# basic concepts

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```					1.Basic Concepts and
Terminologies
1.1    Introduction
1.2    Conservation Principle
1.3    Property, State and Phase
1.4    Process and Cycle
1.5    The 0th Law of Thermodynamics
1.6    Units and Dimensions

Basic Concepts and Terminologies
1.1 Introduction

<Power plant>

Basic Concepts and Terminologies             Introduction
<Liquid oxygen plant>

Basic Concepts and Terminologies            Introduction
<Turbofan jet engine>

Basic Concepts and Terminologies               Introduction
<Liquid-propellant rocket engine>

Basic Concepts and Terminologies        Introduction
1.2 Conservation Principle
Any thermal-fluid phenomena can be described by a
closed set of the conservation equations of mass,
momentum and energy with relevant property and
constitutive relationships.

Integral and Differential Approaches
There are two different approaches to mathematically
describe any thermal-fluid phenomena involving
mass, momentum and energy transfer.

Basic Concepts and Terminologies       Conservation Principle
Integral Method
A system is defined in terms of definite mass or
definite volume in space.

-control mass (closed system)
-control volume (open system)

Differential Method
The conservation principle is applied to an
infinitesimal volume resulting in partial differential
equations.

Basic Concepts and Terminologies      Conservation Principle
-Control mass (closed system)

Fixed amount                        Surroundings
of matter
Momentum
Energy
isolated system - no interaction with the surrounding

-Control volume (open system)

V(t) may change
with time.                         Surroundings
V(t) is defined as
a definite volume                 Mass
in space.                  Momentum
Energy
Basic Concepts and Terminologies              Conservation Principle
Conservation Principle
for any conserved quantity, , per unit mass

convection                                  A(control surface)
V(control
volume)
diffusion

t V  dV  A  v dA  A J dA  V SdV

V t    dV  V    v  dV  V  JdV  V SdV

      v    (D )  S
t
The diffusive flux, J, is given as             J  D (Fick's law)
Basic Concepts and Terminologies                 Conservation Principle
Mass Conservation for a Control Volume

 mt  dt  mt     me  mi
                         0
      t         t    t

dmc.v.
  me   mi  0
dt

Basic Concepts and Terminologies         Conservation Principle
Mass Conservation in a Differential Form

 rate of  rate of  rate of 
                              
   mass        mass    mass 
accumlation   in   out 
                              


   v 
t

Basic Concepts and Terminologies            Conservation Principle
Momentum Conservation for a Control Volume

d
Ptot  miVi  meVe  pi Ai  pe Ae  F  mtot g
dt

Basic Concepts and Terminologies              Conservation Principle
Momentum Conservation in a Differential Form
 rate of   rate of   rate of  sum of forces 
                                               
 momentum  = momentum   mometum  +  acting on 
accumulation    in      out   system           
                                               


 v     vv   p   τ    g
t

Basic Concepts and Terminologies               Conservation Principle
Energy Conservation for a Control Volume

      Vi 2       
Qc.v.   mi  hi        gZi 
       2         
dEc.v.                Ve2        
          me  he         gZ e   Wc.v.
dt                  2         

dE
Q    W
dt

Basic Concepts and Terminologies                  Conservation Principle
Energy Conservation in a Differential Form

Total energy balance
       1 2               1 2 
  u  v      v  u  v                 q   
t      2                 2 
   v  g     pv      τ v 

Thermal energy balance

u     vu      q   p   v    τ : v 
t

Basic Concepts and Terminologies                        Conservation Principle
In either integral and differential descriptions there can
be many different combinations of the conservation
equations and complementary constitutive relationships.

- The proper choice depends on the problem under
consideration and the information required as a
solution.
- The essence of this course is to understand these
basic approaches and how to apply them to real
engineering problems involving various thermal-fluid
phenomena.

Basic Concepts and Terminologies     Conservation Principle
How is Energy stored in Gas?

Intermolecular potential energy; negligible at low 
Molecular kinetic energy; translation
Intramolecular energy; rotation, vibration, electronic

Degree of freedom: f (Equipartition Principle)
f=3 for monatomic gas, such as He
f=6 for diatomic gas, such as O2
(3 for translation, 2 for rotation, 1 for vibration)
f=9 for H2O
(3 for translation, 3 for rotation, 3 for vibration)

Basic Concepts and Terminologies        Conservation Principle
Example 1 (WSB p131)

Control volume: Turbine
Inlet state: Fixed
Exit state: Fixed
Process: SSSF
Model: Steam tables

      Vi 2                   Ve2        
Qc.v.  m  hi        gZ i   m  he       gZ e   Wc.v.
       g                      g         

Basic Concepts and Terminologies                        Conservation Principle
In classical thermodynamics we do not care about
how energy is stored in a system. It may be of interest
to understand thermodynamic properties, e.g. the
amount of energy required to raise the temperature by
a given amount.

However it helps conceptually to understand the
relationship between the classical or macroscopic
views and the statistical or microscopic views.

Basic Concepts and Terminologies    Conservation Principle
1.3 Property, State, Phase
We need to know various thermodynamic properties
for any quantitative description of matter.

