Chapter 5 Flashcards
Fluids
A fluid is any material that has the ability to
Flow
Both liquid & gases are considered to be
Fluids
Basic forces cause
Fluids to flow
Fluids assume
The shape of the container they are placed in
Hydrostatics is the study of
Fluids that are not moving
Hydrodynamics is the study of
Fluids in motion
For fluids that are static, 2 important properties are
Density & Pressure
The total pressure at the top of the water will be
Less than that of the bottom
At the same depth, fluid exerts the
Same pressure in all directions
Pressure is independent of
Container shape
When an external pressure is applied to a confined fluid, it is
transmitted unchanged to every point within the fluid
All fluids exert a buoyant force on
Objects immersed int hem (Archimedes’ Principle)
An object immersed either totally or partially in a fluid feels
A buoyant force equal to the weight of fluid displaced
if the density of an object is greater than the fluid, the object will
Sink
What is a hydrometer?
A device used to measure the specific gravity of liquids such as urine or milk
Smooth flow is known as
Laminar
Flow that is not smooth is
Turbulent
Laminar flow is characterized by
Unchanging flow pattern where adjacent layers of fluid smoothly slide past each other
Smooth & orderly
Turbulent flow has a
Continuous varying pattern
Chaotic & abruptly changing
Flow rate is
The volume of fluid passing a particular point
Units of volume divided by time
Cubic meters/second (m3/s)
As the diameter of a tube decreases,
Speed of the fluid increases
As speed of a fluid increases, the pressure
Exerted by the fluid decreases
(Bernoulli effect)
The change in pressure exerted by a fluid depends on
The change in speed & the density of the fluid
Venturi tube flowmeters are
Devices used to measure fluid speeds in pipes
Ideal fluids are those in which there is
No loss of energy due to friction
No interactions between the molecules that make up the fluid
No interactions between the fluid molecules & the pipe, tubing or container
Viscosity is the measure of a
Fluids resistance to flow
The speed of the molecules next to the pipe walls are
Zero
Molecules near the center of a pipe are moving
The fastest
The closer the molecule is to a wall,
The slower it moves
A force must be introduced in order to
Maintain the flow of a real fluid
The force required to maintain the flow of a real fluid is due to
A pressure difference over the length of the pipe
The difference in pressure to maintain flow is
Proportional to the pipe length & the average speed of the fluid & INVERSELY proportional to the cross-sectional area
Poiseuille’s equation applies to
Laminar flow only
Increasing pressure can
Increase flow rate
Flow type depends upon the
Physical arrangement of the particular location & other factors such as fluids speed, density & viscosity
Reynolds number less than 2,000 will
Have laminar flow
Reynolds number greater than 3,000 will have
Turbulent flow
When Reynolds number is between 2,000 & 3,000, then
The fluid flow will be unstable & the flow can transition between laminar & turbulent flow
Fluids are defined by their
Response to stress
Stress is the
Distribution of force per unit area
The stress or force distribution may be
tangential (shear stress) or perpendicular (normal force)
Strain is the
Deformation caused by stress
Fluids can resist__________ or become ________
Compression like liquids; compressible & easily expandable like gases
Forces associated with fluids are
Gravity
Pressure
Friction
Friction is
Resistace to flow from surface interaction & is proportional to viscosity
Viscosity is the physical
Property of a fluid that relates shear stress to the rate of strain
Viscosity is the inherent property of
A fluid that resist flow
Flow is the result of pressure forces in a fluid established by
Difference in pressure from one point to another, which creates a gradient
In laminar flow, the molecules in the center of the. tube
Encounter the least adhesive force from the walls
Move at a velocity twice that of the mean flow
True laminar flow predominates in the
Smallest airways (terminal bronchioles)
What is transitional flow?
A mixture of laminar flow along the walls & turbulent in the center
According to Poiseuille’s Law, the radius will have
The most dramatic effect on flow
Doubling the radius will result in
A 16-fold increase in flow
triple=81-fold
When viscosity increases,
Flow decreases
Increasing the length of a tube will
Decrease the flow
Of all the changes to be made, which will have the greater effect on increasing flow?
Increasing the diameter
The larger the endotracheal tube,
The better flow of gas for ventilation
Increasing the peak inspiratory pressure establishes a
Higher pressure gradient, which improves flow & delivered tidal volume
Risk of turbulent flow
Reynolds number is directly proportional to the
Density of the fluid, linear velocity of the flow & tube diameter
Flow is inversely proportional to
Fluid viscosity
Reynolds number equation
Reynolds number = vpd/n
V=linear velocity of fluid
P= density of fluid
d=diameter of tube
n= viscosity
> 2300=turbulent
<2300=laminar
As flow passes through a narrowing in a tube, the velocity
Of that flow increases 7 there is a corresponding decrease in pressure at the area of narrowing
Pressure & velocity are
Inversely proportional
Bernoulli equation does not account for
Friction & it assumes no changes in density or flow rate
Hydrostatics is the study of
Fluids not movingdr
Hydrodynamics if the study
Fluid in motion
Gravity or pressure equals
Flow
Hydrostatics involve these 2 things
Density & pressure
Pressure increases with
Depth
Gauge pressure is
Measured relative to atmospheric pressure
Total pressure includes
Atmospheric pressure
Gauge pressure does NOT include
Atmospheric pressure
Pressure at the same depth
Fluids will exert pressure in all directions depending on depth
What is Pascals principle?
pressure applied to an enclosed fluid will be transmitted to every point of the fluid walls of the container
Pascals principle is essential in
Hydraulics
Buoyancy is
Weight if displaced water, due to Archimedes principle
If fluid displacement is more____
If less________
More=Float
Less=Sink
Something immersed in a fluid is subject to an
Upward force equal to the weight of fluid it displaces (Archimedes Principle)
If density of the object is greater than…
Less than…..
Greater than= Sink
Less than=Float
Id density of an object is the same,
Fluid will be neutrally buoyant & will remain stationary
Hydrometer measures
Specific gravity
Fluids are defined by
Their response to stress
Tangential is
Shear stress
Perpendicular (normal stress) will either
Resist compression (liquids)
Become compressible & easily expandable (gases)
Fluids change shape/flow when
Subjected to shear stress
Friction is
Resistance of flow from surface interaction & its proportional viscosity
What is flow rate
Quantity of fluid passing a point per unit time
Flow rate must be
Equal throughout a system
When there is a decrease in tube size. flow velocity must
Increase
Bernoulli Principle happens when
There is an increase in velocity, but decrease in pressure
Bernoulli Principle does not take into account
Friction & assumes no change in density
Venturi effect is caused by
Bernoulli principle
Coanda effect is
Fluid flowing around curved surface; if there is a bifurcation, one tube will be chosen over the other
What has a dramatic effect on flow?
Radius
Increased length will
Decrease flow
What are 4 ways to increase flow
Increase pressure
Larger Diameter
Shorter catheter
Decreased viscosity
Quickest & most effective way to increase flow
Quickest= increase pressure gradient
Most effective= increase radius
Reynolds number determines
If flow will be laminar of turbulent
Less than 2,000=laminar
Greater than=turbulent
In between=flow unstable & can transition between the two
Law of Laplace cylinder? Spheres?
Cylinder T=Pr
Spheres= 2T=Pr
Tension is stress/force
Exerted over a given area measured in Newtons/cm
law of Laplace explains the relationship between
Wall tension, radius & pressure in cylinders & spheres
