Scroll Expander for Carbon Dioxide Cycle

Scroll Expander for Carbon Dioxide Cycle Purdue University Purdue e-pubs International Refrigeration and Air Conditioning Conference School of Mechanical Engineering 26 Scroll Expander for Carbon Dioxide Cycle Detlef Westphalen John Dieckmann

More information

A Large Modern High Speed Reciprocating Compressor

A Large Modern High Speed Reciprocating Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1998 A Large Modern High Speed Reciprocating Compressor H. H. Van der Linden Grasso Products

More information

An Experimental Analysis on the Flow Rate in Scroll Compressors

An Experimental Analysis on the Flow Rate in Scroll Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1998 An Experimental Analysis on the Flow Rate in Scroll Compressors D. H. Kim LG Electronics

More information

Diesel-Driven Compressor Torque Pulse Measurement in a Transport Refrigeration Unit

Diesel-Driven Compressor Torque Pulse Measurement in a Transport Refrigeration Unit Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 214 Diesel-Driven Compressor Torque Pulse Measurement in a Transport Refrigeration Unit

More information

A Low Friction Thrust Bearing for Reciprocating Compressors

A Low Friction Thrust Bearing for Reciprocating Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering A Low Friction Thrust Bearing for Reciprocating Compressors Shuhei Nagata shuhei.nagata.wq@hitachi.com

More information

A Novel Automotive Two-Stage A/C Compressor

A Novel Automotive Two-Stage A/C Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2000 A Novel Automotive Two-Stage A/C Compressor Y. Huang S. Harte L. Sud V. K. Khetarpal

More information

Numerical Simulation and Performance Analysis of Rotary Vane Compressors for Automobile Air Conditioner

Numerical Simulation and Performance Analysis of Rotary Vane Compressors for Automobile Air Conditioner Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 24 Numerical Simulation and Performance Analysis of Rotary Vane Compressors for Automobile

More information

Developments in Dry Running Seals for Reciprocating Compressors

Developments in Dry Running Seals for Reciprocating Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1996 Developments in Dry Running Seals for Reciprocating Compressors K. Graunke Sulzer-Burckhardt

More information

The Development of a New Generation of Miniature Long-Life Linear Coolers

The Development of a New Generation of Miniature Long-Life Linear Coolers The Development of a New Generation of Miniature Long-Life Linear Coolers W. van de Groep, J. Mullié, D. Willems, F. van Wordragen, T. Benschop Thales Cryogenics Eindhoven, The Netherlands ABSTRACT Thales

More information

Resonance Optimization in Linear Compressor

Resonance Optimization in Linear Compressor Resonance Optimization in Linear Compressor Madhura Sevekari; Prof.Suneeta Phadkule; Dr. Virendra Bhojwani Lecturer, Prof, Dept of Mechanical engg, Prof, Dept of mechanical engg, Dept of mechanical engg,

More information

Performance Improvement of a Reciprocating Air Microcompressor

Performance Improvement of a Reciprocating Air Microcompressor Purdue University Purdue e-pubs International Compressor ngineering Conference School of Mechanical ngineering 1998 Performance Improvement of a Reciprocating Air Microcompressor M. Fujiwara Muroran Institute

More information

Discharge Characteristics of an Oil Feeder Pump Using Nozzle Type Fluidic Diodes for a Horizontal Compressor Depending onthe Driving Speed

Discharge Characteristics of an Oil Feeder Pump Using Nozzle Type Fluidic Diodes for a Horizontal Compressor Depending onthe Driving Speed Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1988 Discharge Characteristics of an Oil Feeder Pump Using Nozzle Type Fluidic Diodes for

More information

Noise Reduction in Bus A/C Systems with Screw Compressors Part II

Noise Reduction in Bus A/C Systems with Screw Compressors Part II Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2008 Noise Reduction in Bus A/C Systems with Screw Compressors Part II Lars I. Sjoholm Thermo

More information

Available online at ScienceDirect. Physics Procedia 67 (2015 )

Available online at  ScienceDirect. Physics Procedia 67 (2015 ) Available online at www.sciencedirect.com ScienceDirect Physics Procedia 67 (2015 ) 518 523 25th International Cryogenic Engineering Conference and the International Cryogenic Materials Conference in 2014,

More information

Reciprocating Air Microcompressor

Reciprocating Air Microcompressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1996 Reciprocating Air Microcompressor M. Fujiwara Muroran Institute of Technology T. Kazama

More information

Experimental Investigation of Damping Coefficient for Compressor Reed Valves

Experimental Investigation of Damping Coefficient for Compressor Reed Valves Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2016 Experimental Investigation of Damping Coefficient for Compressor Reed Valves Sergio

