Thermal Energy Management in Vehicles E-Book

Vincent Lemort

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Automotive Series
• Sprache: Englisch

Seitenzahl: 663

Veröffentlichungsjahr: 2023

Beschreibung

THERMAL ENERGY MANAGEMENT IN VEHICLES Comprehensive coverage of thermal energy management systems and components in vehicles In Thermal Energy Management in Vehicles, a team of distinguished researchers delivers a robust and authoritative account of thermal energy management systems and components in vehicles. Covering three main areas--the thermal management of internal combustion engines, mobile air-conditioning, and thermal management of hybrid electric vehicles and electric vehicles--the book discusses and proposes simulation models for many of the components and systems introduced in the book. The authors also cover state-of-the-art and emerging technologies, as well as likely future industry trends, and offer an accompanying website with supplementary materials like downloadable models. Readers will also find: * Material that bridges the gap between academia and industry * Proposed simulation models for vehicular components and systems * Fulsome discussions of industry trends likely to take hold in the near future * Accompanying online resources, including downloadable simulation models, on a complimentary website Perfect for researchers, graduate students, and practitioners in automotive engineering, Thermal Energy Management in Vehicles will also benefit anyone seeking a comprehensive treatment of vehicular thermal energy management systems and components.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Acknowledgments

Nomenclature

About the Companion Website

Introduction

1 Genesis

2 Vectors of Evolution of Thermal Systems

3 The Regulatory Constraints of Change

4 The First Three Revolutions of the Twenty‐First Century

5 Ambition of the Authors

6 Organization of the Book

References

1 Fundamentals

1.1 Introduction

1.2 Fundamental Definitions in Thermodynamics

1.3 Fluids

1.4 Heat Transfers

1.5 First Law of Thermodynamics

1.6 Second Law of Thermodynamics

1.7 Flows in Hydraulic Circuits

1.8 Heat Exchangers

References

2 Internal Combustion Engine Thermal Management

2.1 Introduction

2.2 Fundamentals of Internal Combustion Engines

2.3 Engine Cooling and Heating

2.4 Oil Cooling

2.5 Charge Air Cooling (CAC)

2.6 Exhaust Gas Recirculation (EGR) Cooling

2.7 Front‐End Module

2.8 Engine Waste Heat Recovery

References

3 Cabin Climate Control

3.1 Introduction

3.2 Thermal Comfort

3.3 Cabin Thermal Loads

3.4 Distribution of Thermal Energy Through the Cabin

3.5 Production of Cooling Capacity

3.6 Production of Heating Capacity

3.7 Local Cooling and Heating Systems

3.8 Thermal Energy Storage

References

4 Thermal Energy Management in Hybrid and Electric Vehicles

4.1 Introduction

4.2 Classification of Electric and Hybrid Electric Vehicles

4.3 Cabin Thermal Control in HEVS and EVs

4.4 Battery Thermal Management (BTM)

4.5 E‐Motor and Power Electronics Cooling

4.6 Overall Thermal Energy Management of Electrified Vehicles

References

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1 Heat of vaporization of three different fluids at 0°C.

Table 1.2 Major characteristics of mobile A/C refrigerants.

Table 1.3 Typical values of convection heat transfer coefficients.

Table 1.4 Classification of the heat exchangers according to the phases of ...

Table 1.5 Relation between epsilon, NTU, and Cr for different flow configur...

Chapter 2

Table 2.1 Properties of Gasoline and Light Diesel.

Table 2.2 Typical operating conditions of the different heat exchangers loc...

Chapter 3

Table 3.1 Metabolic rate during vehicle driving (ISO 14505‐2:2007).

Table 3.2 Thermal sensation scale.

Table 3.3 Recommended whole body equivalent temperature as a function of me...

Table 3.4 Optical properties of conventional glazing and advanced glazing....

Table 3.5 Values of working cycle frequency for different compressor techno...

Table 3.6 Comparison of specific energy contents and energy densities of di...

Chapter 4

Table 4.1 Comparison of thermal properties of glycol water and air.

List of Illustrations

Introduction

Figure 1 Self‐propelled wagon as drawn by da Vinci.

Figure 2 One of the first steam‐driven cars by Belgian Ferdinant Verbiest....

Figure 3 Cugnot's Steamer (“Fardier de Cugnot”), tested in Paris in 1770.

Figure 4 “La Jamais contente (or Never‐Happy)”.

Figure 5 Yearly evolution of the allowed emission limits in CO

2

per kilomete...

Figure 6 Allowed emission limits for diesel engines from Euro 1 (1992) to Eu...

Figure 7 Evolution of the European GHG emissions relative to 1990 per sector...

Figure 8 Global greenhouse gas emissions per sector.

Figure 9 Evolution of regulations regarding pollutant emissions.

Figure 10 CO

2

emission level for RW, NEDC, and WLTP regulation evolutions.

Chapter 1

Figure 1.1 System, boundary, surroundings, and universe.

Figure 1.2 Mechanisms of energy transfer between an open system and its surr...

Figure 1.3 Example of an open system with a moving boundary.

Figure 1.4 Steady‐flow period following a transient period.

Figure 1.5 Moving boundary work interaction in a piston‐cylinder apparatus....

Figure 1.6 Work transmitted at a shaft.

Figure 1.7 Spring work.

Figure 1.8 Work necessary to raise and accelerate a system.

Figure 1.9 Temperature–volume diagram of a pure fluid (different lines of co...

Figure 1.10 Pressure–enthalpy diagram of a pure fluid (different lines of co...

Figure 1.11 Liquid–vapor saturation curves for different fluids commonly use...

Figure 1.12 Evolution of the freezing temperature of an aqueous solution of ...

Figure 1.13 Working principle of a psychrometer.

Figure 1.14 Visualization of the specific enthalpy of water vapor in the pre...

Figure 1.15 Example of a psychrometric diagram.

Figure 1.16 Basic processes in the psychrometric diagram.

Figure 1.17 Spectral distribution of the ratio of the emissive power to the ...

Figure 1.18 Coupling between a heat engine (a)/heat pump (b) and the heat so...

Figure 1.19 Carnot heat engine and refrigerator.

Figure 1.20 Description of the flow in a hydraulic circuit.

Figure 1.21 Flow arrangement in a counter‐flow heat exchanger.

Figure 1.22 Flow arrangements in a parallel‐flow heat exchanger.

Figure 1.23 Flow arrangements in a cross‐flow heat exchanger.

Figure 1.24 Classification of heat exchangers according to the type of const...

Figure 1.25 Shell‐and‐tube heat exchangers used as EGR coolers. (a) Cutaway ...

Figure 1.26 Plates from a plate heat exchanger used as coolant‐to‐oil cooler...

Figure 1.27 Multi‐pass configuration of a BPHEX.

