Fluids rate of flow homework help

  • Thread starter domyy
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  • #1
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Homework Statement



Two cylindrical pipes both carry an ideal fluid (zero viscosity) in laminar flow. Pipe A has radius Ra = 2 and flow velocity Va = 8cm/s. Pipe B has radius Rb = 4cm and flow velocity Vb = 4cm/s.

A) Calculate the cross section of pipe A and pipe B.
B) Calculate the rate of flow in liters/second (1l = 1000cm cubic)

Homework Equations



maybe v1a1 = v2a2 ?

The Attempt at a Solution



v1a1 = v2a2
= (8cm/s)(2cm) = (4cm/s)(4cm) = 1 ?

It`s wrong.
 
Last edited:

Answers and Replies

  • #2
387
8


okay. Now tell me what is a1, a2?
 
  • #3
tms
644
17


Homework Equations



maybe v1a1 = v2a2 ?
Just what do [itex]a_1[/itex] and [itex]a_2[/itex] represent?

Also, are these pipes connected end to end, or are they in parallel?
 
  • #4
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you mean...
 
Last edited:
  • #5
tms
644
17


What has pressure got to do with it?

Go back to your first equation: what is [itex]a_1[/itex]? This is not a trick question.
 
  • #6
196
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I have to calculate cross section of pipe A and B.

My book says cross-sectional area is VA.

I am confused with these formulas because I have the following:

Flow rate = VA
Flow rate = V/T

So, flow rate = cross sectional area = VA?
 
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  • #7
196
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R = 2 = area 1 = 4
R = 4 = area 2 = 16
?
 
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  • #8
196
0


I think I know it...
 
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  • #9
196
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would that be correct?
 
  • #10
196
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I just need this to finish my homework.
 
  • #11
196
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I think I know it:

I think I am supposed to use pi. So, could it be: 3.14 x 4^2 = 50.24 for cross section pipe B?
 
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  • #12
196
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I know the answer! I got the answer! I got the answer!! Just a question: how should I leave the flow rate considering the answer for B = 0.20096, should I say the answer is 0.20 or 0.200 l/s ?
 
  • #13
tms
644
17


I have to calculate cross section of pipe A and B.

My book says cross-sectional area is VA.
Assuming [itex]V[/itex] is volume and [itex]A[/itex] is area, something is wrong, either the book or your reading of it. The units are odd, too: [itex]\mathrm{L}^5[/itex]. If [itex]V[/itex] and [itex]A[/itex] mean something else, then I don't know.

I am confused with these formulas because I have the following:

Flow rate = VA
Flow rate = V/T
What is [itex]T[/itex]?

So, flow rate = cross sectional area = VA?
Think units. What units must flow rate have?
 
  • #14
tms
644
17


I know the answer! I got the answer! I got the answer!! Just a question: how should I leave the flow rate considering the answer for B = 0.20096, should I say the answer is 0.20 or 0.200 l/s ?
Since the problem, as you gave it, uses only one significant figure, then your answer should have no more than one significant figure.
 

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