Drying Of Liquid Film Research Articles

Time-evolving dry patches in a flowing film around a horizontal tube

Dry patches could occur on the heat exchanger wall even if the initial liquid film covers the tube surface entirely. Here, we propose a simple three-dimensional model to predict the formation and evolution of dry patches in a water film coating on a horizontal tube, considering thermocapillary and evaporation of the liquid film. Results indicate that the film thickness distribution along the axis is not uniform, convex at ends and concaves at the center. Under the action of axial thermocapillary force, the growth rate of the dry patch in the circumferential direction is more significant than that in the axial direction and finally forms an elliptical shape. Comparative analysis reveals that the appearance of dry patches is delayed as the spray temperature decreases or Re increases. Tube radius has little influence on the drying of liquid film, which is not recommended to control dry patch formation by reducing the tube radius. This work could be beneficial to assist the feasibility design of falling film heat exchangers.

The drying of liquid films on cylindrical and spherical substrates

The drying of liquid films from binary solid–solvent mixtures on cylindrical and spherical substrates is investigated by solving the diffusion equation on the cylindrical or spherical domains with account for the shrinkage of the systems due to the solvent evaporation. As a main result of the gas phase analysis, d 2 -laws for both the cylindrical and the spherical cases are found. The spatio-temporal evolution of the component mass fractions in the liquid are obtained for varying initial film thickness and drying conditions. Large mass fraction gradients, formed at high drying rates, lead to a skin-core morphology with low product quality. Initially very thin films dry very uniformly, which is analogous to the flat temperature profiles in unsteady heat conduction at small Biot numbers. The maximum initial film thickness allowable to ensure flat solute mass fraction profiles in the films, and thus high quality of the dry films, is computed for varying drying rates. From these results a guideline for the drying of liquid films on cylindrical and spherical substrates is deduced.

Micrometer-sized particles in a two-dimensional self-assembly during drying of liquid film

We computed the self-organization process of a monodisperse collection of spherical micrometer-sized particles trapped in a two-dimensional thin liquid film isothermally dried on a chemically inert substrate. The substrate is either flat or indented to create linear stripes on its surface. The numerical results are illustrated and discussed in the light of experimental ones obtained from the drying of a water-based suspension of diamond particles (d{50}=10 microm) on a glass substrate. The drying of the suspension on a flat substrate leads to the formation of linear patterns and small clusters of micrometer-sized particles distributed over the whole surface of the substrate, whereas the drying of the suspension on an indented substrate leads to the aggregation of the particles along one side of the stripe which has a higher roughness than the other side of the stripe. This is an easy experimental way to obtain colloidal self-organized patterns.