What is called the efficiency factor. The topic of efficiency and fuel efficiency

Physics is a science that studies processes occurring in nature. This science is very interesting and curious, because each of us wants to satisfy ourselves mentally by gaining knowledge and understanding of how and what works in our world. Physics, the laws of which have been deduced over centuries and by dozens of scientists, helps us with this task, and we should only rejoice and absorb the knowledge provided.

But at the same time, physics is a far from simple science, like, in fact, nature itself, but it would be very interesting to understand it. Today we will talk about the coefficient useful action. We will learn what efficiency is and why it is needed. Let's look at everything clearly and interestingly.

Explanation of the abbreviation - efficiency. However, even this interpretation may not be particularly clear the first time. This coefficient characterizes the efficiency of a system or any individual body, and more often, a mechanism. Efficiency is characterized by the output or conversion of energy.

This coefficient is applicable to almost everything that surrounds us, and even to ourselves, and in to a greater extent. After all, we do useful work all the time, but how often and how important it is is another question, and the term “efficiency” is used with it.

It is important to consider that this coefficient is an unlimited value, it usually represents either mathematical values, for example, 0 and 1, or, as is more often the case, as a percentage.

In physics, this coefficient is denoted by the letter Ƞ, or, as it is commonly called, Eta.

Useful work

When using any mechanisms or devices, we necessarily perform work. As a rule, it is always greater than what we need to complete the task. Based on these facts, two types of work are distinguished: this is expended, which is designated capital letter, A with a small z (Az), and useful - A with the letter p (Ap). For example, let's take this case: we have a task to lift a cobblestone with a certain mass by a certain height. In this case, work characterizes only overcoming the force of gravity, which, in turn, acts on the load.

In the case when any device other than the gravity of the cobblestone is used for lifting, it is also important to take into account gravity of the parts of this device. And besides all this, it is important to remember that while we win in strength, we will always lose along the way. All these facts lead to one conclusion that the work expended in any case will be more useful, Az > An, the question is how much more it is, because you can reduce this difference as much as possible and thereby increase the efficiency, ours or our device.

Useful work is the portion of expended work that we do using a mechanism. And efficiency is just that physical quantity, which shows what part is useful work of the total expended.

Result:

• The expended work Az is always greater than the useful work Ap.
• The greater the ratio of useful to expended, the higher the coefficient, and vice versa.
• Ap is found by multiplying the mass by the acceleration of gravity and the height of ascent.

There is a certain formula for finding efficiency. It goes like this: to find efficiency in physics, you need to divide the amount of energy by the work done by the system. That is, efficiency is the ratio of energy expended to work performed. From this we can draw a simple conclusion that the better and more efficient the system or body is, the less energy is spent on doing the work.

The formula itself looks short and very simple: it will equal A/Q. That is, Ƞ = A/Q. This brief formula captures the elements we need for the calculation. That is, A in this case is the used energy that is consumed by the system during operation, and capital letter Q, in turn, will be the expended A, or again the expended energy.

Ideally, the efficiency is equal to unity. But, as usually happens, he is smaller than her. This happens because of physics and because, of course, the law of conservation of energy.

The thing is that the law of conservation of energy suggests that more A cannot be obtained than energy received. And even this coefficient will be equal to one extremely rarely, since energy is always wasted. And work is accompanied by losses: for example, in an engine, the loss lies in its excessive heating.

So, the efficiency formula:

Ƞ=A/Q, Where

• A is the useful work the system performs.
• Q is the energy consumed by the system.

Application in various fields of physics

It is noteworthy that efficiency does not exist as a neutral concept, each process has its own efficiency, it is not a friction force, it cannot exist on its own.

Let's look at a few examples of processes with efficiency.

For example, let's take an electric motor. The job of an electric motor is to convert electrical energy into mechanical energy. In this case, the coefficient will be the efficiency of the engine in terms of converting electrical energy into mechanical energy. There is also a formula for this case, and it looks like this: Ƞ=P2/P1. Here P1 is the power in the general version, and P2 is the useful power that the engine itself produces.

It is not difficult to guess that the structure of the coefficient formula is always preserved; only the data that needs to be substituted in it changes. They depend on the specific case, if it is an engine, as in the case above, then it is necessary to operate with the power expended, if it is a job, then the initial formula will be different.

Now we know the definition of efficiency and we have an idea about it physical concept, as well as about its individual elements and nuances. Physics is one of the largest sciences, but it can be broken down into small pieces to understand it. Today we examined one of these pieces.

