lecture slides: lecture thermodynamics

1Challenge the future

P‐L‐1

Thermodynamics

The Modelling Team Department of Design Engineering

Faculty of Industrial Design EngineeringDelft University of Technology


Aim

To develop basic understanding of thermodynamics;

To demonstrate that products with simple heat transfer behaviour can be modelled to provide useful data for designs;

To communicate with experts in their professional languages.

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2

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The contents

• 0th law of thermodynamics• 1st law of thermodynamics

• Case study: The cool box

• Conduction• Convection• Radiation

Fundamentals 1

Heat transfer2

Thermal resistance network3

`Industrial applications4

Summary5


FundamentalsThermodynamics is the study of transformations of energy


0th law of thermodynamics

0th Law of thermodynamics

Object ATemperature T0

Object BTemperature T0

Object CTemperature T0

Thermal Equilibrium

Thermal Equilibrium

Thermal Equilibrium

If two systems (A, B) are in thermal equilibrium with a third system (C), they are also in thermal equilibrium with each other.


0th law of thermodynamics

Thermal Equilibrium Thermal Equilibrium

No Energy transferNo Energy transfer

Temperature

Courtesy of http://iceworld2008.wordpress.com/


Measuring temperature

Ref. http://en.wikipedia.org/wiki/ThermometerCourtesy of http://en.wikipedia.org/wiki/File:Pakkanen.jpg,

http://en.wikipedia.org/wiki/File:Thermocouple0002.jpg,http://www.kaz-europe.com/in/braun-thermoscan-3020/, Braun' is a registered trademark of Braun GmbH, Kronberg, Germany

Glass thermometer

Thermocouple

Infrared sensors

others

Thermo resistant

Gas thermometer

Langmuir probe

Etc.


1th law of thermodynamics 1st Law of thermodynamics

Q System

Boundary Surroundings

W

ΔU

U Q - W

The change in the internal energy (ΔU) of a system is equal to the amount of energy added (Q) by heating the system minus the amount lost as a result of the work done (W) by the system to its surroundings

Ref. http://en.wikipedia.org/wiki/First_law_of_thermodynamics


Conservation of energy

Any other energy change

Heat exchanged through the boundary

System

Sub‐system 1

Sub‐system 4Sub‐system 6

Sub‐system ...Sub‐system 2

Sub‐system 5Sub‐system 3

A: Area of the boundary


The three classical states


Latent heat – During the change of state

Q mL

SolidSolid liquidliquid GasGas

Courtesy of http://www.gabrielweinberg.com/blog/2010/11/code-icebergs.html


Specific heat capacity – With in a state

SolidSolid liquidliquid GasGas

Q mC T In the differential form

q t Heat flow rate


Heating & Cooling curve

Slope 2

Slope 1

Does slope 1 = slope 2?


Specific heat capacity

Slope 2

Slope 1Does slope 1 = slope 2?

Substance Phase Cp [J/(g·K)] Volumetric heat capacity [J/(cm3·K)]

Gold solid 0.129 2.492

Silver solid 0.233 2.44

Copper solid 0.385 3.45

Iron solid 0.450 3.537

Carbon dioxide CO2 gas 0.839

Glass solid 0.840

Aluminium solid 0.897 2.422

Air (Sea level, dry, 0 °C) gas 1.004 0.001297

Nitrogen gas 1.040

Water at -10 °C (ice) solid 2.050 1.938

Water at 100 °C (steam) gas 2.080

Polyethylene (rotomolding grade) solid 2.303

Animal (and human) tissue mixed 3.500 3.7*

Water at 25 °C liquid 4.181 4.186

Hydrogen gas 14.30

Specific heat capacity of common materials

Ref. http://en.wikipedia.org/wiki/Heat_capacity


Specific heat capacity: Case study

At a temperature of 15 °C, the heat required to raise the temperature of a water sample by 1 K (equivalent to 1 °C) is:

Key factors of radiation regarding heat transfer► 4186 joules per kilogram►This is the same amount of energy to lift a 1kg object to level of 418,6m (Potential energy of mechanics)

Case StudyCase Study1


Heat transfer


Three ways of heat transfer

1

2

In physics and thermodynamics, heat transfer is the process of energy transfer from one body or system due to thermal contact.

Heat transfer is defined as an energy transfer to a body in any other way than

due to work performed on the body.


Three ways of heat transfer3 ways of heat transfer

Hot object

Cold Object

Conduction via solid contact

Convection via fluid contact

Radiation via electromagnetic waves

Courtesy of http://www.roasterproject.com/2010/01/heat-transfer-the-basics/


Three ways of heat transfer

3 ways of heat transfer

Hot object

Cold Object

Conduction via solid contact

Convection via fluid contact

Radiation via electromagnetic waves

Temperature difference

Energy transfer happens due to


Conduction


Conduction: An case study

Case study: ConductionCase study: Conduction

373K

293K

A steel beamInitial Temperature 293K


Conduction

( ) ( ( ) ( ))hot coldkAq t T t T tL


Key parameters in conduction: K & A


Thermal conductivity

Material Thermal conductivity k [W/(m·K)]Air 0.025Wood 0.04 - 0.4Polypropylene 0.25Rubber 0.16Cement, Portland 0.29Water (liquid) 0.6Thermal grease 0.7 - 3Glass 1.1Concrete, stone 1.7Ice 2Stainless steel 12.11 ~ 45.0Steel, Carbon 1% 43Aluminium 237 (pure) 120—180 (alloys)Gold 318Copper 401Silver 429

