The relative density of gases is indicated. Gas density: absolute and relative

Natural gas is a mixture of mainly hydrocarbon gases that occur in the subsoil in the form of separate deposits and deposits, as well as in dissolved form in oil deposits or in the form of so-called "gas caps". The main physical and chemical properties of natural gas are:

The density of gases is the mass of a substance per unit volume - g / cm 3. For practical purposes, the relative density of the gas relative to air is used, i.e. ratio of gas density to air density. In other words, it is an indicator of how much a gas is lighter or heavier than air:

where ρ in under standard conditions is 1.293 kg / m 3;

The relative density of methane is 0.554, ethane is 1.05, and propane is 1.55. That is why household gas (propane) in the event of a leak accumulates in the basement of houses, forming an explosive mixture there.

Heat of combustion

The calorific value or calorific value is the amount of heat that is released during the complete combustion of 1 m 3 of gas. On average, it is 35160 kJ / m 3 (kilojoules per 1 m 3).

Gas solubility

Solubility in oil

The solubility of gas in oil depends on the pressure, temperature and composition of the oil and gas. As the pressure increases, the solubility of the gas also increases. As the temperature rises, the solubility of the gas decreases. Low molecular weight gases are more difficult to dissolve in oils than fatter ones.

With an increase in oil density, i.e. as the content of macromolecular compounds in it increases, the solubility of the gas in it decreases.

An indicator of the solubility of gas in oil is the gas factor - G, which shows the amount of gas in 1 m 3 (or 1 ton) of degassed oil. It is measured in m 3 / m 3 or m 3 / t.

According to this indicator, deposits are divided into:

1) oil - G<650 м 3 /м 3 ;

2) oil with a gas cap - G-650 - 900 m 3 / m 3;

3) gas condensate - G>900 m 3 /m 3.

Solubility of water in compressed gas

Water dissolves in compressed gas at high pressure. This pressure makes it possible to move water in the subsoil not only in the liquid, but also in the gas phase, which ensures its greater mobility and permeability through rocks. As the mineralization of water increases, its solubility in the gas decreases.

Solubility of liquid hydrocarbons in compressed gases

Liquid hydrocarbons dissolve well in compressed gases, creating gas condensate mixtures. This creates the possibility of transfer (migration) of liquid hydrocarbons in the gas phase, providing an easier and faster process of its movement through the rock mass.

With increasing pressure and temperature, the solubility of liquid hydrocarbons in gas increases.

Compressibility

Formation gas compressibility is a very important property of natural gases. The volume of gas in reservoir conditions is 2 orders of magnitude (ie, approximately 100 times) less than its volume under standard conditions on the earth's surface. This is because the gas has a high degree of compressibility at high pressures and temperatures.

The degree of compressibility is depicted in terms of the reservoir gas volume ratio, which is the ratio of the volume of gas in reservoir conditions to the volume of the same amount of gas under atmospheric conditions.

Condensate formation is closely related to the phenomena of compressibility of gases and the solubility of liquid hydrocarbons in them. In reservoir conditions, with increasing pressure, liquid components pass into a gaseous state, forming "gas-dissolved oil" or gas condensate. When the pressure drops, the process goes in the opposite direction, i.e. partial condensation of a gas (or vapor) into a liquid state. Therefore, during gas production, condensate is also extracted to the surface.

Condensate factor

The condensate factor - CF - is the amount of raw condensate in cm 3 per 1 m3 of separated gas.

Distinguish between raw and stable condensate. Raw condensate is a liquid phase in which gaseous components are dissolved.

Stable condensate is obtained from crude by its degassing. It consists only of liquid hydrocarbons - pentane and higher.

Under standard conditions, gas condensates are colorless liquids with a density of 0.625 - 0.825 g / cm 3 with an initial boiling point from 24 0 C to 92 0 C. Most of the fractions have a boiling point up to 250 0 C.

