Dissipation

Dissipation (from the Latin for " scatter " ) referred to in the physics of the process in a dynamic system, in which, for example, by friction, is about the energy of a macroscopically -directed motion can be converted into other forms of energy into thermal energy, ie. energy in a disordered motion of the molecules, which only is then partially converted. Such a system is called dissipative. This term occurs in the physical areas of thermodynamics and acoustics or generally in the wave theory. An example of a dissipative system, the damped oscillation.

In thermodynamics, the work to be converted due to friction, throttling or impact processes in thermal energy (internal energy ), referred to as Dissipationsarbeiten. It involves irreversible processes in which entropy increases, in other words, exergy is converted into anergy ( cf. Second Law of Thermodynamics ). These works are process variables, that is path-dependent.

The so-called Dissipationskonstante for a thermistor ( thermistor negative temperature coefficient, NTC ) is the thermal conductivity, generally specified for stagnant air. On contact with water, the Dissipationskonstante changes.

In materials science is understood in the context of the material cycle under dissipation the consumption of raw materials - so do not be compensated losses, such as corrosion, abrasion and other loss in a broadly diversified distribution over the whole surface of the earth, so that the raw material can not be recovered.

Dissipation in the thermodynamics

For example, it is converted back by friction between the piston rings and the cylinder walls of an engine part of the work produced from this thermal energy into internal energy so that the transmitted external work is thereby reduced.

The image illustrates various dissipative processes in a closed adiabatic system:

The work of a fan because of the rigid system does not limit change in volume work, is therefore completely dissipated as did the electrical system limit on the work entrusted.

If the temperature compensation process within the system could be reversibly produced work on a Carnot cycle and discharged to the outside. Since the heat wasted by "warm", " cold" flows, their exergetic content is dissipated.

Instead of the restriction process could have a movable piston ( with power transmission to the outside) pressure equalization take place reversibly, or behind the nozzle could afford a wind turbine work. This possibility remains unused, the work is dissipated.