Heat Engines & Second Law Of Thermodynamics Video Lecture | Thermodynamics - Mechanical Engineering

heat engines and second law of
thermodynamics according to the first
law of thermodynamics heat and work are
mutually interchangeable this law does
not mention about the direction flow of
heat second law of thermodynamics gives
the direction of flow of heat energy
before stating the law let us see how
heat energy is converted into mechanical
energy in a heat engine heat engine is a
device used for converting heat energy
constantly into mechanical work
the schematic diagram of a heat engine
is shown here the three essential parts
of a heat engine are source or hot body
working substance and sink or cold body
the working substance is taken along a
cycle of operations in this process the
working substance absorbs heat from the
source transforms part of it into
mechanical energy and the remaining part
of heat is rejected to the sink after
completing the operation the working
substance comes back to its original
state heat energy is never converted
completely into mechanical energy that
as efficiency of a heat engine is never
equal to 100%
thus we can define efficiency of an
engine as the ratio of external work
done to the amount of heat absorbed from
the source in heat engines the working
substance takes heat q1 from source at
temperature t1 rejects the heat q2 to
the sink at temperature t2 and does some
work W eta is equal to q1 minus q2 by q1
eta is equal to 1 minus q2 by q1
there are two types of heat engines they
are internal combustion engine and
external combustion engine petrol and
diesel engines are internal combustion
engines steam engine is an external
combustion engine click on the link
provided to see the working of an
internal combustion engine
you
the fact that heat energy is never
completely converted to mechanical
energy has become the second law of
thermodynamics
there are several equivalent statements
of the second law of thermodynamics
Lord Kelvin stated it is impossible to
construct a device operating in a cycle
for the sole purpose of extracting heat
from a reservoir and changing it
entirely into an equal amount of work
without rejecting a part of the heat
this statement simply means an engine
can convert only a part of the heat
energy into mechanical work
Clausius statement it is not possible
for a self-acting machine unaided by any
external agency to transfer heat from a
body at low temperature to another body
at higher temperature the statement also
means no heat engine is hundred percent
efficient