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. The majority of radiators are constructed to function in automobiles, buildings, and electronics.
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". 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.
n automobiles, with a liquid-cooled internal combustion engine, a radiator is connected to channels running through the engine and cylinder head, through which is pumped a liquid (coolant). This liquid is typically a mixture of water with ethylene glycol (a.k.a. antifreeze) and a little corrosion inhibitor.
Fluid cycle
The fluid is pumped in a closed system from the radiator to the engine, where it absorbs and conducts heat away from the engine parts and carries the heat, primarily, to the radiator. The radiator is, on many conventional vehicles, typically mounted behind the vehicle's grille, with outside air driven through the radiator by the vehicle's forward motion.
There are other mounting options for the radiator, especially in mid- and rear-engined vehicles, and some vehicles have characteristic body ducts and vents to ensure that air is conducted through the radiator core.
Movement of the air through the radiator usually needs to be supplemented by a fan so that the engine can be cooled while stationary or working hard. However the fan will absorb excessive power at speed, so variable pitch, or friction drive, mechanical fans and electric fans are normally used on faster vehicles such as cars. Some vehicles, such as some liquid-cooled motorcycles, do not have any supplementary feature for inducing airflow through the radiator.
The radiator transfers the heat from the fluid inside to the air outside, thereby cooling the engine.
2007年11月28日星期三
2007年11月21日星期三
Valve operating positions
Valve positions are operating conditions determined by the position the disc or rotor in the valve. Some valves are made to be operated in a gradual change between two or more positions.
2-way valves
2-port valves are commonly called 2-way valves. Operating positions for such valves can be either shut (closed) so that no flow at all goes through, fully open for maximum flow, or sometimes partially open to any degree in between. Many valves are not designed to precisely control intermediate degree of flow; such valves are considered to be either open or shut, which maybe qualitative descriptions in between. Some valves are specially designed to regulate varying amounts of flow. Such valves have been called by various names like regulating, throttling, metering, or needle valves. For example, needle valves have elongated conically-tapered discs and matching seats for fine flow control. For some valves, there may be a mechanism to indicate how much the valve is open, but in many cases other indications of flow rate are used, such as separate flow meters.
In some plants with fluid systems, some 2-way valves can be designated as normally shut or normally open during regular operation. Examples of normally shut valves are sampling valves, which are only opened while a sample is taken. Examples of normally open valves are isolation valves, which are usually only shut when there is a problem with a unit or a section of a fluid system such as a leak. Then, isolation valve(s) are shut in order to isolate the problem from the rest of the system.
Although many 2-way valves are made in which the flow can go in either direction between the two ports, when a valve is placed into a certain application, flow is often expected to go from one certain port on the upstream side of the valve, to the other port on the downstream side. Pressure regulators are variations of valves in which flow is controlled to produce a certain downstream pressure, if possible. They are often used to control flow of gas from a gas cylinder. A back-pressure regulator is a variation of a valve in which flow is controlled to maintain a certain upstream pressure, if possible.
3-way valves
3-way valves have three ports. 3-way valves are commonly made such that flow coming in at one port can be directed to either the second port in one position or the third port in another position or in an intermediate position so all flow is stopped. Often such 3-way valves are ball or rotor valves. Many faucets are made so that incoming cold and hot water can be regulated in varying degrees to give outcoming water at a desired temperature. Other kinds of 3-port valves can be designed for other possible flow-directing schemes and positions; for example, see Ball valve.
The "motor valve" on a domestic heating system is an example of a 3-way valve. Depending on demand the motor head rotates the spindle to control the proportion of the flow that goes to the two outlet pipes: One to radiators, one to hot water system. In a conventional system the valve usually sits just after the pump and by the cylinder ("hot tank").
In valves having more than 3 ports, even more flow-directing schemes are possible. For examples, see this external site. Such valves are often rotor valves or ball valves. Slider valves have been used also.
Control
A valve controlled by a wheel (left).
A valve controlled by a wheel (left).
