Radiators and convectors are types of heat exchangers designed to transfer thermal energy from one medium to another for the purpose of cooling and heating. A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media Thermal energy is the sum of the sensible energy and latent energy. The majority of radiators are constructed to function in automobiles, buildings, and electronics. In Architecture, Construction, Engineering and real estate development the word building may refer to one of the following Any man-made Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical

One might expect the term "radiator" to apply to devices which transfer heat primarily by thermal radiation (see: infrared heating), while a device which relied primarily on natural or forced convection would be called a "convector". Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature. An infrared heater is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation Convection in the most general terms refers to the movement of molecules within Fluids (i 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.

Automobiles

A typical automobile coolant radiator

In automobiles with a liquid-cooled internal combustion engine a radiator is connected to channels running through the engine and cylinder head, through which a liquid (coolant) is pumped. The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a An engine is a mechanical device that produces some form of output from a given input In an Internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the Combustion chamber and the Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of For information on Wikipedia project-related discussions see WikipediaVillage pump. This liquid is typically a half-and-half mixture of water and ethylene glycol or propylene glycol (with a small amount of corrosion inhibitor) known as antifreeze. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Ethylene glycol ( monoethylene glycol ( MEG) 12-ethanediol, IUPAC name: ethane-12-diol) is an Alcohol with two -OH Propylene glycol, known also by the systematic name propane-12-diol is an Organic compound (a Diol Alcohol) usually a faintly sweet odorless and A corrosion inhibitor is a chemical compound that when added to a fluid or gas decreases the corrosion rate of a Metal or an Alloy. Antifreeze is a Cryoprotectant used in Internal combustion engines and for many other heat transfer applications such as electronics cooling and Chillers The radiator transfers the heat from the fluid inside to the air outside, thereby cooling the engine. Radiators are generally mounted in a position where they will receive airflow from the forward movement of the vehicle such as behind the grill.

Heater

A system of valves or baffles, or both, is usually incorporated to simultaneously operate a small radiator inside the car. This small radiator, and the associated blower fan, is called the heater core, and serves to warm the cabin interior. A heater core is a Radiator -like device used in heating the cabin of a Vehicle. Like the radiator, the heater core acts by removing heat from the engine. For this reason, automotive technichians often advise operators to turn on the heater and set it to high if the engine is overheating.

Temperature control

The engine temperature is primarily controlled by a wax-pellet type of thermostat, a valve which opens once the engine has reached its minimum operating temperature. A thermostat is a device for regulating the Temperature of a System so that the system's temperature is maintained near a desired setpoint A thermostat is a device for regulating the Temperature of a System so that the system's temperature is maintained near a desired setpoint When the engine is cold the thermostat is closed. Coolant flows to the inlet of the circulating pump and is returned directly to the engine, bypassing the radiator. Directing water to circulate only through the engine allows heat to build up. Once the coolant reaches the thermostat's activation temperature it opens, allowing water to flow through the radiator. Optimum operating temperature is maintained by the cyclic opening and closing of the thermostat valve.

Other factors influence the temperature of the engine including radiator size and the type of radiator fan. The size of the radiator (and thus its cooling capacity) is chosen such that it can keep the engine at the design temperature under the most extreme conditions a vehicle is likely to encounter (such as climbing a mountain while fully loaded on a hot day). On modern vehicles, further regulation of cooling rate is provided by either variable speed or cycling radiator fans. Electric fans are controlled by a thermostatic switch or the engine control unit. An engine control unit (ECU is an Electronic control unit which controls various aspects of an Internal combustion engine 's operation Pulley driven fans are often regulated by a friction-drive clutch which increases the fan speed when coolant temperature increases.

Coolant pressure

Because the thermal efficiency of internal combustion engines increases with internal temperature the coolant is kept at higher-than-atmospheric pressure to increase its boiling point. In Thermodynamics, the thermal efficiency (\eta_{th} \ is a dimensionless performance measure of a thermal device such as an Internal combustion The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid A calibrated pressure-relief valve is usually incorporated in the radiator's fill cap.

As the coolant expands with increasing temperature its pressure in the closed system must increase. Ultimately the pressure relief valve opens and excess fluid is dumped into an overflow container. Fluid overflow ceases when the thermostat modulates the rate of cooling to keep the temperature of the coolant at optimum. When the coolant cools and contracts (as conditions change or when the engine is switched off) the fluid is returned to the radiator through additional valving in the cap.