Figure 1.28 Components of a plate‐fin heat exchanger used as an evaporator....

Figure 1.29 Cutaway photograph of a bar and plate heat exchanger used as a c...

Figure 1.30 Cutaway photograph of a (flat) tube‐fin heat exchanger used as c...

Figure 1.31 Desegregation of the heat exchanger conductance into thermal res...

Chapter 2

Figure 2.1 Main components of an internal combustion reciprocating engine.

Figure 2.2 Internal combustion reciprocating engine main geometrical charact...

Figure 2.3 Strokes in a four‐stroke engine.

Figure 2.4 Definition of the heating value of the fuel.

Figure 2.5 Difference between a SI engine (a) and a CI engine (b).

Figure 2.6 WLTC cycle for class 3b vehicles (vehicles with maximum speed lar...

Figure 2.7 Representation of engine energy balance (engine equipped with a t...

Figure 2.8 Example of a measured indicated diagram. Engine: Toyota SI NA (na...

Figure 2.9 Representation of the Otto (a) and Diesel (b) cycles in the P—V d...

Figure 2.10 Typical operating temperatures in an ICE.

Figure 2.11 Conventional architecture of the engine liquid coolant loop.

Figure 2.12 Thermal energy transfer between the engine and the coolant and b...

Figure 2.13 Illustration of a tube‐and‐fin radiator.

Figure 2.14 Different louvered fins designs for brazed and mechanically asse...

Figure 2.15 Assembly of water tank, gasket, header, and tubes.

Figure 2.16 Horizontal flow (“cross flow”) and vertical flow (“down flow”) c...

Figure 2.17 I and U flow configurations in radiators.

Figure 2.18 Illustration of a radiator with a multi‐temperature configuratio...

Figure 2.19 Evolution of the heat rate dissipated by the radiator as a funct...

Figure 2.20 Schematic representation of an expansion tank.

Figure 2.21 Components and working principle of a wax‐type thermostat.

Figure 2.22 Simplified schematic representation of a wax‐type thermostat val...

Figure 2.23 Engine cooling circuit equipped with a thermostat with by‐pass v...

Figure 2.24 Engine cooling circuit equipped with a thermostat with by‐pass v...

Figure 2.25 Engine cooling circuit equipped with a thermostat located at the...

Figure 2.26 Characteristic curves of a wax‐type thermostat: visualization of...

Figure 2.27 Schematic representation of the integration of an electrically a...

Figure 2.28 Evolution of the coolant temperature at the engine outlet on the...

Figure 2.29 Air‐to‐oil cooler, tube–fin technology.

Figure 2.30 Coolant circuit associated with the use of an engine mounted oil...

Figure 2.31 Donut‐type coolant‐to‐oil cooler.

Figure 2.32 Stacked plate coolant‐to‐oil cooler.

Figure 2.33 Coolant and oil circuits associated with the use of an in‐tank o...

Figure 2.34 Illustration of the control of oil temperature by cooling water....

Figure 2.35 Schematic representation of a turbocharger connected to a water‐...

Figure 2.36 Schematic representation of a supercharger connected to an air‐c...

Figure 2.37 Electrically driven centrifugal compressor (e‐Supercharger).

Figure 2.38 Example of compound forced induction with a supercharger and a t...

Figure 2.39 Components of an air‐cooled CAC.

Figure 2.40 View of an air‐cooled CAC.

Figure 2.41 Components of a tubular water‐cooled CAC.

Figure 2.42 Schematic representation of the air/gas circuit of a diesel engi...

Figure 2.43 Schematic representation of the air/gas circuit of a diesel engi...

Figure 2.44 Illustration of a shell and round tubes EGRC (length × diameter:...

Figure 2.45 Illustration of a shell and flat oval tubes EGRC (width × height...

Figure 2.46 Schematic of a plate and fin EGRC – I‐flow.

Figure 2.47 Illustration of a plate and fin EGRC – U‐flow.

Figure 2.48 Illustration of a tube‐fin EGRC.

Figure 2.49 Thermal effectiveness and heat transfer rate of the EGRC as a fu...

Figure 2.50 Examples of heat exchangers configurations inside the front‐end ...

Figure 2.51 Cooling airflow path.

Figure 2.52 Example of air speed as a function of the vehicle speed (with an...

Figure 2.53 Coupling of the fan and system of heat exchangers.

Figure 2.54 Elements of the truck front‐end module.

Figure 2.55 Active Grille Shutters.

Figure 2.56 Schematic representation of the connection of the EHRS with the ...

Figure 2.57 Waste heat recovery from both EGR and exhaust gas: Series config...

Figure 2.58 Representation of the ORC in the T–s diagram. Green: working flu...

Chapter 3

Figure 3.1 Definition of the operative temperature.

Figure 3.2 (a): Actual environment; (b): Definition of the mean radiant temp...

Figure 3.3 Example of a human manikin divided into 27 heated zones.

Figure 3.4 (a) Practical realization of a thermal manikin.(b) Assembly p...

Figure 3.5 Example of use of omnidirectional sensors.

Figure 3.6 Split A/C system.

Figure 3.7 Evolution of the predicted percent dissatisfied (PPD) with the pr...

Figure 3.8 Definition of the angle of incidence.

Figure 3.9 Definition of the main angles used in the calculation of the dire...

Figure 3.10 Main energy transfer mechanisms between the cabin and its surrou...

Figure 3.11 Energy transfers through the cabin body.

Figure 3.12 Optical properties of a laminated glass.

Figure 3.13 Time evolution of the measured dashboard and head air temperatur...

Figure 3.14 Modeling of the cabin body by a R‐C approach.

Figure 3.15 Moisture transfer mechanisms between the cabin and its environme...

Figure 3.16 Time evolution of CO

2

concentration in cabin.

Figure 3.17 Time evolution of the cabin indoor temperature (1‐hour simulatio...

Figure 3.18 Different HVAC units.

Figure 3.19 Sectional drawing indicating components of the HVAC unit.

Figure 3.20 Partial recirculation of cabin indoor air.

Figure 3.21 Active cooling mode.

Figure 3.22 Control of the heating capacity with an air mix‐type configurati...

Figure 3.23 Demisting and defrosting modes.

Figure 3.24 Ventilation and heating mode.

Figure 3.25 Example of evolution of supply air temperature with the outdoor ...

Figure 3.26 Example of evolution of supply air flow rate with the outdoor ai...

Figure 3.27 Schematic representation of a vapor‐compression refrigerator.

Figure 3.28 Representation of the subcritical refrigeration cycle in a P‐h d...

Figure 3.29 Schematic of the integration of the A/C system in the vehicle th...

Figure 3.30 Integration of the A/C loop in the engine compartment.

Figure 3.31 Components of an A/C loop including an air‐cooled condenser and ...

