Development of Aperture Total Internal Reflection (A-TIR) for Droplet Profiles With 3-D Ray Tracing and Modified Fresnel Equation

This study proposes and demonstrates a new approach using aperture total internal reflection (A-TIR) by means of various apertures in front of a detector to characterize micro/macro droplet. Pure liquid is used to make micro and macro scale droplets. An aperture in front of a detector in TIR configuration generates unique reflectance curve by filtering the amount of aberrated beams from the top curved profiles of droplets. A scheme of three-dimensional (3-D) ray tracing is developed for the reflected beam profile from the curved surface of the droplet with the modified Fresnel modeling to show a good agreement with the measurement. The modified Fresnel modeling is proposed to consider the morphological features of the droplet such as the thickness, the surface coverage fraction, the effective flatness ratio, and the quantum phenomenon of Goos-Hänchen (G-H) shift effect. Various sizes of apertures are employed to demonstrate the A-TIR reflectance depending on the aperture sizes for the macro and micro-sized droplets with a good agreement between the experiment and the simulation. Furthermore, it is demonstrated that important morphological features of the droplet such as the thickness (micrometer-range) and the ultra small contact angle less than 6 degree can be successfully determined with a reasonable agreement with the measurement. This outcome can be used to measure the morphological features of droplets and to characterize uneven surface features like human fingerprinting.

Direct measurement of selective evaporation of binary mixture droplets by dissolving materials

We investigate experimentally and theoretically how a droplet of a binary mixture evaporates when placed on a solid substrate. Our focus is the limit at which the two liquid components have different vapour pressures. Using physicochemical effects, we directly visualize the selective evaporation of the more volatile component and so document the space and time dependence of the chemical distribution in the droplet. In particular, we observe that a mixture consisting of an organic solvent and deionized water dissolves suspended fluorescent polystyrene particles if the lower volatility organic solvent reaches a critical concentration. Consequently, we show that for a small contact angle ($\unicode[STIX]{x1D703}<\unicode[STIX]{x03C0}/2$) the suspended polystyrene particles begin to disappear from near the contact line, which indicates that the volatile component, here water, evaporates rapidly compared to the other component(s). Finally, we show that a diffusion-dominated model for evaporation of a binary mixture can predict well the experimental results where convective and diffusive mixing effects are negligible, in which case there is significant chemical segregation in the drop.

Dropwise condensation on bioinspired hydrophilic-slippery surface

A hydrophilic-slippery copper surface is fabricated, reconciling two required factors, enhanced condensation and efficient water transport. Nucleation rate, droplet mobility and heat transfer are enhanced by the small contact angle and sliding angle.

Effect of characteristics of fine iron ores on the granulation behavior of concentrate in sintering granulation process

Concentrates have advantages of high ferrous grade, less harmful impurities and lower price. However, the small size and poor granulation behavior of concentrates could deteriorate the permeability of the sinter bed and reduce sinter productivity, thus making it difficult to use concentrates effectively. Therefore, in order to strengthen the granulation behavior of concentrates, granulation experiments were carried out and experiment samples made with one kind of concentrates and five kinds of fine iron ores were produced in this paper. Then, the effects of water absorbility and wettability of fine iron ores on granulation behavior of concentrates were investigated. Furthermore, optimized ore blending recipes were proposed to strengthen the granulation behavior of concentrates by sinter pot tests. Results show that the granulation behavior of concentrates was improved for the samples exhibiting high maximum capillary water and small contact angle in fine iron ores. Compared with the scheme of blending ores containing 15 mass% concentrate, the growth index of quasi-particles increased by 20.62% in the case of iron ore BR-2 replacing half of iron ore BR-1, the vertical sintering speed went up from 26.32 to 29.26 mm min−1, the productivity increased from 1.95 to 2.20 t m−2 h−1. The growth index of the quasi-particles increased by 30% when using iron ore AR-2 to replace half of iron ore AR-1. The vertical sintering speed and the productivity of sinter improved to 29.82 mm min−1 and 2.24 t m−2 h−1, respectively. The results help to improve the granulation behavior of concentrates by optimizing the blending ore recipes, based on the characteristics of fine iron ores, and thus use these concentrates more efficiently in the sintering process.