Property: Any quantity of the system, which is
independent of the path or history how the state is
reached.
State: The state is defined in terms of a certain
observable     macroscopic      properties  such    as
temperature, volume, pressure, etc. Each property in a
given state of the system should have only one definite
value.
Phase: A homogeneous quantity of matter of the same
type of molecules, e.g. solid or gas phase.
Basic Concepts and Terminologies    Property, State, Phase
Properties:
density, volume,
temperature, etc

Matter
System

Phase:
solid, liquid, or gas

Basic Concepts and Terminologies     Property, State, Phase
Relationship between State and Properties

State                   Properties

T ,  , P, u ,
s, x, etc

Basic Concepts and Terminologies       Property, State, Phase
Extensive and Intensive Properties

Extensive Property : proportional to mass

U,      H, V

Intensive Property : independent of mass
M     M    M
v , h , u
V     H    U

Basic Concepts and Terminologies      Property, State, Phase
(Thermodynamic) Properties

Specific volume : volume per unit mass

Density : inverse of the specific volume

Pressure : the normal component of force per unit
area. The pressure is the same in all directions in a
fluid in equilibrium.

Temperature : measure of hotness or coldness.
Exact definition depends on the 0th law                       of
thermodynamics and the temperature scale.
etc.

Basic Concepts and Terminologies     Property, State, Phase
Transport Properties

Diffusive transport by chaotic molecular motions

Mass: diffusion coefficient(D)
Momentum: viscosity()
Energy: thermal conductivity()

Dimensionless numbers:
Prandtl number= /
Schmidt number= /D
Lewis number= /D

Basic Concepts and Terminologies     Property, State, Phase
1.4 Process and Cycle
Process: A path of states through which the system
passes
Cycle: A process the initial and final states are identical

Property                     Final
B                         state

Initial           Cycle
state

Property A

Basic Concepts and Terminologies                 Process and Cycle
Equilibrium: A state of balance, which goes through
no change with time when it is isolated from the
surrounding.

-Mechanical Equilibrium
-Thermal Equilibrium
Thermodynamic Equilibrium
-Phase Equilibrium
-Chemical Equilibrium

Nonequilibrium

Equilibrium
Basic Concepts and Terminologies                  Process and Cycle
Quasi-equilibrium process: A process in which the
deviation from equilibrium is infinitesimal. All the
states the system passes through may be
considered as equilibrium states.

Property                               FS
B
FS
Intermediate states
IS                       cannot be defined
if they are not
IS
in equilibrium

Property A

Basic Concepts and Terminologies                    Process and Cycle
Processes

Isothermal: temperature fixed
Isobaric: volume fixed
Isochoric: pressure fixed
Isentropic: entropy fixed
Isenthalpic: enthalpy fixed

Basic Concepts and Terminologies   Process and Cycle
1.5 The 0th Law of Thermodynamics
Temperature
When two systems are in thermal equilibrium with a
third system, they also are in thermal equilibrium with
each other.

This is the basis of any temperature measurement
using a reference system, called a thermometer.

Basic Concepts and Terminologies   The 0th Law of Thermodynamics Temperature
Temperature Scale
Ice point: the temperature of a mixture of ice and water in
equilibrium with saturated air at 1atm
Steam point: the temperature of a mixture of steam and
water in equilibrium with saturated air at 1atm

Celsius(°C): ice point=0°C
steam point=100°C
Fahrenheit(F): ice point=32F
steam point=212F

At the 10th GPM(1954) the Celsius scale was redefined in
terms of the triple point of water(0.01°C) and the ideal
gas temperature scale.
Basic Concepts and Terminologies   The 0th Law of Thermodynamics Temperature
Absolute Temperature Scale
K(Kelvin) = °C + 273.15
R(Rankine) = F + 459.67

ITS-90: International Temperature Scale(1989)
Fixed and easily reproducible points that are
assigned definite numerical values of temperature

Specified formulas relating temperature to the
instruments for interpolation between the defining
fixed points

Basic Concepts and Terminologies   The 0th Law of Thermodynamics Temperature
Basic Concepts and Terminologies   The 0th Law of Thermodynamics Temperature
1.6 Units and Dimensions
SI unit: second, meter, kilogram are the basic
units for time(t), length(L) and mass(M).
F=ma
Force: ML/t2 – Newton(N)
Energy: ML2/t2 – Joule(J)
Pressure: M/Lt2 – Pascal(Pa)
English Engineering System: sec, ft, lbm, lbf
Do you understand the difference?
Force, Weight, Mass ?
Energy, Power ?
Momentum, Pressure, Force ?
Basic Concepts and Terminologies    Units and Dimensions
Conversion of Units

1 lbm = 0.45359237 kg                           ma
F
1 ft =      0.3048 cm                           gc
1 ft =          12 in

1 lbm  32.174 ft / s 2
1 lbf                                 1 lbf  32.174 lbm ft / s 2
gc
or                  lbm ft
lbm ft                    g c  32.174           1
g c  32.174                                                2
lbf s 2                                  lbf s

Basic Concepts and Terminologies                Units and Dimensions
Specific Volume

V
v  lim
 V  V   m

V  : the smallest volume in the continuum domain
1

v

Basic Concepts and Terminologies         Units and Dimensions
Pressure
δFn
P = lim
 A A ' δA

1 Pa = 1 N/m2
1 bar = 0.1 MPa = 105 Pa
1 atm = 101325 Pa = 14.696 lbf/in2 (psi)
Absolute pressure and gauge pressure

gauge pressure
1 atm

absolute pressure

0
Basic Concepts and Terminologies                 Units and Dimensions

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