What is efficiency?
Coefficient of efficiency (EFFICIENCY) - the term,perhaps, apply to every system and device. Even a person has EFFICIENCY, though, probably, there is no objective formula for finding it yet. In this article, we will describe in detail what the efficiency is and how it can be calculated for different systems.
Efficiency-determination
Efficiency is an indicator that characterizesthe effectiveness of a given system with respect to energy recycling or conversion. Efficiency is an immeasurable value and is represented either as a numerical value in the range from 0 to 1, or as a percentage.
The general formula
The efficiency is denoted by the symbol Ƞ.
The general mathematical formula for finding the 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 a useful output.
Coefficient of efficiency, unfortunately,is always less than one or equal to it, because, according to the law of conservation of energy, we can not get more work than energy is spent. In addition, efficiency, in fact, very rarely equals unity, since useful work is always accompanied by the presence of losses, for example, heating the mechanism.
Thermal engine efficiency
A thermal engine is a device that turnsthermal energy in the mechanical. In a heat engine, the operation is determined by the difference in 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 = Qn-Qx / Qn, where Qn is the amount of heat received from the heater, and Qx 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 source, T2 is the temperature of the cold source.
Efficiency of electric motor
An electric motor is a device thatconverts electrical energy into mechanical energy, so that the efficiency in this case is the efficiency factor of the device with respect to the conversion of electrical energy into mechanical energy. The formula for finding the efficiency of an electric motor is as follows:
- Ƞ = P2 / P1, where P1 is the supplied electrical power, P2 is the useful mechanical power generated by the motor.
Electric power is found as the product of the current and voltage of the system (P = UI), and the mechanical power is the ratio of the work to a unit of time (P = A / t)
Transformer efficiency
A transformer is a device thatconverts an alternating current of one voltage into an alternating current of another voltage while maintaining the frequency. In addition, transformers can also convert AC to DC.
The efficiency of the transformer is found by the formula:
- Ƞ = 1/1 + (P0 + PL * n2) / (P2 * n), where P0 is the idle speed loss, PL is the load loss, P2 is the active power given to the load, and n is the relative loading.
Efficiency or not efficiency?
It should be noted that in addition to the efficiency, there are a number ofindicators, which characterize the efficiency of energy processes, and sometimes we can meet descriptions of the type - efficiency of about 130%, but in this case it should be understood that the term is not applied correctly, and most likely the author or producer understands by this abbreviation a slightly different characteristic .
For example, heat pumps differ in thatthey can give more warmth than they expend. So, the refrigerating machine can remove more heat from the cooled object, than it is spent in the energy equivalent for the organization of tap. The efficiency index of a refrigerating machine is called the refrigeration coefficient, is denoted by the letter Ɛ and is determined by the formula: Ɛ = Qx / A, where Qx is the heat drawn from the cold end, A is the work spent on the tap process. However, sometimes the cooling coefficient is also called the efficiency of the refrigerating machine.
It is also interesting that the efficiency of boilers operating atorganic fuel, is usually calculated from the lowest heat of combustion, and it can be more than one. Nevertheless, it is still traditionally called efficiency. It is possible to determine the efficiency of the boiler at the highest calorific value, and then it will always be less than one, but in this case it will be inconvenient to compare the performance of the boilers with the data of other units.
Read also the article Laws of Thermodynamics.
