Bruce's Fluid Dynamics Final Prep Flashcards
Pressure definition ?
the force per unit area applied in a direction perpendicular to the surface of an object
Hydrostatic pressure
(AKA: Stagnation Pressure) The pressure at any given point of a non-moving fluid
what do we measure with our manometers ?
Static Pressure
Hydrostatic Pressure - Static Pressure =
Dynamic Pressure
‘Where the velocity of the fluid is high
the (static) pressure is low’
Static Pressure + dynamic pressure =
Total Pressure
Bernoulli’s Priciple =
P+1/2pv^2 = Po P=static pressure p=density of the fluid v=flow velocity Po=total pressure
Velocity is directly related to ?
=Flow
and inversely related to cross sectional area.
Boundary layers are slower in ?
the edge
Boundary layers are faster in ?
the middle
3 types of fluid flow in pipes ?
- laminar
- turbulent
- transient
Laminar Flow =
happens when dealing with small pipes and low flow velocities
Turbulent Flow =
- vortices, eddies and wakes make the flow unpredictable
- happens in general at high flow rates and with larger pipes
Transitional Flow =
mixture of laminar and turbulent flow, with turbulence in the center of the pipe, and laminar flow near the edges
Transient flow range =
2300 < 4000
Laminar Flow range =
RE < 2300
Turbulent flow range =
RE > 4000
Reynolds number (Formula) =
Re =
(velocity)(radius)(density)
_____________________
Viscocity
Poiseuille’s law on blood circulation in the body is dependent on what?
Laminar flow
In turbulent flow the flow rate is proportional to the
square root of the pressure gradient
atheroma = turbulent flow
is an accumulation of degenerative material in the tunica intima (inner layer) of artery walls.
Rapid changes in vessel diameter may lead to what?
Turbulent flow
As the blood leaves the arterial cannula, it is ____ flow?
Turbulent
Poiseuille’s Law:
Delta P =8u L Q / pi r^4
Delta P = pressure loss L = length of pipe u = dynamic viscosity Q = volumetric flow rate r = radius d = diameter pi = mathematical constant Pi
As length increases. .
-Resistance Increases
-Flow decreases
for a given pressure
As radius increases. .
-Resistance decreases
-Flow increases
for a given pressure
which oxygenator circuit has a lower resistance ?
series or parallel?
parallel
Two variable that we manipulate that alter blood viscosity:
1-Temperature
2-Hematocrit
Viscosity definition ?
a measure of the resistance of a fluid which is being deformed by either shear or tensile stress
water is “thin”, having a ?
lower viscosity
honey is “thick”, having a
higher viscosity
the less viscous the fluid is, the . . . .
greater its ease of movement (fluidity).
State the units of viscosity
Viscosity centipoise (cP)
Sheer stress is directly proportional to . . .
viscosity
Sheer stress is inversely proportional to . . ..
the distance from the wall
Newtonian fluids have
a constant viscosity
Thixotropic fluids become
less viscus as the sheer force increases
Thixotropy definition
property of certain gels or fluids that are thick (viscous) under normal conditions, but flow (become thin, less viscous) over time when shaken, agitated, or otherwise stressed.
A thixotropic fluid displays a decrease in viscosity
over time at a constant shear rate.
A shear thinning fluid displays decreasing viscosity with
increasing shear rate.
anti-thixotropic causes:
causes an increase in viscosity or even solidification when exposed to constant shear stress for a period of time.
This property is called = rheopectic
Blood is often referred to as Non-Newtonian but the most appropriate term would be ?
Thixotropic
Smaller capillaires have greater sheer forces, what happens to the blood?
becomes less viscous
Roller pumps have what 3 qualities ?
- Positive displacement
- resistance independent
- predictable flow output
1/4” tubing =
13 ml/revolution
3/8” tubing =
27 ml/revolution
1/2” tubing =
44 ml/revolution
Centrifugal pumps =
Preload and afterload dependent
The Afterload of the centrifugal pump is determined by
everything down stream from it in the circuit:
- oxygenator,
- arterial filter
- size / length of the arterial line
- arterial cannula
- patient.
During Vacuum Assisted Venous Drainage (VAVD) the preload is determined by
the amount of suction in the venous reservoir
greater negative pressures reducing preload to the pump and thereby
reducing blood flow.
Safety features of centrifugal pumps
- Cannot generate extreme pressures
- ## deprime when challenged with large bolus of air.
