Loss coefficient K in a pipe?

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Homework Statement



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The Attempt at a Solution


Usually we are given a table, but how do we calculate the loss coefficient between 2 different pipes with different diameters? In this case, between the 5 and the 3 cm^2 pipes?
 

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  • #2
SteamKing
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Homework Statement



Screen_Shot_2016_06_16_at_8_30_06_pm.png

Homework Equations


N/A

The Attempt at a Solution


Usually we are given a table, but how do we calculate the loss coefficient between 2 different pipes with different diameters? In this case, between the 5 and the 3 cm^2 pipes?
The K-factors for a given diameter of pipe are proportional to the fourth power of that diameter, as described in this article:

http://www.pipeflowcalculations.com/pipe-valve-fitting-flow/flow-in-valves-fittings.php

The usual method is to express the K-factors or equivalents for the system in terms of one common pipe size.
 
  • #3
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You should be able to look up the equation for the loss coefficient for the transition between two pipes of different diameter. Do you not have a text book?
 
  • #5
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You should be able to look up the equation for the loss coefficient for the transition between two pipes of different diameter. Do you not have a text book?
My textbook just says to refer to appendix for K values. It doesn't say anything between the transition of 2 different pipes with different diameters.
 
  • #6
SteamKing
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So the answer between the transition of two pipes is (0.03/0/05)^4 ?
The K-factor for each length of straight pipe is f (L/D). Call one K-factor K-3 for the 3-cm. pipe and the other K5 for the 5-cm. pipe.

Now, according to the relation

##\frac{K_a}{K_b}=(\frac{d_a}{d_b})^4##

If you make Ka = K3, then Kb becomes K5. Putting the value of the K-factor for the 5-cm. straight pipe into the relation will give you the equivalent K-factor as if the 5-cm. pipe was actually 3-cm. pipe.
 
  • #7
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My textbook just says to refer to appendix for K values. It doesn't say anything between the transition of 2 different pipes with different diameters.
What geometries does it give K values for?
 

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