The document provides an overview of basic physics concepts relevant to anaesthetists. It discusses the physics of fluid flow, describing the different types of flow (laminar, turbulent, transitional) and factors that determine flow such as pressure, resistance, diameter and viscosity. It also covers gas laws including Boyle's law, Charles' law and Gay-Lussac's law, defining the relationships between pressure, volume and temperature for gases. The document aims to explain these fundamental physical principles in order to avert accidents and ensure safe use of anaesthetic equipment.
The anaesthetic machine (UK English) or anesthesia machine (US English) or Boyle's machine is used by anaesthesiologists, nurse anaesthetists, and anaesthesiologist assistants to support the administration of anaesthesia. The most common type of anaesthetic machine in use in the developed world is the continuous-flow anaesthetic machine, which is designed to provide an accurate and continuous supply of medical gases (such as oxygen and nitrous oxide), mixed with an accurate concentration of anaesthetic vapour (such as isoflurane), and deliver this to the patient at a safe pressure and flow. Modern machines incorporate a ventilator, suction unit, and patient monitoring devices.
mapleson circuits used in anesthesia practice, are in their way out but it is as important to know the mechanism with which the gases flow to and fro through them.
Rev. August 2014 ME495 - Pipe Flow Characteristics… Page .docxjoyjonna282
Rev. August 2014 ME495 - Pipe Flow Characteristics… Page 2
2
ME495—Thermo Fluids Laboratory
~~~~~~~~~~~~~~
PIPE FLOW CHARACTERISTICS
AND PRESSURE TRANSDUCER
CALIBRATION
~~~~~~~~~~~~~~
PREPARED BY: GROUP LEADER’S NAME
LAB PARTNERS: NAME
NAME
NAME
TIME/DATE OF EXPERIMENT: TIME , DATE
~~~~~~~~~~~~~~
OBJECTIVE— The objectives of this experiment are
to: a) observe the characteristics of flow in a pipe,
b) evaluate the flow rate in a pipe using velocity
and pressure difference measurements, and c)
perform the calibration of a pressure transducer.
Upon completing this experiment you should have
learned (i) how to measure the flow rate and average
velocity in a pipe using a Pitot tube and/or a resistance
flow meter, and (ii) how to classify the general
characteristics of a pipe flow.
Nomenclature
a = speed of sound, m/s
A = area, m
2
C = discharge coefficient, dimensionless
d = pipe diameter, m
d0 = orifice diameter, m
E = velocity approach factor, dimensionless
f = Darcy friction factor, dimensionless
K0 = flow coefficient, dimensionless
k = ratio of specific heats (cp/cv), dimensionless
L = length of pipe, m
M = Mach number, dimensionless
p = pressure, Pa
p0 = stagnation pressure, Pa
p1, p2 = pressure at two axial locations along a
pipe, Pa
Q = volumetric flow rate, m
3
/s
R = specific gas constant, J·kg/K
Re = Reynolds number, dimensionless
T = temperature, K
V = local velocity, m/s
V = average velocity, m/s
Y = adiabatic expansion factor, dimensionless
= ratio of orifice diameter to pipe diameter,
dimensionless
p = pressure drop across an orifice meter, Pa
= dynamic viscosity, Pa·s
= air density, kg/m3
INTRODUCTION— The flow of a fluid (liquid or
gas) through pipes or ducts is a common part of many
engineering systems. Household applications include
the flow of water in copper pipes, the flow of natural
gas in steel pipes, and the flow of heated air through
metal ducts of rectangular cross-section in a forced-air
furnace system. Industrial applications range from the
flow of liquid plastics in a manufacturing plant, to the
flow of yogurt in a food-processing plant. Because the
purpose of a piping system is to transport a desired
quantity of fluid, it is important to understand the
various methods of measuring the flow rate.
In order to work with a fluid system, and certainly to
design a fluid system that will deliver a prescribed
flow, it is necessary to understand certain fundamental
aspects of the fluid flow. For this, one should be able
to answer questions like: Are compressibility effects
important? Is the flow laminar or turbulent? Is the
viscosity of the fluid important or not? Is the flow
steady or varying with time? What are the primary
forces of importance? For internal ...
