El Ventilador

Un ventilador es una máquina de fluido concebida para producir una corriente de aire mediante un rodete con aspas que giran produciendo una diferencia de presiones. Entre sus aplicaciones, destacan las de hacer circular y renovar el aire en un lugar cerrado para proporcionar oxígeno suficiente a los ocupantes y eliminar olores, principalmente en lugares cerrados; así como la de disminuir la resistencia de transmisión de calor por convección. Fue inventado en 1882 por el estadounidense Schuyler S. Wheeler.

Se utiliza para desplazar aire o gas de un lugar a otro, dentro de o entre espacios, para motivos industriales o uso residencial, para ventilación o para aumentar la circulación de aire en un espacio habitado, básicamente para refrescar. Por esta razón, es un elemento indispensable en climas cálidos.

Un ventilador también es la turbomáquina que absorbe energía mecánica y la transfiere a un gas, proporcionándole un incremento de presión no mayor de 1.000 mmH2O aproximadamente, por lo que da lugar a una variación muy pequeña del volumen específico y suele ser considerada una máquina hidráulica.

En energía, los ventiladores se usan principalmente para producir flujo de gases de un punto a otro; es posible que la conducción del propio gas sea lo esencial, pero también en muchos casos, el gas actúa sólo como medio de transporte de calor, humedad, etc; o de material sólido, como cenizas, polvos, etc.

Entre los ventiladores y compresores existen diferencias. El objeto fundamental de los primeros es mover un flujo de gas, a menudo en grandes cantidades, pero a bajas presiones; mientras que los segundos están diseñados principalmente para producir grandes presiones y flujos de gas relativamente pequeños. En el caso de los ventiladores, el aumento de presión es generalmente tan insignificante comparado con la presión absoluta del gas, que la densidad de éste puede considerarse inalterada durante el proceso de la operación; de este modo, el gas se considera incompresible como si fuera un líquido. Por consiguiente en principio no hay diferencia entre la forma de operación de un ventilador y de una bomba de construcción similar, lo que significa que matemáticamente se pueden tratar en forma análoga.

También de forma secundaria, se utiliza el ventilador para asistir un intercambiadores de calor como un disipador o un radiador con la finalidad de aumentar la transferencia de calor entre un sólido y el aire o entre los fluidos que interactúan. Una clara aplicación de esto se ve reflejada en evaporadores y condensadores en sistemas de refrigeración en que el ventilador ayuda a transferir el calor latente entre el refrigerante y el aire, y viceversa. Asimismo, equipos de acondicionamiento de aire como la Unidad manejadora de aire (UMA), ocupan un ventilador centrífugo de baja presión estática para circular el aire por una red de ductos al interior de una edificación o instalación industrial.

Suele haber circulación de aire o ventilación a través de los huecos en las paredes de un edificio, en especial a través de puertas y ventanas. Pero esta ventilación natural, quizá aceptable en viviendas, no es suficiente en edificios públicos, como oficinas, teatros o fábricas. Los dispositivos de ventilación más sencillos utilizados en lugares donde se necesita mucha ventilación son ventiladores instalados para extraer el aire viciado del edificio y favorecer la entrada de aire fresco. Los sistemas de ventilación pueden combinarse con calentadores, filtros, controladores de humedad y dispositivos de refrigeración.

Tipos de ventiladores Industriales: Centrífugos, Helicocentrífufos, Helicoidales de distintas presiones y caudales
De pared: son fijados en la pared, permitiendo una mayor circulación en lugares pequeños, donde el uso de ventiladores no es soportado debido a la largura del ambiente, o en conjunto con otros ventiladores, proporcionando una mayor circulación de aire.
De mesa: son ventiladores de baja potencia utilizados especialmente en oficinas o en ambientes donde necesitan poca ventilación.

De piso: son portátiles y silenciosos, posibilitan que sean colocados en el suelo en cualquier ambiente de una casa, pudiendo ser trasladados a cualquier parte. Podemos encontrarlos en varios modelos y formas.

De techo: son ventiladores verticales, sus aspas están en posición horizontal, y por lo tanto el aire va hacia abajo. Muy comunes, utilizados en habitaciones donde no hay espacio disponible en las paredes o el suelo.

The Ventilator

A fan is a powered device used to create flow within a gas, usually air.
A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic motors and internal combustion engines.

Fans produce air flows with high volume and low pressure, as opposed to compressors which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air stream, and devices that take advantage of this, such as anemometers and wind turbines, often have designs similar to that of a fan.

