The efficiency of the real thermal machine formula. Maximum efficiency of thermal machines (Carno theorem)

Modern realities suggest the broad operation of thermal engines. Numerous attempts to replace them on electric motors are still fail. The problems associated with the accumulation of electricity in autonomous systems are solved with great difficulty.

The problems of the production of electricity batteries are still relevant, taking into account their long-term use. High-speed characteristics of electric vehicles are far from those in the car on internal combustion engines.

The first steps to create hybrid engines make it possible to significantly reduce harmful emissions in megalopolis, solving environmental problems.

A bit of history

The ability to transform the energy of steam into the energy of motion was known in antiquity. 130 BC, Heron Alexandrian philosopher presented to the audience a steam toy - Eolipale. The sphere filled with steam came into rotation under the action of jets emanating from it. This prototype of modern steam turbines in those days did not find applications.

For many years and century, the development of a philosopher was considered only a fun toy. In 1629, the Italian D. Branca created an active turbine. Couple led the disk, equipped with blades.

From that moment began the rapid development of steam engines.

Heat machine

The conversion of fuel into the energy of the movement of parts of machines and mechanisms is used in thermal machines.

Main parts of machines: Heater (energy production system from the outside), working body (makes a useful action), refrigerator.

The heater is designed to ensure that the working fluid has accumulated an sufficient supply of internal energy to make useful work. The refrigerator removes excess energy.

The main characteristic of efficiency is called efficiency efficiency. This value shows which part spent on the heating of energy is spent on the performance of useful work. The higher the efficiency, the more profitable the operation of the machine, but this value cannot exceed 100%.

Calculation of efficiency

Let the heater acquired from outside the energy equal to q 1. The working fluid made work a, with the energy given to the refrigerator, was Q 2.

Based on the definition, we calculate the magnitude of the efficiency:

η \u003d A / Q 1. Assess that A \u003d Q 1 - Q 2.

Hence the efficiency of the heat machine, the formula of which has the form η \u003d (Q 1 - Q 2) / Q 1 \u003d 1 - Q 2 / Q 1, allows you to draw the following conclusions:

• Efficiency cannot exceed 1 (or 100%);
• to maximize the increase in this magnitude, it is necessary either an increase in the energy obtained from the heater, or a decrease in the energy given to the refrigerator;
• an increase in the heater energy is achieved by changing the quality of fuel;
• reducing the energy given to the refrigerator makes it possible to achieve the structural features of the engines.

Perfect thermal engine

Is it possible to create such an engine, the efficiency of which would be maximal (ideally - equal to 100%)? Find the answer to this question tried the French physicist and talented engineer Sadi Carlo. In 1824, its theoretical calculations on the processes occurring in the gases were made public.

The main idea laid in the perfect car can be considered to carry out reversible processes with perfect gas. We begin with the expansion of gas isothermally at temperatures T 1. The amount of heat required for this, q 1. After gas without heat exchange expands, reaching the temperature T 2, the gas is compressed isothermally, transmitting the refrigerator with the energy Q 2. The return of gas to the initial state is made adiabato.

The efficiency of the ideal thermal engine of carno, with an accurate calculation, is equal to the ratio of the temperature difference of heating and cooling devices to the temperature that the heater has. It looks like this: η \u003d (T 1 - T 2) / T 1.

Possible efficiency of the heat machine, the formula of which has the form: η \u003d 1 - T 2 / T 1, depends only on the temperature of the heater and the cooler and can not be more than 100%.

Moreover, this ratio allows us to prove that the efficiency of thermal machines can be equal to one only when the temperature is reached with the temperature refrigerator. As you know, this value is unattainable.

Theoretical calculations of carno allow you to determine the maximum efficiency of the heat machine of any design.

Proven carno theorem sounds the following way. An arbitrary thermal machine under no circumstances is capable of having a useful effect of a similar value of the efficiency of the perfect heat machine.

An example of solving tasks

Example 1. What is the efficiency of the perfect heat machine, if the heater temperature is 800 ° C, and the temperature of the refrigerator is 500 ° C below?

T 1 \u003d 800 ° C \u003d 1073 K, Δt \u003d 500 o c \u003d 500 k, η -?

By definition: η \u003d (T 1 - T 2) / T 1.

We are not given the temperature of the refrigerator, but Δt \u003d (t 1 - t 2), hence:

η \u003d Δt / T 1 \u003d 500 k / 1073 K \u003d 0.46.

