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Vapor shearing is a common issue encountered in the operations of falling film heat exchangers. The vapor stream effect depends on its orientation. This study investigates liquid film hydrodynamics and heat transfer performance under the influence of vapor streams from different orientations. The results indicate that both orientation and velocity of vapor determine the encountering time and position of the films on the tube's two sides. The liquid film thickness uniformity and the liquid column deflection vary significantly depending on the orientation and velocity of the vapor. Zones of accelerated liquid film, climbing liquid film, liquid stagnation, and transition of liquid film flow pattern are observed. The gradient of film thickness along the tube axis and the deflection in time-averaged peripheral film thickness increase as the vapor orientation varies from 0° to 90° and subsequently decrease as the vapor orientation varies from 90° to 180°. Vapor streams have more pronounced effects on time-averaged peripheral film thickness in regions close to the liquid inlet and outlet. Vapor streams result in changes in peripheral heat transfer coefficients toward the downstream side depending on the orientation and velocity of the vapor. The impact of vapor streams on the overall heat transfer coefficient does not directly correlate with the velocity of the vapor when maintaining the same orientation. [ABSTRACT FROM AUTHOR]

Two-phase flow patterns are critical in falling film heat devices. Hydrodynamic characteristics of turbulent falling films across a horizontal triangular tube bundle were studied under a range of film Reynolds numbers and contact angles. A flow pattern map based on the k-means clustering approach was proposed after the intercolumn two-phase flow patterns were grouped. The results demonstrated that that the intercolumn liquid-vapor flow patterns in a horizontal tube bundle could be effectively and reasonably grouped using the k-means clustering approach according to the results of the void fraction and interface area. There are four intercolumn liquid-vapor flow patterns that were identified: bubbles flow, annular-slug-column flow, half-annular flow, and multi-bridges flow. The annular-slug-column flow pattern and the multi-bridges flow pattern are next to one another in the flow pattern map and are capable of transitioning one into the other. It is only through the two transitional flow patterns that the half-annular-column flow pattern and bubbles flow pattern can turn to one another. In the bubbles' flow pattern and half-annular-column flow pattern, respectively, the highest and least averaged heat transfer coefficients are attained. Simply raising the film Reynolds number or lowering the contact angle will not produce the best heat transfer results. [ABSTRACT FROM AUTHOR]

Falling film technology has been widely applied in various industrial processes, but vapor shearing effects cause significant problems. The mechanism by which vapor affects the hydrodynamics of a falling film has not yet been fully understood, particularly for cross vapor streams. In this paper, a three-dimensional model is developed to investigate the hydrodynamics of a falling film on a horizontal tube with a cross vapor stream. The results indicate that (1) there are valley and peak zones during the spreading of the liquid film; (2) the effect of cross vapor flow on the hydrodynamics of the falling film depends on the film flow rate, the cross vapor velocity, and the position on the tube; (3) with increasing vapor velocity, the peripheral film thickness increases on both the upwind and downwind sides for values of z* (the dimensionless axial coordinate) from 0 to 0.1, while decreasing on the upwind side but increasing on the downwind side for values of z* from 0.2 to 0.5; and (4) under the action of the cross vapor stream, liquid film offset occurs, characterized by the formation of new stagnation and detachment zones on the downwind side of the tube. [ABSTRACT FROM AUTHOR]

Wettability determines the spreading or adherence behavior of fluids at the solid surface and significantly influences the displacement and entrapment of multiphase fluids in porous media. The present study sets out to determine how wettability controls the imbibition physics of oil and water in a matrix–fracture medium. The displacement and distribution characteristics of fluids, the types of flow regimes, and the fluid morphology under various conditions were revealed in depth. The influences of wettability on oil recovery and energy conversion were analyzed. Finally, the application of the conventional scaling model to simulated imbibition data was also discussed. Results show that the imbibition front is complete and stable in a water-wet medium with the one-end open boundary condition. There are three flow regimes occurring in countercurrent imbibition, depending on the wettability and Ca (capillary number) situations. Increasing θ (contact angle, the affinity of wetting phase to the solid) or Ca can shift the flow pattern from the capillary regime to the capillary-viscous regime to the viscous regime. Additionally, the imbibition oil recovery is greatly affected by wettability, and a more water-wet state does not signify a larger oil recovery. There is a power-law relationship between the oil recovery and the fractal dimension of the nonwetting phase. On the other hand, we performed the energy conversion analysis in the strongly water-wet condition. The external work is positive for both the capillary-viscous and viscous regimes and declines with the decreased Ca. Oil recovery could be linked to the surface energy ratio to some degree, which is relevant to Ca. For the capillary regime, oil recovery is proportional to the final reduced surface energy and does not have an evident relationship with the dissipation energy ratio. Through scaling the recovery factor data vs time via the linear, the power-law, and the conventional models, we find that the conventional scaling model can be used to fit the data point, and the fitting performance is good when Ca is relatively high. However, the linear model is more appropriate when scaling the data in low Ca. Overall, our pore-scale simulation study could pave the way for a further step toward investigating other influencing factors on imbibition behaviors of fluids in more complex media like natural rock materials, which exhibit strong heterogeneity of wettability and pore structure. [ABSTRACT FROM AUTHOR]

The peripheral heat transfer correlation of the subcooled falling liquid film outside the horizontal tube was established using the present numerical data under different liquid flow rates, heat fluxes, tube sizes, distributor heights, and liquid temperatures. The results indicated that the present correlation can predicate 93% of 2654 data within ±25% in θ = 2°–15°, 92% of 2254 data within ±15% in θ = 15°–165°, and 80% of 1442 data within ±30% in θ = 165°–178°. The peripheral heat transfer correlation can predict 74% of 903 data and 80% of 700 data, respectively, within 0°–180° and 15°–165° with the deviations of ±30%. The sensitivity analysis indicated that the parameter angle and the distributor height have the most and least significant impact on the peripheral heat transfer correlation, respectively. [ABSTRACT FROM AUTHOR]

This work employed theoretical and experimental methods to study the drag reduction performance of flexible channels for low Reynolds number pulsating flow. A novel theoretical model was proposed to describe flow in a flexible rectangular channel. According to the model, the drag reduction of the flexible channel was speculated. Subsequently, experiments were carried out to verify the theoretical results and to illuminate the drag reduction performance of the flexible channel in detail under the impacts of pulsating frequency, nondimensional velocity amplitude, average Reynolds number, and the thickness of the flexible wall. The results indicated that the flexible channel exhibited superior drag reduction performance for pulsating flow as compared to that for steady flow. Meanwhile, the drag reduction rate increased with the increase of pulsating frequency, nondimensional velocity amplitude, and average Reynolds number, and smaller thickness of the flexible wall was in favor of drag reduction at the same flow parameters. Moreover, the current experimental data were utilized to establish a correlation predicting the drag reduction rate of the flexible channel for pulsating flow, which fits 76.4% of 195 data within ±25%. [ABSTRACT FROM AUTHOR]