§33. Air heating and temperature

Aerodynamic heating

heating of bodies moving at high speed in air or other gas. A. n. - the result of the fact that air molecules incident on the body are decelerated near the body.

If the flight is made at the supersonic speed of cultures, braking occurs primarily in the shock wave (See shock wave) , occurring in front of the body. Further deceleration of air molecules occurs directly at the very surface of the body, in boundary layer (See boundary layer). When air molecules decelerate, their thermal energy increases, i.e., the temperature of the gas near the surface of the moving body increases, the maximum temperature to which the gas can be heated in the vicinity of the moving body is close to the so-called. braking temperature:

T 0 = T n + v 2 /2c p ,

where T n - incoming air temperature, v- body flight speed cp is the specific heat capacity of the gas at constant pressure. So, for example, when flying a supersonic aircraft at three times the speed of sound (about 1 km/sec) the stagnation temperature is about 400°C, and when the spacecraft enters the Earth’s atmosphere with the 1st cosmic velocity (8.1 km/s) the stagnation temperature reaches 8000 °C. If in the first case, during a sufficiently long flight, the temperature of the aircraft skin reaches values ​​close to the stagnation temperature, then in the second case, the surface of the spacecraft will inevitably begin to collapse due to the inability of the materials to withstand such high temperatures.

Heat is transferred from regions of a gas with an elevated temperature to a moving body, and aerodynamic heating occurs. There are two forms A. n. - convective and radiation. Convective heating is a consequence of heat transfer from the outer, "hot" part of the boundary layer to the surface of the body. Quantitatively, the convective heat flux is determined from the ratio

q k = a(T e -T w),

where T e - equilibrium temperature (the limiting temperature to which the surface of the body could be heated if there was no energy removal), T w - actual surface temperature, a- coefficient of convective heat transfer, depending on the speed and altitude of the flight, the shape and size of the body, as well as other factors. The equilibrium temperature is close to the stagnation temperature. Type of coefficient dependence a from the listed parameters is determined by the flow regime in the boundary layer (laminar or turbulent). In the case of turbulent flow, convective heating becomes more intense. This is due to the fact that, in addition to molecular thermal conductivity, turbulent velocity fluctuations in the boundary layer begin to play a significant role in energy transfer.

As the flight speed increases, the air temperature behind the shock wave and in the boundary layer increases, resulting in dissociation and ionization. molecules. The resulting atoms, ions and electrons diffuse into a colder region - to the surface of the body. There is a back reaction (recombination) , going with the release of heat. This makes an additional contribution to the convective A. n.

Upon reaching the flight speed of about 5000 m/s the temperature behind the shock wave reaches values ​​at which the gas begins to radiate. Due to the radiant transfer of energy from areas with elevated temperature to the surface of the body, radiative heating occurs. In this case, radiation in the visible and ultraviolet regions of the spectrum plays the greatest role. When flying in the Earth's atmosphere at speeds below the first space speed (8.1 km/s) radiative heating is small compared to convective heating. At the second space velocity (11.2 km/s) their values ​​become close, and at flight speeds of 13-15 km/s and higher, corresponding to the return to Earth after flights to other planets, the main contribution is made by radiative heating.

A particularly important role of A. n. plays when spacecraft return to the Earth's atmosphere (for example, Vostok, Voskhod, Soyuz). To combat A. n. spacecraft are equipped with special thermal protection systems (see Thermal protection).

Lit.: Fundamentals of heat transfer in aviation and rocket technology, M., 1960; Dorrens W. Kh., Hypersonic flows of viscous gas, transl. from English, M., 1966; Zeldovich Ya. B., Raiser Yu. P., Physics of shock waves and high-temperature hydrodynamic phenomena, 2nd ed., M., 1966.

