Thermodynamics Formulas by Thanga

1. Applied Thermodynamics for Mechananical Engineering:

Heat Engine:
It is a device a machine which converted heat energy into mechanical work.

Absolute pressure = Atmospheric pressure± Gauge pressure
Absolute temperature = Temperature in C + 273
Heat transfer, Q = m .C .(T2 – T1) in kJ
Atmospheric pressure = 1.01325 bar
=760 mm of Hg
Standard temperature = 15 C = 288K
Standard pressure = 760 mm of Hg = 101.325 kN/m2

2. For air : Cp =1.005 kJ/kgK Cv = 0.718 kJ/kgK
Ɣ = 1.4
For water : Cp = 4.19 kJ/kgK
Characteristic gas equation : p.V = m.R.T
General gas equation : p.V/T = C
First law of Thermodynamics : Q = W+ΔU kJ
p.V = C (Boyle’s law)
V/T = C (Charle’s law)
Gas constant : R= 0.287 kJ/kgK
Universal gas constant = 8.314 J / kg mole K

3. Constant volume process =Iso- chloric
Constant pressure process = Iso- baric
Constant Temperature process = Iso- thermal



Law of conservation of Energy:
It states that, energy can neither be created nor destroyed, but it may be
converted from one form into another form.

4. Zeroth law of Thermodynamics:
It states that, when two systems are separately in thermal equilibrium
with a third system, then they themselves are in thermal equilibrium with each
other.
First law of Thermodynamics:
It states that, when a system undergoes a cycle,the network transfer is equal
to the net heat transfer.

5. Second law of thermodynamics:
1. Kelvin planck statement:
2. Clausius statement
Kelvin planck statement:
It is impossible to construct a heat engine working on a cyclic process ,
whose only purpose is to convert all the heat energy supplied to it into an equal
amount of work.
Clausius statement:

6. Heat can flow from a hot body to a cold body without any help. But heat
cannot flow from a cold body to a hot body without any external work

Thermodynamic cycles:
 Carnot cycle (constant temperature cycle)
 Otto cycle (constant volume cycle)
 Diesel cycle
 Joule or Brayton cycle (constant pressure cycle)
 Dual combustion cycle
 Rankine cycle

7. Reversible cycle:
A device which operates on a reversed cycle is known as heat pump.


Mean effective pressure:
The mean effective pressure of a cycle or heat engine is the average
pressure acting on the piston during the working stroke. It is given by the mean
height of the p-V diagram. It is expreesed in N/ m²

8. Diagram factor (Card factor)
Diagram factor is the ratio of area of actual indicator diagram to the area of
theoretical Indicator digarm.
Heat engine:
 Internal combustion engine
 External combustion engine

Internal combustion engine:

9. In internal combustion engines, the combustion of fuel takes place inside
the engine cyclinder.
External combustion engine:
In external combustion engines, the combustion of fuel takes place outside
the working cylinder.
Major components of an internal combustion engine:
 Cylinder block
 Cylinder head
 Cylinder liners

10.  Crankcase
 Oil sump
 Piston
 Piston rings
 Connecting rod
 Crankshaft
 Camshaft
 Valves
 Valve actuating mechanism
Fuel supply system in petrol (S.I) engines:

11. Storage tank
Fuel tank
Fuel filter
Carburettor


Fuel pumps:
 Mechanical pump
 Electrical fuel pump

12. Carburettors:
A carburetter is a device, which vaporizes the fuel &mixes it with the
air. The process of vapourizing the fuel & mixing it with air in a carburetor is
called carburation.

Requirements of a carburetor:
 It should atomize & vaporize the fuel
 It should prepare a mixture of petrol & air in correct properties
 It should supply the fuel air mixture to the engine

13.  It should measure & supply the proper quantity &
Propotion of air & fuel under all conditions of engine operations such as
temperature, speed & load
 It should maintain a small reserve of fuel at a constant head
 It should withstand vibrations & jerks
Types of Carburettor:
1. Simple Carburettor
2. Solex Carburettor

14. Simple Carburettor:
It is consists of float chamber, Throttle valve, Mixing chamber,
Venturi, Choke or Stranglar, Float.
Solex Carburettor:
It is consists of Float, Main jet, Venturi, Emulsion tube, Air
correction jet, Spraying nozzels, Butterfly valve, Float disc, Starter petrol
jet, Starter air jet, Cold starting passage, Bi-starter lever, Pilot jet, Air

15. bleeded orifice, Volume control screw, Idle port, Slow speed operating,
Pump injector, Pump lever, Pump jet, Pump inlet valve, Well

Fuel air ratio:
Air- fuel ratio plays an important role in an engine. Mixing of less
fuel with the same amount of air gives lean or weak mixture.The metering
rod in the carburetor measures the amount of fuel flowing into the mixing
chamber.
Types of System:

16. 1. Open System(Control Volume)
2. Closed System(Control Mass)
3. Isolated System
4. Homogeneous System
5. Heterogeneous System


Open system:
In this type of system mass&energy both can cross the boundry of the
system.

17. Ex :
Air compressor
Turbine
Pump
Boiler
Closed System:
Energy can cross the bountry but not the mass.
Ex:
Gas enclosed in piston cylinder assembly

18. Dry cell
Isolated System:
Mass & energy doth cannot cross the boundry of
the system . It is completely uninfluenced from the surroundings. It has fixed
mass & Energy.
Examples;
1.Thermoflask
2.Universe
Homogeneous System:

19. A System consisting of a single phase is called a homogeneous system.
Hetrogeneous System:
A System which consist more than one place at a time is called a
heterogeneous system.
Thermodynamic Equilibrium:
A System is said to be in a state of thermodynamic equilibrium when
no change in any
macroscopic property is registered , if the system is isolated from its
surroundings.

20. Types:
1. Mechanical Equilibrium.
2. Chemical Equilibrium.
3. Thermal Equilibrium.
Mechanical Equilibrium:
There is no unbalanced force within the system itself & also between
the system & its surroundings.

Chemical Equilibrium:

21. There is no chemical reaction within the system& no transfer of matter
from one part of the system to another.
Thermal Equilibrium:
There is no temperature difference parts of the system or between the
system & its surroundings.

State:
When all the properties of a system have definite values, the system is said
to exist at a definite state.

22. Path:
Any operation in which one or more of the properties of a system changes is
called a change of state.
Process:
When the path is completely specified, the change of state is called a
process.
Cycle:

23. A thermodynamic cycle is defined as a series of two or more processes for
which the final state is identical with the initial state.