Typical applications include climate control, vehicle and machinery cooling systems, personal comfort (e.g., an electric table fan), ventilation, fume extraction, winnowing (e.g., separating chaff of cereal grains), removing dust (e.g. in a vacuum cleaner), drying (usually in combination with heat) and to provide draft for a fire. It is also common to use electric fans as air fresheners, by attaching fabric softener sheets to the protective housing. This causes the fragrance to be carried into the surrounding air.

In addition to their utilitarian function, vintage or antique fans, and in particular electric fans manufactured from the late 19th century through the 1950s, have become a recognized collectible category, and in the U.S.A. an active collector club, the Antique Fan Collectors Association, supports the hobby.

New to the market are sleek portable fans that showcase a modern design sensibility. The New York Times lamented that inexpensive and effective fans abound at drug and discount stores, but they are often eyesores. The writer quoted contemporary ceiling fan designer Ron Rezek as saying: “Portable fans are the ugly ducklings of the fan industry. Not many designers, including myself, have tackled them.” Rezek praised several appealing contemporary fan designs that have found alternatives to the traditional metal cage and have incorporated innovative approaches to safety, such as the Otto fan by Swiss designer Carlo Borer.

Types of fans

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 space 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 create a wind chill, but do not lower temperatures directly.

Axial fans

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.

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.

A Ceiling fan is an example of an axial fan.

Ceiling fan: A fan suspended from the ceiling of a room is a ceiling fan.
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

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.

Centrifugal fan

Main article: centrifugal fan

Typical centrifugal fan.

Often called a "squirrel cage" (because of its similarity in appearance to exercise wheels for pet rodents), the centrifugal fan has a moving component (called an impeller) that consists of a central shaft about which a set of blades, or ribs, are positioned. Centrifugal fans blow air at right angles to the intake of the fan, and spin the air outwards to the outlet (by deflection and centrifugal force). The impeller rotates, causing air to enter the fan near the shaft and move perpendicularly from the shaft to the opening in the scroll-shaped fan casing. A centrifugal fan produces more pressure for a given air volume, and is used where this is desirable such as in leaf blowers, blowdryers, air mattress inflators, inflatable structures, climate control, and various industrial purposes. They are typically noisier than comparable axial fans.

Crossflow fan.

The crossflow or tangential fan, sometimes known as a tubular fan was patented in 1893 by Mortier, and is used extensively in the HVAC industry. The fan is usually long in relation to the diameter, so the flow approximately remains two-dimensional away from the ends. The CFF uses an impeller with forward curved blades, placed in a housing consisting of a rear wall and vortex wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice.

The flow within a crossflow fan may be broken up into three distinct regions: a vortex region near the fan discharge, called an eccentric vortex, the through-flow region, and a paddling region directly opposite. Both the vortex and paddling regions are dissipative, and as a result, only a portion of the impeller imparts usable work on the flow. The crossflow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the crossflow fan in the HVAC industry comes from its compactness, shape, quiet operation, and ability to provide high pressure coefficient. Effectively a rectangular fan in terms of inlet and outlet geometry, the diameter readily scales to fit the available space, and the length is adjustable to meet flow rate requirements for the particular application.

Much of the early work focused on developing the crossflow fan for both high- and low-flow-rate conditions, and resulted in numerous patents. Key contributions were made by Coester, Ilberg and Sadeh, Porter and Markland, and Eck. One interesting phenomenon particular to the crossflow fan is that, as the blades rotate, the local air incidence angle changes. The result is that in certain positions the blades act as compressors (pressure increase), while at other azimuthal locations the blades act as turbines (pressure decrease).

Fan motor

A standalone fan is typically powered with an electric motor. Fans are often attached directly to the motor's output, with no need for gears or belts. The electric motor is either hidden in the fan's center hub or extends behind it. For big industrial fans, three-phase asynchronous motors are commonly used, placed near the fan and driving it through a belt and pulleys. Smaller fans are often powered by shaded pole AC motors, or brushed or brushless DC motors. AC-powered fans usually use mains voltage, while DC-powered fans use low voltage, typically 24 V, 12 V or 5 V. Cooling fans for computer equipment exclusively use brushless DC motors, which produce much less electromagnetic interference.

In machines that already have a motor, the fan is often connected to this rather than being powered independently. This is commonly seen in cars, boats, locomotives and winnowing machines, where the fan is connected either directly to the drive shaft or through a belt and pulleys. Another common configuration is a dual-shaft motor, where one end of the shaft drives a mechanism, while the other has a fan mounted on it to cool the motor itself.

Fan collecting as a hobby

Electromechanical fans, among collectors, are rated according to their condition, size, age, and number of blades. Four-blade designs are the most common. Five- or six-blade designs are rare. The materials from which the components are made, such as brass, are important factors in fan desirability.