Fundamentals of Mechanical Engineering

MD. Imran Hosen

Lecturer- IPE
Primeasia University
 Fundamentals of Mechanical Engineering

1. Thermodynamics
1. Solid Mechanics
2. Engineering Mechanics
2. Heat Transfer
3. Fluid Mechanics
Thermo means Heat

Dynamics means motion under the action of force

Thermodynamics is the branch of science dealing with heat or work (Broadly

energy interaction) and related changes in the physical properties of substance.
 System , Surroundings and Boundary

System A quantity of matter or a region in space chosen for study.

Surroundings The mass or region outside the system

Boundary The real or imaginary surface that separates the system from its surroundings.
 Closed Isolated
Open system system system
• Both mass and • Only energy can • No transfer of
energy can cross the energy and
cross the boundary matter across
boundary • e.g. the boundary
• e.g. Pump, Refrigerator, AC • e.g.
compressor, Thermo flask,
turbine, Heat universe
exchanger
 Properties of system
 Pressure, temperature, volume, entropy, internal energy.

Pressure
 Thermodynamic point and path functions

A Point function (also known as state

function) is a function whose value depends
on the final and initial states of the
thermodynamic process.
Example of point functions are density,
enthalpy, internal energy, entropy etc.

A Path function is a function whose value

depends on the path followed by
the thermodynamic process.
An example of path function is work done
in a thermodynamic process. Work done
in a thermodynamic process is dependent
on the path followed by the process.
 Thermodynamic State, Process & Cycle
Thermodynamic state of a system is its
condition at a specific time; that is fully
identified by values of a suitable set of
parameters known as state parameters or
state variables thermodynamic variables.

When a system changes its state from one equilibrium state to

another equilibrium state, then the path of successive states through
which the system has passed is known as thermodynamic process.
1-2 represents a thermodynamic process.

When a process or processes are performed on a system in such a way

that the final state is identical with the initial state, it is then known as
a thermodynamic cycle or cyclic process. 1-A-2 and 2-B-1 are
processes whereas 1-A-2-B-1 is a thermodynamic cycle.
 The Laws of Thermodynamics

There are 4 laws of thermodynamics:

• Zeroth law
• 1st law of thermodynamics
• 2nd law of thermodynamics
• 3rd law of thermodynamics
 Thermodynamic Laws

Zeroth law
The zeroth law of thermodynamics states that if two thermodynamic systems
are each in thermal equilibrium with a third system, then they are in thermal
equilibrium with each other

First law
The first law of thermodynamics states that, “Energy can
neither be created nor destroyed it can only be transferred from
one form to another”.
For example, turning on a light would seem to produce
energy; however, it is electrical energy that is converted.

First law is also known as Law of Conservation of Energy.

 2nd Law of Thermodynamic

The Kelvin–Planck statement of the second law of thermodynamics, also known as the heat engine statement,
states that it is impossible to devise a heat engine that takes heat from the hot reservoir ( ) and converts all the energy
into useful external work without losing heat to the cold reservoir .

Heat Engine
 2nd Law of Thermodynamic

Clausius Statement from the second law of thermodynamics states that: “It is impossible to design a device which
works on a cycle and produce no other effect other than heat transfer from a cold body to a hot body.”

Refrigerator

Co efficient of Performance (COP)

Heat Pump

• Show that COP(Heat pump) >COP(Refrigerator)

• An Engine works between 400°C and 40°C. Find out the engine
efficiency.

• A cold storage is to be maintained at -5°C while the surroundings are at

35°C. The heat leakage to the surroundings from the cold storage is
estimated to be 29 kJ. The actual C.O.P of the refrigeration plant is one-
third of an ideal plant working between the same temperatures. Find
the work done required to drive the plant.