More information

A Practical Guide to Free Energy Devices

A Practical Guide to Free Energy Devices A Practical Guide to Free Energy Devices Part PatD20: Last updated: 26th September 2006 Author: Patrick J. Kelly This patent covers a device which is claimed to have a greater output power than the input

More information

Reduction of Self Induced Vibration in Rotary Stirling Cycle Coolers

Reduction of Self Induced Vibration in Rotary Stirling Cycle Coolers Reduction of Self Induced Vibration in Rotary Stirling Cycle Coolers U. Bin-Nun FLIR Systems Inc. Boston, MA 01862 ABSTRACT Cryocooler self induced vibration is a major consideration in the design of IR

More information

CHAPTER 1. Introduction and Literature Review

CHAPTER 1. Introduction and Literature Review CHAPTER 1 Introduction and Literature Review 1.1 Introduction The Active Magnetic Bearing (AMB) is a device that uses electromagnetic forces to support a rotor without mechanical contact. The AMB offers

More information

Reducing the Fuel Consumption by Speed Control of the Air Conditioning Compressor

Reducing the Fuel Consumption by Speed Control of the Air Conditioning Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 28 Reducing the Fuel Consumption by Speed Control of the Air Conditioning Compressor Rico

More information

Developing a Compact Automotive Scroll Compressor

Developing a Compact Automotive Scroll Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2008 Developing a Compact Automotive Scroll Compressor Fengshou Yi Nanjing Aotecar Refrigeration

More information

SAMPLE STUDY MATERIAL

SAMPLE STUDY MATERIAL IC Engine - ME GATE, IES, PSU 1 SAMPLE STUDY MATERIAL Mechanical Engineering ME Postal Correspondence Course Internal Combustion Engine GATE, IES & PSUs IC Engine - ME GATE, IES, PSU 2 C O N T E N T 1.

More information

A Study On The Oil Supply System Of A Horizontal Rotary Compressor With Vane Utilized For Oil Feeding

A Study On The Oil Supply System Of A Horizontal Rotary Compressor With Vane Utilized For Oil Feeding Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 00 A Study On The Oil Supply System Of A Horizontal Rotary Compressor With Vane Utilized

More information

Theoretical and Experimental Evaluation of the Friction Torque in Compressors with Straddle Bearings

Theoretical and Experimental Evaluation of the Friction Torque in Compressors with Straddle Bearings Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1998 Theoretical and Experimental Evaluation of the Friction Torque in Compressors with

More information

Application of Trunk Piston Labyrinth Compressors in Refrigeration and Heat Pump Cycles

Application of Trunk Piston Labyrinth Compressors in Refrigeration and Heat Pump Cycles Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1992 Application of Trunk Piston Labyrinth Compressors in Refrigeration and Heat Pump Cycles

More information

Transmission Error in Screw Compressor Rotors

Transmission Error in Screw Compressor Rotors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2008 Transmission Error in Screw Compressor Rotors Jack Sauls Trane Follow this and additional

More information

Experimental Study Of The Oil Injection Screw Air Compressor

Experimental Study Of The Oil Injection Screw Air Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2002 Experimental Study Of The Oil Injection Screw Air Compressor Z. Zhang Y. Tan G. Shi

More information

Cooling Enhancement of Electric Motors

Cooling Enhancement of Electric Motors Cooling Enhancement of Electric Motors Authors : Yasser G. Dessouky* and Barry W. Williams** Dept. of Computing & Electrical Engineering Heriot-Watt University Riccarton, Edinburgh EH14 4AS, U.K. Fax :

More information

CFD Simulation of a Scroll Compressor Oil Pumping System

CFD Simulation of a Scroll Compressor Oil Pumping System Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2000 CFD Simulation of a Scroll Compressor Oil Pumping System J. de Bernardi Danfoss Maneurop

More information

The Influence of Discharge Ports on Rotor Contact in Screw Compressors

The Influence of Discharge Ports on Rotor Contact in Screw Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2006 The Influence of Discharge Ports on Rotor Contact in Screw Compressors Nikola Stosic

More information

Verification of Flapper Suction-Va1ve Simulation Program

Verification of Flapper Suction-Va1ve Simulation Program Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1980 Verification of Flapper Suction-Va1ve Simulation Program H. Richardson G. W. Gatecliff

More information

A Study on the Starting Characteristics of a Reciprocating Compressor for a Household Refrigerator

A Study on the Starting Characteristics of a Reciprocating Compressor for a Household Refrigerator Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1996 A Study on the Starting Characteristics of a Reciprocating Compressor for a Household

More information

Long Transfer Lines Enabling Large Separations between Compressor and Coldhead for High- Frequency Acoustic-Stirling ( Pulse-Tube ) Coolers

