What is efficiency? Concept, definition, application

Today we will tell you what efficiency (efficiency factor) is, how to calculate it, and where this concept is applied.

Man and machine

What unites a washing machine and a cannery? The desire of a person to relieve himself of the need to do everything on his own. Before the invention of the steam engine, people had only their muscles at their disposal. They did everything themselves: they plowed, sowed, cooked, caught fish, wove flax. To ensure survival during the long winter, each member of the peasant family worked daylight hours from the age of two until his death. The youngest children looked after the animals and were helping (bring, tell, call, take) the adults. The girl was first put behind a spinning wheel at the age of five! Even deep old people cut spoons, and the most elderly and infirm grandmothers sat at looms and spinning wheels, if their eyesight allowed. They had no time to think about what stars are and why they shine. People got tired: every day they had to go and work, regardless of the state of health, pain and morale. Naturally, a person wanted to find assistants who would at least slightly relieve his overworked shoulders.

funny and strange

The most advanced technology in those days was the horse and the mill wheel. But they did only two or three times more work than a human. But the first inventors began to come up with devices that looked very strange. In the movie "The Story of Eternal Love", Leonardo da Vinci attached small boats to his feet to walk on water. This led to several funny incidents when the scientist plunged into the lake with his clothes on. Although this episode is just an invention of the screenwriter, such inventions certainly looked like that - comical and funny.

19th century: iron and coal

But in the middle of the 19th century, everything changed. Scientists have realized the pressure force of expanding steam. The most important goods of that time were iron for the production of boilers and coal for heating water in them. Scientists of that time had to understand what efficiency is in steam and gas physics, and how to increase it.

The formula for the coefficient in the general case is:

Work and warmth

Efficiency (abbreviated efficiency) is a dimensionless quantity. It is defined as a percentage and is calculated as the ratio of energy expended to useful work. The latter term is often used by mothers of negligent teenagers when they force them to do something around the house. But in fact, this is the real result of the effort expended. That is, if the efficiency of the machine is 20%, then it only converts one-fifth of the energy received into action. Now, when buying a car, the reader should not have a question about what engine efficiency is.

If the coefficient is calculated as a percentage, then the formula is:

η - efficiency, A - useful work, Q - expended energy.

Loss and reality

Surely all these arguments cause bewilderment. Why not invent a car that can use more fuel energy? Alas, the real world is not like that. At school, children solve problems in which there is no friction, all systems are closed, and the radiation is strictly monochromatic. Real engineers at manufacturing plants are forced to take into account the presence of all these factors. Consider, for example, what this coefficient is and what it consists of.

The formula in this case looks like this:

η \u003d (Q 1 -Q 2) / Q 1

In this case, Q 1 is the amount of heat that the engine received from heating, and Q 2 is the amount of heat that it gave to the environment (in the general case, this is called a refrigerator).

The fuel heats up and expands, the force pushes the piston, which drives the rotary element. But the fuel is contained in some vessel. When heated, it transfers heat to the walls of the vessel. This leads to energy losses. In order for the piston to descend, the gas must be cooled. To do this, part of it is released into the environment. And it would be good if the gas gave all the heat to useful work. But, alas, it cools very slowly, so hot steam comes out. Part of the energy is spent on heating the air. The piston moves in a hollow metal cylinder. Its edges fit snugly against the walls; when moving, friction forces come into play. The piston heats the hollow cylinder, which also leads to a loss of energy. The translational movement of the rod up and down is transmitted to a torque through a series of joints that rub against each other and heat up, that is, part of the primary energy is also spent on this.

Of course, in factory machines, all surfaces are polished to the atomic level, all metals are strong and have the lowest thermal conductivity, and piston oil has the best properties. But in any engine, the energy of gasoline goes to heat parts, air and friction.

Saucepan and cauldron

Now we propose to understand what the efficiency of the boiler is, and what it consists of. Any housewife knows: if you leave water to boil in a saucepan under a closed lid, then either water will drip onto the stove, or the lid will “dance”. Any modern boiler is arranged in much the same way:

• heat heats a closed container full of water;
• water becomes superheated steam;
• when expanding, the gas-water mixture rotates turbines or moves pistons.

Just like in an engine, energy is lost to heat the boiler, pipes and friction of all joints, so no mechanism can have an efficiency equal to 100%.

The formula for machines that operate on the Carnot cycle looks like the general formula for a heat engine, only instead of the amount of heat - temperature.

η=(T 1 -T 2)/T 1 .

Space station

And if you put the mechanism in space? Free solar energy is available 24 hours a day, cooling of any gas is possible literally to 0 degrees Kelvin almost instantly. Maybe in space the efficiency of production would be higher? The answer is ambiguous: yes and no. All these factors could indeed significantly improve the transfer of energy to useful work. But delivering even a thousand tons to the desired height is still incredibly expensive. Even if such a factory operates for five hundred years, it will not pay back the cost of raising the equipment, which is why science fiction writers are so actively exploiting the idea of ​​a space elevator - this would greatly simplify the task and make it commercially profitable to transfer factories into space.