Carnot cycles are not encountered in reality since
achieving isothermal heat transfer is very difficult
(needs very large heat exchangers and long time). Also process 3-4 requires a pump or compressor that can handle two phase mixture (liquid and vapor) which is impractical.
What are the difficulties in Carnot cycle in practice?
1] In the Carnot cycle,
all the processes are reversible and it is not possible in the case of actual engines
. 2] The isothermal heat transfer is not possible in real heat engines as these processes are quasi-static. 3] The frictionless movement of components is not possible in actual engines.
Why is Carnot cycle not 100% efficient?
The efficiency is 100% only when T
2
is zero or T
1
is infinite. This is not possible since
some amount of heat gets rejected to the sink
.
Why is it not possible to develop a Carnot heat engine?
This is impossible to attain practically because
isothermal is very slow and adiabatic is very fast
. The heat exchange in carnot cycle is isothermal which needs the working fluid to either phase change or the process be extremely slow. Thus constant pressure process is used in rankine cycle.
Is Carnot engine 100 efficient?
In order to achieve 100% efficiency (η=1), Q
2
must be equal to 0 which means that all the heat form the source is converted to work. The temperature of sink means a negative temperature on the absolute scale at which the temperature is greater than unity.
Why is a heat engine not 100% efficient?
A heat engine is considered to be 100% efficient if only all the heat is converted into useful work or mechanical energy. Since
heat engines cannot convert all the heat energy into mechanical energy
, their efficiency can never be 100%.
What is efficiency of Carnot cycle?
The thermal efficiency of a Carnot cycle operating between these two reservoirs is
η = 1−T
C
/T
H
. This value is significantly higher than that of the Otto cycle operating between the same reservoirs.
What does Zeroth Law of Thermodynamics states?
The zeroth law of thermodynamics states that
if two bodies are each in thermal equilibrium with some third body, then they are also in equilibrium with each other
.
What is Carnot cycle explain in detail?
Definition of Carnot cycle
: an ideal reversible closed thermodynamic cycle in which the working substance goes through the four successive operations of isothermal expansion to a desired point, adiabatic expansion to a desired point, isothermal compression, and adiabatic compression back to its initial state.
Why is 100 efficiency impossible?
It is impossible for heat engines to achieve 100% thermal efficiency () according to the Second law of thermodynamics. This is impossible because
some waste heat is always produced produced in a heat engine
, shown in Figure 1 by the term.
Why is Carnot efficiency maximum?
The Carnot Efficiency is the theoretical maximum efficiency one can get
when the heat engine is operating between two temperatures
: The temperature at which the high temperature reservoir operates ( T
Hot
). The temperature at which the low temperature reservoir operates ( T
Cold
).
Can thermal efficiency of a heat engine be 100 % explain?
The impossibility of converting heat energy completely into mechanical energy, limits the efficiency of heat engines. Since heat energy can never be transformed completely into mechanical energy, so
the efficiency of a heat engine can never be 100 per cent
.
Why Kelvin Planck statement is true?
A well-equipped engine with fuel is essential to move the boat forward. This works as an external heat supply for the functioning of propulsion. Thus, we realize that
it is impossible to build an engine that converts heat from one reservoir completely into work
. This aids the Kelvin Planck statement.
Which engine works on Carnot cycle?
Carnot engine is a theoretical thermodynamic cycle proposed by Leonard Carnot. It estimates the maximum possible efficiency that a
heat engine
during the conversion process of heat into work and, conversely, working between two reservoirs can possess.
What is reverse Carnot cycle?
Reversed Carnot Cycle
Carnot cycle is
a totally reversible cycle which consists of two reversible isothermal processes and two isentropic processes
. It has the maximum efficiency for a given temperature limit. Since it is a reversible cycle, all four processes can be reversed.
Which cycle has highest efficiency?
Explanation:
Carnot engine
: A theoretical thermodynamic cycle proposed by Leonard Carnot. This engine gives the maximum possible efficiency that a heat engine can have during the conversion process of heat into work or vice-versa, working between two reservoirs.
What is Lord Kelvin statement?
The Kelvin-Planck Statement:
It is impossible to construct a device which operates on a cycle and produces no other effect than the transfer of heat from a single body in order to produce work
.
Which is the most efficient cycle?
The most efficient heat engine cycle is the
Carnot cycle
, consisting of two isothermal processes and two adiabatic processes. The Carnot cycle can be thought of as the most efficient heat engine cycle allowed by physical laws.
Why do we need second law of thermodynamics?
The second law of thermodynamics
helps us to predict whether the reaction is feasible or not and also tell the direction of the flow of heat
. It also tells that energy cannot be completely converted into equivalent work.
What is concept of entropy?
entropy,
the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work
. Because work is obtained from ordered molecular motion, the amount of entropy is also a measure of the molecular disorder, or randomness, of a system.
Is entropy a function of volume?
We can express the entropy as a function of temperature and volume
. It can be derived from the combination of the first and the second law for the closed system. For ideal gas the temperature dependence of entropy at constant volume is simply Cv over T.
Is Carnot efficiency in Kelvin?
Carnot efficiency equation
Both Th and Tc are absolute temperatures (expressed in Kelvins)
. For example, you can try to calculate the Carnot efficiency of an engine operating between two bodies: one at a temperature of 25°C, and the other at 135°C.
Can entropy be destroyed?
Entropy is generated everywhere and always, at any scale without exception, and
cannot be destroyed by any means at any scale
. “Entropy of an isolated, closed system (or universe) is always increasing” is a necessary but not sufficient condition of the Second Law of thermodynamics.
What do you mean by heat death of universe?
The heat death of the universe (also known as the Big Chill or Big Freeze) is
a hypothesis on the ultimate fate of the universe, which suggests the universe would evolve to a state of no thermodynamic free energy and would therefore be unable to sustain processes that increase entropy
.
Why is zeroth law named so?
The Zeroth law is called so
because the first two laws of thermodynamics were established before, and they were named before
. It was later found that zeroth law was more fundamental than the other laws of thermodynamics, that is the reason why it is called zeroth law of thermodynamics.
What is thermometry in thermodynamics?
Thermometry is
the process of measuring temperature
. Temperature is basically a measure of the amount of kinetic energy, particles possess. Nowadays, there are many different types of thermometers, for example glass in tube, thermistor, thermocouple, radiation thermometer etc.
