An investigation on dissolutive wetting of porous urea surface

Abstract

Dissolutive spreading over a porous surface is a phenomenon involving spreading, penetration, as well as dissolution. Droplet spreading forms the basis of numerous industrial operations including the spray coating of urea fertilizer to produce slow release urea. The slow release characteristics of urea highly depend on the coating uniformity that can be achieved by sound knowledge of droplet spreading behaviour over the urea surface. Since numerous waterborne coating materials are being studied presently, dissolutive wetting of the urea surface has been investigated in the current work. Response surface methodology has been utilized to study the interactive effects of process parameters on the dissolutive wetting of an aqueous glycerin solution on a porous urea surface. The effect of impact velocity, surface porosity, and urea solubility has been investigated on three response objectives namely contact angle, spreading factor, and normalized residual drop volume. The results have been compared with an earlier work performed under similar conditions for non-dissolutive wetting. The comparison reveals that dissolutive wetting shows lesser optimum contact angle (81 %) and greater optimum spreading factor (21 %) as compared to non-dissolutive wetting.

Experimental methods in chemical engineering: Contact angles

“…In five of these papers, CA is only an inlet parameter in a model or a numerical simulation. The twelve remaining involve experimental measurements, all of which were performed with an optical goniometer or derived instruments . The latter enables analysis at a liquid/liquid/solid or a liquid/gas/solid interface instead of a gas/liquid/solid one (Figure ).…”

“…The latter enables analysis at a liquid/liquid/solid or a liquid/gas/solid interface instead of a gas/liquid/solid one (Figure ). Works performed with an optical goniometer mainly employed the static sessile drop method with only two employing dynamic methods . Three studies included qualitative surface analysis through scanning electron microscopy images to estimate the substrate roughness: Ahmmed et al published the only manuscript in which both advancing and receding contact angles are reported and in which an estimation of the hysteresis is provided.…”

“…Studies containing experimental work on contact angles were mostly interested in investigating the wettability of powders: nanoparticles and microparticles . Other surfaces of interest included polymeric films, rocks, and glass .…”

“…Other applications involve nanofluids: in one case, a nanopowder was used as an interfacial modifier to alter the wettability of a reservoir surfaces; in two others, nanoparticles were left in suspension to act as modifiers of the physical properties (viscosity, thermal conductivity, surface tensions) of water or bitumen . Probe liquids employed include water, salted water, toluene, denatured ethanol, n ‐dodecane, bitumen, and various oils …”

“…Contact angle measurements were performed in order to probe the wetting behaviour (usually hydrophobicity or oleophilicity) and assess the success of a modification method (application (1), red cluster in the Figure ). In two circumstances the hysteresis was investigated (application (2)), either in terms of kinetic hysteresis (penetration of the liquid in a porous substrate) or in terms of surface anisotropy, while in another the free surface energy of the solid was estimated through the OWRK model (application (3)). Vafaei performed a theoretical work by deriving two analytical expressions to refine Young's equation (Equation ) and predict contact angles formed by gas bubbles and droplets growing underwater (blue cluster, Figure ).…”