thermodynamics-an easy approach (rasikh tariq)
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By Rasikh Tariq
An Easy Approach-Thermodynamics
Thermodynamics is the branch of natural science concerned with heat and its relation to other forms of energy and work.
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What is Thermodynamics?
Basis of Thermodynamics
Thermodynamics is entirely based upon following items : Zeroth Law of Thermodynamics First law of Thermodynamics Second Law of Thermodynamics Entropy
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Basics of Thermodynamics
Surroundings:-Any mass or region outside the
system is called the surroundings.
System:-A system is defined as a quantity of matter or a
region in space chosen for study.
Boundary:-The Real or Imaginary surface that separates the system from its surroundings is called the boundary. Mathematically, the boundary has zero thickness.
System
Closed System
Open System
Isolated System
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Types of System
A closed system consists of a fixed amount Of mass, and no mass can cross its boundary.
In open systems, matter may flow in and out of the system boundaries.
Human Body is a Open System
Characteristic of a system is called a Property.Common are:-
Pressure PTemperature TVolume VMass m
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Properties of a System
Property
Extensive Intensive
Depends upon Size-or extent-of the system. E.g. Total mass, total
volume and momentum
Properties Independent of the mass of the system.
E.g. Temperature, pressure and density
Note This Specially
Density is defined as Mass per unit Volume.
The Reciprocal of Density is called Specific Volume.
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Density and Specific Volume
Equilibrium
Thermal Equilibrium Mechanical Equilibrium Phase Equilibrium Chemical Equilibrium
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Equilibrium
Thermodynamics deals with Equilibrium States. The Word “Equilibrium” implies a state of balance
If the Temperature is
the same throughout the entire system
If there is no change in
pressure at any point of the system with
time
When the mass of each phase reaches an equilibrium level & stays
there
If the Chemical
Composition does not
changes with time
A System will not be in Equilibrium unless all the relevant equilibrium criteria are satisfied
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The State PostulateAny two independent intensive thermodynamic properties are sufficient to describe
the state of a system containing a single pure substance.
Processes and CyclesAny Change that a System undergoes from one
equilibrium state to another is called a Process.And the series of states through which a system passes is called the Path of the Process
Quasi-Equilibrium StateA Quasi-equilibrium process can be viewed as a sufficiently slow process that allows the system to
adjust itself internally so that properties in one part of the system do no change any faster than those at
the Other parts.
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Zeroth Law of Thermodynamics
By Replacing the third body with a thermometer, The Zeroth Law can be
restated as “Two Bodies are in Thermal equilibrium
if both have the same temperature reading even if they are not in contact.”
The Zeroth Law of Thermodynamics states that if two bodies are in Thermal Equilibrium with a third body, they are also in Thermal Equilibrium
with each other
Zeroth Law serves as the basis of
validity of TEMPERATURE
measurement.
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Temperature ScalesWe had 4 temperature Scales:1. Celsius Scale2. Kelvin Scale3. Fahrenheit Scale4. Rankine ScaleThe Kelvin Scale is related to Celsius scale by
The Fahrenheit Scale is related to Celsius scale by
The Rankine Scale is related to scale by
Ice-Point:- Mixture of ice and liquid water that is in equilibrium with air saturated with vapor at1atm pressure
Steam-Point:- Mixture of Liquid water and water vapor that is in equilibrium at1atm pressure
Pressure is defined as normal force exerted by a fluid per unit area.
Unit is Pascal Some different units of Pressure are
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Pressure
Absolute Pressure:- The actual pressure at a given position is called Absolute Pressure and is measured relative to absolute Vacuum.Gage Pressure:-The difference between the absolute pressure and the local atm. Pressure are called the Gage Pressure.Vacuum Pressure:-Pressure below the atm. Pressure are called Vacuum pressure measured by vacuum gauges.
