Efficient droplet removal from a cool super-repellent surface is highly desired in various industrial applications, such as condensation, water collection, anti-icing, and so on. However, designing ...surfaces that maintain their non-wetting properties in condensation conditions is still a challenge. Here, we develop a facile one-step vapor-deposition technique to fabricate transparent superhydrophobic surfaces that allows for the attainment of sustained and dry condensation. Careful optimization of the synthesis procedure, surface morphology, wettability and departure dynamics of condensate droplets was implemented, leading to enhanced dry condensation performances at a wide range of surface subcooling. The maximum diameter and coverage rate of condensation droplets were strictly confined to ∼50 µm and ∼20%, respectively. Moreover, the designed surfaces exhibit excellent self-cleaning performance in condensation environments. We envision that the facile and fluorine-free strategy for fabricating excellent dry condensation surfaces could be valuable in popularizing their practical applications.
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•A transparent superhydrophobic surface that allows for the attainment of sustained and dry condensation surface was prepared.•The maximum diameter and coverage rate of condensation droplets were strictly confined at a wide range of surface subcooling.•The designed surfaces exhibit excellent self-cleaning performance in condensation environments.
The moist condensation and thermal comfort are two important issues for the radiant cooling systems. To investigate the safe temperature without condensation, and the comfort of the composite system, ...experiments and simulations are conducted in this work. As the temperature of the floor surface is decreased to approximately 13 °C, slight condensation appears underneath the table. For which, the relative humidity is in the range of 88% ∼ 92%. The dew point temperature is measured especially considering the high humidity environments. Simulations, considering moist air infiltration on rainy days, are performed to evaluate both condensation and thermal comfort of various systems with different positions of fan coil and radiant surface. Of nine cases, case 5 has the maximum humidity, representing the most easily condensed. Out of the 54 localized PMVs, containing two people's ankle, waist and head level in 9 cases, 61.1% are in the range of −0.5 to 0.5. Of these, cases 3 and 5 have the largest proportions. For cases 1, 4, and 7, PMVs of the waist level of person 1 are less than 1, influenced by convective airflow. Increasing the upward angle of airflow can improve thermal comfort, but it is not suitable for the ceiling cooling because the humidity is increased to 89.6%, to condense easily, when the upward inclination is 30°. Multi-perspective findings provide a powerful basis for the optimized configuration of composite cooling systems. Especially, the locations of the minimum temperatures on the radiant surfaces should be given special attention to avoid water condensation for high-humidity environments.
Electricity harvest from ubiquitous water has been endeavored, using nanogenerators based on carbon nanomaterials, to acquire renewable and clean energy and cope with fossil depletion and pollution ...as well. Meanwhile, though many biological organisms can harness water for bioelectricity, it is still challenging to produce biological nanogenerators based on biological nanomaterials with billions of tons of annual production in nature. Herein biological nanofibrils, including cellulose, chitin, silk fibroin, and amyloid, are produced either by liquid‐exfoliation of biomasses or by supramolecular assembly of bio‐macromolecules. With the intrinsic hydrophilicity and charged states, they can capture moisture from air and form hydrated nanochannels, in analogue to ionic channels of cytomembranes. When exposing their aerogels to moist air flow, there is a balance of water absorption and evaporation, thus producing a streaming potential and an open‐circuit voltage across the aerogel. With flexibility, sustainability, biocompatibility, and biodegradability, these biological nanogenerators can harvest electricity from moist air flow in nature (e.g., wind, respiration and perspiration) and in industry, and serve for environmentally‐friendly, low‐cost, high‐efficiency, wearable, and miniaturized power devices.
Biological nanofibrils, having intrinsic hydrophilicity and diverse charged states, can capture moisture and form hydrated channels like the ionic channels of cytomembranes. Their aerogels are able to produce a streaming potential when exposed to moist airflow. These biological nanogenerators could harvest energy from nature and industry (e.g., moist wind, respiration and perspiration), and serve as sustainable, high‐efficiency and wearable power devices.
•Condensation rate of superhydrophobic surfaces in quiescent air is investigated.•Buffer water method is developed to measure condensate mass.•Condensation rates are close to empirical correlation ...predictions.•The effects of surface wettability on condensation rates in moist air is minor.