Long Transfer Lines Enabling Large Separations between Compressor and Coldhead for High- Frequency Acoustic-Stirling ( Pulse-Tube ) Coolers Long Transfer Lines Enabling Large Separations between Compressor and Coldhead for High- Frequency Acoustic-Stirling ( Pulse-Tube ) Coolers P. S. Spoor and J. A. Corey CFIC-Qdrive Troy, NY 12180 ABSTRACT

More information

A Recommended Approach to Pipe Stress Analysis to Avoid Compressor Piping Integrity Risk

A Recommended Approach to Pipe Stress Analysis to Avoid Compressor Piping Integrity Risk A Recommended Approach to Pipe Stress Analysis to Avoid Compressor Piping Integrity Risk by: Kelly Eberle, P.Eng. Beta Machinery Analysis Calgary, AB Canada keberle@betamachinery.com keywords: reciprocating

More information

Numerical Investigation of the Gas Leakage through the Piston-Cylinder Clearance of Reciprocating Compressors

Numerical Investigation of the Gas Leakage through the Piston-Cylinder Clearance of Reciprocating Compressors Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2014 Numerical Investigation of the Gas Leakage through the Piston-Cylinder Clearance of

More information

CHBE320 LECTURE III ACTUATOR AND CONTROL VALVE SELECTION. Professor Dae Ryook Yang

CHBE320 LECTURE III ACTUATOR AND CONTROL VALVE SELECTION. Professor Dae Ryook Yang CHBE320 LECTURE III ACTUATOR AND CONTROL VALVE SELECTION Professor Dae Ryook Yang Spring 2018 Dept. of Chemical and Biological Engineering 3-1 Visit Actuator Road Map of the Lecture III + - Controller

More information

Dynamic Modeling of a Poppet Valve for use in a Rotating Spool Compressor

Dynamic Modeling of a Poppet Valve for use in a Rotating Spool Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2016 Dynamic Modeling of a Poppet Valve for use in a Rotating Spool Compressor Nathaniel

More information

Free-CHP: Free-Piston Reciprocating Joule Cycle Engine

Free-CHP: Free-Piston Reciprocating Joule Cycle Engine PRO-TEM Special Session on Power Generation and Polygeneration Systems Free-CHP: Free-Piston Reciprocating Joule Cycle Engine Rikard Mikalsen, Tony Roskilly Newcastle University, UK Background: micro-chp

More information

SEMA Technology Redundancy Advantages

SEMA Technology Redundancy Advantages SEMA Technology Redundancy Advantages Authored by Kinetic Art & Technology Revised May 11, 2009 Purpose The purpose of this document is to describe some of the advantages of Kinetic Art & Technology's

More information

Stepless Variable Capacity Control

Stepless Variable Capacity Control Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1974 Stepless Variable Capacity Control W. J. Tuymer Hoerbiger Corporation of America Follow

More information

Transient Modeling of Vapor Compression Refrigeration Systems Using Measured Compressor COP

Transient Modeling of Vapor Compression Refrigeration Systems Using Measured Compressor COP Purdue University Purdue e-pubs International Refrigeration and Air Conditioning Conference School of Mechanical Engineering 2004 Transient Modeling of Vapor Compression Refrigeration Systems Using Measured

More information

Design Parameters to Determine Tangential Vibration of Rotary Compressor

Design Parameters to Determine Tangential Vibration of Rotary Compressor Purdue University Purdue e-pubs nternational Compressor Engineering Conference School of Mechanical Engineering 2 Design Parameters to Determine Tangential Vibration of Rotary Compressor. Hwang United

More information

Effects of Refrigerant Injection on the Scroll Compressor

Effects of Refrigerant Injection on the Scroll Compressor Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2006 Effects of Refrigerant Injection on the Scroll Compressor Baolong Wang Xianting Li

More information

Development of Rotary Compressor for Highefficiency CO2 Heat-pump Hot-Water Supply System

Development of Rotary Compressor for Highefficiency CO2 Heat-pump Hot-Water Supply System Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2014 Development of Rotary Compressor for Highefficiency CO2 Heat-pump Hot-Water Supply

More information

Measuring equipment for the development of efficient drive trains using sensor telemetry in the 200 C range

Measuring equipment for the development of efficient drive trains using sensor telemetry in the 200 C range News Measuring equipment for the development of efficient drive trains using sensor telemetry in the 200 C range Whether on the test stand or on the road MANNER Sensortelemetrie, the expert for contactless

More information

YASKAWA AC Drives. Compressor Applications Application Overview

YASKAWA AC Drives. Compressor Applications Application Overview YASKAWA AC Drives Compressor Applications Application Overview This document provides a general application overview and is intended to familiarize the reader with the benefits of using AC drives in compressor

