SECOND LAW AND AVAILABILITY ANALYSIS
1.
Define Clausius statement.
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 a higher temperature without the aid of an external
agency.
2.
Define Kelvin Planck Statement.
It is impossible for a heat engine to
produce network in a complete cycle if it exchanges heat only with bodies at a
single fixed temperature.
3.
Define Heat pump.
A heat pump is a device, which is
working in a cycle and transfers heat from lower temperature to higher
temperature.
4.
Define Heat engine.
Heat engine is a machine, which is used
to convert the heat energy into mechanical work in a cyclic process.
5. What
are the assumptions made on heat engine?
1. The
source and sink are maintained at constant temperature.
2. The
source and sink has infinite heat capacity.
6. State
Carnot theorem.
It states that no heat engine operating
in a cycle between two constant temperature heat reservoirs can be more
efficient than a reversible engine operating between the same reservoirs.
7.
What is meant by reversible process?
A reversible process is one, which is
performed in such a way that at the conclusion of process, both system and
surroundings may be restored to their initial state, without producing any
changes in rest of the universe.
8.
What is meant by irreversible process?
The mixing of two substances and
combustion also leads to irreversibility. All spontaneous process is
irreversible.
9.
Explain entropy?
It is an important thermodynamic property of the
substance. It is the measure of molecular disorder. It is denoted by S. The
measurement of change in entropy for reversible process is obtained by the
quantity of heat received or rejected to absolute temperature.
10.
Define availability.
The maximum useful work obtained during
a process in which the final condition of the system is the same as that of the
surrounding is called availability of the system.
11.
Explain the term source and sink.
Source is a thermal reservoir, which
supplies heat to the system and sink is a thermal reservoir, which takes the
heat from the system.
12.
What do you understand by the entropy principle?
The entropy of an isolated system can
never decrease. It always increases and remains constant only when the process
is reversible. This is known as principle of increase in entropy or entropy
principle.
13.
What are the important
characteristics of entropy?
1. If
the heat is supplied to the system then the entropy will increase.
2. If
the heat is rejected to the system then the entropy will decrease.
3. The
entropy is constant for all adiabatic frictionless process.
4. The
entropy increases if
temperature of heat
is lowered without
work being
done
as in throttling process.
5. If
the entropy is maximum, then there is a minimum availability for conversion in
to work.
6. If
the entropy is minimum, then there is a maximum availability for conversion into
work.
14.
What is reversed Carnot heat
engine? What are the limitations of Carnot cycle?
1. No
friction is considered for moving parts of the engine.
2. There
should not be any heat loss.
15.
Define an isentropic process.
Isentropic process is also called as reversible
adiabatic process. It is a process which follows the law of pV = C is known as
isentropic process. During this process entropy remains constant and no heat
enters or leaves the gas.
16.
What are the Corollaries of Carnot
theorem?
(i) In
the entire reversible engine operating between the two given thermal reservoirs
with
fixed temperature, have the same efficiency.
(ii) The efficiency of any reversible heat engine
operating between two reservoirs is independent of the nature of the working
fluid and depends only on the temperature of the reservoirs.
17.
Define –PMM of second kind.
Perpetual motion machine of second kind
draws heat continuously from single reservoir and converts it into equivalent
amount of work. Thus it gives 100% efficiency.
18.
What is the difference between a heat pump and a refrigerator?
Heat pump is a device which operating in
cyclic process, maintains the temperature of a hot body at a temperature higher
than the temperature of surroundings.
A refrigerator is a device which operating
in a cyclic process, maintains the temperature of a cold body at a temperature
lower than the temperature of the surroundings.
19.
Define the term COP?
Co-efficient of performance is defined as the ratio
of heat extracted or rejected to work
COP = input. Heat extracted or rejected / Work input
20.
Write the expression for COP of a heat pump and a refrigerator?
COP
of heat pump:
COP HP = Heat Supplied / Work input = T2 / T2 - T1
COP
of Refrigerator:
COP Ref = Heat extracted / Work input = T1 / T2 - T1
21.
Why Carnot cycle cannot be realized
in practical?
(i) In
a Carnot cycle all the four processes are reversible but in actual practice
there is no
process
is reversible.
(ii) There
are two processes to be carried out during compression and expansion. For
isothermal process the piston moves very slowly and for adiabatic process the
piston moves as fast as possible. This speed variation during the same stroke
of the piston is not possible.
(iii) It
is not possible to avoid friction moving parts completely.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.