Today we will tell you what efficiency is (efficiency), how to calculate it, and where this concept is applied.
Man and mechanism
What combines 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: plowed, sowed, cooked, hunted fish, weaved flax. To ensure long winter survival, each member of a peasant family worked daylight hours from two years until his death. The youngest children looked after the animals and were on hand (bring, say, call, take) in adults. The girl was first put behind a spinning wheel at the age of five! Even deep old men cut spoons and weaved bast shoes, and the oldest and weakest grandmothers sat behind looms and spinning wheels, if vision allowed. They had no time to think about what stars are and why they shine. People got tired: every day I had to go and work, regardless of my state of health, pain and morale. Naturally, the man wanted to find assistants who would at least slightly relieve his strained shoulders.
Funny and weird
The most advanced technology in those days was the horse and the mill wheel. But they did only two to three times more work than a man. But here the first inventors began to come up with devices that looked very strange. In 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 plopped down into the lake right in his clothes. Although this episode is just a fiction of the scriptwriter, for sure, such inventions looked so - comical and funny.
Century XIX: iron and coal
But in the middle of the XIX 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 needed to understand what efficiency is in the physics of steam and gas, and how to increase it.
The formula for the coefficient in the general case is as follows:
Ξ· = A / Q
Ξ· - efficiency, A - useful work, Q - energy expended.
Work and heat
Coefficient of performance (abbreviated as efficiency) is a dimensionless quantity. It is determined 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 adolescents when they are forced to do something at home. But in fact, this is the real result of the effort. That is, if the efficiency of the machine is 20%, then it turns only one fifth of the energy received into action. Now, when buying a car, the reader should not have a question what is engine efficiency.
If the coefficient is calculated as a percentage, then the formula is as follows:
Ξ· = 100% * (A / Q)
Ξ· - efficiency, A - useful work, Q - energy expended.
Loss and reality
Surely all these arguments are puzzling. 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 consider the presence of all these factors. Consider, for example, what is the efficiency of a heat engine, and what this coefficient is made up of.
The formula in this case looks like this:
Ξ· = (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 rotational element. But the fuel is contained in some kind of vessel. When heated, it transfers heat to the walls of the vessel. This leads to energy loss. To lower the piston, the gas must be cooled. For this, part of it is released into the environment. And it would be good if all the heat the gas gave to useful work. But, alas, it cools very slowly, so hot steam comes out. Part of the energy is spent to heat 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 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 an atomic level, all metals are durable and have the lowest thermal conductivity, and piston lubrication oil has the best properties. But in any engine, the energy of gasoline is used to heat parts, air and friction.
Pan and Cauldron
Now we offer to understand what the efficiency of the boiler is, and what it consists of. Any housewife knows: if you leave the water to boil in a pan under a closed lid, then either the water will drip onto the stove, or the lid will βdanceβ. Any modern boiler is designed in approximately the same way:
- heat heats a closed container full of water;
- water becomes superheated steam;
- during expansion, the gas-water mixture rotates the turbines or moves the pistons.
As well as in the engine, energy losses are caused by heating the boiler, pipes and friction of all joints, therefore, no mechanism can have an efficiency equal to 100%.
The formula for machines that operate on the Carnot cycle looks like a general formula for a heat engine, but instead of the amount of heat - temperature.
Ξ· = (T 1 -T 2 ) / T 1 .
Space station
And if you put the mechanism in space? Free energy of the Sun is available 24 hours a day, cooling of any gas is possible literally to 0 about Kelvin almost instantly. Maybe in space production efficiency 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 at the right height even a thousand tons is incredibly expensive so far. Even if such a factory works for five hundred years, it will not pay back the costs of raising equipment, which is why science fiction authors are so actively exploiting the idea of ββa space elevator - this would greatly simplify the task and make the transfer of factories into space commercially viable.