The anaesthetic machine (UK English) or anesthesia machine (US English) or Boyle's machine is used by anaesthesiologists, nurse anaesthetists, and anaesthesiologist assistants to support the administration of anaesthesia. The most common type of anaesthetic machine in use in the developed world is the continuous-flow anaesthetic machine, which is designed to provide an accurate and continuous supply of medical gases (such as oxygen and nitrous oxide), mixed with an accurate concentration of anaesthetic vapour (such as isoflurane), and deliver this to the patient at a safe pressure and flow. Modern machines incorporate a ventilator, suction unit, and patient monitoring devices.
mapleson circuits used in anesthesia practice, are in their way out but it is as important to know the mechanism with which the gases flow to and fro through them.
Rev. August 2014 ME495 - Pipe Flow Characteristics… Page .docxjoyjonna282
Rev. August 2014 ME495 - Pipe Flow Characteristics… Page 2
2
ME495—Thermo Fluids Laboratory
~~~~~~~~~~~~~~
PIPE FLOW CHARACTERISTICS
AND PRESSURE TRANSDUCER
CALIBRATION
~~~~~~~~~~~~~~
PREPARED BY: GROUP LEADER’S NAME
LAB PARTNERS: NAME
NAME
NAME
TIME/DATE OF EXPERIMENT: TIME , DATE
~~~~~~~~~~~~~~
OBJECTIVE— The objectives of this experiment are
to: a) observe the characteristics of flow in a pipe,
b) evaluate the flow rate in a pipe using velocity
and pressure difference measurements, and c)
perform the calibration of a pressure transducer.
Upon completing this experiment you should have
learned (i) how to measure the flow rate and average
velocity in a pipe using a Pitot tube and/or a resistance
flow meter, and (ii) how to classify the general
characteristics of a pipe flow.
Nomenclature
a = speed of sound, m/s
A = area, m
2
C = discharge coefficient, dimensionless
d = pipe diameter, m
d0 = orifice diameter, m
E = velocity approach factor, dimensionless
f = Darcy friction factor, dimensionless
K0 = flow coefficient, dimensionless
k = ratio of specific heats (cp/cv), dimensionless
L = length of pipe, m
M = Mach number, dimensionless
p = pressure, Pa
p0 = stagnation pressure, Pa
p1, p2 = pressure at two axial locations along a
pipe, Pa
Q = volumetric flow rate, m
3
/s
R = specific gas constant, J·kg/K
Re = Reynolds number, dimensionless
T = temperature, K
V = local velocity, m/s
V = average velocity, m/s
Y = adiabatic expansion factor, dimensionless
= ratio of orifice diameter to pipe diameter,
dimensionless
p = pressure drop across an orifice meter, Pa
= dynamic viscosity, Pa·s
= air density, kg/m3
INTRODUCTION— The flow of a fluid (liquid or
gas) through pipes or ducts is a common part of many
engineering systems. Household applications include
the flow of water in copper pipes, the flow of natural
gas in steel pipes, and the flow of heated air through
metal ducts of rectangular cross-section in a forced-air
furnace system. Industrial applications range from the
flow of liquid plastics in a manufacturing plant, to the
flow of yogurt in a food-processing plant. Because the
purpose of a piping system is to transport a desired
quantity of fluid, it is important to understand the
various methods of measuring the flow rate.
In order to work with a fluid system, and certainly to
design a fluid system that will deliver a prescribed
flow, it is necessary to understand certain fundamental
aspects of the fluid flow. For this, one should be able
to answer questions like: Are compressibility effects
important? Is the flow laminar or turbulent? Is the
viscosity of the fluid important or not? Is the flow
steady or varying with time? What are the primary
forces of importance? For internal ...
Multiphase Flow Performance in Piping SystemsChrisJAlexisJr
Multiphase flow refers to the simultaneous flow of more than one fluid phase. It can be found in various places however it is most prevalent in the petroleum engineering field. This phenomenon brings about a major problem of pressure loss in the petroleum industry and results in a loss in production. Multiphase flow has been studied for years but there are few universally accepted solutions to calculate pressure drop. To accomplish this study, we used peer-review journals and articles in order to determine the flow regimes and characteristics of the different pipe orientations. This allowed us to determine the pressure drop calculations which were best suited for our study. We used a system that was designed with different pipe orientations that are found in the petroleum field and simulated the different flow regimes. Doing so allowed us to perform the calculations using two different pipe sizes; 1 inch and 1.5 inches. The results from the calculations showed that the pressure drop in the small pipe was greater than that of the bigger pipe.
