[HN Gopher] Canned Air is Unexpectedly Supersonic [video]
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       Canned Air is Unexpectedly Supersonic [video]
        
       Author : zdw
       Score  : 31 points
       Date   : 2024-02-18 15:54 UTC (2 days ago)
        
 (HTM) web link (www.youtube.com)
 (TXT) w3m dump (www.youtube.com)
        
       | pfdietz wrote:
       | One sometimes sees Mach diamonds in geysers (the speed of sound
       | can be quite low in steam loaded with water droplets):
       | 
       | https://seismo.berkeley.edu/~manga/kieffer1989.pdf (see figure
       | 26)
        
       | AnotherGoodName wrote:
       | I'm guessing that the speed of sound being different in the high
       | pressure side vs low pressure side helps this occur.
       | 
       | When you think about it it's hard for air to push itself faster
       | than the speed of sound since the speed of sound is literally the
       | speed that a wave of compression in air will propagate.
       | 
       | So how can it go faster than the max speed a wave of compression
       | can travel at when it's powered by that? Well compressed air has
       | a much higher speed of sound. So it's accelerated to the below
       | speed of sound inside the nozzle and on exit it's now faster than
       | the speed of sound, not due to further acceleration beyond the
       | speed of sound but due to the speed of sound suddenly dropping in
       | the lower pressure.
        
         | jarvist wrote:
         | The speed of sound does not depend on pressure, only
         | temperature.
         | 
         | I suspect this is occurring because the (sonic) flow through
         | the nozzle cools as it expands, therefore the speed of sound
         | drops, making the same flow now supersonic in the cooled gas.
        
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       (page generated 2024-02-20 23:00 UTC)