Pipe size for best Pump flow, Need Advise! 1

I just found this place, and hope you guys can help me.
First, excuse me for beeing a newb.
Secondly, my post seems to have gotten quite long.
I usually over explain things, so it shouldn't take too long to read. Please read?

I have a watercooling project underway, and am not sure what size pipe i should use.
In case you are interested, i am supercooling my computer, i can provide some pictures of the project thus far.


I have a 6 foot vertical acrylic pipe being powered by a pump (outlet is a showerhead).

A flow chart of the pump can be found here:

http://www.wonbrothers.com/product/pumps/gapumps.htm

(900GA model)
I believe the chart applies to 3/4" pipe, because that is its outlet size.

I have consulted many "head loss calculators" and charts, and with 3/4" pipe i would lose under 5 feet in dynamic (frictional) head loss. (this is one of the calculators

http://reefcentral.com/calc/hlc.htm)

With 1" pipe the loss goes down to about 1-1/2 feet.

Adding 6 feet of static head to the dynamic head results in a figure (total head) which you match up w/ the chart given by the 900GA pump flow chart (linked above).
In this case with 1" pipe, head loss is 7.5 feet, which equals 700GPH.

However, it is not actaully 7.5 feet of head, i don't think.
With 1" pipe, the additional volume (1.778 times more volume than 3/4&quot, creates additional pressure.
This can equate to additional head (if you simply consider a 3/4" pipe of the additional volume, it would be much taller).

A 1" pipe 3.375 feet high should create the same pressure as a 3/4" pipe 6 feet tall, correct?
(i calculated this by volume)

Using the "head loss calculator" (2nd link) with my assumption that a 1" pipe results in 1.778 times more head pressure that a 3/4" pipe, i calculated that a 3/4" pipe would result in a higher GPH output, despite the high friction level!
Please correct me if this is not accurate in any way.



The reason i am not so sure is because I have recieved varied information on the internet, some sites saying the volume of the pipe has no effect on pressure.
Also there is a formula which states that the PSI can be found be dividing the level of head by 2.31. This does not account for the volume of the pipe, however?

Is the volume of the pipe directly proportional to the amount of head pressure that the pump must push against?
Or does 1" pipe not produce 1.778 times more pressure than 3/4" pipe?

Does it make sense that I choose 3/4" pipe?

(waterflow is CRITICAL to this application, i am avoiding additional watts (added heat) w/ a bigger pump (1200gph), so every loss counts with this smaller pump)


Thanks So Much,

-Joe Kuta

 

[KenRad]

Two misconceptions:

1. - When considering differences in system head due to differences in elevation (as with your vertical pipe), the pipe volume is not a factor, only the vertical distance. You might want to look up a discussion of the Bernoulli equation.

2. - A pump curve or chart defines the pressure and flow characteristics of the pump itself, independent of the piping system. So your pump curve is the same whether you use it with 3/4" or 1" piping. The piping system attached to the pump determines WHERE the pump operates on its curve/chart. The way this is determined is by plotting the pressure and flow characteristics of the system on the same graph as the pump curve is on. The intersection of the two curves will define your operating point (what the pump will actually flow).

Your should consult a textbook for a complete discussion of fluid flow and pumps before starting any system design.

--KenRad

 

Thank You Very Much

I got some info:

((u2)^2-(u1)^2)/2+g(z2-z1)+(p2-p1)/p= -F-w

Where u is velocity, g is gravity, z is height, p is pressure, greek ro is density, F is friction, and w is work done by the pump.

We can remove many variables from the bernoulli balance that do not change.
First, the velocity terms can be removed. u2 - u1 = 0 The water velocity in the pipe of a system with small pipe does not change at steady flow. This is because the pipe diameter remains the same and is not enlarged (resulting in lower velocity) or increased (resulting in higher velocity). The same is true for a setup with large pipe, except that the velocity will be lower than that of the smaller pipe. Volumetric flowrates will be roughly the same, however.

The pressure term can also be removed because the pressure of the system does not change at p1 or p2. Both tanks are open to atmospheric pressure in both cases.

This reduces the equation to the following:

g(z2-z1)= -F-w

This means the work the pump has to do is only dependant on the change in height and the amount of friction in the system. Not dependant in any way on the size of the pipe.

So in my situation, I could use 1.5" pipe, and pump flow would only INCREASE.

Is this correct?

 

[mrakan]

Hi,
I will suggest you to take your university books and refresh your knowledge from school, don't learn designing from internet.

 

[MortenA]

Being less rude than mrakan i would like to point out that when you decrease pipesize you increase fluid velocity and thus increase friction (a function of fluid velocity).

I do however think that unless you have very long pipes the bulk of the pressure loss will be in the showerhead and in elevation change anyway.

Best Regards

Morten

 

[pipesnpumps]

This thread is hilarious!

What is the loss coefficient for your shower head? You should call the manufacturer and ask them for the pressure drop. Remember that it makes a difference whether you are on "Full Stream" or "Massage"

Seriously though, I'm guessing a shower head at the flows you mention would be a really significant drop! What you might can do is drill out the orifice in the shower head larger and larger until you get the flow you need.

If you want to calculate all this out, you will need the loss of the shower head at a certain flow. This can be used to estimate the loss at any other flow. L2=(L1*F2*F2)/(F1*F1). Where L is loss (in either psi or feet) and F is the flowrate (in any unit)

You also need the pressure drop per foot of pipe for 3/4" and 1" diameter piping (using water I assume). You add up the total feet of piping and multiply this by the ft head loss/foot of pipe.

You will also need the equivalent feet of pipe for any fittings. A good guess for elbows, off the top of my head, is 30/(Inside Diameter in Inches x 12).

But the real question is WHY a water pump? Are you directly cooling the fins? If so, how are you going to seal the water in?

If you are cooling an airstream, what kind of coil are using? You will need to know the pressure drop across it too.

I figure you are using the shower head to evaporatively cool the water. Be sure and change the water regularly, and be aware that your water may pick up lint and dust and foul up whatever you are pumping through.

To answer your last question, the larger diameter, the less the frictional head loss. If u make the pipe large enough, the frictional loss is effectively zero. Loss is related to diameter by the following.. L2=L1*(D1^5/D2^5) where D is diameter in any units, and ^5 means "to the fifth power" or D1*D1*D1*D1*D1, and L is the head(pressure) loss. I also assume that you don't have an engineering degree, forgive me if I overexplain. If you make it 1-1/2" pipe, you can pretty much chalk it up as a big Zero - the shower head will be the controller on your flow.

Really you could just pump it into something that let it drip out instead of spraying out. Or put a dorm fridge nearby, with a cold plate in the freezer section and REALLY supercool. Here is one for $68.

http://www.morebeer.com/index.html?page=detail.php3&pid=COLDPLATE1

Yes, the internet is truly a dangerous thing. A fish tank pump circulated processor supercooler - who'da thunk it. I feel like I am feeding the beast, but its fun to play with stuff sometimes.

IMO a really oversized muffin fan would do about the same thing.