Improving heat and mass transfer rates through continuous drop-wise condensation

Drop-wise condensation (DWC) has been the focus of scientific research in vapor condensation technologies since the 20th century. Improvement of condensation rate in DWC is limited by the maximum droplet a condensation surface could sustain and the frequency of droplet shedding. Furthermore, The presence of non-condensable gases (NCG) reduces the condensation rate significantly. Here, we present continuous drop-wise condensation to overcome the need of hydrophobic surfaces while yet maintaining micron-sized droplets. By shifting focus from surface treatment to the force required to sweep off a droplet, we were able to utilize stagnation pressure of jet impingement to tune the shed droplet size. The results show that droplet size being shed can be tuned effectively by tuning the jet parameters. our experimental observations showed that the effect of NCG is greatly alleviated by utilizing this technique. An improvement by multiple folds in mass transfer compactness factor compared to state-of-the-art dehumidification technology was possible.

Features of the interaction of molecular oxygen with the condensation surface in the plasma of a low-pressure arc discharge

A model has been developed for studying the features of the thermal interaction of molecular oxygen in the near-surface condensation layer in the plasma of a low-pressure arc discharge. It was found that the input power and pressure of the gas mixture exert the main influence on the electron temperature and on the density of positive ions (O_2^+ and O+). It is shown that at a fixed pressure, the ion density increases with an increase in the power of the system, and vice versa.

Dew formation characteristics of meadow plants canopy at different heights in Hulunbuir grassland, China

A plant's foliar uptake of dew can mitigate the adverse effects caused by drought stress. However, in grassland ecosystems, it is inconclusive whether the dew condensation characteristics of plants at different heights are consistent. In this study, we wanted to know whether plant height had a significant effect on the formation of dew. In addition, we wanted to understand the difference of dew formation between C3 plant Leymus chinensis (LC) and C4 plant Cleistogenes squarrosa (CS) which have different heights and can succeed each other in the community. In nine dew nights, we measured the amount of dew formed on simulated condensation surface (different heights) and two plants at the same time. The results showed that in the height range of 5–80 cm, the dew amount increases with the canopy height, but its increase rate gradually slows down and approaches zero. The shorter CS (5–15 cm) has a similar dew amount (0.095 mm) as LC (40–70 cm) due to its compact structure of the leaves with pubescence and the more stable micro-meteorological conditions. The CS can obtain more potential dew per unit organic matter, and this may be one of the potential mechanisms for the succession from LC communities to CS communities under drought stress.

Effects of tilt angle on droplets condensation on hydrophobic surface

Condensation surface modification was an important research direction to realize droprise condensation and erhance heat transfer. In order to explore the condensation process and mechanism of droplets on the hydrophobic surface, the condensation process of droplets on the natural Donghu lotus leaves with tilt angle of 30°,60° and 90° were studied. The results show that the tilt angle had a significant effect on the droplets condensation behavior on Donghu lotus leaves hydrophobic surface. Increasing the tilt angle would short the detachment time of condensate droplets. The growth rate of droplets increased with the increase of hydrophobic surface tilt angle. And the condensation droplets diameter also decreased with the increase of incl ination angle.

Optimization of Nodule and Height Sizes for Mixed Hydrophilic and Hydrophobic Surfaces

Patterned surfaces of hydrophobic and hydrophilic materials are considered to sustain dropwise condensation, providing the benefits of both materials and creating a surface with a low energy barrier for nucleation and capable of sustaining dropwise condensation. Surface heights, nodule sizes, and flow rates are evaluated on square-patterned surfaces to maximize mass collection. A thermal model is used to assess surface performance and includes an equivalent thermal resistance for diffusion. Flow rates of 15, 25, 50, and 100 m/s with nodule sizes between 0.1 mm to 3.6 mm are evaluated. Surface heights of 0.25, 0.5, 1, and 2 m are also assessed. For flow rates greater than 50 m/s, turbulent flow optimum nodule size is between 0.2 mm and 0.6 mm. Surfaces greater than 1 m in height at flow rates less than 50 m/s maximize mass with nodule sizes of 1.4 mm and 2 mm.

A PROTOTYPE DEVICE FOR PRODUCING FRESH WATER FROM ATMOSPHERIC AIR

Objectives.The aim of the article is to develop the design and carry out the physical and mathematical modelling of a device for producing fresh water from atmospheric air in coastal areas, as well as under the conditions of sea transport.A Method for constructing the device for producing fresh water from atmospheric air is developed on the basis of a physical and mathematical model. Fresh water is obtained by condensation on a cold surface, which dew point is created using the natural cold of seawater with the application of the energy of moving waves for its circulation. The heating of the surface air layer adjacent to the cold surface by solar concentrators intensifies the process of the moisture condensation.Results. Data is obtained on the quantity (mass) of fresh water produced per unit of condensation surface area (1 m2 ) for 1 hour depending on the temperature difference between the condensation surface and seawater. The influence of the characteristics of solar concentrator and liquid heat remover with seawater on the device parameters is studied.Conclusion. It is established that the amount of the fresh water obtained from atmospheric air strongly depends on the temperature difference between the condensation surface and seawater. Thus, according to calculations, with an increase of the latter by 45 K, the mass of fresh water obtained from a condensation surface of 1 m2 in 1 hour approximately doubles to 5.8 kg.

Controllable fabrication of Ag-NP-decorated porous ZnO nanosheet arrays with superhydrophobic properties for high performance SERS detection of explosives

An efficient hydrophobic condensation surface was developed and used as an ultrasensitive and stable SERS sensor based on ZnO–Ag hybrid mesoporous nanosheet (MNS) arrays for natural explosive sample detection.