MEC 520 F15 Lecture 2(1)

04/18/2023 MEC 520 – Energy Technology Thermodynamics 1

LECTURE 2MEC 520

AUGUST 31, 2015

Infrared Radiation

Thermography

All bodies give out infrared (IR) radiationThe infrared energy is dependent on the absolute

surface temperatureThe infrared energy is dependent on the surface

emissivity

PRINCIPLES OF THERMOGRAPHY

Infrared Radiation (EM Waves)

WHAT IS THERMOGRAPHY?

Thermography is the science of acquisition and analysis of thermal information from objects using non-contact thermal imaging devices.

Non-contact infrared imagers provide fast, safe, accurate measurements for objects that are: Moving or very hot Difficult to reach Impossible to shut-off Dangerous to contact Where contact would

damage, contaminate or

change temperature

WHY IS THERMOGRAPHY IMPORTANT?

Heat Amount of heat energy in an object is the total kinetic

energy of the molecules that compose it Joule, watt-hr, etc.

Temperature A measure of the average speed of the molecules and

atoms that make up the object Kelvin (°K), Celsius (°C), Fahrenheit (°F),

Defines the state of an object, relative to other object Its value depends on energy level of a body Indicates the direction of heat flow

BASICS

Conservation of energy Sum of all energy in a closed system is constant (1st

Law of thermodynamics)

Direction of heat flow Heat flows from a hotter object to a colder one by

transferring energy from one body to another If there is a temperature difference, there will be heat

flow (2nd law of thermodynamics) Temperature defines the existence of heat

PRINCIPLES OF HEAT TRANSFER

RADIATIVE HEAT TRASNFER

Radiative heat transfer is the transfer of heat from one body to another by the emission and absorption of radiation

What is thermal radiation?

Thermal radiation is a form of electromagnetic radiation

It will easily pass through most gases, but will pass with difficulty or will be blocked by most liquids and solids

Objects emit thermal radiation as a consequence of their absolute temperature

All objects above 0°K emit thermal radiation. The higher the temperature, the more thermal

radiation will be emitted.

THERMAL RADIATION

The colors humans can see

ELECTROMAGNETIC WAVES

c = f * lf = c / l

All matter (gases, planets, etc.) emit some amount of electromagnetic radiation across a range of energies (or wavelengths).

Infrared ranges from .7µm to 14 µmBroken into near, mid, and far infrared

Near IR: – 0.75–1.4 µm (e.g. fiber optics, night vision) Mid-wavelength infrared IR: 3-8 µm (e.g. Missile

homing) Long-wavelength IR: – 8-15 µm (e.g. thermal imaging) Far IR: 15–1000 µm

IR CLASSIFICATION

Emission is the radiation that is given off by the body

Absorption is radiation that is taken in by the body

Reflection is reflected radiation from another source

Transmission is radiation that has passed through the body

TOTAL RADIATION

Incident radiation is all the radiation that strikes an object from its surroundings.

INCIDENT RADIATION

Absorption

Source

ReflectionTransmissionTarget

Exitant radiation is all the radiation that leaves an object regardless of the source.

EXITANT RADIATION

Absorption

Source

Reflection

TransmissionTarget

Source

Transmission

Of all the total exitant radiation from a target, a certain portion will be Emitted from the target itself Reflected from a source in front of the object Transmitted from a source behind the object

Total radiation energy is a combination of Emitted, e Reflected, r Transmitted, t

e + r + t = 1

EXITANT RADIATION

An infrared camera detects the electromagnetic radiation at a certain wavelength, E( )l

But we want to measure the temperature?

RADIATED ENERGY AND TEMPERATURE

BACKGROUND

How much radiation will be emitted from a source as a function of temperature

and wavelength ?

HISTORY

In the late 1890’s, Wien and Rayleigh had attempted to formulate an equation expressing the intensity of electromagnetic radiation as a function of wavelength and the temperature of the source.

In 1900, Planck derived the correct relationship from fundamental principles.

