Investigation of failure in performance of linear compressor & its rectifications

Investigation of failure in performance of linear compressor & its rectifications #1 M.B.Nirali, #2 Dr.V.K.Bhojwani #1 mechanical Engineering, Jscoe, Savitribai Phule Pune University, Pune India #2 mechanical Engineering, Savitribai Phule Pune University,Pune India ABSTRACT The compressor is one of the essential components viz a refrigerator, together with the evaporator, condenser and expansion valve. The compressor draws in low-pressure gas-phase refrigerant from the evaporator and discharges it in the high pressure-liquid state to the condenser. The reciprocating compressor [1, 2] in which a crankshaft mechanism converts the motor s rotary motion into reciprocating motion to draw in and discharge refrigerant, has been the design of choice. More recently however, the linear compressor where linear motors directly drives a piston in a back and forth motion to change the control volume and pressure, has come into wide use. The linear compressor offers higher energy efficiency than the reciprocating compressor, in that its direct piston motion minimizes the significant transformation loss incurred by the reciprocating compressor. The linear compressor consists of a cylinder, a suction valve, a discharge valve and a discharge cover (muffler). When the control volume is expanded by the piston movement, the discharge valve is closed and the suction valve attached to the piston is opened widely. Then, the linear compressor draws in refrigerant, which passes through the evaporator. Keywords Linear compressor, suction pressure and discharge pressure, Rota meter, clamp mete, Flexures, Coil former. I. INTRODUCTION Reciprocating compressors have been used for many years, and provide the power for much of our refrigeration needs. Invariably, these compressors are driven by a rotating electrical motor through a mechanism such as a crank or a scotch yoke. A lesser known area of development is the linear compressor, where the power is provided by a linear oscillating motor, directly coupled to a piston. Such machines have the advantages that all of the forces acting on the system are co-linear, so any bearings and seals have relatively light loading. A prototype compressor was made to realize both the conventional linear compressor & the inherent capacity modulated linear compressor. Linear compressor Definition: A linear compressor is a positive displacement compressor that uses piston driven by a linear motor to deliver gases at a high pressure. Application Theory In cryogenic applications, LG electronics have developed a linear compressor for 680L capacity refrigerator. In 1999 Linear compressor for household purpose of COP 2.5-4.9 was designed power required for linear compressor is 25% less compared to conventional compressor. Problem Statement The main application of linear compressor is refrigeration. For the required cooling effect 6 LPH refrigerant flow is required. The compressor gave negligible flow initially. Therefore the main task is to achieve the required flow. Using the linear stroke of piston in linear compressor. 2015, IERJ All Rights Reserved Page 1

Significance & Relevance 1. A linear compressor can easily adapt to variable capacity. 2. In linear compressor piston stroke varies with input voltage. 3. In linear compressor oil lubrication is not necessary. 4. Ideally no lateral forces involved due to linear motion produces less noise & vibration. 5. Less wear & tear. 6. A linear compressor is a positive displacement machine. II. LITERATURE REVIEW Yong-sik Choi1, Jun-ho Lee [1] investigated refrigeration design for the linear compressor is suitable for the reciprocating types of compressor. The linear compressor s valve system, however, causes significant noise, not only in the steady state but also in the transient state. They found the effects of pre-load of the conical compressor spring on the dynamic characteristics of the valve system. Paul Bailey, Mike Dadd & Richard Stone [2] describes the development of linear compressor and outline their future potential. Investigated refrigeration technology, with the addition of valves, can be used for vapor compression system, by using ammonia. H. K. Lee, G. Y. Song [3] investigated experimental study on energy efficiency of the linear compressor with various refrigerants convinces the usefulness of linear motors along various refrigerants. These all technologies of the linear compressor for air conditioners, cryocoolers and the other types of cooling devices. Wen WANG, Xiaoliang TAI [4] paper states that the linear motor for linear compressor should satisfy some demands, such as: 1. Enough actuating force for piston with compact structure; 2. It s better to have lighter piston for better performance. The less weight of mover is helpful to reduce the inertia of the mover and the involved vibration; it benefits to reduce the total weight of the compressor as well. All components should be easy for the manufacturing. Craig R. Bradshaw et al. [5] worked on the comprehensive compressor model consists of a solution to two compression process equations that provide the temperature and density, and thus fix the state within each control volume. These equations require inputs from the five sub-models representing the valve flows, leakage flows, motor losses, heat transfer from the cylinder, and piston dynamics. The compression cycle is discretized and an initial guess of temperature and density is made within each control volume. Craig R. Bradshaw et al. [6] Linear compressors for electronics cooling: Energy recoveryand its benefits. to explore the energy recovery characteristicsof a linear compressor as compared to those of a reciprocating compressor. Nomenclature P1-Suction pressure P2-Discharge pressure T1-Temperature Objectives The developed linear compressor hasto build pressure & deliver satisfactory mass flow rate. The current project work will focus on rectifying the failure in performance & rectifying the design to achieve design mass flow rate inside compressor cylinder. 2015, IERJ All Rights Reserved Page 2

