Radiator
Overview
 
Radiators are heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...

s used to transfer thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

 from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

. The radiator is always a source of heat to its environment, although this may be for either the purpose of heating this environment, or for cooling the fluid or coolant
Coolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...

 supplied to it, as for engine cooling.

The heating radiator
Radiator (heating)
Radiators and convectors are heat exchangers designed to transfer thermal energy from one medium to another for the purpose of space heating. The heating radiator was invented by Franz San Galli, a Prussian-born Russian businessman living in St. Petersburg, between 1855–1857.- Radiation vs...

 was invented by Franz San Galli
Franz San Galli
Franz San Galli was a Russian businessman who invented the radiator, which significantly contributed to modern central heating systems. Born in Stettin , he was mostly of Italian and German descent. He spent most of his life in St...

, a Polish-born Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n businessman living in St.
Encyclopedia
Radiators are heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...

s used to transfer thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

 from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

. The radiator is always a source of heat to its environment, although this may be for either the purpose of heating this environment, or for cooling the fluid or coolant
Coolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...

 supplied to it, as for engine cooling.

The heating radiator
Radiator (heating)
Radiators and convectors are heat exchangers designed to transfer thermal energy from one medium to another for the purpose of space heating. The heating radiator was invented by Franz San Galli, a Prussian-born Russian businessman living in St. Petersburg, between 1855–1857.- Radiation vs...

 was invented by Franz San Galli
Franz San Galli
Franz San Galli was a Russian businessman who invented the radiator, which significantly contributed to modern central heating systems. Born in Stettin , he was mostly of Italian and German descent. He spent most of his life in St...

, a Polish-born Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n businessman living in St. Petersburg, between 1855–1857.

Radiation and convection

One might expect the term "radiator" to apply to devices that transfer heat primarily by thermal radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....

 (see: infrared heating), while a device which relied primarily on natural or forced convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

 would be called a "convector". In practice, the term "radiator" refers to any of a number of devices in which a liquid circulates through exposed pipes (often with fins or other means of increasing surface area), notwithstanding that such devices tend to transfer heat mainly by convection and might logically be called convectors. The term "convector" refers to a class of devices in which the source of heat is not directly exposed.

Heating

Radiators are commonly used to heat buildings. In a central heating system, hot water or sometimes steam is generated in a central boiler, and circulated by pumps through radiators within the building. There are two types: Single-pipe and double-pipe. The single-pipe radiators work with steam, while the double-pipe radiators work with steam or hot water.

Engine cooling

Radiators are used for cooling internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

s, chiefly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...

s, stationary generating plants or any similar use of such an engine.

They operate by passing a liquid coolant through the engine block, where it is heated, then through the radiator itself where it loses this heat to the atmosphere. This coolant is usually water-based, but may also be oil. It is usual for the coolant flow to be pumped.

To cool down the engine, coolant heated from flowing through the engine is fed into the header of the radiator via the inlet and then cools down as it circulates through the tubes to the opposite header and cold coolant exits back into the engine via the outlet, and the cycle is repeated. As it circulates through the tubes, the coolant transfers its heat to the tubes which, in turn, transfer the heat to the fins that are lodged between each row of tubes. The fins then radiate the heat transferred by the tubes to the surrounding air, hence the term radiator.

Traditionally radiator cores are made of a Copper and Brass material construction which has proven to provide a high performance of cooling in most environments, although it is now being increasingly common for OEM radiators to be manufactured from Aluminium. Although aluminium radiator cores have less effective cooling properties, they are lower cost to produce as Copper prices continue to rise.

Radiators are often paired with a fan that blows air through the radiator. Air is an important part of the heat transfer process because it takes the heat away from the radiator. Air heats up relatively quickly and that in order for the radiator to continue to transfer heat to the surrounding air effectively, the heated air must continuously be replaced by cool air so that the heat transfer process can continue. That’s why the radiator is located behind the grill at the front end of the car. As the car moves, air flows through the radiator and continuously "takes" away heat. However, when the car is not moving or when natural airflow is insufficient, a fan pointed directly at the core forces more air through it and more heat is transferred.

Electronics

As electronic devices become smaller yet more capable, the problem of dispersing waste heat becomes more difficult. Tiny radiators known as heat sink
Heat sink
A heat sink is a term for a component or assembly that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems and the radiator in a car...

s are used to convey heat from the electronic components into a cooling air stream.

Heat sinks, which dissipate thermal energy, should not be confused either with electric radiators or electromagnetic radiator elements
Electrical element
Electrical elements are conceptual abstractions representing idealized electrical components, such as resistors, capacitors, and inductors, used in the analysis of electrical networks...

, a subdivision of antenna in electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 which transmit or receive electromagnetic
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...

 energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

.

Theory of operation

From an engineering perspective, a radiator varies from an ideal black body
Black body
A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum...

 by a factor, , called the emissivity
Emissivity
The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...

, which is a spectrum-dependent property of any material.
Commonly, a fluid thermal mass
Thermal mass
Thermal mass is a concept in building design which describes how the mass of the building provides "inertia" against temperature fluctuations, sometimes known as the thermal flywheel effect...

, containing the heat to be rejected, is pumped from the heat source to the radiator, where it conducts to the surface and radiates into the surrounding cooler medium. The rate of heat flow depends on the fluid properties, flow rate, conductance to the surface, and the surface area of the radiator. Watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

s per square metre
Square metre
The square metre or square meter is the SI derived unit of area, with symbol m2 . It is defined as the area of a square whose sides measure exactly one metre...

 are the SI units used for radiant emittance. If the system is not limited by the heat capacity
Heat capacity
Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...

 of the fluid, or the thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

 to the surface, then emittance, M is found by a fourth-power relation to the absolute temperature at the surface. The Stefan-Boltzmann constant is used to calculate it, as .
Since heat may be absorbed as well as emitted, a radiator's ability to reject heat will depend on the difference in temperature between the surface and the surrounding environment. For particular operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...

s, a system's overall heat flow may be given in thermal watts, abbreviated Wt.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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