Application of an ideal gas. What is an "ideal gas" in simple words

As is known, many substances in nature can be in three states of aggregation: solid, liquid And gaseous.

The doctrine of the properties of matter in various states of aggregation is based on ideas about the atomic and molecular structure material world. The molecular kinetic theory of the structure of matter (MKT) is based on three main principles:

• all substances are made up of tiny particles(molecules, atoms, elementary particles), between which there are gaps;
• particles are in continuous thermal motion;
• there are interaction forces between particles of matter (attraction and repulsion); the nature of these forces is electromagnetic.

Means, state of aggregation of a substance depends on the relative position of the molecules, the distance between them, the forces of interaction between them and the nature of their movement.

The interaction between particles of a substance is most pronounced in the solid state. The distance between molecules is approximately equal to their own sizes. This leads to a fairly strong interaction, which practically makes it impossible for the particles to move: they oscillate around a certain equilibrium position. They retain their shape and volume.

The properties of liquids are also explained by their structure. Particles of matter in liquids interact less intensely than in solids, and therefore can change their location abruptly - liquids do not retain their shape - they are fluid. Liquids retain volume.

A gas is a collection of molecules moving randomly in all directions independently of each other. Gases do not have their own shape, occupy the entire volume provided to them and are easily compressed.

There is another state of matter - plasma. Plasma is a partially or fully ionized gas in which the densities are positive and negative charges almost identical. When heated strongly enough, any substance evaporates, turning into a gas. If you increase the temperature further, the process of thermal ionization will sharply intensify, i.e., gas molecules will begin to disintegrate into their constituent atoms, which then turn into ions.

Ideal gas model. Relationship between pressure and average kinetic energy.

To clarify the laws that govern the behavior of a substance in the gaseous state, an idealized model of real gases is considered - an ideal gas. This is a gas whose molecules are considered as material points, not interacting with each other at a distance, but interacting with each other and with the walls of the vessel during collisions.

Ideal gas – It is a gas in which the interaction between its molecules is negligible. (Ek>>Er)

An ideal gas is a model invented by scientists to understand the gases that we actually observe in nature. It cannot describe any gas. Not applicable when the gas is highly compressed, when the gas turns into a liquid state. Real gases behave like ideal gases when the average distance between molecules is many times larger than their sizes, i.e. at sufficiently large vacuums.

Properties of an ideal gas:

1. there is a lot of distance between molecules more sizes molecules;
2. gas molecules are very small and are elastic balls;
3. the forces of attraction tend to zero;
4. interactions between gas molecules occur only during collisions, and collisions are considered absolutely elastic;
5. the molecules of this gas move randomly;
6. movement of molecules according to Newton's laws.

The state of a certain mass of gaseous substance is characterized by physical quantities dependent on each other, called state parameters. These include volumeV, pressurepand temperatureT.

Gas volume denoted by V. Volume gas always coincides with the volume of the container it occupies. SI unit of volume m 3.

Pressure– physical quantity equal to the ratio of forceF, acting on a surface element perpendicular to it, to the areaSthis element.

p = F/ S SI unit of pressure pascal[Pa]

Until now, non-systemic units of pressure are used:

technical atmosphere 1 at = 9.81-104 Pa;

physical atmosphere 1 atm = 1.013-105 Pa;

millimeters of mercury 1 mmHg Art. = 133 Pa;

1 atm = = 760 mm Hg. Art. = 1013 hPa.

How does gas pressure arise? Each gas molecule, hitting the wall of the vessel in which it is located, acts on the wall with a certain force for a short period of time. As a result of random impacts on the wall, the force exerted by all molecules per unit area of ​​the wall changes rapidly with time relative to a certain (average) value.

Gas pressureoccurs as a result of random impacts of molecules on the walls of the vessel containing the gas.

Using the ideal gas model, we can calculate gas pressure on the wall of the vessel.

During the interaction of a molecule with the wall of a vessel, forces arise between them that obey Newton’s third law. As a result, the projection υ x the molecular speed perpendicular to the wall changes its sign to the opposite, and the projection υ y the speed parallel to the wall remains unchanged.

Devices that measure pressure are called pressure gauges. Pressure gauges record the time-average pressure force per unit area of ​​its sensitive element (membrane) or other pressure receiver.

Liquid pressure gauges:

1. open – for measuring small pressures above atmospheric
2. closed - for measuring small pressures below atmospheric, i.e. small vacuum

Metal pressure gauge– for measuring high pressures.

Its main part is a curved tube A, open end which is soldered to tube B, through which gas flows, and the closed one is connected to the arrow. Gas enters through the tap and tube B into tube A and unbends it. The free end of the tube, moving, sets the transmission mechanism and the pointer in motion. The scale is graduated in pressure units.

Basic equation of the molecular kinetic theory of an ideal gas.

Basic MKT equation: the pressure of an ideal gas is proportional to the product of the mass of the molecule, the concentration of the molecules and the mean square of the speed of the molecules

p= 1/3m 0· n·v 2

m 0 - mass of one gas molecule;

n = N/V – number of molecules per unit volume, or concentration of molecules;

v 2 - root mean square speed of movement of molecules.

Since the average kinetic energy of translational motion of molecules is E = m 0 *v 2 /2, then multiplying the basic MKT equation by 2, we obtain p = 2/3 n (m 0 v 2)/2 = 2/3 E n

p = 2/3 E n

Gas pressure is equal to 2/3 of the average kinetic energy of translational motion of the molecules contained in a unit volume of gas.

