ENGINEERING THERMODYNAMICS
M.R.SWAMINATHAN
Lecturer
Internal Combustion Engineering Division
Department of Mechanical Engineering
ANNA UNIVERSITY CHENNAI
CHENNAI-25.
ENGINEERING THERMODYNAMICS
Dr. M.R.SWAMINATHAN
Assistant Professor
Internal Combustion Engineering Division
Department of Mechanical Engineering
ANNA UNIVERSITY
CHENNAI-25.
PERPETUAL MOTION MACHINE-I
• First law of thermodynamics says
that energy is conserved
• There can be no machine which
would continuously supply work
without some other form of energy
getting dissipated
• A machine violating this is PMM-I
• Physical processes in nature can proceed
toward equilibrium spontaneously:
•
•
Water flows down a waterfall.
Gases expand from a high pressure to a
low pressure.
•
Heat flows from a high temperature to a
low temperature.
INTRODUCTION TO II LAW
• Once taken place, a spontaneous
process cannot be reversed by itself.
• Some external inputs, energy, must
be expended to reverse the process.
• As it falls down the waterfall, water
can be collected in a water wheel,
cause a shaft to rotate, coil a rope
onto the shaft, and lift a weight.
• Thus the energy of the falling water
is captured as potential energy
increase in the weight, and the first
law of thermodynamics is satisfied.
• There are losses associated with
this process (friction)
• What are the losses?
• IRREVERSIBILITY
Spontaneous Processes
• Spontaneous processes
are those that can
proceed without any
outside intervention.
• The gas in vessel B will
spontaneously
effuse
into vessel A, but once
the gas is in both
vessels, it will not
spontaneously
Spontaneous Processes
Processes that
are
spontaneous in
one
direction
are
non
spontaneous in
the
reverse
direction.
Spontaneous Processes
• Processes that are spontaneous at one
temperature may be non spontaneous at
other temperatures.
• Above 0C it is spontaneous for ice to
melt.
• Below 0C the reverse process is
spontaneous.
Reversible Processes
In a reversible process
the system changes in
such a way that the
system and
surroundings can be
put back in their original
states by exactly
reversing the process.
Changes are
infinitesimally small in
a reversible process.
Irreversible Processes
• Irreversible processes cannot be undone by
exactly reversing the change to the system.
• All Spontaneous processes are irreversible.
• All Real processes are irreversible.
Model Heat Engine
• Qhot= W+Qcold
or
• Qhot-Qcold=W
(what goes in must
come out)
II LAW OF THERMODYNAMICS