Thermodynamics
PERSONAL NOTES::
1 st Law Of Thermodynamics
Concepts::
~Energy conservation
~Energy can not be created nor destroyed but can change its form.
~Heat is a form of energy
~Absolute values of internal energies cant be calculated
~If heat is added to a system then it has a + sign convection
~If work is done by the system it has a - sign convection
Gibbs Phase Rule
It determines minimum no of intensive variables that must be arbitarirly fixed to fix all the other properties iof the system.
The phse ruke variables are the Temperature, Pressure and the Composition.
At F=0 system in invarient, Then maximum no of pahses that can exist in equilibrium in given by P= 2+N
At equilibrium driving forces are zero
Chemical potential causes mass to flow across phases rather concentraction difference
PVT BEHAVIOR OF PURE FLUIDS
When a fuel is burned under adiabatic conditions in the presence of oxygen or air , the maximum temp. attained by the system is called the adiabatic flame temperature.
Max temp. is attainable when the fuel is burned in the theoretically amount of pore oxygen.
Combustion in the presence of excess air or the oxygen will have adiabatic flame temp less than the maximum attainable theoretical adiabatic flame temp.
Flame temperature calculation are applicable for the exothermic reactions only.
The terms B/V, B/V2 etc of the virial expansion depends upon molecular interaction in ideal gases such interaction do not exist
When Papproches to 0 volume increses and term like B/v approaches to less contribution
Hence as P approaches 0 Z approaches 1
Internal energy is a function of temperature and pressure.
But for an ideal gas it is the function of Temperature only
For an ideal gas cp, cv, Δu, Δ H are all functions of functions of temperature only
2nd Law Of Thermodynamics
Concepts
Heat is a less useful form of energy in contrast to the forms like electrical, mechanical or work
Work can be converted into other forms of energy and neglecting the frictional losses the conversion can approach to the efficiency of 100%
It is impossible by a cyclic process to convert heat absorbed by the system to convert completely into work done
No engine can have efficiency greater than that of Carnot engine operating between same temperature levels.
The thermal efficiency of the Carnot engine depends only on the temperature levels and not upon the working substance of the engine.
Coefficient of performance (COP) of heat pumps can never be infinity.
Entropy
The entropy change of a heat reservoir is always given by Q/T
Entropy change is a state function and change is identical whether the change is bought about by a reversible or irreversible processes
Appliactions of Thermodynamics
Turbines
Turbines uses superheated steam as working fluid exoands to convert internal energy as shaft work of the turbine.
Work of a turbine is
Ws= H2-H1
Isentropic work of a turbine is the maximum work obtainable from expansion process of a aturbine
Efficiency, n= Ws/w(isentropic)=ΔH/ΔH isentropic
Efficiency of an expander is in the range 0.7 to 0.8
Isentropic expansion results in greater change in enthalpy and hence more work
Isentropic expansion is proceede at constant entropy
Calculations are first made for isentropic expansion and then taking into consideration efficiency for actual expansio calculations
PERSONAL NOTES::
1 st Law Of Thermodynamics
Concepts::
~Energy conservation
~Energy can not be created nor destroyed but can change its form.
~Heat is a form of energy
~Absolute values of internal energies cant be calculated
~If heat is added to a system then it has a + sign convection
~If work is done by the system it has a - sign convection
Gibbs Phase Rule
It determines minimum no of intensive variables that must be arbitarirly fixed to fix all the other properties iof the system.
The phse ruke variables are the Temperature, Pressure and the Composition.
At F=0 system in invarient, Then maximum no of pahses that can exist in equilibrium in given by P= 2+N
At equilibrium driving forces are zero
Chemical potential causes mass to flow across phases rather concentraction difference
PVT BEHAVIOR OF PURE FLUIDS
When a fuel is burned under adiabatic conditions in the presence of oxygen or air , the maximum temp. attained by the system is called the adiabatic flame temperature.
Max temp. is attainable when the fuel is burned in the theoretically amount of pore oxygen.
Combustion in the presence of excess air or the oxygen will have adiabatic flame temp less than the maximum attainable theoretical adiabatic flame temp.
Flame temperature calculation are applicable for the exothermic reactions only.
The terms B/V, B/V2 etc of the virial expansion depends upon molecular interaction in ideal gases such interaction do not exist
When Papproches to 0 volume increses and term like B/v approaches to less contribution
Hence as P approaches 0 Z approaches 1
Internal energy is a function of temperature and pressure.
But for an ideal gas it is the function of Temperature only
For an ideal gas cp, cv, Δu, Δ H are all functions of functions of temperature only
2nd Law Of Thermodynamics
Concepts
Heat is a less useful form of energy in contrast to the forms like electrical, mechanical or work
Work can be converted into other forms of energy and neglecting the frictional losses the conversion can approach to the efficiency of 100%
It is impossible by a cyclic process to convert heat absorbed by the system to convert completely into work done
No engine can have efficiency greater than that of Carnot engine operating between same temperature levels.
The thermal efficiency of the Carnot engine depends only on the temperature levels and not upon the working substance of the engine.
Coefficient of performance (COP) of heat pumps can never be infinity.
Entropy
The entropy change of a heat reservoir is always given by Q/T
Entropy change is a state function and change is identical whether the change is bought about by a reversible or irreversible processes
Appliactions of Thermodynamics
Turbines
Turbines uses superheated steam as working fluid exoands to convert internal energy as shaft work of the turbine.
Work of a turbine is
Ws= H2-H1
Isentropic work of a turbine is the maximum work obtainable from expansion process of a aturbine
Efficiency, n= Ws/w(isentropic)=ΔH/ΔH isentropic
Efficiency of an expander is in the range 0.7 to 0.8
Isentropic expansion results in greater change in enthalpy and hence more work
Isentropic expansion is proceede at constant entropy
Calculations are first made for isentropic expansion and then taking into consideration efficiency for actual expansio calculations