Lattice Boltzmann simulation of immiscible displacement in the cavity with different channel configurations

In this work, the immiscible displacement in a cavity with different channel configurations is studied using an improved pseudo-potential lattice Boltzmann equation (LBE) model. This model overcomes the drawback of the dependence of the fluid properties on the grid size, which exists in the original pseudo-potential LBE model. The approach is first validated by the Laplace law. Then, it is employed to study the immiscible displacement process. The influences of different factors, such as the surface wettability, the distance between the gas cavity and liquid cavity and the surface roughness of the channel are investigated. Numerical results show that the displacement efficiency increases and the displacement time decreases with the increase of the surface contact angle. On the other hand, the displacement efficiency increases with increasing distance between the gas cavity and the liquid cavity at first and finally reaches a constant value. As for the surface roughness, two structures (a semicircular cavity and a semicircular bulge) are studied. The comprehensive results show that although the displacement processes for both the structures depend on the surface wettability, they present quite different behaviors. Specially, for the roughness structure constituted by the semicircular cavity, the displacement efficiency decreases and displacement time increases evidently with the size of the semicircular cavity for the small contact angle. The trend slows down as the increase of the contact angle. Once the contact angle exceeds a certain value, the size of the semicircular cavity almost has no influence on the displacement process. While for the roughness structure of a semicircular bulge, the displacement efficiency increases with the size of bulge first and then it decreases for the small contact angle. The displacement efficiency increases first and finally reaches a constant for the large contact angle. The results also show that the displacement time has an extreme value in these cases for the small contact angles.

Optimization of Diamond-Like Carbon Thin Film on Copper Substrate for Carbon Nanotubes Synthesis by ACVD Technique

In this research, demonstrate plasma treatment on copper substrate by Radio Frequency Plasma (RF) using a mixture of 70%C2H2 + 30%H2 as the working gases. The plasma exposure time were varied from 10, 20 and 30 min under the electrical power of 50 Watts for synthesizing the diamond-like carbon (DLC) thin film on copper substrate. Thereafter, the substrates were used for synthesizing the carbon nanotubes (CNTs) via alcohol chemical vapor deposition technique (ACVD). It could be found that the plasma treatment for 10 min exhibited the small contact angle less than those of substrates treated with 20, 30 min and untreated sample which relate to the hydrophilic and affect to improve the adhesion and distribution of catalyst on substrate. The roughness of DLC film showed the different high and low level like hillock. After that, the 10 min treatment time sample was used for synthesizing the CNTs and the results found that the obtained CNTs showed good distribution on substrate.

Effect of the Surface/Water Chemistry on the Creation of Watermarks

Although evaporation as a pure bulk phase transformation is well understood, when one adds solutes to the liquid, or brings the liquid into contact with a substrate, we obtain a new and rich variety of possible behaviors that we can access experimentally to better understand the drying dynamics of residual water droplets. Evaporation of sessile droplets with a small contact angle (below 90°) is studied here extensively on silicon substrates. We focused our work on the origin of the creation of watermarks on silicon wafers. A thorough understanding of droplet evaporation is of vital importance for examining the drying rate, the flow patterns observed inside drying drops, and the residual deposits. The concentration of each potential dissolved species (e.g. silica or silicic acid) can also be predicted and confronted to their solubility. We developed a theoretical model to predict the evaporation rate and the behavior of submillimetric droplets taking into account the characteristics of the ambient and the substrate during the drying process. We discuss also the topology of watermarks on silicon wafers in the case of a predominant evaporation phenomenon.

Photocatalytic and Self-Cleaning Properties of TiO2-Cu Thin Films on Glass Substrate

TiO2-Cu thin films containing 0 to 1%Cu coated on glass slides were prepared by sol gel-dip coating method. The prepared thin films were synthesized at the temperature of 400 ◦C for 2 h with a heating rate of 10◦C/min. The microstructures of synthesized TiO2-Cu thin films were characterized by XRD, FT-IR and SEM. The photocatalytic activities of TiO-2Cu thin films were tested using methylene blue (MB) solution under UV irradiation. Finally, the self-cleaning property was evaluated by means of contact angle of water droplet on the films. The results show all samples have the thickness in range of 1 um and surfaces are dense with a large surface area. It can be noted that TiO2-1.0Cu thin films were found to give the highest photocatalytic efficiency and exhibited self-cleaning effect (small contact angle, 17°) under UV irradiation.

A Heat Transfer Model of Dropwise Condensation Underneath a Horizontal Substrate

For finding influence of the condensing surface to dropwise condensation heat transfer, a fractal model for dropwise condensation heat transfer has been established based on the self-similarity characteristics of droplet growth at various magnifications on condensing surfaces with considering influence of contact angle to heat transfer. It has been shown based on the proposed fractal model that the area fraction of drops decreases with contact angle increase under the same sub-cooled temperature; Varying the contact angle changes the drop distribution; higher the contact angle, lower the departing droplet size and large number density of small droplets; dropwise condensation translates easily to the filmwise condensation at the small contact angle ;the heat flux increases with the sub-cooled temperature increases, and the greater of contact angle, the more heat flux increases slowly.