Thermal motors: principle of operation, device, scheme
Let's consider thermal engines, the principle of operationthese mechanisms. In the earth's crust and oceans, the reserves of internal energy can be considered unlimited. In order to solve practical problems, it is clearly not enough. The device and principle of operation of the heat engine must be known in order to drive lathes and vehicles. A person needs such devices that can do useful work.
Thermal engines, the principle of action of which we will consider, are the main ones on our planet. It is in them that the internal energy transforms into a mechanical form.
Features of a heat engine
What is the principle of the heat engine? Briefly it can be represented on a simple experiment. If you pour water into a test tube, close it with a cork, bring it to a boil, it will fly out. The reason for the jamming of the plug is that the steam performs internal work. The process is accompanied by the transformation of the internal energy of the vapor into a kinetic value for the plug. Thermal engines, the principle of operation of which is similar to the described experiment, differ in structure. Instead of a test tube, a metal cylinder is used. The plug is replaced by a piston that fits snugly against the walls moving along the cylinder.
The algorithm of action
What is the principle of the heat engine? Grade 10 considers this issue in physics lessons. Thermal machines the guys call the mechanisms where the transformation of the internal energy of fuel into a mechanical form is observed.
To make a useful work of the engine,a differential pressure is created on both sides of the piston or blades of a powerful turbine. To achieve this pressure difference, the temperature of the working fluid rises by thousands of degrees compared to its average in the environment. There is a similar increase in temperature during the combustion of fuel.
All modern thermal machines are distinguishedworking body. They are called gas, which makes useful work in the process of expansion. The initial temperature, designated T1, he acquires in the steam boiler machines or turbines. This is called the temperature of the heater. During the performance of work, a gradual loss of gas energy occurs. This leads to the inevitable cooling of the working fluid to a certain T2. The temperature should be lower than the ambient temperature, otherwise the gas pressure will have a lower value than the atmospheric pressure and the engine will not work.
The index T2 is called the temperature of the refrigerator. In its quality there is an atmosphere or a special device necessary for the condensation and cooling of the exhaust steam.
So, thermal engines, the principle of actionwhich is based on the expansion of the working body, can not give all the internal energy for the performance of work. In any case, some of the heat will be transferred to the atmosphere (refrigerator) along with the exhaust steam or exhaust gases of turbines or internal combustion engines.
Efficiency of thermal machines
What is the operating principle of a heat engine? The efficiency of a heat engine depends on the amount of useful work done by the gas. Taking into account the fact that it is impossible to completely turn internal energy into the work of a heat engine, it is possible to explain the irreversibility of natural processes and phenomena. In the event that there was a spontaneous return of heat to the heater from the refrigerator, the internal energy in full would be turned into useful work by means of a heat engine.
The coefficient of efficiency is calledthe ratio of the useful work done by the heat engine, to the amount of heat that is transferred to the refrigerator. In physics, it is customary to express this value as a percentage. This is the principle of the heat engine. Its scheme is clear and simple, accessible even to high school students. The laws of thermodynamics make it possible to calculate the maximum value of the efficiency.
The invention of a thermal machine
The first inventor of a machine using heat,became Sadi Carnot. He developed an ideal machine in which the ideal gas was the working body. In addition, the scientist was able to determine the efficiency index for such a device, using the temperatures of the refrigerator and heater.
Carnot was able to determine the relationship betweena real thermal machine operating on the basis of a heater, and a condenser, which is an air or a condenser. Due to the mathematical formula proposed by Carnot for his first ideal thermal machine, the maximum efficiency is determined. There is a direct connection between the temperature of the heater and the refrigerator.
In order for the machine to function fully,The temperature should not be less than its value in the ambient air. If desired, you can raise the temperature of the heater, not forgetting that each solid body has a certain heat resistance. As it heats up, it loses its elasticity, and when the melting point is reached it simply melts.
Internal combustion engine
It is a thermal machine, where in the formworking body use high-temperature gases, obtained during the combustion of various types of fuel inside the chamber. There are four cycles in the operation of the car engine. Among its constituent parts are the inlet and outlet valves, the combustion chamber, the piston, the cylinder, the spark plug, the connecting rod, and the flywheel.
Currently use different types ofautomobile engines: diesel, carburetor. Despite the differences in the fuel used, they have a similar operating principle. Due to the thermal energy generated during the combustion of gasoline, the conversion of thermal energy into another type takes place.
At the first stage there is a smooth movementvalve down, the process is due to the filling of the chamber with the working mixture. At the end of the first bar, the intake valve closes. Further the piston moves upwards, thus the compression of a working mix occurs. The appearance of a spark in a candle leads to the ignition of a combustible mixture. The pressure exerted by the vapor of air and gasoline on the piston leads to its spontaneous downward movement, so the clock is called the "working stroke". The crankshaft is driven into motion. At the fourth stage, the exhaust valve opens, the exhaust gases are expelled into the atmosphere.