Video

This video will help you understand what efficiency is.

Didn't get an answer to your question? Suggest a topic to the authors.

Efficiency factor (efficiency) is a term that can be applied to, perhaps, every system and device. Even humans have efficiency, although there is probably no objective formula for finding it yet. In this article we will explain in detail what efficiency is and how it can be calculated for various systems.

Efficiency definition

Efficiency is an indicator that characterizes the effectiveness of a system in terms of energy output or conversion. Efficiency is an immeasurable quantity and is represented either as a numerical value in the range from 0 to 1, or as a percentage.

General formula

Efficiency is indicated by the symbol Ƞ.

The general mathematical formula for finding efficiency is written as follows:

Ƞ=A/Q, where A is the useful energy/work performed by the system, and Q is the energy consumed by this system to organize the process of obtaining useful output.

The efficiency factor, unfortunately, is always less than or equal to unity, since, according to the law of conservation of energy, we cannot obtain more work than the energy expended. In addition, the efficiency, in fact, extremely rarely equals unity, since useful work is always accompanied by the presence of losses, for example, for heating the mechanism.

Heat engine efficiency

A heat engine is a device that converts thermal energy to mechanical. In a heat engine, work is determined by the difference between the amount of heat received from the heater and the amount of heat given to the cooler, and therefore the efficiency is determined by the formula:

• Ƞ=Qн-Qх/Qн, where Qн is the amount of heat received from the heater, and Qх is the amount of heat given to the cooler.

It is believed that the highest efficiency is provided by engines operating on the Carnot cycle. In this case, the efficiency is determined by the formula:

• Ƞ=T1-T2/T1, where T1 is the temperature of the hot spring, T2 is the temperature of the cold spring.

Electric motor efficiency

An electric motor is a device that converts electrical energy into mechanical energy, so efficiency in this case is the efficiency ratio of the device in terms of conversion electrical energy to mechanical. The formula for finding the efficiency of an electric motor looks like this:

• Ƞ=P2/P1, where P1 is the supplied electrical power, P2 is the useful mechanical power generated by the engine.

Electrical power is found as the product of system current and voltage (P=UI), and mechanical power as the ratio of work per unit time (P=A/t)

Transformer efficiency

A transformer is a device that converts alternating current of one voltage to alternating current of another voltage while maintaining the frequency. In addition, transformers can also convert alternating current into direct current.

The efficiency of the transformer is found by the formula:

• Ƞ=1/1+(P0+PL*n2)/(P2*n), where P0 is the no-load loss, PL is the load loss, P2 is the active power supplied to the load, n is the relative degree of load.

Efficiency or not efficiency?

It is worth noting that in addition to efficiency, there are a number of indicators that characterize the efficiency of energy processes, and sometimes we can come across descriptions like - efficiency of the order of 130%, however in this case we need to understand that the term is not used entirely correctly, and, most likely, the author or the manufacturer understands this abbreviation to mean a slightly different characteristic.

For example, heat pumps differ in that they can give off more heat than they consume. Thus, a refrigeration machine can remove more heat from the object being cooled than was expended in energy equivalent to organize the removal. The efficiency indicator of a refrigeration machine is called the refrigeration coefficient, denoted by the letter Ɛ and determined by the formula: Ɛ=Qx/A, where Qx is the heat removed from the cold end, A is the work expended on the removal process. However, sometimes the refrigeration coefficient is also called the efficiency of the refrigeration machine.

It is also interesting that the efficiency of boilers operating on organic fuel, is usually calculated based on the lower calorific value, but it can be greater than unity. However, it is still traditionally called efficiency. It is possible to determine the efficiency of a boiler by the higher calorific value, and then it will always be less than unity, but in this case it will be inconvenient to compare the performance of boilers with data from other installations.

Content:

Each system or device has a certain coefficient of performance (efficiency). This indicator characterizes the efficiency of their work in releasing or converting any type of energy. In terms of its value, efficiency is an immeasurable quantity, represented in the form numerical value ranging from 0 to 1, or as a percentage. This characteristic fully applies to all types electric motors.

Efficiency characteristics in electric motors

Electric motors belong to the category of devices that convert electrical energy into mechanical energy. The efficiency of these devices determines their effectiveness in performing the main function.

How to find engine efficiency? The formula for electric motor efficiency looks like this: ƞ = P2/P1. In this formula, P1 is the electrical power supplied and P2 is the useful mechanical power produced by the engine. The value of electrical power (P) is determined by the formula P = UI, and mechanical power - P = A/t, as the ratio of work per unit time.