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3. Objectives
• After completion of this course students will be able to
describe:-
– Basic concept on physics of fluid
– Basic concepts on gas laws and its implications
11/2/2018 3WUBIE B
4. INTRODUCTION
For the safe & efficient use of anaesthetic apparatus, the
anaesthetist must have a clear concept of the physical aspects of
the equipment in use.
Understanding of basic concepts may avert unnecessary
accidents & near misses.
Measurable terms and the physical laws apply to all states of
matter (i.e. solids, liquids and gases).
11/2/2018 4WUBIE B
6. Flow is defined as the quantity of liquid(gas, vapour or
sublimate) that passes a point per unit time
A simple equation to represent this is:
• Flow is sometimes written as ∆Q (rate of change of a
quantity)
• Due to the number of different fluids that are given to
our patients during a routine anesthetic, flow is
obviously an important area of physics to understand.
11/2/2018 WUBIE B 6
7. Biophysics flow
Flow is determined by 2 factors
1. Pressure difference (P) -
Flow(Q) from high pressure to low pressure.
Q depends on P1-P2 (P) (pressure gradient)
2. Resistance (R)
R= measure of friction between
tube/blood vessel and moving fluid
Fluid molecules within themselves
711/2/2018 WUBIE B
8. As fluid flows through tubes there is resistance, between
the fluid and vessel wall that opposes the flow.
For any given system, this resistance is constant and can be
expressed as:
Q = P (Ohm’a law)
R
R Depends on type of fluid and dimension of tube and on:
Viscosity of fluid ( ) – directly proportional
Tube length (L)- directly proportional
Tube radius (r) - indirectly proportional (R as radius
)
11/2/2018 8WUBIE B
10. Hagen– Poiseuille equation
where p is pressure drop along the
tube (p1 − p2).
r is radius of tube
l is length of tube and
η is viscosity of fluid.
11/2/2018 10WUBIE B
11. • Determinants of laminar flow
A. Pressure across tube
B. Diameter of tube
C. length of tube
D. Viscosity of tube
11/2/2018 11WUBIE B
12. A. Gradient pressure (ΔP)
For flow to occur, there must be a pressure difference (ΔP)
between the ends of a tube.
ΔQ is directly proportional to ΔP.
• The greater the pressure difference, the greater the flow.
11/2/2018 12WUBIE B
13. B. Tube diameter /Radius
• flow is proportional to the 4th power of the radius.
• If the diameter of the tube is halved the flow through it reduces
to one sixteenth.
• If the radius doubles, the flow through the tube will increase by
16 times
11/2/2018 13WUBIE B
15. C. Length
Flow is inversely proportional to the length of the tube.
If the length is doubled the flow is halved
A central line is much longer than a cannula, and for the same
diameter fluid flows more slowly.
11/2/2018 15WUBIE B
16. D. Viscosity
Viscosity of fluid also affects the flow of fluid
viscosity increase in following condition
- Polycythemia , Increased fibrinogen level
- Hypothermia , cigarette smoking
- Age
Increased viscosity leads to increase risk of vascular
occlusion .
11/2/2018 16WUBIE B
17. 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.
11/2/2018 17WUBIE B
18. The physics of flow
o Flow can be divided into Three different types
1. Laminar flow
2. Transitional flow
3. Turbulent flow
o A number of different physical characteristics determine
whether a fluid obeys the principles of one or the other.
11/2/2018 18WUBIE B
19. 1.Laminar flow
• Normal and noiseless.
All elements of the fluid move in a stream line, that are parallel
to the axis of the tube.
No fluid move in radial or circumferential direction.
Layer of fluid in contact with the wall is motionless (thin layer,
adherent to wall, hence motionless)
Fluid that move along the axis of the tube has maximum Velocity.
