CLAUSIUS STATEMENT OF SECOND LAW

▀Clausius Statement of second law:

It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a system at low temperature to another system at high temperature.

Clausius statement points-out the essence of work input required in Refrigerators & Heat pumps

Fig

Heat can’t flow from low temperature to high temperature systems.

COP=Q/W=Q/0=∞.............(impossible)

It is impossible to construct a refrigerator, which operates without an input of work.

Fig

CLAUSIUS STATEMENT

▀Clausius Statement of second law:

It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a system at low temperature to another system at high temperature.

Clausius statement points-out the essence of work input required in Refrigerators & Heat pumps

Fig

Heat can’t flow from low temperature to high temperature systems.

COP=Q/W=Q/0=∞.............(impossible)

It is impossible to construct a refrigerator, which operates without an input of work.

Fig

ENTROPY

Entropy

Entropy represents the energy in the system which couldn't be utilised due to some deficiency of the system. As we know that when we burn oil, only part of heat energy is utilised and rest goes un-utilised. This resents that efficiency of system is not equal to input of heat energy into Heat-Engine and it is always less than heat input. This is as brought out in 2nd Law of Thermodynamics.

Whether it is a case of Heat Input (heat engine) or Heat extraction (Refrigeration), the system output will be < total input. The most ideal case for thermodynamic cycle is Carnot-Cycle. It is defined as follows:

"Entropy" is defined as a measure of unusable energy within a closed or isolated system (the universe for example). As usable energy decreases and unusable energy increases, "entropy" increases.

Entropy is also a gauge of randomness or chaos within a closed system. As usable energy is irretrievably lost, disorganization, randomness and chaos increase.

For more details refer my scanned hand notes.

Teacher's notes

Questions Sessional-1

Dear students,

Go through the following questions and prepare for the Sessional test.

1. Machine Tools:

Q1 Write about the machine tools used in workshop and main parts of all machines.

Q2. Specifications of machines and operations performed on every machine tool.

Q3. Differentiate shaper & planer, milling & lathe.

Q4. General questions on NC & CNC machines.

B Basic concept of Thermodynamics:

Q1. What is thermodynamics? Laws of thermodynamics and statements/ experiments.

Q2. Work, Heat, Temperature & pressure and their units.

Q3. Ideal gas, Boyle’s and Charles laws.

Q4. Isothermal & Adiabatic process.

Q5. Open & Closed system, Queasi-statement process, Reversibility.

C Stresses and Strain:

Q1. Stress, Strain(Tensile, Compressive, Shear), Young Modulus, Bulk Modulus, Modulus of Rigidity, Elasticity, Poisson’s ratio etc.

D. Q1. Write notes on:

Enthalpy, Entropy, Thermal Equilibrium, Internal Energy, Zeroth Law, Dryness Fraction, etc.

E. Steam & its Properties.

Q1. Draw graph for steam’s properties, steps and saturation points.

Q2. Basic thermodynamic properties.

Q3. Specific Enthalpy, Entropy, Internal Energy.

First Law of Thermdynamics

First Law of thermodynamics:

Deals with concept of energy conservation (protection) and introduces the concept of internal energy (IE)
Explain Joule's Paddle Wheel Experiment.

Joule observed that:

“During the cyclic process---net amount of heat produced is proportional to the net amount of work done on the system”

∫dQ ∞ ∫dW

In SI system heat & work have same unit thus

∫dQ = ∫dW ∫dQ - ∫dW= 0

∫ (dQ–dW) is same for both systems A & B connecting two state points 1 & 2 in figure.

∫ (dQ–dW) does not depend on paths of process, but depend on point 1 & 2.

Therefore it is point function and hence property of system and overall energy is denoted by E.

E= U+KE+PE, PE is potential energy, KE is kinetic energy, U is Internal energy

Second Law of Thermodynamics:

This law is needed to remove the limitation of first law i.e. as per 1^st law there is no restriction on the direction of flow of heat & work.

e.g. Flywheel on friction braking , brakes get hot as there is loss of KE.

1^st law satisfy that brakes were to be cool and given IE back to wheel for resuming motion again, but this will never occur.

Braking is irreversible process.

1^st law imposes no restriction on flow of heat from lower temperature reservoir to higher temperature reservoir.

The 2^nd law is helpful in following ways:

- It provides means for measuring quality of energy

- Performance of engineering devices i.e. efficiency.

- Determines direction of change for spontaneous process.

- Establishes final equilibrium for spontaneous process.

- Establishes parameters for measuring losses in energy process.

Heat Engine exchanges heat with a single body in equilibrium state and produce work creating any other effect called PMM-2, therefore it follows the “First Law of Thermodynamics” but…………

Fails to conform the “ KELVIN-PLANKS STATEMENT” of 2^nd law.

Hence it is not possible to construct such machine,……..e.g. if condenser is eliminated, simple power plant will be PMM-2.

KELVIN-PLANKS STATEMENT of second law:

It is impossible to construct an engine that operates in a cycle and produces no effect other than work as output i.e. heat is exchanged with a single heat reservoir---means

η = W/Q=1 i.e. efficiency=100% such a system satisfies the principle of energy conservation (First Law), but violates the Kelvin statement of second law i.e. no engine can have 100% efficiency.

Fig

The only alternative is that power output from a heat engine , a portion of heat received must be rejected to heat reservoir(SINK). Engine receives Q1 unit of heat and rejects Q2 unit of heat. Thus coverts (Q1-Q2) heat into work done(WD) per cycle

Fig

Clausius Statement of second law:

Zeroth Law

Laws of thermodynamics

Zeroth Law:
Deals with the concept of thermal equlibrium and provides means of measuring temperature.

This law by R.H.Fowler in 1931.

If two systems say A & B are separately in thermal equilibrium with the third system C. i.e.
TA=TC and TB=TC then systems A & B are to be in equilibrium i.e. TA=TB........means
If two bodies have equality in temperature with a third body, they have to be equality mutually with each other. This law is basis of temperature measuring. The only device working on this principle is thermometer. Draw the sketch.






First Law of thermodynamics: Deals with concept of energy conservation(protection) and introduces the concept of internal energy (IE )
Explain Joule's Paddle Wheel Experiment.