Since m 0 n = m 0 N/V = m/V = ρ, where ρ is the gas density, we have p= 1/3· ρ·v 2

United gas law.

Macroscopic quantities that unambiguously characterize the state of a gas are calledthermodynamic parameters of gas.

The most important thermodynamic parameters of a gas are itsvolumeV, pressure p and temperature T.

Any change in the state of a gas is calledthermodynamic process.

In any thermodynamic process, the gas parameters that determine its state change.

The relationship between the values ​​of certain parameters at the beginning and end of the process is calledgas law.

The gas law expressing the relationship between all three gas parameters is calledunited gas law.

p = nkT

Ratio p = nkT relating the pressure of a gas to its temperature and concentration of molecules was obtained for a model of an ideal gas, the molecules of which interact with each other and with the walls of the vessel only during elastic collisions. This relationship can be written in another form, establishing a connection between the macroscopic parameters of a gas - volume V, pressure p, temperature T and the amount of substance ν. To do this you need to use the equalities

where n is the concentration of molecules, N is total number molecules, V – volume of gas

Then we get or

Since at a constant gas mass N remains unchanged, then Nk – constant number, Means

At a constant mass of a gas, the product of volume and pressure divided by the absolute temperature of the gas is the same value for all states of this mass of gas.

The equation establishing the relationship between pressure, volume and temperature of a gas was obtained in the middle of the 19th century by the French physicist B. Clapeyron and is often called Clayperon equation.

The Clayperon equation can be written in another form.

p = nkT,

considering that

Here N– number of molecules in the vessel, ν – amount of substance, N A is Avogadro’s constant, m– mass of gas in the vessel, M – molar mass gas As a result we get:

Product of Avogadro's constant N A byBoltzmann constantk is called universal (molar) gas constant and is designated by the letter R.

Its numerical value in SI R= 8.31 J/mol K

Ratio

called ideal gas equation of state.

In the form we received, it was first written down by D.I. Mendeleev. Therefore, the equation of state of the gas is called Clapeyron–Mendeleev equation.`

For one mole of any gas this relationship takes the form: pV=RT

Let's install physical meaning molar gas constant. Let us assume that in a certain cylinder under the piston at temperature E there is 1 mole of gas, the volume of which is V. If the gas is heated isobarically (at constant pressure) by 1 K, then the piston will rise to a height Δh, and the volume of the gas will increase by ΔV.

Let's write the equation pV=RT for heated gas: p (V + ΔV) = R (T + 1)

and subtract from this equality the equation pV=RT, corresponding to the state of the gas before heating. We get pΔV = R

ΔV = SΔh, where S is the area of ​​the base of the cylinder. Let's substitute into the resulting equation:

pS = F – pressure force.

We obtain FΔh = R, and the product of the force and the movement of the piston FΔh = A is the work of moving the piston performed by this force against external forces when gas expands.

Thus, R = A.

The universal (molar) gas constant is numerically equal to the work done by 1 mole of gas when it is heated isobarically by 1 K.

One of which is gas. Its constituent particles - molecules and atoms - are located at a great distance from each other. At the same time, they are in constant free movement. This property indicates that the interaction of particles occurs only at the moment of approach, sharply increasing the speed of the colliding molecules and their size. This distinguishes the gaseous state of a substance from solid and liquid.

The word “gas” itself translated from Greek sounds like “chaos”. This perfectly characterizes the movement of particles, which is actually random and chaotic. The gas does not form a specific surface; it fills the entire volume available to it. This state of matter is the most common in our Universe.

The laws that determine the properties and behavior of such a substance are easiest to formulate and consider using the example of a state in which molecules and atoms are low. It was called the “ideal gas”. In it, the distance between particles is greater than the radius of interaction of intermolecular forces.

So, an ideal gas is a theoretical model of matter in which there is almost no interaction between particles. The following conditions must exist for it:

Very small molecular sizes.

There is no interaction force between them.

Collisions occur like collisions of elastic balls.

A good example of such a state of matter is gases in which the pressure at low temperatures does not exceed atmospheric pressure by 100 times. They are considered discharged.

The very concept of “ideal gas” has enabled science to build a molecular kinetic theory, the conclusions of which are confirmed in many experiments. According to this doctrine, ideal gases are distinguished between classical and quantum.

The characteristics of the first are reflected in the laws of classical physics. The movement of particles in this gas does not depend on each other; the pressure exerted on the wall is equal to the sum of the impulses that, during a collision, are transmitted by individual molecules over a certain time. Their total energy is that of the individual particles. The work of an ideal gas in this case is calculated p = nkT. A striking example This is based on the laws derived by such physicists as Boyle-Marriott, Gay-Lussac, Charles.

If an ideal gas lowers the temperature or increases the density of particles to a certain value, its wave properties. There is a transition to a quantum gas, in which atoms and molecules are comparable to the distance between them. There are two types of ideal gas:

The teaching of Bose and Einstein: particles of the same type have an integer spin.

Fermi and Dirac statistics: another type of molecules that have half-integer spin.

The difference between a classical ideal gas and a quantum one is that even at absolutely zero temperature the energy density and pressure differ from zero. They become larger as density increases. In this case, the particles have maximum (another name is boundary) energy. From this point of view, the theory of the structure of stars is considered: in those of them in which the density is higher than 1-10 kg/cm3, the law of electrons is clearly expressed. And where it exceeds 109 kg/cm3, the substance turns into neurons.