Answer: KPD \u003d 46%.

Example 2. Determine the efficiency of the ideal heat machine, if a useful work of 650 j. What is the temperature of the heat carrier heater, if the cooler temperature is 400 k?

Q 1 \u003d 1 kJ \u003d 1000 J, A \u003d 650 J, T 2 \u003d 400 K, η -?, T 1 \u003d?

This task we are talking about a thermal installation, the efficiency of which can be calculated by the formula:

To determine the temperature of the heater, we use the Formula of the efficiency of the perfect heat machine:

η \u003d (T 1 - T 2) / T 1 \u003d 1 - T 2 / T 1.

After performing mathematical transformations, we get:

T 1 \u003d T 2 / (1- η).

T 1 \u003d T 2 / (1- A / Q 1).

Calculate:

η \u003d 650 J / 1000 J \u003d 0.65.

T 1 \u003d 400 K / (1- 650 J / 1000 J) \u003d 1142.8 K.

Answer: η \u003d 65%, t 1 \u003d 1142.8 K.

Real conditions

The ideal thermal engine is designed with ideal processes. The work is performed only in isothermal processes, its value is defined as an area limited by a carno cycle schedule.

In fact, to create conditions for the process of changing the state of gas without accompanying temperature changes is impossible. There are no such materials that would exclude heat exchange with the surrounding objects. The adiabatic process becomes impossible. In the case of heat exchange, the temperature of the gas must change.

The efficiency of thermal machines created in real conditions is significantly different from the efficiency of ideal engines. Note that the flow of processes in real engines occurs so quickly that the varying of the inner heat energy of the working substance in the process of changing its volume cannot be compensated by the flow of the amount of heat from the heater and the return of the refrigerator.

Other thermal engines

Real engines work on other cycles:

• otto cycle: the process with a constant volume is changing adiabat, creating a closed cycle;
• diesel cycle: isobar, adiabat, isoof, adiabat;
• The process occurring at constant pressure is replaced by adiabat, closes the cycle.

Create equilibrium processes in real engines (to bring them to ideal) in the conditions of modern technology, it is not possible. The efficiency of thermal machines is significantly lower, even taking into account the same temperature modes as in the perfect thermal installation.

But it is not necessary to reduce the role of the design formula for the efficiency because it becomes the point of reference in the process of working on improving the efficiency of real engines.

Ways to change the efficiency

Conducting a comparison of the ideal and real heat engines, it is worth noting that the temperature of the recent refrigerator cannot be any. Typically, the refrigerator is considered an atmosphere. Take the temperature of the atmosphere only in approximate calculations. Experience shows that the temperature of the cooler is equal to the temperature of the gases spent in engines, as it occurs in internal combustion engines (abbreviated inboard).

DVS is the most common heat machine in our world. The efficiency of the heat machine in this case depends on the temperature created by the combustible fuel. The essential difference in the engine from steam vehicles is the fusion of the functions of the heater and the working fluid of the device in the air-fuel mixture. Burning, the mixture creates pressure on moving parts of the engine.

Increased working gases reaches significantly changing the properties of fuel. Unfortunately, it is impossible to do it indefinitely. Any material from which the engine combustion is made has its melting point. The heat resistance of such materials is the main characteristic of the engine, as well as the ability to significantly affect the efficiency.

Values \u200b\u200bof efficiency engines

If we consider the temperature of the working pair at the entrance of which is 800 K, and the spent gas is 300 k, then the efficiency of this machine is 62%. In fact, this value does not exceed 40%. Such a decrease occurs due to heat losses when the turbine housing is heated.

The greatest value of internal combustion does not exceed 44%. Increasing this value is the question of the near future. Changing the properties of materials, fuel is a problem that the best minds of humanity work.

The work of many types of machines characterizes such an important indicator as the efficiency efficiency. Engineers every year seek to create a more advanced technique, which, with smaller, would give the maximum result from its use.

Thermal engine device

Before dealing with that it is necessary to understand how this mechanism works. Without knowledge of the principles of its action, it is impossible to find out the essence of this indicator. The thermal engine is called a device that makes a job due to the use of internal energy. Any thermal machine that turns into mechanical uses thermal expansion of substances with an increase in temperature. In solid-state engines, it is possible not only a change in the volume of the substance, but also body shape. The effect of such an engine is subject to the laws of thermodynamics.

