This article is about radiators in automobiles, buildings, and electronics. For other uses, see Radiator (disambiguation)
Water-air convective cooling radiator, made from aluminum, from a 21st-century carA radiator is a heat exchanger used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics.
A radiator is always a source of heat to its environment, although this may be for either the purpose of heating an environment, or for cooling the fluid or coolant supplied to it, as for automotive engine cooling and HVAC dry cooling towers. Despite the name, most radiators transfer the bulk of their heat via convection instead of thermal radiation.[citation needed]
History
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The Roman hypocaust is an early example of a type of radiator for building space heating. Franz San Galli, a Prussian-born Russian businessman living in St. Petersburg, is credited with inventing the heating radiator around 1855,[1][2] having received a radiator patent in 1857,[3] but American Joseph Nason developed a primitive radiator in 1841[4] and received a number of U.S. patents for hot water and steam heating.[4]
Radiation and convection
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A cast iron convector radiator from 1904Heat transfer from a radiator occurs by two mechanisms: thermal radiation and convection into flowing air or liquid. Conduction is not normally a major source of heat transfer in radiators.. A radiator may even transfer heat by phase change, for example, drying a pair of socks. 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). The term "convector" refers to a class of devices in which the source of heat is not directly exposed.
To increase the surface area available for heat exchange with the surroundings, a radiator will have multiple fins, in contact with the tube carrying liquid pumped through the radiator. Air (or other exterior fluid) in contact with the fins carries off heat. If air flow is obstructed by dirt or damage to the fins, that portion of the radiator is ineffective at heat transfer.
Heating
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A panel convector radiator, typical of a standard central heating system in the UKRadiators are commonly used to heat buildings on the European continent. In a radiative central heating system, hot water or sometimes steam is generated in a central boiler and circulated by pumps through radiators within the building, where this heat is transferred to the surroundings.
In some countries, portable radiators are common to heat a single room, as a safer alternative to space heater and fan heater.
Heating, ventilation, and air conditioning
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Radiators are used in dry cooling towers and closed-loop cooling towers for cooling buildings using liquid-cooled chillers for heating, ventilation, and air conditioning (HVAC) while keeping the chiller coolant isolated from the surroundings.
Engine cooling
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Car engine bay, with radiator in front Auto radiators with double grids of tubes: staggered grids on the left, parallel grids on the rightRadiators are used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plants and other places where heat engines are used (watercrafts, having an unlimited supply of a relatively cool water outside, usually use the liquid-liquid heat exchangers instead).
To cool down the heat engine, a coolant is passed through the engine block, where it absorbs heat from the engine. The hot coolant is then fed into the inlet tank of the radiator (located either on the top of the radiator, or along one side), from which it is distributed across the radiator core through tubes to another tank on the opposite end of the radiator. As the coolant passes through the radiator tubes on its way to the opposite tank, it transfers much of 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 release the heat to the ambient air. Fins are used to greatly increase the contact surface of the tubes to the air, thus increasing the exchange efficiency. The cooled liquid is fed back to the engine, and the cycle repeats. Normally, the radiator does not reduce the temperature of the coolant back to ambient air temperature, but it is still sufficiently cooled to keep the engine from overheating.
This coolant is usually water-based, with the addition of glycols to prevent freezing and other additives to limit corrosion, erosion and cavitation. However, the coolant may also be an oil. The first engines used thermosiphons to circulate the coolant; today, however, all but the smallest engines use pumps.[5]
Up to the 1980s, radiator cores were often made of copper (for fins) and brass (for tubes, headers, and side-plates, while tanks could also be made of brass or of plastic, often a polyamide). Starting in the 1970s, use of aluminium increased, eventually taking over the vast majority of vehicular radiator applications. The main inducements for aluminium are reduced weight and cost.[citation needed]
Since air has a lower heat capacity and density than liquid coolants, a fairly large volume flow rate (relative to the coolant's) must be blown through the radiator core to capture the heat from the coolant. Radiators often have one or more fans that blow air through the radiator. To save fan power consumption in vehicles, radiators are often behind the grille at the front end of a vehicle. Ram air can give a portion or all of the necessary cooling air flow when the coolant temperature remains below the system's designed maximum temperature, and the fan remains disengaged.[citation needed]
Electronics and computers
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A passive heatsink on a motherboardAs electronic devices become smaller, the problem of dispersing waste heat becomes more difficult. Tiny radiators known as heat sinks are used to convey heat from the electronic components into a cooling air stream. Heatsinks do not use water, rather they conduct the heat from the source. High-performance heat sinks have copper to conduct better. Heat is transferred to the air by conduction and convection; a relatively small proportion of heat is transferred by radiation owing to the low temperature of semiconductor devices compared to their surroundings.
Radiators are also used in liquid cooling loops for rejecting heat.
Spacecraft
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Radiators are found as components of some spacecraft. These radiators work by radiating heat energy away as light (generally infrared given the temperatures at which spacecraft try to operate) because in the vacuum of space neither convection nor conduction can work to transfer heat away. On the International Space Station, these can be seen clearly as large white panels attached to the main truss. They can be found on both crewed and uncrewed craft.[6]
See also
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References
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Radiator heaters are ubiquitous in older homes and new construction alike due to their incredible energy efficiency and cost-effectiveness. Understanding how radiator heaters work is important if you want to learn how to maintain your home’s radiator heating system or if you’re considering purchasing a new system for your home.
In this guide, we explain how radiator heaters work, covering the basic operating principles, the different types of radiators, and how to keep your radiators functioning smoothly.
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Radiator heaters are a family of home heating devices that use hot water or steam to heat your home through a combination of radiation and convection. They are one of the oldest forms of indoor heating and remain popular today because they are relatively inexpensive to maintain, efficient, and already installed in many homes and buildings.
