Page 18 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

1.5 Property, State, Process and Cycle.

Properties are macroscopic characteristics of a system such as mass, volume, energy,

pressure, and temperature to which numerical values can be assigned at a given time

without knowledge of the history of the system. Many other properties are considered

during the course of our study of engineering thermodynamics. Thermodynamics also
deals with quantities that are not properties, such as mass flow rates and energy transfers

by work and heat. Properties are considered to be either intensive or extensive.

Intensive properties are those which are independent of the size of the system such as
temperature, pressure and density.

Extensive properties are those whose values depend on the size or extent of the system.

Mass, volume and total energy are some examples of extensive properties.

The word state refers to the condition of system as described by its properties. Since

there are normally relations among the properties of a system, the state often can be

specified by providing the values of a subset of the properties.

A process is a transformation from one state to another. When there is a change in any

of the properties of a system, the state changes. Processes may be reversible or actual

(irreversible).. A reversible process is one that is wholly theoretical, but can be

imagined as one which occurs without incurring friction, turbulence, leakage or anything
which causes unrecoverable energy losses , while the irreversible process is the natural

process that is commonly found in the nature.

Processes may be constrained to occur at constant temperature (isothermal), constant

pressure, constant volume, polytropic and adiabatic (with no heat transfer to the
surroundings).

Cycle, and in some cases cyclic, may refer to a process that returns to its beginning and
repeats itself in the same sequence. Such processes are seen in many fields, such as

physics, mathematics, biology, astronomy, economics, audio frequency, etc.

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