Many valves are controlled manually with a handle attached to the valve stem. If the handle is turned a quarter of a full turn (90°) between operating positions, the valve is called a quarter-turn valve. Butterfly valves, ball valves, and plug valves are often quarter-turn valves. Valves can also be controlled by devices called actuators attached to the stem. They can be electromechanical actuators such as an electric motor or solenoid, pneumatic actuators which are controlled by air pressure, or hydraulic actuators which are controlled by the pressure of a liquid such as oil or water. Actuators can be used for the purposes of automatic control such as in washing machine cycles, remote control such as the use of a centralized control room, or because manual control is too difficult; for example, the valve is huge. Pneumatic actuators and hydraulic actuators need pressurized air or liquid lines to supply the actuator: an inlet line and an outlet line. Pilot valves are valves which are used to control other valves. Pilot valves in the actuator lines control the supply of air or liquid going to the actuators.
The fill valve in a commode water tank is a liquid level-actuated valve. When a high water level is reached, a mechanism shuts the valve which fills the tank.
In some valve designs, the pressure of the flow fluid itself or pressure difference of the flow fluid between the ports automatically controls flow through the valve. In an open valve, fluid flows in a direction from higher pressure to lower pressure.
Other considerations
Valves are typically rated for maximum temperature and pressure by the manufacturer. The wetted materials in a valve are usually identified also. Some valves rated at very high pressures are available. When a designer, engineer, or user decides to use a valve for an application, he/she should ensure the rated maximum temperature and pressure are never exceeded and that the wetted materials are compatible with the fluid the valve interior is exposed to.
Some fluid system designs, especially in chemical or power plants, are schematically represented in piping and instrumentation diagrams. In such diagrams, different types of valves are represented by certain symbols.
Valves in good condition should be leak-free. However, valves may eventually wear out from use and develop a leak, either between the inside and outside of the valve or, when the valve is shut to stop flow, between the disc and the seat. A particle trapped between the seat and disc could also cause such leakage.
2-way valves
2-port valves are commonly called 2-way valves. Operating positions for such valves can be either shut (closed) so that no flow at all goes through, fully open for maximum flow, or sometimes partially open to any degree in between. Many valves are not designed to precisely control intermediate degree of flow; such valves are considered to be either open or shut, which maybe qualitative descriptions in between. Some valves are specially designed to regulate varying amounts of flow. Such valves have been called by various names like regulating, throttling, metering, or needle valves. For example, needle valves have elongated conically-tapered discs and matching seats for fine flow control. For some valves, there may be a mechanism to indicate how much the valve is open, but in many cases other indications of flow rate are used, such as separate flow meters.
In some plants with fluid systems, some 2-way valves can be designated as normally shut or normally open during regular operation. Examples of normally shut valves are sampling valves, which are only opened while a sample is taken. Examples of normally open valves are isolation valves, which are usually only shut when there is a problem with a unit or a section of a fluid system such as a leak. Then, isolation valve(s) are shut in order to isolate the problem from the rest of the system.
Although many 2-way valves are made in which the flow can go in either direction between the two ports, when a valve is placed into a certain application, flow is often expected to go from one certain port on the upstream side of the valve, to the other port on the downstream side. Pressure regulators are variations of valves in which flow is controlled to produce a certain downstream pressure, if possible. They are often used to control flow of gas from a gas cylinder. A back-pressure regulator is a variation of a valve in which flow is controlled to maintain a certain upstream pressure, if possible.
3-way valves
3-way valves have three ports. 3-way valves are commonly made such that flow coming in at one port can be directed to either the second port in one position or the third port in another position or in an intermediate position so all flow is stopped. Often such 3-way valves are ball or rotor valves. Many faucets are made so that incoming cold and hot water can be regulated in varying degrees to give outcoming water at a desired temperature. Other kinds of 3-port valves can be designed for other possible flow-directing schemes and positions; for example, see Ball valve.