Condensation heat transfer at superhydrophobic surfaces has raised a lot of interest due to their potential application in atmospheric water harvesting and air-conditioning. In moist air, the condensation heat transfer using a superhydrophobic surface can be negatively affected by the existence of a large amount of non-condensable gas, namely, the dry air. Besides, the air flow pattern would substantially affect the surface condensation rate due to the convective mass transfer of water vapor. In this study, the condensation regime of a superhydrophobic aluminum surface vertically positioned in quiescent moist air was visualized and the condensation rate was experimentally investigated. Condensation experiments were also performed by using hydrophobic, hydrophilic, and superhydrophilic surfaces for comparison. The condensation rate of the superhydrophobic surface was consistent with that of other surfaces, though the condensation regimes of the four surfaces were quite different. The average deviation between the experimental condensation rate and the empirical correlation of natural convection heat and mass transfer was within 12%. The result indicates that vapor transfer induced by diffusion and convection in the boundary layer rather than the heat transfer resistance associated with condensate dominates the condensation heat and mass transfer between the moist air and the superhydrophobic surface.
•Effect of fogging on cooling in transonic compressors was numerically investigated.•Causal relation between wetness and particle deposition on blades was clarified.•Moist-air flows through 1.5-stage ...full annulus blade rows were simulated.•Shock played the leading role in evaporating and cooling the moist air.•Effect of condensation on particle deposition was further investigated.•Fogging and deposition may be in a trade-off relation for the performance.
Moist air flows with and without consideration of inlet wetness and assuming fogging were numerically investigated in a transonic compressor of an industrial gas turbine, and the causal relationship between the wetness and the deposition of water droplets on the blade surface was clarified. First, we simulated three-dimensional moist-air flows through the 1.5-stage rotor and stator blade rows in the transonic compressor of an industrial gas turbine operating at a Tokyo Electrical power plant, considering variations in the inlet wetness and the number of aerosol particles. The results indicated that the shock generated in the first-stage rotor passage was the primary factor in the evaporation of the moist air, decreasing its temperature, whereas the wetness was highly dependant on the deposition of water droplets on the blade surface. We further simulated two-dimensional humid-air flows through a transonic compressor cascade channel under a number of conditions, varying the aerosol particle size, number of aerosol particles, humidity, blade chord length and pressure ratio. The results indicated that the condensation of humid air was captured locally in the supersonic region, while the deposition of the condensed water droplets was mainly influenced by the first three factors. Overall, this study indicates that wetness and deposition are in a trade-off relationship with regard to the performance of gas turbines.
In this study, warm and moist air intrusions (WaMAI) over the sea sectors of Kara, Laptev, East Siberian and Beaufort from 1979 to 2018 are identified in ERA5 reanalysis and their air-mass ...transformation is analysed using interpolation in ERA5 and satellite products along trajectories. The analysis shows that WaMAIs, driven by blocking high-pressure systems over the respective ocean sectors, induce surface warming (11–18 W m−2) and sea ice melt from positive anomalies of net longwave radiation (5–8 W m−2) and turbulent flux (8–13 W m−2) to the surface, although the anomaly of net shortwave radiation (−9 ~ +1 W m−2) is negative. From a Lagrangian perspective, the surface energy-budget anomaly decreases linearly, while total column cloud liquid water (TCLW) increases linearly with the downstream distance from the sea-ice edge. However, the cloud radiative effects of both longwave and shortwave radiation reach an equilibrium as TCLW increases in a much lower rate beyond 7 degrees north of the sea ice edge. The boundary-layer energy-budget pattern can be categorized into two classes: radiation-dominated and turbulence-dominated, comprised of 26% and 62% WaMAIs respectively. Statistically, turbulence-dominated cases occur with 3 times stronger large-scale subsidence, and also feature a larger anomaly in net shortwave radiation. In radiation-dominated WaMAIs, stratocumulus develops more strongly and hence exerts larger longwave and shortwave forcing to the surface. In both categories, a well-mixed boundary layer deepens by 500 m along the trajectories, from the continuous turbulent mixing.
•Blocking high-pressure systems drive warm-air advections in summer Arctic.•The total column cloud liquid water increases linearly with the distance from the sea-ice edge.•A well-mixed boundary layer deepens along the trajectories, from the continuous turbulent mixing.•The boundary-layer energy-budget pattern can be mainly categorized into radiation-dominated and turbulence-dominated.
Spontaneous condensation processes are common in the industry and have a significant impact on the aerodynamic characteristics of turbines. The spontaneous condensation process of moist air in a ...high-speed turbo-expander was investigated experimentally and numerically. Temperature and humidity of the moist air into the turbo-expander were controlled independently in a psychrometric chamber. A liquid fraction of 0.8% was achieved at the turbo-expander outlet which was corresponding to a relative humidity of 76.9% at 303.2 K. The non-equilibrium condensation model was validated against the experimental results, and the maximum relative deviations of outlet temperature, absolute humidity, and moist efficiency were 0.16%, 3.23%, and 2.15%, respectively. Based on numerical simulations, the nucleation process and droplet distribution in the turbo-expander were studied. Compared with the suction surface, the nucleation region near the pressure surface was more extensive. The effect of inlet temperature, humidity, and pressure was compared. The inlet pressure had the most significant impact on the nucleation initial position, and the inlet temperature mainly determined the nucleation rate and droplet number. The wetness loss due to the vapor condensation mainly occurred in the impeller, and the efficiency drop could reach 2.17% when the pressure ratio was 2.1.
