Surface Tension Of Water Droplet Research Articles

How condensation causes dusty solar panels

The surface tension of water droplets on photovoltaic surfaces is a driving force in dust agglomeration, impeding photoelectric efficiency.

Effect of the surface tension correction coefficient on the nonequilibrium condensation flow of wet steam

In view of the nonequilibrium characteristics of water vapor in the condensation process, various models have different degrees of deviation in the prediction of the condensation process. Water droplet surface tension appears in the exponential term of the nucleation rate in the form of a third power, which has a significant effect on the distribution of parameters such as condensation location, water droplet number and wetness. In order to improve the accuracy of numerical simulation, the correction coefficient is used to modify the plane surface tension calculation model. The nonequilibrium condensation process in the Moses-Stein nozzle is simulated. By comparison with the experimental data, the influence of the surface tension correction coefficient on the calculation accuracy of the model is analysed. The functional relationship between the superheat at the steam inlet and the optimal surface tension correction coefficient is obtained. After correction, the error between the simulation results and the experimental values of each working condition of the nozzle is reduced to less than 2%. In addition, this conclusion is verified by the nonequilibrium condensation flow in the turbine cascades. The deviations between the three simulation results and the experimental values are 1.86%, 2.10% and 1.88% respectively, and the simulation accuracy is significantly improved. The results show that with the increase in the surface tension correction coefficient, condensation will be inhibited under the same working conditions. There is an optimal value of the correction coefficient. Under different working conditions, there is a significant positive correlation between the optimal surface tension correction coefficient and the inlet superheat. It can significantly improve the simulation accuracy by using the corrected surface tension value. The results can provide a reference for the calculation of wet steam condensation flow.

Water droplet surface tension method – An innovation in quantifying saponin content in quinoa seed

Quinoa surface borne saponins are bitter tasting anti-nutritional compounds that must be removed before consumption of the seed. To determine saponin content, the currently available standard afrosimetric foam test method only determines the presence of saponin via a rating of either ‘acceptable’ or ‘unacceptable’. A water droplet surface tension (WDST) based innovative method was developed that can quantify saponin content in aqueous solutions with greater accuracy. The method comprised four steps: solution preparation, droplet creation, image capture and image analysis using Axisymmetric Drop Shape Analysis computer software. The method applied satisfactorily to saponin content up to 0.2 mg.ml−1 as higher concentrations did not further reduce the surface tension. Results demonstrated that saponin concentration may be measured in the range 0.05 to 0.15 mg.ml−1 (0.05 – 0.15% saponin by weight of seed). Validation of the WDST method on commercial and experimental samples offers quinoa processors an accurate inexpensive way of measuring saponin concentration to satisfy current seed quality specifications.

Surface tension of water droplets upon homogeneous droplet nucleation in water vapor

A method has been proposed for determining interfacial free energy from the data of molecular dynamics simulation. The method is based on the thermodynamic integration procedure and is distinguished by applicability to both planar interfaces and those characterized by a high curvature. The workability of the method has been demonstrated by the example of determining the surface tension for critical nuclei of water droplets upon condensation of water vapor. The calculation has been performed at temperatures of 273–373 K and a pressure of 1 atm, thus making it possible to determine the temperature dependence of the surface tension for water droplets and compare the results obtained with experimental data and the simulation results for a “planar” vapor–liquid interface.

Calculation of effective transport properties of partially saturated gas diffusion layers

Abstract A large number of currently available Computational Fluid Dynamics numerical models of Polymer Electrolyte Membrane Fuel Cells (PEMFC) are based on the assumption that porous structures are mainly considered as thin and homogenous layers, hence the mass transport equations in structures such as Gas Diffusion Layers (GDL) are usually modelled according to the Darcy assumptions. Application of homogenous models implies that the effects of porous structures are taken into consideration via the effective transport properties of porosity, tortuosity, permeability (or flow resistance), diffusivity, electric and thermal conductivity. Therefore, reliable values of those effective properties of GDL play a significant role for PEMFC modelling when employing Computational Fluid Dynamics, since these parameters are required as input values for performing the numerical calculations. The objective of the current study is to calculate the effective transport properties of GDL, namely gas permeability, diffusivity and thermal conductivity, as a function of liquid water saturation by using the Lattice-Boltzmann approach. The study proposes a method of uniform water impregnation of the GDL based on the “Fine-Mist” assumption by taking into account the surface tension of water droplets and the actual shape of GDL pores.

On the wettability diversity of C/SiC surface: Comparison of the ground C/SiC surface and ablated C/SiC surface from three aspects

The coefficient of thermal conductivity was influenced by the wetting state of material. The wetting state usually depends on the surface wettability. C/SiC is a promising ceramic composites with multi-components. The wettability of C/SiC composites is hard to resort to the classical wetting theory directly. So far, few investigations focused on C/SiC surface wettability diversity after different material removal processes. In this investigation, comparative studies of surface wettability of ground C/SiC surface and laser-ablated C/SiC surface were carried out through apparent contact angle (APCA) measurements. The results showed that water droplets easily reached stable state on ground C/SiC surface; while the water droplets rappidly penetrated into the laser–ablated C/SiC surface. In order to find out the reason for wettability distinctions between the ground C/SiC surface and the laser–ablated C/SiC surface, comparative studies on the surface micro-structure, surface C–O–Si distribution, and surface C–O–Si weight percentage were carried out. The results showed that (1) A large number of micro cracks in the fuzzy pattern layer over laser-ablated C/SiC surfaces easily destoried the surface tension of water droplets, while only a few cracks existed over the ground C/SiC surfaces. (2) Chemical components (C, O, Si) were non-uniformly distributed on ground C/SiC surfaces, while the chemical components (C, O, Si) were uniformly distributed on laser-ablated C/SiC surfaces. (3) The carbon weight percentage on ground C/SiC surfaces were higher than that on laser-ablated C/SiC surfaces. All these made an essential contribution to the surface wettability diversity of C/SiC surface. Although more investigations about the quantitative influence of surface topography and surface chemical composition on composites wettability are still needed, the conslusion can be used in application: the wettability of C/SiC surface can be controlled by different material removal process without individual following up surface modification process.