1911/2/2018 WUBIE B
20. • Laminar flow
• Reynold’s number < 2000
• 'low' velocity
• Fluid particles move in
straight lines.
11/2/2018 20WUBIE B
21. fig. Diagrammatic representation of laminar flow
• If the mean velocity of the
flow is v, then the molecules
at the centre of the tube are
moving at approximately 2v
(twice the mean),
• the molecules at the side of
the tube are almost
stationary.
11/2/2018 21WUBIE B
22. 2. Turbulent blood flow
Various elements of fluid move irregularly in axial,
radial and circumferential direction.
• More pressure required to drive blood than laminar
• Energy wasted in propelling blood radially and axially
• Often accompanied by noise(murmurs).
• Occur at valves and aorta (normal), at site of blood
clot(pathological).
2211/2/2018 WUBIE B
25. Turbulent Flow
• The fluid particles do not move in orderly manner and
they occupy different relative positions in successive
cross-sections.
• The flow is unpredictable
• High velocity
• Average motion is in the direction of the flow
• Changes / fluctuations are very difficult to detect.
• Most common type of flow.
• Particle paths completely irregular
11/2/2018 25WUBIE B
26. • Laminar flow change to turbulent flow if constriction is
reached
– Velocity of fluid increases
– Fluid is no longer in a smooth fashion
– Resistance is higher than for the same laminar flow .
– Flow is no longer directly proportional to pressure
11/2/2018 26WUBIE B
27. Occurrence of turbulent flow depends on:
• Velocity of blood flow (v)- directly proportional
Diameter of the tube (d) – directly proportional
Density of the tube (p)-directly proportional
Viscosity of the fluid ()- indirectly proportional.
Turbulence in normal circulation:
Heart chambers -- - - -v & d large
Big arteries near heart ----v & d large
2711/2/2018 WUBIE B
28. Reynold’s number (Re).
• There is a number that can be calculated in order to
identify whether fluid flow is likely to be laminar or
turbulent and this is called Reynold’s number (Re).
11/2/2018 28WUBIE B
29. Re : Reynold’s number,
ρ: Density of fluid
v: Velocity of fluid
d: Diameter of tube and
η : viscosity of fluid.
• Reynold’s number is dimensionless (it
has no units).
• Re < 2000 flow is likely to be
laminar
• Re > 2000 flow is likely to be
turbulent.
• Reynold’s number of 2000 delineates
laminar from turbulent flow.
11/2/2018 29WUBIE B
32. Clinical Aspects Of Flow
• Laminar flow is present in bronchioles, 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.
11/2/2018 32WUBIE B
33. 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
11/2/2018 33WUBIE B
34. 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.
11/2/2018 34WUBIE B
36. Coanda effect
is the tendency of the fluid jet to be attached to a nearby
surface.
When a narrow tube encounters a Y junction of the wide bore,
because the flow tends to cling to one side, the flow will not
evenly divide between the two outlets, but flows through only one
limb of the Y piece. This behavior is called Coanda Effect.
11/2/2018 36WUBIE B
37. Coanda Effect
If a constriction occurs at bifurcation because of increase in
velocity and reduction in the pressure, fluid (air, blood) tends to
stick to one side of the branch causing maldistribution.
11/2/2018 37WUBIE B
38. Coanda Effect
Application:
1. Mucus plug at the branching of tracheo-bronchial tree may
cause maldistribution of respiratory gases.
2. Unequal flow may result because of atherosclerotic plaques in
the vascular tree
3. Fluid logic used in ventilators employs this principle to
replace valves or mobile parts.
11/2/2018 38WUBIE B
41. Introduction
• As anesthetists we deal with liquids & gases under pressure at
varying temperatures and volumes.
• These inter-relationships are simple, measurable and their
understanding ensures a safe outcome for the patient.
11/2/2018 41WUBIE B
42. • Definitions
• What is a gas?
Gas : is a substance that is in its gaseous phase, but is above its
critical temperature.
Vapour: a substance in the gaseous phase but is below its critical
temperature.
Critical temperature : the temperature above which a gas cannot be
liquefied no matter how high the pressure.
