Applied Physics

Applied Physics

RET 2274Respiratory Therapy Theory IModule 1.0

Three Primary States of Matter

States of Matter

GasSolid Liquid

States of Matter

Solid Atoms are kept in

place by strong mutual attractive forces and are limited to back-and-forth motion about a central position

States of Matter

Liquid Atoms are kept in place

by mutual attraction (much weaker than that of solids) and can move about freely and can take the shape of their container – capable of flow. Like solids, liquids are dense and cannot easily be compressed

States of Matter

Gas Molecular attractive forces

are very weak and their movement is rapid and random with frequent collisions. Gases have no inherent boundaries and are easily compressed and expanded. Like liquids, gases can flow. Liquids and gases are considered fluids.

Temperature Scales

Absolute Zero The concept that a temperature exists at which there

is no kinetic energy (energy of motion) – exists in theory only

Kelvin (K) Zero degrees K = absolute zero Freezing point of water = 273 K Boling point of water = 373 K

Temperature Scales

Celsius (C) Freezing point of water = 0º C Boiling point of water = 100º C

Note: To covert degrees Celsius to degrees Kelvin, simply add 273

Example: 25º C = 25 + 273 = 298º K

Temperature Scales

Fahrenheit Freezing point of water = 32º F Boiling point of water = 212º F

To covert degrees Fahrenheit to degrees Celsius, use the following formula

ºC = 5/9 (ºF – 32)

To covert degrees Celsius to degrees Fahrenheit, use the following formula

ºF = (9/5 x ºC) + 32

Temperature Scales

Linear relationship between gas molecular activity, or pressure, and temperature. The graph shows comparable readings on three scales for five temperature points

Freezing point of water

Boiling point of water

Change of State

Liquid-Solid Phase Changes

The changeover from the solid to liquid state is called MELTING

The temperature at which solid change to liquid is called the MELTING POINT

Change of State

Liquid-Solid Phase Changes

The changeover from the liquid to solid state is called FREEZING; it is the opposite of melting

The FEEZING POINTS and MELTING POINTS of a substance are the same

Change of State

Liquid-Vapor Phase Changes

As the temperature of a liquid increases, its state changes to VAPOR

Change of State


This change of state is called VAPORIZATION Two different forms of vaporization

EVAPORATIONBBOILING

Change of State


Boiling occurs at the BOILING POINT The boiling point of a liquid is the

temperature at which its vapor pressure equals atmospheric pressure – its molecules must have enough kinetic energy to force themselves into the atmosphere against the opposing pressure

Change of State


Boiling occurs at the BOILING POINT The boiling point of liquid oxygen at 1

atmosphere pressure is -183º C

Change of State


EVAPORATION is when a liquid changes into a gas at temperatures lower than its boiling point

After water is converted to a vapor, it acts like any gas. This invisible gaseous form of water is called MOLECULAR WATER MOLECULAR WATER

Change of State


When a gas is fully saturated with water vapor, slight cooling of the gas causes its water vapor to turn back into the liquid state, a process called CONDENSATION CONDENSATION

The temperature at which condensation begins is called the DEW POINTDEW POINT

Changes of State

Critical Temperature The highest temperature

at which a substance can exist as a liquid

Critical Pressure The pressure needed to

maintain equilibrium between the liquid and gas phases of a substance at its critical temperature A typical phase diagram. The dotted

green line gives the anomalous behavior of water

Phase Diagram

Properties of Liquids

Pressure in Liquids Liquids exert pressure The pressure exerted by a liquid depends on both its

height (depth) and weight density (weight per unit volume)

Pascal’s principle. Liquid pressure depends only on the height (h) and not on the shape of the vessel or the total volume of liquid. (Modified from Nave CR, Nave BC: Physics for the health

sciences, ed 3, Philadelphia, 1985, WB Saunders.)


Buoyancy Liquids exert buoyant

force because the pressure below a submerged object always exceeds the pressure above it.

