Quasi static process Thermodynamic cycle Thermo dynamic property Classification of properties
Table of Content (toc)
• A property of a system is an observable characteristic of the system.
• The quantities which define the state of the system are called properties.
• Whose value must be independent of the process
• The property is a point function
Thermodynamic properties are generally divided into two classes
surface tension, thermal conductivity etc.
Examples: mass, weight, enthalpy, entropy, internal energy etc.
• State of the system is a condition and is identified through certain observable properties such as pressure, volume, temperature, density etc.
• Two independent properties are sufficient to represent the state.
• The path is the series of states through which the system passes represented as shown in fig.
• Thermodynamic process: A system is said to have undergone a process when heat and work cross its boundary (state change)
• A system is said to have undergone a process if change of state occurs.
1. Expansion or compression of a gas
2. Expansion of steam through a nozzle
3. Conversion of water into steam
• The process during which the system remains almost in a state of thermodynamic equilibrium from one end state to other end state is called quasi static process.
• A system exists in a state of thermodynamic equilibrium when no change in anymacroscopic property is registered if the system isolated from surroundings.
• When a system from a given state undergoes a number of different processes and finally return to its initial state, then the system is said to have under gone a cycle.
• Any process whose end states are identical is called a cycle.
• Example: water (steam) that circulates through a steam power plant under goes a cycle
• In the fig the system has under gone a process
• from State 1 to state 2 along path A And again from State 2 to state 1 along path B System returns to its initial state completing a cycle
• Pressure of a gas is the force exerted by it per unit area on the sides or walls of the container due to the continuous collision of gas molecule.
• or Simply the force normal to the unit area of surface is called pressure acting on the surface.
• The S.I unit of pressure is Pascal.
• 1 Pascal = 1N/m2
• 1KPa =10³ N/m2
• 1 MPa =10⁶ N/m2
• 1 GPa = 10⁹ N/m2
Additional units of pressure are bar and atm
• 1 bar =10⁵ N/m2 =100 KN/m² =100Kpa
• 1 atm = 760 mm Hg = 1.01325 bar
• The normal force exerted by the atmospheric air on a unit system area is called atmospheric pressure.
• Atmospheric pressure is measured by the mercury barometer.
• The standard atm pressure is taken as 760 mm Hg.
• 760 mm Hg =1.01325 bar = 101.325 KN /m² =101.325Kpa
• The pressure recorded by the instrument pressure gauge above the atmospheric is called gauge pressure.
• The gauge measures the difference between the fluid pressure and pressure of fluid surrounding of the gauge (Generally air).
• When pressure of the system is less than atmospheric pressure, the gauge reads on the negative side of the atmospheric pressure. This Pressure is known as Vacuum or negative pressure.
• Absolute zero pressure will occur when molecules momentum is zero. Such a situation occurs only when there is perfect vacuum. The pressure measured from this level is called absolute pressure.
• Absolute pressure is obtained by the following relations.
• Absolute pressure = Atm Pressure + Gauge Pressure
• P abs = P atm + P g
• Absolute pressure= Atmospheric pressure –Vacuum Pressure
• P abs = P atm - P vac
• Volume is the space occupied by the substance
• Volume per unit mass of a substance is called Specific Volume.
• Units volume (V) m3 or liters
• Specific Volume (v) m3 / kg
• 10³ liters = 1 m³
• Or 1 Litre = 10-³ m³
• Density is the reciprocal of the Specific Volume
• Density, (rho)= 1/v = m/V Kg/m3
where,
• m = mass
• v = specific volume
• V = volume
What is property of thermodynamic system?
• A property of a system is an observable characteristic of the system.
• The quantities which define the state of the system are called properties.
• Whose value must be independent of the process
• The property is a point function
Classification of properties
Thermodynamic properties are generally divided into two classes
1. Intensive properties:
These are independent of mass of the substance Eg: pressure, temperature, density, specific gravity, specific volume,surface tension, thermal conductivity etc.
2. Extensive properties:
These are dependent on mass of the substanceExamples: mass, weight, enthalpy, entropy, internal energy etc.
State:
• State of the system is a condition and is identified through certain observable properties such as pressure, volume, temperature, density etc.
• Two independent properties are sufficient to represent the state.
Path:
• The path is the series of states through which the system passes represented as shown in fig.
Thermodynamic process
• Thermodynamic process: A system is said to have undergone a process when heat and work cross its boundary (state change)
• A system is said to have undergone a process if change of state occurs.
Examples of thermodynamic processes:
1. Expansion or compression of a gas
2. Expansion of steam through a nozzle
3. Conversion of water into steam
What is quasistatic process?
• The process during which the system remains almost in a state of thermodynamic equilibrium from one end state to other end state is called quasi static process.
• A system exists in a state of thermodynamic equilibrium when no change in anymacroscopic property is registered if the system isolated from surroundings.
What is the thermodynamic cycle?
• When a system from a given state undergoes a number of different processes and finally return to its initial state, then the system is said to have under gone a cycle.
• Any process whose end states are identical is called a cycle.
• Example: water (steam) that circulates through a steam power plant under goes a cycle
• In the fig the system has under gone a process
• from State 1 to state 2 along path A And again from State 2 to state 1 along path B System returns to its initial state completing a cycle
Pressure
• Pressure of a gas is the force exerted by it per unit area on the sides or walls of the container due to the continuous collision of gas molecule.
• or Simply the force normal to the unit area of surface is called pressure acting on the surface.
Units of pressure
• The S.I unit of pressure is Pascal.
• 1 Pascal = 1N/m2
• 1KPa =10³ N/m2
• 1 MPa =10⁶ N/m2
• 1 GPa = 10⁹ N/m2
Additional units of pressure are bar and atm
• 1 bar =10⁵ N/m2 =100 KN/m² =100Kpa
• 1 atm = 760 mm Hg = 1.01325 bar
Atmospheric pressure
• The normal force exerted by the atmospheric air on a unit system area is called atmospheric pressure.
• Atmospheric pressure is measured by the mercury barometer.
• The standard atm pressure is taken as 760 mm Hg.
• 760 mm Hg =1.01325 bar = 101.325 KN /m² =101.325Kpa
Gauge Pressure
• The pressure recorded by the instrument pressure gauge above the atmospheric is called gauge pressure.
• The gauge measures the difference between the fluid pressure and pressure of fluid surrounding of the gauge (Generally air).
Vacuum Pressure (Pvac)
• When pressure of the system is less than atmospheric pressure, the gauge reads on the negative side of the atmospheric pressure. This Pressure is known as Vacuum or negative pressure.
Absolute Pressure (Pabs or P)
• Absolute zero pressure will occur when molecules momentum is zero. Such a situation occurs only when there is perfect vacuum. The pressure measured from this level is called absolute pressure.
• Absolute pressure is obtained by the following relations.
• Absolute pressure = Atm Pressure + Gauge Pressure
• P abs = P atm + P g
• Absolute pressure= Atmospheric pressure –Vacuum Pressure
• P abs = P atm - P vac
Volume
• Volume is the space occupied by the substance
• Volume per unit mass of a substance is called Specific Volume.
• Units volume (V) m3 or liters
• Specific Volume (v) m3 / kg
• 10³ liters = 1 m³
• Or 1 Litre = 10-³ m³
Density
• Density is the reciprocal of the Specific Volume
• Density, (rho)= 1/v = m/V Kg/m3
where,
• m = mass
• v = specific volume
• V = volume
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