Carnot cycle, Joule cycle, Dual combustion cycle

Thermodynamics Cycles & its Types

1. cArnot cycle, joule cycle, dual combustion cycle Imran Sattar 2017-BT-Mech-759 Muhammad Imtiaz 2017-BT-Mech-760 Jamshed Khan 2017-BT-Mech-761 Hafiz Arsalan Hassan 2017-BT-Mech-762

2. DEFINATION This cycle devised by Francis Engineer Nicolas Leonard Sadi Carnot. In a Carnot cycle, the following substance is subjected to a cyclic operation consisting of two isothermal and two reversible adiabatic or isentropic operations. It is obvious that it is impossible to realize Carnot’s engine in actual practice.

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4. Theory A reversible isothermal gas expansion process. In this process, the ideal gas in the system absorbs  q in  amount heat from a heat source at a high temperature T h , expands and does work on surroundings.  A reversible adiabatic gas expansion process. In this process, the system is thermally insulated. The gas continues to expand and do work on surroundings, which causes the system to cool to a lower temperature, T l . A reversible isothermal gas compression process. In this process, surroundings do work to the gas at T l , and causes a loss of heat,  q out .  A reversible adiabatic gas compression process. In this process, the system is thermally insulated. Surroundings continue to do work to the gas, which causes the temperature to rise back to T h .

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7. Joule cycle Defination The cycle for the air engine proposed by Joule. It consist of two constant pressure and two reversible adiabatic or isentropic processes. This cycle, reversed, is used in refrigeration machines.

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9. Theory 1)-First stage (Constant Pressure Process). The air is heated at a constant pressure from initial temperature T 1 to a temperature T 2 represented by the curve 1-2 in fig . Heat supplied to the air , Q 1-2 = m c p (T 2 – T 1 ) 2)-Second stage (Reversible Adiabatic or Isentropic Expansion). The air is allowed to expand reversibly and adiabatically from v 2 to v 3 . The reversible adiabatic expansion is represented by the curve 2-3 in fig. The temperature of the air falls from T 2 to T 3 . In this process, no heat is absorbed or rejected by the air .

10. Theory 3)-Third stage (Constant Pressure Cooling). The air is now cooled at constant pressure from temperature T 3 to a temperature T 4 represented by 3-4 in fig. 4)-Fourth stage (Reversible Adiabatic or Isentropic Compression). The air is now compressed reversibly and adiabatically from v 4 to v 1 . The reversible adiabatic compression is represented by the curve 4-1 in fig. The temperature of the air increases from T 4 to T 1 . Again no heat, is absorbed or rejected by the air. Work done = Heat supplied – Heat rejected = m c p (T 2 – T 1 ) – m c p (T 3 – T 4 ) And efficiency, η = m c p (T 2 – T 1 ) – m c p (T 3 – T 4 ) m c p (T 2 – T 1 )

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12. Dual combustion cycle This cycle is a combination of Otto and Diesel cycles. It is sometimes called semi-diesel cycle, because semi-diesel engines work on this cycle. In this cycle, heat is absorbed partly at a constant volume and partly at a constant pressure. The ideal dual combustion cycle consist of two reversible adiabatic or isentropic, two constant volume and a constant pressure processes. It can be used to describe internal combustion engines.

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14. theory 1)-First stage (Constant Pressure Heating). The air is heated at constant pressure from initial temperature T 1 to a temperature T 2 represented by the curve 1-2 in fig. Heat absorbed by the air, Q 1-2 = m c p (T 2 -T 1 ) 2)-Second stage (Reversible Adiabatic or isentropic expansion). The air is expended reversibly and adiabatically from temperature T 2 to a temperature T 3 as shown by the curve 2-3 in fig. In this process, no heat is absorbed or rejected by the air. 3)-Third stage (Constant Volume Cooling ). The air is now cooled at constant volume from temperature T 3 to temperature T 4 as shown by the curve 3-4 in fig. Heat rejected by the air, Q 3-4 = m c v (T 3 -T 4 )

15. Theory 4)-Fourth stage (Reversible Adiabatic or Isentropic Compression). The air is compressed reversibly and adiabatically from temperature T 4 to a temperature T 5 as shown by the curve 4-5in fig. In this process, no heat is absorbed or rejected by the air. 5)-Fifth stage (Constant Volume Heating). The air is finally heated at constant volume from temperature T 5 to a temperature T 1 as shown by the curve 5-1 in fig. Heat absorbed by the air, Q 5-1 = m c v (T 1 - T 5 ) We see that air has been brought back to its original conditions of pressure, volume and temperature, thus completing the cycle. We know that, Work done = Heat absorbed – Heat rejected = [m c p (T 2 – T 1 ) + m c v (T 1 – T 5 )] – m c v (T 3 – T 4 )

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