3. MAIN PARAMETERS OF GAS STATE
In a thermodynamic system, heat and mechanical energy are converted into a gas or steam in the form of a working fluid. Vapors and gases are used as working substances, which change their volumes greatly when heated and cooled. When studying theoretical problems in thermodynamics, ideal gases are considered to be very small in size as molecules and do not take into account the gravitational forces between them.
The thermodynamic parameters of gas are pressure, volume and temperature.
Pressure. According to the molecular kinetic theory of gases, pressure is the result of the impact of the gas molecules on the wall of the container in which they are located, and is defined as follows:
(1)
burada n - is the number of molecules in a single volume; m - is the mass of the molecule; c - is the root mean square velocity of the molecules.
Because the number of molecules and their strokes is so large, it is impossible to track individual molecules. Therefore, the pressure is characterized by the average value of all shocks and always acts in the normal direction on the wall of the vessel in which the gas is present. The force per unit area is called the pressure, the unit of measurement is: 1 Pa =1 N/m2, 1 kPa =103 Pa, 1 MPa =106 Pa, 1 bar=105 Pa. Liquid columns are also used as a unit of pressure: 1 bar=10,2 m water column.= 750 mm mercury column. at temperature tC Indication of mercury barometer B, 0C to the appropriate temperature indication p > pbar is.
P = piz + pbar (2)
When p < pbar
P = pbar – pvak (3)
is determined by the expressions. Piz, pvak - are the excess and dilution pressures of the gas;
Pbar – is the barometric pressure of the environment.
Volume. The volume of a unit mass is called the specific volume:
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