Haifeng Liu

The liquid film cooling formed by jet-wall impingement plays a crucial role in thermal protection of thrust chamber walls in rocket engines. Accurate prediction of hydraulic jump formation is essential for enhancing cooling reliability. This study systematically investigates the effects of fluid properties, wall wettability, and downstream obstacle parameters on jump patterns and sizes. Visualization results reveal that jump patterns are predominantly governed by flow conditions. Reduced volume flow rate or increased obstacle height induces instability in low-viscosity fluid jump structures. Quantitative analysis demonstrates a strong linear correlation between jump radius and volume flow rate, with the slope and intercept governed by different combinations of key parameters including dynamic viscosity, gravitational acceleration, surface tension coefficient, downstream obstacle parameters, and other factors. A novel empirical correlation is established through scaling analysis and coefficient of variation optimization, utilizing two characteristic lengths and two constants to precisely predict jump radius. The proposed empirical correlation demonstrates improved predictive accuracy compared to existing models, with 95.90% of predictions for 244 experimental cases falling within engineering-acceptable error margins.

This study investigates the flow and heat transfer characteristics of the liquid film formed by fluid with different physical properties (surface tension and viscosity) on the heated surface. The regulation of fluid properties is achieved by the combined use of glycerol and two surfactants with distinct mechanisms. The liquid film flow is visualized using a high-speed camera. The temperature change during the liquid film cooling is measured using a thermocouple, and the surface heat flux is obtained by combining the inverse heat transfer algorithm. Results demonstrate that increased liquid viscosity suppresses surface wave amplitude and reduces liquid film coverage, while decreased surface tension diminishes interfacial stability, weakening the hydraulic jump characteristics. In addition, lower surface tension enhances bubble nucleation density in the boiling zone. Bubble cluster compresses liquid in wetting regions, inducing inward liquid accumulation. Subsequent bubble collapse creates a transient dry patch, leading to the formation of wavy film edges. Heat transfer analysis confirms that bubble clusters form a structure similar to a vapor film, reducing heat flux at wetting fronts by 9%–13.7%. Simultaneously, higher viscosity decreases effective cooling area, resulting in 12.6%–34.8% heat flux reduction across different zones. A dimensionless correlation between maximum heat flux and fluid parameters is established; the correlation exponents quantitatively validate the dominant influence of viscosity and surface tension on heat transfer performance.

High-pressure differential liquid-solid two-phase flow is widely used in the chemical industry, energy, and power fields. In this study, a multistage segmental throttling orifice pressure-reducing pipe was developed to address the bridging risk and erosion challenges associated with batch slag discharge in coal gasification. Ultrasonic technology was used to evaluate the erosion distribution inside the pipe and to establish the erosion mechanism. The research results demonstrate a rapid increase in the pressure drop of the pressure-reducing pipe with a rising flow rate, indicating its high-pressure drop characteristics. However, after the experiment was conducted for 30 h, the pipe failed at 5.56 m3/h operating conditions and the pressure drop performance of the pressure-reducing pipe was significantly decreased as erosion time increased. The pipe structure experiences severe deformation, expansion, and formation of pits due to impact, which exacerbated erosion and led to more complex erosion behavior.

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In the chemical engineering area, impinging flow plays a significant role in process intensification and energy consumption reduction. Thoroughly revealing the formation and evolution of vortices within the reactor has emerged as a crucial scientific issue. This paper systematically studies the steady-state flow at low Re (1 ≤ Re ≤ 200, where Re is the Reynolds number) in a cross-shaped reactor by particle image velocimetry technology. The evolution, distribution, and intensity characteristics of vortices in the reactor chamber are focused on. We show that at 55 ≤ Re ≤ 120, the distribution of vorticity and shear rate in the chamber show unimodal and bimodal patterns, respectively, and the center of the chamber is a local area with high vorticity and low shear. In contrast, for 120 < Re ≤ 200, the distribution of vorticity turns into a bimodal pattern, and the shear rate develops into a trimodal pattern. The center of the chamber constitutes a local area characterized by low vorticity and high shear. Additionally, based on the modified monopole vortex model, the distributions of vorticity and velocity of vortices in the steady engulfment flow are accurately depicted.

Carbon black from methane pyrolysis for hydrogen is an alternative resource and can be improved for conductive material supplication. Our current work uses an ultrafast Joule heating technique to modify the methane-pyrolyzed carbon black and prepare nanoparticles of electrode material for supercapacitor application, coupled with density functional theory, structural, and electrochemical analyses. Evolution rules of the carbon and pore structures of the modified sample with an increase in temperature reveal good structure improvements. The graphitization degree of modified carbon black nanoparticles increases, and the particle morphology changes from a smooth surface, disordered structure removal, and pore formation to graphite crystallization. Band structure and state density analytical results show that the modified carbon black with a defect-free structure possesses metallic properties and exhibits good electrical conductivity. A temperature around 1576 degrees C to the initial graphitization was defined based on the critical point of the evolution of ordered and disordered structures, while the electrical conductivity of the carbon black nanoparticles at 2000 degrees C reaches 2300 S/m. The modified carbon black performed with stable charge/discharge characteristics, exhibiting a 4.31% capacitance drop at a current load of 2 A/g and a 18.31% capacitance drop at a current load of 20 A/g.

A series of novel phenomena emerges when the coaxial airflow rapidly blows over the quasi-solid paste jet surface, leading to the direct solid-like exfoliation breakup of protrusions on the side face and the liquid-like tensile breakup on the end face. The experimental findings unequivocally demonstrate that the vertical protrusion formation on the side face under high gas velocity serves as a precursor to the subsequent exfoliation breakup, while the tensile breakup is a consequence of axial elongation of the protrusions at the junction between the side and end faces. A crucial step in interpreting the exfoliation breakup is to discern the individual force competition at the jet interface. As gas velocity increases, the radial shear force maintains stronger than the axial drag force and becomes the dominant factor. After the formation of protrusions, the airflow component directly impacts the upper surface of the protrusion in a vertical manner and causes it to fracture similar to the cutting off of a rod-shaped solid. During tensile breakup, the protrusions on the end face develop into liquid threads, which rotate and elongate under axial airflow drag and reflux, ultimately leading to the breakup. Mathematical force models are established to elucidate this intriguing phenomenon observed in the experiments. This study of quasi-solid pastes in airflow will expand the new understanding of the interaction between gas, liquid, and solid states.