The "motor valve" on a domestic heating system is an example of a 3-way valve. Depending on demand the motor head rotates the spindle to control the proportion of the flow that goes to the two outlet pipes: One to radiators, one to hot water system. In a conventional system the valve usually sits just after the pump and by the cylinder ("hot tank").
In valves having more than 3 ports, even more flow-directing schemes are possible. For examples, see this external site. Such valves are often rotor valves or ball valves. Slider valves have been used also.
Control
A valve controlled by a wheel (left).
A valve controlled by a wheel (left).
Many valves are controlled manually with a handle attached to the valve stem. If the handle is turned a quarter of a full turn (90°) between operating positions, the valve is called a quarter-turn valve. Butterfly valves, ball valves, and plug valves are often quarter-turn valves. Valves can also be controlled by devices called actuators attached to the stem. They can be electromechanical actuators such as an electric motor or solenoid, pneumatic actuators which are controlled by air pressure, or hydraulic actuators which are controlled by the pressure of a liquid such as oil or water. Actuators can be used for the purposes of automatic control such as in washing machine cycles, remote control such as the use of a centralized control room, or because manual control is too difficult; for example, the valve is huge. Pneumatic actuators and hydraulic actuators need pressurized air or liquid lines to supply the actuator: an inlet line and an outlet line. Pilot valves are valves which are used to control other valves. Pilot valves in the actuator lines control the supply of air or liquid going to the actuators.
The fill valve in a commode water tank is a liquid level-actuated valve. When a high water level is reached, a mechanism shuts the valve which fills the tank.
In some valve designs, the pressure of the flow fluid itself or pressure difference of the flow fluid between the ports automatically controls flow through the valve. In an open valve, fluid flows in a direction from higher pressure to lower pressure.
Other considerations
Valves are typically rated for maximum temperature and pressure by the manufacturer. The wetted materials in a valve are usually identified also. Some valves rated at very high pressures are available. When a designer, engineer, or user decides to use a valve for an application, he/she should ensure the rated maximum temperature and pressure are never exceeded and that the wetted materials are compatible with the fluid the valve interior is exposed to.
Some fluid system designs, especially in chemical or power plants, are schematically represented in piping and instrumentation diagrams. In such diagrams, different types of valves are represented by certain symbols.
Valves in good condition should be leak-free. However, valves may eventually wear out from use and develop a leak, either between the inside and outside of the valve or, when the valve is shut to stop flow, between the disc and the seat. A particle trapped between the seat and disc could also cause such leakage.
2007年11月16日星期五
Shower Head
Kramer and Jerry are not pleased with the new "low-flow" shower heads that the building's maintenance people have put in for them. Elaine is surprised to find out that she has tested positive for opium. Mr. Peterman denies her a trip to Africa they were going to take. Kramer asks to use Elaine's shower, and is mistaken by Peterman as a drug addict. Jerry is frustrated by the fact that his parents aren't moving back to Florida and George is elated because his parents are considering moving to Florida. George's parents decide to go to annoy the Seinfelds, but the Seinfelds find out and decide to stay, causing the Costanzas to stay.
Jerry's Uncle Leo complains about an overcooked hamburger and says the cook is anti-Semitic, which Jerry jokes about on the Tonight Show. Leo's girlfriend laughs at this, Leo calls her anti-Semitic, and they break up. Elaine discovers her opium results were from her eating poppyseed muffins. After she is about to retake the test and believes she accidentally ate poppyseeds in some chicken, and still desperate to go to Africa, she asks Jerry's mom to take a urine sample for her. Elaine is later shocked to find that the urine sample proved that Jerry's mom has osteoporosis and is menopausal.
Kramer and Newman get new showerheads from the black market. The one Kramer gets is for elephants at a circus, and the pressure is too high as a result.
Jerry's Uncle Leo complains about an overcooked hamburger and says the cook is anti-Semitic, which Jerry jokes about on the Tonight Show. Leo's girlfriend laughs at this, Leo calls her anti-Semitic, and they break up. Elaine discovers her opium results were from her eating poppyseed muffins. After she is about to retake the test and believes she accidentally ate poppyseeds in some chicken, and still desperate to go to Africa, she asks Jerry's mom to take a urine sample for her. Elaine is later shocked to find that the urine sample proved that Jerry's mom has osteoporosis and is menopausal.