Radiators rely on a boiler or water heater to create steam or hot water that subsequently gets pumped throughout your home via a network of pipes. When the steam or hot water enters the radiator, it heats up a series of fins or coils that, in turn, heat the air around the radiator, heating your home.
Here’s a breakdown of the key components that make up a radiator heater:
Let’s take a closer look at how radiators work so you can better understand their advantages and disadvantages.
Radiator heating systems depend on a centralized boiler or water heater to produce steam or hot water that travels throughout your home via pipes to your baseboard heaters or standalone radiator units. The heat from the pipes radiates to increase the temperature of the air surrounding the radiator, which then circulates throughout your home via convection.
While a pipe full of hot water or steam will feel incredibly hot to the touch, it’s not very good at transferring that heat to the air in your home. A key design element of radiators is a set of fins or coils that serve to increase the surface area of hot material that makes contact with the air. These fins or coils are generally made of a metal with a high heat conductivity to increase your heating system’s overall efficiency and reduce the amount of time it takes your home to heat up.
The primary heating loop for radiator heaters works like this:
All radiators need either hot water or steam to function, but how they get that hot water or steam varies. The following sections summarize three of the most popular radiator designs: hot water radiators, steam radiators, and radiators with electric water heaters.
Below is a video detailing how steam radiator heaters work. The principles in the video are similar to how baseboard heaters work as well:
Hot water radiators use a water boiler to heat water to near-boiling — usually around 180°F — and circulate it throughout your home when your home needs to be heated. An inlet allows hot water to enter the system from the boiler, and an outlet allows it to leave the system and return to the boiler’s water tank, where it can be reheated.
Hot water radiators require a circulator or pump to transport hot water throughout your home, making them slightly more prone to malfunctions than steam radiators since they have an extra component that may break down.
Steam radiators function similarly to hot water radiators, but they don’t use a pump. Instead, a set of valves control when steam is allowed to flow through the system. The valves open when your home needs to be heated and close once it reaches the desired temperature. The main advantage of steam radiators vs hot water radiators is that they don’t need a pump since steam naturally flows from high pressure to low pressure.
As the steam flows through the radiator, it loses heat, eventually condensing to water and flowing back to the boiler through a return pipe.
Not all hot water systems heat their water the same way. Electric water heaters use electricity to raise the temperature of a heating element inside the system’s water tank. The heating element transfers heat to the water, raising its temperature so it can flow through the system and heat your home.
Electric water heaters are typically more efficient and cheaper to run than traditional oil or gas-based water heaters. They’re especially economical when paired with solar panels since you can use the power generated by your panels to heat your home. Even if your solar system doesn’t generate enough power to run your heating system entirely, it can still greatly reduce your monthly heating bill.
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Radiators are still one of the most popular home heating options, even as forced air systems become more prevalent. A properly cared-for radiator is highly efficient, easy to maintain, and poses virtually zero health risks. Here is a more detailed look at the main benefits of radiator heaters:
Radiator heaters are relatively low-maintenance compared to other heating systems, but they still require a bit of attention to keep them running smoothly.
If your hot water radiators are taking longer than normal to heat up or if they’re making unusual gurgling sounds, it could be time to bleed them. Bleeding your radiators is fairly straightforward and shouldn’t take much time. Use the bleed key your radiator came with to turn the bleed valve counterclockwise until you hear a hissing sound. Close the valve as soon as the water starts escaping instead of air.
Steam radiators can become clogged over time if you don’t clean out their air vents. Clogged vents make your radiator less efficient and effective, which wastes money and makes it harder to keep your home comfortable during the winter. You can use a thin wire, needle, or other hard, narrow object to clean any gunk out of the air hole.
You should also inspect your radiator’s pipes once per year to make sure they’re still in good shape. Pipes wear out over time, and small cracks or pinholes can turn into big problems quickly if they’re not taken care of. A quick visual inspection is enough to catch most problems, but you can ask a plumber to check during a routine visit if you want to be extra careful.
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Most radiators don’t require regular visits from a professional, but it can be helpful to have your burner and circulator inspected to stay ahead of potential problems. Many companies recommend yearly inspections, which is a good option if you don’t want to spend the time inspecting your radiators yourself.
Understanding how radiators work makes it easier to diagnose problems when they crop up so you can keep your home nice and toasty during the winter. We hope you’ve found this guide helpful for learning how radiators operate and now have a better idea of whether a radiator heating system is the right choice for your home. Radiators are efficient, cost-effective, and easy to maintain, making them a great choice for most homeowners.
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Home heating radiators usually last between 15 and 20 years, depending on the type of heater you have and the level of care it’s given throughout its life. With regular bleeding and routine checkups to inspect the circulator and water boiler, you can easily get 20 years out of a radiator heater.
Radiator heaters are very safe, especially compared to forced air systems that can cause respiratory illness from mold and bacteria. The primary concern with radiator heaters is the dry air they create in your home, which can lead to minor problems like dry skin and a scratchy throat. Radiators can also cause burns if they’re not calibrated correctly, so make sure to have a professional set the contact temperature during a routine maintenance visit.
Radiators are also much safer than electric space heaters, which are a common cause of household fires.
Radiator heaters are not likely to make you sick since they are closed systems. Home heating options that use ducts to pump air throughout your room can cause respiratory problems if you don’t have them cleaned regularly. Radiators don’t have the same problem and are generally considered much safer.
Experts recommend bleeding your radiators at least once per year, preferably well before the winter months when the system will see heavy use. It can be a good idea to bleed your radiators more frequently if you notice they’re taking longer to heat up or if they’re making a lot of noise when they turn on.