note 1 temperature & thermometers

7/23/2019 Note 1 Temperature & Thermometers

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Heat and Temperatur

Eng.A.A.Hafeel

Ahamed

BSc(

Eng

)(1

st

Class honor)

Design Engineer



What is Heat??

Heat = Thermal Energy!!

Thermal Energy = the total energy of all of the particlesmaterial or object.

Throughout the ages people have invented a variety odevices to help create and capture heat for use.

2

Eng.A.A.Hafeel Ahamed



Using Energy from Heat……

What are some ways that we use heat?

Cook food

Warm buildings

Dry clothes

3


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Sources of Thermal Energy

Energy appears in many forms

Potential Energy: Stored energy

E.g. elastic pulled back and ready t

Kinetic Energy: Energy of motion

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Chemical Energy

Stored chemical energy is released in the formthermal energy when it is burned.

5


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Electrical Energy

Electricity

Example: hydro-electric dams – falling water ischanged to electrical energy

6




Geothermal Energy

Energy that we get from the Earth’s

interior

7




Active Solar Energy

Uses mechanicaldevices to distributestored thermal energy

Example: fans

Solar Collectors – usestored water or air onthe roof, heats it, andthen pumps it throughthe building

10




Wind Energy

Moving air

Is a result of solarenergy – as the sunheats the air, thewarmer air rises and

cools off. Cooler airfalls, creating aconvection current – this forms wind

11




Fossil Fuels

Chemicals made from plants and animals thadecomposed millions of years ago and have deep underground.

12




Energy Converters

Energy can be converted into another for

For example a candle can convert chemienergy into heat and light energy.

Candles are energy converters (devices wconvert or change energy from one form another.)

Other examples????

13


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Renewable Resources

Definition:Renewableresources are anatural resourcethat grow at about

the same rate theyare used up.

14




Non-Renewable Resource

Definition:

A resource whiclimited in supplcannot be replonce it is used.

15




Renewable Resources in Albert

Examples:

Trees (Forestry)

Wind (Wind Farms)

Agriculture ( One of the biggest crop producers in Canada)

Water (Dams and water conservation)

Solar ( Solar Panels and Solariums)

16




Non-Renewable Resources in

Alberta

Examples:

Oil (Oil Wells)

Natural Gas (Pipelines across the province)

Coal (Mining in Alberta)

17




Temperature & it s Measureme

LORD KELV


18

http://localhost/var/www/apps/conversion/tmp/scratch_5/LORD%20KELVIN.doc



Temperature

Temperature is a measure of hotness or coldneS.I. unit: Kelvin (K)

Celsius scale(Practical Scale)

Temperature (in degree Celsius) =

Temperature in Kelvin – 273.15

Note: 0o C = 273.15 K

100o C = 373.15 K

The current working temperature scale is the International Scale of 1990 (ITS-90) and is measured in degrees Celsius

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http://localhost/var/www/apps/conversion/tmp/scratch_5/THE%20INTERNATIONAL%20TEMPERATURE%20SCALE.doc







20Temperature

Temperature

• is a measure of how hot or coldan object is compared toanother object.

• indicates that heat flows from theobject with a higher temperature

to the object with a lowertemperature.

• is measured using a thermometer.




Measuring Temperature….

Thermometer: Mechanical or electrical device for temperature. Early thermometer was invented by G

Scale: A series of equally measured sections that aand numbered for use in measurement.

21




Measuring Temperature

1. The length is taken at 0o C (inmelting ice) = l0

2. The length is taken at 100o C(in boiling water) = l100

3. A graph of temperature versuslength is plotted

4. Any temperature can then beread from the graph = lθ

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http://localhost/var/www/apps/conversion/tmp/scratch_5/Calculations%20on%20Temperature%20Scales.doc

http://localhost/var/www/apps/conversion/tmp/scratch_5/TRH%2027-28.doc



23Temperature Scales

TemperatureScales

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

• are Fahrenheit,Celsius, andKelvin.

• have reference

points for theboiling andfreezing pointsof water.




24

• On the Fahrenheit scale, there are 180°F between

the freezing and boiling points and on the Celsiusscale, there are 100°C.

180°F = 9°F = 1.8°F

100°C 5°C 1°C

• In the formula for the Fahrenheit temperature,adding 32 adjusts the zero point of water from 0°C

to 32°F.

