Bez tytulu slajdu

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O n t h e T r a c k o f M o d e r n
P h y s i c s
Hot or cold?
With full throttle
Sadi-Nicolas Carnot, son of general died of
cholera at 36 years. Its only work Reflexions on
the horse-power of fire and the machines suitable
to develop this power provided fundations of
thermodynamics.
http//www.mpshq.com/images/products_gasturbines1.
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The only method "to circumvent" the laws of
Carnot is to increase the temperature of
combustion (by using new materials for the
turbines). At temperatures of 1400C efficiency
from about 60 can be reached.
S. -N. Carnot (1976-1832)
An important conclusion of the analysis of the
cycle of Carnot it is that the maximum
theoretical yield of the engines with heat is
directly related to efficiency (TH-TC)/TH
Selection of outputs peak of efficiency of the
action or of tools() human, swimming, surface
2 human, swimming, underwater
4 human, shoveling 3 steam engine
17 human, cycling
25 reciprocating gasiline
engine 30 natural gas turbine 40 muscle
contractions 50 combined cycle (gas-steam)
turbine 60 fuel cell 60 electric
motor 80 combined heat and power turbine 95
The cycle of Carnot is a idealization, since no
process of a real engine is reversible and any
physical process implies a small "loss of energy"
known as entropy.
The cycle of Carnot in graphical form was
introduced by Emile Clapeyron in 1834.
For any irreversible process, the efficiency is
smaller than that of the cycle of Carnot. That
can be associated a smaller heat flow towards the
system or an outgoing larger flow of the system.
The inevitable result is the inequality of
Clausius.
http//hypertextbook.com/physics/thermal/engines/
The silent Stirling
In 1769, the very first vehicle with autonomous
propulsion was a military tractor invented by a
French engineer and mechanic, Nicolas Joseph
Cugnot (1725 - 1804). Cugnot used a steam engine
to propulse its vehicle, built following his
instructions in Arsenale of Paris by the mechanic
named Brezin. It was used by the French Army to
trail artillery at the exorbitant speed of 4 km/h
on just 3 wheels.
Sometimes it is important to use small
differences in temperature. The invention of
pastor Robert Stirling is equipped with two
pistons and uses either the reheating or the
cooling of a gas. It reaches an efficiency up to
40.
These two engines on the right need differences
in very small temperature differences. The duck
which drinks and the thermometer of the love.
Not only Carnot
Fuel cells
In a diesel engine, the air is compressed
adiabatically of a factor from 15 to 20. This
compression increases the temperature until the
temperature of ignition of the mixture of fuel
which is formed by injecting fuel once that one
compressed the air.
The fuel cells are a way "of cheating" on the
equation of Carnot. Hydrogen and oxygen are not
flarings, but recombined in a chemical way
initially they dissociate in the respective ions
and after filter through a special membrane and
recombine by giving water and energy. They would
be a real alternative to the combustion engines,
if the membranes were not expensive and not
reliable and it did not have problems of storage
for hydrogen.
http//hyperphysics.phy-astr.gsu.edu/hbase/thermo/
diesel.html
In the Otto cycle the mixture of air and gasoline
is taken with pressure, then compressed
adiabatically and lit (3-4) with constant volume
the course of work is 4-5, and in 5-6 the fume is
discharged.
Thanks to the heat pump based on the Peltier
effect, one can heat or cool dishes attached to
our neck. The Peltier effect is a thermo-electric
principle where an electrical current makes it
possible heat to be absorbed on a side when heat
is rejected the different one.
The gas turbine is a usual example of a system
with open Brayton cycle. The air is aspired in a
compressor, is heated and relaxed through
turbine, and is discharged in the atmosphere.
The Brayton cycle is not only used in the
turbines of plane, but also in the gas turbines
used to produce electricity.
Like that, the question if they is necessary heat
or cold for us, Carnot answered either heat, or
cold.
http//thermalmotion.net/Brayton.html
Peltier effect "to carry"
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