In metals, the use of the theory in which a classical ideal gas transforms into a quantum one makes it possible to explain most state of matter: the denser the particles, the closer it is to the ideal.

With strongly expressed low temperatures various substances in liquid and solid states, the collective motion of molecules can be considered as the work of an ideal gas represented by weak excitations. In such cases, the contribution to the energy of the body that the particles add is visible.

The science of physics plays a significant role in the study of the surrounding world. Therefore, its concepts and laws begin to be taught at school. The properties of a substance are measured in different aspects. If we consider its state of aggregation, then there is a special technique. An ideal gas is a physical concept that allows us to evaluate the properties and characteristics of the material that makes up our entire world.

General definition

An ideal gas is a model in which interactions between molecules are neglected. The process of interaction of particles of any substance with each other is quite complex.

When they fly close to each other and are at a very short distance, they strongly repel each other. But at great distances, relatively small forces of attraction act between molecules. If the average distance at which they are from each other is large, this position of the substance is called a rarefied gas. The interaction of such particles manifests itself as rare collisions of molecules. This only happens when they fly close to each other. In an ideal gas, the interaction of molecules is not taken into account at all. In an ideal gas the number of molecules is very large. Therefore, calculations occur only using a statistical method. Moreover, it should be noted that the particles of the substance in this case are distributed evenly in space. This is the most common state of an ideal gas.

When can a gas be considered ideal?

There are several factors due to which a gas is called ideal. The first sign is the behavior of molecules as absolutely elastic bodies; there are no attractive forces between them. In this case, the gas will be very discharged. The distance between the smallest components of the substance will be much larger than their sizes. In this case, thermal equilibrium will be achieved instantly throughout the entire volume. To achieve the position of an ideal gas in laboratory conditions, the real type is rarefied accordingly. Some substances in a gaseous state, even at room temperature and normal atmospheric pressure, practically do not differ from the ideal state.

Limits of application of the model

Natural gas is considered depending on the tasks assigned. If a researcher is tasked with determining the relationship between temperature, volume and pressure, then the ideal state of matter can be considered in which the gas has high accuracy up to pressures measured in several tens of atmospheres. But in the case of studying phase transitions, for example, evaporation and condensation, the process of achieving equilibrium in a gas, the model under consideration cannot be used even at very low pressure. Gas pressure on the wall of the test tube occurs when molecules randomly hit the glass. When such shocks are frequent, the human body can perceive these changes as a continuous impact.

Ideal gas equation

Based on the main principles of molecular kinetic theory, the main equation of an ideal gas was derived.

The work of an ideal gas has the following expression: p = 1 / 3 m 0 nv 2, where p is the pressure of an ideal gas, m 0 is the molecular weight, v 2 is the average particle concentration, the square of the molecular speed. If we define the average kinetic movement particles of matter, as Ek = m 0 n/ 2, then the equation will have the following form: p = 2 / 3 nEk. Gas molecules, hitting the walls of the vessel, interact with them as elastic bodies according to the laws of mechanics. The impulse from such impacts is transmitted to the walls of the vessel.

Temperature

By calculating only the gas pressure on the walls of a vessel, it is impossible to determine the average kinetic energy of its particles.

Moreover, this cannot be done either for an individual molecule or for their concentration. Therefore, to measure gas parameters, it is necessary to determine one more quantity. It is temperature, which is also related to the kinetic energy of molecules. This indicator is scalar physical quantity. Temperature describes thermodynamic equilibrium. In this state, there is no change in parameters at the micro level. Temperature is measured as the deviation from zero. It characterizes saturation chaotic movement smallest gas particles. It is measured by the average value of their kinetic energy. This indicator is determined using thermometers in degrees of various marks. There is a thermodynamic absolute scale (Kelvin) and its empirical varieties. They differ in their starting points.

Equation of position of an ideal gas taking into account temperature

Physicist Boltzmann states that the average kinetic energy of a particle is proportional to absolute indicator temperature. Ek = 3 / 2 kT, where k = 1.38∙10-23, T is temperature. The work of an ideal gas will be equal to: P = NkT/V, where N is the number of molecules, V is the volume of the vessel. If we add the concentration n = N/V to this indicator, then the above formula will look like this: p = nkT. These two equations have various shapes records, but they relate pressure, volume and temperature for an ideal gas. These calculations can be applied to both pure gases and their mixtures. In the latter version, n should be understood as the entire number of molecules of substances, their total concentration or the total number of moles in the substance.

Three gas laws

The ideal gas and its particular laws were discovered experimentally and only then confirmed theoretically.

The first particular law states that an ideal gas at constant mass and temperature will have pressure inversely proportional to its volume. A process in which the temperature is constant is called isothermal. If the pressure is constant during the study, then the volume is proportional to the absolute temperature. This law bears the name of Gay-Lussac. An isochoric process occurs at a constant volume. In this case, the pressure will be proportional absolute temperature. Its name is Charles's law. These are three particular laws of behavior of an ideal gas. They were confirmed only after mastering knowledge about molecules.

Absolute measurement scale

In the absolute scale of measurement, the unit is usually called Kelvin. It was chosen based on the popular Celsius scale. One Kelvin corresponds to one degree Celsius. But in the absolute scale, zero is taken to be the value at which the pressure of an ideal gas at constant volume will be zero.

