The annular centrifugal contactor (ACC) is a vital element in liquid-liquid separation processes. However, despite its advancements, the flow characteristics within the ACC rotor remain intricate, necessitating the use of empirical geometrical guidelines. In order to gain a comprehensive understanding of the complete flow characteristics, a well-structured design becomes essential. This study addresses this need by presenting a systematic and meaningful three-dimensional numerical simulation, which effectively analyzes the impact of the ACC on the flow field and separation performance within the rotor, utilizing dimensional analysis. The simulation employs a combination of the Eulerian-Eulerian multiphase model, volume of fluid, and k-ε turbulence model to effectively separate two liquids. Through careful analysis, the oil separation efficiency and quality are calculated at the oil outlet. The findings reveal that the ACC’s overall separation performance is notably affected by factors such as the Reynolds number, dimensionless angular velocity, and aspect ratio. More specifically, the oil separation efficiency exhibited a considerable improvement, rising from approximately 48

The primary moisture separator—a key component in the PWR nuclear power plant—determines the quality of supplied steam to a turbine. Investigating its characteristics is important because supplying steam with excessive droplet entrainment results in damages to pipes, valves, and turbines in power plant circuits. In this numerical study, the particle tracking method in the Eulerian–Lagrangian methodology is used to investigate the characteristics of a primary moisture separator. Various swirl vanes with different bending angles, vane quantities, and vane locations are chosen to investigate the effect of design parameters on characteristics of the primary moisture separator. Additionally, the water droplet size is considered to vary from 0.01 to 50 μm in this study. The pressure drop between the inlet and outlet, the steam quality at the orifice outlet, and the particle collection ratio are discussed in this paper. The results show that steam quality increases as the bending angle decreases, and increasing the number of swirl vanes increases both the pressure drop and the steam quality.

Critical Weber numbers (Wecr) for droplet splashing are investigated by considering the geometrical morphologies of hydrophobic micro/nano-textured surfaces and the viscosity of lubricants. A decreasing trend of Wecr with respect to pillar spacing is evident for all textured and lubricant-infused surfaces (LISs), but it is independent of the pillar diameter effect. Additionally, the overall Wecr of the LIS exceeded that of the micro/nano-textured surfaces. The results show that the early droplet splash on micro/nano-textures may be attributed to the slip condition, decreasing the friction loss of airflow and increasing Uair/U0 and K-H instability. Moreover, the slip velocity on the LISs decreases as the lubricant viscosity increases in the order uslip (101) > uslip(105) > uslip(107). Therefore, an increase in slip velocity facilitates earlier droplet splashing on low-viscosity LIS101 than on high-viscosity LIS105 and LIS107. Furthermore, the droplet retraction behavior beyond the maximum spreading varied significantly based on the surface wetting characteristics.

Cylindrical structures are widely used in offshore and marine engineering, but they may suffer from vortex-induced vibration under the influence of ocean or wave currents, which can lead to severe fatigue damage. In this study, we applied the open-source software Open-Source Field Operation and Manipulation (OpenFOAM) to investigate the characteristics of fluid flow around offshore cylindrical structures, taking into account the effect of helical strake parameters, such as pitch and strake number. The aim of this study is to explore the possibility of suppressing vortex shedding with different helical strake parameters. Numerical simulation results demonstrated that attaching a helical strake to the bare cylinder destroyed vortex shedding in offshore cylindrical structures. The vortex visualization showed that the helical strake destroyed the three-dimensional vortex structures. Moreover, the lift coefficient data showed that the vibration frequency of the cylinder decreased after attaching the helical strake, indicating that the vortex-induced vibrations on the wake flow tended to fade. The results suggest that the helical strake is a promising option for suppressing the wake vortex shedding of cylindrical structures in offshore engineering.

Dynamic contact angles have investigated by numerous researchers for understanding interfacial behavior at moving contact lines However, due to limitation of visualization techniques, previous experiments for dynamic contact angles have conducted limitedly in hydrophilic capillary tubes based on visible ray. Recently, there is continuous need for research on dynamic contact angles in hydrophobic capillary tubes on various research and industrial fields. Therefore, in this study, we measure the dynamic contact angles of water-glycerol mixture slug in hydrophobic microtubes using synchrotron X-ray imaging. Based on the visualized data, we verified the previous experimental correlations for dynamic contact angles.