More information

Availability Analysis For Optimizing A Vehicle A/C System

Availability Analysis For Optimizing A Vehicle A/C System Purdue University Purdue e-pubs International Refrigeration and Air Conditioning Conference School of Mechanical Engineering 2002 Availability Analysis For Optimizing A Vehicle A/C System Y. Zheng Visteon

More information

VALVE TIMING DIAGRAM FOR SI ENGINE VALVE TIMING DIAGRAM FOR CI ENGINE

VALVE TIMING DIAGRAM FOR SI ENGINE VALVE TIMING DIAGRAM FOR CI ENGINE VALVE TIMING DIAGRAM FOR SI ENGINE VALVE TIMING DIAGRAM FOR CI ENGINE Page 1 of 13 EFFECT OF VALVE TIMING DIAGRAM ON VOLUMETRIC EFFICIENCY: Qu. 1:Why Inlet valve is closed after the Bottom Dead Centre

More information

ENGINES ENGINE OPERATION

ENGINES ENGINE OPERATION ENGINES ENGINE OPERATION Because the most widely used piston engine is the four-stroke cycle type, it will be used as the example for this section, Engine Operation and as the basis for comparison in the

More information

Research on the Structure of Linear Oscillation Motor and the Corresponding Applications on Piston Type Refrigeration Compressor

Research on the Structure of Linear Oscillation Motor and the Corresponding Applications on Piston Type Refrigeration Compressor International Conference on Informatization in Education, Management and Business (IEMB 2015) Research on the Structure of Linear Oscillation Motor and the Corresponding Applications on Piston Type Refrigeration

More information

MODELING SUSPENSION DAMPER MODULES USING LS-DYNA

MODELING SUSPENSION DAMPER MODULES USING LS-DYNA MODELING SUSPENSION DAMPER MODULES USING LS-DYNA Jason J. Tao Delphi Automotive Systems Energy & Chassis Systems Division 435 Cincinnati Street Dayton, OH 4548 Telephone: (937) 455-6298 E-mail: Jason.J.Tao@Delphiauto.com

More information

COMPARING SLOTTED vs. SLOTLESS BRUSHLESS DC MOTORS

COMPARING SLOTTED vs. SLOTLESS BRUSHLESS DC MOTORS COMPARING SLOTTED vs. SLOTLESS Authored By: Engineering Team Members Pittman Motors Slotless brushless DC motors represent a unique and compelling subset of motors within the larger category of brushless

More information

Rotary Internal Combustion Engine: Inventor: Gary Allen Schwartz

Rotary Internal Combustion Engine: Inventor: Gary Allen Schwartz Rotary Internal Combustion Engine: Inventor: Gary Allen Schwartz 1 The following is a design for a circular engine that can run on multiple fuels. It is much more efficient than traditional reciprocating

More information

Transient Analysis of Offset Stator Double Sided Short Rotor Linear Induction Motor Accelerator

Transient Analysis of Offset Stator Double Sided Short Rotor Linear Induction Motor Accelerator Transient Analysis of Offset Stator Double Sided Short Rotor Linear Induction Motor Accelerator No. Fred Eastham Department of Electronic and Electrical Engineering, the University of Bath, Bath, BA2 7AY,

More information

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

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

More information

Noise Reduction in a Reciprocating Compressor by Optimizing the Suction Muffler

Noise Reduction in a Reciprocating Compressor by Optimizing the Suction Muffler Noise Reduction in a Reciprocating Compressor by Optimizing the Suction Muffler Katakama Nagarjuna ¹ K.Sreenivas² ¹ M.tech student, ²Professor, dept of mechanical engineering kits, markapur, A.P, INDIA

More information

ENHANCED ROTORDYNAMICS FOR HIGH POWER CRYOGENIC TURBINE GENERATORS

ENHANCED ROTORDYNAMICS FOR HIGH POWER CRYOGENIC TURBINE GENERATORS The 9th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery Honolulu, Hawaii, February -1, ENHANCED ROTORDYNAMICS FOR HIGH POWER CRYOGENIC TURBINE GENERATORS Joel V. Madison

More information

OBSERVATIONS ABOUT ROTATING AND RECIPROCATING EQUIPMENT

OBSERVATIONS ABOUT ROTATING AND RECIPROCATING EQUIPMENT OBSERVATIONS ABOUT ROTATING AND RECIPROCATING EQUIPMENT Brian Howes Beta Machinery Analysis, Calgary, AB, Canada, T3C 0J7 ABSTRACT This paper discusses several small issues that have occurred in the last

More information