Flattened-Top Domical Water Drops Formed through Self-Organization of Hydrophobin Membranes: A Structural and Mechanistic Study Using Atomic Force Microscopy

The Trichoderma reesei hydrophobin, HFBI, is a unique structural protein. This protein forms membranes by self-organization at air/water or water/solid interfaces. When HFBI forms a membrane at an air/water interface, the top of the water droplet is flattened. The mechanism underlying this phenomenon has not been explored. In this study, this unique phenomenon has been investigated. Self-organized HFBI membranes form a hexagonal structured membrane on the surface of water droplets; the structure was confirmed by atomic force microscopy (AFM) measurement. Assembled hexagons can form a planar sheet or a tube. Self-organized HFBI membranes on water droplets form a sheet with an array of hexagonal structures or a honeycomb structure. This membrane, with its arrayed hexagonal structures, has very high buckling strength. We hypothesized that the high buckling strength is the reason that water droplets containing HFBI form flattened domes. To test this hypothesis, the strength of the self-organized HFBI membranes was analyzed using AFM. The buckling strength of HFBI membranes was measured to be 66.9 mN/m. In contrast, the surface tension of water droplets containing dissolved HFBI is 42 mN/m. Thus, the buckling strength of a self-organized HFBI membrane is higher than the surface tension of water containing dissolved HFBI. This mechanistic study clarifies why the water droplets formed by self-organized HFBI membranes have a flattened top.

Study on the Heat Transfer Characteristics in Aircraft Icing

Investigation on the heat transfer mechanisms of liquid and solid is important to predicting the icing process. Messige model is a typical model for the process of mass and heat transfer, but the effect of surface tension of water droplet is been ignored in the model. We established a model which was add the infection of surface energy based on traditional thermodynamic model. Some cases at NACA0012are simulated with our model in order to verify its correctness. The calculated results show that, ourmodel was consistent with the traditional thermodynamic model in Low temperature, but our model havebetterresults in high temperatures

Nonlinearities in sedimentation: a microscopic study

Effect of temperature and surface tension on surface during sedimentation is studied using atomic force microscopy. Effects of surface tension is incorporated by using ∼1 mm radius water droplets. Surface tension of water droplet directed the deposition of dissolved particles around the perimeter of the droplet; leaving almost hollow circle in the middle with light deposition due to the particles being close to the surface. Evaporating shallow water solutions left random salt structures on the surface. Growth exponents are calculated along with the fractal dimension. For sedimentation process in shallow water (depth of ∼2 mm), a transition is observed from continuum model (1.88±0.2) to KPZ (0.406±0.082) universality class around ∼1 μm at room temperature. For droplets evaporation, turbulent (multi-affine) to self-affine transition is observed. Fractal dimensions (FD) for the droplets are found to be between one and two. The FD values are consistent with the fact that competing nonlinear terms are present in the system.

Surface tension of water droplets: A molecular dynamics study of model and size dependencies

The applicability of two frequently used interaction potentials for water, the five-site ST2 model and the four-site TIP4P model, is investigated in computer simulations of water droplets of varying cluster size from N=64 to N=512. The orientation of the water molecules in the surface region is investigated for the both models. Surface properties, such as work of cluster formation, local density profiles, kinetic and total energy profiles, and pressure profiles as a function of the droplet size, obtained using the two models are compared. Moreover, the surface potential and the electric potential profiles are calculated. Surface tension is calculated and its dependence on the cluster size is investigated. It is found that surface properties are very sensitive to the used potential models. For example, the water molecules are found to lie differently in the inner region of the surface layer, the ST2 molecules being predominantly perpendicular to the surface, while the TIP4P molecules lie mainly parallel to the surface. In the outer surface region, the molecular planes are perpendicular to the surface for the both models. The TIP4P model allows a calculation of the surface tension, giving a value 54 mN/m which is somewhat lower than the experimental value for the plane surface, while for the ST2 model, larger clusters are needed than those treated in the present study.

Surface tension of water droplets at the critical radius

In die Theorie der homogenen Keimbildung wird fur die Oberflachenspannung kleiner Tropfchen eine vonTolman vorgeschlagene Korrektur eingefuhrt, die kleinere kritische Keimradien ergibt. Diese Verkleinerung ist zwar abhangig von Temperatur und Ubersattigung, jedoch praktisch konstant oberhalb vierfacher Ubersattigung. Die hier berechneten Werte kritischer Keimradien, der Molekulzahlen pro kritischen Keim, der Anzahl kritischer Keime sowie der Keimbildungsrate mit und ohne Korrektur sind in den Tabellen 1 und 2 dargestellt; Keimzahl und Keimbildungsrate sind zudem in Figur 1 fur die Temperatur 283,2° K graphisch dargestellt. Um Vergleiche mit den Ergebnissen von Wolkenkammer-Versuchen anstellen zu konnen, wird der «Schwellenwert der Kondensation» neu definiert unter Einschluss des Korrekturterms; die so erhaltenen Werte sind in Tabelle 3 aufgefuhrt. Die Ubereinstimmung mit dem Experiment ist besser als im Fall, in dem lediglich die Oberflachenspannung der ebenen Oberflache in Rechnung gesetzt wird.