Density is usually called such a physical quantity that determines the ratio of the mass of an object, substance or liquid to the volume they occupy in space. Let's talk about what density is, how the density of a body and matter differs, and how (using what formula) to find density in physics.

Types of density

It should be clarified that the density can be divided into several types.

Depending on the object under study:

• The density of a body - for homogeneous bodies - is the direct ratio of the mass of the body to its volume occupied in space.
• The density of a substance is the density of bodies consisting of this substance. The density of substances is constant. There are special tables where the density of different substances is indicated. For example, the density of aluminum is 2.7 * 103 kg / m 3. Knowing the density of aluminum and the mass of the body that is made of it, we can calculate the volume of this body. Or, knowing that the body consists of aluminum and knowing the volume of this body, we can easily calculate its mass. How to find these values, we will consider a little later, when we derive a formula for calculating the density.
• If the body consists of several substances, then to determine its density, it is necessary to calculate the density of its details for each substance separately. This density is called the average density of the body.

Depending on the porosity of the substance of which the body is composed:

• True density is the density that is calculated without taking into account the voids in the body.
• Specific gravity - or apparent density - is that which is calculated taking into account the voids of a body consisting of a porous or friable substance.

So how do you find density?

Density Formula

The formula to help find the density of a body is as follows:

• p = m / V, where p is the density of the substance, m is the mass of the body, V is the volume of the body in space.

If we calculate the density of a particular gas, then the formula will look like this:

• p \u003d M / V m p is the density of the gas, M is the molar mass of the gas, V m is the molar volume, which under normal conditions is 22.4 l / mol.

Example: the mass of a substance is 15 kg, it occupies 5 liters. What is the density of matter?

Solution: Substitute the values ​​into the formula

• p = 15 / 5 = 3 (kg/l)

Answer: the density of the substance is 3 kg / l

Density units

In addition to knowing how to find the density of a body and a substance, it is also necessary to know the units of density measurement.

• For solids - kg / m 3, g / cm 3
• For liquids - 1 g / l or 10 3 kg / m 3
• For gases - 1 g / l or 10 3 kg / m 3

You can read more about density units in our article.

How to find density at home

In order to find the density of a body or substance at home, you will need:

1. Scales;
2. centimeter if the body is solid;
3. Vessel, if you want to measure the density of a liquid.

To find the density of a body at home, you need to measure its volume with a centimeter or vessel, and then put the body on the scales. If you're measuring the density of a liquid, don't forget to subtract the mass of the vessel into which you poured the liquid before calculating. It is much more difficult to calculate the density of gases at home, we recommend using ready-made tables in which the densities of various gases are already indicated.

ρ = m (gas) / V (gas)

D by Y (X) \u003d M (X) / M (Y)

That's why:
D by air. = M (gas X) / 29

Dynamic and kinematic viscosity of gas.

The viscosity of gases (the phenomenon of internal friction) is the appearance of friction forces between gas layers moving relative to each other in parallel and at different velocities.
The interaction of two layers of gas is considered as a process during which momentum is transferred from one layer to another.
The force of friction per unit area between two layers of gas, equal to the momentum transferred per second from layer to layer through a unit area, is determined by Newton's law:

Velocity gradient in the direction perpendicular to the direction of motion of the gas layers.
The minus sign indicates that momentum is carried in the direction of decreasing velocity.
- dynamic viscosity.
, where
is the density of the gas,
- arithmetic average speed of molecules,
is the mean free path of the molecules.

Kinematic coefficient of viscosity.

Critical gas parameters: Тcr, Рcr.

The critical temperature is the temperature above which, at any pressure, the gas cannot be transferred to the liquid state. The pressure required to liquefy a gas at a critical temperature is called critical pressure. Given gas parameters. The given parameters are dimensionless quantities that show how many times the actual parameters of the state of the gas (pressure, temperature, density, specific volume) are greater or less than the critical ones:

Downhole production and underground gas storage.

Gas density: absolute and relative.