Figure 3.32 Practical realization of a mechanical compressor.

Figure 3.33 Internal structure of an electric scroll compressor.

Figure 3.34 Theoretical indicator diagram of a piston compressor.

Figure 3.35 Evolution of the clearance volume contribution to the volumetric...

Figure 3.36 Section view of a fixed‐displacement swash plate compressor with...

Figure 3.37 Section view of a variable‐displacement swash plate compressor w...

Figure 3.38 Schematics of different designs of sliding vane compressors.

Figure 3.39 View of a sliding vane compressor (centered rotor).

Figure 3.40 Theoretical indicator diagram of compressors with a fixed built‐...

Figure 3.41 View of the fixed and orbiting scrolls of an electrically driven...

Figure 3.42 Operating principle of a scroll compressor.

Figure 3.43 Evolution of the theoretical isentropic effectiveness with the p...

Figure 3.44 Practical realization of a plate‐fin evaporator.

Figure 3.45 Refrigerant states in the condenser: 3‐zone representation.

Figure 3.46 Air‐cooled tube‐fin condenser.

Figure 3.47 Cross‐section of a folded tube used in a condenser with common d...

Figure 3.48 Water‐cooled condenser with an integrated receiver‐drier.

Figure 3.49 Sectional drawing indicating the components of a thermostatic ex...

Figure 3.50 Characteristic curve of a thermostatic expansion valve.

Figure 3.51 Coupling between the evaporator and thermostatic expansion valve...

Figure 3.52 Parallel charge‐type valve characteristic.

Figure 3.53 Quadrant Q1: Evaporator exhaust temperature as function of the e...

Figure 3.54 Position of the in‐line receiver, integrated receiver and accumu...

Figure 3.55 Internal structure of a receiver.

Figure 3.56 Condenser with an integrated receiver–drier.

Figure 3.57 Liquid zones inside the condenser‐receiver assembly for differen...

Figure 3.58 Evolution of the subcooling with the charge of refrigerant insid...

Figure 3.59 Internal structure of an accumulator.

Figure 3.60 Schematic representation of a vapor‐compression A/C loop equippe...

Figure 3.61 Representation of the vapor‐compression A/C cycle with an intern...

Figure 3.62 Automatic climate control.

Figure 3.63 Internally and externally controlled displacement valve

Figure 3.64 Evolution of the air temperature in the HVAC unit: comparison be...

Figure 3.65 Simple model of an A/C loop equipped with a TXV.

Figure 3.66 Simple model of an A/C loop equipped with a TXV (assumption of c...

Figure 3.67 Representation of the refrigeration cycle in the P‐h diagram.

Figure 3.68 Heater core.

Figure 3.69 View of a PTC heater.

Chapter 4

Figure 4.1 EU passenger car CO

2

emissions targets, normalized to NEDC.

Figure 4.2 Energy flow representation of the powertrain of a battery electri...

Figure 4.3 Energy flow representation of the powertrain of a series hybrid c...

Figure 4.4 Energy flow representation of the powertrain of a parallel hybrid...

Figure 4.5 Energy flow representation of the powertrain of a series–parallel...

Figure 4.6 Air‐to‐air heat pump in the cooling mode.

Figure 4.7 Air‐to‐air heat pump in the cooling mode.

Figure 4.8 Air‐to‐air heat pump in the heating mode.

Figure 4.9 Inner condenser: extruded tubes and fins (Courtesy of Valeo).

Figure 4.10 Air‐to‐air heat pump in the dehumidification mode.

Figure 4.11 Air‐to‐air heat pump in the OHEX defrosting mode.

Figure 4.12 Air‐to‐water heat pump in the heating mode.

Figure 4.13 Water‐to‐air heat pump for battery waste heat recovery.

Figure 4.14 Water‐to‐water heat pump in the cooling mode.

Figure 4.15 Water‐to‐water heat pump in the heating mode.

Figure 4.16 Evolution of the powers and COP with the compressor rotational s...

Figure 4.17 Cells, modules, and battery pack.

Figure 4.18 Different geometries of cells.

Figure 4.19 Representation of a Lithium‐Ion battery in discharging and charg...

Figure 4.20 Open Circuit Voltage as a function of the ampere‐hours discharge...

Figure 4.21 Illustration of the state of charge (SOC), depth of discharge (D...

Figure 4.22 Evolution of cell voltage as a function of DOD for different C‐r...

Figure 4.23 Schematic illustrating capacity loss during charging and dischar...

Figure 4.24 Thermal behavior of lithium‐ion battery: calendar and cycle agin...

Figure 4.25 Influence of temperature on battery behavior.

Figure 4.26 Different zones for the description of the heat transfer problem...

Figure 4.27 Active outdoor air‐based system for battery thermal management....

Figure 4.28 Active outdoor air‐based system coupled to an air‐to‐air reversi...

Figure 4.29 Passive cabin air‐based system for battery thermal management.

Figure 4.30 Active cabin air‐based system for battery thermal management.

Figure 4.31 Configuration of the 30 modules of the battery pack.

Figure 4.32 Time evolution of temperature of modules in rows 1, 2, 5, and 10...

Figure 4.33 Different configurations of liquid‐based battery cooling systems...

Figure 4.34 Passive cooling of the coolant loop.

Figure 4.35 Active and passive battery cooling with the coolant loop.

Figure 4.36 View of a chiller (right) and its associated water‐cooling plate...

Figure 4.37 Illustration of the integration of a liquid‐based battery coolin...

Figure 4.38 Refrigerant plate system allowing for the cooling of 6 battery m...

Figure 4.39 Refrigerant‐based system for battery cooling.

Figure 4.40 Connection of the battery to the plate.

Figure 4.41 Visualization of the contact between the battery, the coolant ch...

Figure 4.42 Example of enthalpy‐temperature curve.

Figure 4.43 Heat transfer resistances and thermal capacities to describe the...

Figure 4.44 Time evolution of temperatures of the module, of the module surf...

Figure 4.45 Schematic representation of power electronics cooling system....

Figure 4.46 Different configurations of heat pipes (configuration (c) is ins...

Figure 4.47 Schematic representation of a Permanent Magnet motor.

Figure 4.48 Example of overall thermal management architecture of a PHEV wit...

Figure 4.49 Example of overall thermal management architecture of a PHEV wit...

