This document discusses different types of fluid flow including laminar, turbulent, and transitional flow. It defines these terms and describes their characteristics. Laminar flow occurs at low velocities and involves fluid particles moving in straight lines. Turbulent flow occurs at higher velocities and involves irregular particle paths. Transitional flow occurs between laminar and turbulent. The document also discusses factors that influence flow such as pressure, tube diameter, viscosity, and Reynolds number. It provides examples of different flow types in medical applications such as respiration and the circulatory system.
2. Flow is defined as the quantity of a fluid i.e. a gas
or liquid passing in unit time
F=Q/t
F=flow
Q= quantity of liquid
T=time
3. Flow is of three types:
Laminar flow
Transitional flow
Turbulent flow
4. Laminar Flow
A fluid flows in a steady manner
No eddies or turbulence
Present in smooth tubes
Velocity is low
Flow is greatest at centre ( 2x mean flow)
To draw the fluid , a pressure difference must be
present across the ends of tube.
8. Determinants of laminar flow
Pressure across tube
Diameter of tube
length of tube
Viscosity of tube
9. All these factors are incorporated in an equation
and known as the Hagen- Poiseuille equation
10. Viscosity
Viscosity of fluid also affects the flow of fluid
viscosity increase in following condition
- policythemia
-Increased fibrinogen level
- hypothermia
- cigarette smoking
- Age
Increased viscosity leads to increase risk of
vascular occlusion .
11.
12.
13. Anaesthetic implication
During fluid resuscitation, a short wide bore cannula
e.g.14G is superior to a 20G cannula or a central line.
Intubating patients with very small tube increases
resistance to flow and thus pressure increases to
deliver the same amount of flow through the tube.
14.
15. Critical velocity
This is the velocity for a given fluid for a given tube
beyond which laminar flow gets converted into
turbulent flow.
When velocity of fluid exceeds this critical velocity ,
the character of flow changes from laminar to
turbulent.
This critical velocity applies only for a given fluid in a
given tube.
16. Turbulent flow
Reynolds's number > 4000
'high' velocity
Particle paths completely irregular
Average motion is in the direction of the flow
Cannot be seen by the naked eye
Changes/fluctuations are very difficult to detect.
Must use laser.
Mathematical analysis very difficult - so
experimental measures are used
Most common type of flow.
17. Onset of turbulent flow
Turbulent flow occurs –
2. Sharp increase of flow
3. Increase in viscosity or density of the fluid
4. Decrease in diameter of tube
18. Turbulent flow
Laminar flow change to turbulent flow if constriction
is reached
Velocity of fluid increases
Fluid is no longer in a smooth fashion
Swirls in eddies
Resistance is higher than for the same laminar flow .
Flow is no longer directly proportional to pressure
20. Where turbulent flow is seen ?
Turbulent flow is present where there is an orifice, a
sharp bend and some irregulararity which may lead to
local increase in velocity
21. Factors affecting flow and pressure during
turbulent flow
Q α √P
α 1/√ l
α 1/ √ρ
Q= flow
P = Pressure
l = length of tube
ρ = density of fluid
22. All these factors are combined to an index
known as Reynolds number
Reynold number = vρ∂ / ŋ
v= linear velocity of fluid
ρ = Density
η =viscosity
d = diameter of tube
24. Clinical Aspects Of Flow
Laminar flow is present in bronchi, smaller air
passage as they are narrower than trachea.
Turbulent flow is present in corrugated rubber
tubing .
Sharp bend or angles increase turbulence
In quiet breathing , the flow in resp tract is
laminar, while speaking , coughing or taking deep
breath turbulent flow tends to occur .
A lining layer of mucus may affect the flow .
In circulatory system, bruit and murmur can be
heard due to turbulence of flow.
25. Variable orifice flowmeter
In a variable orifice flow meter there is mixture of
turbulent and laminar flow and for calibration
purposes both viscosity and density is important.
At low flows, gas flow depends on the viscosity of the
gas.
At higher flows, gas flow depends on the viscosity of
the gas.
Recallibration is required if flow meter is used for a
different fluid than for what it was initially desigened.
26. How to measure the resistance
A constant flow is passed through the apparatus
Difference in pressure P1-P2 between the ends of
tube is measured
By dividing pressure difference by flow
Provided the flow is laminar , resistance is
independent of flow
29. Bernoulli’s Principle
Describes the relationship between the velocity and
pressure exerted by a moving liquid.
Applied to both liquids as well as gases.
Venturi effect is based on the Bernoulli’s principle.
Venturi effect is entrainment of fluid (gas or liquid )
due to the drop in pressure
When a fluid flows through a constriction in the tube
there is reduction in fluid pressure.
The fluid velocity correspondingly increases in order
to satisfy the law of conservation of energy.
30. Applications of Venturi effect
Venturi masks used for oxygen therapy.
Sander’s jet injector.
Nebulisation chambers.
Atomizers that disperse perfumes or spray paints.
Water aspirators.
Foam fire fighting nozzles and extinguishers.
Modern vaporizers.
Sand blasters to mix air and sand.
Vehicle carburetors.