The density of a gas is one of its most important characteristics. Speaking of the density of a gas, one usually means its density under normal conditions (i.e., at temperature and pressure). In addition, the relative density of a gas is often used, by which is meant the ratio of the density of a given gas to the density of air under the same conditions. It is easy to see that the relative density of a gas does not depend on the conditions in which it is located, since, according to the laws of the gaseous state, the volumes of all gases change with changes in pressure and temperature in the same way.

The absolute density of a gas is the mass of 1 liter of gas under normal conditions. Usually for gases it is measured in g / l.

ρ = m (gas) / V (gas)

If we take 1 mole of gas, then:

and the molar mass of a gas can be found by multiplying the density by the molar volume.

Relative density D is a value that shows how many times gas X is heavier than gas Y. It is calculated as the ratio of the molar masses of gases X and Y:

D by Y (X) \u003d M (X) / M (Y)

Often, the relative densities of gases for hydrogen and for air are used for calculations.

Relative gas density X for hydrogen:

D by H2 = M (gas X) / M (H2) = M (gas X) / 2

Air is a mixture of gases, so only the average molar mass can be calculated for it.

Its value is taken as 29 g/mol (based on the approximate average composition).
That's why:
D by air. = M (gas X) / 29

Gas density B (pw, g / l) is determined by weighing (mv) a small glass flask of a known volume with gas (Fig. 274, a) or a gas pycnometer (see Fig. 77), using the formula

where V is the volume of the cone (5 - 20 ml) or pycnometer.

The cone is weighed twice: first evacuated and then filled with the gas under investigation. By the difference in the values ​​of the 2 obtained masses, the mass of the gas mv, g is found out. When filling the cone with gas, its pressure is measured, and when weighing, the ambient temperature, which is taken as the temperature of the gas in the cone. The found values ​​of p and T of the gas make it possible to calculate the density of the gas under normal conditions (0 °C; about 0.1 MPa).

To reduce the correction for the loss of mass of a cone with gas in air when it is weighed as a container, a sealed cone of exactly the same volume is placed on the other arm of the balance beam.

Rice. 274. Devices for determining the density of a gas: a cone (a) and liquid (b) and mercury (c) effuiometers

The surface of this cone is treated (cleaned) each time in exactly the same way as that weighed with gas.

During the evacuation process, the cone is slightly heated, leaving it connected to the vacuum system for several hours, since the remaining air and moisture are difficult to remove. An evacuated cone may change volume due to compression of the walls by atmospheric pressure. The error in determining the density of light gases from such compression can reach 1%. In some cases, the relative density dv is also determined for a gas, i.e. the ratio of the density of a given gas p to the density of another gas, chosen as the standard p0, taken at the same temperature and pressure:

where Mv and Mo are, respectively, the molar masses of the investigated gas B and the standard, for example, air or hydrogen, g / mol.

For hydrogen M0 = 2.016 g/mol, therefore

From this ratio, you can determine the molar mass of the gas, if we take it as ideal.

A quick method for determining the density of a gas is to measure the duration of its outflow from a small orifice under pressure, which is proportional to the outflow velocity.

where τv and τo ~ the outflow time of gas B and air, respectively.

The measurement of gas density by this method is carried out with the strip of the effusiometer (Fig. 274.6) - a wide cylinder b about 400 mm high, inside which there is a vessel 5 with a base 7 equipped with holes for the inlet and outlet of the liquid. Vessel 5 has two marks M1 and M2 for reading the volume of gas, the time of which is observed. Valve 3 serves to inlet gas, and valve 2 - to release through capillary 1. Thermometer 4 controls the temperature of the gas.

