Bellows are also used to move air, although not generally considered fans. A hand-operated bellows is essentially a bag with a nozzle and handles, which can be filled with air by one movement, and the air expelled by another. Typically it would comprise two rigid flat surfaces hinged at one end, where a nozzle is fitted, and with handles at the other. The sides of the surfaces are joined by a flexible and air-proof material such as leather; the surfaces and joining material comprise a bag sealed everywhere but at the nozzle. (The joining material typically has a characteristic pleated construction that is so common that similar expanding fabric arrangements not used for moving air, such as on a folding camera, are called bellows.) Separating the handles expands the bag, which fills with air; squeezing them together expels the air. A simple valve (e.g., a flap) may be fitted so that air enters without having to come from the nozzle, which may be close to a fire.
Bellows produce a directed pressurized stream of air; the airflow volume is typically low with moderate pressure. They are an older technology, used mainly to produce a strong and directed airflow unlike non-electric bladed mechanical fans, before the introduction of electricity.
A single-acting bellows will only produce airflow during the exhaust stroke.
A double-acting bellows is a pair of bellows capable of blowing out air from one while inhaling air into the other, but airflow still temporarily ceases when the stroke direction is reversed.
Combining multiple bellows at third-cycle or quarter-cycle arrangements on a crank arm allows for nearly continuous airflow from several bellows at once; each is in a different phase of inhaling and exhausting during the cycle.
Coanda effect[edit source | editbeta]
An open-face supermarket freezer with an air curtain. Cooling air circulates across the food through the dark slot seen at the rear of the freezer, and through another grille not visible along the front.
The Dyson Air Multiplier fans, and the Imperial C2000 series range hood fans,[7] have no exposed fan blades or other visibly moving parts. The airflow is generated using the Coanda effect; a small quantity of air from a high-pressure bladed impeller fan, contained in the base rather than exposed, drives a large airmass via a low-pressure area created by the airfoil.[8][9][10] The US Patent & Trademark Office initially ruled that Dyson's patent was not an improvement on the Toshiba patent on a nearly identical bladeless desktop fan granted in 1981.[8]
Air curtains and air doors also utilize this effect to help retain warm or cool air within an otherwise exposed area that lacks a cover or door. Air curtains are commonly used on open-face dairy, freezer, and vegetable displays to help retain chilled air within the cabinet using a laminar airflow circulated across the display opening, usually generated by a fan in the base of the cabinet.
Bellows produce a directed pressurized stream of air; the airflow volume is typically low with moderate pressure. They are an older technology, used mainly to produce a strong and directed airflow unlike non-electric bladed mechanical fans, before the introduction of electricity.
A single-acting bellows will only produce airflow during the exhaust stroke.
A double-acting bellows is a pair of bellows capable of blowing out air from one while inhaling air into the other, but airflow still temporarily ceases when the stroke direction is reversed.
Combining multiple bellows at third-cycle or quarter-cycle arrangements on a crank arm allows for nearly continuous airflow from several bellows at once; each is in a different phase of inhaling and exhausting during the cycle.
Coanda effect[edit source | editbeta]
An open-face supermarket freezer with an air curtain. Cooling air circulates across the food through the dark slot seen at the rear of the freezer, and through another grille not visible along the front.
The Dyson Air Multiplier fans, and the Imperial C2000 series range hood fans,[7] have no exposed fan blades or other visibly moving parts. The airflow is generated using the Coanda effect; a small quantity of air from a high-pressure bladed impeller fan, contained in the base rather than exposed, drives a large airmass via a low-pressure area created by the airfoil.[8][9][10] The US Patent & Trademark Office initially ruled that Dyson's patent was not an improvement on the Toshiba patent on a nearly identical bladeless desktop fan granted in 1981.[8]
Air curtains and air doors also utilize this effect to help retain warm or cool air within an otherwise exposed area that lacks a cover or door. Air curtains are commonly used on open-face dairy, freezer, and vegetable displays to help retain chilled air within the cabinet using a laminar airflow circulated across the display opening, usually generated by a fan in the base of the cabinet.
