Emitter Constant Question

[Samantha]

Untitled 1.odt

Hi Ya'll,

I've got a quick question.I know the Emitter Constant(constant k) for a tape is 0.159-but it's displayed in the Irricad database, as 0.601815. I know there is a conversion from metric, but i'm not completely understanding it. Can you help me with the formula and also just explain what's going on here. Thank you in advance. Blessings on your day

[jovivier]

Hi Samantha,

Internally IRRICAD uses metric data. Values are converted to metric for internal use and from metric for display in IRRICAD if your units are US or imperial. When calculating flows for tapes and outlets the constants are based upon lph and m. More information on this can be found in the Manual - Technical Reference ->Appendix H: Form of the Equations.

In your particular case if you divide 0.601815 by 0.159 you will get close to 3.79 because your emitter is pressure compensating and the flow does not change (i.e. the index is 0).

The equation used for outlet flow is Q = KHⁿ
where Q is in litres per hour and H is in metres (of pressure). K is the constant and n is the index. The index stays the same regardless of units.

To convert the constant from metric to US units or from US units to metric use the following:

convert US non-comp emitter.png

Note that one psi is equal to 0.70307m. There are 3.78543 litres in one US gallon.

Always check your results after using conversion equations.

If your emitters or outlets are not pressure compensating it may be easier to use the curve fitting utility.

Regards,

Jo

[Samantha]

Thank you!

[rafat]

We know that the equation involving to the Flow Calc. is
Q=K Hn
Where the (K) is the Emitter Constant & (n) is the (exponent) Emitter Index, Now Where is the use of “Emitter Barb Factor” (Kd) in the equation ??
And can you give me an explanation on the methodology of IrriCad for Flow Calc type , “Iteration”
And other

[jovivier]

The emitter barb factor (Kd) is used to calculate the headloss past the emitter and uses the formula H = Kd V² / 2g. The barb factor is given by the manufacturer. Typically the Kd is between 0 and 2 depending on the size of the emitter.

The "Iteration" method uses an iterative process to calculate the headloss down the dripline as the velocity diminishes.

If the "Iteration" option is unchecked then an older method is displayed. Do not use this older method.
For more information please see Help|Help Topics - IRRICAD Database Editor Manual > Irrigation Components > Details of Individual Groups > Tapes.