Determination of the density of the gas by the speed of its expiration is performed as follows. Cylinder b is filled with liquid, in which the gas is almost insoluble, so that vessel 5 is also filled above the mark M2. Then, through the tap 3, the liquid is squeezed out of the vessel 5 by the gas under study below the M1 mark, and all the liquid should remain in the cylinder. After that, having closed tap 3, open tap 2 and allow excess gas to escape through capillary 1. As soon as the liquid reaches the M1 mark, start the stopwatch. The liquid, displacing the gas, gradually rises to the M2 mark. At the moment the meniscus of the liquid touches the mark M2, the stopwatch is turned off. The experiment is repeated 2-3 times. Similar operations are carried out with air, thoroughly washing the vessel 5 with it from the remnants of the test gas. Different observations of the duration of the outflow of gas should not differ by more than 0.2 - 0.3 s.

If it is impossible to select a liquid for the gas under study in which it would be slightly soluble, a mercury effusion meter is used (Fig. 274, c). It consists of a glass vessel 4 with a three-way cock 1 and a surge vessel 5 filled with mercury. Vessel 4 is located in glass vessel 3, which functions as a thermostat. Gas is introduced through valve 1 into vessel 4, displacing mercury below the M1 mark. The test gas or air is released through the capillary 2, raising the leveling vessel 5. More sensitive devices for determining the density of gases are the Stock gas hydrometer (Fig. 275, a) and gas scales

Stock Alfred (1876-1946) - German inorganic chemist and analyst.

In the Stock hydrometer, one end of the quartz tube is inflated into a thin-walled ball 1 with a diameter of 30 - 35 mm, filled with air, and the other is pulled into a hair 7. A small iron rod 3 is tightly squeezed inside the tube.

Rice. 275. Rod hydrometer (a) and installation diagram (b)

The tip of the cut with a ball rests on a quartz or agate support. The tube with the ball is placed in a quartz vessel 5 with a polished round stopper. Outside the vessel is a solenoid 6 with an iron core. With the help of a current of various strengths flowing through the solenoid, the position of the rocker arm is aligned with the ball so that the hair 7 points exactly to the zero indicator 8. The position of the hair is observed using a telescope or microscope.

The stem hydrometer is welded to tube 2 to eliminate any vibrations.

The ball and tube are in equilibrium for a given density of the surrounding gas. If in vessel 5 one gas is replaced by another at a constant pressure, then the equilibrium will be disturbed due to a change in the density of the gas. To restore it, it is necessary either to pull the rod 3 down with an electromagnet 6 when the gas density decreases, or let it rise upwards when the density increases. The strength of the current flowing through the solenoid, when equilibrium is reached, is directly proportional to the change in density.

The instrument is calibrated for gases of known density. The accuracy of the Rod hydrometer is 0.01 - 0.1%, the sensitivity is about DO "7 g, the measurement range is from 0 to 4 g / l.

Installation with a Rod hydrometer. The stem hydrometer / (Fig-275.6) is attached to the vacuum system so that it hangs on the tube 2 as on a spring. Elbow 3 of tube 2 is immersed in a Dewar vessel 4 with a cooling mixture that allows maintaining a temperature not higher than -80 o C for condensation of mercury vapor, if a diffusion mercury pump is used to create a vacuum in the hydrometer. Valve 5 connects the hydrometer to a flask containing the gas under investigation. The trap protects the diffusion pump from exposure to the test gas, and fixture 7 serves to finely adjust the pressure. The entire system is connected to a diffusion pump through a tube.

The volume of gas is measured using calibrated gas berets (see Fig. 84) with a thermostatically controlled water jacket. In order to avoid corrections for capillary phenomena, the gas 3 and compensation 5 burettes are selected with the same diameter and placed side by side in a thermostatically controlled jacket 4 (Fig. 276). Mercury, glycerin and other liquids that poorly dissolve the gas under study are used as barrier liquids.

Operate this device as follows. First, fill the burettes with liquid to a level above tap 2, raising vessel b. Then the gas burette is connected to a gas source and it is introduced, lowering vessel b, after which valve 2 is closed. To equalize the pressure of the gas in the burette 3 with atmospheric pressure, the vessel b is brought close to the burette and set at such a height that the menisci of mercury in the compensation 5 and gas 3 burettes are at the same level. Since the compensating burette communicates with the atmosphere (its upper end is open), with this position of the meniscus, the gas pressure in the gas burette will be equal to atmospheric pressure.