Principle of operation

In order to understand how the heat engine works, it is necessary to consider the basics of its design. For the functioning of the device, two bodies are needed: hot (heater) and cold (refrigerator, cooler). The principle of action of thermal motors (efficiency of thermal motors) depends on their type. Often, the refrigerator is a steam condenser, and the heater is any type of fuel burning in the furnace. The efficiency of the ideal thermal engine is at such a formula:

Efficiency \u003d (TNAGEV. - Tolod.) / TNAGEV. x 100%.

At the same time, the efficiency of the real engine will never be able to exceed the values \u200b\u200bobtained according to this formula. Also, this indicator will never exceed the aforementioned value. To increase the efficiency, most often increase the temperature of the heater and reduce the temperature of the refrigerator. Both of these process will be limited to real working conditions.

When the thermal engine is functioning, work is performed, as gas starts to lose energy and is cooled to some temperature. The latter, as a rule, is several degrees above the surrounding atmosphere. This is the temperature of the refrigerator. Such a special device is designed for cooling with the subsequent condensation of the spent steam. Where there are capacitors, the refrigerator temperature is sometimes lower than the ambient temperature.

In the heat engine, the body during heating and expansion is not able to give all its internal energy to perform work. Some part of the warmth will be transferred to the refrigerator together with or steam. This part of the thermal is inevitably lost. The working fluid when combustion of fuel receives a certain amount of heat from the heater Q 1. At the same time, it still performs work A, during which he transfers the refrigerator part of thermal energy: Q 2

The efficiency characterizes the efficiency of the engine in the field of conversion and energy transmission. This indicator is often measured as a percentage. Formula efficiency:

η * A / QX100%, where Q is the energy spent, but is a useful job.

Based on the law of conservation of energy, it can be concluded that the efficiency will always be less than one. In other words, useful work will never be more than energy spent on it.

The engine efficiency is the ratio of useful work to the energy reported by the heater. It can be represented as such formula:

η \u003d (q 1 -q 2) / q 1, where Q 1 is heat obtained from the heater, and Q 2 is a given to the refrigerator.

Work of the thermal engine

The work performed by the thermal engine is calculated by this formula:

A \u003d | Q h | - | q x |, where A is the work, Q h is the amount of heat obtained from the heater, Q x is the amount of heat that is given to the cooler.

| Q H | - | Q x |) / | Q h | \u003d 1 - | q x | / | q h |

It equals the attitude of the engine that the engine performs to the amount of warmth obtained. Part of the thermal energy with this transmission is lost.

Engine carno

The maximum thermal engine efficiency is noted at the carno device. This is due to the fact that in the specified system it depends only on the absolute temperature of the heater (TN) and the cooler (TX). The efficiency of the thermal engine operating the software is determined by the following formula:

(TX) / TN \u003d - TX.

The laws of thermodynamics allowed to calculate the maximum efficiency, which is possible. For the first time, this figure calculated the French scientist and engineer Sadi Carlo. He came up with a thermal machine that operated on perfect gas. It works on a cycle of 2 isotherms and 2 adiabat. The principle of its work is quite simple: the heater contact is supplied to the gas vessel, as a result of which the working fluid expands isothermally. At the same time, it functions and receives a certain amount of heat. After the vessel is thermally insulated. Despite this, gas continues to expand, but already adiabato (without heat exchange with the environment). At this time, its temperature decreases to the refrigerator indicators. At this point, the gas contacts with the refrigerator, as a result of which it gives it a certain amount of heat during isometric compression. Then the vessel is heat insulated again. At the same time, the gas is adiabatically compressed to the initial volume and state.

Varieties

Nowadays, there are many types of thermal engines that work according to various principles and on various fuel. All have their own efficiency. These include the following:

Internal combustion engine (piston), which is a mechanism where part of the chemical energy of the combusting fuel goes into mechanical energy. Such devices can be gas and liquid. There are 2- and 4-stroke engines. They may have a working cycle of continuous action. According to the method of preparation of a mixture of fuel, such engines are carburetor (with external mixture formation) and diesel (with internal). By type of energy converter, they are separated on piston, jet, turbine, combined. The efficiency of such machines does not exceed 0.5.

Stirling engine is a device in which the working fluid is in a closed space. It is a variety of external combustion engine. The principle of its action is based on the periodic cooling / heating of the body to produce energy due to changes in its volume. This is one of the most efficient engines.

Turbine (rotary) engine with external combustion of fuel. Such installations are most often found at thermal electric stations.

