On abnormal noise generated from steam gas heater

When a steam gas heater set up in a town was operated, an abnormal noise with a sound pressure level (SPL) of 120 dB was generated at 32% of the rated flow rate. In order to solve this problem, We conducted a field survey to investigate the relationship between the operating conditions and the noise. First, I identified the source of noise and next, the noise level and the mode of sound pressure level (SPL) in a duct were measured and the FFT analysis was carried out to determine the dominant frequency. The results revealed that the abnormal noise was not a mere resonance but rather a self-sustained tone due to the interference of the vortex and the sound field. Furthermore, we measured the SPL outside the gas heater duct and found that the SPL was highest at the center of the gas heater duct. Typically, the first pressure mode should be minimum at the center and maximum at both ends, but the reason for this deviation was clarified in this paper. To address the issue, multiple baffle plates were inserted in a tube array and as a result, the abnormal noise completely disappeared. It was also found that the baffle plate should be inserted at the position where the particle velocity exceeds half of the maximum value.