Liquid–liquid separation is a process of separating two liquids based on their relative solubility; however, separating two liquids with a slight density difference is difficult because of interfacial forces. A newly designed annular centrifugal contactor (ACC) with a funnel–type weir zone was investigated numerically to analyze the flow fields and separation performance of two liquids with slight density differences, such as palm oil and water. Ansys CFX was used to simulate unsteady, turbulent, multiphase flows in the ACC. The simulation was performed using the Eulerian–Eulerian method, in which a homogeneous k–ɛ turbulence model with a scalable wall function is used. The sliding mesh method was adopted to solve the rotational effect of the stator rotor. A detailed parametric analysis of mixing and separation based on the liquid density difference, angular velocity, and inlet velocity of the mixture variations was performed. The oil quality and separation efficiency were calculated at the oil outlet to analyze the performance of the ACC rotor. The results show that oil quality increases with increasing angular and inlet velocities but decreases with an increasing liquid density difference. Moreover, the oil separation efficiency decreases with increasing angular and inlet velocities but increases with an increasing liquid density difference. Maximum oil quality and separation efficiencies of approximately 99% and 79%, respectively, were obtained at the oil outlet. Finally, it can be concluded that the two liquids with a slight density difference can be adequately separated using the newly designed ACC.

Droplet splashing phenomena are observed experimentally on the well-designed hydrophobic micro and micro-/nano-textured surfaces. The critical Weber numbers (We(cr)) for splashing are investigated by considering the geometrical surface conditions. The splashing was facilitated with large micropillar spacing and diameter and suppressed with small ones. Large pillar spacing and diameter enabled easy penetration of liquid by reduced capillary force and increased the outlet of airflow. This air-liquid velocity difference creates instability at the edge of the spreading droplet, thereby generating splashing based on the Kelvin-Helmholtz instability mechanism. Besides, earlier splashing was observed on micro/nano textures than on microtextured surfaces. Since the impacting droplet could not penetrate the nanopillars due to higher capillary pressure and slip boundary condition formation, it reduces airflow friction. Hence an increase in the air-liquid velocity ratio renders splashing.

In this numerical study, a 2D prismatic tank - subjected under horizontal excitation - is used to analyse the sloshing characteristics for a specific range of Reynolds number, from 2.5 × 104 to 2.0 × 105. Three models of geometric variable δ1 - namely, δ1 = 50 mm, δ1 = 150 mm and δ1 = 250 mm - are used to observe the effects of the lower chamfered shape of the prismatic tank, where the Reynolds number for each δ1 ranges from 2.5 × 104 to 2.0 × 105 (12 cases). The volume of fluid (VOF) method is used for the multi-phase flow analysis. The fast Fourier transform (FFT) technique is used to analyse the frequency components of excitation force and the magnitude of the amplitude spectrum. The results show that the sloshing wave fluctuation becomes small when the geometric variable δ1 is larger. Also, the FFT technique shows that the resonance does not occur due to frequencies which are not integral multiple of the excitation frequency. Moreover, for the sloshing load analysis, the free surface length is an important parameter than the shapes of the lower section.

A brake system with hydraulic devices has a pipeline (brake hose) to transmit the fluid force generated by the brake. The layout design of brake hoses is one of the important factors that greatly affects the performance and life of the braking system. In this research, the material properties of each hose composed of composite materials were obtained through direct experiments, and then the layout analysis of brake hoses was carried out. During this layout analysis, an independently developed program was used to reduce the time required. It was confirmed that the shape of brake hose layout obtained followed well that of the actual experiment. In addition, the reinforcing layer (braided layer) was found to have a greater effect than the rubber layer on the formation of the brake hose layout.

