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Snow-making equipment
 
To make sure there is enough snow at the Winter Olympics at Sochi, Russia, the organizers have installed snow-making equipment all around the slopes.
Machines make snow the same way nature does: by freezing small water droplets. But a droplet won’t necessarily freeze on its own. It needs a seed, a particle to adhere to that starts the process.
In nature, dust can do the trick but a snow machine makes its own particles by expelling water and pressurized air through fine nozzles.
As the air expands, it cools rapidly and the water instantly freezes into tiny crystals of ice.
These crystals serve as seeds for a fine mist of water droplets produced by another set of nozzles. A powerful fan blows this mixture over the ski slope.
As they fall to the ground the droplets lose heat through evaporation and become snow.
What snowmakers call ‘hang time’ lasts just a few seconds so there isn’t time for the snow to grow elaborate branches like natural snowflakes. Machine-made snow looks more like tiny pellets.
The process happens so quickly that often only the outside freezes. So before the snow is pushed around the slope it’s left sitting for a while to let the droplets freeze all the way through.
By changing the rate of water flow the snow can be made wetter and heavier – good to build up a base – or dryer and lighter – easier to ski on.
Temperatures below about 20 degrees Fahrenheit are ideal for snow-making but snow can even be made in above-freezing temperatures if the air is dry enough.
Source: nytimes

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