The efficiency factor must be taken into account when choosing an electric motor. Great value have efficiency losses associated with reactive currents, power reduction, engine heating and other negative factors.

The conversion of electrical energy into mechanical energy is accompanied by a gradual loss of power. Loss of efficiency is most often associated with the release of heat when the electric motor heats up during operation. The causes of losses can be magnetic, electrical and mechanical, arising under the influence of friction. Therefore, the best example is a situation where 1000 rubles worth of electrical energy was consumed, but only 700-800 rubles worth of useful work was produced. Thus, the efficiency in this case will be 70-80%, and the entire difference is converted into thermal energy, which heats the engine.

To cool electric motors, fans are used to drive air through special gaps. In accordance with established standards, A-class engines can heat up to 85-90 0 C, B-class - up to 110 0 C. If the engine temperature exceeds the established standards, this indicates a possible imminent.

Depending on the load, the efficiency of the electric motor can change its value:

• For idle speed - 0;
• At 25% load - 0.83;
• At 50% load - 0.87;
• At 75% load - 0.88;
• At full 100% load, the efficiency is 0.87.

One of the reasons for a decrease in the efficiency of an electric motor may be current asymmetry, when a different voltage appears on each of the three phases. For example, if in the 1st phase there is 410 V, in the 2nd - 402 V, in the 3rd - 288 V, then the average voltage value will be (410 + 402 + 388) / 3 = 400 V. Voltage asymmetry will have value: 410 - 388 = 22 volts. Thus, the efficiency loss for this reason will be 22/400 x 100 = 5%.

Decrease in efficiency and total losses in the electric motor

There are many negative factors, under the influence of which the amount of total losses in electric motors is added up. There are special techniques that allow you to determine them in advance. For example, you can determine the presence of a gap through which power is partially supplied from the network to the stator, and then to the rotor.

The power losses that occur in the starter itself consist of several components. First of all, these are losses associated with partial magnetization reversal of the stator core. Steel elements have a negligible impact and are practically not taken into account. This is due to the stator rotation speed, which significantly exceeds the speed magnetic flux. In this case, the rotor must rotate in strict accordance with the declared technical characteristics.

Meaning mechanical power rotor shaft lower than electromagnetic power. The difference is the amount of losses occurring in the winding. Mechanical losses include friction in bearings and brushes, as well as the effect of air barriers on rotating parts.

Asynchronous electric motors are characterized by the presence of additional losses due to the presence of teeth in the stator and rotor. In addition, vortex flows may appear in individual engine components. All these factors together reduce the efficiency by approximately 0.5% of the rated power of the unit.

When calculating possible losses, the engine efficiency formula is also used, which allows one to calculate the reduction in this parameter. First of all, the total power losses, which are directly related to the engine load, are taken into account. As the load increases, losses proportionally increase and efficiency decreases.

The designs of asynchronous electric motors take into account all possible losses in the presence of maximum loads. Therefore, the efficiency range of these devices is quite wide and ranges from 80 to 90%. In high-power engines this figure can reach 90-96%.

Modern realities require the widespread use of heat engines. Numerous attempts to replace them with electric motors have so far failed. Problems associated with the accumulation of electricity in autonomous systems are difficult to solve.

The problems of manufacturing technology for electric power batteries, taking into account their long-term use, are still relevant. The speed characteristics of electric vehicles are far from those of cars with internal combustion engines.

The first steps to create hybrid engines can significantly reduce harmful emissions in megacities, solving environmental problems.

A little history

The possibility of converting steam energy into motion energy was known in ancient times. 130 BC: The philosopher Heron of Alexandria presented a steam toy - aeolipile - to the audience. The sphere filled with steam began to rotate under the influence of the jets emanating from it. This prototype of modern steam turbines was not used in those days.

For many years and centuries, the philosopher's developments were considered just a fun toy. In 1629, the Italian D. Branchi created an active turbine. The steam drove a disk equipped with blades.

From that moment on, the rapid development of steam engines began.

Heat engine

The conversion of fuel into the energy of movement of machine parts and mechanisms is used in heat engines.

The main parts of the machines: heater (system for obtaining energy from the outside), working fluid (performs a useful action), refrigerator.

The heater is designed to ensure that the working fluid accumulates a sufficient supply internal energy to do useful work. The refrigerator removes excess energy.