Turbine (rotary) DVS is used on thermal electric stations in peak mode. Not so much common as others.

The turbinenth engine at the expense of the screw creates some part of the thrust. The rest he gets at the expense of exhaust gases. Its design is a rotary engine on the shaft of which the air screw is planted.

Other types of thermal engines

Rocket, turboactive and which receive cravings due to the return of exhaust gases.

Solid-state engines are used as a fuel solid. When working it changes its volume, but a form. When operating the equipment, an extremely small temperature difference is used.

How can I increase the efficiency

Is it possible to increase the efficiency of the thermal engine? The answer must be sought in thermodynamics. It studies mutual transformations of different types of energy. It has been established that it is impossible to all existing mechanical and so on. At the same time, their transformation into thermal occurs without any restrictions. This is possible due to the fact that the nature of thermal energy is based on an unordered (chaotic) particle movement.

The stronger the body heats, the faster the components of its molecule will move. The movement of particles will be even more disorderly. Along with this, everyone knows that order can be easily turned into chaos, which is very difficult to streamline.

And useful formulas.

Tasks in physics on the efficiency of the thermal engine

Task for calculating the efficiency of the heat engine №1

Condition

Water weighing 175 g is heated on the alcohol. While the water was heated from T1 \u003d 15 to T2 \u003d 75 degrees Celsius, the mass of the alcohol decreased from 163 to 157 g. Calculate the efficiency of the installation.

Decision

The efficiency of the useful operation can be calculated as the ratio of useful work and the total amount of heat generated by the alcohol:

Useful work in this case is the equivalent of the amount of heat that went exclusively for heating. It can be calculated according to the well-known formula:

The total amount of heat is calculated, knowing the mass of burnt alcohol and its specific heat of combustion.

We substitute the values \u200b\u200band calculate:

Answer: 27%

Task for calculating the efficiency of the heat engine №2

Condition

The old engine made a job of 220.8 MJ, while spending 16 kilograms of gasoline. Calculate the engine efficiency.

Decision

We find the total amount of heat that produced the engine:

Or, multiplying by 100, we obtain the value of the efficiency in percent:

Answer: 30%.

Task for calculating the efficiency of the heat engine №3

Condition

The heat machine works on the carno cycle, with 80% of the heat obtained from the heater, is transmitted to the refrigerator. For one cycle, the working body receives 6.3 J heat from the heater. Find the work and efficiency of the cycle.

Decision

Efficiency of the perfect heat machine:

By condition:

Calculate first work and then efficiency:

Answer: twenty%; 1.26 J.

Task for calculating the efficiency of the heat engine №4

Condition

The diagram depicts a diesel engine cycle consisting of adiabat 1-2 and 3-4, isobara 2-3 and isoohra 4-1. Gas temperatures at points 1, 2, 3, 4 are t1, T2, T3, T4, respectively. Find the CCD cycle.

Decision

Let us analyze the cycle, and the efficiency will be calculated through the subordinate and allotted amount of heat. On adiabats, heat is not supplied and not allocated. On Isobara 2 - 3 heat is supplied, the volume increases and, accordingly, the temperature grows. On isoore, 4 - 1 heat is given, and the pressure and temperature fall.

Similarly:

We get the result:

Answer: See above.

The challenge for calculating the efficiency of the heat engine No. 5

Condition

The thermal car operating on the carboy cycle makes it possible for one cycle A \u003d 2.94 kJ and gives the cooler for one cycle the amount of heat Q2 \u003d 13.4 kJ. Find the CCD cycle.

Decision

We write a formula for efficiency:

Answer: 18%

Questions on the topic of thermal engines

Question 1. What is a heat engine?

Answer. The heat engine is a machine that makes work due to the energy coming to it in the process of heat transfer. The main parts of the thermal engine: heater, refrigerator and working body.

Question 2. Give examples of thermal motors.

Answer. The first thermal engines that have received widespread were steam machines. Examples of a modern heat engine can serve:

• rocket engine;
• aircraft engine;
• gas turbine.

Question 3. Can the engine efficiency be equal to one?

Answer. Not. The efficiency is always less than one (or less than 100%). The existence of an engine with an efficiency is equal to one contrary to the first beginning of thermodynamics.

The efficiency of real engines rarely exceeds 30%.

Question 4. What is kpd?

Answer. Efficiency (efficiency) - the ratio of the work that the engine performs to the amount of heat obtained from the heater.

