Babaria Institute of TechnologyEngineering

Thermodynamics

Prepared by :- Burhani Burhan A.(9011) Bhimani Vipul (9010)

Mchanical-1-A

Second law of thermodynamics

Concept • Introduction of 1st law of thermodynamics.• Limitation of 1st law of thermodynamics.• Introduction to 2nd law of thermodynamics.• Kelvin-plank statement• Clausius statement • Equivalence of Kelvin-plank and Clausius statement• PPM 2• Carnot cycle and Carnot heat engine • conclusion

Why 2nd law of thermodynamics

• The 1st law of thermodynamics states that a certain energy flow takes place when a system under goes a process or change of state.

• δW=δQ • But , it does not give any information on whether

that process or change of state is possible or not.

According to 1st law of thermodynamics

• Work is completely converted in to heat or heat is completely converted into work.

(δW = δQ and δQ=δW)• Potential energy can be transformed into kinetic

energy or kinetic energy can be transformed into Potential energy.

(PE→KE and KE→PE)• Heat flows from hot to cold or from cold to hot.(Th → Tl and Tl → Th)• Gas expands from high pressure to low pressure or

from low pressure to high pressure .

Limitation of 1st law of thermodynamics

• Heat is not completely converted into work.(Q ˃ W)• kinetic energy can not be transformed into

Potential energy.(KE ≠> PE)• Heat flow from cold to hot is not possible.(Tl ≠> Th)• Gas expands from low pressure to high pressure is

not possible.

Limitation of 1st law of thermodynamics

• 1st law does not help to predict whether the certain process is possible or not.

• A process can be proceed in particular direction only , but 1st law does not gives information about direction.

• 1st law not provides sufficient condition for certain process to take place.

2nd law of thermodynamics

Heat can not flow itself from cold body to hot body.

• The 2nd law of thermodynamics is also used to determine the theoretical limits for the performance of mostly used in engineering systems like heat engines and refrigerators.

Thermal energy reservoirs

• It is system that supply or absorb finite amount of heat without any change in its temperature.

Heat engine • Heat engine is a system that converts heat into work or

mechanical energy .• It absorb heat at higher temp body and rejects at

lower tem body.• It is work producing device.Ex – power plant (it operates on a complete cycle)

Heat engines Process -1. they receive heat from a high-temperature source.2. they convert part of this heat to work.3. they reject the remaining waste heat

to a low temperature sink atmosphere.4. they operate on a cycle.

Heat engines

• For a heat engine the efficiency is the ratio of net work done and the heat supplied.

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Heat pump and Refrigerator

• A device that transfers heat from a low temperature medium to a high temperature is the heat pump.

• Refrigerator operates exactly like heat pump , but difference is that heat pump maintain heated space at high temperature reservoir and refrigerator maintain heated space at low temperature reservoir.

• They are work consuming device

Heat pump and Refrigerator

Heat pump and

Refrigerator

Kelvin plank statement It is impossible to construct a heat engine that

operates on cycle to receive heat from single reservoir and produce equivalent amount of work.

It implies that it is impossible to build a heat engine that has 100% thermal efficiency .

Clausius statement It is impossible to construct a device as heat

pump that operates in a cycle and produces no effect other then the transfer of heat from a lower temp body to higher temp body.

Heat can not itself flow from colder body to hater body.

It can be shown that the violation of one statement leads to a violation of the other statement, i.e. they are equivalent.

1. Violation of Kelvin-plank statement leading to violation of Clausius statement .

2. Violation of Clausius statement leading to violation of Kelvin-plank statement .

Equivalence of the Two Statements

Violation of Kelvin-plank statement leading to violation of Clausius statement .

Violation of Clausius statement leading to violation of Kelvin-plank

statement .

PMM2 - Perpetual Motion Machines of the Second Kind

• It is against the Kevin-Planck statement: it is impossible to build an 100% heat engine.

Violate the Second Law of Thermodynamics

-:Thank you:-

Any questions ?