Advanced Research Journals of Science and Technology
ADVANCED RESEARCH JOURNALS OF SCIENCE AND TECHNOLOGY
(ARJST)
MODELING AND ANALYSIS OF MOUNTING PLATE OF A ROTARY COMPRESSOR
2349-1845
MD Saroj Basha1, B.Kailash2, 1 Research Scholar, Department of Mechanical Engineering,Eswar College of Engineering, Narasaraopet, Guntur,India. 2 Associate professor, Department of Mechanical Engineering, Eswar College of Engineering, Narasaraopet, Guntur,India.
Abstract In the Tecumseh Compressors, the compressors manufactured are using mounting plates having the pitch circle diameter of 211mm. This mounting plate is welded to the compressor bottom and through the holes of this plate; the compressor gets mounted on to the A/C housing. The vibrations from the compressor get transferred to the A/C housing there by producing noise, which is undesirable. These vibrations will be greater enough to produce noise when the natural frequencies of the compressor, the mounting plate and the A/C housing coincide resulting in resonance. To avoid this, there should be a frequency shift in either of the components. Frequency shift in Mounting Plate will give better results as that is the media of transfer of Vibrations form compressor to the A/C housing. Under this Project, determination of the Natural frequencies of the mounting plate, amplitudes of vibration in it are studied. This determination is done using Static, Modal and Harmonic Analyses. Three models have been considered and on the existing model experiments have been carried out. The analysis results of the existing model are compared with the experimental results and validating the analysis procedure, the same analyses are carried out to the rest of the two models. Upon analysis of the three models, the better one out of them is suggested. *Corresponding Author: MD Saroj Basha, Research Scholar, Department Of Mechanical Engineering, Eswar College of Engineering, Narasaraopet, Guntur,India. Published: January 04, 2016 Review Type: peer reviewed Volume: III, Issue : I Citation: MD Saroj Basha,Research Scholar (2016) MODELING AND ANALYSIS OF MOUNTING PLATE OF A ROTARY COMPRESSOR
INTRODUCTION Compressor is the heart of the refrigeration circuit. It pumps and pressurizes the refrigerant to move it through the A/C system. Compressors work hard and run hot, up to several hundred degrees and several hundred pounds per square inch of internal pressure. They rely on only a few ounces of lubricant to keep their parts moving. If the lubricant is lost because of a leak, or the lubricant breaks down due to contamination, the compressor will not last. Sooner or later, the compressor will call it quits. A helical screw rotary compressor for a closed loop refrigeration system such as an air conditioning system for a bus or like vehicle is connected in series with a condenser and an evaporator, in that order, with the evaporator at a raised position relative to the compressor and utilizes a vaporizable refrigerant which is miscible with a lubricating oil employed to lubricate the moving components of the screw compressor. A slide valve underlies the intermeshed rotors and forms a portion of the screw compressor envelope, the rotors opening to a suction port connected to the outlet side of the evaporator above the rotors. A high pressure discharge port at one end of the intermeshed rotors leads to an auxiliary chamber bear-
ing an unload cylinder which drives the slide valve and which opens at the top to a housing discharge port leading to the condenser. An oil separator is interposed within the auxiliary chamber above the unload cylinder. An oil drain passage leads from the auxiliary chamber to an oversized oil sump within the housing beneath the rotors. The slide valve slides in a recess within the casing underlying the rotors. This structural arrangement permits all condensed refrigerant and the oil to return by gravity flow to the oil sump whose capacity is at least 1.5 times the volume of the normal oil charge for the system. Condensed refrigerant miscible in the oil and the oil entraining the refrigerant, upon compressor shut down, accumulates in the sump but does not reach the intermeshed rotors and thus prevents clutch burnout by liquid locking during initiation of compressor operation with the clutch mechanically connecting the engine to the intermeshed helical screw rotors. TYPES OF COMPRESSOR The three basic types of air compressors generally available include: 1. Reciprocating compressor, 2. Rotary compressor, 3. Centrifugal compressor. RECIPROCATING COMPRESSORS Reciprocating compressors are positive displacement compressors. This means they are taking in successive volumes of air, which is confined within a closed space, and elevating this air to a higher pressure. The reciprocating compressor accomplishes this by using a piston within a cylinder as the compressing and displacing element. The reciprocating compressor is considered single acting when the compressing is accomplished using only one side of the piston. A compressor using both sides of the piston is considered double acting. The reciprocating compressor uses a number of automatic spring loaded 76
Advanced Research Journals of Science and Technology
valves in each cylinder that open only when the proper differential pressure exists across the valve. Inlet valves open when the pressure in the cylinder is slightly below the intake pressure. Discharge valves open when the pressure in the cylinder is slightly above the discharge pressure. A compressor is considered to be single stage when the entire compression is accomplished with a single cylinder or a group of cylinders in parallel. Many applications involve conditions beyond the practical capability of a single compression stage. Too great a compression ratio may cause excessive discharge temperature or other design problems.
