# Simple Fluid Problem Challenge



## CASADOCS (Mar 3, 2011)

:tardbang: I have been trying to work out this problem and it is driving me nuts. It seems simple but I cannot arrive to the answer. I plugged it into a calculator on the website and it works out there but not on paper. Here it is:

A liquid with a specific gravity of 1.26 flows in a pipe at 25 cfs. At 45 psi, the liquid enters the pipe's entrance which is 24 inches in diameter and the leaves the pipe's 12 inch diameter exit. The exit is 3 feet lower than the entrance. Neglecting losses, what is the exit pressure in psi? The answer is supposed to be 38.6 psi.


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## civilized_naah (Mar 3, 2011)

CASADOCS said:


> :tardbang: I have been trying to work out this problem and it is driving me nuts. It seems simple but I cannot arrive to the answer. I plugged it into a calculator on the website and it works out there but not on paper. Here it is:
> A liquid with a specific gravity of 1.26 flows in a pipe at 25 cfs. At 45 psi, the liquid enters the pipe's entrance which is 24 inches in diameter and the leaves the pipe's 12 inch diameter exit. The exit is 3 feet lower than the entrance. Neglecting losses, what is the exit pressure in psi? The answer is supposed to be 38.6 psi.


Correct answer seems to be 26.13. There appears to be a 'factor of 12 error' that would give the pressure differential as 13.6 instead of 1.13 as I calculated. Or maybe I screwed up!


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## CASADOCS (Mar 3, 2011)

civilized_naah said:


> CASADOCS said:
> 
> 
> > :tardbang: I have been trying to work out this problem and it is driving me nuts. It seems simple but I cannot arrive to the answer. I plugged it into a calculator on the website and it works out there but not on paper. Here it is:
> ...


The equation I end up with is:

P2= pg(P1/pg + (V1^2 - V^2)/2g + Z1-Z2)

Z1=3 ft and Z2=0 ft or Z1=0 ft and Z2=-1 ft.

By Q = 25 cfs = A1V1=A2V2, I attained that V1=7.96 ft/s and V2=31.83 ft/s. I also converted the 45 psi to 6480 lbf/ft. Also, for p I used 1.26 x 62.4 lbm/ft^3. I also divided pg by gc (32.2 lbm-ft/lbf-s^2) for the units. What the heck am I doing wrong?

Click on this for Bernoulli Calculator Link

I tried the calculator on this site and by plugging the variables and the 38,6 psi for the exit pressure, I do get the entrance 45 psi!


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## civilized_naah (Mar 3, 2011)

CASADOCS said:


> Z1=3 ft and Z2=0 ft or Z1=0 ft and Z2=-1 ft.


You mean Z1=0 ft and Z2=-3 ft, right, or did you use Z2=-1 ?


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## civilized_naah (Mar 3, 2011)

CASADOCS said:


> By Q = 25 cfs = A1V1=A2V2, I attained that V1=7.96 ft/s and V2=31.83 ft/s. I also converted the 45 psi to 6480 lbf/ft. Also, for p I used 1.26 x 62.4 lbm/ft^3. I also divided pg by gc (32.2 lbm-ft/lbf-s^2) for the units. What the heck am I doing wrong?


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## CASADOCS (Mar 4, 2011)

civilized_naah said:


> CASADOCS said:
> 
> 
> > Z1=3 ft and Z2=0 ft or Z1=0 ft and Z2=-1 ft.
> ...



Typo, I used -3 ft.


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## CASADOCS (Mar 4, 2011)

civilized_naah said:


> CASADOCS said:
> 
> 
> > By Q = 25 cfs = A1V1=A2V2, I attained that V1=7.96 ft/s and V2=31.83 ft/s. I also converted the 45 psi to 6480 lbf/ft. Also, for p I used 1.26 x 62.4 lbm/ft^3. I also divided pg by gc (32.2 lbm-ft/lbf-s^2) for the units. What the heck am I doing wrong?


I thought this is what I did, ....Thanks so much, it ended up being the way I was inputting the equation into my calculator. Good Casio calculator, I just acquired it and I am still trying to get used to it.


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