1. TECHNICAL THERMODYNAMICS
2. THERMODYNAMIC SYSTEM
One of the basic concepts in technical thermodynamics is a thermodynamic system, a substance that is mechanically and thermally exposed to each other as well as to the external environment. An example of a simple thermodynamic system is the expansion or contraction of a gas in a cylinder by a moving piston. The substance that does not enter the system is called the external environment. The thermodynamic system is separated from the environment by a control surface (coating). In the example above, the cylinder wall and piston control surface are the ambient air. The mechanical and thermal interactions of the thermodynamic system occur through the control surface. A thermodynamic system can work in mechanical contact. Thermal interactions occur between the individual components of a thermodynamic system and between the system and the environment. In the example under consideration, the gas can be heated from the cylinder wall.
A thermodynamic system is called a closed system if there is no metabolism between it and the environment, otherwise it is called an open system. A flow system is a special case of an open thermodynamic system in which matter enters one part of the system and leaves the other.
When there is no exchange of matter and heat between the control surface of the thermodynamic system and the environment, it is called an insulated system. A system that is thermally insulated from the environment is called an adiabatic system.
In technical thermodynamics, thermodynamic systems in which heat and work interact are studied.
In the absence of macroscopic exchange of matter and energy between different parts of a thermodynamic system, it is called an equilibrium system. In an unbalanced thermodynamic system, state parameters change over time. In order for a system to be in equilibrium, its parameters, which cause the exchange of matter and energy, must be evenly distributed in matter. Thus, temperature and pressure must be the same at all points in the thermodynamic system in equilibrium. Insulated systems are balanced over time.
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