The critical heat flux (CHF) of minichannel heat sinks is crucial, as it helps prevent thermal safety incidents and equipment failure. However, the underlying mechanisms of CHF in minichannels remain poorly understood, and existing CHF prediction models require further refinement. This study systematically investigates the characteristics and influencing factors of critical heat flux (CHF) in rectangular minichannels through combined experimental and theoretical approaches. Experiments were conducted using microchannels with hydraulic diameters ranging from 0.5 to 2.0 mm, with ethanol employed as the working fluid. Key parameters-including mass flux, channel geometry, system pressure, and inlet subcooling-were analyzed to assess their influence on CHF. Results indicate that CHF increases with mass flux; however, the increase rate diminishes under higher mass flux. Larger channel dimensions significantly enhance CHF by delaying liquid film dryout. System pressure further improves CHF by reducing bubble detachment frequency and promoting flow stability. Increased inlet subcooling enhances CHF by delaying the onset of nucleate boiling and improving convective heat transfer. Four classical CHF prediction models were evaluated, revealing significant overprediction-up to 148.69% mean absolute error (MAE)-particularly for channels with hydraulic diameters below 1.0 mm. An ANN deep learning model was developed, achieving a reduced MAE of 8.93%, with 93% of predictions falling within ±15% error. This study offers valuable insights and a robust predictive model for optimizing microchannel heat sink performance in high heat flux applications.

This paper addresses the issue of circumferential cracks appearing at the bottom of the trapezoidal sealing groove of the 321H stainless steel elbow flange at the inlet of reactor R103I in a residual oil hydrogenation unit at a certain refining and petrochemical company. Using methods such as macroscopic observation, chemical composition analysis, room-temperature mechanical property testing, metallographic analysis, and scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS), and ANSYS finite element simulation, the study systematically investigated the morphological characteristics, causes of formation, and propagation mechanisms of the cracks. The results indicate that while the chemical composition of the flange base metal complies with the requirements of the NB/T 47010-2010 standard, the tensile strength (approximately 450 MPa) and elongation after fracture (approximately 24%) are below the lower limit of the standard, and the hardness of the overlay weld (approximately 210 HBW) significantly exceeds the standard limit. The δ-ferrite content in the overlay layer (5.2%–7.8%) is much higher than that in the base metal (<1%), which is the main reason for the increased hardness and SCC sensitivity of the overlay layer. The cracks originated in the 5–6 mm-thick overlay layer on the surface of the sealing groove. Cracking within the overlay layer was primarily intergranular and occurred along quasi-cleavage planes, indicating that these were heat-affected zone cracks or reheat cracks formed during the manufacturing stage. During service, chlorides (0.49%–0.61% wt) and sulfides in the medium induced stress corrosion. Cracks propagated dendritically through the grain from the overlay weld layer across the fusion line into the base metal, ultimately leading to the failure of the sealing groove. The research findings provide important evidence for the manufacturing quality control and in-service safety monitoring of flanges in similar pressure-bearing equipment.

The safe and stable operation of pressure vessels is crucial for industrial production. However, during long-term service, they are prone to defects that gradually evolve under the superposition of multiple factors, eventually leading to failure. Taking an over-designed service-life pressure vessel from a power enterprise as the research object, this study systematically analyzed the crack defects detected in the vessel using macro inspection, chemical composition analysis, mechanical property testing, metallographic analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results show that the cracks initiate from the ends of incomplete fusion defects in the weld. The direct cause is that incomplete fusion defects destroy the continuity of the material, resulting in local stress concentration. Additionally, the material itself contains excessive levels of elements such as S, Si, and Mn, and this composition reduces its crack resistance. The pressure vessel has been in service under fluctuating working pressure for a long time, causing the cracks to propagate to the outer surface of the vessel under alternating stress. Based on the analysis results, strategies for risk management and control of the same batch of pressure vessels in the enterprise are proposed, providing a reference for the safety assessment of similar aging pressure vessels in the future.