N. A. Anfimov.

Big soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what "Aerodynamic heating" is in other dictionaries:

Heating of bodies moving at high speed in air or other gas. A. n. the result of the fact that air molecules incident on the body are decelerated near the body. If the flight is made with supersonic. speed, braking occurs primarily in shock ... ... Physical Encyclopedia

Heating of a body moving at high speed in air (gas). Noticeable aerodynamic heating is observed when the body moves at supersonic speed (for example, when the warheads of intercontinental ballistic missiles) EdwART. ... ... Marine Dictionary

aerodynamic heating- Heating of the surface of a body streamlined with gas, moving in a gaseous medium at high speed in the presence of convective, and at hypersonic speeds and radiative heat exchange with the gaseous medium in the boundary or shock layer. [GOST 26883… … Technical Translator's Handbook

An increase in the temperature of a body moving at high speed in air or other gas. Aerodynamic heating is the result of deceleration of gas molecules near the surface of the body. So, when a spacecraft enters the Earth's atmosphere at a speed of 7.9 km / s ... ... encyclopedic Dictionary

aerodynamic heating- aerodinaminis įšilimas statusas T sritis Energetika apibrėžtis Kūnų, judančių dujose (ore) dideliu greičiu, paviršiaus įšilimas. atitikmenys: engl. aerodynamic heating vok. aerodynamische Aufheizung, f rus. aerodynamic heating, m pranc.… … Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas- an increase in the temperature of a body moving at high speed in air or other gas. A. i. the result of deceleration of gas molecules near the surface of the body. So, at the entrance of the cosmic. apparatus into the Earth's atmosphere at a speed of 7.9 km / s, the rate of air at the surface pa ... Natural science. encyclopedic Dictionary

Aerodynamic heating of the rocket structure- Heating of the surface of the rocket during its movement in dense layers of the atmosphere at high speed. A.n. - the result of the fact that air molecules incident on a rocket are decelerated near its body. In this case, the transfer of kinetic energy occurs ... ... Encyclopedia of the Strategic Missile Forces

Concorde Concorde at the airport ... Wikipedia

All life processes on Earth are caused by thermal energy. The main source from which the Earth receives thermal energy is the Sun. It radiates energy in the form of various rays - electromagnetic waves. The radiation of the Sun in the form of electromagnetic waves propagating at a speed of 300,000 km / s is called, which consists of rays of various lengths that carry light and heat to the Earth.

Radiation can be direct or diffuse. If there were no atmosphere, the earth's surface would receive only direct radiation. Therefore, radiation that comes directly from the Sun in the form of direct sunlight and with a cloudless sky is called direct. It carries the greatest amount of heat and light. But, passing through the atmosphere, the sun's rays are partially scattered, deviate from the direct path as a result of reflection from air molecules, water droplets, dust particles and turn into rays going in all directions. Such radiation is called diffuse. Therefore, it is also light in those places where direct sunlight (direct radiation) does not penetrate (forest canopy, shady side of rocks, mountains, buildings, etc.). Scattered radiation also determines the color of the sky. All solar radiation coming to the earth's surface, i.e. direct and scattered, called the total. The earth's surface, absorbing solar radiation, heats up and itself becomes a source of heat radiation into the atmosphere. It is called terrestrial radiation, or terrestrial radiation, and is largely delayed by the lower layers of the atmosphere. The solar radiation absorbed by the earth's surface is spent on heating water, soil, air, evaporation and radiation into the atmosphere. Earthy, not defining temperature regime troposphere, i.e. the sun's rays passing through everything do not heat it. The largest amount of heat is received and heated to the highest temperatures by the lower layers of the atmosphere, directly adjacent to the heat source - the earth's surface. As you move away from the earth's surface, the heating weakens. That is why in the troposphere, with height, an average of 0.6 ° C decreases for every 100 m of ascent. This is a general pattern for the troposphere. There are times when the overlying layers of air are warmer than the underlying ones. This phenomenon is called temperature inversion.

The heating of the earth's surface differs significantly not only in height. The amount of total solar radiation directly depends on the angle of incidence of the sun's rays. The closer this value is to 90°, the more solar energy the earth's surface receives.