This is a generally accepted system. This temperature value is called absolute zero. Having made the appropriate calculations, you can get the answer that the value of this indicator will be -273 degrees Celsius. This confirms that there is a relationship between the absolute and Celsius scales. It can be expressed in the following equation: T = t + 237. It should be noted that it is impossible to achieve absolute zero. Any cooling process is based on the evaporation of molecules from the surface of a substance. Approaching absolute zero, the translational motion of particles slows down so much that evaporation stops almost completely. But from a purely theoretical point of view, if it were possible to actually reach the point of absolute zero, then the speed of movement of the molecules would decrease so much that it could be called absent altogether. The thermal movement of molecules would cease.

By studying the concept of an ideal gas, you can understand the principle of operation of any substance. By expanding knowledge in this area, one can understand the properties and behavior of any gaseous substance.

ideal gases

Thermodynamic system, thermodyne. process, parameters ideal. gas

Continuous change in the state of the working fluid as a result of its interaction with the environment. called environment thermodynamic process

There are equilibrium and nonequilibrium processes. A process that occurs at a significant difference in t and pressure of the environment and the working fluid and their uneven distribution over the entire mass of the body is called. nonequilibrium. If the process occurs infinitely slowly and the difference t surrounding is small. environment and working fluid and uniform distribution of t and pressure throughout the entire body mass, called. equilibrium.

To the main parameters of the state of gases include: pressure, t and specific volume, density.

· Pressure is the result of the impact of gas on the walls of the vessel in which it is located..

A distinction is made between absolute pressure (total) and excess pressure. Under absolute pressure refers to the total pressure under which the gas is located.

Rab=Rb+gph, gph=Rizb

Where Rabs is the absolute (total) gas pressure in the vessel, Pb- Atmosphere pressure in the barometer, g - st. pad. at the measurement point, p is the density of the liquid, h is the height of the liquid column.

Overpressure is the difference between absolute pressure greater than atmospheric pressure and atmospheric pressure.

1 atm = 735.6 mm Hg = 1 kg/cm2 = 10 4 kg/m2 = 10 5 Pa = 1 bar = 10 m. water column

· Temperature is a measure of the average kinetic energy of the chaotic movement of the molecules of the working fluid. Temperature is a parameter characterizing the thermal state of the body. Body temperature determines the direction of the possible spontaneous transfer of heat from a body with a higher temperature to a body with a lower temperature.

The centigrade scale, Kelvin scale, and Fahrenheit scale are used to measure temperatures. In the centigrade scale at pb = 101.325 kPa (760 mm Hg), the melting temperature of ice is taken as 0 0 C, and the boiling temperature of water is taken as 100 0 C. The degree of this scale is indicated by 0 C.

· Specific volume, v, m3/kg, is the volume of a unit mass of gas, i.e. v=V/M where V is the total volume of gas, m3; M - gas mass, kg, Reciprocal value, kg/m3, P=G/V phenomenon. Density, which is the amount of substance contained in 1 m3, i.e. the mass of a unit volume.

Internal energy of an ideal gas. State parameter.

Internal energy of gas U, J/kg – reserve of kinetic energy of gas, characterized by the sum of kinetic energies of translational, rotational movement molecules, the energy of intramolecular vibrations of atoms and the energy of intermolecular interaction (potential energy).

The first 3 components are a function of temperature, the last ( potential energy) = 0 (for an ideal gas), therefore the internal energy of an ideal gas depends only on its temperature and does not depend on volume: U=f(T).

Change internal energy of the working fluid does not depend on its intermediate states and the progress of the process and is determined by the final and initial state: ∆U=U 2 -U 1, J/kg, where U 2 is the final internal energy, U 1 is the initial.

In all thermodynamic processes, if V=const, i.e. the working fluid does not expand and does not do work, the heat imparted to it q=c v (T 2 -T 1) goes only to increase its internal energy, i.e.:

∆U= c v (T 2 -T 1); ∆U= M(U 2 -U 1); ∆U= c v ∙dT

For an infinitesimal change in internal energy: dU= c v ∙dt

Heat capacity of gas.

Heat capacity (C) - the amount of thermal energy required to change the temperature of a gas by 1 0 C. Measured in J/K.

Specific heat capacity is heat capacity per one quantitative unit (kg, mol, m3).

C, J/kg∙K – mass heat capacity (to 1 kg)

C ", J/m 3 ∙K – volumetric heat capacity (k 1 m3)

µС, J/k mol∙K – molar heat capacity (per 1 kmol)

Between them there are traces. Relationship:

If an infinitely small amount of heat is supplied to the body, then this is the instantaneous heat capacity: C = dq/dt, J/kg∙0 C.

If a certain amount of heat q is supplied to a body with temperature T1, then its temperature becomes equal to T2 - average heat capacity: C m =q/T2-T1

T 1 →T 2 q=∫Cdt C m | T 1 T 2 =q/T 2 -T 1

C m | T 2 T 1 =∫Cdt/T 2 -T 1 =(C m | 0 T 2 ∙T 2 -C m | T 1 0 ∙T 1)/T 2 -T 1

Of particular importance for heating (or cooling) a gas are the conditions under which the process of adding (or removing) heat occurs. In heating engineering the most important are:

Heating (or cooling) at constant volume – isochoric heat capacity;

Heating (or cooling) at constant pressure is isobaric heat capacity.