This Project deals with the Static, Modal and Harmonic analysis of 211mm PCD plate and to compare 176mm PCD plate with 211mm PCD plate there by suggesting a better mounting plate for the compressor.
ROTARY COMPRESSORS
The compressor’s Mounting Plate is a sheet metal model that is modeled in UNI GRAPHICS. Three models are made, which the three cases are considered in this project they are: 211mm Regular plate, 176mm Regular plate, 176mm Flat Plate. Here in these three models, 211mm and 176mm regular plates have the same design and 176mm Flat plate is considered with the only objective that the tooling cost can be reduced by avoiding the curves in the model. Hence the models of 211mm and 176mm look alike.
Rotary compressors are positive displacement compressors [3]. The most common rotary air compressor is the single stage helical or spiral lobe oil flooded screw compressor. These compressors consist of two rotors within a casing where the rotors compress the air internally. There are no valves. These units are basically oil cooled, where the oil seals the internal clearances. Since the cooling takes place right inside the compressor, the working parts never experience extreme operating temperatures. The rotary compressor, therefore, is a continuous duty, air-cooled or water cooled compressor package. Because of the simple design and few wearing parts, rotary screw air compressors are easy to maintain, operate and provide great installation flexibility. Rotary compressors can be installed on any surface that will support the static weight.
MODELING AND ANALYSIS OF MOUNTING PLATE The major steps involved are • Modeling using Unigraphics • Pre-processing using Hypermesh • Processing and Post-processing using Ansys.
Top view of 211mm and 176mm Mounting Plates
Compression cycle of a Rotary Compressor
After modeling, for meshing the model Altair Hyper Mesh is used, which is a high-performance finite element preand post-processor for major finite element solvers, allowing engineers to analyze design conditions in a highly interactive and visual environment. Hyper Mesh’s userinterface is easy to learn and supports the direct use of CAD geometry and existing finite element models, providing robust interoperability and efficiency
CENTRIFUGAL COMPRESSORS The centrifugal compressor is a dynamic compressor, which depends on transfer of energy from a rotating impeller to the fluid. The rotor accomplishes this by changing the momentum and pressure of the fluid. This momentum is converted to useful pressure by slowing the fluid down in a stationary diffuser. The centrifugal compressor is an oil free compressor by design. The oil-lubricated running gear is separated from the by shaft seals and atmospheric vents. The centrifugal is a continuous duty compressor, with few moving parts, that is particularly suited to high volume applications-especially where oil free air is required. Centrifugal air compressors are water-cooled and may be packaged; typically the package includes the after cooler and all controls
Mesh model of “176mm PCD FLAT” Plate with Boundary Conditions
PROBLEM DEFINITION Mounting Plate of a rotary compressor in use is having PCD of 211mm. As per the requirement there is a change of PCD of the mounting plate from 211mm to 176mm. 77
Advanced Research Journals of Science and Technology
STATIC ANALYSIS 211mm PCD Mounting Plate shows variation of Deflection in the mounting plate under static loading condition. The static load applied is the weight of the compressor applied along the inner circumference of the mounting plate. From the figure it is observed that the Maximum Displacement of 41.656mm (0.00164�) has occurred at a point on the inner circumference near Leg-1, which is shown as MX in the figure.