Kramer and Newman get new showerheads from the black market. The one Kramer gets is for elephants at a circus, and the pressure is too high as a result.
2007年11月13日星期二
Plastic pressure pipe systems
Plastic pressure pipe systems are used for the conveyance of drinking water, waste water, chemicals, heating and cooling fluids, foodstuffs, ultra-pure liquids, slurries, gases, compressed air and vacuum system applications, both for above and below ground applications. Plastic pressure pipe systems have been in use since the 1950s
The most common pipe systems are named after the materials they are made from. The type of pipe in use is dependent on the material passed through the pipe, the operating pressure, and the operating temperature. To ensure pipes from different vendors work together, the ISO set standards for manufacturers to follow.
Polypropylene is suitable for use with foodstuffs, potable and ultra pure waters, as well as within the pharmaceutical and chemical industries.[citation needed] Polypropylene is adversely affected by UV radiation and requires insulation or a protective coating if installed outside.
The most common pipe systems are named after the materials they are made from. The type of pipe in use is dependent on the material passed through the pipe, the operating pressure, and the operating temperature. To ensure pipes from different vendors work together, the ISO set standards for manufacturers to follow.
Polypropylene is suitable for use with foodstuffs, potable and ultra pure waters, as well as within the pharmaceutical and chemical industries.[citation needed] Polypropylene is adversely affected by UV radiation and requires insulation or a protective coating if installed outside.
2007年11月8日星期四
Vice premier calls for public participation in saving energy
China's vice premier Zeng Peiyan called on ordinary people in China to get involved in the ongoing campaign of energy reduction on Sunday, the first day of a nationwide publicity week themed with energy conservation.
"The publicity week is a good chance to enhance the public awareness of energy conservation," said Zeng, who attended activities of the publicity week organized by the government of Nanjing in Jiangsu Province.
The whole nation, including the sectors of construction, production, circulation and consumption, should be mobilized to practice energy saving in a down-to-earth manner, he added.
Zeng urged government departments and public places to set air conditioners at or above 26 degrees Celsius during this summer, and asked residents to do the same at home, in a bid to save more energy.
During the nationwide publicity week, which lasts from June 10 to 16, various parts of China will hold all types of activities to publicize the importance of energy saving.
The Ministry of Communications would shut off the air conditioners in all of its offices on June 12, and staff who drive to work are encouraged to take buses, ride bicycles or go on foot.
East China's Anhui Province said it would cut the use of air conditioners in office by two hours every day, and elevators would be made available above the fifth floor only.
Under a five-year plan up to 2010, China pledged to cut energy consumption per unit of gross domestic product (GDP) by 20 percent, or four percent each year, but consumption fell by just 1.23 percent last year.
"The publicity week is a good chance to enhance the public awareness of energy conservation," said Zeng, who attended activities of the publicity week organized by the government of Nanjing in Jiangsu Province.
The whole nation, including the sectors of construction, production, circulation and consumption, should be mobilized to practice energy saving in a down-to-earth manner, he added.
Zeng urged government departments and public places to set air conditioners at or above 26 degrees Celsius during this summer, and asked residents to do the same at home, in a bid to save more energy.
During the nationwide publicity week, which lasts from June 10 to 16, various parts of China will hold all types of activities to publicize the importance of energy saving.
The Ministry of Communications would shut off the air conditioners in all of its offices on June 12, and staff who drive to work are encouraged to take buses, ride bicycles or go on foot.
East China's Anhui Province said it would cut the use of air conditioners in office by two hours every day, and elevators would be made available above the fifth floor only.
Under a five-year plan up to 2010, China pledged to cut energy consumption per unit of gross domestic product (GDP) by 20 percent, or four percent each year, but consumption fell by just 1.23 percent last year.
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