Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help Understanding Volume Flow Rate / Bernoulli's

  1. Oct 30, 2011 #1

    KendrickLamar

    User Avatar

    Hey guys, just have a question cuz i'm having a little trouble understanding like how exactly to use the volume flow rate with bernoulli's equation. (wasnt sure which section to put this in but is more of a concept question using hw examples)

    Like the volume flow rate i understand A1v1=A2v2
    for example i was doing this problem : https://www.physicsforums.com/showthread.php?t=80584

    Well its inversely proportional right but (im just being stupid probably cuz i'm really tired) but if A2 is 1/4 the size of A1 for example, then v2 is going to be 4 x the size of V1? like

    A1v1 = 1/4A2v2 so 4A1/v1 = A2v2 then v2 = 4(A1/A2)(v1), well like in the problem i linked, what happens to that A1/A2? why does it disappear when being plugged into bernoulli's equation?

    Also another question is the A = cross sectional area right? whats that even mean like is that the same as surface area, or regular area, or what? because in a problem like this https://www.physicsforums.com/showthread.php?t=65810 (now im not sure if the member solved it 100% correct) but the person here puts Volume Flow Rate = pir^2v1 for example, what is the volume flow rate in this case i dont understand and is A just the area of a circle on the tube , even tho its open its not used like a cylinder's area?

    thanks if anyone can help me out im like brain dead at the moment.
     
    KendrickLamar, Oct 30, 2011
  2. jcsd
    Phys.org - latest science and technology news stories on Phys.org
  3. Oct 30, 2011 #2

    cdotter

    User Avatar

    If [itex]A_2[/itex] is 1/4 [itex]A_1[/itex] then yes, [itex]V_2[/itex] will be 4 times [itex]V_1[/itex].

    I'm not really sure what you mean when you say it "disappears?"

    Cross sectional area is the area of a cross section. Say you have a piece of pipe. Stand the pipe on it's end on top of a piece of paper, then trace the inside of the pipe onto the paper. Find the area of that circle ([itex]A=\pi r^2[/itex]) and that's the cross sectional area.

    Volumetric flow rate is a volume per unit time (e.g., [itex]\frac{m^3}{sec}[/itex]) If you do unit analysis you'll see that cross sectional area (e.g., [itex]m^2[/itex]) times fluid velocity (e.g., [itex]\frac{m}{sec}[/itex]) gives you volumetric flow rate.
     
    cdotter, Oct 30, 2011
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Help Understanding Volume Flow Rate / Bernoulli's

  1. Rate of Water Flow help. (Replies: 1)

  2. Pressure and flow rate - a novice seeks help! (Replies: 3)

  3. Flow rate (Replies: 18)

  4. Help In understanding Rate Of Change in mm per sec (Replies: 3)

  5. Stuck understanding Bernoulli's Principle, would love some help! (Replies: 1)

Loading...