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Loss due to contraction

  1. Mar 23, 2016 #1
    1. The problem statement, all variables and given/known data
    what does the author mean by D2/ D1 = 0 ? when D2/ D1 = 0 , the pipe doesn't exist , right ?

    2. Relevant equations


    3. The attempt at a solution
     

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  3. Mar 23, 2016 #2

    SteamKing

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    Right. The limiting case when D2/D1 = 0 applies when fluid is flowing from a wide-open volume, say a reservoir, into a pipe suddenly. The diameter of flow from the reservoir D1 is so huge in comparison to the diameter of the pipe D2 that the quantity D2/D1 → 0 in the limit.
     
  4. Mar 23, 2016 #3
    so it's not exactly = 0 , it's approaching 0 , am i right ?
     
  5. Mar 23, 2016 #4
    Right. Think about a drain pipe going straight down from the floor of a swimming pool. The area of the pipe is negligible in comparison to the area of the pool. The next entry in the table is D2/D1 = 0.1, so the big pipe is ten times the diameter of the small pipe (and you use K=0.45). Anything much bigger than that, use 0.5.

    Keep in mind these K factors are approximate; they will give you "pretty close" results. For really critical applications, pressure losses are determined by testing. If you're designing something where K=0.45 gives acceptable results but 0.5 does not, you need to re-think your approach.
     
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