Reversible and irreversible process (Reversibility and Irreversibility)

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When a thermodynamic process occurs the change of state will happen. the process will Change from initial state to final state. the change in state in the process occurs in two ways. Here, the thermodynamic properties will undergo some changes to change the state or to complete the process. there are two ways of thermodynamic process and these are reversible or irreversible process.

Reversible process or Reversibility

Reversible process is a thermodynamic process which is capable of attaining its initial state by following the same path by which the process is reach to final state of the process from its initial state to complete the process.

Reversible process in thermodynamics
Reversible process
As shown in the graph the initial state of the system  is A. when the thermodynamic process changes its state from A to B to complete the process the system will follow the path A-O-B. If the process is reversible then it will have the capability to get its initial state by following the same path B-O-A. this is called reversibility of a thermodynamic process.

Reversible process is not a practical phenomenon because there is always some deviations in the process So it is a theoretical consideration.

Quasi Static process is an example of reversible process, but one thing should be kept in mind that Quasi static process is itself an assumption. To understand the reversible process and thermodynamics equilibrium quasi static process it is analysed.

Irreversible process or Irreversibility

Irreversible process is different from reversible process. The system will be able to regain its initial state after a process but it has to take a different path than the process is completed previously.

Irreversible process in thermodynamics
Irreversible process
In the graph an Irreversible processes shown. In the system When the state is changed from state A to state B the process is completed. To complete this process the path which is taken is A-O-B. When the system will try to attain its initial state A, it has to follow a different path A-Q-B. this makes this process an Irreversible process and This is called irreversibility of a process.

There is a lot depends on the properties of the system because thermodynamic properties of the system decides reversibility and irreversibility of the thermodynamic process.    

This is a short description about reversible process and irreversible process. Thermodynamic analysis largely depends on these phenomenon. 

Quasi Static Process or Quasi Equilibrium Process in Thermodynamics.

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when a system in which matter in enclosed, undergoes a thermodynamic process, the thermodynamic equilibrium will no longer remain in the system. Although, it is impossible to have a system in thermodynamic equilibrium when it undergoes a process but there is an assumption with some considerations in which a process can be occurred while maintaining system in thermodynamic equilibrium. This process is called Quasi Static process or Quasi Equilibrium Process.

Define Quasi Static 

The words 'Quasi' literally means 'Almost' and "Quasi static" means 'Almost Static'. So the Quasi static process is one which is almost remains in a single state. This process shows very small or infinitesimal deviation from its original state.  due to this negligible change of state the process is seems to be in thermodynamic equilibrium.

Quasi Static process Analysis

In the process a piston-cylinder setup is taken in which gas is filled inside it.
when the heating of the cylinder or container is done the inside gas temperature will increase and the piston will be raised up. here the system will not be in equilibrium.

Quasi Static Process
Quasi Static Process

But if we put Some Weight on the piston such that the height at which piston is raised is covers back by this weight as the piston will go downward due to this weight. when we further heat the cylinder the piston will be raised again so we again put some more weight on it to compensate the raising of the piston. we will do it until the heat is added and we make sure the piston is at its initial position by putting appropriate amount of weight in it.

In this way we will keep the piston at static position and avoid the change of state in the system. the change of state will be infinitesimal

This is a short description about Quasi static or quasi equilibrium process. it is an experimental assumption to show the thermodynamic equilibrium in a system. To maintain thermodynamic equilibrium in a system is a difficult thing. but in this experiment system remains closed to the equilibrium state.

What Is Thermodynamics. Important Terms Related To Thermodynamics ( Path, Process, Properties, State And Cycle)

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Thermodynamics is a part of science which is related with heat, temperature and energy. It is concerned with various forms of energy and its mutual conversion. The Thermodynamic behavior of different quantities or matter is controlled by 4 laws of thermodynamics. In this universe there is always a relation between any matter and energy. Thermodynamics is applicable in wide range of Science, Technology and Engineering world.

The motive of studying thermodynamics is to understand various forms of energy and develop the efficient energy systems.

Important terms related to thermodynamics

There are some important terms related to thermodynamics which is often used during thermodynamic analysis.

Thermodynamic Properties

Properties are the parameters which describes the nature and characteristics of a system. these parameters are used to define the thermodynamic system and its behaviour. Some examples of thermodynamic properties are pressure, volume, temperature, viscosity etc.

Properties are categorized into two parts "Intensive properties and extensive properties"

Intensive properties

Intensive properties are those which are independent of the mass of the system in which matter is enclosed. As the properties are independent of mass, the properties will have identical value at every point of the system. Examples of intensive properties are pressure temperature etc.

Extensive properties

Extensive properties are dependable on the mass of the system these properties do not have same value in the whole system. Examples of these properties are volume, viscosity, energy etc.

Thermodynamic State

State of a system can be defined as a certain position or condition in which properties of the system will have certain quantitative values. These Values defines a specific state. Changing these values will lead to the different state of the system. this change is called 'change of state'.

Thermodynamic Process

Due to the energy and mass transfers from the system and to the system, change of state takes place. This changing of state is called process. for example heating of a gas in a vessel can lead to change in pressure and temperature viscosity etc. In such ways properties of system can be altered and a thermodynamic process is completed.