At the same time, atmospheric pressure is measured using a barometer and the temperature of the water in the jacket 4 using a thermometer 7.

The found volume of gas is brought to normal conditions (0 ° C; 0.1 MPa) using the equation for an ideal gas:

V0 and V are the volume (l) of gas reduced to normal conditions and the measured volume of gas at temperature t (°C), respectively; p - atmospheric pressure at the time of measuring the gas volume, torr.

If the gas contains water vapor or was before measuring the volume in a vessel above water or an aqueous solution, then its volume is brought to normal conditions, taking into account the water vapor pressure p1 at the temperature of the experiment (see Table 37):

The equations apply if the atmospheric pressure when measuring the gas volume was relatively close to 760 Torr. The pressure of a real gas is always less than that of an ideal gas due to the interaction of molecules. Therefore, in the found value of the gas volume, a correction for the imperfection of the gas, taken from special reference books, is introduced.

Ministry of Education and Science of the Russian Federation

Federal State Budgetary Educational Institution of Higher Professional Education

Russian State University of Oil and Gas named after A.I. I.M. Gubkin"

A.N. Timashev, T.A. Berkunova, E.A. Mammadov

GAS DENSITY DETERMINATION

Guidelines for the implementation of laboratory work in the disciplines "Technology of operation of gas wells" and "Development and operation of gas and gas condensate fields" for students of specialties:

WG, RN, RB, MB, MO, GR, GI, GP, GF

Under the editorship of Professor A.I. Ermolaeva

Moscow 2012

Determination of gas density.

Guidelines for laboratory work / A.N. Timashev,

T.A. Berkunova, E.A. Mammadov - M.: Russian State University of Oil and Gas named after I.M. Gubkina, 2012.

Methods for laboratory determination of gas density are outlined. It is based on the current GOST 17310 - 2002.

Methodical instructions are intended for students of oil and gas universities of specialties: RG, RN, RB, MB, MO, GR, GI, GP, GF.

The publication was prepared at the Department of Development and Operation of Gas and Gas

zocondensate deposits.

Printed by decision of the educational and methodological commission of the faculty

botki oil and gas fields.

Introduction

The physical properties of natural gases and hydrocarbon condensates are used

are used both at the design stage, development and development of the field

densities of natural gases, and in the analysis and control of field development,

operation of the system for collecting and preparing products from gas and gas condensate wells. One of the main physical properties to be studied is the gas density of the deposits.

Since the gas composition of natural gas fields is complex,

consisting of hydrocarbons (alkanes, cycloalkanes and arenes) and non-hydrocarbons

components (nitrogen, helium and other rare earth gases, as well as acidic components

nites H2 S and CO2), there is a need for a laboratory determination of density

sti gases.

This methodological instruction discusses the calculation methods for determining

determination of gas density according to a known composition, as well as two laboratory methods for determining gas density: pycnometric and the method of flow through a capillary

1. Basic definitions

1.1. Density of natural gas at atmospheric pressure

The density of a gas is equal to the mass M contained in a unit volume v of the substance

va. Distinguish gas density at normal n P 0.1013 MPa, T 273K and

Where M is the molecular weight of the gas, kg/kmol; 22.41 and 24.04, m3 / kmol - the molar volume of gas, respectively, at normal (0.1013 MPa, 273 K) and standard

(0.1013 MPa, 293 K) conditions.

For natural gases consisting of hydrocarbon and non-hydrocarbon components (acidic and inert), the apparent molecular weight M to

is determined by the formula

where M i is the molecular weight of the i-th component, kg/kmol; n i is the molar percentage of the i-th component in the mixture;

k is the number of components in the mixture (natural gas).

Density of natural gas cm is equal to

i is the density of the i-th component at 0.1 MPa and 293 K.

Data on individual components are shown in table 1.