Guide

Cover

Table of Contents

Title Page

Copyright

Acknowledgments

Nomenclature

About the Companion Website

Introduction

Begin Reading

Index

End User License Agreement

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Automotive Series

Series Editor: Thomas Kurfess

Fundamentals of Vehicle Dynamics and Modelling: A Textbook for Engineers with Illustrations and Examples

Minaker

August 2019

Design and Analysis of Composite Structures for Automotive Applications: Chassis and Drivetrain

Kobelev

April 2019

Advanced Battery Management Technologies for Electric Vehicles

Xiong and Shen

December 2018

Noise and Vibration Control in Automotive Bodies

Pang

October 2018

Automotive Power Transmission Systems

Zhang and Mi

June 2018

High Speed Off‐Road Vehicles: Suspensions, Tracks, Wheels and Dynamics

Maclaurin

June 2018

Hybrid Electric Vehicles: Principles and Applications with Practical Perspectives, 2nd Edition

Mi and Masrur

October 2017

Hybrid Electric Vehicle System Modeling and Control, 2nd Edition

Liu

April 2017

Thermal Management of Electric Vehicle Battery Systems

Dincer, Hamut, and Javani

March 2017

Automotive Aerodynamics

Katz

April 2016

The Global Automotive Industry

Nieuwenhuis and Wells

September 2015

Vehicle Dynamics

Meywerk

May 2015

Vehicle Gearbox Noise and Vibration: Measurement, Signal Analysis, Signal Processing and Noise Reduction Measures

Tůma

April 2014

Modeling and Control of Engines and Drivelines

Eriksson and Nielsen

April 2014

Modelling, Simulation and Control of Two‐Wheeled Vehicles

Tanelli, Corno and Savaresi

March 2014

Advanced Composite Materials for Automotive Applications: Structural Integrity and Crashworthiness

Elmarakbi

December 2013

Guide to Load Analysis for Durability in Vehicle Engineering

Johannesson and Speckert

November 2013

Thermal Energy Management in Vehicles

Vincent LemortUniversity of Liège

Gérard OlivierRenault

Georges de PelsemaekerValeo Thermal Systems & University of Liège

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The right of Vincent Lemort, Gérard Olivier, and Georges de Pelsemaeker to be identified as the authors of this work has been asserted in accordance with law.

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Acknowledgments

The authors would like to thank all the people who have contributed to the content of this book by sharing their knowledge. This content has relied heavily on the technical documentation prepared over the years by many Valeo and Renault experts. It is not possible to list all of them, but the authors hope that they will recognize each other.

In addition, many colleagues from the University of Liège and other universities as well as industrial partners took the time to answer the many technical questions they received. The authors would like to thank them for their time and consideration. Again, it is not easy to provide a complete list without forgetting anyone, and the authors hope that no one will take offense.

Finally, the authors would like to thank their families and their beloved for their support during this long project.

Above all, Vincent Lemort thanks his wife, children, family, and friends for their patience during these last two months of writing.

Nomenclature

List of Abbreviations

AC 

accumulator

A/C 

air‐conditioning

ACAC 

air‐cooled charge air cooler

BDC 

bottom dead center

BEV

battery electric vehicle

BMEP 

brake mean effective pressure

BMS 

battery management system

BPHEX 

Brazed Plate Heat Exchanger

BTM 

battery thermal management

BTMS 

battery thermal management system

BOL

beginning of life

CAC 

charge air cooler

CC 

cooler core

CFC 

chlorofluorocarbon

COP 

coefficient of performance

CP 

compressor

DN 

direct normal

DOC 

diesel oxidation catalyst

DP 

damper

DPF 

diesel particulate filter

ECV

externally controlled valve

EG

ethylene glycol

EGR

exhaust gas recirculation

EGRC

exhaust gas recirculation cooler

EHRS

exhaust heat recovery system

EM

electric motor

EOL

end of life

EREV

extended range electric vehicle

EV

electric vehicle

EXV

electronic expansion valve

HC

hydrocarbon

HEV

hybrid electric vehicle

HP

high pressure

FC

fuel cell

FCEV

fuel cell electric vehicle

FMEP 

friction mean effective pressure

GWP 

global warming potential

HC 

heater core

HVAC

heating, ventilation, and air‐conditioning

HFC 

hydrofluorocarbon

HFO 

hydrofluoroolefin

HHV 

high heating value

ICD 

internal condenser

ICE 

internal combustion engine

ICT

information and communications technology

ICV

internally controlled valve

IEV 

internal evaporator

IMEP 

indicated mean effective pressure

IR 

infrared

LHV 

low heating value

LP 

low pressure

LT 

low temperature

MEP 

mean effective pressure

NEDC

new European driving cycle

NTU 

number of transfer units

ORC 

organic Rankine cycle

OCR 

oil circulation ratio

OCV 

open circuit voltage

OHEX 

outdoor heat exchanger

OT 

orifice tube

PCM 

phase change material

PE 

power electronics

PHEV

plug‐in hybrid electric vehicle

PMV 

predicted mean vote

PPD 

predicted percent dissatisfied

PTC 

positive temperature coefficient

PVB

polyvinyl butyral

RC 

Rankine cycle

RMS 

root mean square

SCR

selective catalytic reduction

SHGC 

solar heat gain coefficient

SHR 

sensible heat ratio

SOC 

state of charge

SOH 

state of health

TDC 

top dead center

TIM 

thermal interface material

TXV 

thermostatic expansion valve

WCAC 

water‐cooled charge air cooler

WCD 

water‐cooled condenser

WLTP

worldwide harmonized light vehicles test procedure

ZEV

zero emission vehicle

Nomenclature

a

specific Gibbs free energy

[J kg

−1

]

A

area

[m

2

]

AU

conductance

[W K

−1

]

B

bore

[m]

c

specific heat

[J kg

−1

 K

−1

]

C

speed, velocity

[m s

−1

]

C

heat capacity

[J K

−1

]

C

clearance factor

[−]

C

concentration

[−]

e

specific total energy

[J kg

−1

]

e

thickness

[m]

e

amount of excess air

[−]

E

total energy

[J]

E

emissive power

[W m

−2

]

f

fuel–air ratio

[−]

F

force

[N]

F

view factor

[−]

g

gravitational acceleration

[m s

−2

]

g

specific Helmoltz free energy

[J kg

−1

]

G

irradiation

[W m

−2

]

h

specific enthalpy

[J kg

−1

]

h

convective heat transfer coefficient

[W m

−2

K

−1

]

H

enthalpy

[J]

H

height

[m]

i

working cycle frequency

[−]

I

irradiance

[W m

−2

]

I

electric current

[A]

k

spring constant

[N m

−1

]

k

thermal conductivity

[W m

−1

K

−1

]

L

length

[m]

m

mass

[kg]

mass flow rate

[kg s

−1

]

MM

molar mass

[kg kmol

−1

]

n

number

[−]

N

rotational speed

[Hz]

P

pressure

[Pa]

q

heat flux

[W m

−2

]

rate of heat transfer

[W]

r

ratio

[−]

R

heat transfer resistance

[K W

−1

]

RH

relative humidity

[−]

rpm

rotational speed

[rpm]

T

temperature

[°C or K]

s

specific entropy

[J kg

−1

 K

−1

]

