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Various Important Properties of Substance.

In thermal engineering, State means the exact condition of a substance and the variables which determine the state are known as properties. These properties are sub-divided into principal properties and fundamental properties. Fundamental properties are,

01) Pressure
02) Volume
03) Temperature

Above properties are also known as basic properties as they may be found out by direct observation or simple measurements. You will found details about these properties as below,

01) Pressure: -It is the force applied over a unit area. In international system (SI) of units, the unit for pressure is the force of one Newton (N) acting on a square meter area which is known as Pascal (Pa) so,

1 Pa = 1 N/meter square
1 Kilo pascal = 1000 Pa = 1 KPa
1 Mega Pascal = 10, 00,000 Pa = 1 MPa

Other unit for pressure is bar and atmosphere pressure (atm.)
Gauges are used to measure the pressure of fluid. Pressure gauges which used to measure

The pressure which is greater than atmosphere where as the vacuum gauges is used to measure pressure less than atmospheric pressure. The absolute pressure in pressure gauge is equal to the observed gauge pressure plus the atmospheric pressure where as the absolute pressure in vacuum gauge is equal to atmospheric pressure minus the vacuum.

02) Volume: - It is the space which the given substance occupies and it is measured in cubic meters. The most known unit of volume is liter.

The specific volume of a substance is its volume per unit mass and generally expressed in cubic meter per kilogram of air at zero degrees centigrade and under a pressure of 760 mm of mercury has a volume of 0.7734 cubic meters. Therefore, the specific volume of air under this condition is 0.7734 meter cube per kilogram.

The density of substance is its mass per unit volume is generally expressed in kilogram per cubic meter. So, under same conditions of pressure and temperature, if the specific volume of air is 0.7734 meter cube per kilogram then its density is 1.293 kilogram per meter cube.

03) Temperature: - It is the measurement of hotness or degree of coldness of a given substance.

Ordinarily temperatures are measured by thermometers, high temperatures are measured by pyrometers, small and precise changes of temperature can be measured by resistant thermometers and thermocouples.

In centigrade thermometer the freezing point of water is marked as zero and the boiling point as 100 at the atmospheric pressure, these points are called as fixed points of a thermometer.

Absolute zero is the temperature at which the internal energy of a substance becomes zero. The measurement of temperature taken above the absolute zero is known as absolute temperature and expressed in degrees of Kelvin scale or K.

The exact relationship between Kelvin scale and Celsius scale is,

Temperature K = Temperature degree centigrade + 273.15

I hope the above important information will help you to understand about some fundamental properties.

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