In turn, the angle of incidence of the sun's rays on a certain point on the earth's surface is determined by its geographical latitude. The strength of direct solar radiation depends on the length of the path that the sun's rays travel through the atmosphere. When the Sun is at its zenith (near the equator), its rays fall vertically on the earth's surface, i.e. overcome the atmosphere in the shortest way (at 90 °) and intensively give up their energy to a small area. As you move away from the equatorial zone to the south or north, the length of the path of the sun's rays increases, i.e. the angle of their incidence on the earth's surface decreases. More and more, the rays begin to slide along the Earth, as it were, and approach the tangent line in the region of the poles. In this case, the same beam of energy is scattered over a larger area, and the amount of reflected energy increases. Thus, where the sun's rays fall on the earth's surface at an angle of 90 °, they are constantly high, and as they move towards the poles, it becomes progressively colder. It is at the poles, where the sun's rays fall at an angle of 180 ° (i.e., tangentially), that there is the least amount of heat.

Such an uneven distribution of heat on the Earth, depending on the latitude of the place, makes it possible to distinguish five thermal zones: one hot, two and two cold.

The conditions for heating water and land by solar radiation are very different. The heat capacity of water is twice that of land. This means that with the same amount of heat, the land heats up twice faster than water, but the opposite happens on cooling. In addition, water evaporates when heated, which consumes a considerable amount of heat. On land, heat is concentrated only in its upper layer, only a small part of it is transferred to the depth. In water, the rays immediately heat up a significant thickness, which is also facilitated by the vertical mixing of water. As a result, water accumulates heat much more than land, retains it longer and spends it more evenly than land. It heats up slower and cools down slower.

The surface of the land is not uniform. Its heating largely depends on the physical properties of soils and, ice, exposure (the angle of inclination of land areas in relation to the incident sun rays) slopes. Features of the underlying surface determine the different nature of the change in air temperatures during the day and year. The lowest air temperatures during the day on land are observed shortly before sunrise (no influx of solar radiation and strong terrestrial radiation at night). The highest - in the afternoon (14-15 hours). During the year in the Northern Hemisphere, the highest air temperatures on land are observed in July, and the lowest in January. Above the water surface, the daily maximum air temperature is shifted and is observed at 15-16 hours, and the minimum is 2-3 hours after sunrise. The annual maximum (in the Northern Hemisphere) is in August, and the minimum is in February.

2005-08-16

In a number of cases, it is possible to significantly reduce capital and operating costs by providing autonomous heating of premises with warm air based on the use of heat generators running on gas or liquid fuel. In such units, it is not water that is heated, but air - fresh supply, recirculation or mixed. This method is especially effective for providing autonomous heating of industrial premises, exhibition pavilions, workshops, garages, service stations, car washes, film studios, warehouses, public buildings, gyms, supermarkets, greenhouses, greenhouses, livestock complexes, poultry farms, etc.

Advantages air heating

There are many advantages of the air heating method over the traditional water heating method in large rooms, we list only the main ones:

1. Profitability. Heat is produced directly in the heated room and is almost entirely consumed for its intended purpose. Thanks to direct combustion of fuel without an intermediate heat carrier, a high thermal efficiency of the entire heating system is achieved: 90-94% for recuperative heaters and almost 100% for direct heating systems. The use of programmable thermostats provides the possibility of additional savings from 5 to 25% of thermal energy due to the "standby mode" function - automatically maintaining the temperature in the room in work time at the level of + 5-7 ° С.
2. The ability to "turn on" the supply ventilation. It's no secret that today in most enterprises the supply ventilation does not work properly, which significantly worsens the working conditions of people and affects labor productivity. Heat generators or direct heating systems warm up the air by ∆t up to 90°C - this is quite enough to “make” the supply ventilation work even in the conditions of the Far North. Thus, air heating implies not only economic efficiency, but also an improvement environmental situation and working conditions.
3. Little inertia. Units of air heating systems enter the operating mode in a matter of minutes, and due to the high air turnover, the room is completely warmed up in just a few hours. This makes it possible to quickly and flexibly maneuver when heat needs change.
4. The absence of an intermediate heat carrier makes it possible to abandon the construction and maintenance of a water heating system that is inefficient for large premises, a boiler house, heating mains and a water treatment plant. Losses in heating mains and their repair are eliminated, which makes it possible to drastically reduce operating costs. In winter, there is no risk of defrosting the heaters and the heating system in the event of a prolonged shutdown of the system. Cooling even to a deep "minus" does not lead to defrosting of the system.
5. A high degree of automation allows you to generate exactly the amount of heat that is needed. Combined with high reliability gas equipment this significantly increases the safety of the heating system, and a minimum of maintenance personnel is sufficient for its operation.
6. Small costs. The method of heating large rooms with the help of heat generators is one of the cheapest and most quickly implemented. The capital costs of building or refurbishing an air system are generally much lower than those of hot water or radiant heating. The payback period for capital expenditures usually does not exceed one or two heating seasons.

