Hilly terrain pipeline is a common form of pipeline in oil and gas storage and transportation industry. Due to the hilly terrain influence, the liquid at the elbow of the gathering pipeline is easy to flow back and accumulate to form slug flow, so it is necessary to remove the accumulated liquid by gas purging. In this paper, experiment is carried out in hilly terrain pipelines. Three flow patterns of stratified flow, slug flow and stratified entrained flow are observed. The process of gas purging accumulated liquid is divided into four stages, namely liquid accumulation, liquid rising, continuous outflow and tail outflow. At the same time, the flow pattern maps of each stage are drawn. The pressure drop signal is analyzed in time domain and frequency domain, and the contour map of pressure drop distribution is drawn. It is found that the ratio of range to average value can well distinguish the occurrence range of each flow pattern. Based on visualization, the transition process of slug flow to stratified flow and stratified entrained flow is studied, and the transition boundary prediction model is established. An image processing method is proposed to convert the image signal into a similarity curve, and PSD analysis is performed to calculate the slug frequency. The normal distribution is used to fit the slug frequency, and the predicted correlation is in good agreement with the experimental data.

Solar-driven photothermal catalytic CO₂ conversion into fuels offers a promising approach to reducing fossil fuel dependence. To enhance the efficiency of photothermal CO₂ reduction, photothermal catalyst design must not only sustain the high temperatures required for the reaction but also effectively utilize the entire solar spectrum. In this study, we present a novel photothermal catalyst architecture BiVO₄/Bi/BiOCl that surpasses traditional designs by integrating plasmonic metal Bi as the “hot spot” and BiOCl as the thermal insulation layer on the outermost part. This structure realizes thermal management, contributing to maintaining the high temperatures required for the reaction. The BiVO₄/Bi/BiOCl multi-component system synergistically absorbs the full solar light spectrum and achieves band-division utilization: short- and mid-wavelengths drive reduction and oxidation reactions, respectively, while long-wavelengths induce the photothermal effect. The BiVO₄/Bi/BiOCl catalyst demonstrates high-efficiency CO₂ conversion performance in an outdoor concentrating system, achieving a CO production rate of 9.5 μmol/h. This work presents a design strategy for functional photothermal catalysts, making them viable candidates for industrial-scale CO₂ conversion processes.

Large vertical pipes are key structures connecting subsea wells to offshore platforms. However, existing studies mainly focus on small vertical pipes. In a vertical acrylic pipe with 80 mm inner diameter and 11 m height, a high-speed camera was used to visually research the influences of pipe diameters, liquid properties and inlet effect on air-water co-flow characteristic. Different flow regime maps of vertical pipes (diameters are in the range of 50–189 mm) were compared and the critical gas velocity of the transition boundary from bubble to slug flow tended to increase with the increase of diameters at D ≥ 80 mm. Drift-flux models were established in different flow regimes and liquid properties have a significant effect on drift coefficients of bubble flow and slug flow (void fraction α ≤ 0.4). The influence of inlet turbulent effect on the gas-liquid interface distribution gradually weakened and disappeared from the pipe base to 85D, where the flow was fully developed. Slug frequency has a trend of increase first and then decrease with the gas Weber numbers increasing at low liquid superficial velocities (J_L ≤ 0.31 m/s). And on the basis of this law, a new slug frequency correlation was proposed. It was found that there was an exponential relationship between the ratio of lengths of Taylor bubble to slug and the void fraction.

Photoelectrochemical (PEC) water splitting using semiconductors offers a promising way to convert renewable solar energy to clean hydrogen fuels. However, due to the sluggish reaction kinetics of water oxidation, significant charge recombination occurred at the photoanode/electrolyte interface and cause decrease of its PEC performance. To reduce the surface recombination, we deposit different transition metal complexes on BiVO₄ nanocone arrays by a versatile light driven in-situ two electrode photodeposition approach without applied bias. Conformal cobalt phosphate "Co-Pi" , nickel borate "Ni-Bi" and manganese phosphate "Mn-Pi" complexes were deposited on BiVO₄ nanocone arrays to form core-shell structure photoanode, all of which lead to enhanced photoelectrochemical performance. The photocurrent of the Co-Pi/BiVO₄ photoanode under front-side illumination for 5 min is increased by 4 folds comparing to that of bare BiVO₄ photoanode at 0.6 V vs. RHE, reaching a hole transfer efficiency as high as 94.5% at 1.23 V vs. RHE. The proposed photodeposition strategy is simple and efficient, and can be extended to deposite cocatalyst on other semiconductors with a valence band edge located at a potential more positive than the oxidation potential of transition metal ion in the cocatalyst.

Oxygen evolving catalyst (OEC) is a critical determinant for the efficiency of photoelectrochemical (PEC) water splitting. Here we report an approach to depositing a novel manganese borate (Mn-Bi) OER catalyst on BiVO₄ nanocone photoanode by photodeposition in sodium borate buffer solution containing Mn(Ⅱ) ions. Due to the spontaneous photo-electric-field-enhancement effect at the vertically oriented BiVO₄ nanocone structure, spherical Mn-Bi nanoparticle was selectively photodeposited at the apex of BiVO₄ nanocone. Significant improvement of photocurrent was observed for the obtained hierarchical Mn-Bi/BiVO₄ photoanode which could be ascribed to enhanced hole injection efficiency, especially in low bias region. It was observed that the injection efficiency of Mn-Bi/BiVO₄ is 98% which gave a photocurrent of 0.94 mA/cm² at 1.5 V vs. RHE.

A novel pure cubic-phase pyrochlore structure tin(Ⅱ) antimonate nanophotocatalyst, stoichiometric Sn₂Sb₂O₇, has been prepared by a modified ion-exchange process using an antimonic acid precursor, and employed in visible-light-driven photocatalytic H₂ evolution for the first time. The physicochemical properties (crystal phase, chemical composition and state, textural properties, and optical properties) of the material were investigated by different instrumental techniques. Compared with the antimonic acid precursor, the as-prepared Sn₂Sb₂O₇ had a narrower bandgap, smaller crystal size, and larger BET surface area. The as-prepared Sn₂Sb₂O₇ was validated as a promising candidate for visible-light-driven photocatalytic H₂ evolution with a constant rate of 40.10 μmol·h⁻¹·g_cat⁻¹.

Hematite (α-Fe₂O₃) nanorod films with their surface tuned by W⁶⁺ doping have been investigated as oxygen-evolving photoanodes in photoelectrochemical cells. X-ray diffraction, field emission scanning electron microscopy, UV-visible absorption spectroscopy, and photoelectrochemical (PEC) measurements have been performed on the undoped and W⁶⁺-doped α-Fe₂O₃ nanorod films. W⁶⁺ doping is found to primarily affect the photoluminescence properties of α-Fe₂O₃ nanorod films. Comparisons are drawn between undoped and W⁶⁺-doped α-Fe₂O₃ nanorod films, WO₃ films, and α-Fe₂O₃-modified WO₃ composite electrodes. A close correlation between dopant concentration, photoluminescence intensity, and anodic photocurrent was observed. It is suggested that W⁶⁺ surface doping promotes charge transfer in α-Fe₂O₃ nanorods, giving rise to the enhanced PEC performance. These results suggest surface tuning via ion doping should represent a viable strategy to further improve the efficiency of α-Fe₂O₃ photoanodes.