Thermodynamic system

A thermodynamic system is a spatially limited deems to physical system for which an energy balance - the open system, together with a mass balance - can be created. The closed system, only the energy ( heat and work ) may be considered, the flow through the system boundary thereby changing with the change of internal energy of the state of the system. In an isolated system no exchange with the environment takes place.

Open System

If there is an open system, so the system can both energy and matter with its environment exchange. An example of an open system in which a process runs continuously, is a turbine. In stationary operation, the system is flowed through by a constant mass flow. The conditions of the fluid to remain at the entry and at the exit of each of the fluid is constant and will change state on the way through the system. The shaft work is supplied in compressing the system, made upon expansion. It is called technical work.

She is described by:

(This is the change in the external energy. Definition of the technical work is different in the literature. Variously understood as including only the first term ).

Alongside this work occur at inlet and outlet of the system to push projects. Has in the steady operation, the mass particles at the inlet and at the outlet of the volume, then the shift operation at the entry corresponding to the outlet

This displacement works are included in addition to the internal energy in the respective enthalpies. With the definition of enthalpy

Is the balance sheet for the open stationary system:

And the symbol for the power

And the external energy

Is the first law for the application of the open system:

The internal combustion engine shown in the sketch as an example of an open system is actually alternately open and closed. Only over long periods of time, they can be regarded as an open system.

Closed system

A system is called a closed whenever no mass exceeds the system limit. Heat, radiation, and work can be supplied or removed. As work are:

Since, according to the first law of thermodynamics, energy is neither created nor be destroyed, the internal energy increases by the supplied energy. The balance for the stationary closed system is:

With

( The subscripts 1 and 2 designate respectively the initial and the final state, the index 1.2 the path from 1 to 2)

If through the influence of the supplied energy, the external energy of the system, ie the potential energy and / or the kinetic energy of the system is changed, is the balance after 1 main set for the closed system:

An isolated system

When completed, or isolated refers to a closed system when it is energy dense ( Example 4 in the diagram ). The ideal case requires no further consideration because in the energy balance of all terms vanish.

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