Transcript U3MEA02 Basic Engineering Thermodynamics

Basic Engineering Thermodynamics
U3MEA02
Prepared by
Mr.N.Dilip Raja, Assistant Professor,
Department of Mechanical Engineering,
VelTech Dr. RR & Dr. SR Technical University.
UNIT - 1
SYSTEM
• In thermodynamics – “system is a closed region
in space or a body upon which experiments or
study is conducted”.
• Types of system
▫ Open system : Energy transfer and mass transfer
take place. Eg: Pump, compressor, turbine.
▫ Closed system: Only energy transfer take place but
no mass transfer. Eg: Earths atmosphere, inflated
baloon
▫ Isolated system: Neither energy transfer nor mass
transfer take place. Eg: Flask
• Surrounding: Every thing apart from system is
called as surroundings
• Universe: Both system and surrounding together
is called as universe
• Boundary: The invisible layer which separates
system and surrounding is called boundary
• Control volume: The maximum volume occupied
by a system is called control volume
PROPERTIES
• In thermodynamics, properties are the
quantities used to determine the state of a
system
• Types of properties
▫ Intrinsic properties: These depend upon mass of
the system. Eg: mass, density, specific heat, etc.
▫ Extrinsic properties: These do not depend upon
mass of the system. Eg: pressue, temperature,
time, etc.
• State: In thermodynamics state is the term used
to denote the present conditions of the system
• Process: If a system experiences changes in
state, then it is called as process
• Cycle: A series of process in which the initial and
final states are the same is called as a cycle.
▫ Types of cycle
 Open cycle
 Closed cycle
• Equilibrium: In thermodynamics equilibrium is
a term used to determine whether there is a
process taking place in a system. If there is no
changes in states of a system, then it is said to be
in equilibrium
• Types of equilibrium
▫ Chemical
▫ Mechanical
▫ Thermodynamic
HEAT
• Heat is the form of energy transfer taking place
in a system by virtue of temperature difference.
• It is denoted by the symbol ‘Q’.
• Its unit is J (joules). Rate of heat transfer is ‘W’.
• Sign conversion
+ for heat given to a system
- For heat taken from a system
WORK
• Work is the form of energy transfer taking place
in a system because of change in volume.
• It is denoted by the symbol ‘W’.
• Its unit is J (joules).
• Sign conversion
+ for work taken from a system
- For heat given to a system
INTERNAL ENERGY
• The energy available within a system is called as
internal energy
• It is denoted by the symbol ‘U’.
• Change in internal energy is denoted by the
symbol ‘ U’.
• Its unit is J (joules).
ENTHALPY
• Enthalpy is a measure of the total energy of a
system. It includes the system's internal energy,
as well as its volume and pressure.
• It is denoted by the symbol ‘H’.
• Change in internal energy is denoted by the
symbol ‘ H’.
• Its unit is J (joules).
• H = U + pV
LAWS OF THERMODYNAMICS
• Zeroth law of thermodynamics:
• First law of thermodynamics:
▫ For open system: W = Q
▫ For closed system: Q = W + U
STEADY FLOW ENERGY EQUATION
UNIT - 2
SECOND LAW OF THERMODYNAMICS
• Kelvin statement: It is impossible, by means
of inanimate material agency, to derive
mechanical effect from any portion of matter by
cooling it below the temperature of the coldest of
the surrounding objects.
• Clausius statement: Heat can never pass
from a colder to a warmer body without some
other change, connected therewith, occurring at
the same time.
CARNOT THEOREM
• Carnot’s theorem(1824) is a principle that limits the maximum efficiency for any possible
engine. The efficiency solely depends on the temperature difference between the hot and
cold thermal reservoirs. Carnot's theorem states:
• All irreversible heat engines between two heat reservoirs are less efficient than a Carnot
engine operating between the same reservoirs.
• All reversible heat engines between two heat reservoirs are equally efficient with a Carnot
engine operating between the same reservoirs.
