Corrugated pipes are extensively used in engineering applications that require flexibility and enhanced heat exchange, such as drainage and compact heat exchangers, and recently as inner layers in cryogenic flexible hoses for offshore liquid ship-to-ship transfer. The great flexibility of these hoses makes them well-suited for deployment in dynamic and harsh marine environments. However, the corrugated geometry also induces flow separation, elevated turbulence, and intricate heat transfer behaviors. This study focuses on the flow and heat transfer characteristics in corrugated pipes with various geometries, addressing the current lack of systematic comparative studies on the performance of different Reynolds-Averaged Navier–Stokes (RANS) models in such configurations. Despite their limitations in accuracy compared to high-fidelity methods, RANS models remain the workhorse for engineering analysis due to their computational efficiency. This study employs several RANS models to simulate flow and heat transfer in three corrugated pipe geometries—sinusoidal (Sin), C-type, and U-type—over a Reynolds number range of O(10⁴) to O(10⁵) and assesses their performance against high-fidelity Large Eddy Simulation benchmarks. The results show that prediction accuracy decreases with increasing corrugation depth, with the most significant errors in trough regions where reverse flow dominates, and that the choice of turbulence model has a strong influence on the predicted flow and heat transfer behavior. Among all models, the $k-ϵ$ models overall provide the most consistent and accurate predictions for friction factor, velocity distribution, and Nusselt number, while the $k-\omega$ models perform the worst. The Reynolds Stress Model improves friction factor prediction accuracy at high Reynolds numbers and provides marginally better accuracy in mean Nusselt number prediction, but its advantages are limited relative to its substantially higher computational cost. The Standard $k-ϵ$ model with Enhanced Wall Treatment demonstrates robust and balanced performance across geometries and flow regimes, making it a practical choice for engineering use. This work provides engineers and researchers guidance for choosing RANS models that balance accuracy and computational efficiency in simulations of LNG ship-to-ship transfer, compact heat exchangers, and other industrial systems that employ corrugated pipes.

With the increasing severity of climate change, Carbon Capture, Utilization, and Storage (CCUS) technology has become essential for reducing atmospheric CO₂. Marine carbon sequestration, which stores CO₂ in seabed geological structures, offers advantages such as large storage capacity and high stability. Cryogenic hoses are critical for the ship-to-ship transfer of liquid CO₂ from transportation vessels to offshore carbon sequestration platforms, but their design methods and mechanical analysis remain inadequately understood. This study reviews existing cryogenic hose designs, including reinforced corrugated hoses, vacuum-insulated hoses, and composite hoses, to assess their suitability for liquid CO₂ transfer. Based on CO₂’s physicochemical properties, a conceptual composite hose structure is proposed, featuring a double-spring-supported internal composite hose, thermal insulation layer, and outer sheath. Practical recommendations for material selection, corrosion prevention, and monitoring strategies are provided to improve flexibility, pressure resistance, and thermal insulation, enabling reliable long-distance tandem transfer. A mechanical analysis framework is developed to evaluate structural performance under conditions including mechanical loads, thermal stress, and dynamic responses. This manuscript includes an introduction to the background, the methodology for data collection, a review of existing designs, an analysis of CO₂ characteristics, the proposed design methods, the mechanical analysis framework, a discussion of challenges, and the conclusions.

The armor layer is one of the core components of flexible risers. It provides essential mechanical properties such as tensile strength, pressure resistance, and torsional performance, which are necessary for operation in complex marine environments. However, due to the significant disparity between the cross-sectional dimensions of the armor wires and the overall riser size, severe computational costs are often incurred when a finite element (FE) model is employed for the performance analysis of an armor layer. To address this, an asymptotic homogenization method for flexible risers is established in the present study. In this method, the armor wires, modeled as beam elements, are equivalent to an anisotropic shell structure, and the equivalent elastic properties of the armor layer are obtained with unit-cell analysis. These properties are then used for the overall analysis of the flexible riser’s armor layer response, without considering the specific characteristics of the steel wires, thereby improving the efficiency of the performance analysis. The effectiveness of the proposed method is verified in a numerical example based on a comparison with a finite element (FE) model. Moreover, the effect of the unit cell size is investigated by introducing a size factor. A significant size effect is observed, unlike in the truss-based unit cell, for which an explanation based on the stiffness coefficient is given. The proposed method offers a new technique for efficient performance analysis of the armor layer of flexible risers.

This study employs a combined approach of theoretical calculation and numerical simulation to systematically optimize the impeller of a turbine expander, the core component of a 10-ton/day hydrogen liquefaction system. First, based on thermodynamic analysis and one-dimensional calculations, a three-factor four-level orthogonal experiment optimizes the parameters of reaction degree, radius ratio, and blade height ratio. Building upon this foundation, the influence of two-dimensional meridional profiles on impeller efficiency is investigated to establish design criteria. Subsequently, the effects of three-dimensional parameters including tip clearance, blade count, and blade thickness on performance are analyzed. Finally, the impact of rotational speed and flow rate on efficiency is explored, identifying high-efficiency operational ranges. Through multi-parameter collaborative optimization, an impeller configuration achieving low outlet temperature (53.67 K) and high efficiency (about 93.6%) is obtained, providing critical references for designing high-efficiency turbine expanders in hydrogen liquefaction systems.

In this study, we perform molecular dynamics simulations to investigate the desublimation of carbon dioxide (CO₂) on hydrophilic and hydrophobic surfaces with nanostructures. The results reveal that the presence of surface nanostructures substantially reduces the temperature threshold for CO₂ desublimation relative to that observed on smooth surfaces. On hydrophilic surfaces, the adsorption layer is found to be considerably thicker, and the surface topography disrupts the spatial ordering of CO₂ molecules at the liquid–solid interface, delaying nucleation onset by 65.68% relative to the smooth surface in the representative trajectory. In contrast, the introduction of nanostructures effectively increases the heat transfer area on hydrophobic surfaces, thereby promoting CO₂ condensation and accelerating the overall desublimation process, with a 42.86% reduction in nucleation onset time on structured surfaces. These findings suggest that the judicious selection of surface wettability and morphology enables tunable control over both condensation and nucleation kinetics, which holds practical implications for the design of efficient carbon capture systems.