popping noise, household refrigerator, expansion device, capillary tube, shock wave
An intermittent noise that occurs around 30 seconds after compressor start-up has been disturbing customers of many domestic refrigerator manufacturers over the past 10 years. This noise is very similar to that produced by popcorn popping, being referred to as popping noise. The most probable cause of this strange and unpleasant noise is thought to be CIS (Condensation Induced Shock). The aim of this study was firstly to check the possible occurrence of CIS in a specific household refrigerator and, secondly, to identify ways to avert it without affecting the product performance. To this end some changes were made to the refrigerator: i) the diameter of the filter dryer was altered; ii) the slope of the filter dryer was altered; iii) the compressor mass flow rate was changed and iv) an additional internal heat exchanger was installed. The replacement of the filter dryer made the sound even more unpleasant, while the replacement of the original compressor by another of smaller capacity considerably reduced the noise. The noise was effectively eliminated only by placing the filter dryer horizontally or by installing an additional internal heat exchanger. Visualization studies were also carried out, making it clear that the occurrence of the popping noise is closely related to the flow pattern at the inlet of the capillary tube.