The Cyclic Devices P M V Subbarao Professor Mechanical Engineering Department Create Resources Parallel to Nature…..

Cyclic Device: A single system or a group of thermodynamic systems, which are responsible for execution of thermodynamic cycle by a pure substance.

Steam Power Plant: A Heat Engine Q in Q out W out W in

Turbojet Engine: A Heat Engine Q in Q out W out

Reciprocating IC Engine : A Heat Engine Q in Q out W out

Greatness of Heat Engines Balance Sheet for A Heat Engine: –All heat inputs consume resources : Total Input Heat : Q in (Cost incurred). –All heat outputs are just mere a loss. –Net work Out put is positive and this is the final benefit : W net (Benefit Achieved) –Performance : Benefit to cost ratio (in energy units).

Thermodynamic Model for a General Heat Engine W net First law: W net = Q in - Q out Q in High Temperature Reservoir (Source) Q out Low Temperature Reservoir (Sink) HE

If Q in = W net, then the efficiency of A Heat Engine will be 100% Cost Benefit Analysis

Air Conditioner

Vapour Compression Refrigeration System : A Heat Pump Q out Q in W in

Greatness of A Heat Pump Heat Pump or Refrigerator: –Input : W in (Cost incurred) –Out put : Q in or Q out (Benefit Achieved) –Performance : Benefit to cost ratio. If W in = 0, then COP = . While using as a Refrigerator : While using as a heat pump :

Thermodynamic Model for a General Heat Pump Q out Q in W in First law: W in = Q in - Q out HTR (Sink) LTR (Source) HP

Kelvin Planks postulate “ It is impossible to construct a heat engine which produces no effect other than the extraction of heat from a single source and the production of an equivalent amount of work” On the other side It is possible to construct a heat engine which produces no effect other than the extraction of work from a single source and the production of an equivalent amount of heat

The Impossible Engine Q in Q out = 0 W net First law: W net = Q in HTR (Source) LTR (Sink)

Clausius postulate “ The Clausius statement: It is impossible to construct a heat pump produces no effect other than the transfer of heat from a cooler body to a hotter body. ” However, It is possible to construct a heat pump produces no effect other than the transfer of heat from a hotter body to a colder body.

The Impossible Heat Pump Perpetual Motion Machine II : Heat Pump Model QHQH QLQL First law |Q H | = Q L HTR (Sink) LTR (Source) 

Discussion of Second Law It is impossible to construct a heat engine with 100% efficiency. It is impossible to construct a heat pump or refrigerator with infinite COP. Both are negative statements. They cannot be proved. They will remain correct till they are disproved. Violation of Kelvin Planks statement leads to violation of Clasius statement and vice versa. Can a heat engine be reversed to work as heat pump or refrigerator? If yes, what will be the COP of this reversed engine? Can a reversed engine perform same as forward engine between same reservoirs? What can really affect the performance of a reversible engine?

Violation of any one Statement lead to violation of the other automatically!

Perpetual Heat Pump Model QHQH QLQL First law |Q H | = QL HTR (Source) LTR (Sink) Let us assume this is possible 

Perpetual Heat Pump & A General Heat Engine Q HP Q LP HTR LTR  Q HE Q LE E Wnet

Compound Heat Engine Q HP Q LP LTR (Sink) Q HE E  Wnet Q LE = Q LP -Wnet HTR Q LE HTR Q HE = Q HP = Q LP

Perpetual Motion Machine II : Compound Engine Q HP Q LP First law Q HP = Q LP Q HE E  Wnet Q HE = Q LP Q LE = Q LP -W net Q LP - Q LE =W net LTR (Source) HTR (Sink)

Perpetual Motion Machine II : Compound Engine Q HP Q LP Q HE E  Wnet Q HE = Q HP Q LE = Q LP -Wnet Q LC =Q LP - Q LE =Wnet LTR (Source)