Density conversion under different temperature and pressure conditions

0.1013 MPa (101.325 kPa) in Annex B.

1.2. Relative gas density

In the practice of engineering calculations, the concept of relative

nye density, equal to the ratio of the density of gas to the density of air at the same values ​​of pressure and temperature. Normally, normal or standard conditions are taken as reference, while the air density is

responsibly amounts to 0 1.293 kg / m 3 and 20 1.205 kg / m 3. Then the relative

The density of natural gas is equal to

1.3. Density of natural gas at pressures and temperatures

Gas density for conditions in the reservoir, wellbore, gas

wires and devices at appropriate pressures and temperatures determine

is calculated according to the following formula

where P and T are pressure and temperature at the place where the gas density is calculated; 293 K and 0.1013 MPa - standard conditions when found cm;

z ,z 0 are the coefficients of gas supercompressibility, respectively, at Р and Т and

under standard conditions (value z 0 = 1).

The simplest way to determine the supercompressibility factor z is the graphical method. The dependence of z on the given parameters is

placed in Fig. one.

For a one-component gas (pure gas), the given parameters are determined

divided by formulas

inclusive, and all other components are combined into a remainder (pseudo-component

component) C5+ or C7+, in this case, the critical parameters are determined by the formula

At 100 M with 5 240 and 700d with 5 950,

М с 5 is the molecular weight of С5+ (С7+) kg/kmol;

d c 5 is the density of the С5+ (С7+) pseudo-component, kg/m3.

Table 1

Indicators of natural gas components

DEFINITION

atmospheric air is a mixture of many gases. Air has a complex composition. Its main components can be divided into three groups: constant, variable and random. The former include oxygen (the oxygen content in the air is about 21% by volume), nitrogen (about 86%) and the so-called inert gases (about 1%).

The content of constituents practically does not depend on where in the world the sample of dry air was taken. The second group includes carbon dioxide (0.02 - 0.04%) and water vapor (up to 3%). The content of random components depends on local conditions: near metallurgical plants, noticeable amounts of sulfur dioxide are often mixed into the air, in places where organic residues decay, ammonia, etc. In addition to various gases, air always contains more or less dust.

Air density is a value equal to the mass of gas in the Earth's atmosphere divided by a unit volume. It depends on pressure, temperature and humidity. There is a standard air density value - 1.225 kg / m 3, corresponding to the density of dry air at a temperature of 15 o C and a pressure of 101330 Pa.

Knowing from experience the mass of a liter of air under normal conditions (1.293 g), one can calculate the molecular weight that air would have if it were an individual gas. Since a gram-molecule of any gas occupies under normal conditions a volume of 22.4 liters, the average molecular weight of air is

22.4 × 1.293 = 29.

This number - 29 - should be remembered: knowing it, it is easy to calculate the density of any gas in relation to air.

Density of liquid air

With sufficient cooling, the air becomes liquid. Liquid air can be stored for quite a long time in vessels with double walls, from the space between which air is pumped out to reduce heat transfer. Similar vessels are used, for example, in thermoses.

Freely evaporating under normal conditions, liquid air has a temperature of about (-190 o C). Its composition is unstable, since nitrogen evaporates easier than oxygen. As nitrogen is removed, the color of liquid air changes from bluish to pale blue (the color of liquid oxygen).

In liquid air, ethyl alcohol, diethyl ether and many gases easily turn into a solid state. If, for example, carbon dioxide is passed through liquid air, it turns into white flakes, similar in appearance to snow. Mercury immersed in liquid air becomes solid and malleable.

Many substances cooled by liquid air change their properties dramatically. Thus, chink and tin become so brittle that they easily turn into powder, a lead bell makes a clear ringing sound, and a frozen rubber ball shatters if dropped on the floor.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Air density is a physical quantity that characterizes the specific mass of air under natural conditions or the mass of gas in the Earth's atmosphere per unit volume. The value of air density is a function of the height of the measurements, its humidity and temperature.