Question 5. What is the specific heat combustion of fuel?

Answer. Specific heat combustion q. - The physical value that shows how much heat is released when combustion of fuel weighing 1 kg. When solving the Tasks of the efficiency, it is possible to determine the power of the engine n and the amount of fuel incinerated per unit of time.

Tasks and questions about the carno cycle

By affecting the theme of heat engines, it is impossible to leave the carno cycle aside - perhaps the most famous cycle of the heat machine in physics. We give additionally several tasks and questions to the carno cycle with the solution.

The cycle (or process) of carno is the perfect circular cycle consisting of two adiabat and two isotherms. Named so in honor of the French engineer Sadi Carno, who described this cycle in his scientific work "On the driving force of fire and about machines that can develop this power" (1894).

Task on the carno cycle №1

Condition

The ideal thermal car operating on the carboy cycle makes it possible for one cycle a \u003d 73.5 kJ. Heater temperature T1 \u003d 100 ° С, temperature of the refrigerator T2 \u003d 0 ° C. Find the efficiency of the cycle, the amount of heat obtained by the machine for one cycle from the heater, and the amount of heat released for one cycle of the refrigerator.

Decision

Calculate the CPD of the cycle:

On the other hand, to find the amount of heat obtained by the machine, we use the ratio:

The amount of heat, given to the refrigerator, will be equal to the difference in total heat and useful work:

Answer: 0.36; 204.1 kJ; 130.6 kJ.

The task of the carno cycle №2

Condition

The ideal thermal car operating in the carno cycle makes it possible for one cycle a \u003d 2.94 kJ and gives the amount of heat quality Q2 \u003d 13.4 kJ for one cycle. Find the CCD cycle.

Decision

Formula for efficiency cycle carno:

Here a - perfect work, and Q1 is the amount of heat that needed to make it. The amount of heat that the perfect car gives the refrigerator, equal to the difference of these two values. Knowing it, we find:

Answer: 17%.

Task on carno cycle №3

Condition

Picture carno cycle on the diagram and describe it

Decision

The carno cycle on the PV diagram is as follows:

• 1-2. Isothermal extension, the working body receives from the heater the amount of heat Q1;
• 2-3. Adiabatic expansion, heat is not supplied;
• 3-4. Isothermal compression, during which the heat is transferred to the refrigerator;
• 4-1. Adiabatic compression.

Answer: see above.

Question on the carno cycle №1

Word the first carno theorem

Answer. The first carno theorem states: the efficiency of the heat machine operating on the carno cycle depends only on the temperatures of the heater and the refrigerator, but does not depend on the machine device, nor from the type or properties of its working fluid.

Question on the carno cycle №2

Can the efficiency in a carno cycle to be 100%?

Answer. Not. The efficiency of the carno cycle will be 100% only if the temperature of the refrigerator is equal to the absolute zero, and this is not possible.

If you have any questions about the theme of thermal engines and the carno cycle, you can safely ask them in the comments. And if you need help in solving tasks or other examples and tasks, contact

« Physics - Grade 10 »

What is a thermodynamic system and which parameters is characterized by its state.
Word the first and second laws of thermodynamics.

It is the creation of the theory of thermal engines and led to the formulation of the second law of thermodynamics.

Internal energy reserves in the earth's crust and oceans can be considered practically unlimited. But to solve practical tasks, it is still not enough to have energy reserves. It is also necessary to be able to drive the machine to the factory and other machines at the expense of energy, the means of transport, tractors and other machines, rotate the rotors of electrical current generators, etc. Humanity needs engines - devices capable of doing work. Most of the engines on Earth are heat engines.

Heat engines - These are devices that convert the internal energy of fuel into mechanical work.

The principle of action of thermal motors.

In order for the engine to work, the pressure difference is needed on both sides of the engine piston or turbine blades. In all thermal motors, this pressure difference is achieved due to temperature increase. working body (Gas) for hundreds or thousands of degrees compared to the ambient temperature. Such an increase in temperature occurs when fuel combustion.

One of the main parts of the engine is a gas-filled vessel with a movable piston. All thermal engines are a working fluid that makes work when expanding. Denote the initial temperature of the working fluid (gas) through T 1. This temperature in steam turbines or machines acquires pairs in a steam boiler. In internal combustion engines and gas turbines, the temperature increase occurs when combustion of the fuel inside the engine itself. Temperature T 1 is called heater temperature.

