Pressure and Flow Flashcards
Pressure and Force
Pressure = force/area
Force = pressure x area
Pressure (pascal)
Force (newton)
area (m2)
Explain Force
Force = anything that causes an object to undergo a change in either movement, direction or geometrical conctruction.
Measured in Newton.
Explain Pressure
Pressure = force per unit area
1Pascal = the pressure of a piece of paper resting flat on a table.
Unit = KPA
1KPA = 1000 pascals
1KPA=1bar=1atm=14.5psi=760mmHg
Hagen Poiseulle equation
Q = pie P d^4 / 128nl
or
q = pie P r^4/ 8nl
Q - flow
P - pressure drop along the tube
d - diameter of the tube
r - radius of the tube
n - viscosity of the fluid
l - length of the tube
pie/128 - proportionality constant if diameter is used in the equation
pie/8 - proportionality constant if radius is used.
Explain Hage Poiseulle and laminar flow
Equation used to describe the characteristics of laminar flow through a tube.
Flow is directly proportional to the pressure drop along the tube, as well as either radius ^4 or diameter ^4
Flow is inversely proportional to viscosity and length
As the diameter or radius of the tube increases, flow increases by the fourth power.
- if radius doubles, flow increases by 16 times.
Only applies to newtonian fluids
Examples of Hagen Pouiselle
- IV cannula gauge and length
- ETT tubes size
- Anaesthetic breathing circuits designed to maintain laminar flow.
Reynolds Number
Re = pvd/n
Re- Reynolds number
p = density of fluid
v - velocity of fluid
d- diameter of tube
n - viscosity of fluid.
Describe Reynolds number
Describes the factors that determine the critical velocity when flow becomes turbulent rather than laminar.
Once flow is turbulent, Hagenn Pouselle no longer applies.
Turbulent flow is unpredictable, nil single equation that defines turbulent flow
Reynolds number <2000 = more likely laminar
Re 2000-4000= transitional flow
Re >4000 = turbulent.
Therefore as density and velocity of fluid, and diameter of tube increases the flow is more turbulent