S

entropy

[J K

−1

]

S

stroke

[m]

t

time

[s]

T

torque

[N m]

u

specific internal energy

[J kg

−1

]

U

internal energy

[J]

U

overall heat transfer coefficient

[W m

−2

 K

−1

]

v

specific volume

[m

3

 kg

−1

]

V

volume

[m

3

]

volume flow rate

[m

3

 s

−1

]

Vol

volume

[m

3

]

w

specific work

[J kg

−1

]

W

work

[J]

power

[W]

x

displacement, distance

[m]

x

quality

[−]

X

ratio

[−]

X

concentration

[ppm]

z

elevation, altitude

[m]

Subscripts

a

acceleration

a

air

adiab

adiabatic

amb

ambient

atm

atmospheric

a

vg

average

a

ux

auxiliaries

b

boundary

b

black body

bod

body

c

cold

c

cylinder

c

combustion

c

cutoff

c

convection

cab

cabin

cc

combustion chamber

cd

condenser

cl

cloth

cond

conduction

cond

condensate

cool

coolant

cp

compressor

cr

crank chamber

CV

control volume

d

displacement

d

diffuse

d

discharge

diff

diffusion

dh

diffuse horizontal

dp

dew point

el

electric, electrical

eng

engine

eq

equivalent

ex

exhaust

exf

exfiltration

exp

expander

ev

evaporator

f

saturated liquid

f

fluid

f

fuel

f

fin

f

free

f

final

form

formation

fric

friction

g

gravity

g

saturated vapor

g

gas

gc

gas cooler

gen

generated

gw

glycol water (coolant)

glaz

glazing

h

hydraulic

h

hot

ha

humid air

he

heat engine

i

initial

in

inside, indoor, internal

in

indicated

inf

infiltration

int

internally

k

kinetic

l

liquid

l

leakage

lat

latent

m

maximum

m

mechanical

m

metabolism

m

masses

mech

mechanical

mod

module

n

natural

o

operative

occ

occupant

out

outside, outdoor

p

constant pressure

p

potential

p

piston

plas

plastic

pp

pump

r

radiated

r

refrigerant

rad

radiator

rec

recirculated

ref

reference

rel

relative

rev

reversible

s

isentropic

s

surface

s

swept

s

solar

sa

sol‐air

sat

saturated

sens

sensible

sf

secondary fluid

sh

shaft

sk

skin

st

stoichiometric

su

supply

surf

surface

th

thermal

th

theoretical

tot

total

tp

two‐phase

turb

turbine

v

constant volume

v

vapor

vent

ventilation

w

water

w

wall

wb

wetbulb

wf

working fluid

wg

waste gate

0

at 0°C

0

clearance

II

second Law of Thermodynamics

∞

freestream

Exponents

°

ideal gas contribution

r

residual contribution

Greek Symbols

α

absorptivity

[−]

β

solar altitude

[rad]

γ

specific heat ratio

[−]

Δ

difference

[−]

ɛ

emissivity

[−]

ɛ

effectiveness

[−]

η

efficiency

[−]

θ

specific total energy of flowing fluid

[J kg

−1

]

θ

crank angle

[rad]

λ

wavelength

[m]

μ

dynamic viscosity

[kg m

−1

s

−1

]

ρ

density

[kg m

−3

]

ρ

reflectivity

[−]

σ

Stefan–Boltzmann constant

[5.67 × 10

−8

 W m

−2

K

−4

]

Σ 

surface tilt angle

[rad]

τ

transmissivity

[−]

τ

time

[s]

φ

solar azimuth

[rad]

Φ

equivalence ratio

[−]

ψ

surface azimuth

[rad]

ω

specific humidity

[kg kg

−1

]

About the Companion Website

This book is accompanied by a companion website:

www.wiley.com/go/lemort/thermal

This website includes:

• EES files

Introduction

1 Genesis

The paternity of the automobile is still debated between several inventors among whom are Francesco di Giorgio Martin (1470), Roberto Valturio (1472), or Leonardo da Vinci whose sketches can be found in the Codex Atlantico (1478) and whose drawings are preserved in his engineering notebooks. A study of a self‐propelled wagon probably for a theatrical machine, able to move for a short stretch on a stage, is known. For a long time, it was wrongly interpreted as a kind of ancestor of the automobile (Figure 1).

However, thanks to the first functional models of the Belgian Jesuit Ferdinant Verbiest (1623–1688), we can discover the description of a thermodynamic system that allows the movement of the vehicle. In 1672, to put into practice his studies on boilers, he installed one on a small cart. The jet of steam actuated a paddle wheel which drove the wheels through a set of gears.

The drawing in Figure 2 is by the hand of the inventor, as in his description, published in 1685, in Latin, in his treatise “Astronomia Europea.”

The Frenchman Joseph Cugnot presented his “Fardier (or steamer)” developed during the period 1769–1771, a cart propelled by a steam boiler. As shown in Figure 3, it was difficult to brake the steamer, leading to probably the first car accident in history.

Other models followed, but steam propulsion was a stalemate in terms of the relationship between weight and performance. This is how the automobile evolved towards the electric car. The first electric car model was built by Sibrandus Stratingh (1835).

We could not resist quoting Camille Jenatzy's electric car, “La Jamais contente (or Never‐Happy)” (Figure 4). This is the first motor vehicle to reach the 100 km h−1 mark.

This electric car, in the shape of a torpedo on wheels, set this record on 29 April 1899 in Achères (France).

The first times of the electric car remained chaotic and inefficient. So, the German Carl Benz built the first automobile in history driven by a thermal engine (1886).

Several revolutions followed that led to changes to steam engines, electric, gasoline, diesel, fuel cell, and electric propulsion again.

Each time, the thermal systems have been adapted or reinvented themselves to meet the new challenges that the automotive industry has encountered. The necessary revolution towards carbon neutrality has accelerated those changes.

Figure 1 Self‐propelled wagon as drawn by da Vinci.

Source: Leonardo da Vinci – http://history-computer.com, public domain, https://commons.wikimedia.org/w/index.php?curid=14619567.

Figure 2 One of the first steam‐driven cars by Belgian Ferdinant Verbiest.

Source: Unknown author/Wikimedia/Public Domain.

Figure 3 Cugnot's Steamer (“Fardier de Cugnot”), tested in Paris in 1770.

Figure 4 “La Jamais contente (or Never‐Happy)”.

Source: Unknown author/Wikimedia/Public Domain.

2 Vectors of Evolution of Thermal Systems

The vectors of the evolution of the automobile world and of its motorization were successively: a race for speed record, increase in the reliability of the engines, increase in the specific power of the engines, introduction of heating and then of air conditioning of the passenger compartment, reduction of vehicle consumption, regulatory constraints governing the environmental impact of engines, reduction in vehicle weight, conservation of the autonomy of electric vehicles, and finally, an improved comfort for passengers of electric and autonomous vehicles.

