Research ArticleAPPLIED SCIENCES AND ENGINEERING

Electrostatically driven fog collection using space charge injection

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Science Advances  08 Jun 2018:
Vol. 4, no. 6, eaao5323
DOI: 10.1126/sciadv.aao5323
  • Fig. 1 Trajectories of fog droplets around a cylinder with and without the application of corona discharge.

    (A and B) Schematic of air streamlines and droplet trajectories and photograph of droplet trajectories in the absence of an electric field. The inset shows the velocities of the wind Embedded Image and the particle Embedded Image and the drag force acting on the droplet. The bright ring is the edge of the cylinder. (C and D) Schematic of air streamlines, electric field lines, and droplet trajectories and photograph under corona discharge. Droplets closely follow the electric field lines in this case. The inset shows the additional electric force acting on a droplet. The cylinders in (B) and (D) have a diameter of 1.88 mm.

  • Fig. 2 Mechanism of droplet collection on a cylindrical wire.

    (A) Schematic of simplified experimental setup and droplet trajectories. (B) Schematic of the acceleration phase undergone by droplets. The electric field, the initial and terminal velocities, as well as the forces acting on a droplet are shown. (C) Added velocity as a function of V2. A linear fit of the data (R2 = 0.94) gives a slope of 0.006 m/s per kV2. The gray area is where the voltage is not high enough to induce corona discharge. The error bars reflect the SD over four measurements. (D) Schematic of the cross section of the collection phase near the cylinder. Streamlines, field lines, and trajectories of the droplets are shown. (E) Nondimensional collection area as a function of V2 for four different wind speeds. The gray area is where there is no corona discharge.

  • Fig. 3 Dependence of the deposition efficiency on the electrical number.

    The data correspond to five values of the wind speed and five values of the voltage. The colors represent different wind speeds (red, 0.55 m/s; blue, 0.6 m/s; green, 1 m/s; yellow, 1.65 m/s; purple, 3.3 m/s). The solid line is a linear fit (R2 = 0.92), with a slope of 0.26.

  • Fig. 4 Mechanism of droplet collection on two parallel cylindrical wires.

    (A) Schematic of droplet trajectories with two distant wires. The collection area of each single wire Asw and the distance D are shown. (B) Schematic of droplet trajectories in a two-wire system with spacing saturation. The parameters Ain, Aout, and D are shown. The white arrows show the single-wire areas of collection Asw. (C) Photograph of the droplet trajectories for two distant wires. The wire diameters are 1.88 mm. The distance between them is 10 mm. The applied voltage is 10 kV. (D) Photograph of the droplet trajectories in a spacing saturation case. The wire diameters are 1.88 mm. The distance between them is 6 mm. The applied voltage is 14 kV. (E) Embedded Image as a function of Ke for three different wire distances. The gray region covers theoretically inaccessible values. The vertical dashed lines represent the predicted spacing saturation values for D* = 1.7 and 4.2.

  • Fig. 5 Fog collection on meshes.

    (A) Snapshots of meshes at different time intervals of fog exposure. In the first row, a 15-kV voltage was applied, while there was no electric field in the second row. Red dye was added to the dispersed fog for visualization purposes. (B) Photographs showing the collection mesh and the storage beaker for collected water after 30 min of exposure. The case with high voltage resulted in the collection of 30 ml of water, while only three droplets were collected without electric field. Complete video of collection is shown in movies S3 to S4. (C) Mass of the collected water as a function of Ke for different meshes. The vertical dashed lines represent the predicted onset of spacing saturation from the two-wire model for meshes 1 to 3. (D) Deposition efficiency of the five meshes as a function of Ke. The colors represent different meshes according to the color code of (C).

  • Table 1 Characteristics of meshes.
    MeshWire diameter (mm)Opening size (mm)D*Open area (%)
    Mesh 11.61.571.9825
    Mesh 21.62.62.6539
    Mesh 31.64.753.9756
    Mesh 41.66.865.2966
    Mesh 51.611.107.9476

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaao5323/DC1

    Supplementary Text

    fig. S1. Nondimensional collection area as a function of the inverse of wind speed for five different voltages.

    fig. S2. Nondimensional collection area for two wires as a function of Ke for three different wire distances.

    fig. S3. Continuous 10-hour fog collection experiment.

    movie S1. Droplet trajectories in the absence of an electric field.

    movie S2. Droplet trajectories with corona discharge.

    movie S3. Ninety-second video of fog collection on meshes with and without corona discharge.

    movie S4. Thirty-minute video of fog collection on meshes with and without corona discharge.

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. Nondimensional collection area as a function of the inverse of wind speed for five different voltages.
    • fig. S2. Nondimensional collection area for two wires as a function of Ke for three different wire distances.
    • fig. S3. Continuous 10-hour fog collection experiment.
    • Legends for movies S1 to S4

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Droplet trajectories in the absence of an electric field.
    • movie S2 (.mp4 format). Droplet trajectories with corona discharge.
    • movie S3 (.mp4 format). Ninety-second video of fog collection on meshes with and without corona discharge.
    • movie S4 (.mp4 format). Thirty-minute video of fog collection on meshes with and without corona discharge.

    Files in this Data Supplement: