Mechanical Engineers: 2011

Monday, October 17, 2011

properties of a system

The thermodynamic properties of a system is basically divided into two general clases

1)Extensive Property:

the property of a system whose value for the entire system is equal to the sum of their values for the individual parts of the system are called extensive properties

ex:Total volume ,total mass,Total energy

Intensive property :

The property of a system (like temperature density ,pressure )is not equal to the sum of their individual parts of the system are called intensive properties

centigrade to fahrenheit or fahrenheit to centigrade

The relation between celsius scale and fahrenheit scale is given by

C/100 = F-32/180

C/5=F-32/9

Enthalpy Definition

enthalpy is an thermodynamic property .It can be used to calculate the heat transfer during a Quasi static process taking place in a closed thermodynamic system under constant pressure

In thermodynamics "The sum of internal energy(U) and the product of pressure and volume (pv)is termed as enthalpy

It denoted as H

H=U+pv

For better explanation

watch the below video link

http://www.youtube.com/watch?v=fucyI7Ouj2c

Quasi static process

a quasistatic process is a thermodynamic process that happens infinitely slowly. However, it is very important of note that no real process is quasistatic

Any reversible process is necessarily a quasistatic one.

However, some quasisatic processes are irreversible,

Latent Heat

Heat that causes a change of state with no change in temperature is called latent heat.

example, water remains at 100°C while boiling

Sensible heat

Sensible heat
When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat.

Similarly,

when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat.

Heat that causes a change in temperature in an object is called sensible heat.

Entropy

it is a function of a quantity of heat which shows the possibiliy of conversion of that heat into work

Entropy is a thermodynamic property that can be used to determine the energy available for useful work in athermodynamic process, such as in energy conversion devices, engines, or machines

LAWS OF THERMODYNAMICS

Basically there are four laws of thermodynamics:

zeroth law

first law

it defines light on concept of energy

second law

it defines the limit of converting heat into work and introduces the increase of entropy

third law

it defines the absolute zero of entropy

zeroth law of thermodynamics recognizes that if two systems are in thermal equilibrium with a third, they are also in thermal equilibrium with each other, thus supporting the notions of temperature and heat.

first law of thermodynamics may be expressed by several forms of the fundamental thermodynamic relation:

Increase in internal energy of a system = heat supplied to the system + work done on the system

For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system.

second law of thermo dynamics

Its main import is to tell about irreversibility.

The prime example of irreversibility is in the transfer of heat by conduction or radiation. It was known long before the discovery of the notion of entropy that when two bodies of different temperatures are connected with each other by purely thermal connection, conductive or radiative, then heat always flows from the hotter body to the colder one

Third law of thermodynamics:

The entropy of a substance is zero if the absolute temperature is zero.