With each step, the thermal management of the vehicle has evolved toward more performance and functionality, less weight, and lower cost.

To cope with these new challenges, the number of independent thermal systems has increased initially, their interconnection has evolved, and today, many of these systems are fully connected to ensure optimal energy management.

3 The Regulatory Constraints of Change

Pollution regulations have been important vectors for the evolution of propulsion systems and they asked for the energy sobriety of the auxiliaries (all components and systems not directly contributing to propulsion, such as heating, air‐conditioning, battery thermal management systems, etc.)

The evolution of the allowed emission limits, in CO2 per kilometer, for the four main geographical areas, namely the USA, Europe, Japan, and China, is shown in Figure 5.

European CO2 pollution standards imposed since 1992 refer to the New European Driving Cycle (NEDC). In addition to CO2 reduction, the European regulations have imposed limitations on emissions of other pollutants, including NOx, CO, particulate matter (PM), and HC + NOx.

As an example, Figure 6 gives the allowed emission limits for diesel engines from July 1992 (Euro 1) to September 2015 (Euro 6).

To comply with these emission regulations, car manufacturers and tier one suppliers have developed major new systems such as turbocharger, fuel direct injection, high‐pressure and low‐pressure exhaust gas recirculation systems (EGR), selective catalytic reduction (SCR), and diesel particulate filter (DFP).

Figure 5 Yearly evolution of the allowed emission limits in CO2 per kilometer.

Figure 6 Allowed emission limits for diesel engines from Euro 1 (1992) to Euro 6 (2015) regulations.

Each of these systems requires optimal operating conditions and specific cooling or heating systems, which have complicated the thermal architecture of the vehicle.

The introduction of electrical motorization created new demands, which included cooling of the battery, fast cooling of the battery during charging, and compensation of the thermal deficit in winter for passenger comfort, and the problem is even more important for fuel cell systems.

The optimization of thermal energy for full electric vehicles is no more an option but a condition to secure vehicle range.

Despite the demands for reduction in the consumption of internal combustion engine vehicles following the oil crises (1973 and 1979) and finally since 1992, the increasingly stringent depollution regulations enacted, the GHG (greenhouse gas) emissions of the transport sector are the only one increasing compared to other sectors responsible of GHG emissions (power generation, industry, buildings, etc.). The index shown in Figure 7 is a relative measurement of the emissions of gases responsible for the greenhouse effect.

In addition, the share of road transport represents 11.9% of GHG emissions. Figure 8 shows the distribution of the GHG emission per sector. The energy sector represents 73.2% of the global emissions.

For this reason and following the Diesel Gate (2008–2015), state and city standards have been tightened, and the NEDC standard has been replaced by the worldwide harmonized light vehicles test procedure (WLTP) standard, which represents more real‐time driving of the vehicle by integrating the consumption of accessories.

Furthermore, real driving emissions (RDE) pollution standards were introduced. These standards refer to a fleet of vehicles in real use during their lifetime and not only for a new vehicle.

Figure 9 shows that the reduction of the pollution has accelerated mainly after the Diesel Gate.

Figure 10 shows a schematic illustration of average CO2 emission levels in the EU between 2014 and 2030, assuming a 3.9% per year and 6.8% per year CO2 reduction scenario.

Figure 7 Evolution of the European GHG emissions relative to 1990 per sector.

Source: Data from Transport & Environment (1998), UNFCC (1990‐2016 data) and EEA's approximated EU greenhouse inventory (2017 data).

Figure 8 Global greenhouse gas emissions per sector.

Figure 9 Evolution of regulations regarding pollutant emissions.

Figure 10 CO2 emission level for RW, NEDC, and WLTP regulation evolutions.

4 The First Three Revolutions of the Twenty‐First Century

Three major revolutions are shaking the automotive industry, namely decarbonization, driving automation, and connectivity, which makes it possible to create more and more embedded digital services and a better transition between modes of transport, home, and road.

Because of their emissions of nitrogen oxide and fine particles, real or perceived values, diesel engines have been discarded to the benefit of the hybridization of gasoline engine (hybrid electric vehicle [HEV]) and electric motors (battery electric vehicle [BEV]).

The ratio of sales of diesel to gasoline vehicles is reversed in less than a year and several developments of heat engines have been discontinued and replaced by developments of electric motors.

Fuel cell motorization is seen as a potential alternative to electric vehicles.

This electric revolution is causing new constraints such as cooling the batteries to prevent battery cell degradation during use or rapid charging under hot conditions.

With the arrival of electric motors, the energy consumed by the auxiliaries and, first and foremost, the comfort in winter leads to a strong reduction in the driving range of vehicles when the temperature falls.

In addition to decarbonization (electricity) constraints, new needs are emerging for autonomous, connected, and shared vehicles, such as cooling of on‐board computers or adaptation and personalization of passenger comfort.

Since 1769, thermal systems have evolved as multiple, connected, complex, efficient, and adaptive.

Challenges linked to the revolutions of the twenty‐first century, electrification of the powertrain, automation of connected vehicles, and digital mobility will allow once again the thermal management of the vehicle to evolve with elegance toward global management.

5 Ambition of the Authors

The target audience of this book are not engineering students but also more experienced engineers who wish to perfect their knowledge in thermal sciences (heat transfer, thermodynamics, and fluid mechanics) applied to vehicle thermal management systems.

The authors were inspired by several reference works published; some of them were published several decades ago and have been the reference of several generations of students. Among these reference works, we would like to mention the following books:

“Automotive Climatization (La climatisation Automobile)” from André Colinet (

1993

)

“Technical refrigeration manual – Le Pohlman” translated in French by Maake et al. (

1993

). This reference is the evolution of a pocketbook published in 1908 (Taschenbuch der Kältetechnik) for refrigeration technicians. In 1908, the 1st International Cold Congress was held in Paris, which brought together all the minds interested in low temperatures.

“Automotive Air conditioning and Climate control systems” by Steven Daly (

2006

)

The classroom Manual For Automotive Heating & Air Conditioning written by Schnubel (

2016

)

The present book goes one step further by presenting the impact of electrification on the overall thermal management of vehicles. The present book also introduces some simple modeling techniques of vehicle thermal management components and systems.

6 Organization of the Book

The book is organized as follows. The first chapter covers the fundamentals of thermal systems and highlights applications to vehicle thermal management components. The second chapter presents the thermal management systems associated with internal combustion engines. The third chapter is dedicated to passenger thermal comfort and cabin air conditioning. Finally, the last chapter explains the specific thermal management solutions for hybrid and electric vehicles.

