Experimental Correlation for Splashing Condition of Droplets on Solid Substrates

Droplet splashing behaviors of water-ethanol binary mixture liquids on roughened solid surfaces were experimentally observed in order to investigate the effects of surface tension, viscosity, and wettability/surface roughness on the splashing occurrence. The range of the droplet volumes was from 1.7 μL to 32.6 μL. The ranges of the surface tension and the viscosity were from 21.1 mN/m to 71.9 mN/m, and from 1 mPas to 2.91 mPas, respectively. The surface roughness range was from 0.03 μm to 1.25 μm for Ra. The present experimental data were evaluated on the basis of the existing models. Resulting from these experiments, a simple model using the Ohnesorge number evaluated by the capillary length was proposed and the accuracy of the predicted critical values such as the critical Weber and Reynolds numbers were discussed. The result indicated that the liquid properties and the quantification of the surface condition such as surface roughness are important factors for the prediction of the splashing behavior.

Technology and Theory of Mechanically Activated Water in Bakery Industry

Introduction. Bakery products are an important part of traditional Russian menu. Activated water helps to improve the quality of flour products. The present research objective was (1) to activate water with mechanical energy to change the physicochemical properties of the dough; (2) to evaluate the energy efficiency of the new technological process, and (3) to determine the quality indicators of bread. Study objects and methods. The research featured high quality wheat flour, drinking water, and pressed baking yeast (Saccharomyces cerevisiae). Standard research methods were used to assess the physical and chemical properties of water, namely acidity index (pH), surface tension coefficient, and biological activity. The physico-chemical properties of the dough were studied by maximum shear stress and adhesion. Results and discussion. The samples of activated water demonstrated the following technological properties. Its acidity due decreased as pH fell down to 6.05. With a total mixing time of 10 min, the surface tension decreased by about 10%; after 5 min, it decreased by 4%, while the biological activity of activated water increased by 1.5 times. Mechanically treated water used for bread production contributed to the overall energy saving during kneading and increased its water-binding ability. Moisture removal was by 30–40% more intensive than in the control dough sample. Also, the quality of gluten changed as a result of higher shear stress, which gave the experimental dough better forming properties necessary for the production of high-quality bread. The mechanically activated water increased the specific volume of bread from 2.05 to 2.38 cm3/g. Conclusion. The activated water improved the physico-chemical and rheological properties of dough, as well as the main sensory indicators of bread, e.g. porosity and bread crumb elasticity.

Analysis of Uniform Film Thickness and Stationarypoints for the Thin Film Flow of Carreau Fluid Model in the Presence of Surface Tension Gradient

This article addresses the analysis of the uniform film thickness and stationary points forthe Carreau thin fluid film flow. The flow of fluid on a vertically upward moving cylinder takesplace in the presence of a surface tension gradient. The resulting non-linear and inhomogeneousordinary differential equation is solved for the series form solution using Adomian decompositionmethods (ADM). Stokes number St, inverse capillary number C, Weissenberg number W e andfluid behavior index n emerged as flow control parameters. The analysis showed that thepositions of stationary points transferred towards the surface of the cylinder by the increase ofSt and C while towards the fluid-air interface by the increase of n. W e delineated vice versaeffects on positions of stationary points for the shear thickening fluid film and shear thinningfluid film. The width of uniform film thickness reduces by an increment in the St and Cwhereas it increases by an increment in the n. The width of shear thickening uniform filmthickness increases whilst shear thinning uniform film thickness decreases as the W e increases. A comparison between the linearly viscous fluid and Carreau fluid is also made.

Removing Gas from a Closed-End Small Hole by Irradiating Acoustic Waves with Two Frequencies

Filling microstructures in the air with liquid or removing trapped gases from a surface in a liquid are required in processes such as cleaning, bonding, and painting. However, it is difficult to deform the gas–liquid interface to fill a small hole with liquid when surface tension has closed one end. Therefore, it is necessary to have an efficient method of removing gas from closed-end holes in liquids. Here, we demonstrate the gas-removing method using acoustic waves from small holes. We observed gas column oscillation by changing the hole size, wettability, and liquid surface tension to clarify the mechanism. First, we found that combining two different frequencies enabled complete gas removal in water within 2 s. From high-speed observation, about half of the removal was dominated by droplet or film formation caused by oscillating the gas column. The other half was dominated by approaching and coalescing the divided gas column. We conclude that the natural frequency of both the air column and the bubbles inside the tube are important.