TransWikia.com

Fluid mechanics - Question Poiseuille exercise

Physics Asked by Daphoque on January 15, 2021

A little help/direction would be very helpful:

The needle of a syringe has a diameter $d=0.6mm$ and its length is
$l=2cm$. The water flow forced in the needle is $Q=10^{-7} m^3 s^{-1}$

Assuming laminar flow, calculate:

  1. The average speed of water
  2. What is the pressure drop necessary to have such a flow
    I think I’m OK with the 1:
    $Q=S×V$ so:

$$V=Q/S=10^{-7}/( 6×10^{-3} × 6 ×10^{-3}) = 8.84×10^{-4} m s^{-1}$$

2/ For this one I assume I have to use Poiseuille equation:

$$Delta P = frac{8mu LQ}{pi R^4}$$

but I don’t know how to do as I don’t have the dynamic viscosity of the water ($mu$). I don’t know if I suppose to know this value (as it depend on temperature I presume?) or if I have to / can express the pressure drop without knowing this value.

Can someone help me/push me a little in the right direction?

2 Answers

Less than 5 seconds of googling and I found the dynamic viscosity of water:

$$mu=8.90times 10^{-4}text{ }mathrm{Pa.s}$$

at $25^{circ}mathrm{C}$ of temperature.

A table of dynamic viscosity dependence on temperature is also provided in that link.

or if I have to / can express the pressure drop without knowing this value.

No, of course you can't calculate $Delta P$ without knowing $mu$.

Answered by Gert on January 15, 2021

I don't confirm your velocity calculation. The cross sectional area of the capillary is $$frac{pi D^2}{4}=2.83times 10^{-7} m^2$$So the velocity is 0.354 m/s.

Answered by Chet Miller on January 15, 2021

Add your own answers!

Ask a Question

Get help from others!

© 2024 TransWikia.com. All rights reserved. Sites we Love: PCI Database, UKBizDB, Menu Kuliner, Sharing RPP