Max Planck1858 - 1947

A black body is an object that absorbs all incident radiation, i.e. has no reflection

BLACKBODY

A small hole cut into a cavity is the most popular and realistic example.

None of the incident radiation escapes

What happens to this radiation?

• Black-bodies do not "reflect" any incident radiation• They may re-radiate, but the emission is its only characteristic• The emission from a black-body depends only on its temperature• The emitted "thermal" radiation characterizes the equilibrium

temperature of the black-body

Black bodies are used to calibrate thermal imaging equipment as it cancels the emitted and reflected radiations.

In reality transmitted radiation can be negated as most objects are considered “opaque”

Therefore the only problem is splitting the emitted radiation from that of the reflected radiation.

A black-body reaches thermal equilibrium when the incident radiation power is balanced by the power re-radiated, i.e. if you expose a black-body to radiation, its temperature rises until the incident and radiated powers balance.

BLACKBODY

RAYLEIGH-JEANS LAW

The intensity emitted from the blackbody is proportional to the temperature divided by the fourth power of the wavelength.

c is the speed of light, kB is the Boltzmann constant and T is the temperature in kelvin

I( , l T) = 2pckBT l-4 It agrees with experimental

measurements for long wavelengths.

It predicts an energy output that diverges towards infinity as wavelengths grow smaller, known as the ultraviolet catastrophe

PLANCK'S LAW

Intensity of Radiation vs. Wavelength

Also [exp(hc/lkBT)] goes to infinity faster than (l5), i.e. I(l) 0 as l 0.

From a fit between Planck's law and experimental data, one obtains Planck's constant to be:

h = 6.626 × 10-34 J.s

Note also: for very large :l 4exp / 1B BB

hchc k T u k T

SUN’S INTENSITY CURVE

BLACKBODY SPECTRUM

WIEN’S LAW

Wien’s law states that the dominant wavelength at which a blackbody emits electromagnetic radiation is inversely proportional to the Kelvin temperature of the object

WIEN’S LAW

Wien’s law allows us to calculate the temperature of an object if we know the wavelength of its maximum emission.

Example: lmax for the Sun = 502 nm

Therefore, T = 5770K = 5500C.

lmaxT = 2.8979 106 nmK.

STEFAN BOLTZNANN LAW

The Stefan-Boltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux E directly proportional to the fourth power of the Kelvin temperature T of the object

EBB = T4

s is called the Stefan-Boltzman constant (5.6705 × 10-8 Wm-

2K-4) and T is the temperature in kelvins

The law can be derived from Plank’s Law by considering a small flat black body surface radiating out into a half-sphere.

EMISSIVITY DEFINED

Emissivity is the ratio of radiation emitted by a real body compared to the

radiation emitted by a black body at the same temperature and same

wavelength

e = ERB/EBB

REAL BODY

A real body

ERB = esT4

ERB = Radiated energy from a real body

T = Temp (K) = e emissivitys = 5.6705 × 10-8 Wm-2K-4

EMISSIVITY

Emissivity that describes the efficiency with which an object radiates or emits heat and has value from 0-1.0

Thermal and electrical insulators are excellent emitters and its measurement is not a problem

Woods, rubber , plastic, paper, concrete, building materials, etc.

Metals are poor emitters unless heavily oxidized and its measurement is delicate

Copper, steel, brass, zinc, aluminum, lead, etc.

Thermal devices Utilize temperature dependent material property such as the electrical conductivity

or thermal expansion.

they have a broad flat spectral response compared to photon devices.

lower thermal sensitivity and a relatively slow response time (~milliseconds)

operated at room temperature thus overcoming the logistic burden of providing cooling

Photonic devices utilize semiconductors whose electrical properties may be altered by photon-

induced transitions that can be monitored as an electrical output signal.

It is necessary that the incident radiation has energy equal to or greater than the energy gap between the bound and mobile states, thus the detector has a long wavelength cut-off determined by the energy gap.

necessary to cool them to improve performance by minimizing the thermal excitation of carriers which is a noise contribution to the output signal.

Examples include photoconductors (monitor the changes in resistivity) and photovoltaic devices (monitor voltage is generated across p-n junction.)

