Thin-water-film-enhanced TiO2-based catalyst for CO2 hydrogenation to formic acid

Carbon dioxide (CO2) hydrogenation can not only mitigate global warming, but also produce value-added chemicals. Herein, we report a novel three-phase catalytic system with an in-situ generated and dynamically updated...

Adsorption of Gas-Phase Cyclohexanone on Atmospheric Water Films

The fate of atmospheric volatile organic compounds (VOCs) strongly depends on the partitioning processes on the surface of aerosols, which are coated with a thin water film. However, the behavior of VOCs in the aqueous film of aerosols is difficult to measure. In this work, the interfacial partition constant of cyclohexanone was determined using a novel flow-tube reactor. A thin, aqueous film placed in the reactor was exposed to cyclohexanone gas. The subsequent partitioning was measured using chromatography techniques. The quality control tests were first conducted to ensure the accuracy of the adsorption experiments. The cyclohexanone concentration was then plotted as a function of film thickness to obtain the partitioning constants. As the thickness of the water film decreased, the aqueous concentration of cyclohexanone increased, indicating that surface adsorption played a dominant role in the uptake of cyclohexanone. According to the temperature dependence of the interfacial partition constant, the solvation enthalpy and entropy of cyclohexanone were obtained. The results of this study would help to elucidate the effect of atmospheric water film on the gas–aerosol partitioning of VOCs, and thus can help to better understand the fate of VOCs in the atmosphere.

Modeling of hot-point drilling in ice

Hot-point drills have been widely used for drilling boreholes in glaciers, ice caps and ice sheets. A hot-point drill melts ice through the thermal head at its bottom end. Penetration occurs through a close-contact melting (CCM) process, in which the ice is melted, and the meltwater is squeezed out by the exerted force applied on the thermal head. During the drilling, a thin water film is formed to separate the thermal head from the surrounding ice. For the hot-point drill, the rate of penetration (ROP) is influenced by several variables, such as thermal head shape, buoyancy corrected force (BCF), thermal head power (or temperature) and ice temperature. In this study, we developed a model to describe the CCM process, where a constant power or temperature on the working surface of a thermal head is assumed. The model was developed using COMSOL Multiphysics 5.3a software to evaluate the effects of different variables on the CCM process. It was discovered that the effect of thermal head shape and the cone angle of conical thermal head on ROP is less significant, whereas the increase in the BCF and the power (or temperature) of the thermal head can continuously enhance the ROP.

Thickness Measurement of Water Film/Rivulets Based on Grayscale Index

This study proposed a nonintrusive and cost-efficient technique to measure the thickness of a thin water film/rivulet based on the grayscale index. This technique uses millions of probes and only needs a digital camera, fill lights, and pigment. For water colored with diluted pigment, the grayscale index of the water captured by a digital camera depends on the water thickness. This relationship can be utilized to measure the water thickness through digital image processing. In the present study, the relationship between the grayscale index and water thickness was theoretically and experimentally investigated. Theoretical derivation revealed that when the product of water thickness and the color density approaches to 0, the grayscale index is inversely proportional to the thickness. The experimental results show that under the color density of 0.05%, the grayscale index is inversely proportional to the thickness of water film when the thickness is less than 6 mm. This linear relationship was utilized to measure the distribution and profile of a water rivulet flowing on the lower surface of a cable model.

Airside Performance of Fin-and-Tube Heat Exchangers Having Nonrepeating Nonsymmetrical Slit Fins under Wet Condition

In this study, heat-transfer and friction characteristics of newly developed nonsymmetric slit-finned-tube heat exchangers are experimentally investigated. The newly developed slit fin had more slits in the second row than the first row. As a result, different row effect on [Formula: see text] factor than that of conventional enhanced finned-tube heat exchangers was observed. In other words, two-row configuration yielded larger [Formula: see text] factor than the one-row configuration. Comparison with conventional louver fin or slit fin heat exchangers revealed that the present slit fin heat exchangers show superior heat-transfer characteristics, especially at the second row. The reason was attributed to the many narrow slits that formed at the second row, which maintain thin water film along the slits and smooth the condensate flow.

Investigation on Thermal Conductivity and Viscosity of Thin Water Film by Molecular Dynamics Simulation

This work provides a molecular dynamics simulation of the thermal conductivity and viscosity of thin water film. The results show that the average normal thermal conductivity and viscosity of thin water film is about an order of magnitude lower than those of bulk water, and they increase nonlinearly with the increase of thin film thickness. However, the viscosities at different sub-layers of a thin water film are apparently different. The density profiles at different positions of the thin water films are given to indicate their influence on the normal thermal conductivity and viscosity. The large increase of the viscosity and substantial decrease of the normal thermal conductivity in the near wall region of the substrate is influenced by the structural transition of thin water film because of its high density, which has prominent impact on the mean free path at the nanoscale. It provides a viable guidance for the mechanism study on the heat and mass transfer of an evaporating thin liquid film near the triple line.

Active particle aggregate on complex bubble surfaces

Recently, colloids have been shown to form complex structures on bubble surfaces on demand. With the help of a high power pulse laser shining on a thin water film, water bubbles can be formed and heat unbalance creates a convective flow, which carries colloids on the surface of these water bubbles to form aggregates. Here, active particles are studied in a similar setup and conditions are laid out to form aggregates on water bubble surfaces. The effect of motility and chirality of active particles on formation of aggregate are discussed. The simulation results obtained here will hopefully help the experimental endeavors in future.