Depending on the tasks to be solved, various types of heaters can be used in air heating systems. In this article, we will consider only units that operate without the use of an intermediate heat carrier - recuperative air heaters (with a heat exchanger and removal of combustion products to the outside) and direct air heating systems (gas mixing air heaters).

Recuperative air heaters

In units of this type, fuel mixed with the required amount of air is supplied by the burner to the combustion chamber. The resulting combustion products pass through a two- or three-way heat exchanger. The heat obtained during the combustion of the fuel is transferred to the heated air through the walls of the heat exchanger, and the flue gases are discharged through the chimney to the outside (Fig. 1) - that is why they are called "indirect heating" heat generators.

Recuperative air heaters can be used not only directly for heating, but also as part of a supply ventilation system, as well as for process air heating. The rated thermal power of such systems is from 3 kW to 2 MW. The heated air is supplied to the room through a built-in or remote blower, which makes it possible to use the units both for direct air heating with its delivery through louvered grilles, and with air ducts.

Washing the combustion chamber and the heat exchanger, the air is heated and sent either directly to the heated room through the louvered air distribution grilles located in the upper part, or distributed through the air duct system. An automated block burner is located on the front part of the heat generator (Fig. 2).

The heat exchangers of modern air heaters, as a rule, are made of stainless steel (the furnace is made of heat-resistant steel) and serve from 5 to 25 years, after which they can be repaired or replaced. The efficiency of modern models reaches 90-96%. The main advantage of recuperative air heaters is their versatility.

They can run on natural or liquefied gas, diesel fuel, oil, fuel oil or waste oil - you just have to change the burner. It is possible to work with fresh air, with an admixture of internal and in full recirculation mode. Such a system allows some liberties, for example, to change the flow of heated air, to redistribute the heated air flows into different branches of the air ducts “on the go” using special valves.

In summer, recuperative air heaters can operate in ventilation mode. The units are mounted both in a vertical and horizontal position, on the floor, wall, or built into a sectional ventilation chamber as a heater section.

Recuperative air heaters can even be used for heating rooms of a high comfort category, if the unit itself is moved outside the immediate service area.

Main disadvantages:

1. The large and complex heat exchanger increases the cost and weight of the system compared to mixing type air heaters;
2. They need a chimney and a condensate drain.

Direct air heating systems

Modern technologies have made it possible to achieve such purity of combustion natural gas that it became possible not to divert combustion products "into the pipe", but to use them for direct air heating in supply ventilation systems. The gas supplied to combustion completely burns out in the stream of heated air and, mixing with it, gives it all the heat.

This principle is implemented in a number of similar ramp burner designs in the USA, England, France and Russia and has been successfully used since the 1960s at many enterprises in Russia and abroad. Based on the principle of ultra-clean combustion of natural gas directly in the heated air flow, gas mixing air heaters of the STV type (STARVEINE - “star wind”) are produced with a rated thermal output from 150 kW to 21 MW.

