Thermodynamics
Introduction
The thermodynamics is the branch of engineering science which deals with energies possessed by gases and vapors. It also includes the conversion of these energies in terms of heat and mechanical work.
Thermodynamic Systems
It may be defined as a definite area where some thermodynamic process take places.Thermodynamic system may be classified into three groups.
1: Closed System
This is a system of fixed mass whose boundaries are determined by the space of the working substance occupied in it. In a closed system, heat and work cross the boundary of the system, but there is no addition or loss of the original mass of the working substance.
2: Open System
In this system the working substance crosses the boundary of the the system.
3: Isolated System
It is a system of fixed mass and no heat or work cross the boundary.
Law of Thermodynamics
1: Zeroth law of thermodynamics
When two bodies are in thermal equilibrium with the third body, they are also in thermal equilibrium with each other.
2: First law of thermodynamics
The heat and work are mutually convertible. As describe this law, a definite amount of mechanical work needed to produced a definite amount of heat and vice versa.This law also states that energy can neither be created or destroyed, through it can be transformed from one form to another.
3: Second law of thermodynamics
There is a definite limit to the amount of mechanical energy, which can be obtained from a given quantity of heat energy.It can also described that " It is not possible for a self-acting machine working in a cyclic process, to transfer heat from lower temperature body to higher temperature body without the any addition of an external energy.
Thermodynamics processes of Perfect gases.
It can be described as the process of heating or cooling of a gas. The process of thermodynamics relates with changes in the properties of gas pressure,volume,temperature,specific energy etc. Following are the important thermodynamic processes.
1: Constant volume process or isochoric process.
When the gas is heated at a constant volume, its temperature and pressure will increase.Since there is no change in the volume and no external work is done by the gas. All the heat supplied is stored in the body of the gas in the form of internal energy.
2: Constant pressure process or isobaric process.
When the gas is heated constant pressure, temperature and volume of gas will increase. Since there is a change in the volume, the heat supplied is utilized in increasing the internal energy of the gas, and also for doing some external work.
3: Hyperbolic process.
A process in which the gas is heated or expanded in such a way that the product of its pressure and volume remain constant.
4: Constant temperature process or isothermal process.
A process in which the temperature of the substance remain constant during its expansion or compression. So there is no change in the temperature and there is no change in the internal energy.
5: Adiabatic process or isentropic process.
A process in which the working substance neither receives nor gives out heat to its surroundings,during expansion or compression. This will happen when the substance remain thermally isolated.This process is also called constant entropy process.
6: Polytropic process.
The Polytropic process is known as the general law for the expansion or compression of gases. relation is described
n = log (p2/p1)/log (v1/v2)
where n is polytropic index, which may have any value frome zero to infinity, depending to the manner in which the expansion or compression take places.
7: Free expansion ( or unresisted expansion) process.
A free expansion occurs when a fluid is allowed to expand suddenly into vacuum chamber through an orifice of large dimensions.In this process, no heat is supplied or rejected and no work is done.Hence the total heat of the fluid remains constant.
8: Throttling Process.
When a perfect gas is expanded through an aperture of minute dimensions, such a narrow throat or slightly opened valve, the process is termed as throttling process.During the process, no heat is supplied or rejected and also no external work is done. Moreover, there is no change in the temperature and so the total heat of the fluid remains constant.
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