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