In hydrophobic mini- and microchannels, slug flow with moving contact lines is typically generated under various two-phase flow conditions. There is a significant pressure drop in this flow pattern with moving contact lines, which is closely related to the dynamic contact angles. Researchers have investigated dynamic contact angles experimentally for decades, but due to the limitations of visualization techniques, these experiments have typically been conducted in low Weber number regions (We < 10-3). In this study, we clearly visualized the dynamic contact angles of a liquid slug in high Weber number regions (10-3 < We <1) via synchrotron X-ray imaging with high temporal (∼1000 fps) and spatial (∼2 μm/pixel) resolutions. We precisely measured the pressure drop with moving contact lines in a hydrophobic minichannel (inner diameter = 1.018 mm). On the basis of our experimental data, we verified previous correlations for dynamic contact angles and explored the relationship between pressure drop with moving contact lines and dynamic contact angles.

In this study, the heat transfer characteristics - in accordance with the operating conditions - of the heat exchanger for re-liquefaction of LNG storage tanks is analyzed. The heat transfer characteristics and structural stability were analyzed for each of the sub-cooler and pre-cooler, which uses an LNG fluid and an N2 fluid respectively. The N2 fluid is used in the actual experiment. Considering the efficiency and cost of the calculation, 1/25 and 1/49 reduced models were used for the number of pipes; the temperature difference among pipes at the outlet was less than 5%. Hence it was confirmed that the analysis of the reduced model was reasonable. Comparing with the one-dimensional analysis results, a discrepancy from 2.2% to 7.4% could be confirmed. By visualizing the flow field through the computational fluid cynamics (CFD) analysis, the cause of inefficiency could be identified. The analysis results will be helpful in understanding the exact performance of the heat exchanger by predicting the design variables in the future.

To investigate the thermal and hydrodynamic behaviors in a rough microchannel, the alternative arrangement of mixing triangular and rectangular ribs for regular and irregular spaced and heights has been considered using thermal lattice Boltzmann method (TLBM). The TLBM is a kinetic method based on the particle distribution function, so it can successfully be implemented to study the flow dependence on Knudsen number including slip velocity, pressure drop in rough microchannel. The friction coefficients in terms of Poiseuille number (Pn) and the rate of heat transfer in terms of Nusselt number (Nu) have been discussed in order to study the effect of surface roughness geometries in the slip flow regime at Knudsen number (Kn), ranging from 0.01 to 0.10. It was found that the effect of surface roughness is more pronounced at low Knudsen numbers as well as random spaced and heights. Finally, the thermo-hydraulic performances have been discussed for various cases numerically and the results are compared with the smooth microchannel.

The performance of the air-trapping mechanism to suppress sloshing impact pressure in a prismatic tank was numerically evaluated. In order to implement the air-trapping mechanism, a short horizontal baffle array was installed on either side of the tank to collect air by the sloshing flow. The impact pressure change was analyzed by setting the ratio of the baffle length to the tank width as a parameter, and the pressure distribution on the wall was observed through eight calculation points (CPs) set between the baffles in the direction of tank height. The suppression performance of impact pressure was evaluated using Eulerian- Eulerian multiphase model to consider the water-air two-phase flow. The visualization results show the generation of sloshing impact pressure and the effects of the air-trapping mechanism. Quantitative comparisons of time series results of pressure were performed using peak pressure comparison and fast Fourier transform (FFT) analysis. The overall sloshing impact pressure reduction was 58.2 % in the FFT analysis and the maximum reduction rate was 70.4 %.

The steam generator in a nuclear power plant should provide high quality steam to the turbine for better efficiency and stability. For this purpose, a steam separator is installed in the steam generator to manage the quality of the steam. In this study, computational fluid dynamics (CFD) technique was carried out to analyze the flow phenomenon of the swirl-vane type steam separator. When the steam enters the swirl-vane separator with droplets, it is affected by the centrifugal force. Some of the droplets are attached to the riser wall, some pass through the outlet (bypass and the downstream pipe) and the remaining droplets enter the next separator. A Lagrangian particle model was used to simulate the behaviors of steam and water droplets. The results show that the removal of the droplets depend on the size of the droplets. When the droplet size is small, it is removed by the outlet. In particular for the droplet size of 0.01 micron, over 75% of them are removed. When the droplet size is large, it is collected on the wall. In particular for the droplet size of 50 micron, over 95% of them are collected on the wall. Thus, the performance of the separator decreases as the droplet enters the next separator directly before being collected on the walls or on the outlet if the length of the riser above the swirl-vane is short.