Boiling or overheating

On this type system, if the coolant in the overflow container gets too low, fluid transfer to overflow will cause an increased loss by vaporizing the engine coolant.

Severe engine damage can be caused by overheating, by overloading or system defect, when the coolant is evaporated to a level below the water pump. This can happen without warning because, at that point, the sending units are not exposed to the coolant to indicate the excessive temperature.

To protect the unwary the cap often contains a mechanism that attempts to relieve the internal pressure before the cap can be fully opened. Some scalding of one's hands can easily occur in this event. Opening a hot radiator drops the system pressure immediately and normally causes a sudden eruption of super-heated coolant which can cause severe burns (see geyser). A geyser is a Hot spring characterized by intermittent discharge of water ejected turbulently and accomplished by a vapour phase

History

The invention of the automobile water radiator is attributed to Karl Benz. Karl Friedrich Benz, sometimes spelled Carl, ( November 25, 1844, Karlsruhe, Germany – April 4, 1929, Ladenburg Wilhelm Maybach designed the first honeycomb radiator for the Mercedes 35hp [1]. Wilhelm Maybach ˈmaibax ( February 9, 1846 &ndash December 29, 1929) was an early German engine designer and industrialist The Mercedes 35 hp was a radical early car model designed in 1901 by Wilhelm Maybach and Paul Daimler, for Emil Jellinek.

Supplementary radiators

Some engines have an oil cooler, a separate small radiator to cool the engine oil. Motor oil, or engine oil, is an Oil used for lubrication of various Internal combustion engines While the main function is to lubricate Moving Cars with an automatic transmission often have extra connections to the radiator, allowing the transmission fluid to transfer its heat to the coolant in the radiator. An automatic transmission (commonly "AT" or "Auto" is an Automobile Gearbox that can change Gear ratios automatically as the vehicle

Turbo charged or supercharged engines may have an intercooler, which is an air-to-air or air-to-water radiator used to cool the incoming air charge—not to cool the engine. A turbocharger, or turbo, is an air Compressor used for forced-induction of an Internal combustion engine. A supercharger is an air compressor used for Forced induction of an Internal combustion engine. An intercooler, or Charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged (forced

Buildings

A cast iron household radiator

In buildings a radiator is a heating device, which is warmed by steam from a boiler, or by hot water being pumped through it from a water heater (usually, if not quite accurately, referred to as a "boiler"). In Architecture, Construction, Engineering and real estate development the word building may refer to one of the following Any man-made HVAC (pronounced either "H-V-A-C" or occasionally " H-vak " is an Initialism or Acronym that stands for " Heating Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work. A boiler is a closed vessel in which Water or other Fluid is heated

Such radiators transfer the majority of their heat by radiation and by convection. Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature. Convection in the most general terms refers to the movement of molecules within Fluids (i

Conventional radiators

A conventional hot-water radiator consists of a sealed hollow metal container, usually flat in shape. Hot water enters at the top of the radiator by way of pressure, from a pump elsewhere in the building, or by convection.

As it gives out heat the hot water cools and sinks to the bottom of the radiator and is forced out of a pipe at the other end. The pipe either has a large surface area or attached fins to increase its surface area and therefore contact with surrounding air. The air near a radiator is then heated and produces a convection current in the room drawing in cold air to heat.

If set up improperly, radiators, and their supply and return pipes, can make loud banging noises like someone hammering on the pipes. This is due to either the pipes rubbing on surrounding surfaces while expanding and contracting due to heat changes or to sudden fluctuations of the supplied water pressure. Thermal Expansion is the tendency of matter to change in Volume in response to a change in temperature Proper mounting of the radiators and supply pipes will reduce expansion noises, while upward-mounted stub ends with a trapped bubble of air (not interfering with flow, as would an un-bled radiator) will provide a cushion against pressure fluctuations, an anti-hammer device. Water hammer (or more generally fluid hammer) is a Pressure surge or wave resulting when a fluid in motion is forced to stop or change direction suddenly (Momentum

Stereotypical cast iron radiators (as pictured) are no longer common in new construction, replaced mostly with copper pipes which have aluminum fins to increase their surface area. Cast iron usually refers to grey cast iron, but identifies a large group of Ferrous Alloys which solidify with a Eutectic. In the U. K. , modern domestic radiators tend to be of sheet steel construction (often with steel fins), though copper/aluminium is often found in industrial Air Handling System heat exchangers.

The radiator was invented in 1855 by Franz SanGalli. He was the first to produce a system of central heating and patented his invention in Germany and the US.

