Quantification and analysis methods aimed at the reduction of flow induced noise in the expansion device

Abstract

A cultural context where acoustic technologies are rapidly growing, and the demand for comfort is increasing exponentially, were all catalysts for the birth of this research project. In particular, noise is one of the major concerns that many companies want to come against, especially in the HVAC & Refrigeration sector. Indeed, noise coming from air conditioning systems can be perceived as very annoying. Thus, one of the main reasons this research is conducted is to increase consumer comfort in all applications where air conditioning noise, especially noise coming from expansion devices, is perceived as very disturbing. At the same time another motivation to conduct research in this area is to improve the understanding of flow induced noise.

The objective of the thesis is to provide a basis for future scientists who would like to come against the problem of noise produced from expansion devices. Basic theories regarding noise and expansion devices are defined and explained. Subsequently the thesis demonstrates how the laboratory was designed and setup (the refrigerant used was R134a), including pressure, acceleration, and microphone measurements. The importance of the anechoic chamber will be shown. After it will be revealed the usefulness of the FFT to convert time domain measurements to frequency domain signals for detailed analysis. Initial measurements have been conducted and similarities between pressure and acceleration measurements will be investigated in the frequency range of interest (< 6 kHz). Lastly, preliminary flow visualization results are available to connect flow regimes to noise measurements.