Basic Engineering Thermodynamics U3MEA02

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Basic Engineering Thermodynamics U3MEA02

• Prepared by
• Mr.N.Dilip Raja, Assistant Professor,
• Department of Mechanical Engineering,
• VelTech Dr. RR Dr. SR Technical University.

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UNIT - 1
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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

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• 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

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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.

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• 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

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• 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

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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

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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

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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).

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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

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LAWS OF THERMODYNAMICS

• Zeroth law of thermodynamics
• First law of thermodynamics
• For open system ?W ?Q
• For closed system Q W ?U

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STEADY FLOW ENERGY EQUATION
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UNIT - 2
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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.

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CARNOT THEOREM

• Carnots 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.

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CARNOT CYCLE
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• 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.

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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

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UNIT - 3
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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. 

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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.

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• Boyels law or
• Charles law or
• Gay Lusacs law or
• Daltons law of partial pressure
• Amagats law of partial volume

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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.

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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
  inter-particle force  (such as the Van der Waals
  force). 

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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

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COMPRESSIBILTY CHART
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UNIT - 4
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THERMODYNAMIC POTENTIAL
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MAXWELL EQUATIONS
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TdS EQUATIONS
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JOULE THOMSON EFFECT

• In thermodynamics, the JouleThomson
  effect or JouleKelvin effect or KelvinJoule
  effect or JouleThomson 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 JouleThomson
  process. At room temperature, all gases
  excepthydrogen, heliun and neon cool upon
  expansion by the JouleThomson 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.

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JOULE THOMSON CO-EFFICIENT

• The rate of change of temperature  with respect
  to pressure  in a JouleThomson process (that is,
  at constant enthalpy ) is the JouleThomson
  (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

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ClausiusClapeyron relation

• The ClausiusClapeyron 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 (PT)
  diagram, the line separating the two phases is
  known as the coexistence curve. The
  ClausiusClapeyron relation gives the slope  of
  the tangents to this curve. Mathematically,

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UNIT - 5
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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. 

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FORMATION OF STEAM
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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.

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P V diagram
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pT diagram
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TV DIAGRAM
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hS diagram
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pVT diagram
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