The role of the refrigerator.

As the operation is performed, gas loses energy and is inevitably cooled to a certain temperature T 2, which is usually slightly higher than the ambient temperature. It is called temperature refrigerator. The refrigerator is the atmosphere or special devices for cooling and condensation of the spent steam - condencators. In the latter case, the temperature of the refrigerator can be slightly lower than the ambient temperature.

Thus, in the engine, the working body during expansion cannot give all its internal energy to performing work. Part of the heat is inevitably transmitted to the refrigerator (atmosphere) together with the exhaust ferry or exhaust gases of internal combustion and gas turbines.

This part of the internal fuel energy is lost. The heat engine makes work due to the internal energy of the working fluid. And in this process, heat transmission from more hot tel (heater) to a colder (refrigerator) occurs. The circuit diagram of the thermal engine is shown in Figure 13.13.

The engine's working body receives from the heater when combustion of fuel, the amount of heat of Q 1, performs work A "and transfers the amount of heat to the refrigerator Q 2.< Q 1 .

In order for the engine to work continuously, the working body must be returned to the initial state at which the temperature of the working fluid is equal to 1. From here it follows that the engine operation occurs in periodically repeated closed processes, or, as they say in the cycle.

Cycle - This is a number of processes, as a result of which the system returns to the initial state.

The efficiency (efficiency) coefficient of the heat engine.

The inability to complete the internal energy of gas into the operation of thermal motors is due to the irreversibility of processes in nature. If the heat could spontaneously return from the refrigerator to the heater, then the internal energy could be fully turned into a useful operation using any thermal engine. The second law of thermodynamics can be formulated as follows:

The second law of thermodynamics:
it is impossible to create an eternal engine of the second kind, which would completely turn the heat into mechanical work.

According to the law of energy conservation, the operation performed by the engine is equal to:

A "\u003d Q 1 - | Q 2 |, (13.15)

where Q 1 is the amount of heat obtained from the heater, A Q2 is the amount of heat, given to the refrigerator.

The efficiency of the useful action (efficiency) of the heat engine is called the ratio of the operation A "engine performed by the engine, to the amount of heat obtained from the heater:

Since all engines have a certain amount of heat transmitted to the refrigerator, then η< 1.

The maximum value of the efficiency of thermal motors.

The laws of thermodynamics make it possible to calculate the maximum possible efficiency of the heat engine operating with a heater having a temperature T 1 and a refrigerator with a temperature T 2, as well as to determine the ways to increase it.

For the first time, the maximum possible efficiency of the heat engine calculated the French engineer and Sadi Carno (1796-1832) in labor "Reflections on the driving force of fire and about cars that can develop this power" (1824).

Carno came up with the perfect thermal machine with perfect gas as a working body. The ideal heat machine carno works on a cycle consisting of two isotherms and two adiabat, and these processes are considered reversible (Fig. 13.14). At first, the gas vessel is in contact with the heater, the gas is isothermally expanding, making a positive work at a temperature of T 1, and it receives the amount of heat Q 1.

Then the vessel is thermally insulated, the gas continues to expand already adiabato, with its temperature drops to the temperature of the refrigerator T 2. After that, the gas is in contact with the refrigerator, during isothermal compression, it gives the refrigerator the amount of heat Q 2, compressing to the volume V 4< V 1 . Затем сосуд снова теплоизолируют, газ сжимается адиабатно до объёма V 1 и возвращается в первоначальное состояние. Для КПД этой машины было получено следующее выражение:

As follows from formula (13.17), the automobile efficiency of the car can directly proportional to the difference in absolute temperatures of the heater and the refrigerator.

The main value of this formula is that it contains the path to increase the efficiency, for this it is necessary to increase the temperature of the heater or lower the temperature of the refrigerator.

Any real heat machine operating with a heater having a temperature T 1 and a refrigerator with a temperature T 2 cannot have an efficiency exceeding the efficiency of the perfect heat machine: The processes of which consists of a cycle of a real heat machine are not reversible.

Formula (13.17) gives the theoretical limit for the maximum value of the efficiency of thermal motors. It shows that the thermal engine is the more efficient than the difference in the temperature of the heater and the refrigerator.

Only at a refrigerator temperature equal to the absolute zero, η \u003d 1. In addition, it was proved that the efficiency calculated by formula (13.17) does not depend on the working substance.

