Power (physics)
The performance as a physical quantity called the converted energy in a time period based on this period. Your character is the formula (of English power), its SI unit, the Watt with the unit symbol W.
In the physical-technical context, the term is used in different meanings performance:
- ( also called nominal output characteristics of a device or a system) or as an installed maximum power
- Than actual performance in an application the supplied power
- Within the meaning of the task output power.
The power consumption and beneficial for a specific application power output may vary considerably depending on the efficiency or waste heat.
- 4.1 Absorbed and emitted power 4.1.1 chillers
- 4.1.2 Heat Exchanger
Definitions
The performance is the ratio of work performed or for energy expended and the time taken:
In time-varying power, for example in a speaker or electrical power grid, there is an instantaneous power or instantaneous power resulting from the limit when the time interval approaches zero:
So as the differential quotient
Rather is measured work done in a time interval of length average power
This specification has particular importance when changes periodically and the period is.
Mechanical Performance
Translation
The simplest case, with the direction of movement parallel force is available at the Drawbar tractive, it is
With the power and speed.
Without this restriction the corresponding vectorial equation
In it, the angular dependence is taken into account by the scalar product, as in the article work (physics) is explained for " force times distance ".
Rotation
For the rotation against a torque M applies analogously
Wherein the angular velocity is parallel to the direction vector at an axis.
For a shaft with torque and speed, the shaft power is given to
Hydraulic
The hydraulic power by working volume is the product of pressure drop and flow rate.
Electrical power
In constant quantities, the electric power is converted into a component with the ohmic resistance is the product of voltage and electrical current
Wherein time-varying size and the power is defined as corresponding to the instantaneous value
Instead of this fluctuating size are preferred over defined averaging, used time-constant performance data for periodic AC quantities:
- Active power,
- Reactive power,
- Apparent power.
Performance information
Recorded and power output
The manufacturer of electrical devices to indicate the maximum wattage committed, ie the power that is taken from the maximum power supply ( mains, battery). This is always a larger value than the power delivery, so the power in that form that the user desires (eg, mechanical power, light output). The output power can be much lower, depending on the efficiency, ie after deduction of the energy loss in the conversion of electrical energy into the desired power. Heat losses, mechanical and other losses reduce the actual power output such as a drill or a vacuum cleaner.
In bulbs the light output in lumens is in addition to the consumption wattage also indicated. Due to their definition of the physiology of the human eye, it can not be directly compared with the electric power. Rather, the luminous efficacy in lumens per watt, the unit can be specified. Approximately an efficiency could be estimated by the radiation power ( 400 to 700 nm) divided by the power consumption in the visible spectral range. This would, for example, for light bulbs, a value of about five percent. However, the boundaries between the visible and the infrared or ultraviolet range are fluid, so that such efficiency would not be clearly defined. Moreover, they do not take account of the different spectral sensitivity of the eye.
In lasers, however, the power actually contained in the laser beam is specified. The electrical consumption ( power input ) of a laser beam source is according to the respective efficiency is always higher.
Household appliances such as an electric lawn mower, the electric power is taken from the outlet provided. The situation is different in electric motors of higher power. There is on the nameplate of the available mechanical power at the motor shaft are listed as well as the amount of money borrowed apparent power. With electric hand drills, the maximum taken from the mains in spindle standstill performance is specified - it has by no means so little to do with the delivered mechanical power. Vacuum cleaners the electrical power is specified, does not have to have much to do with the suction power. The (electrical) power of a heater is always equal to the heat emitted power.
Chillers
Cooling and freezing equipment and heat pumps transfer heat capacity of the cold to the warm side. They are driven by an electric motor which moves a pump. The power consumption of the motor is usually less than the heat output. Therefore, a heat pump heating provide, for example, 2.5 times the electrical power as heat output.
Heat exchanger
The thermal performance of heat exchangers is often proportional to the temperature difference. Also, heat sink and heat-dissipating casing possess this characteristic. Their performance is therefore often given as watts per Kelvin temperature difference (W / K).
Permanent and short-term power
The performance may be limited to a specified "KB xx min", ie short operating time xx minutes. Examples include blender, soldering guns or arc - welding equipment. You need to cool down after the maximum operating time. Similarly, the output per hour of the electric locomotives which can be delivered continuously over an hour.
Ovens with the performance data can identify the performance of the heat while the power due to the temperature control is much smaller later baking, etc..
Units
The performance is given in the International System of Units in watts. In addition to the CGS unit " ergs per second " are still more units in use. Some examples are listed in the table: