M.S.E. – Baripada

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Dept. of Automobile Engineering

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3^rd Semester, Winter - 2020

Air Standard Cycles

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Prepared by :

Er. Sourin Mohanty

H.O.D., Automobile

THERMODYNAMIC CYCLES

A thermodynamic cycle is a series of thermodynamic processes transferring heat and work, while varying pressure, temperature and other state variables, eventually returning a system to its initial state

^A minimum of 3 such processes are required to construct a cycle.

^All processes need not have work interactions (e.g. isochoric process)

^All processes need not involve heat interactions either (e.g. adiabatic process).

“When a system undergoes a thermodynamic cycle then the net heat supplied to the system from the surroundings is equal to the net work done by the system on its surroundings”

ΣQsupplied-ΣQrejected= Wnet

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^The efficiency of the cycle is defined as η= Wnet/ΣQsuppied

Carnot Cycle

It consists of two isotherms and two adiabatics

Carnot Cycle (contd..)

• Carnot cycle is the one with which all other cycles are compared.

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• ^{η= W}net^/ΣQ supplied

= ΣQsupplied-ΣQrejected/ΣQsupplied

=Q41-Q32/Q41 =(T1-T2)/T1

Carnot efficiency of (T1-T2)/T1 is the best we can get for any cycle operating between two fixed temperatures.

OTTO CYCLE

It consists of two isochores and two adiabatics

OTTO CYCLE(contd..)

There is no heat interaction during 1-2 and 3-4

• Heat is added during constant volume heating (2-3) Q23= Cv(T3-T2)
• Heat is rejected during constant volume cooling(4-1) Q14= Cv(T4-T1)

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• η = W /ΣQ

net supplied

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= ΣQsupplied-ΣQrejected/ΣQsupplied

=(Q23-Q14)/Q23= 1 -[(T4-T1) / (T3-T2)]

Diesel Cycle

Diesel cycle consists of two isoentropic, isochoric and one isobaric process

one

Diesel cycle(contd..)

Q₂₃=mCp(T3-T2) Q₁₄=mCv(T4-T1)

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^{η = W}net^/ΣQ supplied

= ΣQsupplied-ΣQrejected/ΣQsupplied

=(Q23-Q14)/Q23

= 1 –(1/γ)[(T4-T1) / (T3-T2)]

Dual Cycle

Process description of dual cycle

Reversible Cycle

• A cycle consisting of all reversible processes is a reversible cycle. Even one of the processes is irreversible, the cycle ceases to be reversible.

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• A reversible cycle with clockwise processes produces work with a given heat input and are

known as power cycles. The same while operating with counter clockwise processes will reject the same heat with the same work as input

and are known as heat pump cycles .

HEAT ENGINE

• A device which produces work by transferring heat from a warmer to a cooler body is called a heat pump.

Carnot Engine

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Carnot engine has one Q +ve process and one Q

-veprocess. This engine has a single heat source at T1and a single sink at T2. If Q +ve> Q -ve; W will be +ve. It is a heat engine

Heat pump

• A device which transfers heat from a cooler to a warmer body (by receiving energy) is called a heat pump.
• A refrigerator is a special case of heat pump.
• Just as efficiency for a heat engine, for a heat pump the coefficient of performance (COP) is a measure of how well it isdoing the job.

• An irreversible engine can’t produce more work than a reversible one.
• An irreversible heat pump will always need more work than a reversible heat pump.
• An irreversible expansion will produce less work than a reversible expansion
• An irreversible compression will need more work than a reversible compression

THANK YOU