Investigation of refrigerant flow-induced noise characteristics and mitigation approaches

In recent decades, flow-induced noise near expansion device has become particularly noticeable to occupants. In automobiles and air conditioning systems, a two-phase flow can occur at the expansion valve inlet under various conditions, such as low system load and condensation pressure. When this happens, high-frequency flow-induced noise becomes audible. In this research, a transparent thermal expansion valve (TXV) was created to visualize the entire range of flow regimes as they pass through the expansion valve. Unlike existing studies, the 3D-printed TXV visualization provides a complete picture of the flow regime variation inside the device, and the synchronized signal can show instantaneous variations of flow-induced noise as the TXV inlet flow regime changes. The visualization showed that the oscillation of bubbles and the vapor core region appeared at the outlet of the TXV, causing flow-induced noise near the TXV. The oscillation of bubbles was identified as a primary noise source. The research also introduced a comprehensive parameter, Wa, which directly correlated flow regimes with the psychoacoustic annoyance (PA) of the flow-induced noise. It was found that Wa and PA had a linear relationship when the inlet flow was in the slug/stratified wavy flow regime in a horizontally placed TXV, with an empirical correlation provided for this regime. However, when the inlet flow regime was stratified wavy, the linearity between Wa and PA disappeared. Additionally, the same linear relationship is investigated between Wa and PA when the TXV was installed in a vertical upward orientation, with an empirical correlation provided for the low-quality region as well. The average PA was smaller in the vertical upward orientation than in the horizontal orientation, suggesting that the vertical upward installation direction for the TXV may reduce noise. An analytical model was also developed to link the waveform of the flow-induced noise to the flow instantaneous void fraction. This model showed that with the help of the flow-induced noise waveform, the local void fraction and flow regimes could be predicted even when visualization was not available. Contradictorily, with flow visualization, the shape of the flow-induced noise waveform could be predicted as well. Controlling the noise frequency was proposed as an effective strategy to mitigate flow-induced noise near the expansion valve. A stainless-steel mesh with a mesh size of 75 μm was optimal for noise reduction. The best mitigation effect was achieved when the mesh was installed close to the expansion valve outlet. Popping noise also frequently occurs near the capillary tube and the suction line heat exchanger (CSHX). Household appliance manufacturers have also reported intermittent high intensity popping noise near refrigerators. This study developed a refrigeration system capable of simulating popping noise in a real refrigerator, enabling the investigation of the relationship between popping noise characteristics and system performance. It was found that two key parameters influencing the occurrence of popping noise were the two-phase flow sound speed and the initial subcooling at the condenser outlet. The initial subcooling determined the bubble size entering the capillary tube, while local sound speed set a limit for the occurrence of popping noise. Two methods were proposed to mitigate popping noise. Increasing the contact length between the capillary tube and the suction line can eliminate the noise, resulting in a 3% to 8% increase in the coefficient of performance (COP). Additionally, introducing nitrogen into the system reduces the bubble collapsing rate, making popping less likely to happen. However, this method reduces system performance, making it a viable option only as a backup plan.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Zhang, Yingyue

Contributors dc:contributor

• Elbel, Stefan
• Miljkovic, Nenad
• Wang, Xiaofei
• Zhang, Yuanhui

• Flow-induced Noise
• Expansion Device
• Flow Regimes

Statement dc:rights

• Copyright 2024 Yingyue Zhang

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/127451

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F127451