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ENGINEERING THERMODYNAMICS. Dr. M.R.SWAMINATHAN Assistant Professor Internal Combustion Engineering Division Department of Mechanical Engineering ANNA UNIVERSITY CHENNAI-25. LIMITATIONS OF I LAW.
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ENGINEERING THERMODYNAMICS Dr. M.R.SWAMINATHAN Assistant Professor Internal Combustion Engineering Division Department of Mechanical Engineering ANNA UNIVERSITY CHENNAI-25.
LIMITATIONS OF I LAW The first law of thermodynamics is simple, general, but does not constitute a complete theory because certain processes it permits do not occur in nature!
Examples of processes which are not prohibited by the first law, but cannot happen in a real world. • Perfect machine • Transfer heat from cold to hot subject • Gas expansion
IRREVERSIBLE PROCESSES A battery discharges through a resistor, releasing energy. The reverse process will not occur. Two gases, initially in separated adjoining chambers, will mix uniformly.
A free expansion of gas (in Gay-Lussac-Joule experiment) Heat flows from a high temperature body to a low temperature reservoir in the absence of other effect
STATEMENTS OF THE SECOND LAW OF THERMODYNAMICS: Kevin-Planck Statement: It is impossible to construct a device that operates in a cycle and produces no other effects than the performance of work and the exchange of heat with a single reservoir.
Model Heat Engine Qhot= W+Qcold or Qhot-Qcold=W (what goes in must come out)
Even the most efficient heat engines reject almost one-half of the energy they receive as waste heat.
It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work.
Clausius Statement: It is impossible to construct a device that operates in a cycle and whose sole effect is to transfer heat from a cooler body to a hotter body.