11/2/2018 42WUBIE B
43. • What is pressure?
• Defined as "the force per unit area acting at
right angles to the surface under consideration”
• Pressure = Force/Area
• The unit of pressure is the Pascal.
Units ,1 Barr = 1 Atm = 100Kpa
=760mmHg=760torr = 14.7Psi = 1000cmH20 .
11/2/2018 43WUBIE B
44. What is temperature?
Measures heat, a form of energy, kinetic energy which comes
from movement of the molecules.
Temperature is measured in the Celsius or Fahrenheit scales.
In Physics it is the Kelvin.
The divisions of the Kelvin and Celsius scale are the same but
the start points differ.
0oC is 273K, so body temperature is 310K on this scale.
11/2/2018 44WUBIE B
45. Basic Concepts of Gas Laws
The relationship between the three variables,
1. Volume
2. Pressure
3. Temperature is explained by the gas laws
11/2/2018 45WUBIE B
46. Definitions of the gas laws
1. Boyle’s Law
o At constant temperature (T) , the volume(V) of a fixed amount of
a gas is inversely proportional to its pressure(P).
o V α 1 / p
o PV = Constant ( if T is kept constant).
11/2/2018 46WUBIE B
47. 2. Charle’s Law
• At constant pressure, volume of a gas is directly proportional to
the temperature. V α T or V / T = K (constant)
• APPLICATION:
• Respiratory gas measurements of tidal volume & vital capacity
etc are done at ambient temperature while these exchanges
actually take place in the body at 37 OC.
11/2/2018 47WUBIE B
48. 3. Gay Lussac’s law/ the third gas Law
• At constant volume pressure is directly proportional to the
temperature. P α T or P/T = K (constant)
Application
• Medical gases are stored in cylinders having a constant volume and
high pressures (138 Barr in a full oxygen / air cylinder).
• If these are stored at high temperatures, pressures will rise causing
explosions
11/2/2018 48WUBIE B
50. Perfect gas
• A gas that completely obeys all three gas laws.
• Or A gas that contains molecules of infinitely small size,
which, therefore, occupy no volume themselves, and
which have no force of attraction between them.
• No such gas actually exists still.
11/2/2018 50WUBIE B
Physics is the world in measurable terms and the physical laws apply to all states of matter (i.e. solids, liquids and gases).
This is the mass of a substance (in this case a fluid), that passes a certain point in one second.” The units are Litres per second
Resistance = ΔP / ΔQ , R (constant) (This can be compared with V=IR in electrical physics).
The Hagen-Poiseuille equation defines the flow through a tube and how this flow is affected by the attributes of the tube; the length and radius, and the attributes of the fluid; the viscosity
(We squeeze a bag of IV fluid, to increase the pressure difference between the bag and the vein, so that the fluid is given quicker!).
This means that flow is directly proportional to D4 (Think about how much more rapidly fluid flows through a 22G and 16G cannula).
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.
This is therefore the type of flow we would expect to see when a fluid floes through a cannula or a tracheal tube.
Transitional flow: the flow occurs between laminar and turbulent flow .
An increase in the flow velocity of an ideal fluid will be accompanied by a simultaneous reduction in its pressure.
Describes the relationship between the velocity and pressure exerted by a moving liquid.
Applied to both liquids as well as gases.
Anaesthesiologist will be dealing with many of the gases which are needed for anaesthetizing patients every day
Pressure is the consequence of molecular bombardment of the surface by the gas.
Kinetic energy is transferred to the surface and a force is produced that creates the pressure.
If the volume falls, the pressure goes up because the area for collisions fall and so more kinetic energy transfer per unit area, and so an increase in pressure.
STP = Standard Temperature and Pressure T = O OC P = 760mmHg
Absolute Temp. O OK = -273 OC
● Gas exists in the gaseous state at room temperature and pressure.
Vapour is the gaseous state of a substance below its critical temperature. At room temperature and atmospheric pressure, the substance is liquid.
It is important to realize that this is a theoretical concept and no such gas actually exists. Hydrogen comes the closest to being a perfect gas as it has the lowest molecular weight. In practice, most commonly used anaesthetic gases obey the gas laws reasonably well.