Thermodynamic And Heat Engine
Processes
Process: It is defined as any change that the system may undergo. A series of processes in which the system returns to its original condition or state is called a cyclic process.
A process in which the system departs from equilibrium state only infinitesimally at every instant is called quasi-static process.
A process may be
divided as
1. Reversible process and 2.
Irreversible process.
Q: What are the conditions of reversibility?
Ans. Conditions of Reversibility:
(i) The
changes must take place at an infinitesimally slow rate.
(ii) The system must always be in thermal and mechanical equilibrium with the surrounding.
(iii) The working parts of the engine must be friction free.
Classification of thermodynamic processes:
1. Non-flow processes: The processes occurring in closed systems which do
not permit the transfer of mass across their boundaries, are known as non-flow processes.
2. Flow processes: The processes occurring in open systems which permit the transfer of
mass across their boundaries are known as flow
processes.
Non-flow processes:
1.
Constant
volume process or Isochoric process,
2.
Constant
pressure process or Isobaric process,
3. Constant temperature process or Isothermal process,
(In it,
internal energy remains constant)
4.
Adiabatic
process or Isentropic process, (PVγ = Constant)
5.
Polytrophic
process (PVn = constant)
6.
Free
expansion process
7.
Throttle process
8. Reversible process
9. Hyperbolic process
Q: State all the laws of Thermodynamics?
Ans. There are three laws of the thermodynamics.
First Law: Energy can be neither created nor destroyed. It can only
change forms. In any process in an isolated system, the total energy remains
the same.
Q = W+E
This law states that the heat and mechanical work are mutually convertible.
Mathematically,
W ∞ Q
or, W = JQ
J= Mechanical equivalent of heat or Joule’s constant = 427 kcal/kgf-m
First
law of thermodynamics was given by Joule.
Second Law: Two statements of Second Law of thermodynamics
According to Clausius: “It is
Impossible for a self-acting machine working in a cyclic process, to transfer
heat from a body at lower temperature to a body at higher temperature without
the aid of an external agency.”
According to Kelvin-Planck, “It
is impossible to construct an engine working on a cyclic process, whose sole
purpose is to convert heat energy into work.”
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