The upward buoyant force will overcome gravity, and the object will float


Buoyancy Gases also exert

buoyant force, which helps keep solid particles suspended in gases

Blue and white smoke ascending


Viscosity Viscosity is the force

opposing a fluid’s flow; viscosity in fluids is like friction in solids

A fluids viscosity is directly proportional to the cohesive forces between it molecules; the stronger the cohesive forces, the greater is the fluid’s viscosity


Viscosity The greater a fluid’s viscosity, the greater is its

resistance to deformation and the greater is its opposition to flow


Viscosity The greater the viscosity

of a fluid, the more energy is needed to make it flow

Example: When there is an increase in red blood cells (polycythemia), the heart must work harder to circulate the blood because it is more viscous


Laminar Flow When fluids move in discrete cylindrical layers called

streamlines


Laminar Flow The difference in the velocity among these concentric

layers is called shear rate

The pressure pushing or driving the fluid is called shear stress


Cohesion and Adhesion The attractive force between like molecules is called

cohesion


Cohesion and Adhesion The attractive forces between unlike molecule is

adhesion


Cohesion and Adhesion The shape of the meniscus

depends on the relative strengths of adhesion and cohesion. A, Water; adhesion stronger than cohesion. B, Mercury; cohesion stronger than adhesion


Surface Tension The force exerted by like molecules at a liquid’s

surface


Surface Tension The force of surface

tension in a drop of liquid. Cohesive force (arrows) attracts molecules inside the drop to one another. Cohesion can pull the outermost molecules inward only, creating a centrally directed force that tends to contract the liquid into a sphere


Surface Tension The lungs resemble clumps

of bubble, it follows therefore that surface tension plays a key role in the mechanics of ventilation

Abnormalities in alveolar surface tension occur in certain clinic conditions, e.g., infant respiratory distress syndrome


Surface Tension Laplace’s Law: In a liquid sphere, the pressure

required to distend the sphere is directly proportional to the surface tension of the liquid and inversely proportional to the sphere’s radius


Surface TensionLaplace’s relationship. Two bubbles of different sizes with the same surface tension. Bubble A, with the smaller radius, has the greater inward or deflating pressure and is more prone to collapse than the larger bubble B. Because the two bubbles are connected, bubble A would tend to deflate and empty into bubble B. Conversely, because of bubble A’s greater surface tension, it would be harder to inflate than bubble B.

Equation for liquid bubble P = 4ST r

P = distending pressureST = surface tension r = spherical radius

Properties of Gases

Gases share many properties with liquids Gases:

Exert pressure Capable of flow Exhibit the properties of viscosity

However, unlike liquids, gases are readily compressed and expanded and fill the spaces available to them through diffusion

Properties of Gases

Gaseous Diffusion Diffusion:The process whereby molecules move from

areas of high concentration to areas of lower concentration

Kinetic Energy: The driving forced behind diffusion. Because gases have high kinetic energy, they diffuse most rapidly

Note: Because diffusion is based on kinetic activity, anything that increases molecular activity will quicken diffusion, e.g., heating

Properties of Gases

Gaseous Diffusion Graham’s Law: The rate of diffusion of a gas (D) is

inversely proportional to the square root of its density:

Lighter gases diffuse rapidly, whereas heavy gases diffuse more slowly

Properties of Gases

Gas Pressure Whether free in the atmosphere, enclosed in a container,

or dissolved in a liquid such as blood, all gases exert pressure

In physiology, the term tension is often used to refer to the pressure exerted by gases when dissolved in liquids

Pressure is a measure of force per unit area PSI: Pounds per square inch (lb/in²)

British fps N/m² : Newton per meter squared (Pascal)

International System of Units (SI)

Properties of Gases

Gas Pressure Pressure can also be measured

indirectly as the height of column of liquid:

Centimeters of water pressure (cm H2O)

Millimeters of mercury (mm Hg)

Both mercury and water columns are still used in clinical practice, especially when vascular pressures are being measured

Properties of Gases

Partial Pressure (Dalton’s Law) Many gases exist together as mixtures, for example

air, which contain mostly oxygen and nitrogen

The pressure exerted by a single gas is called its partial pressure

PressureTotal = Pressure1 + Pressure2 ... Pressuren

Properties of Gases

Partial Pressure (Dalton’s Law

Partial Pressure = Fractional concentration x Total atmospheric pressure

Approximate Fractional Gas Concentrations of Air

Partial Pressures of Gases in Air

PO2 = 0.21 x 760 torr = 160 torr

PN2 = 0.79 x 760 torr = 600 torr

Properties of Gases

Composition of Earth’s Atmosphere

Properties of Gases

Solubility of Gas in Liquids (Henry’s Law) At a constant temperature, the solubility of a gas in a

liquid is proportional to the pressure of that gas above the liquid

William Henry (chemist)

Properties of Gases

Solubility of Gas in Liquids (Henry’s Law) Temperature plays an important role in gas solubility

High temperatures decrease solubility

Low temperatures increase solubility

Leave a carbonated drink open and out of the refrigerator and it will quickly go flat