• In his ideal model, the heat of caloric converted into work could be reinstated by reversing
the motion of the cycle, a concept subsequently known as thermodynamic reversibility.
Carnot however further postulated that some caloric is lost, not being converted to
mechanical work. Hence no real heat engine could realise the Carnot cycle reversibility and
was condemned to be less efficient.
CARNOT CYCLE
• The Carnot cycle when acting as a heat engine consists of the following
steps:
Reversible isothermal expansion of the gas at the "hot"
temperature, T1 (isothermal heat addition or absorption). During
this step (1 to 2 on Figure 1, A to B in Figure 2) the gas is allowed to expand
and it does work on the surroundings. The temperature of the gas does not
change during the process, and thus the expansion is isothermal. The gas
expansion is propelled by absorption of heat energy Q1 and of entropy from
the high temperature reservoir.
Isentropic (reversible adiabatic) expansion of the gas (isentropic
work output). For this step (2 to 3 on Figure 1, B to C in Figure 2) the
piston and cylinder are assumed to be thermally insulated, thus they
neither gain nor lose heat. The gas continues to expand, doing work on the
surroundings, and losing an equivalent amount of internal energy. The gas
expansion causes it to cool to the "cold" temperature, T2. The entropy
remains unchanged.
Reversible isothermal compression of the gas at the "cold"
temperature, T2. (isothermal heat rejection) (3 to 4 on Figure 1, C to
D on Figure 2) Now the surroundings do work on the gas, causing an
amount of heat energy Q2 and of entropy to flow out of the gas to the low
temperature reservoir. (This is the same amount of entropy absorbed in
step 1, as can be seen from the Clausius inequality).
Isentropic compression of the gas (isentropic work input). (4 to 1 on
Figure 1, D to A on Figure 2) Once again the piston and cylinder are
assumed to be thermally insulated. During this step, the surroundings do
work on the gas, increasing its internal energy and compressing it, causing
the temperature to rise to T1. The entropy remains unchanged. At this point
the gas is in the same state as at the start of step 1.
ENTROPY
• Entropy is a measure of the number of specific
ways in which a system may be arranged, often
taken to be a measure of disorder, or a measure
of progressing towards thermodynamic
equilibrium. The entropy of an isolated system
never decreases, because isolated systems
spontaneously evolve towards thermodynamic
equilibrium, which is the state of maximum
entropy.
• Entropy was originally defined as
UNIT - 3
IDEAL GAS
• An ideal gas is a theoretical gas composed of a
set of randomly moving, non-interacting point
particles. The ideal gas concept is useful because
it obeys the ideal gas law, a simplified equation
of state.
IDEAL GAS LAW
• The ideal gas law is the equation of state of a
hypothetical ideal gas. It is a good approximation to
the behaviour of many gases under many conditions,
although it has several limitations. It was first stated
by Emile Clapeyron in 1834 as a combination of
Boyels law and Charles law. The ideal gas law is
often introduced in its common form:
• where P is the absolute pressure of the gas, V is the
volume of the gas, n is the amount if substance of
gas (measured in moles), T is the absolute
temperature of the gas and R is the ideal, or
universal, gas constant.
• Boyel’s law:
or
• Charle’s law
or
• Gay Lusac’s law
or
• Dalton’s law of partial pressure
• Amagat’s law of partial volume
REAL GAS
• Real gases – as opposed to a perfect or ideal
gas – exhibit properties that cannot be
explained entirely using the ideal gas law. To
understand the behaviour of real gases, the
following must be taken into account:
▫
▫
▫
▫
▫
compressibility effects;
Variable specific heat capacity
Van der Waals forces
non-equilibrium thermodynamic effects;
issues with molecular dissociation and elementary
reactions with variable composition.
Van der Waals equation
The van der Waals equation is an equation of
state for a fluid composed of particles that have a
non-zero volume and a pairwise attractive interparticle force (such as the Van der Waals force).
