4 replies to this topic

[Master_Blade]

Hey,

Could someone help me please. How do u calculate duty point using discharge-head performace characteristic curve and you are given the friction factor

Thanks

[sgkim]

Hey,

Could someone help me please. How do u calculate duty point using discharge-head performace characteristic curve and you are given the friction factor

Thanks

Master Blade:
We can't very well understand your question clearly. It looks you are going to calculate flow rate Q from friction factor f and pump characteristic performance curve, does it?

sgkim

[Master_Blade]

Well heres the exact question from my lab:

"Water is to be pumped from a river through a 220mm diameter pipeline 500m long to an open storage tank with a water level of 25m above the river. This laboratory pump is available and can be used at 2000rpm. use the discharge-head performance characteristic curve from the lab experiment. Calculate the duty point for the pump when the friction factor is 0.022"

I've plotted the Characteristic head as-well-as the effeciency graph. After that i'm lost...

Thanks for the reply

Blade...

[Art Montemayor]

Master_Blade:

You are lost because:

1) You haven't understood what it is that is being asked of you;
2) You don't understand the subject under discusstion (fluid flow and fluid transfer);
3) Your instructor(s) haven't been clear in explaining or teaching you what the subject is about.

I believe I understand clearly what is being asked because the problem is a typical industrial-type of application. You are being asked to define the operating point of the pump. This point is defined as the point on the pump performance curve which is also on the system's curve. The system curve is, of course, a curve of points that crosses the pump performance curve. Where both of these intersect is the definition of the operating point. You have been given the required basic data to generate such a curve: the configuration and the friction factor. With these data you can calculate the pipe friction and pressure drop.

You should start a series of calculations (after you have sketched out a realistic and scaled drawing of the hydraulic system) defining what the total head is for the system for a variety of flow rates within the pump's capacity. These values should be plotted on the pump performance curve and you should easily identify the operating point for your system. That point defines the flow rate and pressure drop (total head) achieved by the pump to service the system you have defined for it.

I hope this explains what it is that you should do.

Every engineer should develop a system curve on every fluid transfer operation that he/she designs. This is so elementary and necessary that it startles me when experienced engineers continue to try to understand a pumping system without generating this essential tool. It is fundamentally basic and a requirement for applying a well-engineered pumping system.

[djack77494]

Just a slight addition to what Art said. Since your starting (source) and ending (destination) pressures are the same (atmospheric), you will have two contributors to your system curve. They will be the static head contribution of 25m, which is not affected by your flowrate, and the dynamic portion of the curve, the frictional losses, which are most definitely affected by flowrate. Add the two to get the system curve.
HTH,
Doug