Coalescence and counterflow of droplets on needle electrode with negative corona discharge

Ion wind propulsion systems have potential applications in the field of unmanned aerial vehicle (UAV) due to their compactness, quiet operation, and simple design. Previous studies have focused on the influences of power source, electrode arrangement, size, and shape on the output thrust characteristics. However, few studies have been performed on the environmental conditions, which can be beneficial for the practical applications of ion wind aircraft in various climatic conditions. In this work, a measurement platform of the output characteristics of ion wind propulsion system under various environmental conditions has been established. The experimental pressure range is 1 to 0.7 atm, and the relative humidity (RH) is 30% to 92%. The effects of air pressure and humidity, and voltage level on the thrust, thrust-to-power radio (TPR) corona current have been investigated. The results show that the corona current and thrust of the wire-wing electrode array decrease with RH within the range of 30% to 80%. Under higher humidity, the corona current and thrust tend to increase at most voltage levels. Moreover, the thrust and current both decrease with reduced pressure when keeping the voltage-to-pressure ratio (U/P) unchanged. It was also found that the thrust is roughly proportional to the square of the pressure. Finally, the possible explanations of the coupled influences on the output characteristics were discussed.

“…At extremely high humidity, water molecules may adhere and condense on the electrode [40]. This process leads to greater nonuniformity in the electric field on the emitting electrode.…”

Section: Influence Of Humidity On Thrust Characteristicsmentioning

confidence: 99%

Influence of humidity and air pressure on thrust characteristics of ion wind propulsion systems

Zhao,

Chen,

et al. 2024

“…Atmospheric pressure discharge plasma has been widely used in many applications, such as biomedicine [16], material modification [17,18], soil remediation [19,20], directional transport of droplets [21] and artificial precipitation [22]. As a significant branch of the field, electrostatic fog harvesting has been extensively studied over the last 50 years worldwide.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of the enhancing effect of micro–nano protrusions on electrostatic fog harvesting

Zhang

Xiao

et al. 2023

Self Cite

Fog harvesting is one potential approach to provide supplementary water resources in arid areas. Considerable researches have been devoted to electrostatic fog harvesting technology, but there are still some problems such as high voltage, complex structure and expensive cost. Decorating micro-nano protrusions on the electrode is an effective method to lower operating voltage, improve fog harvesting efficiency, and the enhancement effect of protrusions has already been experimentally demonstrated. However, the enhancement mechanism on the microscopic level is less reported. This manuscript tries to explain why the micro-nano protrusions can enhance the discharge and fog harvesting by numerical simulation. Three key processes of corona discharge, fog droplet migration, and fog harvesting efficiency are discussed in detail, especially the influence of droplet size, tip radius of protrusion, protrusion-protrusion angle and so on. The numerical simulation results show that the inception voltage of barbed electrode decreases from 7 kV to 3 kV (decrease in 57%), and current increases significantly (e.g. 68% at 15 kV). At 15 kV, the fog harvesting efficiency of barbed electrode is higher (29.8%) than that of smooth wire (25.7%), even with less effective collection area. The collection efficiency increases with the droplet size and exists an optimized ratio (~1‰) of protrusion tip radius and wire radius to gain high collection efficiency. This research results are beneficial for understanding the microscopic mechanism of protrusions enhancing electrostatic fog harvesting and providing guidance for further fog harvesting equipment improvement.

“…Considerable challenges remain in developing a fog collection system that can be widely applied for effective collection under light and heavy fog. We have drawn great inspiration to design efficient fog collection systems from the affinity and separation of water molecules by surface wettability, as well as the application of wettability differences in directional fluid transport [28], heat transfer enhancement [29,30], and agricultural irrigation [31].…”

Section: Introductionmentioning

confidence: 99%

Enhancing fog collection by optimizing wettability combination and fork-row collector arrangement: light and heavy fog

Zhang,

Xiao,

et al. 2023

Self Cite

Fog collection is essential to alleviate water scarcity in arid areas. However, the vast majority of existing fog collectors only work effectively in heavy fog. To broaden the fog concentration range for efficient work, an optimization strategy based on wettability combination and fork-row arrangement is proposed in this work. Single-layer experiment results show that a hydrophilic (HL) surface with high deposition capacity collects droplets at a faster rate in light fog (25–80 g h−1), while the collection rate of a hydrophobic (HB) surface with high drainage capacity is higher in heavy fog (220–500 g h−1). Double-layer experiment results show that in light fog, the best combination of double-layer collection electrodes is HL–HL, while HB–HL performs best in heavy fog. A 35% improvement in collection rate can be obtained simply by changing the arrangement from smooth-row (S) to fork-row (F), which is attributed to the increased effective collision area of droplets. In our series of experiments, at 50 g h−1, the collection rate of double-layer combination HL–HL(F) is 56.7% higher than that of single-layer HL. In particular, the collection rate of HB–HL(F) reaches 1434.7 mg cm−2 h−1 at 500 g h−1. Such a good performance is attributed to the force imbalance of hanging droplets caused by wettability differences, which tends to transport small droplets on HB towards HL directionally, resulting in a rapid droplet slippage. Therefore, the HB–HL accelerates drainage and refreshes capture points. Furthermore, fog collection performance is also influenced by layer spacing, which has an optimal distance. These findings provide a promising method for practical applications of fog collectors in a wide range of fog flow quantities, enhancing adaptability to variable environments.