What is Thermodynamics?
Thermodynamics is the branch of science which deals with the energy and energy interactions. More specifically it deals with energy conversion, energy exchange and direction of exchange. We will study the effects on different substances, as we may expose a mass to heating/cooling or to volumetric compression/expansion. During such processes we are transferring energy into or out of the mass, so it changes its conditions expressed by properties like temperature, pressure, and volume.
Beyond the description of basic processes and systems, thermodynamics is extended to cover special situations like moist atmospheric air, which is a mixture of gases, and the combustion of fuels for use in the burning of coal, oil, or natural gas, which is a chemical and energy conversion process used in nearly all power-generating devices.
Table of Contents
THERMODYNAMIC SYSTEM AND CONTROL VOLUME
A thermodynamic system may be broadly defined as a definite area or a space where some thermodynamic process is taking place.
It is embedded in its surroundings or environment; it can exchange heat with, and do work on, its environment through a boundary known as system boundary, which is the imagined wall that separates the system and the surroundings as Fig. 1. In reality, the immediate surroundings of the system are interacting with it directly and therefore have a much stronger influence on its behavior and properties.
For example, if we are studying a car engine, the burning fuel inside the cylinder of the engine is the thermodynamic system; the piston, exhaust system, radiator, and air outside form the surroundings of the system.
Types of Thermodynamic system
Thermodynamic systems may be classified into the following three groups:
1. Closed System: This is a system of fixed mass and identity whose boundaries are determined by the space of the matter (working substance like fuel air mixture in engine) occupied in it.
2. Open System: An open system is a type of thermodynamic system that can exchange energy as well as mass with its surroundings. Boiling water is an example of an open system in which the heat is going out of the vessel and the steam as a mass also goes out of the system to the surroundings.
3. Isolated System: A system which is completely uninfluenced by the surroundings is called an isolated system. It is a system of fixed mass and no heat or work energy cross its boundary.
Control Volume: It is a defined region in space used in thermodynamics to analyze systems where mass and energy can cross the boundary. For thermodynamic analysis of an open system, such as an air compressor, attention is focused on a certain volume in space surrounding the compressor is known as control volume, bounded by a surface called the control surface. Matter as well as energy crosses the control surface.
THERMODYNAMICS PROPERTIES, PROCESS AND CYCLE.
Any Thermodynamic system has certain characteristics by which its physical condition are determined such as Temperature, Pressure, Volume etc. These characteristics are called properties of a thermodynamic system. In other words, properties are the coordinates to describe the the state of a system e.g. A & B is state in the Fig. 5. When all properties of the system has a definite value such as VA & TA in the fig. 6, which represent Volume of state A (VA) and Temperature of state B (TB), the system is said to exist at a definite state.
During any operation, when one or more properties of a system changes is called a change of state, as shown in the fig. 5. from state 1 to state 2. The succesion of state passed through during a change of state is called the path of the change of state. When the path is completely specified, the change of state is called process, shown in Fig. 5.
Thermodynamic cycle:
A Thermodynamic cycle is defined as a series of state changes such that the final state is identical with the initial state as shown in Fig. 7. State 1 is the initial state and going through 2, 3, 4 and final state is also 1. This completed opeartion is call a Thermodynamic cycle.
Thermodynamic properties are two types, Intensive properties and Extensive properties.
THERMODYNAMIC EQUILIBRIUM
Thermodynamic equilibrium is a state where a system’s properties do not change over time, and the system is in balance with the surroundings. An isolated system always reaches in course of time a state of thermodynamic equilibrium and can never depart from it spontaneously.
A system will be in a state of thermodynamic equilibrium, if three types of equilibrium are satisfied. (a) Mechanical Equilibrium, (b) Chemical Equilibrium, (c) Thermal Equilibrium.
QUASI-STATIC & NON QUASI STATIC PROCESS
Quasi-Static Process (Reversible Process)
A quasi-static process is one that proceeds infinitely slowly, such that the system remains in thermodynamic equilibrium at all times. Every intermediate state the system passes through can be considered an equilibrium state. Because of this, quasi-static processes are idealized and reversible.
Example: Slow compression or expansion of gas in a piston-cylinder with negligible friction.
Non-Quasi-Static Process (Irreversible Process)
A non-quasi-static process is a rapid or sudden process in which the system does not remain in equilibrium throughout. Intermediate states are undefined, and the process is typically irreversible.
Example: Free expansion of a gas into vacuum. Sudden compression by a fast-moving piston.
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