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Introduction to the basic characteristics of gas

Basic characteristics of gas

1. Density: refers to the weight contained in the unit volume.

The gaseous density of liquefied petroleum gas is 2.0-2.5kg/Nm 3

2. Specific gravity: The specific gravity of gas refers to the density of gas per unit volume, and the ratio of air density in the same state, also called relative density or relative specific gravity.

3. Calorific value: The heat released by the complete combustion of the unit volume of gas becomes the calorific value of the gas.

The calorific value is divided into a high calorific value and a low calorific value.

The high calorific value refers to the total amount of heat released when the flue gas is completely cooled after the unit gas is cooled to the initial temperature, and the water vapor is discharged in the state of condensed water.

The low calorific value refers to the total amount of heat released when the flue gas is completely cooled after the unit gas is cooled to the initial temperature, and the water vapor is discharged as a vapor.

4. Theoretical air volume: refers to the minimum amount of air required for complete combustion of a unit of gas according to the combustion reaction equation.

The amount of air required for LPG combustion is three times that of natural gas; it is six times that of artificial gas.

5, expansion and compression

The volume of liquid liquefied petroleum gas expands due to an increase in temperature. In a closed container filled with liquefied petroleum gas, its volume rapidly expands as the temperature rises, so that the pressure rises quickly to blast the container. If the volume expansion coefficient of water is set to 1, the volumetric expansion coefficient of liquid liquefied petroleum gas is about 16 times that of water.

6, saturated vapor pressure

The saturated vapor pressure of liquid hydrocarbons, referred to as vapor pressure, is the absolute pressure expressed by the vapor at a certain temperature when the liquid in the closed vessel and its vapor pressure are in dynamic equilibrium.

The saturated vapor pressure is independent of the size of the vessel and the amount of liquid, and is related to the composition and temperature of the liquefied petroleum gas. When the temperature is raised, the saturated vapor pressure is increased; the light component is larger than the saturated vapor pressure of the recombinant component.

7. Gasification latent heat

The latent heat of vaporization is the amount of heat absorbed by a unit mass (1KG) of liquid into its equilibrium vapor.

When a substance changes from a gaseous state to a liquid state, it is called liquefaction; when a gaseous state changes to a liquid state, heat is released. The substance changes from a liquid to a gaseous state, called gasification. When the liquid is converted to a gaseous state, it is necessary to absorb heat.

Liquefied petroleum gas is stored in liquid form, and all kinds of burning appliances use gaseous liquefied petroleum gas. Therefore, the process of liquefied petroleum gas passing through a liquid state to a gaseous state is called gasification or evaporation, and it is necessary to absorb heat. When the outside temperature is low and the heat required for vaporization or evaporation cannot be supplied, the liquefied petroleum gas absorbs its own heat, causing the temperature to decrease until the gasification is stopped.

8, the classification of pressure

The pressure per unit area is called pressure strength, referred to as pressure. The pressure is referred to as pressure on the project. The pressure is divided into relative, absolute and negative pressures.

Relative pressure: The part of the pressure measured by the meter is also called gauge pressure, positive pressure, and working pressure.

Absolute pressure: The sum of atmospheric pressure and gauge pressure is called absolute pressure, also called actual pressure.

Negative pressure: The part of the pressure below atmospheric pressure is measured by a meter. The relative pressure at this time is less than atmospheric pressure, because the value indicated is positive, called negative pressure. Also called vacuum.

9, fire temperature

The lowest temperature at which fuel can be continuously burned, called the fire temperature. Under normal pressure (atmospheric pressure), the ignition temperature of liquefied petroleum gas is 365-460 °C, the ignition temperature of natural gas is 270-540 °C, and the ignition temperature of city gas is 270-605 °C. Its ignition temperature is much lower than other fuels, so it is also called flammable gas.

10. Explosion limit:

The range of flammable gas concentrations when a mixture of combustible gas and air is exposed to an open flame is called the explosion limit. In this mixture, when the content of combustible gas is reduced to a level at which an explosive mixture cannot be formed, it is called the lower explosive limit of the combustible gas; and when the content of the combustible gas is increased to such a level that the explosive mixture cannot be formed, The upper limit of the explosion.

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