Scope of work Investigate the failure. Identify root problem for failure in Performance. Rectify design to overcome failure. Test the modified compressor to achieve design mass flow rate & pressure inside cylinder. Testing Equipment s 1. Refrigerator Capacity:180 Liters (0.1TR) Compressor: 4cc compressor Refrigerant: R134a Model Number: Haier 1905. 2. Temperature sensor with digital indicator Power: 230VAC 50Hz. Input: Thermocouple K-Type-8 No s. 3. Pressure Gauges Type: Compound Gauge. Reading: 0-25 psi. 4. Rota meter Flow rate: 0-10LPH. 5. Clamp meter Range: 0.1-1000 ampere, 0-1000 Volt (Digital). Components of linear compressor 1. Pole Piece 2. Coil Former 3. Flexure Bearing 4. Suction & discharge Valve Plate 5. Compressor Main body 6. Outer spacer 7. Compressor piston. Actual Testing set up of Linear Compressor Fig1.Flexures Bearing Fig.2The linear compressor is fitted in the VCC by replacing reciprocating compressor. 2015, IERJ All Rights Reserved Page 3

Experimental Validation Integration of linear compressor to VCC Fig.3Previous Setup with copper tubes LeakageArrest Fig.4New Setup with copper tubes replaced with Flexible hose pipes. Fig.5Leakages from head 2015, IERJ All Rights Reserved Page 4

Fig.6Leakages from flange CLEARANCE BETWEEN FLEXTURE STACK AND SLEEVE Fig.7Insufficient Clearance(1.5 mm) Fig. 8Sufficient Clearance (3.5 mm) provided 2015, IERJ All Rights Reserved Page 5

Testing Results Table 1 Testing Results Sr.No. Time P1 bar P2 bar T1 ( 0 c) Flow LPH (min) 1 0 0 0 27.5-2 40 3.5 9.7 5.9 1.9 3 65 2.5 8.2-0.2 2 4 90 2.4 8.3-3.4 2.8 5 110 2.3 8.6-8.2 3.4 6 140 2.2 10.2-13 4.2 III. CONCLUSIONS 1. Discharge pressure is obtained 10.2 bar at suction pressure range 3-3.5bar. 2. Flow rate of 4.2 LPH is achieved, as required by system is 6 LPH. 3. Optimized clearance required of 15microns radially is maintained. 4. According to the graph there considerably decrease in freezer temperature up to -13deg respect to time. 5. Fine tuning with addition of one flexure at a time, for performance improvement is done with optimized no of flexure are 30 (stiffness-60000 N/m). IV. REFERENCES Yong-sik Choi,(2010) Dynamic behavior of valve system in linear compressor based on fluid-structure interaction. Paul Bailey,Mike Dadd & Richard Stone Cool and Straight (2011) Linear Compressors for Refrigeration. H.k.Lee,G. Y. Song (2000)Development of the Linear Compressor for a Household Refrigerator. Kyung Bum Heo, Chel Woong Lee, Gye Young Song, Won Hyun Jung,(2013) Capacity modulation of linear compressor for household refrigerator. Wen WANG, Xiaoliang TAI (2014)Modeling and measurement of a moving magnet linear compressor performance. Craig R. Bradshaw et al. (2015) development of green linear compressor. Craig R. Bradshaw et al.(2013)linear compressors for electronics cooling: Energy recoveryand its benefits. 2015, IERJ All Rights Reserved Page 6