TF = 9/5 TC + 32

or

TF = 1.8 TC + 32

Fahrenheit Formula




25

The Kelvin temperature scale

• has 100 units between the freezing and boiling pointsof water.

100 K = 100°C or 1 K = 1°C

• is obtained by adding 273 to the Celsius temperature.

TK = TC + 273

• contains the lowest possible temperature, absolutezero (0 K).

0 K = – 273°C

Kelvin Temperature Scale




THERMO METERS


26



Thermo

Thermometers measure temperature.

Note:

1. Temperature is a number which gives the degreof a body on a chosen scale. (degree at whichoccurred).

2. When we measure temperature we measure a tproperty.

3. Two different thermometers do not necessarily givreading at the same temperature. Different Th

properties vary differently with temperature

27


Thermometric prope



Thermometric prope

Any physical property that changes measurably temperature.

Examples

1. Length of column of Liquid.

2. Electrical resistance.

3. EMF of a Thermocouple Thermometer.

4. Colour.

5. Pressure of a gas at constant volume

6. Volume of gas at constant pressure

28


Standard Thermometer



Standard ThermometerCelsius Scale for given thermometric property

• A temperature scale is needed with two fixed points (normallthe freezing and boiling point of water)

• A thermometric property is needed, such as the length of acolumn of liquid in a glass tube

29

Measuring Temperature(Hg-in-glass thermometer

As School standard)

•Use un-graduated thermometer.

•Place in pure melting ice, mark position = l0 (0 on celsius scale)

•Place in steam above pure boiling water, mark position = l100 (100 on cels

scale)




CALIBRATION CURVE OF A THERMOMETER USING THE LABO

MERCURY THERMOMETER AS A STANDARD

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Celsius Scale

Celsius Scale: Most commonly used in Canadtemperature is called a degree. Based on theand freezing points of water.

Boiling Point: The temperature at which waterC at sea level.

Freezing Point: The temperature at which wat0o C at sea level.

31


Glass Thermo meters

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Glass Thermo meters32




The Liquid in Glass Thermometer

The Liquid in Glass thermometer utilizes the variation in volume

temperature.

They use the fact that most fluids expand on heating. The fluid is

sealed glass bulb, and its expansion is measured using a scale

stem of the thermometer If we consider that the thermom

expand then as physical property it utilizes the variation of lengttemperature.

Liquid in Glass thermometers have been used in science, medic

and industry for almost 300 years.

Liquids commonly used include Mercury and Alcohol.

33




Structu

Two basic parts:

a. The bulb:

Acting as a reservoir holding the liquid whosevolume changes with temperature. The Bulbalso acts as a sensor or gauge which isinserted in the body whose temperature is tobe measured

b. The Stem:

containing the scale that is measuring thetemperature and a capillary through whichthe liquid can accordingly expand and

contract

34


G l P



General Prope

Advantages:

They are cheap to manufactureEasy to carry and handle.

Disadvantages

They tend to have high heat capacities. They are

enough, that is they cannot measure rapid temperatur

35


The mercury in glass therm



The mercury in glass therm

Invented by German physicist Daniel Gabriel Fahrenheit, is a

thermometer consisting of mercury in a glass tube.

Calibrated marks on the tube allow the temperature to be length of the mercury within the tube, which varies accordi

temperature.

To increase the sensitivity, there is usually a bulb of mercury

the thermometer which contains most of the mercury; expa

contraction of this volume of mercury is then amplified in th

narrower bore of the tube. The space above the mercury m

with nitrogen or it may be a vacuum.

Range: Covering a wide temperature range from -38 °C to

although the introduction of a instrument can increase the

°C or beyond.

36




Advantages:

1. Mercury is a naturally opaque liquid (Silver). This means

directly utilized in its pure form

2. Mercury does not wet glass. When it moves up and dow

capillary strong cohesive properties of mercury do not allo

any traces on the inside of the capillary.

3. Mercury is a liquid metal. As a metal it has high conduc

that allow it to be more sensitive than the alcohol in glass

Disadvantages:

1. Mercury poses a potential toxic hazard if the glass cont

ruptured.

37


Alcohol in glass therm



Alcohol in glass therm

As a liquid it utilises ethyl alcohol, toluene and technpentane, which can be used down to -200 °C.

