Radiator is a heat exchanger used to cool internal combustion engines, especially in cars but also on piston-engined aircraft, railroad locomotives, motorcycles, stationary power plants or similar uses of such machines.
The internal combustion engine is often cooled by a fluid circulation called the cooling machine around the engine block, where it is heated, then through the radiator where it loses heat to the atmosphere, and then returns to the engine. The cooling machine is usually water-based, but it can also be oil. It is common to use a water pump to force the engine coolant to circulate, and also for the axial fan to force air through the radiator.
Video Radiator (engine cooling)
Cars and motorcycles
In cars and motorcycles with internal combustion-cooled internal combustion engines, radiators connect to channels that flow through the engine and the cylinder head, where the liquid (coolant) is pumped. These liquids may be water (in climates where water is not likely to freeze), but more commonly a mixture of water and antifreeze in proportion to the climate. Antifreeze itself is usually ethylene glycol or propylene glycol (with a small amount of corrosion inhibitor).
Typical automotive cooling systems consist of:
- a series of channels into the engine block and cylinder head, circling the combustion chamber with fluid circulation to bring heat;
- radiators, consisting of many small tubes equipped with honey fin hives to produce heat quickly, which accepts and cools hot liquids from the engine;
- water pumps, usually of centrifugal type, to circulate liquids through the system;
- a thermostat to control the temperature by varying the amount of liquid entering the radiator;
- fan to draw fresh air through the radiator.
The radiator transfers heat from the liquid into the outside air, thus cooling the liquid, which in turn cools the engine. Radiators are also often used to cool automatic transmission fluids, air conditioning coolers, air intake, and sometimes to cool motor oil or power steering fluid. Radiators are usually installed in a position where they receive airflow from the forward movement of the vehicle, such as behind the front grill. Where the engine is mounted in the middle or back, it is common to install a radiator behind the front grill to achieve sufficient airflow, although this requires a long cooling pipe. Alternatively, the radiator can draw air from the stream above the vehicle or from the side-mounted grill. For long vehicles, such as buses, the side air flow is most common for engine cooling and transmission and the upper air flow is most common for air conditioners.
Construction of radiator
Car radiators are constructed from a pair of header tanks, connected by cores with many narrow alleys, providing a high surface area relative to volume. The core is usually made of a sheet of metal sheet stack, pressed to form a channel and soldered or brazed together. Over the years radiators are made of brass or copper core soldered to brass headers. Modern radiators have an aluminum core, and often save money and weight by using plastic headers. This construction is more vulnerable to failure and less easily repairable than traditional materials.
Previous construction method is honeycomb radiator. The round tubes are converted into hexagons at the ends, then stacked and soldered. Since they just touch the tip, this forms what becomes a solid water tank with many air tubes through it.
Some vintage cars use radiator cores made from circular tubes, less efficient but simpler construction.
Cooling pump
The radiator is first used downward vertical flow, driven solely by the thermosyphon effect. The coolant is heated in the engine, becomes less dense, and up. When the radiator cools the liquid, the coolant becomes denser and falls. This effect is adequate for low-powered stationary engines, but is not adequate for all but the earliest cars. All cars over the years have been using centrifugal pumps to circulate engine coolants because natural circulation has very low flow rates.
Heater
A valve or baffle system, or both, is usually combined to operate a small radiator in a vehicle simultaneously. This small radiator, and the associated blower fan, called the heater core, and serves to warm the cabin's interior. Like a radiator, the heater core works by removing heat from the engine. For this reason, automotive engineers often advise the operator to turn on heater and set it to high if the engine is too hot to help the main radiator.
Temperature control
Water flow control
The engine temperature in modern cars is mainly controlled by wax-pellet type thermostats, valves that open after the engine reaches its optimum operating temperature.
When the engine is cold, the thermostat is closed except for a small bypass flow so that the thermostat changes the temperature of the coolant as the engine heats up. The engine coolant is directed by the thermostat to the inlet of the circulating pump and is returned directly to the engine, passing through the radiator. Directing water to circulate only through the engine allows the temperature to reach the optimum operating temperature as quickly as possible while avoiding local "hotspots". Once the coolant reaches the thermostat activation temperature, it opens, allowing water to flow through the radiator to prevent the temperature from rising higher.
