Thermodynamics can be defined as the science of energy.

Thermodynamics = Therme + Dynamis (Heat) (Power)

Thermodynamics

Conservation of energy principle

Application of thermodynamics

Human BodyRefrigeration and Air conditionersIC EnginesGas TurbinesWater HeaterSolar CollectorsPressure cooker ….

System, Surroundings & Boundary

System

A system is defined as a quantity of matter or a region in space chosen for study.

Surroundings

The mass or region outside the system is called the surroundings.

Boundary

The real or imaginary surface that separates the system from its surroundings is called the boundary.

System, Surroundings & Boundary

Closed System/Control Mass

A closed system consists of a fixed amount of mass, and no mass can cross its boundary. No mass can enter or leave a closed system. But energy, in the form of heat or work, can cross the boundary and the volume of a closed system does not have to be fixed.

In some special case, even energy is not allowed to cross the boundary, that system is called an isolated system.

Close system with fixed and moving boundary

Isolated System

ISOLATED System

m = const.E = const.

Mass NO

Energy NO

Open System/Control Volume

An open system, or a control volume is a properly selected region in space. It usually encloses a device that involves mass flow such as a compressor, turbine, or nozzle.

Any arbitrary region in space can be selected as a control volume.

The boundaries of a control volume are called a control surface, and they can be real or imaginary.

A control volume can be fixed in size and shape, or it may involve a moving boundary, most control volumes, however, have fixed boundaries and thus do not involve any moving boundaries.

e.g. Water Heater, Car Radiator, Turbine, Compressor

A control volume can involve fixed, moving, real, and imaginary boundaries.

An open system (a control volume) with one inlet and one exit.

Properties of a system

Intensive Properties• Intensive properties are those that are independent of the mass of a system, such

as temperature, pressure, and density.

Extensive Properties• Extensive properties are those whose values depend on the size or extent of the

system. Total mass, total volume, and total momentum are some examples of extensive properties

Specific Properties• Extensive properties per unit mass are called specific properties. Some examples of

specific properties are specific volume (v =V/m) and specific total energy (e =E/m).

Criterion to differentiate intensive andextensive properties.

Density & Specific Gravity

Density is defined as mass per unit volume.

The reciprocal of density is the specific volume v, which is defined as volume per unit mass.

The ratio of the density of a substance to the density of some standard substance at a specified temperature .

State & Equilibrium

Set of properties to completely describe the condition of the system

is known as its STATE

m = 2 kgT1 = 25 ºCV1 = 1 m3

STATE 1

m = 2 kgT1 = 25 ºCV1 = 3 m3

STATE 2

State & Equilibrium

Thermal Equilibrium :- NO Temperature Gradient throughout the system.

Mechanical Equilibrium :- NO Pressure Gradient throughout the system.

Phase Equilibrium :- System having more than 1 phase. - Mass of each phase is in equilibrium.

Chemical Equilibrium :- Chemical composition is constant - NO reaction occurs.

EQUILIBRIUM : State of Balance

Path & Process

t=0t=t1

t=0t=t2t

t2 < t1

Quasi-Static

Non-Quasi-Static

Process proceeds in such a manner that

system remains infinitesimally close to

equilibrium conditions at all times. It is

known as QUASI-STATIC or QUASI-

EQUILIBRIUM Process.

Path & Process

State 1 State 2

Pres

sure

Quasi-Static Process Path

Volume

NOTE : Process Path is a CONTINUOUS line only if it is having Quasi-Static Process.

Non-Quasi-Static Process is denoted by a DASHED line.

State 1 State 2

Pres

sure

Volume

Non-Quasi-Static Process Path

Path & ProcessPr

essu

re (P

)

Volume (V)

V=ConstIsochoric

P=ConstIsobaric

Tem

pera

ture

(T)

Enthalpy (h)/ Entropy (s)

T=ConstIsothermal

h=ConstIsenthalpic

s=ConstIsentropic

Cycle

CYCLE :A system is said to have undergone a cycle if it returns to its ORIGINAL state at the end of the process.Hence, for a CYCLE, the INITIAL and the FINAL states are identical.

Property A

State 1

State 2

Prop

erty

B

The End