Gas mixtures.

Ideal gases, whose molecules do not react chemically with each other and between which there are no forces of attraction or repulsion, behave in a mixture as if each of them were alone in the occupied volume. This means that each gas included in the mixture occupies the entire volume provided for the mixture and is under its own so-called partial pressure.

The total pressure of the gas mixture in this case will consist of the sum of the partial pressures (Dalton’s law):

Pi - partial pressure of an individual component - the pressure exerted on the walls of the vessel at t and v of the gas mixture.

Hence:

The temperature of each gas in a steady state will be equal to the temperature of the mixture:

The level of state of a mixture of gases is derived based on the level of state of the individual components of the mixture and has the form: . In order to use this equation, it is necessary to determine the value of the gas mixture constant R cm.

R cm = g 1 *R 1 +g 2 *R 2 +…+g n *R n,

where g 1,g 2,..,g n are the mass fractions of the components. The gas constant of the mixture, J/(kg*K), can also be found using the formula:

The gas mixture can be specified by mass and volume fractions:

Q i =M i /M cm =p i *r i /p cm ;

Carnot cycle. Carnot's theorem.

Consists of 4 processes: 2 isothermal, 2 adiabatic.

As a result of his research, Carnot proposed a cycle that truly has the highest possible thermal efficiency within given temperature limits, i.e., at given temperatures of the heat transmitter and heat sink.

Consider this cycle in p-v coordinates, considering that it is equilibrium and that, in addition, it is carried out by 1 kg of working fluid. At the beginning of the process, the working fluid has parameters p1, v1, T1 (point 1). This point corresponds to the moment when the working fluid communicates with the heat transferr and the expansion process begins at a constant temperature equal to T1 to point 2. During the expansion process along isotherm 1-2, heat in the amount q1 is supplied to the working fluid. The work of isothermal expansion is determined by the area 122 1 1 1 . Process 1-2 is followed by the separation of the working fluid from the heat sink and further expansion occurs along the adiabatic 2-3. This process continues until the piston reaches its extreme position, which corresponds to point 3. The work of adiabatic expansion is determined by an area of ​​233 1 2 1. At this moment, i.e. at point 3, the working fluid communicates with the HIT, which has a temperature T2, and the compression process begins, during which q2 units of heat must be removed. The process of isothermal compression begins - process 3-4. Work 344 1 3 1 is negative. When heat removal q2 stops, the working fluid is disconnected from the heat receiver (point 4); further compression occurs along the adiabatic 4-1. Work 411 1 4 1 is negative. At the end of this process, the working fluid takes on its original parameters.

As a result, we got the result positive work Lts.

Carnot's theorem: the process occurs in heat engine between 2 heat sources with temperatures T1 and T2 and the efficiency of the process depends only on these temperatures.

12. Real gas. Vaporization in PV coordinates. Heat of vaporization. Steam dryness level.

Gases, the molecules of which have interaction forces and have a finite, albeit very small, geometry. sizes, called real gases.

Let us consider the process of vaporization at constant pressure in PV coordinates. If you heat water at constant pressure, then the volume increases and at a temperature that corresponds to the boiling of water, it reaches the value b. with further heat supply to the boiling water, the latter will begin to turn into steam, while the pressure and temperature of the mixture of water and steam remain unchanged. When the last particle turns into steam during the process of vaporization, the entire volume will be filled with steam. Such steam is saturated steam, and its temperature is called saturation temperature.

Location on b-c pairs is moist saturated. After complete evaporation of water (point c), the steam becomes dry, saturated. Wet steam is characterized by the degree of dryness x. The degree of dryness is the mass fraction of dry saturated steam found in 1 kg of wet steam. Let us consider the process of vaporization at more high blood pressure. The specific volume at 0 C does not change with increasing pressure. The specific volume of boiling water will increase. Point C', corresponding to dry saturated steam, is to the left of point C, because the pressure increases more rapidly than the temperature of dry saturated steam. The parameters corresponding to point k are called critical.

Vaporization is depicted line b-c. The amount of heat expended to convert 1 kg of boiling water into dry saturated steam is called the heat of vaporization and is denoted by r. With increasing pressure, the heat of vaporization decreases. At point d, steam does not saturate space and has high temperature. Such steam is called superheated.

To determine the parameters of the state of wet steam, the degree of dryness must be known.

13. Humid air. His saints.

Moist air is called a vapor-gas mixture consisting of dry air and water vapor. Compound humid air: 23% oxygen by mass, 21% oxygen by volume.

Moist air containing the maximum amount of water vapor at a given temperature is called. saturated. Air that does not contain the maximum possible given t amount. water vapor, called unsaturated. Unsaturated moist air consists of a mixture of dry and superheated water vapor, and saturated moist air consists of dry air and saturated water vapor. To turn moist air from unsaturated to saturated, it needs to be cooled.

Of the equations of states of a real gas, the simplest phenomenon is. Van der Waals equation: (p+a/v2)*(v-b)=RT,

where a is a coefficient depending on adhesion forces;

b is a value that takes into account the intrinsic volume of molecules.

Properties: mass, temperature, gas constant, heat capacity.

1) absolute humidity - the amount of water vapor contained in 1 m3 of air (kg\m3),

2) relative humidity-ratio of saturated steam density to maximum saturated steam ϕ=(ρ n \ρ us)*100

where 1.005 is the heat capacity of dry air

1.68 – heat capacity of superheated air.