Once at the optimum temperature, the thermostat controls the flow of the engine coolant to the radiator so that the engine continues to operate at its optimum temperature. Under peak load conditions, such as driving slowly over a steep hill while heavily laden on a hot day, the thermostat will approach fully open because the engine will produce close to maximum power while the airflow velocity crosses the low radiator. (The speed of the airflow in the radiator has a major effect on its ability to get rid of heat.) Conversely, as it slides down the highway on a cold night on the throttle of light, the thermostat will be almost closed because the engine produces less power, and the radiator is able to dissipate more heat than generated machine. Allowing too much cooling flow to the radiator will result in the engine becoming too cold and operating at lower temperatures than optimal temperature, thereby lowering fuel efficiency and increasing exhaust emissions. Furthermore, engine endurance, reliability, and longevity are sometimes compromised, if any component (such as crankshaft bearings) is engineered to account for thermal expansion to match the correct looseness. Another side effect of excessive cooling is to reduce the performance of the cabin heater, although in certain cases it still exhales air at much higher temperatures than the ambient.
Therefore, the thermostat continues to move throughout its range, responding to changes in vehicle operating load, external speed and temperature, to keep the engine at its optimum operating temperature.
In vintage cars you may find a bellows type thermostat, which has fluid bumps containing volatile liquids such as alcohol or acetone. This type of thermostat does not work well on the coolant system pressure above about 7 psi. Modern motor vehicles usually run about 15 psi, which blocks the use of bellows type thermostats. In direct air-cooled engines, this is not a problem for bellows thermostats that control flap valves in the airways.
Airflow control
Other factors affect the engine temperature, including the radiator size and radiator fan type. The size of the radiator (and thus its cooling capacity) is chosen in such a way that it can keep the engine at design temperature under the most extreme conditions a vehicle may have to face (such as climbing a mountain while it is fully charged on a hot day).
The speed of the airflow through the radiator greatly affects the heat lost. The speed of the vehicle affects this, in rough proportion to machine effort, thus providing rough self-regulatory feedback. Where additional cooling fans are driven by the engine, it also keeps track of the same engine speed.
Engine-driven fans are often governed by a viscous-drive clutch of drivebelt, which slips and reduces fan speed at low temperatures. This improves fuel efficiency by not wasting power to drive the fan in excess. In modern vehicles, further arrangement of cooling rate is provided by variable speed or cyclic radiator fan. The fan is controlled by a thermostatic switch or machine control unit. The electric fan also has the advantage of providing good air flow and cooling at low engine spin or when stationary, as in slow moving traffic.
Prior to the development of thick movers and electric fans, the engine is mounted with a simple fan that pulls the air through the radiator at all times. Vehicles whose designs require the installation of large radiators to tackle heavy work at high temperatures, such as commercial vehicles and tractors will often run cold in cold weather under light loads, even with the presence of a thermostat, such as large radiators and fixed fans causing rapid coolant temperature drop and significant immediately after the thermostat is opened. This problem can be solved by installing a radiator (or shroud radiator ) to a partially adjustable radiator or completely blocking airflow through radiator. The simplest of the blind is a roll of material such as a canvas or rubber that extends along the radiator to cover the desired part. Some older vehicles, such as the era of World War I S.E.5 and single-engine SPAD S.XIII single fighter, have a series of adjustable windows from the driver's seat or the pilot to provide a level of control. Some modern cars have a series of windows automatically opened and closed by the engine control unit to provide cooling and aerodynamic balance as needed.
Coolant pressure
Because the thermal efficiency of the internal combustion engine increases with the internal temperature, the coolant is stored at a higher pressure from the atmosphere to increase its boiling point. The calibrated pressure release valve is usually inserted in the radiator charge cap. This pressure varies between models, but typically ranges from 4 to 30 psi (30 to 200 kPa).