There are many designs and varieties of radiators, from conventional to modern style. Radiators are sometimes seen as an art form, much like sculpture.

Steam

Single-pipe steam radiator

Steam has the advantage of flowing through the pipes under its own pressure without the need for pumping. For this reason, it was adopted earlier, before electric motors and pumps became available. Steam is also far easier to distribute than hot water throughout large, tall buildings like skyscrapers. A skyscraper is a tall continuously habitable Building. There is no official definition or a precise cutoff height above which a building may clearly be classified as a skyscraper However, the higher temperatures at which steam systems operate make them inherently less efficient, as unwanted heat loss is inevitably greater.

Steam pipes and radiators are also prone to producing banging sounds (known as "water hammer") if condensate fails to drain properly; this is often caused by buildings settling and the resultant pooling of condensate in pipes and radiators that no longer tilt slightly back towards the boiler. A boiler is a closed vessel in which Water or other Fluid is heated

Fan assisted radiators

A more recent type of heater used in homes is the fan assisted radiator. It contains a heat exchanger fed by hot water from the heating system. A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media A thermostatic switch senses the heat and energises an electric fan which blows air over the heat exchanger. A thermostat is a device for regulating the Temperature of a System so that the system's temperature is maintained near a desired setpoint A mechanical fan is an electrically powered device used to produce an airflow for the purpose of creature comfort (particularly in the heat ventilation, exhaust

Advantages of this type of heater are its small size and even distribution of heat around the room. Disadvantages are the noise produced by the fan, and the need for an electricity supply.

Underfloor heating

During construction, tubing is placed on the floor throughout the room, and later covered with a concrete layer. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag

The current trend in radiant heating is towards underfloor heating, where warm water is circulated under the entire floor of each room in a building. Radiant heating is a technology utilized for the heating of both indoor and outdoor areas Underfloor heating is a form of Central heating which utilizes Heat conduction and Radiant heat for indoor climate control, rather than forced A network of pipes, tubing or heating cables is buried in the floor, and a gentle heat rises into the room. Because of the large area of this type of radiator, the floor only needs to be heated a few degrees above the desired room temperature, and as a result, convection is almost non-existent. Convection in the most general terms refers to the movement of molecules within Fluids (i These systems are reputed to have a high level of comfort, but are generally difficult to install into existing buildings. For best results, a floor covering that conducts heat well (such as tiles) should be used. A tile is a manufactured piece of hard-wearing material such as Ceramic, stone, metal or even Glass.

The hypocaust was a Roman heating system using a similar principle of operation. A hypocaust (Latin hypocaustum) is an ancient Roman system of Central heating.

Bleeding

All "radiant" (ie. heat radiates from hot water) systems need to be bled, or purged of air, on occasion.

If there is air (or other gases such as Hydrogen) trapped inside the radiator, then the water cannot rise to the top, and only the bottom area gets hot. A bleed screw near the top of the radiator allows the trapped air to be 'bled' from the system, and thus restore correct operation. A bleed screw is a device used to create a temporary opening in an otherwise closed system which facilitates the removal of air or another substance from the system by way of pressure Often radiators located on upper floors will accumulate more air than ones on lower floors as the air will tend to rise to the topmost point in the system. These may have to be bled more often. Usually radiators are bled once or twice per season, or as needed. Another reason to exclude air is to minimise corrosion of the steel pressed radiators. Note that most central heating systems need a corrosion inhibitor added into the circulating hot water, so that the production of Hydrogen is minimised. A corrosion inhibitor is a chemical compound that when added to a fluid or gas decreases the corrosion rate of a Metal or an Alloy. This is created in untreated systems, by the action of the hot water on the iron in the absence of air (stripping off the oxygen atom to leave hydrogen as H2 when iron oxide is created). Altogether there are sixteen known Iron Oxides and oxyhydroxides Note that if air is getting into the radiators frequently, this may be the sign of a leak somewhere, such as a dripping valve, or loose joint.

Electronics

In electronics, a radiator is also known as a radiating element. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical The concept of electrical elements is used in the analysis of Electrical networks. Radiating elements are a basic subdivision of an antenna. An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into Radiating elements are capable of transmitting or receiving electromagnetic energy. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός

See also

• Heater core
• Intercooler
• Coolant
• Internal combustion engine

Sources

1. Haynes Opel Omega & Senator Service and Repair Manual, 1996, ISBN 1-85960-342-4

External links

• How Car Cooling Systems Work