• Suppose a water melon was kept in a fridge whose temperature was

30°C which is equal to room temperature. After 1 hour the water
melon got cold and also the temperature of the room was raised into
35°C. What will be the COPR?
Work done for Adiabatic Process
Work done in Isovolumetric Process

Work done in Isobaric Process

• A balloon contains 5.00 moles of monatomic Ideal gas. As energy is
added to the system by heat ( absorption from the sun), the volume
increases by 25% at a constant temperature of 27°C. find the work
done by the gas in expanding the balloon, the thermal energy Q
transferred to the gas and the work done on the gas.
 Thermodynamic Cycle
• Otto cycle ( SI/Petrol Engine)
• Diesel cycle ( CI/ Diesel Engine)
• Rankine cycle ( Boiler)
• Brayton cycle ( Gas Engine)
• Reverse Carnot cycle ( Refrigerator)
Petrol/SI Engine and Otto Cycle
• Process 0–1 a mass of air is drawn into piston/cylinder arrangement at constant pressure.
• Process 1–2 is an adiabatic (isentropic) compression of the charge as the piston moves from bottom dead
center (BDC) to top dead center (TDC).
• Process 2–3 is a constant-volume heat transfer to the working gas from an external source while the piston is
at top dead center. This process is intended to represent the ignition of the fuel-air mixture and the
subsequent rapid burning.
• Process 3–4 is an adiabatic (isentropic) expansion (power stroke).
• Process 4–1 completes the cycle by a constant-volume process in which heat is rejected from the air while
the piston is at bottom dead center.
• Process 1–0 the mass of air is released to the atmosphere in a constant pressure process.
Air Standard Efficiency for Otto cycle
Diesel/CI Engine and Diesel Cycle
0 → 1 and 1 → 0
When the engine is working on the full throttle, the Process 0 → 1 and 1 → 0 represents the suction and the exhaust process of Thermodynamic
cycle in the P-V diagram and the effect of these two processes considered as nullified.
1→2
The process 1 → 2 is the isentropic compression of the air in the cylinder while piston moves from the bottom dead center (BDC) to the top dead
center (TDC)
2→3
During the process, 2 → 3 the heat is supplied at a constant pressure. This is the compression ignition and the combustion of the injected fuel is
takes place in the cylinder during this process 2 → 3.
3→4&4→1
These two processes 3 → 4 & 4 → 1 will represent the isentropic expansion (Piston moves from the Top dead center to the bottom dead center) and
the constant volume heat rejection respectively.
 Efficiency of an IC Engine

B.
k = Number of cylinders
Pm = Mean effective pressure in bar.
B. A = Area of the piston in meter square.
n = Rotational speed of the engine or RPM speed. n= N
N= Revolution per min for 2 stroke engine, n=N/2 for 4 stroke engine
W= Brake load in Newton L = Length of stroke in meters,
L= Length of arm in meter
= Indicated thermal Efficiency \ Air standard efficiency
Problem-1
A four stroke diesel engine has a cylinder bore of 150 mm and a stroke of 250 mm. The crankshaft
speed is 300 RPM and fuel consumption is 1.2 kg/h, having a calorific value of 39 900 kJ/kg. The
indicated mean effective pressure is 5.5 bar. If the compression ratio is 15 and cut-off ratio is 1.8,
calculate the relative efficiency, taking y= 1.4.
Problem-2
The diameter and stroke length of a single cylinder two stroke gas engine, working on the constant
volume cycle, are 200 mm and 300 mm respectively with clearance volume 2.78 liters. When the
engine is running at 135 RPM, the indicated mean effective pressure was 5.2 bar and the gas
consumption 8.8 m³/hour. If the calorific value of the gas used is 16 350 kj/m³, find
1. Air standard efficiency;
2. Indicated power developed by the engine;
3. Indicated thermal efficiency of the engine.
Problem-2
An engine uses 6.5 kg of oil per hour of calorific value 30 000 kJ/kg. If the B.P. of the engine is 22 kW
and mechanical efficiency 85%, calculate:
1. Indicated thermal the four efficiency;
2. Brake thermal efficiency;
3. Specific fuel consumption in kg/B.P/h.