As the coolant expands with increasing temperature, its pressure in a closed system must increase. Ultimately, the pressure release valve is open, and excess fluid is thrown into an overflowing container. Fluid overflow stops when the thermostat modulates the cooling rate to keep the coolant temperature at optimal level. When the engine coolant cools and contracts (when conditions change or when the engine is turned off), the liquid is returned to the radiator through the addition of a valve on the lid.
Engine cooler
Before World War II, cooling machines were usually plain water. Antifreeze is only used to control freezing, and this is often only done in cold weather.
The development of high performance aircraft engines requires better cooling with higher boiling points, leading to the application of glycols or water-glycol mixtures. This leads to the adoption of glycols for their antifreeze properties.
Since the development of aluminum or metal alloy machinery, corrosion inhibition is more important than antifreeze, and in all regions and seasons.
Boiling or overheating
A drying overflow tank can lead to evaporative cooling, which can cause engine heat to localize or overheat. Severe damage may occur, such as a bursting headgasket, cracked cylinder head or cylinder block. Sometimes there will be no warning, because the temperature sensor that provides data for the temperature gauge (either mechanical or electrical) is not exposed to overheated cooling, giving the wrong wrong reading.
Opening the heat radiator will lower the system pressure, which can cause it to boil and remove harmful fumes and hot steam. Therefore, the radiator cap often contains a mechanism that tries to diffuse internal pressure before the lid can be fully opened.
History
The discovery of a car air radiator is associated with Karl Benz. Wilhelm Maybach designed the first honeycomb radiator for the Mercedes 35hp.
Radiator tambahan
Sometimes it takes a car to be equipped with a second radiator, or additional, to increase the cooling capacity, when the size of the original radiator can not be upgraded. The second radiator is cast in series with the main radiator on the circuit. This is the case when the Audi 100 is the first turbocharged created 200. It does not get confused with the intercooler.
Some engines have an oil cooler, a small separate radiator to cool engine oil. Cars with automatic transmissions often have extra connections to the radiator, allowing the transmission fluid to transfer its heat to the coolant in the radiator. This could be an air oil radiator, as for the smaller version of the radiator. More simply they are oil-water coolers, where an oil pipeline is inserted into the water radiator. Although water is hotter than ambient air, the higher thermal conductivity offers a comparable cooling (within limits) of a more complex and cheaper and more reliable oil cooler. Less commonly, power steering fluid, brake fluid, and other hydraulic fluids can be cooled by additional radiators on the vehicle.
Turbo or supercharged engines may have an intercooler, the air-to-air or air-to-air radiator used to cool the incoming air charge - not to cool the engine.
Maps Radiator (engine cooling)
Aircraft
Aircraft with liquid-cooled piston engines (usually inline engines rather than radials) also require radiators. Because the air speed is higher than the car, it is efficiently cooled in flight, so it does not require a large area or cooling fan. Many high-performance aircraft but experience extreme overheating problems when stopping on the ground - just 7 minutes to Spitfire. This is similar to the current Formula 1 car, when it stops on the grid with the engine in operation, they require forced air into their radiator pod to prevent overheating.
Surface radiator
Reducing drag is a major goal in aircraft design, including cooling system design. The initial technique was to utilize the abundant airflow of aircraft to replace the honeycomb core (multiple surfaces, with the ratio of surface height to volume) by radiators mounted on the surface. It uses a single surface that is integrated into the fuselage or wing skin, with a coolant flowing through the pipe at the back of this surface. Such designs are seen mostly on World War I planes.
Since they are heavily dependent on air velocity, surface radiators are even more prone to overheating when walking on the ground. Racing aircraft such as Supermarine S.6B, racing amphibious aircraft with radiators built on the top surface of their buoys, have been described as "flown on the temperature gauge" as a major limitation on their performance.
The surface radiator has also been used by some high speed racing cars, such as Malcolm Campbell Blue Bird of 1928.
Pressure cooling system
This is generally the limitation of most cooling systems where the coolant is not allowed to boil, since the need to handle gas in the flow makes design difficult. For water-cooling systems, this means that the maximum amount of heat transfer is limited by the specific heat capacity of the water and the temperature difference between the ambient and 100 ° C. This provides more effective cooling in winter, or in higher places where temperatures are low.
