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System Curve Units

mamorro2
1-Visitor

System Curve Units

I am having trouble using units in this Hazen-Williams derived system curve. I can add units to all of the variables but the equation fails when I raise to the power of "b".

i.e. headloss = a*(q(Q))^b

Can anyone help me?

Thanks,

Mark
3 REPLIES 3

You have two issues.

First, SUC does not allow raising of a quantity with units to a power that is not a constant. And it takes a very narrow view of "constant", accepting only literal constants. Yes, SUC SUX. But if you're going to use MC14, learn to live with it.

The other point is that it is physically meaningless to raise a quantity to an arbitrary power, as you have. Physically, only simple rational powers have meaning. A power as you have has no physical meaning and the equation is purely empirical. The quantity being raised to that power needs to be dimensionless. If you look closely at the specification for the formula you are using, it will say that you must use the flow rate in particular units. The number is just that number, not the actual physical quantity (physical quantities have dimensions, but not units -- they can be equivalently expressed in any units representing the dimensions).
__________________
� � � � Tom Gutman

I think your calculation may begin so - see the attach.
See too how we can work with an empirical formula:
http://twt.mpei.ac.ru/TTHB/5/2/Fig/2_17_Empirical_formula.png
Val
http://twt.mpei.ac.ru/ochkov/v_ochkov.htm
RichardJ
19-Tanzanite
(To:mamorro2)

To make an empirical equation work with units you need to divide each term by the units that are specified for that term, then multiply the entire expression by the specified output units.

Richard




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