5) Dalton's law. Humid air pressure Rvv equals Рвв = Рсв + Рп, Where RSV, Rp- partial pressures of dry air and

Kirchhoff's and Lambert's law.

Z-Kirchhoff. According to Kirchhoff's law, the ratio of the emissivity of a body E to its absorption capacity A for all bodies the same and equal to the emissivity of a black body E 0 at the same temperature and depends only on temperature, i.e. E/A=E 0 =f(T). Because E/E 0 = a, then for all gray bodies A=a, those. the absorption capacity of a body is numerically equal to the degree of its blackness.

Let us consider the case of heat exchange by radiation between 2 walls that have a large surface and are located parallel at a short distance from one another, i.e. so that the radiation from each wall completely hits the opposite one.

Let the temperatures on the surface of the walls be constantly maintained T1 and T2, with T1>T2, and the absorption coefficients of the walls are equal, respectively. A1 and A2, with A1=a1, A=a2, i.e. absorption coefficients and emissivity, respectively. are equal. for this, based on the Stefan-Boltzmann equation, we obtain:

Spr - reduced radiation coefficient, W/m2*K.

Here C1 and C2 are the radiation constants of the bodies between which the process of radiant heat exchange occurs.

Equation (1) can be used to calculate heat transfer, one of which has a convex shape and is surrounded by the surface of the other, i.e. nah. in a confined space. Then:

; F1, F2-surfaces of the 1st and 2nd bodies participating in radiant heat transfer.

With an arbitrary arrangement of bodies between which heat exchange occurs by radiation E1-2, the calculation of the formula will take the form:

In this case, Spr = C1*C2/Co, and the coefficient fi (the so-called angular coefficient or irradiation coefficient) is a dimensionless quantity, depending on the relative position, shape and size of the surfaces and showing the fraction of the radiant flux , which falls on F2 from the entire flux given off by F1 radiation.

Z-Lambert- determines the dependence of the energy emitted by the body on its direction. E φ =E 0 ∙cosφ. E 0 - the amount of energy emitted normal to the surface; E φ is the amount of energy emitted in the direction forming an angle φ with the normal, then according to Lambert’s principle:

That., Mr. Lambert determines the dependence of the energy emitted by a body on its direction.

Indoor microclimate.

Microclimate is a set of values ​​of such parameters as temperature, relative. Humidity, speed and avg. temperature internal surfaces, providing standards. human life activity indoors. and normal. the course of production processes.

Microclimate: comfortable, acceptable and uncomfortable.

The intensity of human heat transfer depends on the microclimate of the room, characterized by t-swarm internal. air tb , radiation t-room tr , speed and relative humidity φв air. The combination of these microclimate parameters, with CTR, maintains thermal equilibrium in the human body and there is no tension in its thermoregulation system, called. comfortable. It is most important to maintain, first of all, favorable t-conditions in the room, because air mobility and relative humidity fluctuate significantly. In addition to the optimal ones, there are acceptable combinations of microclimate parameters at which a person feels slight discomfort.

The part of the room in which a person is primarily located work time, is called the service or working area. Comfort should be ensured primarily in this area.

Thermal conditions in the room depend mainly on tв and tr , those. from its t-th situation, ktr. It is customary to characterize it by two conditions of comfort. The first condition for a comfortable temperature environment is defined. such a region of combinations t and tr , at ktr. man in the center working area, does not experience either overheating or hypothermia.

The second comfort condition determines the permissible temperatures of heated and cooled surfaces when a person is in close proximity to them.

To avoid unacceptable radiation overheating or hypothermia of the human head, the surfaces of the ceiling and walls can be heated to an acceptable temperature

Two-pipe forced circulation water heating system. Eyeliner options.

Expansion tank.

It is a cylinder-shaped metal container with a removable lid and pipes for connecting the following pipes: extended d1, control d2, led to the sink in the boiler room to monitor the water level, overflow d3 to drain excess water when the tank is overfilled or expanded, circulation d4, connecting the expansion tank with the return main heat pipeline to prevent freezing of water in the expansion vessel and in the connecting pipe.

The useful volume (l) of the expansion tank is determined by the formula:

,

where - 0.0006 1/ 0 C – coefficient of volumetric expansion of water;

Change in water temperature from initial to average calculated, 0 C;

Total volume of water in the system, l

Where - the volume of water, respectively, in water heaters, pipes, appliances, l, per 1000 W of thermal power of the water heating system.

An expansion tank designed to compensate for pressure arose. in res. temperature expansion of the coolant with increasing temperature; equalization of pressure differences and compensation of hydraulic shocks with max. temp. coolant up to 100°C; protection of components in the circuits of heating and hot water systems. from excess pressure; compensation for operational coolant losses arose. in current heating season; removing air from the system.

Ext. tanks: open and closed versions.

Ext. tanks open such as technologically outdated and to this day. vr. practical are not used. Open ext. the tank is placed above the top point of the heating system, usually in the attic of the building or on the stairs. cage and covered with thermal insulation.

To extension tanks closed type include membrane tanks, cat. comp. made of a steel body divided by an elastic membrane into two parts - liquid and gas cavities. The liquid part of the tank is designed to receive coolant from heating systems and hot water, the gas part of the tank is filled to a higher level. pressure with air or nitrogen. To maintain the required pressure in the gas chamber of the tank there is a nipple.

