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To provide further insight into humid air condensation on hybrid surfaces, an experiment was conducted to visually investigate the condensation process on wettability-interval grooved surfaces, which had hydrophobic ridges and hydrophilic grooves. The droplet dynamic behavior and heat transfer performance of condensation on a wettability-interval grooved surface were explored and compared with four other functional surfaces, including the plain hydrophilic surface, plain hydrophobic surface, hydrophilic grooved surface, and hydrophobic grooved surface. The presence of hydrophobic ridges perpendicular to the groove direction and hydrophilic grooves allowed for the exclusion and easy spreading of droplets, respectively. Compared with the other four functional surfaces, the coupling phenomena during condensation, i.e., the spontaneous suction and directional drainage via hydrophilic grooves, were only found on the wettability-interval grooved surface. These could not only remove condensate quickly but also suppress the formation of the flooded liquid film, which was beneficial to the enhancement of heat transfer performance. It was proven by the experimental results that at subcooling 12 K, the condensation heat flux on the wettability-interval grooved surface reached 1280 W/m2, which was 1.25 times that of the plain hydrophobic surface (1030 W/m2), and 15% higher than that of the hydrophobic grooved surface (1110 W/m2). This indicated that the wettability-interval microgrooves could effectively enhance humid air condensation heat transfer performance. [ABSTRACT FROM AUTHOR]

Two-phase mass transfer is a critical process in preparing the inertial confinement fusion target microsphere. It is essential to reveal the effect of Marangoni convection on the flow and mass transfer in double emulsions to prepare high-quality microspheres. This paper develops a two-dimensional two-phase flow and mass transfer model based on multi-relaxation time lattice Boltzmann method and finite difference method. The study of the Marangoni effect within the double emulsion under a shear flow is carried out. The results indicate that the slope parameter (which measures the sensitivity of surface tension to the variation of solvent) and initial solvent concentration crucially affect the mass transfer behavior and the magnitude of the Marangoni convection of double emulsions. When the slope parameter is zero, there is no Marangoni convection in the flow field, the magnitude of the vorticity field is minimal, and solvent diffuses uniformly and slowly to the outer water phase. However, at low values of slope parameter, the Marangoni vortex formed within the emulsion is weak, and few plumes appear in the concentration field; at higher values, the magnitude of the vorticity field increases, and a large number of plumes appear and merge. Compared with the slope parameter, the mass transfer process is less sensitive to the initial solvent concentration. Plumes appear and merge at three different initial solvent concentrations. The time required for double emulsions to develop into equilibrium is inversely proportional to the initial solvent concentration. [ABSTRACT FROM AUTHOR]

The dynamic formation characteristics of droplets in a cross-junction can be captured via a high-speed image setup. The experimental results show four flow regimes: slug, dripping, jetting (threading and tubing), and viscous displacement. When Cad and Cac are small, the slug regime occurs. The dripping regime occurs when Cac is relatively high. The jetting regime appears when Cad increases to a considerable value. When Cac is much smaller than Cad, the viscous displacement regime occurs. In the slug and dripping regimes, the dispersed phase will experience growing, squeezing, and pinching off stages in the formation of droplets. These four flow regimes are strongly affected by Cac and Cad. In addition, the flow rates of the two phases can be changed to adjust the sizes of the generated droplet in the cross-junction under the slug regime and dripping regime. The dimensionless droplet length l* can be predicted via l* = (0.248 + 0.55Q)Cac−0.203. [ABSTRACT FROM AUTHOR]

Based on the multiphase lattice Boltzmann method, a transient model of vapor–liquid phase change in an enclosed narrow space during startup operation is developed and numerically analyzed to investigate the two-phase dynamics and heat transfer behaviors in the confined flat two-phase thermosiphon. The transient temperature distribution, vapor–liquid interface evolution and thermal performance are investigated over a wide range of heat load and liquid filling ratio. The results indicate that, as heat load increases, the intermittent nucleation boiling, fully developed nucleation boiling and film boiling sequentially takes place at the evaporator section of the confined flat two-phase thermosiphon. Correspondingly, the transient temperature evolution shows the periodic large-amplitude fluctuation, the random medium-amplitude fluctuation, and gentle small-amplitude fluctuation. The fully developed boiling is desirable for the heat transfer enhancement on the evaporator surface due to smaller temperature fluctuation and lower thermal resistance. The moderate liquid filling ratio ensures the desired interaction between the evaporator and condenser, resulting in superior thermal performance. To optimize the thermal performance, the optimal liquid filling ratio is about 40%. [ABSTRACT FROM AUTHOR]