Investigation of natural circulation flow instability based on thermal effect during steady-state condition using wavelet and chaotic analysis

The thermal effect as an initial condition plays a critical role in determining flow characteristics and must be thoroughly studied to better understand the behavior of natural circulation flow. Thus, this research aims to investigate the instability level of natural circulation flow for steady-state conditions, using wavelet and chaotic analysis. The research method experimented with the natural circulation loop by varying the water temperature settings inside the heating tank section with 60 °C, 70 °C, 80 °C, and 90 °C. Temperature and natural circulation flow data are further processed using post-processing signal processing wavelet and chaotic analysis to determine the instability flow level. The results during the steady-state show a laminar flow regime with an average Reynolds number of 784 and the average Reynolds numbers with a transition flow regime of 1137, 1537, and 2020. The results of the analysis using wavelets show that the dominance of the wavelet variance for all heating tank section temperature setting conditions occurs at the fifth and sixth decomposition band level. Meanwhile, the results of the chaotic analysis show that low natural circulation flow instability occurs at the lowest entropy value for the heating tank section temperature setting of 90 °C. The study shows that from signal processing point of view, wavelet and chaotic analysis can be suitable approaches to identify the behavior of natural circulation flow instability levels.