A novel methodology to study shape and surface tension of drops in Electric Fields

A novel methodology is introduced that can be used to study the behavior of conducting drops in electrostatic fields, when gravity effects are negligible. This methodology, called Axisymmetric Drop Shape Analysis — Electric Field (ADSA-EF), generates numerical drop profiles in the electrostatic field, for a given surface tension. Then, it calculates the true value of the surface tension by matching the theoretical profiles with the shape of the experimental drops, with the surface tension as an adjustable parameter. ADSA-EF can be employed for simulating drop shapes in the electric field, detecting the effect of an electric field on liquid surface tensions, and measuring surface tensions in microgravity, where current drop-shape techniques are not applicable. The predicted drop shapes in the electric field were compared with experimental images, indicating good agreement. Preliminary experiments according to ADSA-EF methodology suggested that the surface tension of water increases by about one percent in the electric field.     

Effects of liquid viscosity and surface tension on atomization in two-phase, gas/liquid fluid coker nozzles

This is an experimental study of the effects of liquid viscosity (μ_L) and surface tension (γ) on the size of droplets produced by an atomizer fed with a two-phase gas/liquid (TPGL) mixture. The nozzle is a one-quarter scale model of an industrial fluid coker nozzle used for bitumen upgrading. The primary objective of this study was to compare the Sauter mean diameter of the TPGL sprays for different μ_L and γ. Compressed air was used as the gas phase; the liquid phases were water, canola oil and a glycerine-water solution. The μ_L was varied from 1 mPa s to 67 mPa s, and γ was varied from 25 mN/m to 61 mN/m. The liquid flow rates were varied from 0.095 L/s to 0.105 L/s, and the gas-to-liquid ratio , by mass, was fixed at 2%, similar to the ratio used in commercial fluid coker nozzles. Fluid mixing pressures in the test were between 400 kPa and 700 kPa. The D₃₂ within the spray was measured using a Dantec 2D-Fibre mode Phase-Doppler-Particle-Anemometer (PDPA). With measurements performed at axial distances of 100 and 202 mm from the nozzle orifice and within a spray radius of 40 mm. The results showed that the 67-fold increase in μ_L results in 46 μm increase in D₃₂ which roughly extrapolates to a power law relationship exponent of 0.11 (based on two points). In contrast, the 2.4-fold increase in γ indicates roughly 42 μm increase in D₃₂, giving an exponent of −0.24. For both parameters the exponent is small, indicating weak dependence. The γ effects appear stronger, but the modest increase is barely exceeds the margin of error.     

基于聚多巴胺的超疏水棉织物的一锅法制备及其油水分离性能

将棉织物浸入多巴胺、硝酸银、十六烷基三甲氧基硅烷的乙醇溶液中,取出烘干制备出超疏水棉织物。用扫描电子显微镜和X射线光电子能谱表征其表面形貌和元素,用接触角测量仪测量其接触角并进行摩擦或液体浸泡(如酸、碱、沸水)实验检测其耐用性。结果表明,聚多巴胺的强附着性使原位生成的银纳米粒子能经受摩擦或不同液体的浸泡,从而使超疏水织物具有良好的耐用性。超疏水棉织物还具有良好的油水分离性能,其油水分离效率高达97%,油流量最高可达15.93 m³·m^-2·h^-1。     

Fracture strength of micro-tubular solid oxide fuel cell anode in redox cycling experiments

The maximum fracture strength of Ni/8YSZ anodes exposed to several redox cycles is compared. The anodes were fabricated using fine and coarse particle size powders. Fine-structured powders show a 77% increase in mechanical strength after exposure to three redox cycles. The coarse-structured material did not produce similar results and redox cycling resulted in gradual decrease in the mechanical stability of the supports.     

Effect of Gravity on the Macroscopic Advancing Contact Angle of Sessile Drops

A series of experiments were conducted in a reduced gravity (near‐free‐fall) environment (g = 0) and on ground (g = 1) to study the effect of gravity on the advancing contact angles of sessile drops. The reduced net acceleration force was produced by parabolic flights. The ground experiments were conducted for various three‐phase contact‐line advancing rates whereas the reduced gravity experiments were conducted for only one advancing rate due to the short duration of reduced gravity. The experimental results show that for water sessile drops on Teflon‐coated silicon wafers, the advancing contact angle in the reduced gravity environment is less than that of the advancing contact angle in 1g (126°) by about 5° for the same three‐phase contact line advancing rates.     

ON THERMODYNAMICS OF THIN FILMS: THE MECHANICAL EQUILIBRIUM CONDITION AND CONTACT ANGLES

A thermodynamic model for plane parallel thin liquid films applicable to solid-liquid-vapor systems was presented using the detailed method. The film was modeled as a bulk phase bound by two dividing surfaces. The thermodynamic thickness of the film was established as well as excess properties such as film tension. The analysis using this model yielded disjoining pressure definition identical to the literature reports. The effect of definition for contact angle on the resulting mechanical equilibrium condition was also demonstrated. It was concluded that from a theoretical perspective it is important to clearly define contact angles as the angle a sessile drop makes with either the solid phase or the thin film. However, on a practical level for most cases, the difference between using either of the two mechanical equilibrium conditions to determine film tension or contact angle will be minimal (ascertained by an order of magnitude analysis). The attempt was also made to bring about clarity concerning some of the questions in the literature regarding the thermodynamic model for thin films presented by Li and Neumann.