tion of the mode shape. When Normalization of the mode shape is taken to Mass Matrix, the resulted mode shape will be the value of deflection of the overall vector sum and not for the individual direction. NATURAL FREQUENCIES (Hz) SET
Mounting Plate 211mm
176mm
176mm Flat
1
58.564
89.064
66.088
2
59.571
89.071
66.261
3
59.572
98.912
67.076
4
78.688
127.48
116.42
5
78.688
127.54
128.63
6
98.564
131.82
129.16
7
103.55
140.29
142.85
8
131.66
170.51
160.06
9
131.66
170.52
160.67
10
147.95
181.99
177.92
Maximum Deflections under External Load, 0.00164
HARMONIC ANALYSIS
Vonmises Stresses
Mode shape
Harmonic analysis is carried out under the application of the weight of the compressor as the force on the model with in the Frequency range of 0-100Hz. This particular range is selected since the working range of frequency of the compressor is from 50-60Hz. That is 50Hz for some models that are used by the Indian Clients and for some models it is 60Hz for other clients. In Harmonic analysis, Displacement is measured in the frequency range of 0Hz to 100Hz dividing the frequency range into 10 sub steps. The response of the system to this excitation frequency is measured at the three locations that are at each Leg. A node near to each leg is selected and at that node, its displacements are measured along all the directions. In the below graphs displacement along Z direction are shown, as the Force is applied in Z-direction. FREQ (Hz)
AMPLITUDE (Inch)
10
2.96E-07
20
6.63E-07
30
1.23E-06
Modal analysis results in Mode shapes with Natural Frequencies of the model.
40
2.38E-06
50
6.28E-06
60
4.50E-05
In modal analysis, Normalization of the Mode shapes is taken to Unity. Taking to Unity, the mode shapes when taken individually for each Translational and Rotational directions of each mode step, the orientation in which the mode shape will be equal to or near to Unity is the direc-
70
6.97E-06
80
4.91E-06
90
5.72E-06
100
2.32E-05
Maximum Deflections
MODAL ANALYSIS
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Advanced Research Journals of Science and Technology
FUTURE SCOPE OF THE PROJECT Considering the Grommets along with the mounting plate, further study can be carried out. Considering the Seismic load from the Compressor as input, further study can be carried out. REFERENCES 1. Karczub, D.G., “Fundamentals Of Noise And Vibration Analysis For Engineers”, Cambridge University Press, April 2003, p 15-22..
Amplitude Vs Frequency
2. Gorman, “Vibration Analysis of Plates by the Superposition Method”, World Scientific Publishing Company, Volume 3, Oct. 1999, p 127-141.
CONCLUSIONS AND FUTURE SCOPE
3. Bloch, H.P. and Hoefner, J.J. (1996). Rotary Compressors, Operation and Maintenance. Gulf Professional Publishing. ISBN 0-88415-525-0. p 206-213.
• Maximum displacement and stress in Z direction for 211mm PCD plate is observed to be 41.656µm and 37.36 MPa respectively.
4. John P. Wolf , “Foundation Vibration Analysis Using Simple Physical Models”, Prentice Hall PTR, Dec. 1994, p 261-272.
• 211mm PCD Plate has the fundamental frequency of 58.564Hz and it results in higher amplitude of vibrations.
5. Akella S, 1992, A Finite Element Approach, Proceedings Of The International Compressor Engg Conference At Purdue Pp. 1477-1486.
• The First maximum displacement of 4.53E-05” (1.15µm) occurred at a frequency of around 60Hz • Maximum displacement and stress in Z direction for 176mm PCD plate is observed to be 37.36µm and 67.44 MPa respectively. • 176mm PCD Plate has the fundamental frequency of 89.064Hz. So this mounting plate doesn’t cause much of vibrations.
6. Cook.R.D, Malkus.D.S., Plesh .M.E., Concepts and applications of Finite Element Analysis ,Wiley International ,3rd Edition,1985, p 441-451 Author
• First maximum displacement of 5.68E-04” (4.26µm) occurred at a frequency of around 90Hz • Maximum displacement and stress in Z direction for 176mm PCD Flat plate is observed to be 98.47µm and 62.42 MPa respectively. • 176mm PCD Flat Plate has the fundamental frequency of 66.088Hz and so results in causing much of vibrations.
MD Saroj Basha, Research Scholar, Department of Mechanical Engineering, Eswar College of Engineering, Narasaraopet, Guntur,India.
• First maximum displacement of 1.18E-04” (2.99µm) occurred at a frequency of around 70Hz • By increasing the thickness of the Mounting Plate, frequency shift is possible. Hence, two thicknesses are considered such as 0.123” (3.12mm) and 0.133” (3.38mm). • Considering the thickness of plate as 0.123” (3.12mm) the fundamental frequency is at 69.02HZ and for the plate of 0.133” (3.38mm) thickness fundamental frequency is at 71.823Hz. These are still lesser than the Fundamental Frequency of 176mm Regular plate, and so are not suggestible.
B.Kailash, Associate professor, Department of Mechanical Engineering, Eswar College of Engineering, Narasaraopet, Guntur,India.
• 176mm Regular Plate is the better one with the thickness of 0.113” (2.87mm) having the highest fundamental frequency, which is also away from working frequency range.
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