The very technology of combustion organization, as well as a high degree of dilution of combustion products, make it possible to obtain clean warm air in installations in accordance with all applicable standards, practically free of harmful impurities (no more than 30% of MPC). STV air heaters (Fig. 3) consist of a modular burner unit located inside the housing (air duct section), a DUNGS gas line (Germany) and an automation system.

The housing is usually equipped with a hermetic door for ease of maintenance. The burner block, depending on the required thermal power, is assembled from the required number of burner sections of different configurations. The automation of the heaters provides a smooth automatic start according to the cyclogram, control of the parameters of safe operation and the possibility of smooth regulation of the heat output (1:4), which makes it possible to automatically maintain the required air temperature in the heated room.

Application of gas mixing air heaters

Their main purpose is direct heating of fresh supply air supplied to production facilities to compensate for exhaust ventilation and thus improve the working conditions of people.

For premises with a high air exchange rate, it becomes expedient to combine the supply ventilation system and the heating system - in this regard, direct heating systems have no competitors in terms of price / quality ratio. Gas mixing air heaters are designed for:

• autonomous air heating of rooms for various purposes with a large air exchange (K  great.5);
• air heating in air-thermal curtains of a cut-off type, it is possible to combine it with heating and supply ventilation systems;
• pre-heating systems for car engines in unheated parking lots;
• thawing and defrosting of wagons, tanks, cars, bulk materials, heating and drying products before painting or other types of processing;
• direct heating of atmospheric air or drying agent in various process heating and drying installations, for example, drying of grain, grass, paper, textiles, wood; applications in painting and drying booths after painting, etc.

Accommodation

Mixing heaters can be built into the air ducts of supply ventilation systems and thermal curtains, into the air ducts of drying plants - both in horizontal and vertical sections. Can be mounted on the floor or platform, under the ceiling or on the wall. As a rule, they are placed in supply and ventilation chambers, but they can also be installed directly in a heated room (according to the category).

With additional equipment, the corresponding elements can serve rooms of categories A and B. Recirculation of indoor air through mixing air heaters is undesirable - a significant decrease in the oxygen level in the room is possible.

Strengths direct heating systems

Simplicity and reliability, low cost and efficiency, the ability to heat up to high temperatures, a high degree of automation, smooth regulation, do not need a chimney. Direct heating is the most economical way - the efficiency of the system is 99.96%. The level of specific capital costs for a heating system based on a direct heating unit combined with forced ventilation is the lowest with the highest degree of automation.

Air heaters of all types are equipped with a safety and control automation system that provides smooth start, maintaining the heating mode and shutting down in case of emergencies. In order to save energy, it is possible to equip air heaters with automatic control taking into account external and internal temperature control, functions of daily and weekly heating programming modes.

It is also possible to include the parameters of a heating system consisting of many heating units into a centralized control and dispatching system. In this case, the operator-dispatcher will have operational information about the operation and status of the heating units, clearly displayed on the computer monitor, as well as control their operation mode directly from the remote control center.

Mobile heat generators and heat guns

Designed for temporary use - at construction sites, for heating during off-season periods, technological heating. Mobile heat generators and heat guns run on propane (liquefied bottled gas), diesel fuel or kerosene. Can be both direct heating, and with removal of products of combustion.

Types of autonomous air heating systems

For autonomous heat supply of various premises, various types of air heating systems are used - with centralized heat distribution and decentralized; systems operating entirely on the inflow fresh air, or with full/partial recirculation of internal air.

In decentralized air heating systems, heating and air circulation in the room are carried out by autonomous heat generators located in various sections or work areas - on the floor, wall and under the roof. The air from the heaters is supplied directly to the working area of ​​the room. Sometimes, for better distribution of heat flows, heat generators are equipped with small (local) air duct systems.

For units in this design, the minimum power of the fan motor is typical, so decentralized systems are more economical in terms of power consumption. It is also possible to use air-thermal curtains as part of an air heating system or supply ventilation.