Air removal.

In water systems heating systems with overhead wiring, use an expansion vessel without additional devices. In the system from the bottom there is a special air exhaust network, connected. her to the expansion tank or air collector (using air release valves or screws). For reliable air removal and water drainage, main heat pipelines are laid. with a slope. (not less than 0.002) in the direction of coolant movement. In systems with arts circus the speed of movement. water> speed of air ascent, so the lines are laid with rises to the outer risers and air collectors are installed at the highest points.

Fans.

According to the principle of operation and purpose of the fans are divided into radial (centrifugal), axial, roof and ceiling.

Radial (centrifugal) fans . A typical radial (centrifugal) fan consists of three main parts: an impeller with blades (sometimes called a rotor), a volute-shaped casing, and a frame with a shaft, pulley, and bearings.

Radial fan operation is as follows: when the impeller rotates, air enters through the inlet into the channels between the wheel blades, moves through these channels under the action of centrifugal force, is collected by a spiral casing and directed to its outlet. Thus, air enters the centrifugal fan in the axial direction and leaves it in a direction perpendicular to the axis.

Axial fans. The simplest axial fan consists of an impeller mounted on a sleeve and mounted on an electric motor shaft, and a casing (shell), the purpose of which is to create a directed air flow. When the wheel rotates, air moves along the axis of the fan, which determines its name.

An axial fan, compared to a radial one, creates more noise during operation and is not able to overcome greater resistance when moving air. In residential and public buildings, axial fans should be used to supply large volumes of air, but if pressure above 150-200 Pa is not required. Fans V-06-300-8A, V-06-300-10L and V-06-300-12.5A are widely used in exhaust ventilation systems of public and industrial buildings.

Fan selection . The fan is selected according to the flow L, m 3 / h, and the required total fan pressure p, Pa, using the operating characteristics. In them, for a certain wheel speed, dependencies are given between the fan air supply, on the one hand, and the pressure created, power consumption and efficiency, on the other.

The total pressure p, by which the fan is selected, is the sum of the static pressure spent on overcoming the resistance along the suction and discharge networks, and the dynamic pressure that creates the air speed.

The value p, Pa, is determined by the formula

When selecting a fan, you should strive to ensure that the required pressure and flow correspond to maximum value Efficiency This is dictated not only by economic considerations, but also by the desire to reduce fan noise when operating at high efficiency levels.

The required power, kW, of the electric motor for the fan is determined by the formula

where L- fan flow, m 3 /h; R- pressure created by the fan, kPa; d], - fan efficiency, taken according to its characteristics; t 1рп is the efficiency of the belt drive, with a V-belt drive equal to 0.95, with a flat belt -0.9.

The installed power of the electric motor is determined by the formula

Where A- power reserve factor

The type of electric motor for the fan should be selected taking into account the operating conditions of the latter - the presence of dust, gas and vapors, as well as the fire and explosion hazard category of the room.

Gas household appliances.

Stove burners installed in household heating stoves when converting them to gas combustion. The device is used in furnaces without gates, equipped with draft stabilizers, with continuous and periodic firing modes.

The device has two operating modes - normal, when the main and pilot burners are working, and reduced, when only the pilot burner is working. When operating in reduced mode, the main burner valve must be closed.

Heating furnaces can be equipped with burner devices and other types of automatic safety devices that have been tested in the prescribed manner, accepted for production and have a passport.

Household gas stoves

The stoves are divided into floor and tabletop (portable). Tabletop stoves do not have oven, and they are also called tagans. Four-, three- and two-burner stoves are in use.

According to the design, the slabs are produced in standard and increased comfort. Deluxe gas stoves have oven lighting, a high-power burner, table burner taps with a fixed “small flame” position, and a device for adjusting the horizontal position of the table. They can also be additionally equipped with a low-power table burner, electric ignition of the table and oven burners, an oven fry burner, an oven spit with electric and manual drive, an oven thermostat, and automatic combustion control.

1. Ideal gas, definition and its properties.

2. Thermodynamics. system, thermodynamics. process, ideal gas parameters.

3. Equations of state of an ideal gas. Phys. meaning of the gas constant.

4. Internal energy of an ideal gas. State parameters.

5. Gas work. Process parameter.

6. Heat capacity of gas.

7. Gas mixtures.

8. The first law of thermodynamics, its mathematical expression.

9. Expression of the first law of thermodynamics for decomp. thermodynamics processes

10. Circular cycles. Thermodynamic and refrigeration coefficients.

11. Carnot cycle. Carnot's theorem.

12. Real gas. Steam generation in PV coordinates. Heat of steam generation. Steam dryness level.

13. Wet air. Its properties.

14. I-d diagram of humid air. Study of air treatment processes with using I-d diagrams.

15. Temperature field of the body. Temperature gradient.

16. Thermal conductivity. Fourier's law.

17. Thermal conductivity of a flat wall. Basic heat equation.

18. Convective heat transfer. Newton-Richmann equation. Coeff. heat transfer.

19. Determination of the heat transfer coefficient using criterion equations.

20. Radiant heat transfer. Stefan-Boltzmann equation.

21. Kirchhoff's and Lambert's law.

22. Heat transfer. Ur-e and heat transfer coefficient for a flat wall.

23. Heat exchangers. Definition of heating surfaces for recuperative heat exchangers.

24. Indoor microclimate.

25. Resistance to external heat transfer. fencing. Relationships between them.

26. Thermal resistance of fences. Heat absorption coefficient S. Thermal inertia value D.

27. Air permeability of fences. Resistance to air permeability of fences.

28. Determination of heat losses through fences. Rules for measuring cooling surfaces.

29. Definition of heat losses by enlargement. indicators. Specific thermal characteristics of the building.

30. Heating system: basic El-you, class, requirements, presentation. to the heating installation.

31. Conclusion gravitational pressure for a two-pipe heating system.

32. Definition of circulation pressure in a one-pipe system.

33. Pipelines systems center. heating systems, their connections, installation methods.

34. Expand tank, its purpose, installation, point of connection to the heating system lines, determination of tank volume.