The main characteristic of efficiency is called the efficiency of heat engines. This value shows how much of the energy spent on heating is spent on doing useful work. The higher the efficiency, the more profitable the operation of the machine, but this value cannot exceed 100%.

Efficiency calculation

Let the heater acquire from the outside energy equal to Q 1 . The working fluid performed work A, while the energy given to the refrigerator amounted to Q 2.

Based on the definition, we calculate the efficiency value:

η= A / Q 1 . Let's take into account that A = Q 1 - Q 2.

Hence, the efficiency of the heat engine, the formula of which is η = (Q 1 - Q 2) / Q 1 = 1 - Q 2 / Q 1, allows us to draw the following conclusions:

• Efficiency cannot exceed 1 (or 100%);
• to maximize this value, it is necessary either to increase the energy received from the heater or to decrease the energy given to the refrigerator;
• increasing the heater energy is achieved by changing the quality of the fuel;
• reducing the energy given to the refrigerator allows you to achieve design features engines.

Ideal heat engine

Is it possible to create an engine whose efficiency would be maximum (ideally equal to 100%)? The French theoretical physicist and talented engineer Sadi Carnot tried to find the answer to this question. In 1824, his theoretical calculations about processes occurring in gases were made public.

The main idea inherent in the ideal machine can be considered the implementation of reversible processes with ideal gas. We start by expanding the gas isothermally at temperature T 1 . The amount of heat required for this is Q 1. Afterwards, the gas expands without heat exchange. Having reached the temperature T 2, the gas compresses isothermally, transferring energy Q 2 to the refrigerator. The gas returns to its original state adiabatically.

Ideal efficiency heat engine When accurately calculated, Carnot is equal to the ratio of the temperature difference between the heating and cooling devices to the temperature of the heater. It looks like this: η=(T 1 - T 2)/ T 1.

The possible efficiency of a heat engine, the formula of which is: η = 1 - T 2 / T 1, depends only on the temperatures of the heater and cooler and cannot be more than 100%.

Moreover, this relationship allows us to prove that the efficiency of heat engines can be equal to unity only when the refrigerator reaches temperatures. As is known, this value is unattainable.

Carnot's theoretical calculations make it possible to determine the maximum efficiency of a heat engine of any design.

The theorem proved by Carnot is as follows. Under no circumstances can an arbitrary heat engine have an efficiency greater than the same efficiency value of an ideal heat engine.

Example of problem solving

Example 1. What is the efficiency of an ideal heat engine if the heater temperature is 800 o C and the refrigerator temperature is 500 o C lower?

T 1 = 800 o C = 1073 K, ∆T = 500 o C = 500 K, η - ?

By definition: η=(T 1 - T 2)/ T 1.

We are not given the temperature of the refrigerator, but ∆T= (T 1 - T 2), hence:

η= ∆T / T 1 = 500 K/1073 K = 0.46.

Answer: Efficiency = 46%.

Example 2. Determine the efficiency of an ideal heat engine if, due to the acquired one kilojoule of heater energy, useful work of 650 J is performed. What is the temperature of the heater of the heat engine if the cooler temperature is 400 K?

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

In this problem we're talking about about a thermal installation, the efficiency of which can be calculated using the formula:

To determine the heater temperature, we use the formula for the efficiency of an ideal heat engine:

η = (T 1 - T 2)/ T 1 = 1 - T 2 / T 1.

After performing mathematical transformations, we get:

T 1 = T 2 /(1- η).

T 1 = T 2 /(1- A / Q 1).

Let's calculate:

η= 650 J/ 1000 J = 0.65.

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

Answer: η= 65%, T 1 = 1142.8 K.

Real conditions

An ideal heat engine is designed with ideal processes in mind. Work is performed only in isothermal processes, its value is determined as the area, limited by schedule Carnot cycle.

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

Efficiency of heat engines created in real conditions, differ significantly from the efficiency of ideal engines. Note that the processes in real engines occur so quickly that the variation in the internal thermal energy of the working substance in the process of changing its volume cannot be compensated by the influx of heat from the heater and transfer to the refrigerator.

Other heat engines

Real engines operate on different cycles:

• Otto cycle: a process with a constant volume changes adiabatically, creating a closed cycle;
• Diesel cycle: isobar, adiabatic, isochore, adiabatic;
• the process occurring at constant pressure is replaced by an adiabatic one, closing the cycle.

