Basic theory of compressed air

Basic theory of compressed air

Basic theory of compressed air

     Compression and compression ratio

1 , the compression

Is an adiabatic compression of the gas in the compression process does not produce significant heat of compression process incoming or outgoing . In a cylinder of a fully insulated above process can be a reality . Isothermal compression is a compression process in the gas compression process to keep the temperature constant .

2, the compression ratio : (R)

Compression ratio refers to the compressor discharge and intake of the ratio of the absolute pressure . Example: In the inlet absolute pressure at sea level is 0.1 MPa, the exhaust pressure is absolute pressure 0. 8MPa. The compression ratio:

P2 0.8

R = - = - = 8

P1 0.1

Multi-stage compression advantages:

( 1 ) , save the compression work ;

( 2 ) reduce the exhaust gas temperature ;

( 3 ) , to improve the capacity coefficient ;

( 4 ) , the piston compressors , reduce the gas thrust on the piston .

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Compression media

Why use compressed air to make the media ?

Because air is compressible , clear and transparent, and easy to transport ( non-condensing ) , harmless , safe and inexhaustible .

Inert gas is a function of the inert gas environment , the standard compressor can be the same compressed inert gases. Dry nitrogen and carbon dioxide are inert gases.

Air properties:

Dry air components : nitrogen (N2) oxygen (O2) Carbon dioxide (CO2)

20.93% 0.03% 78.03%

Weight: 28.96

Weighting : In 0 ℃, 760mmHg column when , r0 = 1.2931kg/m3

Specific heat: at 25 ℃, 1 atm , Cp = 0.241 Kcal / kg-℃

At t ℃, pressure of H (mmhg) , the air gravity:

273 H

rt = 1.2931 × - × -kg/m3

273 + t 760

The proportion of wet air should also be considered saturated water vapor partial pressure (0.378ψ, Pb).

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Pressure

1, the pressure

This is a force per unit area , such as the square on the intensity of the pressure by one unit of 1 Newton Pascal :

Namely : 1Pa = 1N/m2

1Kpa = 1,000 Pa = 0.01 kg/cm2

1Mpa = 106Pa = 10 kg / cm2

2 , absolute pressure

Absolute pressure is taken into account with full vacuum or absolute zero compared to our live ambient atmosphere absolute pressure with 0.1Mpa . At sea level , gauge pressure plus atmospheric pressure of 0.1MPa absolute pressure can be drawn . The higher the altitude the lower the atmospheric pressure .

3 , the atmospheric pressure

Barometer is used to measure atmospheric pressure. When coupled with the pressure on the instrument can come to absolute pressure .

Absolute pressure = gauge pressure + atmospheric pressure

Atmospheric pressure mercury MM usually as a unit, but any one can make the same pressure unit good explanation :

A physical atmospheric pressure = 760 mm Hg = 10.33 m water column = 1.033kgf/cm2 ≌ 0.1MPa.

Atmospheric pressure with altitude relation:

H

P = P0 × (1 -) 5.256 mmHg

44300

H - altitude ,

P0 = atmospheric pressure (0 ℃, 760mmHg)

4, the pressure unit conversion :

Unit : MPa, Psi (bf/in2)

1Psi = 0.006895MPa,

1bar = 0.1MPa,

1kgf/cm2 = 98.066KPa = 0.098066MPa ≌ 0.1Mpa