1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Viscosity-injection problem

  1. Apr 4, 2010 #1
    1. The problem statement, all variables and given/known data
    Question Details:
    A hypodermic syringe is attached to a needle that has an internal radius = .300mm and Length=3.00cm
    The needle is filled with solution of viscosity= 2.00 x 10^(-3) Pa.S
    And injected at a vein with a gauge pressure of 16mm Hg
    What must the pressure of the fluid in the syringe be in order to inject the solution at a rate of .250 mL/s?

    Answer = 6850 Pa


    2. Relevant equations
    Poisellous equation


    3. The attempt at a solution
    I attempted to use Poisellous Law for Viscous flow
    this is my setup

    delta p =
    [(8/pi *delta V/ delta t)/(r4)]*L*Viscosity

    and here i should be able to solve for fluid pressure

    my gauge pressure us 16mm Hg-do i need to convert it to Pa?
     
    Last edited: Apr 4, 2010
  2. jcsd
  3. Apr 4, 2010 #2

    ideasrule

    User Avatar
    Homework Helper

    Re: Viscosity-injection

    Why do you need to "manipulate velocity into the equation"? 0.250 mL/s is the volumetric flow rate, delta-V/delta-t.
     
  4. Apr 4, 2010 #3
    Re: Viscosity-injection

    oh wow...my bad...never mind -_-

    thanks!
     
  5. Apr 4, 2010 #4
    Re: Viscosity-injection

    does anyone how delta p and gauge pressure are related?
    i need to find pressure of fluid, and delta p is only unkown variable i have...so i know
    i am solving for it, right?
     
  6. Apr 4, 2010 #5

    ideasrule

    User Avatar
    Homework Helper

    Re: Viscosity-injection

    Well, blood pressure is at 16mm Hg + atmospheric pressure and you just found delta-P, so just add them together and you'll get the pressure in the needle.
     
  7. Apr 4, 2010 #6
    Re: Viscosity-injection

    ok im not getting the answer which is suppose to be 6850 Pa.
    anyone able to help me out here??
     
  8. Apr 4, 2010 #7

    ideasrule

    User Avatar
    Homework Helper

    Re: Viscosity-injection

    It looks like the question is looking for the gauge pressure inside the syringe, not total pressure.
     
  9. Apr 4, 2010 #8
    Re: Viscosity-injection

    yes it is-so how would i approach the problem?
     
  10. Apr 5, 2010 #9

    ideasrule

    User Avatar
    Homework Helper

    Re: Viscosity-injection

    You know the pressure inside the blood vessel and you know delta-P, the difference in pressure. It's very easy to get the answer from those two values.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Viscosity-injection problem
  1. Find Viscosity (Replies: 1)

  2. Viscosity question (Replies: 1)

  3. Relativity & Viscosity (Replies: 2)

  4. Calculating Viscosity (Replies: 1)

Loading...