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The interface tends to behave as a circular shape under the effect of surface tension in the two-dimensional two-phase fluid flow. In this study, based on the coupled volume-of-fluid and level set (VOSET) method, an accurate circle-based interface reconstruction (CIR) algorithm for structured meshes is proposed, which features a straightforward implementation procedure. A portion of the standard circle is employed to approximate the curve interface, without the need for complex classification, coordinate transformation, and equation transformation. The radius of this circle is computed simply by the curvature and signed distance at the mixed cell center, and the center of this circle is determined using a straightforward dichotomy method under the mass conservation constraints. Results indicate that the coupled VOSET and CIR (VOSET-CIR) method maintains superior computational accuracy in the signed distance, interface curvature, and dynamic interface reconstruction compared to the coupled VOSET and piecewise linear interface calculation (VOSET-PLIC) method, with accuracy improvements ranging from 34% to 1490% across different test cases. Furthermore, the VOSET-CIR method outperforms the efficient least squares volume-of-fluid interface reconstruction (ELVIRA) and PLIC algorithms in reconstructing random circles and surpasses the quadratic spline based interface reconstruction (QUASI) algorithm in reconstructing random squares. In terms of computational efficiency, except for the initial PLIC algorithm, the time costs of the VOSET-CIR method are substantially lower than those of the ELVIRA and QUASI algorithms, as well as the VOSET-PLIC method. [ABSTRACT FROM AUTHOR]

Carbon capture, utilization, and storage have been an effective way to deal with global climate issues. Injecting CO2 into depleted oil reservoirs can reach the dual goal of carbon storage and enhanced oil recovery. To optimize the gas injection strategy, it is necessary to understand the underlying mechanisms of three-phase fluid flow of oil, water, and gas. In this study, a lattice Boltzmann color gradient model is used to investigate the pore-scale three-phase displacement process in porous media. Gas is injected into the porous domain initially occupied by water and oil. Typical microscopic behaviors, including coalescence and split-up, pinch-off, double and multiple displacement, as well as parallel flow, are identified and discussed. Effects of water content (ϕ), capillary number (Ca), wettability and viscosity ratio (M) on the flow pattern, and oil recovery rate are explored. The oil ganglia inhibit the development of gas fingers, causing stronger viscous fingering characteristics with increasing ϕ. The fingering pattern is located in the crossover zone for the Ca from 5 × 10−5 to 5 × 10−4. As ϕ increases, the oil recovery rate reduces. The oil ganglia tend to occupy small pores as oil wettability enhanced, making it more difficult to be drained out. The reduction of oil viscosity is beneficial to improve connectivity, thereby effectively enhancing the oil recovery. Finally, the CO2 storage rate is also evaluated. It is found that the storage rate is very sensitive to the initial oil–water distributions. In general, the storage rate increases as ϕ decreases, Ca increases, and oil wettability enhances. [ABSTRACT FROM AUTHOR]

Three-dimensional numerical studies were performed for the performance of wavy fin-and-tube heat exchangers in Body-Fitted Coordinates (BFC) system. Effects of geometric parameters on air-side heat transfer and fluid flow characteristics and fin efficiency were examined. The results showed that with the increase in Reynolds number, wavy angle, fin thickness and the decrease in fin pitch and transverse tube pitch, the heat transfer performance are enhanced; however, pressure drops are also increased. So, in practical applications, the wavy angle had better be located between 10° and 20° and the fin pitch should be located between 1.2 mm and 2.0 mm. The fin efficiency and average fin surface temperature decrease with the increase of Reynolds number, wavy angle, fin pitch and transverse tube pitch. With the increase of fin thickness, the fin efficiency and average temperature on fin surface also increase. [ABSTRACT FROM AUTHOR]

Three immiscible fluids systems are often encountered in energy and environmental disciplines, especially in the oil exploration field. It is essential to enhance oil recovery (EOR) by identifying the three-phase fluid flow mechanism of oil-gas-water system in complex geological structures. In the present study, a lattice Boltzmann (LB) color gradient model for three immiscible fluid flow in three-dimensional porous media is employed and validated using five benchmarks (i.e., the multiphase spinodal decomposition; the multiphase Young-Laplace test; the liquid lens; contact angles and 3D channel layered three-phase fluid flow). The effects of wettability, viscosity ratio (M) and capillary number (Ca) on the relative permeability curves are analyzed in detail. When the wetting condition is enhanced, the results indicate that the relative permeability of non-wetting phase raises while that for the wetting phase exhibits a decline. When M is not equal 1, the relative permeability of high viscosity phase is significantly increased, while the other two phases are less affected. Meanwhile, the maximal value of relative permeability does not exceed unity because of the low porosity in the porous medium. For the influence of Ca , simulation results indicate the relative permeability shows weak sensitivity to Ca. • A lattice Boltzmann color gradient model for three-phase fluid flow is proposed. • Pore-scale three-phase fluid flow in porous media is studied. • Three-phase relative permeability is predicted. • Effects of wettability, viscosity ratio and capillary number are explored. [ABSTRACT FROM AUTHOR]

• Porous structures of Gyroid structure are reconstructed. • Pore-scale fluid flow, heat and mass transfer inside Gyroid are simulated. • Permeability, effective diffusivity and thermal conductivity are predicted. • Hydraulic and diffusive tortuosity of Gyroid are evaluated. Gyroid structure is a kind of triply periodic minimum surface, which presents several advantages such as free-standing, highly ordered and interconnected pore network and high specific surface area. Understanding transport processes inside the Gyroid structure is important for its application. In this study, porous structures of the Gyroid are reconstructed, and then pore-scale studies of fluid flow, diffusion and heat transfer in the two phases of Gyroid structures are numerically implemented using the lattice Boltzmann method (LBM). Pore-scale velocity, concentration and temperature fields inside the Gyroid structures are discussed, based on which macroscopic properties including permeability, effective diffusivity, effective thermal conductivity, and tortuosity are predicted. There are two phases in the Gyroid structures, and both phases are continuous, leading to the bicontinuous characteristic of Gyroid structures. The results show that transport resistance in one phase is lower than that in the other phase. Thus from the perspective of enhancing transport process, it is desirable to choose the phase with higher transport properties for transporting the slower process. The present study provides guidance for subsequent applications of Gyroid structure. [ABSTRACT FROM AUTHOR]