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Response surface methodology is used in this study to model and optimize a solar thermal-photovoltaic vacuum membrane distillation (STPVMD) system with PVDF hollow fiber membrane. Regression models have been developed to forecast the effect of various operation factors on the permeate flux and the energy consumption. The operation factors in the model include the feed inlet temperature, the feed flow rate and the vacuum pressure. Analysis of variance is used to statistically validate the regression models. With permeate flux as the objective function of optimization, the optimal operation parameters are found to be 63 °C for the feed inlet temperature, 237 L / h for the feed flow rate, and 750 kPa for the vacuum pressure. Experimental tests show that the resulting permeate flux is 6.26 L / m 2 · h , which is slightly higher than the predicted value of 6.05 L / m 2 · h . The corresponding energy consumption is predicted to be 12.52 L / kW · h , demonstrating the effectiveness and reliability of the models.

Theoretical arguments and numerical investigations were conducted to understand the transport of oil droplets under ice. It was found that the boundary layer (BL) in the water under ice produces a downward velocity that reaches up to 0.2% of horizontal current speed, and is, in general, larger than the rise velocity of 70 μm oil droplets. The eddy diffusivity was found to increase with depth and to decrease gradually afterward. Neglecting the gradient of eddy diffusivity when conducting Lagrangian transport of oil droplets would result in an unphysical spatial distribution. When the downward velocity of water was neglected, oil accumulated at the water-ice interface regardless of the attachment efficiency. The lift force was found to scrape off droplets of the ice, especially for droplets ≤ 70 μm. These findings suggest that previous oil spill simulations may have overestimated the number of small droplets (≤70 μm) at the water-ice interface.

Langmuir supercells (LS) are full-depth Langmuir circulations in unstratified shallow shelves. A Reynolds-averaged Eulerian formulation is developed resolving LS as a secondary component to the wind-driven mean shear current. This formulation is combined with Lagrangian particle tracking to investigate oil droplet entrainment induced by LS as a function of wind stress. Two cases are simulated, one in which 500-μm oil droplets are released into a steady field of LS generated by a wind stress of 0.1 N m−2 and waves of intermediate wavelength λ = 6 H where H = 15 m is the water column depth, significant amplitude of 0.6 m and period of 8 s. In the second case, the 500-μm oil droplets are released into a steady field of LS generated by the same wave forcing but with a weaker wind stress of 0.025 N m−2. It is found that the greater wind stress leads to LS able to spread the droplets throughout upwelling and downwelling limbs of the cells within the first 80 minutes after release. The weaker wind leads to weaker LS that, within the same time after release, limit the dispersion of the droplets to the downwelling limbs of the cells forming Stommel retention zones for a prolonged time.

Understanding the shear breakup in jet flows and the formation of droplets from ligaments is important to determine the final droplet size distribution (DSD). The initial droplet size, which affects the final DSD, is considered to be generated by the shear breakup. Large eddy simulation (LES) was performed to investigate the shear breakup in liquid-liquid jet flows. The explicit Volume of Fluid (VOF) model with the geometric reconstruction scheme was used to capture the oil-water interface. The estimated oil distribution including wave peaks, ligaments, droplets and water streaks were compared to the experiments with a good agreement. The estimated DSD matched with the measurements favorably well. In the simulation, the formation of droplets with a smooth and curved surface from ligaments or sheet-like structures was obtained. Different mechanisms were observed along with the shear layer including the formation of droplets from ligament through the capillary forces, breakage of a droplet into smaller ones and attachment of a droplet to a ligament. The destructive shear forces and resisting surface tension forces were quantified on stretching and retracting ligaments. The influence of internal viscous force was found to be negligible due to low oil viscosity. The critical capillary number was found to be larger than 5.0 for ligaments breaking with the shear breakup. The capillary number was below unity for retracting ligaments. The coalescence of two equal-sized droplets was obtained in the shear breakup region. The shear stress magnitude at the contact region increased more than two folds. The total surface area decreased nearly 20% after the coalescence.

A numerical study was undertaken to investigate subsurface release and fate of benzene and toluene in a tidally influenced beach. The simulations were conducted by using a numerical model BIOMARUN, which coupled a multi-Monod kinetic model BIOB to a density-dependent variably saturated groundwater flow model MARUN. The fate and transport of the contaminant plume were characterized by computing its centroid trajectory, spreading area and percentage of biodegradation in beach saturated and unsaturated zone, respectively. Key factors likely affecting this process were investigated, including tide amplitude, capillarity and hydraulic conductivity. It was found that aerobic biodegradation was the major fate of the contaminant plume in the beach. Tidal action twisted the centroid of the contaminant plume during its migration in the beach, which increased the residence time of the plume in the beach. High tidal range significantly altered the spatial distribution of the contaminant biodegradation in the beach. In contrast, the capillary fringe had impacts on the percentage of benzene biodegraded in the saturated and unsaturated zone of the beach. The increase in capillary fringe enhanced the percentage of the contaminant biodegraded in the unsaturated zone, up to 40%, which is comparable to that in the saturated zone. Hydraulic conductivity seemed to have large impacts on the biodegradation rate of the contaminant in the beach. Higher hydraulic conductivity induced faster contaminant biodegradation in the beach.