TYPES OF INFRARED DETECTORS

THE FLUKE CAMERA

Learning to use the Fluke Ti20TM

X-rays

Ultra-violet

Near Infrared

Short WaveInfrared

MiddleInfrared

Long WaveInfrared

Microwave

0.280.40

Thermal

The Ti20 is a digital imager that takes long wave infrared thermal pictures in the 7.5 to 14 micron range.

The electromagnetic (EM) spectrum.

Infrared radiation, like light and radio waves, is a form of electromagnetic energy.

THE ELECTROMAGNETIC SPECTRUM

INFRARED RADIATION

Ti20, and all infrared cameras and thermometers detect infrared radiation.

As an object becomes warmer, they radiate more energy which the camera detects, creating a thermogram.

The Ti20, convert this information into a radiometric temperature measurement which provides 12,288 independent temperature values in each thermal image.

HOW DO WE GET THE PICTURE?

96 Elements

128 Elem

When an image is captured using the Ti20, all of the background data is also saved along with the picture allowing in-depth analysis using InsideIR software.

Each of the 12,288 elements, or pixels, contain an accurate temperature value. The Imager, through the use of a complex set of algorithms, assign specific colors that correspond exactly with the temperature value found at the specific X Y coordinate.

Focus control

Optical channel

Laser aperture

Trigger

USB Port

AC adapter terminal

Display

Soft keys

Battery compartment

Tripod mount (under Imager)

OVERVIEW OF CONTROLS

LET’S GET STARTED

Press the F2 key to turn the Imager on and off.

Turn the Imager on by pressing and holding the F2 key for approximately 2 seconds until the date and time appear in the upper right-hand corner of the display.

Turn the Imager off by pressing and holding the F2 key for approximately 2 seconds.

QUALITIES OF A GOOD IMAGE

Brightness

Contrast

Perspective

Composition

Angle of view

A good image should exhibit all of these attributes

QUALITIES OF A GOOD IR IMAGE

Thermal level

Thermal span

Thermal range

Perspective

Composition

Palette

GENERAL MEASUREMENT RULES

Get a good image FIRST. If the image is out of focus, the measurement is WRONG.

By default, most cameras adapt the scale automatically.

Desired target must cover the spot. Do not aim with an angle superior to 45/ 50°. Be

careful that at perpendicular angles, you may be a major source of reflection

Choose a zone of high emissivity to do the measurement

A well focused image provides clarity and depth not witnessed from an out of focus image.

Focus is the most important step when capturing a quality thermal image and cannot be changed after saving the image.

Adjust focus in either directionFull clockwise = 61cm (24 in)Full counter clockwise = Infinity

Focus where there is thermal contrast (temperature differential)

662°F

Span sets the width of window

Level sets the position of the window

Low setting of window

High setting of window

Move window to set thermal level

(350°C)

(-10°C)

LEVEL AND SPAN (RANGE)

F1 F2 F3 F1 F2 F3

Press F1 for LEVEL or F3 for SPAN Adjust levels by pressing either

F1 or F3 and then F2 when done.

F1 F2 F3

SETTING LEVEL AND SPAN

AUTOMATIC OR MANUAL OPERATION

If you take pictures with a digital camera, you can easily use the Ti20. The Ti20 image

level and span can be set automatically by the Imager or manually adjusted, similar to

adjustments you can make on a digital camera.

AUTOMATIC MODE

In the automatic mode, the Imager determines the level and span based on the temperature of the target.However, in a more sophisticated thermal scene (upper right) the Imager expands the level to include all temperatures that are present.

Hot Ambient Cold

MANUAL MODE

Cold Water Cup

Ambient Water Cup

By simply setting the LEVEL slightly higher, a readjusted image appears.

To refine a portion of the image, adjust the level or span settings manually.

F1 F2 F3

The Imager can store up to 50 images. In just a couple of easy steps you can store images for later analysis and adjustment.

Point the imager at the target you want to record, squeeze the trigger once to capture the image.