But the temperature of the refrigerator, the role of which usually plays the atmosphere, can practically be lower than the ambient temperature. You can increase the temperature of the heater. However, any material (solid body) has limited heat resistance or heat-resistance. When heated, it gradually loses its elastic properties, and at a sufficiently high temperature melts.

Now the main efforts of engineers are aimed at increasing the efficiency of the engines due to the decrease in the friction of their parts, the loss of fuel due to its incomplete combustion, etc.

For the steam turbine, the initial and final temperature temperatures are about this: T 1 - 800 K and T 2 - 300 K. At these temperatures, the maximum value of the efficiency of the efficiency is 62% (we note that the efficiency is usually measured as a percentage). The actual value of the efficiency due to the different kind of energy losses is approximately 40%. Maximum efficiency - about 44% - Diesel engines have.

Environmental protection.

It is difficult to imagine the modern world without heat engines. It is they who provide us with a comfortable life. Thermal motors lead traffic. About 80% of electricity, despite the presence of nuclear power plants, is produced using thermal motors.

However, during the operation of thermal engines, the inevitable environmental pollution occurs. This is the contradiction: on the one hand, humanity every year more and more energy is necessary, the bulk of which is obtained by combustion of fuel, on the other hand, the combustion processes are inevitably accompanied by environmental pollution.

When combustion of fuel, the oxygen content is reduced in the atmosphere. In addition, combustion products themselves form chemical compounds, harmful to living organisms. Pollution occurs not only on Earth, but also in the air, since any flight of the aircraft is accompanied by emissions of harmful impurities into the atmosphere.

One of the consequences of the engine work is the formation of carbon dioxide, which absorbs the infrared radiation of the earth's surface, which leads to an increase in the temperature of the atmosphere. This is the so-called greenhouse effect. Measurements show that the temperature of the atmosphere over the year increases by 0.05 ° C. Such a continuous increase in temperature can cause melting of ice, which, in turn, will lead to a change in the water level in the oceans, that is, to the flooding of continents.

We note another negative moment when using thermal motors. So, sometimes water from rivers and lakes is used to cool the engines. Heated water then returns back. The rise in temperature in reservoirs violates the natural equilibrium, this phenomenon is called thermal pollution.

For environmental protection, various cleaning filters are widely used, which prevents the emission of harmful substances into the atmosphere, the engine designs are improved. There is a continuous improvement of the fuel that gives less harmful substances during combustion, as well as its combustion technology. Alternative energy sources are actively developed using wind, solar radiation, kernel energy. Already produced electric vehicles and cars operating on solar energy.

Class: 10

Type of lesson: lesson studying a new material.

The purpose of the lesson: explain the principle of action of the thermal engine.

Tasks lesson:

Educational: introduce students with types of heat engines, develop the ability to determine the efficiency of heat engines, reveal the role and value of TD in modern civilization; To summarize and expand the knowledge of students on environmental issues.

Developing: develop attention and speech, improve the skills of working with the presentation.

Educational: to bring up a sense of responsibility for subsequent generations, in connection with which, consider the effect of the thermal engines to the environment.

Equipment: Computers for students, teacher's computer, multimedia projector, tests (in Excel), physics 7-11 library of electronic visual manuals. "Cyril and Methodius".

The theme of our lesson: "Heat engines". (Slide 1)

Today we will recall the types of thermal engines, consider the conditions for their effective work, talk about the problems of their massive use. (Slide 2)

Before proceeding to the study of the new material, I propose to check how you are ready for this.

Frontal survey:

- Give the formulation of the first law of thermodynamics. (Changing the internal energy of the system when switching it from one state to another equal to the amount of operation of the external strength and the amount of heat transmitted by the system. U \u003d a + Q)

- Can the gas be warm or cool without heat exchange with the environment? How does this happen? (With adiabatic processes.) (Slide 3)

- Write the first law of thermodynamics in the following cases: a) heat exchange between bodies in calorimeter; b) water heating on the alcohol; c) heating the body when hitting. ( but) A \u003d 0., Q \u003d 0, u \u003d 0; b) a \u003d 0, u \u003d q; c) q \u003d 0, u \u003d a)

- The figure shows a cycle performed by the ideal gas of a certain mass. Picture this cycle on the graphs P (T) and T (P). In which areas of the cycle gas allocates warmth and on what - absorbs?

