Technology that works on a large scale can cause spluttering in a smaller one.
Robert Stirling invented a heat engine nearly 200 years ago. Known as
stirling engines, they are powered by the expansion of gas
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| A macro steam engine |
when heated,
making a piston execute a motion such as driving a wheel.
Replicating this on a micro-world scale created some serious
challenges, as the different laws of the micro-world meant that the
thermal motions of a few particles could cause the engine to splutter.
Researchers at the University of Stuttgart and the Max Planck Institute for Intelligent Systems, Germany, have succeeded in developing a micro-world stirling engine.
“We’ve developed the world’s smallest steam engine, or to be more
precise the smallest Stirling engine, and found that the machine really
does perform work,” Professor Clemens Bechinger said. “This was not
necessarily to be expected, because the machine is so small that its
motion is hindered by microscopic processes which are of no consequence
in the macroworld.”
In the micro-engine, the working gas consists of a three micrometre
individual plastic bead which floats in water, rather than countless gas
molecules. The researchers replaced the piston with a focused laser
beam, which controls the motion of the particle.
In a macro-world engine, the system is heated from the outside during
the expansion process, to prevent the contributions to the work from
cancelling each other out during compression and expansion. In the
micro-world engine, the researchers replaced the coal-fire with another
laser, which heats the water surrounding the plastic bead.
However, the water molecules are causing the spluttering, as their
constant motion causes them to collide with the plastic bead. These
collisions cause the plastic particle to exchange energy with its
surroundings on the same order of magnitude as the micromachine converts
energy into work.
“This effect means that the amount of energy gained varies greatly
from cycle to cycle, and even brings the machine to a standstill in the
extreme case,” Valentin Blickle said. These collisions would not matter
in a macro machine, as it converts 20 orders of magnitude more energy to
work.
Bechinger explained the experiments have provided an initial insight
into the energy balance of a heat engine operating in microscopic
dimensions. “Although our machine does not provide any useful work as
yet, there are no thermodynamic obstacles, in principle, which prohibit
this in small dimensions.”
Source: Eureka Alert
