Modeling and measurement of a moving coil oil-free linear compressor performance for refrigeration application using R134a

A prototype of the compressor with moving coil type linear motor has been developed. The developed compressor is integrated with test loop using R134a refrigerant to confirm its performance. The simulation results are validated with the experimental data. The experimental results from the test loop with strokes of 10, 11 and 12 mm for three different pressure ratios of 4, 7, 10 are presented and discussed in this paper. The COP of the system calculated is 1.4 from the test results (for 54 °C condenser temperature and −20 °C evaporator temperature) with the stroke of 10 mm, pressure ratio of 10 and cooling capacity of 134 W. The maximum COP of 2.13 is achieved (for 54 °C condenser temperature and 2 °C evaporator temperature) with the stroke of 12 mm, pressure ratio of 4 and cooling capacity of 325 W. Normal refrigerator compressors utilize lubricant oil but as the refrigerant is changed the oil suitable for particular refrigerant also needs to be changed. The novel linear compressor tested does not utilize lubricant oil. The linear compressor has only one friction point i.e. between the piston and cylinder. The linear compressor utilizes Rulon (low coefficient of friction material) as a special material coated on the piston surface in contact with the cylinder. The oil-free operation of the compressor helps in adapting the refrigerator to different refrigerants without having to consider a change of lubricating oil. Refrigeration system performance with both linear compressor and the conventional reciprocating compressor is measured and compared. System COP with the linear compressor is 18.6% more than with the commercially available reciprocating compressor. The absence of connecting rod and crank mechanism accompanied with oil-free operation due to reduced friction enhance the performance of the linear compressor.