(In areas 3-4 and 2-3, gas allocates a number of heat, and in areas 1-2 and 4-1 of heat absorbed by gas.) (Slide 4)

All physical phenomena and laws are applied in the daily life of a person. Internal energy stocks in the oceans and earthly crust can be considered practically unlimited. But it is not enough to have these reserves. It is necessary at the expense of energy to be able to drive the device capable of doing work. (Slide 5)

What is the source of energy? (Various types of fuel, wind energy, sun, tides and sings)

There are various types of machines that implement in their work the transformation of one type of energy into another.

The heat engine is a device that converts the internal energy of fuel into mechanical energy. (Slide 6)

Consider the device and the principle of the thermal engine. The heat machine works cyclically.

Any heat machine consists of a heater, a working fluid and a refrigerator. (Slide 7)

CPD closed cycle (slide 8)

Q 1 - the amount of heat obtained from heating Q 1\u003e Q 2

Q 2 - the amount of heat is given to the refrigerator Q 2

A / \u003d Q 1 - | Q 2 | - Work performed by the engine per cycle?< 1.

CLO Cycle Carno (slide 9)

T 1 - Heating temperature.

T 2 - the temperature of the refrigerator.

All major types of modern transport are mainly used thermal motors. On the railway transport until the middle of the XX century. The main engine was a steam machine. Now they mainly use diesel installations and electric locomotives. In terms of water transport, steam engines were also used, both internal combustion engines and powerful turbines for large vessels are used.

The use of thermal motors (mainly powerful steam turbines) on thermal power plants, where they lead the rotors of electric current generators in motion. About 80% of all electricity in our country is produced on thermal power plants.

Heat engines (steam turbines) are also installed on nuclear power plants. Gose turbines are widely used in rockets, in railway and road transport.

On vehicles use piston internal combustion engines with an external formation of a combustible mixture (carburetor engines) and engines to form a combustible mixture directly inside the cylinders (diesel engines).

In aviation, piston engines are installed on light aircraft, and on huge liners - turboprop and jet engines, which also belong to thermal motors. Jet engines are used on space rockets. (Slide 10)

(Showing video phrases of the turbojet engine.)

Consider in more detail the operation of the internal combustion engine. View video camera. (Slide 11)

The operation of four-stroke engine.
1 tact: inlet.
2 clock: compression.
3 clock: work move.
4 tact: release.
Device: cylinder, piston, crankshaft, 2 valves (intake and release), candle.
Dead dots - the extreme position of the piston.
Compare operational characteristics of thermal motors.

• Steam engine - 8%
• Steam turbine - 40%
• Gas turbine - 25-30%
• Internal combustion engine - 18-24%
• Diesel engine - 40-4%
• Jet engine - 25% (slide 112)

Heat engines and environmental protection (slide 13)

The steady increase in energy facilities is becoming increasingly distributing of the coded fire - leads to the fact that the amount of heat released becomes comparable to other components of the thermal balance in the atmosphere. This cannot but lead to an increase in the average temperature on Earth. Increase temperature can create a threat to the melting of glaciers and a catastrophic increase in the level of the world's ocean. But this does not exhaust the negative effects of the use of thermal motors. It grows the release into the atmosphere of microscopic particles - soot, ash, crushed fuel, which leads to an increase in the "greenhouse effect" due to an increase in the concentration of carbon dioxide for a long period of time. This leads to an increase in the temperature of the atmosphere.

Emitted toxic combustion products, the products of incomplete combustion of organic fuel - have a harmful effect on the flora and fauna. A special danger in this regard is cars, the number of which is growing threateningly, and the cleaning of exhaust gases is difficult.

All this puts a number of serious problems with society. (Slide 14)

It is necessary to increase the effectiveness of structures that impede the emission of harmful substances into the atmosphere; To achieve a more complete combustion of fuel in car engines, as well as an increase in energy efficiency, saving it at work and in everyday life.

Alternative engines:

• 1. Electric
• 2. Engines operating on the energy of the Sun and Wind (slide 15)

Ways to solve environmental problems:

Use alternative fuel.

Use alternative engines.

Environmental recovery.

Education of environmental culture. (Slide 16)

To all you have to go only in a year to hand over a single state exam. I suggest you solve several tasks from the part and demo-physics for 2009. Task you will find on desktops of your computers.

From the moment the first steam machine was built, over 240 years have passed. During this time, the heat machines have greatly changed the content of human life. It was the use of these machines that allowed humanity to step into space, reveal the secrets of the sea depths.

Estabs the estimates for work in the lesson.

Before leaving the class, please fill in the table.