Tuesday, October 21, 2008

Pump Palpitations

I have an urgent problem. I am the weak link in a group project that is due on Thursday. One guy in the group has completed the initial task of figuring out the cheapest, most efficient pipe diameter and calculating cost. The other guy is going to write up the final report. I need to choose a pump for this particular system, and fast!
See those intersecting green lines? They should be intersecting in one of those orange areas, but the head is too small (7.34 ft) for the volume flow rate (1000 gpm). I've gone through the first guy's calculations several times, and everything looks legit. Here are my four possible options:
  1. The problem was poorly defined by the teacher (always option 1 in my book), but everyone else in the class would have complained this morning.
  2. The pump to choose is 4x6-13, but this will result in gross inefficiencies.
  3. We interpreted the data wrong and got a bad value for head (most probable), but I have scoured the calculations and emailed them to the professor for a second opinion (no response).
  4. I should give up engineering and study law instead.


Bret said...

The answer is intuitively obvious if you just change the words pipe diameter to wire gauge and pump to current source. Then you just use a 1000mA source and be done with it. Plus, in comparison with the rest of the chart, 7.3ft is quite small. Is there another set of pumps you can choose from? I would have a hard time believing pumps only come at a 10 foot minimum. Or is this in meters? There's your problem, someone calculated in metric!

Thaddeus said...

Bret, a pump is really more like a voltage source. (A battery?) You're probably right about there existing other charts with better-matched head values, but this was the best among three charts given by the professor.

Believe me, I like metric better, but it's the same spot on the chart either way. 7.3 ft or 2.2 m.

Beetle said...

4x6-13 is close. Just redraw the . i alm ost just died i was on the ground and couldnt breathe water i blew snot out my nose still am PE hall like 5 mninutes ago a guy turned around and started coming back but then i was walking--Camille

But, like I said, just redraw the graph to fit your answer.

Camille is fine. She choked on some water and about died.

Jinx said...

Holy cow...does Beetle have a disassociated identity disorder I've been unaware of?

Kendra said...

So how did it turn out? Did your professor ever get back with you?

Thaddeus said...

Ta dah!! After several email jabs to the face, my professor threw in the towel!

At first he suggested finding better high-flow, low-pressure pumps from the manufacturer's website (beyond the scope of the original problem statement), and he even provided a pump model number, but this family of pumps was no better. In fact, they were worse!

Finally, he responded sensibly: "I noticed a typo in the project assignment. The flow rate should be 500 gpm, not 1000 gpm. I did not noticed it until one group [i.e. ME!] told me the 1000 gpm value. I apologize for the mistake.

"For that reason, the report due date will be November 30th."

Looks like option 1 prevailed!

Thaddeus said...

He just sent out another correction: "October 30th due date, not November."

Makes sense. I mean, we won't need a whole extra month...

Oh, and Beetle I read about Camille's choking fiasco today on her blog. She should go into writing, because it made me very uncomfortable.

Jancisco said...

Good work! All of that just today, eh? Sweet.

Hosander said...

Thad is always right, you should apply for a teaching position. or at least a proofreading position.

Kendra said...

Thad, I always knew you were a genius!

Jenette said...

No Thad, do not give up engineering for law. Bad idea. Stick with engineering...you already have the clothes for it! (not that you LOOK like an engineer...I'm just saying)