The possibility of local regulation and use of heat generators as needed - by zones, at different times - makes it possible to significantly reduce fuel costs. However, the capital cost of implementing this method is somewhat higher. In systems with centralized heat distribution, air-heating units are used; The warm air produced by them enters the working areas through the duct system.

The units, as a rule, are built into existing ventilation chambers, but it is possible to place them directly in a heated room - on the floor or on the site.

Application and placement, selection of equipment

Each of the types of the above heating units has its undeniable advantages. And there is no ready-made recipe in which case which of them is more appropriate - it depends on many factors: the amount of air exchange in relation to the amount of heat loss, the category of the room, the availability of free space for placing equipment, and financial possibilities. Let's try to form the most general principles appropriate selection of equipment.

1. Heating systems for rooms with little air exchange (air exchange ≤ great,5-1)

The total heat output of the heat generators in this case is assumed to be almost equal to the amount of heat required to compensate for the heat loss of the room, the ventilation is relatively small, so it is advisable to use a heating system based on heat generators of indirect heating with full or partial recirculation of the indoor air of the room.

Ventilation in such rooms can be natural or mixed with outdoor air to recirculate. In the second case, the power of the heaters is increased by an amount sufficient to heat the fresh supply air. Such a heating system can be local, with floor or wall heat generators.

If it is impossible to place the unit in a heated room or when organizing maintenance of several rooms, a centralized type system can be used: the heat generators are located in the ventilation chamber (an extension, on the mezzanine, in the adjacent room), and the heat is distributed through the air ducts.

During working hours, heat generators can operate in partial recirculation mode, simultaneously heating the mixed supply air, during non-working hours, some of them can be turned off, and the rest can be switched to an economical standby mode of + 2-5 ° C with full recirculation.

2. Heating systems for rooms with a large air exchange rate, constantly in need of supplying large volumes of fresh air supply (Air exchange  great)

In this case, the amount of heat required to heat the supply air may already be several times greater than the amount of heat required to compensate for heat losses. Here, it is most expedient and economical to combine an air heating system with a supply ventilation system. The heating system can be built on the basis of direct air heating installations, or on the basis of the use of recuperative heat generators in a design with a higher degree of heating.

The total heat output of the heaters should be equal to the sum of the heat demand for supply air heating and the heat required to compensate for heat losses. In direct heating systems, 100% of the outdoor air is heated, ensuring the supply of the required volume of supply air.

During working hours, they heat the air from outside to the design temperature of + 16-40 ° C (taking into account overheating to ensure heat loss compensation). In order to save money during non-working hours, it is possible to turn off part of the heaters to reduce the supply air consumption, and switch the rest to the standby mode of maintaining +2-5°C.

Recuperative heat generators in standby mode allow for additional savings by switching them to full recirculation mode. The lowest capital costs in organizing centralized heating systems are when using the largest possible heaters. Capital costs for STV gas mixing air heaters can range from 300 to 600 rubles/kW of installed heat output.

3. Combined air heating systems

The best option for rooms with significant air exchange during working hours with a single-shift operation, or an intermittent work cycle - when the difference in the need for supply of fresh air and heat during the day is significant.

In this case, it is advisable to separate the operation of two systems: standby heating and forced ventilation combined with a heating (reheating) system. At the same time, recuperative heat generators are installed in the heated room or in the ventilation chambers to maintain only the standby mode with full recirculation (at the calculated outdoor temperature).

The supply ventilation system, combined with the heating system, provides heating of the required volume of fresh supply air up to + 16-30 ° C and heating of the room to the required operating temperature, and for economy purposes it is switched on only during working hours.

It is built either on the basis of recuperative heat generators (with an increased degree of heating), or on the basis of powerful direct heating systems (which is 2-4 times cheaper). It is possible to combine the forced-air heating system with the existing water heating system (it can remain on duty), the option is also applicable for the staged modernization of the existing heating and ventilation system.

With this method, operating costs will be the lowest. Thus, using air heaters of various types in various combinations, it is possible to solve both problems at the same time - both heating and forced ventilation.