Gas Laws

Several laws help define the relationship among gas pressure, temperature, mass, and volume

Boyle’s Law Charles’ Law Gay-Lussac’s Law Combined Gas Law

Gas Laws

Boyle’s Law

Description Constants Working Formula

The volume of a gas varies inversely with

its pressure

Temperature, mass

P1V1 = P2V2

Gas Laws

Boyle’s Law

Gas Laws

Charles’ Law


The volume of a gas varies directly with

changes in its temperature

Pressure, mass

V1 = V2

T1 T2

Gas Laws

Charles’ Law

Gas Laws

Gay Lussac’s Law


The pressure exerted by a gas varies directly with its

absolute temperature

Volume, mass

P1 = P2

T1 T2

Gay Lussac’s Law

Gas Laws

Gas Laws

Combined Gas Law


Interaction of the all the gas laws

None P1V1 = P2V2

T1 T2

Gas Laws

Combined Gas Law

P1V1 = P2V2T1 T2

Gas Behavior Under Changing Conditions

Effects of Water Vapor Water vapor, like any gas, occupies space

The dry volume of a gas at a constant pressure and temperature is always smaller than it saturated volume

Ptotal - Pwater vapor = Pdry gas


Effects of Water Vapor Correcting from the dry state to saturated state

always yields a larger gas volume

Pdry gas + Pwater vapor = Ptotal


Effects of Water Vapor Addition of water vapor to a gas mixture always

lowers the partial pressures of the other gases present

Pc = Fgas x (PT – PH2O)

Pc = Corrected gas pressure

Fgas = The fractional concentration of gas in the mixture

P = The water vapor pressure at a given temperature


Critical Temperature The highest temperature

at which a substance can exist as a liquid

Critical Pressure The pressure needed to

maintain equilibrium between the liquid and gas phases of a substance at its critical temperature A typical phase diagram. The dotted

green line gives the anomalous behavior of water


Phase Diagram

Fluid Dynamics

Both liquids and gases can flow Flow is the bulk movement of a substance through

space

Flow = Movement of a volume per unit of time

= L/minute

Fluid Dynamics

Pressures in Flowing Fluids Flow Resistance

Available energy decreases because frictional forces (fluid viscosity, tube wall) oppose fluid flow

R = (P1 – P2)

Fluid Dynamics

Patterns of Flow

Laminar Flow

Turbulent

Transitional

Fluid Dynamics

Patterns of Flow Laminar Flow

During laminar flow a fluid moves in discrete cylindrical layers or streamlines

Fluid Dynamics

Patterns of Flow Laminar Flow

Poiseuille’s Law: For fluids flowing in a laminar pattern, the driving pressure will increase whenever the fluid viscosity, tube length, or flow increases; greater pressure is required to maintain a given flow if the tube radius is decreased

P = 8nl _ r4

Fluid Dynamics

Patterns of Flow Turbulent Flow

Under certain conditions, fluid molecules may form irregular eddy currents in a chaotic pattern called turbulent flow

Fluid Dynamics

Patterns of Flow Turbulent Flow

Reynold’s Number >3000 = Turbulent 2000 – 3000 = Transitional <2000 = Laminar

Fluid Dynamics

Patterns of Flow Transitional Flow

Mixture of laminar and turbulent flow Flow in the respiratory tract is mainly transitional

Fluid Dynamics

The Bernoulli Effect As a fluid flows through a constriction, its

velocity increases and its lateral pressure decreases

Fluid Dynamics

The Bernoulli Effect According to the Bernoulli theorem, a flowing fluid’s lateral

pressure must vary inversely with its velocity. a, Flow in tube “a”; va, velocity in tube “a”; vb, velocity in tube “b”; b, flow in tube “b”; Pa, lateral wall pressure in tube “a”; Pb, lateral wall pressure after restriction

Fluid Dynamics

Fluid Entrainment When a flowing fluid encounters a very narrow passage, its

velocity can increase greatly and cause the fluid’s lateral pressure to fall below that exerted by the atmosphere and pull another fluid into the primary flow stream

Fluid Dynamics

Fluid Entrainment The amount of air

entrained depends on both the diameter of the jet orifice and the size of the air entrainment ports

Fluid Dynamics

Fluids and the Coanda Effect The amount of air entrained depends on both the

diameter of the jet orifice and the size of the air entrainment ports

Fluid Dynamics

Fluids and the Coanda Effect Is the tendency of a fluid jet to stay

attached to an adjacent curved surface that is very well shaped

Applied Physics

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