# Reduction of the Cavitation Noise in an Automotive Heater Core
## 5 Conclusions  
This study investigated the generation mechanism of noise and vibration caused by cavitation in the heater core of an automotive HVAC system and proposed an effective design modification to mitigate the issue. Through a combination of controlled experiments, in-vehicle testing, and CFD simulations, the presence and characteristics of cavitation were thoroughly examined under various flow conditions.  
The experimental results confirmed that cavitation occurs in the heater core, particularly near the junction between the upper tank and the outlet pipe, under high flow rate and low coolant temperature conditions. Noise and vibration measurements revealed  
Figure 23: Vibration signal measured at the upper tank of the structurally modified heater core at an engine speed of 5000 RPM.  
Figure 22: Cavitation index distribution on the midplane of the structurally modified heater core.  
that cavitation produces distinct impulsive signals, especially evident in the time-domain vibration data and high-frequency components of the frequency spectra. In-vehicle tests corroborated these findings, demonstrating that cavitation-induced noise manifests as abnormal acoustic events during cold engine start-up at high engine speeds.  
Using transparent tube observations and pressure measurements, cavitation was localized to the heater core rather than the water pump. Accelerometer data further pinpointed the collapse of cavitation bubbles to the area around the upper tank-outlet pipe junction. CFD analysis showed that this region experiences both the highest flow velocity and the lowest pressure, leading to a low cavitation index and confirming the conditions necessary for cavitation onset.  
To address this issue, a redesigned outlet junction with a tapered transition and increased pipe diameter was proposed. CFD simulations demonstrated a significant reduction in flow velocity and a corresponding increase in cavitation index, indicating a substantial decrease in cavitation potential. Experimental validation using a prototype heater core with the modified geometry showed complete elimination of cavitation-induced noise and vibration.  
Overall, this research identifies the root cause of heater core cavitation noise and provides a validated, practical solution through structural optimization. The findings offer valuable insights for improving the acoustic performance and durability of automotive HVAC systems, with potential applications in the broader design of fluid systems where cavitation may be a concern.  
Conceptualization, J.C. and Y.L.; methodology, Y.L., J.L. and W.J.; software, J.L. and W.J.; validation, Y.L. and W.J.; formal analysis, J.C. and J.L.; investigation, J.L. and W.J.; resources, Y.L.; data curation, J.L. and W.J.; writing--original draft preparation, J.L.; writing--review and editing, J.C.; visualization, J.L. and W.J.; supervision, J.C.; project administration, Y.L. and J.C.; funding acquisition, J.C. and Y.L. All authors have read and agreed to the published version of the manuscript.  
The authors declare that this study received funding from Hyundai Motor Co., Ltd. The funder had the following involvement with the study: support for research materials and test equipment.  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
Author [PERSON] was employed by the company Hyundai Motor Company. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.