Noise reduction strategies for screw compressors
The operating noise of twin-screw compressors is an important issue that may limit their scope of application. Two recent IJR papers suggest several noise reduction methods and analyse their efficiency.
Because of their efficiency and reliability, twin-screw refrigeration compressors are widely applied in middle-sized refrigeration and heat pump systems with cooling capacity ranging from 20 to 400 kW.
The noise and vibration of a twin-screw refrigeration compressor is a critical issue that limits its applications in areas where quiet operation is required. Many research studies have concluded that the noise of twin-screw compressors is mainly due to the gas pulsation caused by the intermittent gas flow through the suction and discharge ports. Because the gas density is higher at the discharge port, the aerodynamic noise induced by the discharge gas pulsation is greater than the suction gas pulsation.
Two recent papers written by Chinese researchers published in the IJR provide valuable guidance for the design of low-noise twin-screw refrigeration compressors.
A first paper (1) proposes two noise reduction methods suitable for variable-frequency twin-screw refrigeration compressors : end-face attenuation passage and discharge pipe damping. The first method reduces the gas pulsation amplitude in the discharge chamber which is the main source of noise. The second method is based on Helmholtz resonators installed in the discharge pipe inside the compressor.
Flow field and sound field simulation of the compressor was developped to verify the noise reduction effect of each method. To verify the noise reduction effect experimentally, both methods were simultaneously applied in a semi-hermetic twin-screw compressor. The mean noise reduction value ranges from 5.0 dBA to 10.0 dBA and the highest noise level does not exceed 85.5 dBA at a rotational speed of 5100 rpm. Besides, the mean noise reduction increases with the rotational speed.
A second paper (2) experimentally investigates the noise spectrum characteristics in a twin-screw compressor and evaluates the performance of several noise reduction schemes, including half-wavelength tube, Helmholtz resonator, and multi-cavity series muffler.
The results show that application of these noise attenuation strategies significantly reduced the noise level by 10.7 dBA, 10.9 dBA, 7.2 dBA, and 10.2 dBA on the male rotor side, female rotor side, suction side, and exhaust side, respectively. Comparative test results indicate that the use of the exhaust muffler and the attenuation scheme on the exhaust bearing block were the most effective methods since they reduced the compressor noise level by 8.17 dBA.
(1) S. Jiubing et al. Study on the noise reduction methods for a semi-hermetic variable frequency twin-screw refrigeration compressor. Available in FRIDOC (free of charge for IIR members).
(2) H. Zhilong et al. Noise control of a twin-screw refrigeration compressor. Available in FRIDOC (free of charge for IIR members).