Moving magnet linear compressor: Operating characteristics under resonance and off-resonance frequencies

Abstract

Objectives: This study compared the accuracy of a Linear Equivalent model and a Fourier Transform model in approximating the resonant frequency of a moving magnet oil-free linear compressor. Furthermore, moving magnet linear compressor performance under resonance and off-resonance frequencies was also examined via an experimental approach. Methods: A Linear Equivalent model and a Fourier Transform model were developed and compared with experimental results at low-pressure ratios of 2–2.5. By varying the operating frequency and compressor piston stroke, the power consumption, compressor losses, efficiency, and cooling capacity are assessed experimentally. Results: This study showed that the disparities between resonance frequencies estimated by theoretical models and experimental data were below 10 %. However, the Linear Equivalent model was more accurate than the Fourier Transform model in forecasting the resonance frequency of the linear compressor at a low-pressure ratio of 2–2.5. Both experimental and modelling results showed that the resonance frequency of a linear compressor declined with the increasing compressor stroke but increased with increasing pressure ratio. Experiments were also carried out to compare the performance of linear compressors in resonance and off-resonance frequencies. Results showed that the lowest compressor input power of 91.96 W and the highest motor efficiency of 81.98 % was achieved when the linear compressor was operated at 38 Hz resonance frequency. Moreover, the cooling capacity has been found to increase by 270 W approximately when the linear compressor piston operating stoke extends from 10 mm to 13 mm. Conclusions: In all, this study showed that the linear compressor motor efficiency is the highest when operating at resonance frequency. However, the cooling capacity of the linear compressor system does not vary significantly with operating frequency. A higher cooling capacity can be achieved by increasing compressor piston stroke.

Keywords

• Linear Equivalent model
• Fourier Transform model
• Resonance frequency
• Cooling capacity
• Linear compressor