Range c. -200°C to 80°C, though range tends to be dependent on the type of alcohol used.

38




Advantages:

1. It can measure very low temperatures.

Disadvantages:

1. Alcohol is transparent therefore it requires a dye tvisible. Dyes tend to add impurities that may not hatemperature range as the alcohol making reading

especially at the limits of each liquid.2. Alcohol wets glass.

39


Gas thermometers



Gas thermometers


40



The gas thermometers can be classified into two based on t

method by which the gas can be heated. They are,

Constant Pressure Gas Thermometer

Constant Volume Gas Thermometer.

The constant pressure gas thermometer is not used in practi

because of the errors which arise due to the non – uniformi

bore.

The constant volume gas thermometer is the most accurat

laboratory thermometer and is used for the calibration of o

thermometers.

41




CONSTANT VOLUME GAS THERMOM

When we heat a gas keeping the volume copressure increases and when we cool the gas

decreases.

The relationship between pressure and temp

constant volume is given by the law of pressure.

to this law, the pressure of a gas changes by o

pressure at 0oC for each degree centigrade (or C

temperature at constant volume.

42


CONSTANT VOLUME GAS THERMO




If Po is the pressure of a given volume of a gas at 0oC and

the pressure of the same volume of the gas (i.e., at constant

volume) at toC, then

i.e., (or) (1)

Where is constant and is known as coefficient of

increase of pressure

t P

P P o

ot

273

)273

1( t

P P ot

)1( t P P vot

273

1

v

43


It consists of a glass bulb B connected to a tube A



capillary glass tube ‘C’.

The tube A is connected to a mercury reservoir R

clamped on the board and can be lowered or raise

required to keep the volume of the air constant.

The capillary tube C is provided with a three way

can be used to connect capillary and bulb as well

tube from bulb B.

A pointer is provided such that the end P is projec

the upper part of A.

A scale calibrated in 0o

C is provided between A an

44






The whole apparatus is levelled by adjusting the l

By adjusting the stopper, the bulb ‘B’ is filled witand the pointer is adjusted so that tip of the pointer

level of mercury in the tube A. After filling the bul

ice bath for some time till the air inside the

temperature of ice at which the mercury level becom

Now the reservoir R is adjusted so that the level o

tube A just touches the tip of the pointer P.

46


CONSTANT VOLUME GAS THERMOMETER




The difference between the mercury levels in the two tube

and let it be ho. If Po is the pressure exerted by the air in

then

Now ice bath is removed and the bulb B is surrounded with

Again when the mercury level in both the tubes becomes

tube R is adjusted so that the mercury column in this positi

A touches the tip of the pointer.

0h P P

o

47






Let the difference between the mercury column levels in A an

The pressure of the enclosed gas in B will be given by,

If is the pressure coefficient of the air, then from equathave

100100 h P P o

v

)1001(100 vo P P

1000100 vo

P P P

48





Finally the bulb is brought in contact of the body whose tem

be found out.

After the mercury level becomes stationary, the tube R is adj

the mercury level touches the tip of the pointer again.

Let ht be the difference between the heights of mercury level

the pressure of the air inside the bulb B, then we have,

t ot h P P

49





and

(or) (6)

Dividing equation (6) by equation (4), we get

)1( t P P vot

t P P P vot

0

1000

0

0100 v

vot

P

t P

P P

P P

100

0100

0

P P

P P t

t

50





Substituting and in

equation (7), we get,

(8)

t t h P P 0 1000100 h P P

100)()(

)()(

001000

000

h P h P

h P h P t

t

100

0100

0

hh

hht

t

51




MERITS

Gas thermometers are more sensitive when compared to other t

They work uniformly and regularly over a wide range of tempe

They can be used to measure low and high temperatures and ha

range of operation. ( – 200oC to 1600oC)

Since the expansion of glass is negligible when compared to ththe gas the error due to expansion of glass is negligible.

52


53



DEMERITS

It takes time to measure the temperature and is not a qu

thermometer.

These thermometers can be used only in some cases wh

can be brought in contact with the bulb.

They are not easily portable.

53


Pt resistance thermometer54



54


The resistance thermometer55



The resistance thermometer

Makes use of the change of resistance in a metal wire with tem

As electrons move through a metal, they are impeded by the vibrations of the atoms in the crystal lattice.