Understanding the trajectory of oil droplets in crossflow jets is important to estimate the pathways of hydrocarbons and to plan countermeasures. We report experimental results of an oil jet with release velocity around 1.5 m/s in a crossflow of 0.3 m/s. The hydrodynamics of the jet obtained with the Large Eddy Simulation (LES) were used to predict the migration of the oil droplets. Two Lagrangian techniques were explored, one with the inertia of the droplet is considered and the other that treats the droplets as massless particles with rising velocities corresponding to their size. We did not note a large difference between the two approaches. The droplets showed stronger segregation in the vertical direction, which renders the usage of a Gaussian distribution approximation in the vertical inapplicable. The dispersion coefficient at each direction was computed for different-sized droplets. The eddy diffusivity computed based on Boussinesq gradient approximation using the LES data was compared with the dispersion coefficients obtained based on Lagrangian tracking. We also found that droplets 500 μ m and larger escape the vortex while smaller ones get trapped within the vortex. A similar outcome was observed using a vortex trapping function based on inward–outward force balancing at the elevation of the vortex core. The counter-rotating vortex pair (CVP) altered the distribution of droplets of 1 mm and smaller significantly, and bimodal concentration distributions with peaks near the CVP vortex cores and minimum concentration near the center plane were obtained in the lateral–horizontal​ direction. Therefore, measurements of the oil droplet size distribution (DSD) in the center plane of crossflow jets could underestimate the number of small droplets in the whole plume.

Experimental results were presented for the release of diesel oil from a one-inch (2.5 cm) vertical pipe in a crossflow at 0.27 m/s. The ratio of jet velocity to crossflow speed was 5.0 and the Reynolds number based on jet velocity and pipe diameter was 7.1 × 10 3 . In the experiments, the plume shape was photographed, and the oil droplets were measured at two vertical locations on the center axis of the plume. Acoustic Doppler velocimetry (ADV) data was also obtained and compared to numerical predictions. The plume was simulated using large eddy simulation (LES), and the mixture multiphase model. The impact of the oil buoyancy was captured by adding a transport term to the volume fraction equation. Using the rise velocity based on d50 (volume-median) droplet size in the lower part of the plume allowed us to capture the lower boundary of the plume, but the estimated upper boundary of the plume penetrated less into the crossflow as compared to the experimental findings. However, using the rise velocity of the d50 at the upper part of the plume allowed one to estimate the upper boundary of the plume. As the droplets are too small to be resolved by the LES, we could not use a systematic approach to allow the multiphase plume to spread to mimic the observations. Based on the simulation results, the interaction between the jet and crossflow yielded small-sized flow structures near the upper boundary of the plume. The wake vortices initiated from the leeward side of the plume showed an alternating vorticity pattern in the wake. The shear layer vortices were induced by Kevin-Helmholtz instabilities mostly on the windward side of the plume. The formation of counter rotating vortex pair (CVP) altered greatly the hydrodynamics of the jet from that of a vertical jet to manifest flow reversals in all directions. The formation of CVP is likely to enhance the mixing of chemicals and droplets within the plume.

Shape memory polymers (SMPs) are smart materials that alter their shape in response to external stimuli. Dual-shape SMPs are widely recognized and are characterized by two shapes involved in a typical shape memory cycle. Recently, triple-shape memory polymers (TSMPs) have been introduced that have the ability to remember three shapes. Thermo-sensitive TSMPs can perform two sequential shape changes in response to heat, which were programed previously in a triple-shape creation process (TSCP). TSMPs are technologically significant as their development of has led to emergence of many complex potential applications that cannot be achieved by dual-shape polymers (Zhao et al., 2013). Crystallizable TSMPs are a class of thermo-sensitive TSMPs, where the shape creation is due to formation of crystalline phases. Different TSCPs have been reported which enable to control the triple shape capability of these materials. In this work the mechanical behavior of TSMPs has been modeled using a framework that has been developed recently for studying crystallization in polymers (Rao, 2003; Rao and Rajagopal, 2001, 2002, 2004). The framework has been used successfully to model SMPs (Barot and Rao, 2006; Barot et al., 2008), light activated SMPs (Sodhi and Rao, 2010) and is based upon the theory of multiple natural configurations. The model has been used to simulate a uni-axial deformation cycle for different types of TSCPs and the results have been compared with experimental data.