In Chapters 2–4, several examples of numerical problems are proposed. Equations implemented in Engineering Equation Solver (EES) software are presented. The EES files are available for download on the website associated with the book. EES is a software developed by Prof. Sanford Klein from the University of Wisconsin–Madison. This software combines an acausal equation solver and an accurate database of thermodynamic and transport properties of working fluids typically used in vehicle thermal management systems (humid air, refrigerants, aqueous solution of glycol, etc.). EES allows for solving large systems of coupled nonlinear algebraic equations and differential equations. The acausal feature of the solver allows to focus on the physical modeling of thermal systems (in both steady‐state and transient regimes) rather than on the numerical solving of the models. One very interesting feature of EES is its tool for conducting parametric analyses. This is very convenient to investigate the sensitivity of a thermal component or system to a change in operating conditions or design parameters. More information is available on the F‐Chart website (https://fchartsoftware.com/ees/).

References

Colinet, A. (1993).

La climatisation automobile

. Editions techniques pour l'automobile et l'industrie.

Daly, S. (2006).

Automotive Air Conditioning and Climate Control Systems

. Butterworth‐Heinemann.

Maake, W., Eckert, H.‐J., and Cauchepin, J.L. (1993).

Le Pohlmann : manuel technique du froid

, vol. 2, 1, 1204. PYC Livres.

Schnubel, M. (2016).

Today's Technicians™: Classroom Manual for Automotive Heating & Air Conditioning

, 6the. Boston, USA: Cengage Learning.

Transport & Environment (1998). EU publishes climate strategy to exit oil. Available:

https://www.transportenvironment.org/discover/eu-publishes-climate-strategy-exit-oil/

(accessed 9 May 2022).

1Fundamentals

1.1 Introduction

This textbook deals with the study of different vehicle thermal systems and components from an energy engineering point of view. It is therefore necessary to recall the fundamentals of heat transfer as well as thermodynamics and some elements of fluid mechanics for a good understanding of the content of the next Chapters 2, 3, and 4. This is the objective of the present chapter, the content of which has been largely summarized from major reference textbooks, especially those of Incropera and DeWitt (2002), Çengel and Boles (2006), Braun and Mitchell (2012), and Klein and Nellis (2016).

1.2 Fundamental Definitions in Thermodynamics

Thermodynamics is the branch of physics that studies conversions between heat and work in one or the other direction. Thermodynamics is particularly useful for the analysis of components and systems presented in this book.

Thermodynamics makes use of some important notions to which the reader should become familiar.

1.2.1 System, Surroundings, and Universe

In thermodynamics, a system is defined as a delimited region of space or a quantity of matter that is investigated. The concept of “investigation” may still be a little bit fuzzy and will progressively develop. Let's say that investigating a system means quantifying its energy performance and the relation between this performance and operating conditions. The system is delimited by a boundary (Figure 1.1). A boundary has neither mass nor thickness. The surroundings of the system are the region of space or the quantity of matter that is outside the system. Hence, the boundary is the surface that separates the system from its surroundings. The system and its surroundings constitute the universe.

Among the systems, one can distinguish the closed systems and the open systems. A closed system does not exchange any mass with its surroundings. Consequently, its mass is constant. An open system, also called control volume (CV), exchanges mass with its surroundings. Such a system is represented in Figure 1.2. The system consists of the region in space delimited partially by plain lines and partially by two dashed lines. Some fluid can enter or leave the system through physical connections to the surroundings. Consequently, the mass of the system may vary.

Figure 1.1 System, boundary, surroundings, and universe.

Figure 1.2 Mechanisms of energy transfer between an open system and its surroundings.

In Figure 1.2, part of the boundary is real. It is represented by solid lines and can correspond to the physical envelope of the system. Contrarily, dashed lines represent imaginary boundaries. They are the openings of the system that allow for mass exchange with the surroundings.

As depicted in Figure 1.2, an open system can exchange energy with its surroundings through three mechanisms: heat transfer, work transfer, and mass transfer. It will be shown later that the energy transfer associated with the mass transfer is computed based on the enthalpy of the flow.

In the specific case where the open system does not exchange mass with its surroundings, it becomes a closed system. If the system does not exchange heat with its surroundings, it is said to be adiabatic. If the system exchanges neither heat nor work nor mass, it is said to be isolated. It will be shown later that engineering applications of thermodynamics are particularly interested by (useful) energy transfers between a system and its surroundings.

A very common example of an open system, largely described in textbooks, is the cylinder‐piston assembly equipped with valves represented in Figure 1.3. Since one desires to describe the state of the fluid inside the cylinder, the content of the cylinder is defined as the thermodynamic system. The dashed line represents the boundary of the system. It consists of the cylinder wall, cylinder head (comprising the ports), and the inner surface of the piston. The latter portion of the boundary is moving. Some fluid can enter or leave the control volume through the ports, provided they are not covered by the valves.

Figure 1.3 Example of an open system with a moving boundary.

In this book, many open and closed systems will be investigated. Among the major open systems, one can mention heat exchangers, compressors, turbines, and pumps. All these components have inlet and outlet ports that allow for mass exchange with their surroundings. The vehicle cabin can also be considered as an open system, since it exchanges air with the vehicle outdoor through the ventilation system. When the ventilation is in the recirculation mode (which will be described in Chapter 3) and if infiltrations and exfiltrations of air are neglected, the vehicle cabin can be seen as a closed system. Another example of a closed system could be the whole engine coolant loop. During regular operation, the mass of coolant in the loop is constant.

An appropriate choice of the boundary will simplify the thermodynamic description of the system under investigation.

1.2.2 Properties

When investigating vehicle thermal management, one has to describe numerous thermodynamic systems.

A system can be described by its characteristics, which are named as thermodynamic properties. Describing a system means describing its thermodynamic state. The state of a system is defined when the latter is in equilibrium. The most known properties are pressure P [Pa], temperature T [K], mass m [kg], and volume V [m3]. These properties are internal properties. Speed C [m s−1] and elevation z [m] are external properties and do not depend on the molecular structure of the matter (Klein and Nellis, 2016). Note that these properties are measurable properties. It will be shown later that other properties that cannot be directly measured are also very useful for the description of a system, such as internal energy U [J], enthalpy H [J], or entropy S [J K−1]. Such nonmeasurable properties can be calculated based on measurable ones and thermodynamic relations.

A specific property is a property expressed per unit of mass of the system. Specific properties are usually denoted with lowercase letters. For instance, specific volume v [m3kg−1] is volume V [m3] divided by mass m [kg]. Other properties that will be used in this book are specific internal energy u [J kg−1], specific entropy s [J kg−1K−1], specific enthalpy h [J kg−1], and specific heat at constant pressure cp [J kg−1K−1].