35. Air removal from water heating systems.

36. Syst. steam. heating. Operating principle, class, basic. scheme. Air bleed from system steam. heating. The region uses gas heating systems.

37. Heats up. devices syst. center. heating. Class, requirements for them. Characteristics types of heated devices.

38. Placement and installation, methods of connection and heating. devices for system pipelines heating. Schemes for supplying coolant to heating devices.

39. The heat transfer coefficient is heated. devices. Determination of the heating surface of devices.

40. Features of calculating the surface of heating devices.

41. Adjusting the heat output of heating devices.

42. Fuel. Elementary composition. Fuel calorific value

43. Fuel combustion. Theoretical and action volume of air required for fuel combustion.

44. Methods of fuel combustion. Types of combustion devices, their characteristics.

45. Boiler installation. Def. Types of combustion devices, their characteristics.

46. Centralized heating supply. Thermal power plant diagram.

47. Heating networks, methods of laying heating networks, types of insulation.

48. Connecting local heating systems to heating networks.

49. Air exchange, methods for determining it.

50. Purpose and classification of ventilation systems

51. Natural ventilation: infection, aeration, duct ventilation system.

52. Duct exhaust gravitational ventilation system, design and its aerodynamics. calculation.

53. Mechanical ventilation system. Its elements.

54. Air purification devices.

55. Air heating devices.

56. Fans: classification, operating principle of axial and centrifugal fans. Selection of fans.

57. Gas supply. Basic schemes. Construction of a gas supply system.

58. Gas household appliances.

Ideal gas, definition and properties.

Gases, the molecules of which do not have interaction forces, and the molecules themselves are material points with negligible volumes, are called ideal gases. The concept of an ideal gas was introduced to simplify the study of thermodynamic processes and obtain simpler calculation formulas.

The properties of an ideal gas based on molecular kinetic concepts are determined based on the physical model of an ideal gas, in which the following assumptions are made:

The volume of a gas particle is zero (that is, the diameter of the molecule is negligible compared to the average distance between them);

Momentum is transmitted only during collisions (that is, the attractive forces between molecules are not taken into account, and repulsive forces arise only during collisions);

The total energy of the gas particles is constant (that is, there is no transfer of energy due to heat transfer or radiation);

The interaction time between molecules is negligible compared to the average time between collisions;

The main object of the molecular kinetic theory of gases is the so-called “ideal gas”. An ideal gas is understood as a rarefied medium of many (a very large number) of particles that do not interact with each other except through rare collisions. Each particle of the medium moves chaotically and independently of the others. Each particle has the usual set of physical parameters for classical mechanics, such as mass and speed. And also derivatives of these quantities - energy and impulse. The particle sizes are considered negligible in relation to the other characteristic sizes of the physical system under consideration. More precisely, an ideal gas is characterized by the following properties that directly follow from this definition:

• Since the particles practically do not interact with each other, their potential energy is negligible compared to their kinetic energy. This also applies to fundamental forces, such as gravity, which are not included in the consideration.
• Particle collisions are considered elastic, i.e. the same as collisions of absolutely hard spheres, like billiard balls. When they collide with each other, the particles do not “stick” to each other. This means that the time period occupied by the collision process can be neglected.
• An ideal gas is considered together with a certain volume it occupies. The total volume of particles is assumed to be negligible compared to the volume they occupy.

Bottom line: we are talking about a very rarefied medium without resistance and any other external interactions, consisting of elastic particles of negligible size (molecules, atoms).

Macroscopic characteristics of an ideal gas

An ideal gas in a vessel, considered as a whole (that is, as a macroscopic object), has a certain set of macroscopic characteristics that do not depend on the behavior of its individual particles. These characteristics are derived from the average energies of individual particles of an ideal gas. Such indicators include temperature And pressure ideal gas.

• Temperature ideal gas - is a measure of the average kinetic energy of the molecules of an ideal gas.
• Pressure ideal gas - is a measure of the average kinetic energy of impacts on a small, absolutely elastic area placed in the gas.

Already from the definition of temperature and pressure it should be clear that these parameters depend on each other. Indeed, if the walls of the vessel are allowed to expand freely, then the law of proportionality holds: p~T, where p is pressure and T is temperature.

Laws of ideal gas behavior

Depending on the conditions imposed on the volume of the vessel, the pressure value or the temperature value, it is possible to obtain various particular patterns of the behavior of an ideal gas:

• Boyle-Mariotte Law(temperature is considered constant).
• Gay-Lussac's Law(pressure is considered constant).
• Charles's Law(constant volume).

There are other relationships. The corresponding formulas can be seen in the picture below: