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Due to the existence of phase transition, sub-cooled boiling, as an efficient heat exchange mode, is widely used in most heat exchange equipment. Under specific application conditions, the rod bundles will work under inclined conditions. For example, some heat exchangers need a certain inclination angle for installation due to space constraints, different positions in the elbow area of the U-tube steam generator have different inclination angles, and some rod bundles in marine nuclear power floating platforms or ship nuclear power plant also experience long-term inclination under ocean conditions with large-period waves. Therefore, it is crucial to research the sub-cooled flow boiling heat transfer characteristics on the surface of inclined heating rod bundles. In this paper, combining with the content of bubble dynamics and according to the characteristics of inclined bubble detachment, the bubble detachment criterion under inclined conditions was formulated. The force calculation of the bubble was then carried out, and the correlation parameters such as the diameter of the bubble detachment were-obtained. In the calculation process, it is considered that the bubbles detachment judgment condition on the upper surface of the inclined heating rod bundles is that the force balance in the direction of bubble buoyancy is broken. Additionally, under inclined heating rod bundles, a calculation model of the heat flux on the heating wall was also established adopting the wall heat flux partitioning model in conjunction with the bubble dynamics. Traditional wall heat partitioning models are mostly based on vertical or horizontal heating walls, however, the applicability for inclined conditions is still being investigated. In comparison to traditional heating conditions, the bubble behavior on the heating surfaces of the inclined heating rod bundles is different, resulting in a different heating transfer process. Therefore, the traditional wall heat partitioning model was improved to adapt to the working conditions of inclined heating rod bundles. The calculation results of the model show that 81.25% of the data can be captured within ±20% of the error line, and the average relative error is roughly 13.07%. The model has good applicability to calculate the heat flux of inclined heating rod bundles. However, the model is more applicable to low sub-cooled boiling than high sub-cooled boiling. During the high sub-cooled boiling, the heat flux calculated by the model is too low, which is because of the slowly rising wall temperature in high sub-cooled boiling. During low sub-cooled boiling, since the change of wall temperature is relatively smaller, the model is more applicable compared with that under high sub-cooled boiling.

The swimming pool-type low-temperature heating reactor (SPLTHR) has low thermal parameters, large heat capacity, and high inherent safety, so it is a suitable reactor type for nuclear heating reactors. Because the SPLTHR has a long shutdown time and the temperature difference between the cold and heat sources is small, it has certain requirements on the heat transfer capability of the passive residual heat removal system (PRHRS). Basing on the characteristics of SPLTHR, a singlephase natural circulation experiment system of PRHRS of SPLTHR was designed by H2TS (hierarchical twotiered scaling) proportion analysis method, and the flow and heat transfer characteristics of the singlephase natural circulation of the PRHRS were studied experimentally. In order to get closer to the prototype system, the center height difference of the cold and heat source of the experimental system was the same as that of the prototype system, which was 9 m. The ranges of the pool water temperature, air temperature and air flow rate in the experiment were 50-90 ℃, 15-30 ℃ and 15 000-35 000 m3/h, respectively. The results show that the experimental system designed by H2TS proportion analysis method can achieve the designed heat transfer capacity when the temperature difference between the cold and heat source is 54 ℃, which means the method is suitable for the design of singlephase natural circulation system under low temperature difference. There is flow oscillation in the system startup process, and the system can be stabilized gradually with the operation. The hot and cold water in the primary loop alternately enters the heat exchanger and aircooler, causing the driving force of the system to change, which leads to fluctuations in circulation flow rate and heat transfer capacity. The change of boundary conditions mainly affects the heat transfer capacity of the system and the time to reach stability, but has little effect on the shape and number of fluctuations before the system reaches stability. For the PRHRS heat exchanger tube bundle, which is neither a constant heat flow nor a constant wall temperature boundary, it is more appropriate to use the natural convective heat transfer temperature difference as the parameter of the Grashof number. Due to the tube bundle effect, the traditional singletube natural convection heat transfer correlations have a low predictive value for the natural convection heat transfer outside the tube bundle. According to the experimental data, the correlation of natural convection heat transfer outside the tube bundle with the applicable range 351×103

This study presents a comprehensive method for detecting debonding defects in concrete-filled steel tube (CFST) structures using wave propagation analysis with externally attached piezoelectric ceramic sensors. Experimental tests and numerical simulations were conducted to evaluate the sensitivity and accuracy of two measurement techniques—the flat and oblique measurement methods—in detecting debonding defects of varying lengths and heights. The results demonstrate that the flat measurement method excels in detecting debonding height, while the oblique method is more effective for detecting debonding length. A normalized judgment index (DI) was introduced to quantify the correlation between debonding characteristics and the detected signal amplitude, revealing the significant influence of sensor spacing on detection accuracy. Furthermore, a mathematical model based on wavelet packet energy analysis was developed to establish a linear relationship between wavelet packet energy and debonding size. This model offers a scientific foundation for the quantitative detection of debonding defects and provides a new approach to the health monitoring of CFST structures. The integrated use of both measurement techniques enhances detection precision, enabling both qualitative and quantitative defect analysis, which can significantly guide the maintenance and repair of CFST structures. [ABSTRACT FROM AUTHOR]