The variables which determine the state are known as properties.

In Thermal Engineering, state means the exact condition of a substance.

- Pressure
- Volume
- Temperature

The above properties are also known as basic properties as they may be found by direct observation or simple measurements.

You will find details about these properties as below,

*So, here are the 3 main properties of the substance described below*

*Pressure*

It is the force applied to a unit area.

In an 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/meter²

01 Kilo Pascal = 1000 Pa = 1 KPa

1 Mega Pascal = 10, 00,000 Pa = 1 MPa

Another unit for pressure is a bar and atmosphere pressure (atm.)

Gauges are used to measure the pressure of the fluid.

Pressure gauges which used to measure the pressure which is greater than the atmosphere whereas vacuum gauges are used to measure pressure less than atmospheric pressure.

The absolute pressure in the pressure gauge is equal to the observed gauge pressure plus the atmospheric pressure whereas the absolute pressure in the vacuum gauge is equal to atmospheric pressure minus the vacuum.

*Volume*

It is the space that 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 is generally expressed in meter³/ kg 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-meter³/kg.

The density of a substance is its mass per unit volume is generally expressed in kilogram per cubic meter.

So, under the same conditions of pressure and temperature, if the specific volume of air is 0.7734-meter³/kg then its density is 1.293 kg/mtr³.* *

*Temperature*

It is the measurement of the hotness or degree of the coldness of a given substance.

Ordinarily, temperatures are measured by thermometers; high temperatures are measured by pyrometers.

Also, Small and precise changes in temperature can be measured by resistant thermometers and thermocouples.

In a 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 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 the Kelvin scale and Celsius scale is,

Temperature K = Temperature degree centigrade + 273.15

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

Besides this information, you are suggested to read something more from below *engineering books*

*So, Here you find the Best Engineering Resources for further details*

To get the more details about the topic, I further recommended reading

- Engineering Thermodynamics
- Basic & Applied Thermodynamics
- A Textbook of Engineering Thermodynamics
- A Textbook of Thermal Engineering: Mechanical Technology

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