COMPRESSIBILTY FACTORY
• The compressibility factor (Z), also known as
the compression factor, is the ratio of the
molar volume of a gas to the molar volume of an
ideal gas at the same temperature and pressure.
It is a useful thermodynamic property for
modifying the ideal gas law to account for the
real gas behaviour.
• The compressibility factor is defined as
COMPRESSIBILTY CHART
UNIT - 4
THERMODYNAMIC POTENTIAL
MAXWELL EQUATIONS
TdS EQUATIONS
T
 P 
Tds  cv dT  T 
dv
 dv  cv dT 

 T  v
 v 
Tds  cP dT  T 
 dP  cP dT  Tv dP
 T  P
cv
cP
 T 
 T 
Tds  cP 
dv 
dP
 dv  cv 
 dP 
v

 v  P
 P  v
JOULE THOMSON EFFECT
• In thermodynamics, the Joule–Thomson effect or Joule–
Kelvin effect or Kelvin–Joule effect or Joule–Thomson
expansion describes the temperature change of a gas or liquid
when it is forced through a valve or porous plug while kept insulated
so that no heat is exchanged with the environment.[This procedure
is called a throttling process or Joule–Thomson process.[ At room
temperature, all gases excepthydrogen, heliun and neon cool upon
expansion by the Joule–Thomson process.
• The effect is named for James Prescott Joule and William Thomson,
1st Baron Kelvin, who discovered it in 1852 following earlier work by
Joule on Joule expansion, in which a gas undergoes free expansion
in a vacuum.
• In the Joule experiment, the gas expands in a vacuum and the
temperature drop of the system is zero, if the gas is ideal.
• The throttling process is of the highest technical importance. It is at
the heart of thermal machines such as refrigerators, air
conditioners, heat pumps, and liquefiers. Furthermore, throttling is
a fundamentally irreversible process. The throttling due to the flow
resistance in supply lines, heat exchangers, regenerators, and other
components of (thermal) machines is a source of losses that limits
the performance.
JOULE THOMSON CO-EFFICIENT
• The rate of change of temperature with respect
to pressure in a Joule–Thomson process (that
is, at constant enthalpy ) is the Joule–Thomson
(Kelvin) coefficient . This coefficient can be
expressed in terms of the gas's volume , its heat
capacity atr constant pressure, and hat capacity
at constant pressure, and its coefficient of
thermal expansion as:
Clausius–Clapeyron relation
• The Clausius–Clapeyron relation, named after
Rudolf Clausius and Benoit Paul Emile Clapeyron, is a
way of characterizing a discontinuous phase
transition between two phase of matter a single
constituent. On apressure - temperature (P–T) diagram,
the line separating the two phases is known as the
coexistence curve. The Clausius–Clapeyron relation
gives the slope of the tangents to this curve.
Mathematically,
UNIT - 5
STEAM
• Steam is the technical term for water vapour ,
the gaseous phase of water, which is formed
when water boils.
• Technically speaking, in terms of the chemistry
and physics, steam is invisible and cannot be
seen; however, in common language it is often
used to refer to the visible mist of water droplets
formed as this water vapour condenses in the
presence of (cooler) air.
• Water boils at a lower temperature than the
nominal 100 °C (212 °F) at standard
temperature and pressure.
• If heated further it becomes superheated steam.
FORMATION OF STEAM
TYPES OF STEAM
• Steam is traditionally created by heating a boiler via
burning coal and other fuels, but it is also possible to
create steam with solar energy.] Water vapour that
includes water droplets is described as wet steam.
• As wet steam is heated further, the droplets
evaporate, and at a high enough temperature (which
depends on the pressure) all of the water evaporates
and the system is in vapour-liquid equilibrium.
• Superheated steam is steam at a temperature higher
than its boiling point for the pressure which only
occurs where all the water has evaporated or has
been removed from the system.
P V diagram
pT diagram
TV DIAGRAM
hS diagram
pVT diagram
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