TEKNIK MESIN
FAKULTAS TEKNOLOGI INDUSTRI
UNIVERSITAS MERCU BUANA
MODUL KE SEMBILAN
THERMODINAMIKA DASAR
NANANG RUHYAT
CARNOT CYCLE
The Carnot cycle is a particular thermodynamic cycle, modeled on the Carnot heat
engine, studied by Nicolas Léonard Sadi Carnot in the 1820s and expanded upon by
Benoit Paul Émile Clapeyron in the 1830s and 40s.
Every thermodynamic system exists in a particular state. A thermodynamic cycle occurs
when a system is taken through a series of different states, and finally returned to its initial
state. In the process of going through this cycle, the system may perform work on its
surroundings, thereby acting as
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open systems: exchanging energy (heat and work) and matter with their
environment. A boundary allowing matter exchange is called permeable. The ocean
would be an example of an open system.
It is a fact that, for isolated systems, as time goes by, internal differences in the
system tend to even out. Pressures and temperatures tend to equalize, as do density
differences. A system in which all these equalizing processes have gone practically
to completion, is considered to be in a state of thermodynamic equilibrium. Its
thermodynamic properties are, by definition, unchanging in time. Systems in
equilibrium are much simpler and easier to understand than systems which are not in
equilibrium. Often, when analysing a thermodynamic process, it can be assumed that
each intermediate state in the process is at equilibrium. This will also considerably
simplify the situation. Thermodynamic processes which develop so slowly as to allow
each intermediate step to be an equilibrium state are said to be reversible processes.
In open systems, matter may flow in and out of the system boundaries. The first law
of thermodynamics for open systems states: the increase in the internal energy of a
system is equal to the amount of energy added to the system by matter flowing in
and by heating, minus the amount lost by matter flowing out and in the form of work
done by the system. The first law for open systems is given by:
During steady, continuous operation, an energy balance applied to an open system
equates shaft work performed by the system to heat added plus net enthalpy added.
where Uin is the average internal energy entering the system and Uout is the
average internal energy leaving the system
Open systems
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Ir. Nanang Ruhyat
THERMODINAMIKA DASAR
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·
A heat engine acts by transferring energy from a warm region to a cool region of
space and, in the process, converting some of that energy to mechanical work. The
cycle may also be reversed. The system may be worked upon by an external force,
and in the process, it can transfer thermal energy from a cooler system to a warmer
one, thereby acting as a refrigerator rather than a heat engine.
·
The Carnot cycle is a special type of thermodynamic cycle. It is special because it is
the most efficient cycle possible for converting a given amount of thermal energy into
work or, conversely, for using a given amount of work for refrigeration purposes.
A Carnot cycle acting as a heat engine, illustrated on a temperature-entropy diagram. The
cycle takes place between a hot reservoir at temperature TH and a cold reservoir at
temperature TC. The vertical axis is temperature, the horizontal axis is entropy.
·
·
The Carnot cycle when acting as a heat engine consists of the following steps:
Reversible isothermal expansion of the gas at the "hot" temperature, TH
(isothermal heat addition). During this step (A to B on diagram) the expanding gas
causes the piston to do work on the surroundings. The gas expansion is propelled by
absorption of heat from the high temperature reservoir.
·
Reversible adiabatic expansion of the gas. For this step (B to C on diagram) we
assume the piston and cylinder are thermally insulated, so that no heat is gained or
lost. The gas continues to expand, doing work on the surroundings. The gas
expansion causes it to cool to the "cold" temperature, TC.
·
Reversible isothermal compression of the gas at the "cold" temperature, TC.
(isothermal heat rejection) (C to D on diagram) Now the surroundings do work on
the gas, causing heat to flow out of the gas to the low temperature reservoir.
PUSAT PENGEMBANGAN BAHAN AJAR-UMB
MT.http://www.mercubuana.ac.id
Ir. Nanang Ruhyat
THERMODINAMIKA DASAR
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