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Forms of EnergyThermal Mechanica
l Kinetic Potential Electric Chemical Nuclear
The Total Energy of a system on a unit mass basis is denoted by “e” and is expressed as
Microscopic and Macroscopic Forms of EnergyThe Macroscopic forms of energy are those a system possesses as a whole with respect
to some outside reference frame such as Kinetic Energy and Potential Energies.
The Microscopic forms of Energy are those related to the molecular structure of a system and the degree of the molecular activity, and they are independent of outside
Reference Frames.The sum of all the microscopic forms of energy is called the Internal Energy of a system and is denoted by
“U”.
On Unit Basis
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Total EnergyThe Magnetic, electric and surface tension effects are significant in some
specialized cases only and are usually ignored. Hence, The total Energy is expressed as
And on Unit basis can be expressed as
Mass & Volume Flow RateAmount of mass flowing through as cross section
per unit time is called mass flow rate It is related to the volume flow rate.
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Internal EnergyThe sum of all the microscopic forms of energy is called the Internal Energy of a system.
Energy Transfer by HeatHeat is defined as
“The Form of Energy that is transferred between two systems (or a system and its surroundings) by
virtue of a temperature difference.”
Adiabatic Process:-A process in which there is no heat transfer is called an adiabatic process. i.e dQ=0
Method of Heat Transfer
Conduction Convection Radiation
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Conduction is the transfer of energy from the more energies particle of a substance to the adjacent less energetic ones as a result of interaction between the particles.Convection is the transfer of heat between a solid surface and the adjacent fluid that is in motion.Radiation is the transfer of energy due to emission of electromagnetic waves.
Energy Transfer by WorkWork is energy transfer associated with a force acting through a distance
And on Unit basis can be expressed as:
It is also called Power.
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Path Functions have Inexact differentials designated by a symbolDifferential amount of heat or work is represented by or respectively. However, properties are point functions have exact differentials.
Forms of Work
Mechanical forms of Work
Shaft Work
Spring Work
Non-Mechanical
forms of Work
Electric Work
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The First Law of ThermodynamicsEnergy can not be created nor destroyed but can change its form from one
to another.
Energy BalanceThe net change in the total energy of a system during a process is equal to the difference between the total energy entering and the total energy leaving the
system during that process
Where
A Practical Application
Δz
Here,PE = 10 kJ
KE = 0
Now,PE = 7 kJKE = 3 kJ
Mechanism of Heat Transfer
Mass Flow Work Transfer Heat Transfer
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For a Cycle
And in Ratio Form:
Energy balance for any system
undergoing any kind of process expressed more compactly as
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EfficiencySimply, Desired output divided by desired input is called
Efficiency
Efficiency of Generator
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Pure SubstanceA substance that had a fixed chemical composition
throughout is called a Pure SubstanceAre composed of a single chemical species (e.g., either O2 or CO2
but not a mixture of O2 and CO2).May exist in more than one phase (e.g., solid and liquid)
A mixture of snow, ice, liquid water and water vapor is a pure substance.
Properties Extensive
Intensive
Mass m -
Temperature - T
Pressure - P
Volume V v = V/m (specific volume)
Internal Energy U u = U/m (specific internal energy)
Enthalpy H h = H/m (specific enthalpy)
Any extensive property can be made intensive (specific) by dividing by mass.
Compressed LiquidExistance of pure Substance in Liquid Phase Or the Liquid not about to Vaporize.Saturated LiquidA Liquid about to Vaporize.Satutrated Vapour:-A vapour that is about to condense.Super-Heated Vapour:-A vapor that is not about to condenseThe temprature at which pure Substance changes phase is called a Saturation Temprature.The Pressure at which pure Substance changes phase is called a Saturation Pressure.The point at which saturated liquid and saturated vapour states are identical.
P-v-T Relations
Constant Pressure Heating in Piston-Cylinder at P = 1 atm
Constant Pressure Heating in Piston-Cylinder at P = 2 atm
Temperature-Volume (T-v)Relation
Note directions of Isobars
Pressure-Volume (P-v)Relation
Note directions of Isotherms
P-v-T Surface