Droplet Terminal Fall SpeedThis project is intended to investigate the terminal fall speed of a water droplet. The fall speed of a raindrop for example is related to its size, and understanding this is important in meteorology and cloud physics.A wind tunnel is used to project a stream of air upwards into which a droplet can be injected where it will hover. This is the equivalent to the droplet falling through the atmosphere, and the observer who is monitoring it also falling at the same speed with it. A variety of covers can be placed over the air outlet orifice with various arrangements of wire covering them to alter the profile of the air stream. The speed of the air can be controlled by a voltage controller and can thus be adjusted to the size of the droplet being suspended. The droplets can be captured mid-suspension and weighed to determine their mass, and the air speed where the droplet was located can be measured using a heated-wire probe. The relationship between a droplet’s size and its terminal velocity can then be determined, and how this varies with air stream profile can be investigated.The photos (Fig. 1), videos (Fig. 2), and slow motion videos (Fig. 3) show the apparatus and the experimental process in action. Notice how the droplet is not tear-drop or pear shaped as is commonly thought, but hemispherical. Notice also how the terminal velocity for a given droplet ranges by virtue of how the droplet oscillates up and down. Finally, note how the droplet experiences modes of surface oscillation and rippling.Photos:Videos:Slow motion videos:.Site and content created using Xara Designer Pro 6Fig. 1. A selection of photos of the experimental apparatus and hovering droplets. Click the thumbnails to reveal a larger image and caption.
Fig. 2. A high resolution video of the droplets falling at terminal velocity. Change video resolution by starting video and choosing from bottom right of player.
Fig. 3. A high resolution, slow motion video showing finer temporal detail of water droplet behaviour at terminal velocity. Change video resolution by starting video and choosing from bottom right of player.Click on a photo thumbnail to enlargeChoose resolutionChoose resolution
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M.I.C.C.
Manchester Ice Cloud Chamber
Droplet Terminal Fall Speed
This project is intended to investigate the terminal fall speed of a water droplet. The fall speed of a raindrop
for example is related to its size, and understanding this is important in meteorology and cloud physics.
A wind tunnel is used to project a stream of air upwards into which a droplet can be injected where it will hover.
This is the equivalent to the droplet falling through the atmosphere, and the observer who is monitoring it also
falling at the same speed with it. A variety of covers can be placed over the air outlet orifice with various
arrangements of wire covering them to alter the profile of the air stream. The speed of the air can be
controlled by a voltage controller and can thus be adjusted to the size of the droplet being suspended. The
droplets can be captured mid-suspension and weighed to determine their mass, and the air speed where the
droplet was located can be measured using a heated-wire probe. The relationship between a droplet’s size
and its terminal velocity can then be determined, and how this varies with air stream profile can be
investigated.
The photos (Fig. 1), videos (Fig. 2), and slow motion videos (Fig. 3) show the apparatus and the experimental
process in action. Notice how the droplet is not tear-drop or pear shaped as is commonly thought, but
hemispherical. Notice also how the terminal velocity for a given droplet ranges by virtue of how the droplet
oscillates up and down. Finally, note how the droplet experiences modes of surface oscillation and rippling.
Photos:
Videos:
Slow motion videos:
.
Site and content created using Xara Designer Pro 6
Fig. 1. A selection of photos of the experimental apparatus and hovering droplets. Click the thumbnails to reveal a larger image and
caption.
Click on a photo thumbnail to enlarge
Choose
resolution