There are a lot of examples of the application of air heating systems and the possibilities of their combination are extremely diverse. In each case, it is necessary to carry out thermal calculations, take into account all the conditions of use and perform several options for selecting equipment, comparing them in terms of feasibility, capital costs and operating costs.

When is the sun hottest - when is it higher overhead or lower?

The sun heats up more when it is higher. The sun's rays in this case fall at a right, or close to a right angle.

What kinds of rotation of the Earth do you know?

The earth rotates on its axis and around the sun.

Why does the day and night cycle occur on Earth?

The change of day and night is the result of the axial rotation of the Earth.

Determine how the angle of incidence of the sun's rays differs on June 22 and December 22 at the parallels of 23.5 ° N. sh. and yu. sh.; at the parallels of 66.5° N. sh. and yu. sh.

On June 22, the angle of incidence of the sun's rays at the parallel of 23.50 N.L. 900 S - 430. At the parallel 66.50 N.S. – 470, 66.50 S - sliding angle.

On December 22, the angle of incidence of the sun's rays at the parallel 23.50 N.L. 430 S - 900. At the parallel 66.50 N.S. - sliding angle, 66.50 S - 470.

Think about why the warmest and coldest months are not June and December, when the sun's rays have the largest and smallest angles of incidence on the earth's surface.

Atmospheric air is heated from the earth's surface. Therefore, in June, the earth's surface warms up, and the temperature reaches a maximum in July. It also happens in winter. In December, the earth's surface cools down. The air cools down in January.

Define:

average daily temperature according to four measurements per day: -8°C, -4°C, +3°C, +1°C.

The average daily temperature is -20C.

the average annual temperature of Moscow using the table data.

The average annual temperature is 50C.

Determine the daily temperature range for thermometer readings in Figure 110, c.

The temperature amplitude in the figure is 180C.

Determine how many degrees the annual amplitude in Krasnoyarsk is greater than in St. Petersburg, if the average temperature in July in Krasnoyarsk is +19°С, and in January it is -17°С; in St. Petersburg +18°C and -8°C respectively.

The temperature range in Krasnoyarsk is 360С.

The temperature amplitude in St. Petersburg is 260C.

The temperature amplitude in Krasnoyarsk is 100C higher.

Questions and tasks

1. How does the air in the atmosphere heat up?

When the sun's rays pass through, the atmosphere from them almost does not heat up. As the earth's surface heats up, it becomes a heat source itself. It is from her that it heats up atmospheric air.

2. How many degrees does the temperature in the troposphere decrease for every 100 m ascent?

As you climb up, every kilometer the air temperature drops by 6 0C. So, 0.60 for every 100 m.

3. Calculate the air temperature outside the aircraft, if the flight altitude is 7 km, and the temperature at the Earth's surface is +200C.

The temperature when climbing 7 km will drop by 420. This means that the temperature outside the aircraft will be -220.

4. Is it possible to meet a glacier in the mountains at an altitude of 2500 m in summer if the temperature at the foot of the mountains is + 250C.

The temperature at an altitude of 2500 m will be +100C. The glacier at an altitude of 2500 m will not meet.

5. How and why does the air temperature change during the day?

During the day, the sun's rays illuminate the earth's surface and warm it up, and the air heats up from it. At night, the flow of solar energy stops, and the surface, along with the air, gradually cools. The sun is highest above the horizon at noon. This is the time when the most solar energy comes in. However, the highest temperature is observed after 2-3 hours after noon, since it takes time for heat to transfer from the Earth's surface to the troposphere. The most low temperature happens before sunrise.

6. What determines the difference in the heating of the Earth's surface during the year?

During the year, in the same area, the sun's rays fall on the surface in different ways. When the angle of incidence of the rays is steeper, the surface receives more solar energy, the air temperature rises and summer comes. When the sun's rays are more tilted, the surface heats up slightly. The air temperature at this time drops, and winter comes. The warmest month in the Northern Hemisphere is July and the coldest month is January. In the Southern Hemisphere, on the contrary: the most cold month year - July, and the warmest - January.