Thermodynamic Path

Path is something when change of state happens repeatedly and series of process occurs. In the system this series of process can be traced by
a locii. that locii will be known as Thermodynamic Path.

Thermodynamic cycle

When a system undergoes to several process but at the last it gains its initial state from where the sequence of processes started, then the system is said to be completed a cycle. all in all the initial and final state will be same in a cycle. the cycle will have a closed loop path in the thermodynamic system.

Thermodynamic equilibrium

When the system do not undergo in change of state even when the external efforts are applied, then the system is said to be in Thermodynamic Equilibrium
To get a system in Thermodynamic Equilibrium it should be in equilibrium mechanically, thermally and chemically.

these are some important terms and parameters of thermodynamic. Although, thermodynamics is a broad subject but these terms are very significant. in each and every thermodynamic analysis the terms like path, process, cycle, properties are always used.

System, Surroundings, Boundary and Universe in thermodynamics - types of systems (open, closed, isolated)

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These are some common definitions associated with the basic thermodynamics. every thermodynamic study and analysis is related with these terms. let's get a quick review on these terms.

Thermodynamic System

thermodynamic system is the place which contains certain quantity of matter in which thermodynamic processes happens and thermodynamic analysis can be carried out. in the system the matter will consist of certain properties which can be altered by different processes like transfer of mass and energy.

Thermodynamic System


Everything external to the system i.e. the outside environment is called surrounding to the system.

Boundary of the System

Boundary is something which separates the system and the surroundings. the boundary can be real or imaginary. sometimes a relative boundary is considered so the boundary can be at rest or in a motion.


The combination of system and surroundings is called Universe i.e. when both system and the surroundings are kept together they can be referred as universe.

Types of System

there are three types of systems that are recognized-
1. Open System
2. Closed System
3. Isolated System

Open System

Open Systems are those in which both Mass and Energy can be inserted and can be took out from it. This system is open to any intersection of mass and energy.

Closed System

Closed system is one in which mass remains constant i.e. mass can not be added or subtracted but energy can be manipulated.

Isolated system

Isolated System is one in which mass and energy both can neither be added nor be subtracted from the system.

Electron Beam Welding Process

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Electron Beam Welding in an unconventional Method to Join the two materials. In this two pieces of material are fused by a high speed beam of electrons. The electron beam imposed to the materials will loose its kinetic energy and convert it into the heat energy. this heat energy is used for the fusion of metal Work-piece. The Vacuum medium is required to get a proper flow of electron beam and prevent dissipation of electron.
Electron Beam Welding Process

Advantages of Electron Beam Welding

There is no need to use any filler material.

Electron beam welding enables the single pass welding of thick joints.

There is less chance of impurities to enter into the vacuum medium so the welding would be more efficient.

Hermetic seals of components are uses to retain a vacuum medium for successful welding operation.

Electron beam welding offers the joining of dissimilar materials.

The chances of welding defects to occur is less.

Heat generated by electron fusion will affect fewer area of the specimen.

Disadvantages of Electron Beam Welding

The initial equipment and operational cost is high

The size of specimen depends on the vacuum equipment.

The process of electron beam welding is a time consuming process

In the electron beam welding rapid solidification is required that causes cracks.

What does TDI stands for and how TDI Engine technology Works

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TDI stands for "Turbocharged Direct Injection". TDI is a fuel injection system in a diesel vehicles. A fuel injection system Plays a vital role in the design of a car. The car owner should know about the technology used for the injection system and his / her car. The terms like CRDI and TDI are very common in automobile engineering. The world wide famous brand Volkswagen uses TDI fuel injection Technology in their vehicles.
TDI Line Diagram : Source

TDI ( Turbocharged Direct Injection ) Working Principle

Tdi has the facility of turbo charging and direct fuel injection into the engine cylinder. The fuel injector injects the fuel into the engine and spray it in the combustion chamber. The direct injection atomizes the fuel and transfer it to the combustion chamber. Turbocharger present and system increase the amount of air during combustion or when intake of fuel takes place. It helps in better combustion.

An intercooler is provided in the TDI that help in lowering the temperature. Due to this the amount of fuel injected can be increased for combustion.TDI has less open surface which helps cut down the heat losses and ultimately increase the engine efficiency.

This useful Technology was developed by Volkswagen group. Most of the vehicles of Volkswagen group uses this technology in their vehicles. Volkswagen uses this technology in the commercial vehicle and marine engines. With the use of this technology vibes great power and more efficiency.

Properties Of TDI in Diesel Engine

1. TDI uses turbocharger from exhaust to increase the engine power and efficiency.

2.If we compare the efficiency orbit Technologies, CRDI seems to win. The reason is that CRDI uses sensor and has injector pipe to provide the fuel as per the necessity. So in this criteria CRDI is better than TDI.

3.The cost of TDI engine is less. but TDI is less efficient so it Consume more fuel and money. in other words, operational cost of TDI is expensive than other fuel injection technology like CRDI. 

4. TDI is specially developed exclusively for Volkswagen group Vehicles..

5.The design of TDI Technology is simple.

6.Maintenance of TDI is Economical.