Inspect the image, if satisfactory, press F1 to store the image. If an image is already stored in the memory location a prompt will ask you to confirm.

Squeeze the trigger or press F1 (yes) to return to live viewing.

STORING IMAGES

F1 F2 F3

With the imager turned on, press F2 (MENU) until MEMORY is over the F1 key.

Press F1 twice to review images stored in the Imager.

Press F1 (up arrow) or F3 (down arrow) to cycle through the images.

RETRIEVING IMAGES

F1 F2 F3

Use the Compare function to ensure that you have captured an image from the correct position and distance from the target.

With the captured image on the display, press F3 (COMPARE).

Press F1 to retrieve the next stored image or F3 to review the previous stored image. NOTE: Stored images appear on the right side of the display.

Press F2 (DONE) to save the captured image. This will overwrite the current image location.

COMPARING IMAGES

F1 F2 F3

OTHER IMAGER SETTINGS

Step 1:Press F1 to select Emissivity or F3 to select Reflected Temperature Compensation (RTC).

Step 2:Press F1 to increase the setting or F3 to decrease the setting.

An in depth description of emissivity and RTC follows. F1 F2 F3

Step 1 Step 2

CHANGING PALETTES

RainbowGreat for Reports

IronbowGreat for Routes and easy to focus with

Gray and Reverse GrayEasiest to Focus With

Different palette selections may result in more clarity or definition

Accuracy depends on many factors, including: Calibration of the camera Emissivity correction Reflected temperature

compensation Distance to object ratio

FACTORS FOR MEASUREMENT ACCURACY

F1 F2 F3

When the Imager is first turned on, the image freezes briefly and an hourglass icon appears on the display.

The Imager then momentarily shuts down the optical channel to eliminate offset errors and performs a recalibration sequence.

You can manually activate the internal recalibration sequence at any time by pressing the F3 (FLAG) key from the Home display.

FLAG *(INTERNAL CALIBRATION)

* Also known as the non-uniformity correction or NUC

RADIOMETRIC TEMPERATURES

Reflected

Only emitted radiation relates to the temperature of the object.

Emitted

Not all radiometric temperature measurements are “real”.The Ti20 measures the total radiation coming from a surface, that includes radiation:

Emitted by the objectReflected by the object

THE REASON? EMISSIVITY…

437°F

410°F82°F

424°F

Coated Surface

Shiny Aluminum

HOW TO SET EMISSIVITY

Use emissivity tables as guidelines only

F1 F2 F3

Press F1 or F3 to raise or lower the emissivity setting.

Low-emissivity objects are quite reflective of their thermal surroundings

Many materials are highly reflective to infrared radiation

REFLECTIVITY

MEC 520 – Energy Technology Thermodynamics

04/18/2023 65

REFLECTED TEMPERATURE COMPENSATION

Targets that have low emissivities will reflect energy from nearby objects. This additional reflected energy is added to target’s own emitted energy and may result in inaccurate readings.

Reflected Energy

Emitted Energy

Use the RTC function to compensate for reflected temperature from emitted energy

In some situations objects near the target (machines, furnaces, or other heat sources) have a temperature much higher than that of the target.

And in other cases the reflected temperature may be lower than the target such as when a clear sky is reflected.

F1 F2 F3

Press F3 to select the RTC setting and F3 again to adjust the setting, press F2 when done.

Step 1 Step 2 Step 3

F1 F2 F3 F1 F2 F3

SETTING RTC

CORRECTING MEASUREMENTS

*>48.4°C

*<31.8°C

Accurate measurements require that you adjust the emissivity and reflected temperature compensation values.

Measurements of shiny metal surfaces are not recommended because they will be unreliable.

Whenever possible, make measurements of high-emissivity surfaces, i.e. non-shiny metal, such as paint or electrician’s tape, or on a rough surface. (Avoid touching hot or energized surfaces).

Emissivity tables are useful mainly as guidelines.

Using the correct Reflected Temperature Compensation (RTC) is critical to making accurate radiometric measurements.

QUALITATIVE VS. QUANTITATIVE

Qualitative (Most of the images that are taken)

Qualitative inspections utilize thermal differences to locate anomalies.

