Numerical Simulation of rivulet build up via lubrication equations

A number of engineering problems involve the evolution of a thin layer of liquid over a non-wettable substrate. For example, CO2 chemical absorption is carried out in packed columns, where ost-combustion CO2 flows up while liquid solvent falls down through a collection of corrugated sheets. Further application include, among others, in-flight icing simulations, moisture ondensation on de-humidifier fins, fogging build up and removal. Here, we present a development of an in-house code numerically solving the 2D lubrication equation for a film flowing down an nclined plate. The disjoining pressure approach is followed, in order to model both the contact line discontinuity and the surface wettability. With respect to the original implementation, the full odeling of capillary pressure terms according to Young- Laplace relation allows to investigate contact angles close to /2. The code is thus validated with literature numerical results, obtained by fully 3D approach (VOF), showing satisfying agreement despite a strong reduction in terms of computational cost. Steady and unsteady wetting dynamics of a developing rivulet are investigated and validated) under different load conditions and for different values of the contact angles

Bifurcation analysis of liquid films over low wettability surfaces

Thin liquid layer evolution over a solid substrate and film instability phenomena are involved in a number of engineering applications: in chemical absorption through structured packing, the corrugated sheets are covered by the liquid solvent, offering an enhanced interface surface between the solvent and the gas solute; in coating process, the liquid pattern influences the resulting coating quality; in condensation over finned dehumidifier, heat transfer performances are influenced by the evolving liquid layer, which may arrange as a droplets population or an ensemble of rivulets. Here, the evolution of a liquid layer flowing down an inclined plate bounded by lateral walls, which is the simplest configuration describing hydrodynamics inside structured packing, is numerically investigated. An in-house code, previously developed and largely validated in case of film instability and rivulet buildup, is used in order to solve governing lubrication equations. The full implementation of capillary pressure allows to simulate contact angles up to 60 . Film break is observed due to instability induced by lateral walls, if the imposed liquid flow rate exceeds a critical value, leading to the formation of a rivulet pattern. Fixing the size of the investigated physical domain, the number of observed rivulets, which strongly influences the resulting wetted area, is traced as a function of the flow characteristics (identified by the Bond number), the substrate wettability and the liquid properties; the corresponding bifurcation diagram is presented

Numerical simulation of shear driven film instability over heterogeneous surfaces via enhanced lubrication theory

The prediction of the transition between continuous film, ensemble of rivulets and moving droplets is crucial in applications such as in-flight icing on airfoil wings or a number of chemical reactors. Here, lubrication theory is used to numerically investigate the stability of a continuous liquid film, driven by shear, over a heterogeneous surface. The disjoining pressure is used to model surface wettability, while the full implementation of the film curvature allows to investigate contact angles up to 60◦. Different heterogeneous surface configurations occurring in real problems are investigated. An extended computational campaign records the transition from continuous film to rivulet regime and, if present, the further transition from rivulet to droplets at different flow conditions. A moving grid approach allows for accurate prediction of instability phenomena at low computational cost. The numerical results are successfully validated with experimental evidence in case of critical flow rate leading to a stable dry patch and compared with literature results involving the inherently multiscale in-flight icing phenomenon, providing useful statistical information, required to transfer the present detailed small-scale information into larger scale CFD computational approaches

Polyamines and Gut Microbiota

The microbiota of gut is the community of microbes living in an individual's gastrointestinal tract. Several bacterial genera and species act in a concerted manner to establish metabolic interactions with the host (1). Although there is a general high interest in the study of metabolite flow across the microbe-host, at present, only some studies are targeting specific metabolites produced by intestinal microbiota such as polyamines (PAs

Interactions between Saccharomyces and Oenococcus oeni strains from Amarone wine affect malolactic fermentation and wine composition

Research Note

Microbiological and chemical monitoring of Marsala base wine obtained by spontaneous fermentation during large-scale production

The present work was undertaken to evaluate the effect of the natural winemaking on the microbial and chemical composition of Marsala base wine. To this purpose, a large-scale vinification process of Grillo grape cultivar was monitored from harvesting to the final product. Total yeasts (TY) showed a rapid increase after must pressing and reached values almost superimposable to those registered during the conventional winemakings. Lactic acid bacteria (LAB) were registered at the highest levels simultaneously to yeast growth at the beginning of the process. Saccharomyces cerevisiae was the species found at the highest concentrations in all samples analysed. Several strains (n= 16) was registered at high levels during the alcoholic fermentation and/or aging of wine; only two of them were detected on the grape surface. Lactobacillus plantarum was the LAB species most frequently isolated during the entire vinification process. Ethanol content was approximately 14% (v/v) at the end of vinification. The value of pH did not greatly vary during the process and the volatile acidity (VA) was detected at low concentrations during the entire transformation. The concentration of malic acid rapidly decreased during the AF; on the other hand, lactic acid showed an irregular trend during the entire process. trans-caffeil tartaric acid was the most abundant hydroxycinnamoyl tartaric acid and volatile organic compounds (VOC) were mainly represented by isoamylic alcohol and isobutanol