Create equilibrium processes in real engines (to bring them closer to ideal ones) under conditions modern technology not possible. The efficiency of heat engines is much lower, even taking into account the same temperature conditions, as in an ideal thermal installation.

But the role of the efficiency calculation formula should not be reduced, since it is precisely this that becomes the starting point in the process of working to increase the efficiency of real engines.

Ways to change efficiency

When comparing ideal and real heat engines, it is worth noting that the temperature of the refrigerator of the latter cannot be any. Usually the atmosphere is considered a refrigerator. The temperature of the atmosphere can only be accepted in approximate calculations. Experience shows that the temperature of the coolant is equal to the temperature of the exhaust gases in the engines, as is the case in internal combustion engines (abbreviated as ICE).

ICE is the most common heat engine in our world. The efficiency of the heat engine in this case depends on the temperature created by the burning fuel. A significant difference between internal combustion engines and steam engines is the merging of the functions of the heater and the working fluid of the device in the air-fuel mixture. As the mixture burns, it creates pressure on the moving parts of the engine.

An increase in the temperature of the working gases is achieved, significantly changing the properties of the fuel. Unfortunately, this cannot be done indefinitely. Any material from which the combustion chamber of an engine is made has its own melting point. The heat resistance of such materials is the main characteristic of the engine, as well as the ability to significantly affect efficiency.

Motor efficiency values

If we consider the temperature of the working steam at the inlet of which is 800 K, and the exhaust gas - 300 K, then the efficiency of this machine is 62%. In reality, this value does not exceed 40%. This decrease occurs due to heat losses when heating the turbine casing.

The highest value of internal combustion does not exceed 44%. Increasing this value is a matter of the near future. Changing the properties of materials and fuel is a problem that the best minds of humanity are working on.

Not a single action performed occurs without losses - they always exist. The result obtained is always less than the effort that has to be expended to achieve it. The coefficient of performance (efficiency) indicates how large the losses are when performing work.

What is hidden behind this abbreviation? In essence, this is the efficiency coefficient of the mechanism or indicator rational use energy. The efficiency value does not have any units of measurement; it is expressed as a percentage. This coefficient is determined as the ratio of the useful work of the device to the work expended on its operation. To calculate Efficiency formula The calculation will look like this:

Efficiency =100* (useful work done/work expended)

Various devices use to calculate this ratio. different meanings. For electric motors, efficiency will look like the ratio of useful work performed to electrical energy received from the network. For will be defined as the ratio of the useful work performed to the amount of heat expended.

For determination of efficiency It is necessary that everyone is different and the work is expressed in the same units. It will then be possible to compare any objects, such as electricity generators and biological objects, in terms of efficiency.

As already noted, due to inevitable losses during the operation of mechanisms, the efficiency factor is always less than 1. Thus, the efficiency of thermal stations reaches 90%, the efficiency of internal combustion engines is less than 30%, and the efficiency of an electric transformer is 98%. The concept of efficiency can be applied both to the mechanism as a whole and to its individual components. At overall assessment efficiency of the mechanism as a whole (its efficiency) is taken as the product of the efficiency of individual components this device.

Problem effective use fuel did not appear today. With the continuous increase in the cost of energy resources, the issue of increasing the efficiency of mechanisms turns from a purely theoretical into a practical issue. If the efficiency of a regular car does not exceed 30%, then we simply throw away 70% of our money spent on refueling the car.

Consideration of the efficiency of the internal combustion engine (ICE) shows that losses occur at all stages of its operation. Thus, only 75% of the incoming fuel is burned in the engine cylinders, and 25% is released into the atmosphere. Of all the burned fuel, only 30-35% of the released heat is used to perform useful work; the rest of the heat is either lost in the exhaust gases or remains in the car’s cooling system. Of the received power, about 80% is used for useful work; the rest of the power is spent on overcoming friction forces and is used auxiliary mechanisms car.

Even on this simple example analysis of the efficiency of the mechanism allows us to determine the directions in which work should be carried out to reduce losses. Thus, one of the priority areas is to ensure complete combustion of fuel. This is achieved by additional atomization of fuel and increased pressure, which is why engines with direct injection and turbocharging are becoming so popular. The heat removed from the engine is used to heat the fuel for better vaporization, and mechanical losses are reduced through the use of modern grades

Here we have considered such a concept, as described, what it is and what it affects. Using the example of an internal combustion engine, the efficiency of its operation is considered and directions and ways to increase the capabilities of this device, and, consequently, efficiency are determined.