Thermal conductivity of common materials

Ref. http://en.wikipedia.org/wiki/Thermal_conductivity


Thermal conductivity: A case study

AluminumAluminum

Structural steelStructural steel

Stainless steelStainless steel


Thermal resistant: Conduction

( ) ( ( ) ( ))hot colddQ t kA T t T t

dt L

( ) ( ) ( ) ( )( ) hot cold hot coldT t T t T t T tdQ tLdt RkA

LRkA


Understanding the thermal resistant


Convection


Natural convection


Convection: Newton's law of cooling

( ) ( ( ) ( ))hot coldq t hA T t T t

h Fluid propertiesThe velocity of Fluid

The typical Value of h

Air: 10~100Water: 500 to 10,000

Ref. http://en.wikipedia.org/wiki/Heat_transfer_coefficient


Thermal resistant: Convection

( ) ( ( ) ( ))hot colddQ t hA T t T t

dt

( ) ( ) ( ) ( )( )1

hot cold hot coldT t T t T t T tdQ tdt R

hA

1RhA


Case study: Cool an iron ball

The air is heated

Heat loss Absorb heat

Iron cools down

Effect

Cause

1/ 0

SystemThe iron The air

How long will it take to cool an iron?1. In still air2. With ventilations

Courtesy of http://www.philips.com

Choice: Except the area that exposed to the air, the iron is well insulated.


Case study: Cool an iron ball – The implementation

Ventilated Simulated by h=20

StillSimulated by h=10


Radiation


What is radiations

Courtesy of http://www.nuonsolarteam.nl

Radiation is a process in which energetic particles or energy or waves travel through a medium or space. There are two distinct types of radiation: ionizing and non‐ionizing.

Key factors of radiation regarding heat transfer► Frequency►Areas► Surface

RadiationRadiation

Courtesy of http://en.wikipedia.org/wiki/Radiation


The black body & The grey body

4 4( ) ( ( ) ( ) )obj envq t T t T t A

4 4( ) ( ( ) ( ) )obj envq t T t T t A


Thermal resistance network


Thermal resistances regarding conduction & convection

( ) ( ) ( ) ( )( )1

hot cold hot coldT t T t T t T tdQ tdt R

hA

ConductionConduction

ConvectionConvection

( ) ( ) ( ) ( )( ) hot cold hot coldT t T t T t T tdQ tLdt RkA

A more complicated scenario


Case study: thermal resistance network

Case study 2Case study 2

20 Watt

Inside air(20ºC initial)

OutsideAir (20ºC)

Aluminum

Insulator

Aluminum

Insulator

GoldGold

Case study 1Case study 1

20 Watt

Inside air(20ºC initial)

OutsideAir (20ºC)

Aluminum

Insulator

Aluminum

Insulator

Which one is hotter?Which one is hotter?


Case study: thermal resistance network

Case study 2Case study 2Case study 1Case study 1


Compose the thermal resistance network

22

1

gas

Rh A

13

1

LRK A

24

2

LRK A

51

1

liquid

Rh A

( )hT t ( )cT t

1 2 3 4 5 6

( ) ( )( ) h cT t T tq tR R R R R R

11

1

gas

Rh A

62

1

liquid

Rh A

If we don’t neglect the heat

capacity


Case study: The cool box

Air in the oven

Layer 1 of the cool box

Layer 2 of the cool box

The air inside

Put a cool box in an oven whichis heated to 80 degrees (constant), What is the relations between the Inside temperature and the time? The initial temperature of the cooling box is 20 °C.


Case study: The cooling box - Cause-effect

Layer 1is heated

Hot air

Effect

Cause

Layer 1is heated

Layer 2 is heated

Effect

Cause

Layer 2is heated

Air inside is heated

Effect

Cause

Cause effect: AbstractCause effect: Abstract


Case study: Thermal resistances

1

/2

/2

/2

/2

1


Case study: Cause-effect regarding layer 1

Cause-effect regarding hot air to layer 2

Layer1 temperature higher than layer 2

Heat transferred to layer 2 – q3


Hot air

Effect

Cause

Layer 1 absorb heat

Temperaturearise – q2

1 2 2 20


Case study: Cause-effect regarding layer 2

Cause-effect regarding hot air to layer 2

Layer2 temperature higher than air

Heat transferred to air – q5


Hot air

Effect

Cause

Layer 2 absorb heat


2 2 2 10


Case study: Cause-effect regarding air

Cause-effect regarding hot air

Heat transferred to air – q5

Layer2 temperature higher than air

Effect

Cause

Air absorb heat


2 10


The implementation

T3T4

T2

T1


Industrial design applications


Conduction, Convention or Radiation?

Thermo-dynamics

& heat transfer

Courtesy ofhttp://en.wikipedia.org/wiki/Infrared_heater

http://en.wikipedia.org/wiki/Radiatorhttp://missouribeefcouncil.com/?m=201004

http://www.tefal.comhttp://www.daalderop.nl

http://www.ikea.nl


Summary1

2

3

• Basic law of thermodynamics

• Heat transfer

• Case studies

To develop basic understanding of thermodynamics;

To demonstrate that products with simple heat transfer behaviour can be modelled to provide useful data for designs;

To communicate with experts in their professional languages.

1

2

3


Thank You

The Modelling Team Department of Design Engineering

Faculty of Industrial Design EngineeringDelft University of Technology

lecture slides: lecture thermodynamics

Education

latent heat

heat transferchallenge

simple heat transfer

thermal contact

process of energy transfer

future11courtesy of

system c

thermal grease0