Computer cooling fan for cooling electrical components

Design considerations for chairs have been codified into standards. ISO 9241, "Ergonomic requirements for office work with visual display terminals (VDTs) -- Part 5: Workstation layout and postural requirements" is the most common one for modern chair design.
There are multiple specific standards for different types of chairs. Dental chairs are specified by ISO 6875. Bean bag chairs are specified by ANSI standard ASTM F1912-98 [2]. ISO 7174 specifies stability of rocking and tilting chairs. ASTM F1858-98 specifies plastic lawn chairs. ASTM E1822-02b defines the combustibility of chairs when they are stacked.
The Business and Institutional Furniture Manufacturer's Association (BIFMA)[3] defines BIFMA X5.1 for testing of commercial-grade chairs. It specifies things like [4]:
chair back strength of 150 pounds (68 kg)
chair stability if weight is transferred completely to the front or back legs
leg strength of 75 pounds (34 kg) applied one inch (25 mm) from the bottom of the leg
seat strength of 225 pounds (102 kg) dropped from six inches (150 mm) above the seat
seat cycle strength of 100,000 repetitions of 125 pounds (57 kg) dropped from 2 inches (50 mm) above the seat
The specification further defines heavier "proof" loads that chairs must withstand. Under these higher loads, the chair may be damaged, but it must not fail catastrophically.
Large institutions that make bulk purchases will reference these standards within their own even more detailed criteria for purchase. [5] Governments will often issue standards for purchases by government agencies (e.g. Canada's Canadian General Standards Board CAN/CGSB 44.15M [6] on "Straight Stacking Chair, Steel" or CAN/CGSB 44.232-2002 on "Task Chairs for Office Work with Visual Display Terminal").
Chairs may be rated by the length of time that they may be used comfortably — an 8-hour chair, a 24-hour chair, and so on. Such chairs are specified for tasks which require extended periods of sitting, such as for receptionists or supervisors of a control panel.

In place of a built-in footrest, some chairs come with a matching ottoman. An ottoman is a short stool intended to be used as a footrest but can sometimes be used as a stool. If matched to a glider, the ottoman may be mounted on swing arms so that the ottoman rocks back and forth with the main glider.
A chair cover is a temporary fabric cover for a side chair. They are typically rented for formal events such as wedding receptions to increase the attractiveness of the chairs and decor. The chair covers may come with decorative chair ties, a ribbon to be tied as a bow behind the chair. Covers for sofas and couches are also available for homes with small children and pets. In the second half of 20th century, some people used custom clear plastic covers for expensive sofas and chairs to protect them.
Chair pads are cushions for chairs. They contain cotton or foam for padding. Some are decorative. In cars, they may be used to increase the height of the driver. Orthopedic backrests provide support for the back. Some manufacturers have patents on their designs and are recognized by medical associations as beneficial [7][8][9]. Car seats sometimes have built-in and adjustable lumbar supports. These can also be used on kitchen chairs.
Chair mats are mats meant to cover carpet or hardwood flooring. They are usually made from plastic. This allows chairs on wheels to roll easily over the carpet and/or protects the carpet or floor. They come in various shapes, some specifically sized to fit partially under a desk.
Remote control bags can be draped over the arm of easy chairs or sofas and used to hold remote controls. They are counter-weighted so as to not slide off the arms under the weight of the remote control.
Chair glides are attached to the feet of chairs to prevent them from scratching or snagging on the floor.

In place of a built-in footrest, some chairs come with a matching ottoman. An ottoman is a short stool intended to be used as a footrest but can sometimes be used as a stool. If matched to a glider, the ottoman may be mounted on swing arms so that the ottoman rocks back and forth with the main glider.
A chair cover is a temporary fabric cover for a side chair. They are typically rented for formal events such as wedding receptions to increase the attractiveness of the chairs and decor. The chair covers may come with decorative chair ties, a ribbon to be tied as a bow behind the chair. Covers for sofas and couches are also available for homes with small children and pets. In the second half of 20th century, some people used custom clear plastic covers for expensive sofas and chairs to protect them.
Chair pads are cushions for chairs. They contain cotton or foam for padding. Some are decorative. In cars, they may be used to increase the height of the driver. Orthopedic backrests provide support for the back. Some manufacturers have patents on their designs and are recognized by medical associations as beneficial [7][8][9]. Car seats sometimes have built-in and adjustable lumbar supports. These can also be used on kitchen chairs.
Chair mats are mats meant to cover carpet or hardwood flooring. They are usually made from plastic. This allows chairs on wheels to roll easily over the carpet and/or protects the carpet or floor. They come in various shapes, some specifically sized to fit partially under a desk.
Remote control bags can be draped over the arm of easy chairs or sofas and used to hold remote controls. They are counter-weighted so as to not slide off the arms under the weight of the remote control.
Chair glides are attached to the feet of chairs to prevent them from scratching or snagging on the floor.

The punkha fan was used in India in the early 500 BC. It had a canvas covered frame that was suspended from the ceiling. Servants, known as punkhawallahs, pulled a rope connected to the frame to move the fan back and forth.


