制冷压缩机排气管消声器声学及阻力特性仿真分析

Numerical analysis of acoustic and resistance performance of muffler in refrigeration compressor's discharge pipe

为了降低空调运行过程中制冷压缩机所产生的噪声，采用在制冷压缩机排气管设置消声器的方法。建立了消声器内部制冷剂的有限元模型，利用声学分析软件Virtual Lab Acoustics和计算流体动力学软件Fluent分别对消声器的声学性能和阻力特性进行数值模拟，分析了消声器内部的扩张腔长度、孔板位置、孔板内径等结构参数对排气管消声器传递损失和压力损失的影响。模拟结果表明：随着扩张腔长度的不断减小，消声器的传递损失曲线逐渐向高频方向移动，消声器的有效消声频率范围不断拓宽，而扩张腔长度对消声器压力损失的影响较小，合理选择扩张腔长度能够有效降低压缩机噪声；孔板位置对中高频噪声的降噪效果影响较大，随着孔板位置由扩张腔中心处向其进口端面不断移动，2000～2400 Hz附近频率的消声性能逐渐得到改善，并且消声器内部压力损失不断减小，且其减小幅度越来越大，因此孔板在允许的范围内应尽可能靠近消声器进口端面；随着孔板内径的不断减小，消声器的降噪效果不断增强，但消声器内部压力损失也随之逐渐增大，且增大幅度越来越大，因此孔板内径不宜太小。

The noise level has become an important index to evaluate the quality of air conditioners, and the refrigeration compressor is a major noise source of an air conditioners’ outdoor unit. In order to reduce the noise of an air conditioner, by means of the theories that the noise is spread by fluid and the acoustics impedance mismatch occurs in the pipe with variable cross sections, a muffler was set in a refrigeration compressor’s discharge pipe. The finite element model of a refrigerant in the muffler was established, based on which, the transmission loss could be numerically simulated by acoustics software Virtual Lab Acoustics, as well as the resistance performance by the computational fluid dynamics software Fluent. The effect of various structural parameters on the transmission loss and pressure loss of the muffler was investigated, including the length of the expansion chamber, and the position and the inner diameter of the orifice plate. The simulation results showed that the transmission loss curve of the muffler gradually moved to the higher frequency as the length of the expansion chamber decreases, which could also expand the effective acoustic attenuation frequency range, but it had little effect on the pressure loss of the muffler. To effectively reduce the noise of the compressor, the length of the expansion chamber should be appropriately selected. When the length of the expansion chamber was bigger than 140 mm, the noise of 2000-3000 Hz was effectively reduced, and the frequency of more than 2000 Hz was the main frequency region of the rotary compressor noise, so the length of expansion chamber was suggested to be bigger than 140 mm, but the length cannot be too big for decreasing the pressure loss of the muffler. For middle and high frequency noise, the position of orifice plate had a great influence on the acoustic attenuation performance of the muffler. As the orifice plate moved from the center of expansion chamber to its inlet surface, the acoustic attenuation performance for the frequency of 2000-2400 Hz gradually became better, while the pressure loss of the muffler decreased and the declination rate gradually increased, so the orifice plate should not only deviate from the center of the expansion chamber, but also get as close to the inlet of the muffler as possible within the permitted range. Moreover, the muffler could achieve better acoustic attenuation performance along with the decrease of the inner diameter of orifice plate, but the pressure loss of the muffler increased gradually with its increase rate tending to be bigger. As a result, in order to achieve an effective noise reduction and reduce the pressure loss of the muffler, the inner diameter of the orifice plate should not be too small. If the pressure loss of the muffler is required to less than 600 Pa, the inner diameter of the orifice plate should be bigger than 6 mm. In the design of the muffler, in addition to obtaining better acoustics attenuation performance, the pressure loss of the muffler needs to be considered, so that the performance of an air conditioner system cannot be greatly influenced. The research results would be able to provide a theoretical base for the noise reduction of air conditioners.