1. Thermal differences are sufficient to indicate most abnormalities in electrical and mechanical equipment

2. Schedule corrective maintenance activities based on findings

QuantitativePrecise temperature or temperature distribution

measurement

3. Slight variations caused by changes in emissivity, atmospheric conditions and other factors could distort the readings

4. Distortions in the values measured can be caused by spot size of the target object and the environment in the background

REAL WORLD EXAMPLE

I can see a hot spotBut I can’t measure it!

When I move closer, I can measure it!

Qualitative Quantitative

RESOLVING DETAIL

Resolution defines the ability of the Ti20 to resolve and measure detail at a given distanceIt is possible to detect objects that are too far away or too small to accurately measure.

Just because you can see it doesn’t mean you can accurately measure its temperature

WHAT CAN YOU SEE AND MEASURE?

The Ti20 can detect objects at a “distance

to spot size ratio” (D to S) of

approximately 75:1. For example:

At 75” a 1” spot can be detectedAt 75m a 1m spot can be detectedAt 2m a 2.67cm spot can be detected

To measure, we need to be closer or have

the object be larger

MINIMUM DISTANCE FOR FOCUSING

At the minimum focus distance of 60cm (24”), you can measure a target as small as 7mm (0.27”)

When possible, move as close as you safely can to fill the image with the object of interest

To get a wider field of view step back from the object you are measuring

WE SEE SURFACE TEMPERATURES ONLY

For the most part, we see surfaces

However, the heat we are interested in knowing about usually originates from the inside

What is the relationship between an internal heating source and the outside surface we are viewing?

WHAT DOES THIS MEAN TO YOU?

Many problems will actually be hotter than they appear on the surface

Net flow of energy is from warmer to cooler areas

Flow can be: Transient (changing) Steady-state (stable)

Some problems may not be detectable under certain conditions

ELECTRICAL INSPECTIONS

Typical patterns are:

High resistance connections or contact surfaces

Imbalances and overloads

Many components are normally warm, including:

Normally loaded circuitsContactor coilsTransformersOverload heatersCapacitorsResistors

Key inspection pointsBearingsCouplingsElectrical connectionsOverall temperature

Poor cooling Internal problems

MOTORS

04/18/2023 MEC 520 – Energy Technology Thermodynamics 80-1 8 .8 °C

4 8 .2 °C

L I0 1

TANK LEVELS

Locate fluid, solid, and “floater” levels

Tank sludge clearly identified

11 9 .7 °C

3 0 2 .2 °C

REFRACTORY INSULATION

Look for Hot areas associated

with refractory thinning or failure

Cold areas associated with internal product build-up

STEAM TRAPSWorking traps will have hot and cold sides

Failed-open traps will be hot on both sides

Normal

FaultyMEC 520 – Energy Technology

Thermodynamics04/18/2023 82

An important part of your total solution

INSIDEIR SOFTWARE

IMAGE STORAGE AND ROUTE ORGANIZATION

Organize and store all of your images in a Windows™ style format

IMAGE STORAGE AND ROUTE ORGANIZATION

Change route by simply dragging an image to a new position with your mouse

IMAGE ANALYSIS AND SHARING

Adjust image properties through software after the image is stored

Input location name from your keyboard

Change emissivity and RTC in post processing

Turn on a temperature grid

Insert accurate point measurements or Min/Max/Average area measurements

Insert comments

When the grid is displayed, average temperature values are displayed in each box

Display accurate point or Min/Max/Average area measurements

TEMPERATURE TABLES, PROFILES AND HISTOGRAMS

Logo can be changed from file

Inputs for:Company NameProblem NumberLocation Name and EquipmentProblem DescriptionWeather ConditionsRoute DataMaintenance Action InformationRepair Priority AssignmentReinspection SignoffPre /Post Thermal Image or Pre Thermal /Post Digital Image

THERMOGRAPHIC REPORTING

Export as: PDFWordRTFExcel

MEC 520 F15 Lecture 2(1)

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