Another very important effect in airplane cooling is that specific heat capacity changes with pressure, and this pressure changes faster with altitude than temperature drop. So, generally, the liquid cooling system loses capacity as the plane rises. This was a major threshold on performance during the 1930s when the introduction of the first turbosuperchargers allowed a comfortable ride at altitudes above 15,000 feet, and cooling design became a major area of ​​research.
The most obvious and common solution to this problem is to run the entire cooling system under pressure. It maintains a specific heat capacity at a constant value, while outside air temperature continues to decline. Such a system improves cooling capabilities as they rise. For most uses, this solves the problem of cooling high-performance piston engines, and almost all aircraft-cooled aircraft engines during the World War II period used this solution.
However, the pressurized system is also more complex, and much more susceptible to damage - because the coolant is under pressure, even minor damage in cooling systems such as single-shot caliber bullet holes, will cause the liquid to quickly spray out of the hole. Failure of cooling system, so far, is the main cause of machine failure.
Evaporative cooling
Although it is more difficult to build a plane radiator capable of handling steam, it is by no means impossible. The main requirement is to provide a system that condenses the vapor back into the liquid before returning it to the pump and completing the cooling cycle. Such a system can take advantage of the specific heat of evaporation, which in the case of water is five times the specific heat capacity in liquid form. An additional advantage can be obtained by letting the steam become superheated. Such a system, known as evaporative cooling, was a considerable research topic in the 1930s.
Consider two similarly stated cooling systems operating at ambient temperatures of 20 ° C. The all-liquid design may operate between 30 ° C and 90 ° C, offering a 60 ° C temperature difference to bring heat. An evaporative cooling system may operate between 80 ° C and 110 ° C, which at a glance looks less temperature difference, but this analysis ignores large amounts of heat energy immersed during vapor formation, equivalent to 500 ° C. As a result, the evaporative version operates between 80 ° C and 560 ° C, an effective temperature difference of 480 ° C. Such a system can be effective even with much less water.
The downside to the evaporative cooling system is the area of the condenser required to cool the vapor back below the boiling point. Since the vapor is much denser than water, a larger surface area is required to provide sufficient air flow to cool the vapor back down. Rolls-Royce Goshawk's 1933 design used a conventional radiator-like condenser and this design proved to be a serious problem for dragging. In Germany, GÃÆ'¼nter's brother developed an alternative design that incorporates evaporative cooling and surface radiators scattered throughout the wing of aircraft, aircraft and even steering. Some aircraft are built using their designs and set various performance records, especially Heinkel He 119 and Heinkel He 100. However, this system requires many pumps to restore the fluid from the scattered radiator and it proves very difficult to keep it running properly. , and much more vulnerable to battle damage. The effort to develop this system was generally abandoned in 1940. The need for immediate evaporative cooling should be negated by the wide availability of ethylene glycol based coolant, which has a lower specific heat, but the boiling point is much higher than water.
Thrust radiator
A radiator of the aircraft contained in the channel heats the passing air, causing the air to expand and gain speed. This is called the Meredith effect, and the high-performance piston plane with a well-designed low-drag radiator (especially the P-51 Mustang) stems from it. The drive was significant enough to offset the pull of the enclosed radiator duct and allow the aircraft to achieve zero cooling drag. At one point, there was even a plan to complete Spitfire with afterburner, by injecting fuel into the exhaust duct after the radiator and turning it on. Afterburning is achieved by injecting additional fuel into the downstream engine of the main combustion cycle.
Stationary plant
Machines for stationary plants are usually cooled by the radiator in the same way as a car engine. However, in some cases, evaporative cooling is used through the cooling tower.
See also
- Cooler
- Heating core
- Intercooler
- Internal combustion engine (ICE)
- Waste heat
References
Source
-
Opel Omega & amp; Senator Service and Manual Repair . Haynes. 1996. ISBNÃ, 1-85960-342-4.
External links
- Radiator Replacement and Troubleshooting Guide
- How Car Cooling System Works
- Community Site Powertrain Cooling
Source of the article : Wikipedia
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