Search Results (3)

The instability of a film falling down a vertical plate with lateral walls, which is the base configuration describing the structured packing geometry, is numerically investigated via the lubrication theory. The solid substrate wettability is imposed through the disjoining pressure, while the assumption of a tiny, precursor film thickness allows for modelling a moving contact line. Contact angles up to ${60}^{\circ }$, which falls in the range of structured packing applications, are investigated, thanks to the full implementation of the capillary pressure instead of the small slope approximation. Parametric computations are run for a film falling down a vertical plate bounded by lateral walls, changing the plate width and the flow characteristics. An in-house, finite volume method (FVM) code, previously developed in FORTRAN language and validated in the case of film instability and rivulet flow, is used. The number of observed rivulets, triggered by the instability induced by the lateral walls, is traced for each computation. The numerical results suggest that rivulets with a given wavelength, equal to the one provided by the linear stability analysis, are generated, but only those characterized by a wavelength greater than a minimum threshold, which depends on the substrate wettability, induce partial dewetting of the domain. This allowed for the development of a simplified, statistically based model to predict the effective interface area and the rivulet holdup (required to estimate the mass transfer rate in absorption/distillation applications). Compared to the literature models of the structured packing hydrodynamics, which usually assume a continuous wetting layer, the influence of the flow pattern (continuous film or ensemble of rivulets) on the liquid holdup and on the interfacial area is introduced. The predicted flow regime is successfully verified with evidence from the literature, involving a flow down a corrugated sheet. Full article

This paper reports a stimuli-responsive designer supramolecular polymer gel in dimethylsulphoxide (DMSO)/water (1:2) based on a dipeptide amphiphile and β-cyclodextrin (β-CD) The dipeptide amphiphile contains caproic acid at the N terminus and methyl ester at the C terminus. From X-ray single crystal diffraction, the amphiphile adopts a kink-like conformation. The amphiphile self-assembled to form a parallel sheet-like structure stabilized by multiple intermolecular hydrogen bonds. Moreover, the parallel sheet-like structure is also stabilized by edge-to-edge π–π stacking interactions. In higher-order packing, it forms a corrugated sheet-like structure stabilized by hydrophobic interactions. The dipeptide amphiphile interacts with β-cyclodextrin and forms gel through supramolecular polymer formation in (DMSO)/water (1:2) by a simple heating-cooling cycle. The sol-to-gel transformation is because of a host–guest complex between compound 1 and β-CD and the formation of supramolecular polymer accompanied by microstructure changes from nanofibers to microrods. The gel is temperature responsive with a T_gel of 70 °C. The supramolecular polymer gel is also responsive to stimuli such aspicric acid and HCl. The extensive spectroscopic studies show that the aromatic hydrophobic side chain of compound 1 forms a host–guest complex with β-CD. These results will be helpful for the design of advanced programable eco-friendly functional materials. Full article

The falling film flow characteristics of a liquid on the surface of corrugated sheet packing are crucial for its mass transfer performance in various industrial applications. In this study, a falling film flow experiment with laser-induced fluorescence technology was conducted to validate the flow characteristics of a falling film simulated using computational fluid dynamics (CFD). The influences of Reynolds number (Re) and the packing structure on flow characteristics were analyzed with quantitative film thickness and wetted area obtained through three-dimensional simulation. The results show that the CFD model can accurately predict the liquid falling–film flow behavior and calculate the characteristic parameters. For sinusoidal corrugated sheets, when Re reaches 500, the groove flow changes into a rivulet flow along the adjacent ripples and the wetted area is at its largest, about 0.022 m². However, relative to the geometric area of the corrugated sheet, the wetted area can only reach 20% of the surface area, and the overall wetting performance is still poor. Triangular and trapezoidal corrugated sheets were further proposed and proved to improve the wetting area compared with the sinusoidal sheet, with maximum increases of 23% and 9%, respectively. On this basis, extensive research was carried out on the corrugation angle. The results show that a triangular corrugated sheet with a 75° corrugated angle was more conducive to the flow of the liquid film, and the wetted area was 38.8% of the surface area. Full article