The air density standard is a value equal to 1.29 kg/m3, which is calculated as the ratio of its molar mass (29 g/mol) to the molar volume, which is the same for all gases (22.413996 dm3), corresponding to the density of dry air at 0° C (273.15 °K) and a pressure of 760 mmHg (101325 Pa) at sea level (that is, under normal conditions).

Determination of air density ^

Not so long ago, information about air density was obtained indirectly through observations of auroras, the propagation of radio waves, and meteors. Since the advent of artificial Earth satellites, air density has been calculated thanks to data obtained from their deceleration.

Another method is to observe the spreading of artificial clouds of sodium vapor created by meteorological rockets. In Europe, the air density at the Earth's surface is 1.258 kg/m3, at an altitude of five km - 0.735, at an altitude of twenty km - 0.087, at an altitude of forty km - 0.004 kg/m3.

There are two types of air density: mass and weight (specific gravity).

Air Density Formula ^

The weight density determines the weight of 1 m3 of air and is calculated by the formula γ = G/V, where γ is the weight density, kgf/m3; G is the weight of air, measured in kgf; V is the volume of air, measured in m3. Determined that 1 m3 of air under standard conditions(barometric pressure 760 mmHg, t=15°С) weighs 1.225 kgf, based on this, the weight density (specific gravity) of 1 m3 of air is equal to γ ​​= 1.225 kgf/m3.

What is relative density in air? ^

It should be taken into account that the weight of air is a variable and varies depending on various conditions, such as geographical latitude and the force of inertia that occurs when the Earth rotates around its axis. At the poles, the weight of air is 5% more than at the equator.

The mass density of air is the mass of 1 m3 of air, denoted by the Greek letter ρ. As you know, body weight is a constant value. A unit of mass is considered to be the mass of a weight made of platinum iridide, which is located in the International Chamber of Weights and Measures in Paris.

Air mass density ρ is calculated using the following formula: ρ = m / v. Here m is the mass of air, measured in kg×s2/m; ρ is its mass density, measured in kgf×s2/m4.

The mass and weight density of air are dependent: ρ = γ / g, where g is the free fall acceleration coefficient equal to 9.8 m/s². Whence it follows that the mass density of air under standard conditions is 0.1250 kg×s2/m4.

How does air density change with temperature? ^

As barometric pressure and temperature change, air density changes. Based on the Boyle-Mariotte law, the greater the pressure, the greater will be the density of the air. However, as the pressure decreases with height, the air density also decreases, which introduces its own adjustments, as a result of which the law of vertical pressure change becomes more complicated.

The equation that expresses this law of change in pressure with height in an atmosphere at rest is called basic equation of statics.

It says that with increasing altitude, the pressure changes downwards and when ascending to the same height, the decrease in pressure is the greater, the greater the force of gravity and air density.

An important role in this equation belongs to changes in air density. As a result, we can say that the higher you climb, the less pressure will drop when you rise to the same height. Air density depends on temperature as follows: in warm air, the pressure decreases less intensively than in cold air, therefore, at the same height in a warm air mass, the pressure is higher than in cold air.

With changing values ​​of temperature and pressure, the mass density of air is calculated by the formula: ρ = 0.0473xV / T. Here B is the barometric pressure, measured in mm of mercury, T is the air temperature, measured in Kelvin.

How to choose, according to what characteristics, parameters?

What is an industrial compressed air dryer? Read about it, the most interesting and relevant information.

What are the current prices for ozone therapy? You will learn about it in this article:
. Reviews, indications and contraindications for ozone therapy.

How is vapor density measured in air? ^

Density is also determined by air humidity. The presence of water pores leads to a decrease in air density, which is explained by the low molar mass of water (18 g/mol) against the background of the molar mass of dry air (29 g/mol). Humid air can be considered as a mixture of ideal gases, in each of which the combination of densities allows one to obtain the required density value for their mixture.

Such a kind of interpretation allows density values ​​to be determined with an error level of less than 0.2% in the temperature range from −10 °C to 50 °C. The density of air allows you to get the value of its moisture content, which is calculated by dividing the density of water vapor (in grams) contained in the air by the density of dry air in kilograms.

