FLUIDS and FLOW-CH5 Flashcards
Fluids is a term used to describe
Liquid or gas
Important characteristic of fluids and gases
Flow
Hydrostatic
study fluids are not moving
Hydrodynamics
fluids in motion
Both hydrostatic and hydrodynamics involve
pressure and density
Pressure in a liquid is calculated using
density and height of the fluid
P in a liquid formula:
dhg (pressure = density * height*gravity )
To include pressure exerting force on the liquid’s surface, simply add it to equation
P2 is the ________ and P1 is the
P2 = P1 + dhg
pressure in the liquid; pressure of the gas added.
Calculate the pressure of a depth of 1000m below the surface on the ocean. Density is 1.03x10^3. 1 atm = 101325
P2 =P1 +dhg
P2= 1.07 x10^7
Definition of flow
Quantity of fluid passing a point per unit of time
Flow (definition formula)
V / t
Pressure =
relating to flow
F x R
P= pressure
F= Flow
R= Resistance
Change in flow written as
Q= QDot
2 types of flow
Laminar flow
Turbulent flow
Laminar flow most important factor : Remember mnemonic:
VISCOSITY
LVS
Laminar flow reynolds number:
<2000
Turbulent Flow Reynolds number
Reynolds >3000
Turbulent flow most important factor
Density
Molecules close in the center moving faster in (because of drag)
Laminar
Turbulent flow has a
continuous varying pattern of flow , chaotic and abruptly changing.
Best way to measure flow
POUISELLE”S LAW
What POUISELLE”S LAW
Flow = P /R
Turbulent flow occurs at _____velocity
High
Bigger factor for turbulent flow
density
Viscosity represented by and is defined as __________
n; Viscosity is the resistance a fluid offers to the motion of a solid through it
POUISEILLE’s LAW (KNOW THIS )
F = Pir^4 change P/ 8 nl
Resistance to flow
R = 8nl/Pi r^4
Pouiseille’s Law
F flow in L/s n= viscosity in Pa/s P= Pressure in pascals r= radius l= length
Double length
Flow in half
Biggest factors that affect vessel
Radius of vessel
Radius increase by
area changes power of 4
Volume increases by power of 8
Calculate aortic blood flow
Blood viscosity = 0.0015Pas. Pressure of 13000pa, is applied r=0.0010 ; l= 1.0
F= 3.4 x 10 ^-2 m^3/s
Pouiselle’s law : Arterial occlusion
A small amount of arterial occlusion can have a surprisingly large effect.
A _____decrease in radius will halve the volume flow rate
19%
According to poiseuille’s law
a five fold increase in BP would be required if the increase were supplied by blood pressure alone.
a ____% dilation of resistance in vessel
50
Since the ______Vessels provide most of the resistance to flow, the ______In their position just prior to the capillaries can promise a major controlling influence the volume flow rate
Smaller; arterioles.
first: Flow is _____ ____ to the_______difference and to the ______power of the radius
Directly proportional; pressure; radius
If pressure goes up , the flow
Increases
2nd: Flow is ______ _______ to viscosity and length
Inversely proportionate
Finally, Viscosity only affect
laminar
Bernoulli’s Principe
For a non-compressible, non-viscous fluid undergoing LAMINAR FLOW
Bernoulli’s Principe
For a non-compressible, non-viscous fluid undergoing LAMINAR FLOW, the sum of the pressure, kinetic and potential energies per unit volume remains a constant at all points along the line flow.
What is the pressure differential accross a flow roof having an area of 240m^2 when the wing blow at 25m/s the density of air is 1.29kg/m^3 (assume the speed of air inside is 0)
Change in P =
F=P*A
403Pa
1/2 (V2^2 - V1^2)
F 96700N or 10.9 Tons
Faster air move
Less pressure there is
Fick’s Principle
Vo2 = Co x (aCO2 - vO2)
Fick’s Principle (43)
Vo2 = CO x (aCO2 - vO2)
PRESSURE IS DEFINED AS A ________
FORCE OVER AREA (m^2)
Pascal’s principle is
Force in/ Area in = Force out / Area out
Flow SI units
m^3/s
As the diameter of the tube decreases, the speed of the fluid
decreases.