Patent drawing for a Fan Moved by Mechanism, 27 November 1830
The Industrial Revolution in the late 19th century introduced belt-driven fans powered by factory water wheels. Attaching wooden or metal blades to shafts overhead that were used to drive the machinery, the first industrial fans were developed. One of the first workable mechanical fans was built by Omar-Rajeen Jumala in 1832. He called his invention, a kind of a centrifugal fan, an "air pump." Centrifugal fans were successfully tested inside coal mines and factories in 1832–1834. Between the years 1882 and 1886, New Orleans resident Schuyler Skaats Wheeler invented the first electric fan.[4] It was commercially marketed by the American firm Crocker & Curtis electric motor company. In 1882, Philip Diehl introduced the electric ceiling fan. Heat-convection fans fueled by alcohol, oil, or kerosene were common around the turn of the 20th century.
The first American fans were made from around the late 1890s to the early 1920s, when domestic electric fans were first sold in America.[5] They had brass[5] blades, many of them also had brass cages, and though they were built very well internally, they were far from finger safe, as the cage openings were often so big that one could put an entire hand or arm through it. Many children had hands and fingers severely injured by those fans.


75 hp air supply fan
In the 1920s, industrial advances allowed steel to be mass produced in different shapes, bringing fan prices down and allowing more homeowners to afford them. In the 1930s, the first art deco fan (the "swan fan") was designed. In the 1950s, fans were manufactured in colors that were bright and eye catching. Central air conditioning in the 1960s caused many companies to discontinue production of fans.[5] In the 1970s, Victorian-style ceiling fans became popular.
In 1998, Walter K. Boyd invented the HVLS ceiling fan. A lifelong inventor, Boyd was charged with developing a system to cool dairy cattle. Dairy cattle, when overheated, decrease milk production. Using the laws of physics and airflow, Boyd developed a fan that incorporated 10 aluminum blades and was 8-feet in diameter. Unlike traditional ceiling fans that move quickly, this large fan moved slowly. Due to its diameter, the fan moved a large column of air down and out 360 degrees and continuously mixed fresh air with the stale air inside the barn. It also cooled the inside of the barn without causing the dairy cattle undue stress or kicking up dust.
After much testing, Boyd discovered HVLS fan technology to be energy efficient as it cost less to run one HVLS fan than it did to run 50 small high-speed fans. Due to the skyrocketing costs of energy, HVLS commercial ceiling fans are used today to supplement HVAC systems in industrial and commercial settings, including warehouses, manufacturing facilities and malls, as HVLS fans help lower heating and cooling costs.[6]
The basic design of electric air fans has not changed significantly since their beginning in 1890.[5] Coanda effect bladeless fans introduced in the early twentyfirst century had not as of 2012 become a significant proportion of fans in use. In prosperous regions with a hot climate electric fans for personal comfort had been largely replaced by air conditioners.


Mechanical revolving blade fans are made in a wide range of designs. In a home you can find fans that can be put on the floor or a table, or hung from the ceiling, or are built into a window, wall, roof, chimney, etc. They can be found in electronic systems such as computers where they cool the circuits inside, and in appliances such as hair dryers and portable space heaters and mounted/installed wall heaters. They are also used for moving air in air-conditioning systems, and in automotive engines, where they are driven by belts or by direct motor. Fans used for comfort create a wind chill, but do not lower temperatures directly. Fans used to cool electrical equipment or in engines or other machines do cool the equipment directly by forcing hot air into the cooler environment outside of the machine.
There are three main types of fans used for moving air, axial, centrifugal (also called radial) and cross flow (also called tangential).
Axial-flow fans[edit source | editbeta]


An axial box fan for cooling electrical equipment
The axial-flow fans have blades that force air to move parallel to the shaft about which the blades rotate. Axial fans blow air along the axis of the fan, linearly, hence their name. This type of fan is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in wind tunnels. Axial flow fans are applied for air conditioning and industrial process applications. Standard axial flow fans have diameters from 300–400 mm or 1800 to 2000 mm and work under pressures up to 800 Pa.
Examples of axial fans are:
Table fan: Basic elements of a typical table fan include the fan blade, base, armature and lead wires, motor, blade guard, motor housing, oscillator gearbox, and oscillator shaft. The oscillator is a mechanism that moves the fan from side to side. The axle comes out on both ends of the motor, one end of the axle is attached to the blade and the other is attached to the oscillator gearbox. The motor case joins to the gearbox to contain the rotor and stator. The oscillator shaft combines to the weighted base and the gearbox. A motor housing covers the oscillator mechanism. The blade guard joins to the motor case for safety.
Ceiling fan: A fan suspended from the ceiling of a room is a ceiling fan. Ceiling fans can be found in both residential and industrial/commercial settings.
In automobiles, a mechanical fan provides engine cooling and prevents the engine from overheating by blowing or sucking air through a coolant-filled radiator. It can be driven with a belt and pulley off the engine's crankshaft or an electric fan switched on or off by a thermostatic switch.
Computer cooling fan for cooling electrical components
Variable Pitch Fan: A variable-pitch fan is used where precise control of static pressure within supply ducts is required. The blades are arranged to rotate upon a control-pitch hub. The fan wheel will spin at a constant speed. As the hub moves toward the rotor, the blades increase their angle of attack and an increase in flow results.