Sound Evaluation of Flow-Induced Noise with Simultaneous Measurement of Flow Regimes at TXV Inlet of Automotive Evaporators 2020-01-1255
In the air conditioning system, flow-induced noise is very disturbing, including the noise generated in the expansion device and the heat exchangers. In the past few decades, most researches related to flow-induced noise focused on the relationship between the flow regimes near the expansion device and the amplitude of flow-induced noise when the measurements are not synched. In this paper, an experimental approach is used to explore the simultaneous relationships between flow-induced noise characteristics and flow regimes at the inlet of TXV of evaporators used in automobiles. A pumped R134a loop with microphones and transparent visualization sections is used to simulate the vapor compression system. Also, the paper evaluates the severity of flow-induced noise from not only the amplitude of noise but also the frequency of noise with a parameter called psychoacoustic annoyance (PA). One of the most disturbing flow-induced noise types near the TXV is called gurgling noise and distributes around 9 kHz at an amplitude between 40 dB to 50 dB. When the TXV inlet is subcooled, the annoyance of flow-induced noise is substantially reduced. When the TXV inlet is two-phase flow, different flow patterns result in different types of flow-induced noise. For the annular flow regime, the gurgling noise is continuous with uniform loudness. For stratified-wavy flow, the gurgling noise is discontinuous with ascending loudness. For intermittent flow, the gurgling noise appears intermittently with wavy loudness. It may be useful to predict the flow regimes at the TXV inlet from the waveform of flow-induced noise. A psychoacoustic annoyance map is displayed in terms of flow regimes at the TXV inlet, and the intermittent flow regime was found to result in the most disturbing flow-induced noise while annular flow resulted in the least annoying flow-induced noise. Accelerometer measurements can be used to quantify flow-induced noise which are more economical than sound pressure measurements obtained with microphones.