The velocity of a fluid running through a pipe is _______to the area
Area1 x velocity 1 = Area 2 x velocity 2
INVERSELY PROPORTIONAL to the area
We can also calculate pressure in a liquid at any depth if we know
the density of the liquid.
In an open system P1 would simply be __________
1 atmosphere)
Mnemonic: TD (touch down) =
Turbulence is Density dependent
Reynold’s number attempts to
describe the point at which flow changes from laminar to turbulent, and the
spectrum in-between.
Turbulent flow is
Nonlinear relationship of pressure and flow during turbulent flow
Flow varies ______ with the viscosity (thickness) of a fluid
inversely
Increased Hct = viscosity = resistance = blood flow
increase viscosity
increase resistance
decreased blood flow
Increased Hct secondary to certain conditions:
dehydration, cyanotic congenital heart disease, polycythemia)
Changes in Pressure are________
Changes in viscosity or length are________
directly proportional
inversely proportional
Poiseuille’s law for anesthesia
A small amount of arterial occlusion can have a large effect
The radius component also explains why an 18G cannula
has less flow (105 ml/min) than a 16G (220 ml/min)
Secondly, flow is inversely proportional to _________ and ______Lastly look at the flow rate recorded on a shorter 18G I.V. cannula and compare it with the longer 18G on a 15cm CVP line. The shorter cannula has
viscosity and length; a greater flow rate despite the two having then same radius.
The density of the fluid only comes into play when________
flow is turbulent.
Occlusion is 0% if pressure is 120mmHg Flow rate is _______pressure to restore normal flow rate is ______
100cm^3 ; 120mmHg
Occlusion is 20% if pressure is 120mmHg Flow rate is _______pressure to restore normal flow rate is ______
41cm^3; 293 mmHg
Occlusion is 50% if pressure is 120mmHg Flow rate is _______pressure to restore normal flow rate is ______
6.3cm^3;
Occlusion is 80% if pressure is 120mmHg Flow rate is _______pressure to restore normal flow rate is ______
0.16cm^3; 75,000mmHg
DO2= Delivery of oxygen equation
(HR x SV) x (1.34 x [Hgb] x SaO2) + (0.003 x PO2)
Blood Flow = Rate of uptake or excretion
arterial – venous concentration
Rate of uptake or excretion / arterial – venous concentration
Fick Principle Different than ________
Fick’s Law of Diffusion
Bernouilli’s principle
Total energy = ____ + _____
Total energy is ______ at all points in the streamline
As kinetic energy increases potential energy must decrease
A1V1 = A2V2
PE + KE
the same
decrease
If the cross sectional area is reduced, the velocity is
increased.
Describe viscocity and how it is measured?
Viscosity is the resistance of a fluid to flow
Fluid with high viscosity
Do not readily flow
Viscosity can be determined by measuring the
amount of time it takes for a fluid to flow a known length through a tube of known diameter
Describe how poiseuille’s law theorem relates fluid to viscosity and tube size
The flow rate of a fluid through a tube is directly proportional to the radius of the tube raised to the FOURTH POWER. In addition, the flow rate is inversely proportional to the viscosity (n) of the fluid and the length of the tube through which the fluid flows.
Flow rate is V/T =
(P1-P2) Pi r^4 / 8nL
Explain why moving an IV bag higher above the patient results in flow rate of the IVF
The pressure at the needed (P2) is related to the pressure of the fluid in the IV bag (P1) plus the product of the density of the IV fluid, the acceleration due to gravity and the height of the IV bag above the needle. The pressure of the fluid at the needle can thus be readily increased by simply raising the height of the IV bag above the needle. This will result in an increase in the fluid speed. Finally since the flow rate is directly proportional to the speed of the fluid, the flow rate will increase.