The higher the temperature the greater the impediment to flow

higher the resistance.

This effect is very marked in pure metals, and for a well-behave

enables measurements of temperature to be made to better t

55


56



Usually platinum wire is used in the construction of t

thermometer, since it is a noble metal which is un-re

over a wide range of temperatures.

But copper, nickel and rhodium alloy may also be

various temperature ranges.

Usually a coil of the pure wire is wound onto an alu

or placed in the bores of an alumina tube, and this

mounted in a steel tube.

56


57



Resistance thermometers are slowly replacing therm

in many lower temperature industrial applications (

600°C).

Resistance thermometers come in a number of co

forms and offer greater stability, accuracy and rep

The resistance tends to be almost linear with tempe

A small power source is required.

57


No special extension cables or cold junction compensations are re

58



The resistance of a conductor is related to its temperature.

Platinum is usually used due to its stability with temperature.

The Platinum detecting wire needs to be kept free of contaminatio

stable.

A Platinum wire or film is created and supported on a former in suc

gets minimal differential expansion or other strains from its former, y

reasonably resistant to vibration.

58


Advantages

1. Depending on the metal being used resistance the59



1. Depending on the metal being used resistance theable to cover extensive temperature ranges. Maximugenerally related to the melting points of the metal us

2. Variation of resistance with temperature is stable ov

extensive temperature range.

3. Very accurate

Disadvantages

1. Compared to liquid in glass thermometers, they tenexpensive.

2. Require other equipment to measure temperature.

3. They exhibit high heat capacities thus they are not temperature change meaning that they cannot be umeasure rapid temperature changes.

59


Thermo couple60



60


The Thermocouple61



Wires made up of two different metals aretwisted together.

When the wire tips are heated, a smallelectric current is generated

The amount of current depends on thetemperature.

They can measure higher temperatures than

thermometers. The electric current can be used to turn

switches on or off if the temperaturechanges.

Used in kilns, diesel engines and industrialfurnaces

61


Thermoco As a Thermometric property thermocouples62



As a Thermometric property thermocouplesutilize the variation of EMF generated at abimetallic junction with temperature.

In 1821, the German-Estonian physicistThomas Johann Seebeck discovered thatwhen any conductor (such as a metal) issubjected to a thermal gradient, it willgenerate a voltage. This is now known asthe thermoelectric effect or Seebeck effect.

62


63



Many different thermocouple combinations have been used

are standardized.

These include 3 noble metal thermocouples using platinum a

rhodium alloys, widely used for temperature measurement u

The remaining 5 mainly use nickel-based alloys, which are ch

more suitable for industrial use up to about 1200 °C.

Other refractory alloys can be used up to and beyond 2000

63


64



Advantages:

1. Cheap to manufacture.

2. The simplicity, ruggedness, low cost, small

size and wide temperature range of

thermocouples make them the most

common type of temperature sensor in

industrial use.

3. Low heat capacities making it capable

of measuring rapid temperature changes.

Disadvantages:

1. Sensitivity reduces ac


Bimetallic Strip65



Made of two different

joined together When the strip is heate

metal expands more tother

Thus the strip coils more

Movement of the strip

operate a switch that control furnaces…comused in thermostats in


Another Scale…66



Another Scale…

Kelvin is another way of measuring temperature.

Scientists use Kelvin to explain the behaviour of gases.

“Absolute Zero” is measured in Kelvin – which is the coldest ptemperature

0 Kelvin = -273 ºC


Right Device for the Job67



g

Each thermometer has a sensor – a material which is affectein the environment (such as temperature)

The sensor produces a signal (information about temperatureelectrical current) which affects a responder (a pointer, light mechanism that uses the signal in some way)


Continued68



Recording Thermometer: A bimetallic strip connected to a w

and paper which records temperature fluctuations over time

Infrared Thermogram: Records infrared radiation, (heat sensocolors according to their temperature.


Temperature vs. Thermal Energy69



p gy

Temperature = A measure of the average energy of the partmaterial.

Thermal Energy = The total energy of all the particles in a ma

What is the difference??


Bimetalic70

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•

Filled System/Distant Reading71

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Radiation and optical72



p


note 1 temperature & thermometers

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