Calculating head pressure...

[Shimmishim]

Can someone tell me how to calculate how much head pressure would be required to move 470 ml/min of water through a 1/2 in pipe? 1/4 in pipe?

or a link that shows where i can find how to calculate these?

thanks!

 

[jagec]

what kind of pipe? You'd need a roughness to find the friction factor.

Then, just use the flow rate and inner diameter to find average velocity and from that the Reynolds number, using the Reynolds number and roughness you can find the friction factor, then it's not too hard to perform an energy balance and figure out the required head.

 

[Shimmishim]

lol... why did i just understand everything you said?

the roughness of a PVC pipe is .0015 and that's what we're using.



i think i can figure out the rest.

i also need to find the kinematic viscosity... (you left that out)...



thanks!

 

[jagec]

Originally posted by: Shimmishim

i also need to find the kinematic viscosity... (you left that out)...



thanks!

Normally you look that up on a temperature table. you need it for Reynolds number.

 

[Shimmishim]

yes, i know

hmm... yea i guess i could just look it up on a table... hehehe.... or calculate it.... either way

 

[Mday]

question is, why the hell did i understand what you're talking about..

 

[Peter]

Because YOU'd usually do your homework yourself?

 

[jagec]

Originally posted by: Mday
question is, why the hell did i understand what you're talking about..

why does everyone keep saying that?

 

[Shimmishim]

another question...

let's say you have a cross sectional area of a column of diameter x inches with a flow rate of xx.

now let's say that you're trying to scale everything up to a column of diameter y inches...

if you were to determine how the flow rate of the y diameter column...

would it be proportional to the crossectional area of the y column divided by the cross sectional area of the x column multiplied by xx?

so C.A. of Y / C.A. of X * XX = new flow rate of column Y

does this seem mathematical corect?

 

[DrPizza]

whoa, I know why the hell I understood that....

I'm just amazed it comes back so quickly! It's been quite a few years. Those neurons must have stayed connected.

 

[jagec]

Originally posted by: Shimmishim
another question...

let's say you have a cross sectional area of a column of diameter x inches with a flow rate of xx.

now let's say that you're trying to scale everything up to a column of diameter y inches...

if you were to determine how the flow rate of the y diameter column...

would it be proportional to the crossectional area of the y column divided by the cross sectional area of the x column multiplied by xx?

so C.A. of Y / C.A. of X * XX = new flow rate of column Y

does this seem mathematical corect?

depends on what you're scaling...not everything will be perfectly proportional, once again thanks to that darn Reynolds number. However, if you're keeping average velocity steady, the flow rate will be proportional to the cross sectional area. (w=V*A, actually)

 

[Shimmishim]

our average velocity will be maintained at a steady flow...

good to see that they are related!

we're basically trying to scale from a 3 cm diameter glass column to a 6 in diameter glass column.

btw, are you a student or working?

 

[jagec]

student.

 

[rgwalt]

You'll end up with a pressure drop per some length of pipe, so you'll need to know how far your water will need to travel in order to compute the total pressure drop.

R