Equivalent length of pipe bend

In summary, the smaller the diameter of a pipe bend, the shorter its equivalent length becomes. This is due to the fact that larger pipe diameters have more flow going through it which creates more mixing and turbulent flow. The statement that a 2.5" diameter elbow has the equivalent flow of a 1.6" straight pipe of the same length is based on empirical data and can vary depending on the material of the pipe. The equivalent length is typically used in calculating pressure drop and can be found through various resources and mathematical calculations.
  • #1
smoque
6
0
can someone explain to me why it seems that the smaller the diameter of pipe bend (i.e. 90 degree elbow = 30D) the shorter its equivalent length becomes? for 1.5" diameter = 45" equivalent length while 2" diameter = 60" length. does this mean 1.5" diameter 90 degree elbow has less friction than the 2"? does not make much sense to me

thanks
 
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  • #2
Larger pipe diameters have more flow going through it which hit the "wall" created by the 90. There is more mixing.
There are many reasons, and the fact is a lot of it is empirical data.

It has a bit to do with the amount of flow going around the bend that is laminar and the amount that is turbulent.
 
  • #3
i have read somewhere on the net that a 2.5" diameter of 90 degree elbow have equivalent flow of 1.6" straight pipe of same length as the bend.

any way to figure out how the statement above is derived?
 
  • #4
This is generally an empirical study. In carbon steel piping, a normal 90 elbow of 2.5" pipe is equivalent to 9.3 ft of straight pipe.

So if you have 40ft of pipe, then a 90, then 40 ft. You have an "equivalent length" of 40+40+9.3, or 89.3 ft of pipe. You use this along with the friction factor of the pipe material to determine the pressure drop.

Here is a website that shows you some Leq's (equivalent lengths) based on the steel pipe's nominal diameter:http://www.delftaerospace.org/en/organisation/departments-and-chairs/space-engineering/space-systems-engineering/expertise-areas/space-propulsion/design-of-elements/feed-systems/feed-systems-b/ [Broken] is one that shows you the Leq/D so you can multiply the number by the pipe diameter (in feet) and get the equivalent length

Here Is a site that kind of shows you the math involved
 
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1. What is the equivalent length of a pipe bend?

The equivalent length of a pipe bend is the length of straight pipe that would cause the same pressure drop or head loss as the bend. It takes into account the frictional losses and changes in flow direction caused by the bend.

2. Why is it important to calculate the equivalent length of a pipe bend?

Calculating the equivalent length of a pipe bend is important for determining the overall pressure drop in a piping system. It helps in selecting the appropriate pipe size and designing efficient piping systems.

3. How is the equivalent length of a pipe bend calculated?

The equivalent length of a pipe bend is calculated by multiplying the actual length of the bend by a correction factor, which takes into account the fluid velocity, bend angle, and pipe diameter. The specific equation used may vary depending on the type of bend and the flow regime.

4. What factors affect the equivalent length of a pipe bend?

The equivalent length of a pipe bend is affected by the bend angle, pipe diameter, fluid velocity, and the type of bend (e.g. 90-degree elbow, 45-degree elbow, etc.). The roughness of the pipe material and the flow regime (laminar or turbulent) can also have an impact.

5. Can the equivalent length of a pipe bend be reduced?

The equivalent length of a pipe bend can be reduced by using smoother pipe materials, such as PVC or fiberglass, and by using larger pipe diameters. Additionally, using multiple smaller bends instead of one larger bend can also decrease the equivalent length. However, it is important to consider the overall system design and potential for increased pressure drop when making these modifications.

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