Getting Stuck on Bends Coefficients - Math Equation Help Needed

In summary, the equation used to calculate equivalent lengths for fittings with different flow rates is a modified form of the Bernoulli equation. It includes loss coefficients for frictional effects. If you have the book Fluid Mechanics by Frank M. White (5th Ed), you can find an example on page 392.
  • #1
VMS1
3
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hi, I've been searching around the site and found it pretty useful but I'm having a pretty tough time with a few questions i have

its pretty much the same as This

but the coefficient values are different, the problem I'm having is with the coefficients for the bends, could someone please explain what I'm meant to do with them? and where they go in the equation ?

also I'm using the equation H = 4f *(l/d) * (v^2/19.6) is this right ?

cheers for any help guys :smile:
 
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  • #2
Fittings can be assigned an equivalent length for pipe of the same diameter.
 
  • #3
Like Astronuc said, the coefficients for the bends and restrictions are a method of calculating an equivalent straight run length of pipe that would provide the same energy loss as the fitting. If you look at post #3 in the thread you referenced you will see that they are summed up. That same post also shows the end result of the equation used. It is a modified form of the Bernoulli equation to provide loss terms for frictional effects.
 
  • #4
Ahh right that makes more sense now, i tried it using the coefficient values in that equation and as you can probably guess got some stupid answer lol

if i try and use the equation i quoted i won't get the right answer ?

thanks for the help

Edit: ok I've just tried it using the Eqn in the thread i referenced and got a head of 12.35m if i use L=50m, if i use L=80m (50m plus the equivalent lengths) i get 17.8m neither of those sound right considering the other guy got a 5m head and the only difference in his Q is he has a flow rate of 6litres instead of 5?

Edit: screwed it up, i now have a head of 4.1m
 
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  • #5
Solution

This one's easy...

Use the energy equation:

(p($1)/rho*g)+((v($1)^2)/2g)+z($1)=(p($2)/rho*g)+((v($2)^2)/2g)+z($2)+h($f)+sum(h($m))-h($p)

A $ sign within brackets mean that is a subscript.

h($f)+sum(h($m))=v^2((f*L/d)+sum(k))/2g

where sum(k) is the sum of all your minor loss coefficients due to bends, etc.

If you have the book Fluid Mechanics by Frank M. White (5th Ed), you can find an example on page 392. If you don't and need clarification, just ask.
 
  • #6
Oh yeah, and h(p) is the losses due to a pump, if there is one in the system. Neglect if there is not.
 
  • #7
that's the equation i ended up using and got a value of 4.1 meters which sounded about right to me
 

1. What are bend coefficients in math equations?

Bend coefficients are values used in mathematical equations to represent the curvature or change in direction of a line or curve.

2. How do I calculate bend coefficients?

The specific method for calculating bend coefficients may vary depending on the equation, but in general, it involves finding the slope or derivative of the equation at the point of the bend or curve.

3. Why is it important to understand bend coefficients?

Understanding bend coefficients is important because it allows you to accurately represent and manipulate curved or bent lines in mathematical equations. This is useful in a variety of fields such as engineering, physics, and economics.

4. Can bend coefficients be negative?

Yes, bend coefficients can be negative. A negative bend coefficient indicates a curve or bend that is concave downward, while a positive bend coefficient indicates a curve or bend that is concave upward.

5. Are bend coefficients the same as curvature?

No, bend coefficients and curvature are not the same. Bend coefficients are specific values used in mathematical equations, while curvature is a more general concept that describes the amount of bending or curving in a shape or line.

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