Among the properties, the distinction can also be done between the extensive and intensive properties. The extensive properties depend on the size of the system and vary linearly with its mass. Examples are mass m [kg], volume V [m3], and internal energy U [J]. On the contrary, the intensive properties do not depend on the system size and mass. Examples are pressure P [Pa] and temperature T [°C] and also any specific properties.

As it will be explained later, to specify the state of a system in internal equilibrium (and in the absence of electrical, magnetic, or other effects), two independent intensive properties are needed.

1.2.3 Process

A process is a transformation that brings the system from a given state A to another state B. The initial and final states are described by two independent intensive properties. Therefore, the state of a system is a “picture” of the system and does not depend on its “history” (the way this state was obtained). Indeed, different paths, involving different heat and work transfers, can bring the system from state A to state B. Hence, the properties of the system are called point functions. In contrary, heat and work are called path functions. Examples of processes involved in vehicle thermal management are fluid compression, expansion, cooling, and heating.

A process that brings the system back to its initial state is a cycle. This type of process is encountered in thermal machines where a fluid is circulating in a cyclic manner. One major example of the thermodynamic cycle is the refrigeration cycle that is exploited by the vehicle air‐conditioning loop. It will be described in detail in Chapter 3.

There is one particular operation of open systems that largely simplifies their analysis. This is the steady‐state regime. A fluid flows steadily through a control volume if the properties inside the control volume do not vary with time. The fluid properties can vary from one point to another inside the control volume, but at a given location inside the control volume, the fluid properties do not vary with time (Çengel and Boles, 2006). In such a situation, the control volume is said to undergo a steady‐flow (or steady‐state) process. During such a process, the energy and the mass contained in the system are constant in time. Steady‐flow processes are approximated in practice when a system is operating for a long period of time with no variation in operating conditions.

For instance, when an internal combustion engine is switched on, it will first undergo a transient period during which the temperature of the metal and internal fluids will increase. After this period, the engine temperature and consequently the temperature of the fluids leaving the engine will stabilize. This is represented in Figure 1.4. When acceptable, the assumption of the steady‐flow process simplifies the analysis of the performance of the systems.

Figure 1.4 Steady‐flow period following a transient period.

1.2.4 Energy

This book will extensively make use of the concept of energy. Actually, it will describe different components and systems of components used in vehicles that transfer energy or convert it from one form to another. Defining the energy is not an easy task. Our everyday experience teaches us that energy can appear under different forms, among which thermal energy, mechanical energy, kinetic energy, potential energy, electric energy, or nuclear energy. By summing all the quantities of energy contained in a system under its different forms, one obtains the total energy E [J] of the system. The specific total energy is defined as e = E/m [J kg−1].

It should also be mentioned that the energy contained in a system depends on the reference state for which this energy is null. This is not of primary importance, since the description of thermal systems mainly implies the quantification of energy variations.

Among the different forms of energy, one can also distinguish the microscopic forms and the macroscopic forms of energy. The microscopic forms of energy are sensible energy (energy associated with the movement of molecules, atoms, and nucleons), latent energy (energy associated with the binding forces between the molecules; these forces decrease from the solid phase to the liquid phase and to the gaseous phase), chemical energy (energy associated with the atomic bonds in a molecule), and nuclear energy (energy associated with the bonds between the nucleons inside the nucleus of the atom). The macroscopic forms of energy of a system are associated with its velocity C [m s−1] and altitude z [m], i.e. its kinetic and potential energies.

The internal energy U [J] of a system is the sum of all microscopic forms of energy. The specific internal energy is defined as u = U/m [J kg−1] . The total and internal energies are related by

(1.1)

where

C

is the system velocity,

[m s

−1

]

g

is the gravitational acceleration,

[m s

−2

]

z

is the elevation of the system from a reference altitude,

[m]

.

In the right‐hand side of the previous equation, the second and third terms are the kinetic and potential energies, respectively.

1.2.5 Heat

Heat Q [J] is the form of energy that is exchanged between a system and its surroundings because of their difference in temperatures. A system does not contain heat, but thermal energy. Heat is the visualization of thermal energy transfer through a system boundary under the action of a temperature gradient. To be rigorous, one should not talk about “heat transfer,” but “thermal energy transfer.” However, the latter expression is commonly accepted.

The heat transfer rate is defined as the heat exchanged between a system and its surroundings per unit of time. In the case of an adiabatic system, .

1.2.6 Work

Work is the form of energy that is transferred when a force acts on the system over a distance (Çengel and Boles, 2006). The different forms of work can be categorized as mechanical forms and nonmechanical forms. Different forms of mechanical work can also be distinguished.

1.2.6.1 Mechanical Forms of Work

A mechanical work is exchanged between a system and its surroundings when a force is acting on the system boundary and when this system or its boundary is moving. If these two conditions are met, a work interaction exists between the system and its surroundings. The work is either done by the system or done on the system. In the former case, the external force acting on the system and its motion have opposite directions. In the latter case, the external force acting on the system and its motion has the same direction.

The mechanical forms of work that will be met in the rest of this book are the moving boundary work, the shaft work, the spring work, and the work necessary to raise or to accelerate a system.

1.2.6.1.1 Moving Boundary Work When a fluid is compressed or expanded, the boundary separating the fluid from its surroundings is moving. As a consequence of the displacement of the boundary, moving boundary work Wb[J] is exchanged between the fluid and its surroundings. Such a work interaction is represented in Figure 1.5.

Figure 1.5 Moving boundary work interaction in a piston‐cylinder apparatus.

During the compression (related to distance S = x1 − x2 travelled by the piston), moving boundary work Wb can be computed by integrating the product of the force acting on the piston and incremental displacement dx. That is,

(1.2)

In Eq. (1.2), the force can be related to the pressure acting on the inner surface of the piston, leading to Eq. (1.3). In the case of a reversible evolution (1‐2), since the pressure is uniform within the cylinder, the pressure in Eq. (1.3) is the system pressure. The notion of reversible evolution will be further developed later.

(1.3)

1.2.6.1.2 Shaft Work Shaft work is the work associated with a rotating shaft. This is, for instance, the work transmitted at the shaft of the engine of a car or the work absorbed at the shaft of a compressor (Figure 1.6).

Figure 1.6 Work transmitted at a shaft.

Source: Reproduced from Çengel and Boles (2006).

Shaft work Wsh [J] exchanged after X revolutions of a shaft on which a torque T [N · m] of moment arm r [m] is acting is given by

(1.4)

Shaft power (shaft work per unit of time) can be calculated based on the rotational speed N [Hz] of the shaft, which is the number of revolutions done per second.

(1.5)

1.2.6.1.3 Spring Work According to Hooke's law, the force F [N] needed to compress a linear‐elastic spring of spring constant k [N m−1] by a distance X [m] varies linearly with this distance (Figure 1.7).

(1.6)

Figure 1.7 Spring work.