If the actual amount of inputs used exceeds the amount theoretically required, there is a negative efficiency variance
. On the other hand, if actual inputs are less than the amounts theoretically required, then there would be a positive efficiency variance.
What is thermodynamic cycle efficiency?
Classical thermodynamics indicates that
the most efficient thermodynamic cycle operating between two heat reservoirs is the Carnot engine
[1] , and a basic theorem expresses that any reversible cycle working between two constant temperature levels should have the same efficiency as a Carnot cycle [2].
Why can’t we get 100% efficiency in a thermodynamic cycle?
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.
Can you have an efficiency greater than 1?
Since a machine does not contain a source of energy, nor can it store energy, from conservation of energy the power output of a machine can never be greater than its input, so
the efficiency can never be greater than 1
.
Why turbine is a thermodynamic heat engine?
Since the steam turbine is a rotary heat engine,
it is suited to drive an electrical generator
. The thermal efficiency of a steam turbine is usually higher than that of a reciprocating engine. The very high power-to-weight ratio, compared to reciprocating engines. Fewer moving parts than reciprocating engines.
Can an engine have negative efficiency?
Negative temperatures could be used to create heat engines — engines that convert heat energy to mechanical work, such as combustion engines — that are more than 100-percent efficient, something seemingly impossible. Such engines would essentially not only absorb energy from hotter substances, but also colder ones.
Can efficiency of a Carnot engine be negative?
If we increase the energy of the hot reservoir even further, so that its temperature becomes negative (passing the peak on the S(U) curve),
the maximum possible efficiency becomes greater than 1
, and Qout becomes negative.
Can efficiency be more than 100%?
Due to the conservation of energy, P can never be greater than C, and so
the efficiency r is never greater than 100%
(and in fact must be even less at finite temperatures).
Can thermal efficiency of a heat engine be 100?
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%.
Is it possible practically to have a machine that is 100% efficient?
A machine cannot be 100 percent efficient
because output of a machine is always less than input. A certain amount of work done on a machine is lost to overcome friction and to lift some moving parts of the machine.
Why 100 efficiency is impossible?
It cannot be constructed since
it violates the second law of thermodynamics
: Kelvin Planck Statement. If efficiency = 100%, then Temperature of the sink = 0 K which is again impossible to achieve. Thus, a Carnot engine with 100 % efficiency is not possible.
What is the difference between a thermodynamic process and thermodynamic cycle?
As already said,
a thermodynamic process refers to any change in the thermodynamic variables whereas a cycle is a closed process, where the final and initial state of the system is the same
.
What is the difference between thermodynamic cycle and mechanical cycle?
The engine operates on a mechanical cycle, but the working fluid does not go through a complete thermodynamic cycle
. As we said before, any thermodynamic cycle is essentially a closed cycle in which, the working substance undergoes a series of processes and is always brought back to the initial state (Fig.
How is thermodynamic cycle efficiency calculated?
- is the efficiency of the Carnot cycle, i.e., it is the ratio = W/Q
H
of the work done by the engine to the heat energy entering the system from the hot reservoir. - T
C
is the absolute temperature (Kelvins) of the cold reservoir, - T
H
is the absolute temperature (Kelvins) of the hot reservoir.
Why can COP be greater than 1?
The COP usually exceeds 1, especially in heat pumps, because, instead of just converting work to heat (which, if 100% efficient, would be a COP of 1),
it pumps additional heat from a heat source to where the heat is required
. Most air conditioners have a COP of 2.3 to 3.5.
Why is COP of heat pump greater than refrigerator?
Answer. Note that the COP of a heat pump depends on its duty.
The heat rejected to the hot sink is greater than the heat absorbed from the cold source
, so the heating COP is 1 greater than the cooling COP. applies to heat pumps and applies to air conditioners or refrigerators.
Which cycle has the highest thermal efficiency?
The Carnot cycle
, due to its fully reversible nature, represents the highest cycle efficiency possible for the two temperature limits of T
H
and T
L
; where T
H
represents both the heat source temperature and the temperature of the working fluid, and T
L
is both the working fluid temperature and the temperature of the heat …
What is thermodynamic heat engine?
In thermodynamics and engineering, a heat engine is
a system that converts heat to mechanical energy, which can then be used to do mechanical work
. It does this by bringing a working substance from a higher state temperature to a lower state temperature.
What sets the limits on efficiency of a heat engine?
The efficiency of a heat engine is limited by
the temperature of the cold reservoir
.
How can we increase the efficiency of heat engine?
Therefore, the efficiency of the heat engine can be increased by
decreasing the temperature of the cold sink or increasing the temperature of the hot source
.
Can a heat engine do negative work?
So when a system (like a heat engine) does work ON its surroundings, then the Thermodynamic Work is POSITIVE. (This is the opposite for Mechanical Work.)
If work is done on the heat engine, the Thermodynamic Work is NEGATIVE.
Which of the following is not a factor why machines can never be 100% efficient?
A machine cannot be 100 percent efficient because
output of a machine is always less than input
. A certain amount of work done on a machine is lost to overcome friction and to lift some moving parts of the machine.
Does a heat engine that has a thermal efficiency of 100 percent necessarily violate a the first law and b the second law of thermodynamics explain?
In order to operate, a heat engine must reject some of the heat it receives from the high-temperature source to a low-temperature sink. A heat engine that violates the second law converts 100 percent of this heat to work. This is
physically impossible
.
Does Carnot engine have 100% efficiency?
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. Was this answer helpful?
Why Carnot cycle is practically not possible?
In real engines, the heat transfers at a sudden change in temperature whereas in a Carnot engine, the temperature remains constant.
In our day to day lives, reversible processes can’t be carried out and there is no such engine with 100 % efficiency
. Thus, the Carnot cycle is practically not possible.
Is Carnot engine 100 efficient Why or why not?
Any engine that uses the Carnot cycle enjoys the maximum theoretical efficiency. While Carnot engines are ideal engines, in reality,
no engine achieves Carnot’s theoretical maximum efficiency
, since dissipative processes, such as friction, play a role.