•Spontaneous condensation processes of moist air in the turboexpander are studied.•The aerodynamic parameters distribution with condensation process is analyzed.•Effect of inlet temperature, humidity, and pressure on the condensation process.•Inlet relative humidity of 76.9% at 303.2 K leads to a liquid fraction of 0.8%.
•Moist air condensation on vertical superhydrophobic surface is tested.•Condensate departure mechanism in hydrophilic surface is gravity driven sliding.•Direct and bounced jumping are the departure ...mechanism in superhydrophobic surface.•Superhydrophobic surface offered a 36% enhancement in heat transfer coefficient.•Influence of subcooling temperature on heat transfer coefficient is predominant.
The main objective of the present study is to experimentally investigate the moist air condensation behavior subject to hydrophilic and superhydrophobic surface with a much broader operating conditions such as different relative humidities (RH = 40 – 85%) and degree of subcooling (ΔTsub= 1 – 16 K). The flow visualization of condensation behavior showed that the main condensate departure mechanism of the hydrophilic surfaces is gravity-driven sliding. In contrast, the primary mechanisms for the superhydrophobic surfaces are direct jumping and bounced-jumping caused by the coalescence induced phenomena. The superhydrophobic surfaces yielded a maximum of 36% improvement in heat transfer coefficient at 85% relative humidity over the hydrophilic surfaces, while the enhancement is about 16% for 60% and 40% relative humidities. Similarly, the maximum heat transfer coefficient of 37 W m-2K−1 is attained at the subcooling temperature of 16 K, and it is reduced to 31 W m-2K−1 and 20 W m-2K−1 respectively when the subcooling is reduced to 6 K and 1 K.
•System development on regeneration of water from moist air on zeolite 13X at various temperature settings was proposed.•The significant improvement was offered at normal superficial velocity of ...0.432 mN/s for inlet temperature of 200 °C.•Sufficient regeneration speed was provided by raising the inlet temperature.•Efficiency of the heat pump decreased because of the increase in dew point.•The decrease of the efficiency can be reduced by increasing the inlet temperature.
Although adsorption heat pump systems consist of adsorption and regeneration processes, almost no reported work has investigated regeneration in detail for a packed bed of zeolite particles. Here, we conducted experimental and theoretical analyses on the effects of temperature, dew point, and the flow velocity of high-temperature moist air on the regeneration rate. Normal superficial velocities of 0.108, 0.216, and 0432 mN/s, and inlet temperatures of 140 and 200 °C with various dew point temperatures were examined. Originally, the purpose was to make saturated steam of 180 °C or higher from factory waste heat of 100°C or lower. Regeneration of the zeolite particle layer with high-temperature moist air was analyzed with respect to the effect of air conditions. Numerical simulations of zeolite energy storage were performed using a one-dimensional adsorbent regeneration model. Practical applications of the numerical model were also examined. A sufficient regeneration rate was obtained by raising the temperature, even when environmental air was used. Significant improvements were obtained at a 0.432-mN/s normal superficial velocity and a 200°C inlet temperature. In the particle layer containing only adsorbed water, dew point effects on the regeneration rate and temperature response were small at high temperatures. In the particle layer containing both adsorbed and free water, the effect of the dew point on the regeneration rate was also small. The heat pump efficiency decreased because of the increased dew point; however, the decrease in efficiency was mitigated by increasing the temperature.
•The impact of droplet size on the condensation in internal and external moist air flows.•The evaluation of blend condensation model independent of the droplet size.•Upwind and downwind shock wave ...shift due to heterogeneous condensation.
The aim of this paper is to thoroughly analyse the influence of condensation models on the modelling of condensation phenomena in transonic flows of moist air. The reason for the study was the fact that different condensation models are used by researchers to obtain satisfactory results of numerical modelling. The condensation models tested herein differ in the nucleation rate formula and the droplets growth equation. Four most often used condensation models were selected for detailed investigations. The results obtained from each model were compared with experiments for the internal flow through a nozzle and the external flow around an airfoil. The main focus was on the location of the onset of the nucleation process. Moreover, the droplet growth intensity was compared and discussed. The nozzle flow CFD calculations were performed using the ANSYS Fluent commercial tool. Finally, the condensation model which is the most suitable for the moist air transonic flow was recommended.
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