Remember

• What instrument is used to measure air temperature? What kinds of rotation of the Earth do you know? Why does the day and night cycle occur on Earth?

How does the earth's surface and atmosphere heat up? The sun radiates a huge amount of energy. However, the atmosphere transmits only half of the sun's rays to the earth's surface. Some of them are reflected, some are absorbed by clouds, gases and dust particles (Fig. 83).

Rice. 83. Consumption of solar energy coming to Earth

When the sun's rays pass through, the atmosphere from them almost does not heat up. As the earth's surface heats up, it becomes a heat source itself. It is from it that the atmospheric air is heated. Therefore, the air in the troposphere is warmer near the earth's surface than at altitude. When climbing up, every kilometer the air temperature drops by 6 "C. High in the mountains, due to the low temperature, the accumulated snow does not melt even in summer. The temperature in the troposphere changes not only with height, but also during certain periods of time: days, years.

Differences in air heating during the day and year. During the day, the sun's rays illuminate the earth's surface and warm it up, and the air heats up from it. At night, the flow of solar energy stops, and the surface, along with the air, gradually cools.

The sun is highest above the horizon at noon. This is the time when the most solar energy comes in. However, the highest temperature is observed after 2-3 hours after noon, since it takes time for heat to transfer from the Earth's surface to the troposphere. The lowest temperature is before sunrise.

The air temperature also changes with the seasons. You already know that the Earth moves around the Sun in an orbit and the Earth's axis is constantly inclined to the plane of the orbit. Because of this, during the year in the same area, the sun's rays fall on the surface in different ways.

When the angle of incidence of the rays is steeper, the surface receives more solar energy, the air temperature rises and summer comes (Fig. 84).

Rice. 84. The fall of the sun's rays on the earth's surface at noon on June 22 and December 22

When the sun's rays are more tilted, the surface heats up slightly. The air temperature at this time drops, and winter comes. The warmest month in the Northern Hemisphere is July and the coldest month is January. In the Southern Hemisphere, the opposite is true: the coldest month of the year is July, and the warmest is January.

From the figure, determine how the angle of incidence of the sun's rays differs on June 22 and December 22 at parallels of 23.5 ° N. sh. and yu. sh.; at the parallels of 66.5° N. sh. and yu. sh.

Think about why the warmest and coldest months are not June and December, when the sun's rays have the largest and smallest angles of incidence on the earth's surface.

Rice. 85. Average annual air temperatures of the Earth

Indicators of temperature changes. To identify the general patterns of temperature changes, an indicator of average temperatures is used: average daily, average monthly, average annual (Fig. 85). For example, to calculate the average daily temperature during the day, the temperature is measured several times, these indicators are summed up, and the resulting amount is divided by the number of measurements.

Define:

• average daily temperature according to four measurements per day: -8°C, -4°C, +3°C, +1°C;
• the average annual temperature of Moscow using the table data.

Table 4

Determining the change in temperature, usually note its highest and lowest rates.

The difference between the highest and lowest readings is called the temperature range.

The amplitude can be determined for a day (daily amplitude), month, year. For example, if the highest temperature per day is +20°C, and the lowest is +8°C, then the daily amplitude will be 12°C (Fig. 86).

Rice. 86. Daily temperature range

Determine how many degrees the annual amplitude in Krasnoyarsk is greater than in St. Petersburg, if the average temperature in July in Krasnoyarsk is +19°С, and in January it is -17°С; in St. Petersburg +18°C and -8°C respectively.

On maps, the distribution of average temperatures is reflected using isotherms.

Isotherms are lines connecting points with the same average temperature air for a certain period of time.

Usually show isotherms of the warmest and coldest months of the year, i.e. July and January.

Questions and tasks

1. How is air heated in the atmosphere?
2. How does the air temperature change during the day?
3. What determines the difference in the heating of the Earth's surface during the year?