The basic equation of statics does not allow solving constantly emerging practical problems in real conditions of a changing atmosphere. Therefore, it is solved under various simplified assumptions that correspond to the actual real conditions, by putting forward a number of particular assumptions.

The basic equation of statics makes it possible to obtain the value of the vertical pressure gradient, which expresses the change in pressure during ascent or descent per unit height, i.e., the change in pressure per unit vertical distance.

Instead of the vertical gradient, the reciprocal of it is often used - the baric step in meters per millibar (sometimes there is still an outdated version of the term "pressure gradient" - the barometric gradient).

The low air density determines a slight resistance to movement. Many terrestrial animals, in the course of evolution, used the ecological benefits of this property of the air environment, due to which they acquired the ability to fly. 75% of all land animal species are capable of active flight. For the most part, these are insects and birds, but there are mammals and reptiles.

Video on the topic "Determination of air density"

A gas is a comparison of the relative molecular or molar mass of one gas with that of another gas. As a rule, it is determined in relation to the lightest gas - hydrogen. Gases are also often compared to air.

In order to show which gas is selected for comparison, an index is added before the symbol of the relative density of the test, and the name itself is written in brackets. For example, DH2(SO2). This means that the density was calculated from hydrogen. This is read as "the density of sulfur oxide by hydrogen."

To calculate the gas density from hydrogen, it is necessary to determine the molar masses of the gas and hydrogen under study using the periodic table. If it is chlorine and hydrogen, then the indicators will look like this: M (Cl2) \u003d 71 g / mol and M (H2) \u003d 2 g / mol. If the density of hydrogen is divided by the density of chlorine (71:2), the result is 35.5. That is, chlorine is 35.5 times heavier than hydrogen.

The relative density of a gas does not depend on external conditions. This is explained by the universal laws of the state of gases, which boil down to the fact that a change in temperature and pressure does not lead to a change in their volume. With any changes in these indicators, measurements are made in exactly the same way.

To determine the density of a gas empirically, you need a flask where it can be placed. The flask with gas must be weighed twice: the first time - after pumping out all the air from it; the second - by filling it with the investigated gas. It is also necessary to measure the volume of the flask in advance.

First you need to calculate the mass difference and divide it by the value of the volume of the flask. The result is the density of the gas under the given conditions. Using the equation of state, you can calculate the desired indicator under normal or ideal conditions.

You can find out the density of some gases from the summary table, which has ready-made information. If the gas is listed in the table, then this information can be taken without any additional calculations and the use of formulas. For example, the density of water vapor can be found from the table of properties of water (Reference book by Rivkin S.L. and others), its electronic counterpart, or using programs such as WaterSteamPro and others.

However, for different liquids, equilibrium with vapor occurs at different densities of the latter. This is due to the difference in the forces of intermolecular interaction. The higher it is, the faster the equilibrium will come (for example, mercury). In volatile liquids (for example, ether), equilibrium can only occur at a significant vapor density.

The density of various natural gases varies from 0.72 to 2.00 kg/m3 and above, relative - from 0.6 to 1.5 and above. The highest density is in gases with the highest content of heavy hydrocarbons H2S, CO2 and N2, the lowest is in dry methane gases.

Properties are determined by its composition, temperature, pressure and density. The last indicator is determined by the laboratory. It depends on all of the above. Its density can be determined by different methods. The most accurate is weighing on accurate scales in a thin-walled glass container.

More than the same indicator of natural gases. In practice, this ratio is taken as 0.6:1. Static decreases faster than gas. At pressures up to 100 MPa, the density of natural gas can exceed 0.35 g/cm3.

It has been established that the increase may be accompanied by an increase in the temperature of hydrate formation. Low density natural gas forms hydrates at a higher temperature than higher density gases.

Density meters are just beginning to be used and there are still many questions that are related to the features of their operation and verification.