Patent Grant
7247087
The present invention relates generally to fume hoods, and more particularly to a fume hood provided with an air directing member uniquely formed to direct the inflow of air into the chamber of the fume hood in a path that prevents fumes from exiting the chamber.
Fume hoods are used in laboratories and other similar locations where it is necessary for technicians to work with materials that generate noxious and poisonous fumes. These fume hoods are formed with an interior, generally enclosed chamber in which the work is done, and the front of the chamber has an access opening through which the arms and hands of the technician can extend to work on materials within the chamber. The fume hood includes a sash or door that moves vertically to open and close the access the opening, or to vary the size of the access opening.
Because of the harmful effects of the fumes generated within the chamber of the fume hood, it is imperative that these fumes be maintained within the confines of the fume hood and then be exhausted therefrom so they will not be permitted to escape though the access opening and endanger the technician standing just outside the access opening. For this purpose, fume hoods are provided with exhaust systems of some kind that exhausts the air and fumes from the interior of the chamber and then transports them to a location outside the fume hood where they can be safely disposed of. The exhaust system creates a negative pressure within the chamber that, in turn, causes outside air to flow into the chamber through the partially open access opening between the bottom of the sash and the work surface of the chamber, and this inward flow of outside air tends to prevent the fumes from exiting the chamber through the access opening. However, if this inward flow of air is not properly directed, some of the fumes will leak out through the access opening and present an undesirable and often dangerous situation for the technician working in the fume hood.
For example, where no structure or device is provided for directing the inward flow of air into the chamber, the momentum of the inward flow of air entering a region of lower static pressure tends to cause a vortex of air to form adjacent along the bottom surface of the chamber and adjacent the front edge thereof. This vortex captures some of the fumes within its generally circular flow pattern, and the vortex is very sensitive to any variation of air pressure or airflow. As a result, even movement of the technician, or someone walking past the partially open access opening can create an external pattern of airflow that is sufficient to disrupt the vortex to an extend that fumes will be released from the chamber through the access opening.
One of the first attempts to correct this problem was to add a permanent air directing plate, or airfoil, that was mounted to the fume hood to extend into the chamber through the bottom of the access opening at a location about one inch above the bottom wall of the chamber. The airfoil is shaped to direct the incoming air along the bottom surface of the chamber, beneath the airfoil, and this airflow essentially eliminates the undesirable fume-carrying vortex. However, this airfoil has its own disadvantages. First, because it is a permanent structure extending through the access opening and into the chamber just above the bottom wall thereof, the airfoil creates a stop member for the sash in its downward movement that prevents the sash from fully closing. Therefore outside air constantly flows into the chamber beneath the airfoil which increases the energy costs in operating the fume hood and its exhaust system. Additionally, because of its location, it creates an obstacle when objects and equipment, particularly heavy objects, had to be moved into and out of the chamber through the access opening.
Another solution to the vortex problem is to mount a simple flat air-directing member at the front edge of the bottom wall of the chamber at an incline thereto and outside of the path of vertical movement of the sash. Because of its location, this airfoil does not interfere with the movement of the sash and does not form a barrier to the movement of objects into and out of the chamber. This type of airfoil has been found, in most cases, to effectively eliminate the formation of the undesirable vortex by directing the incoming air along the surface of the bottom wall of the chamber. However, this type of airfoil is effectively only when the velocity of the airflow into the chamber is at or above approximately seventy feet per minute (70 FPM). Energy conservation considerations now make it very desirable to use a smaller-capacity exhaust system, and reduce the airflow velocity into the chamber to something less that 70 FPM, and at this reduced velocity the air flow directed by the airfoil tends to separate from the bottom surface of the chamber and allow “dead” air containing fumes to form along the bottom surface of the chamber and beneath the separated airflow created by the airfoil. This dead air, like a vortex, is sensitive enough that even small disturbance of the air outside of the access opening (e.g. a technician walking by the front of the fume hood) can cause the dead air with the fumes entrained therein to be drawn outwardly though the access opening.
It has also been proposed to mount an airfoil at the front end of the fume hood for pivotal movement between an operable position and a position where the airfoil has not effect on the airflow. In U.S. Pat. No. 5,556,331 there is disclosed a fume hood with a pivoted airfoil having a single air-directing surface that, in its operable position, directs air along a path parallel to the bottom surface of the fume hood. It appears this construction would have the same problem described above where the velocity of the air is less the 70 FPM. U.S. Pat. No. 6,582,292 discloses another pivoted airfoil having multiple air-directing surfaces. In both of these patents, the air directing member is positioned inwardly of the plane of the sash or door, and this location creates problems in terms of maintaining the inward flow of air along the bottom surface of the interior of the fume hood, particularly at low air velocities.
Briefly described, the present invention provides an air foil for use with a fume hood adapted to be connected to an exhaust system. The fume hood includes a cabinet formed with a chamber having a generally flat bottom wall and a sash door mounted at the front end of the chamber for movement in a vertical plane to provide an access opening to the chamber. An air directing member is mounted on the cabinet outside of the plane of movement of the sash door relative to the chamber and generally aligned with the bottom wall. The air directing member is formed with an opening positioned to cause a first path of outside air to flow into the chamber along the surface of the bottom wall and is formed with a second portion for directing a second path of outside air in a direction generally parallel to and above the first path.
In the preferred embodiment of the present invention, the air directing member is formed with a first generally flat guide surface extending upwardly from the opening toward the front edge of the bottom wall, and the second portion of the air directing member includes a second generally flat guide surface extending in a direction generally parallel to the first guide surface, with the second guide surface being spaced outward from the first guide surface relative to the plane of movement of the sash door.
Additionally, if desired, the air directing member may be formed with a connecting wall portion extending between the first and second guide surfaces, and the opening, which is preferably a series of aligned slots, may be formed in the connecting wall portion. The connecting wall may extend in a generally vertical direction between the first and second guide surfaces.
The present invention also includes a method of directing air into the interior chamber of a fume hood that has a bottom wall and a sash door movable in a vertical plane to provide an access opening to the chamber. This method includes the steps of creating a vacuum within the chamber to draw outside air into the chamber through the access opening provided by the sash door, mounting an air directing member on the fume hood outside of the vertical plane of movement of the sash door, and utilizing the air directing member to create a first path of movement of the outside air to flow into the chamber along the surface of the bottom wall and to create a second path of movement of the outside air in a direction generally parallel to and above the first path of air movement so that the second path of movement of the outside air assists in maintaining the first path of movement of the outside air adjacent to the bottom wall of the chamber.
Preferably, the step of creating the second path of movement of the outside air includes passing the outside air along a second generally flat guide surface extending in a direction generally parallel to the first guide surface and spaced outwardly from the first guide surface relative to the plane of movement of the sash door.
It is also preferred that the step of creating the second path of movement of the outside air includes passing the outside air along a second generally flat guide surface, extending in a direction generally parallel to the first guide surface and spaced outwardly from the first guide surface relative to the plane of movement of the sash door.
Looking now in greater detail at the accompanying drawings,
The fume hood 10 includes a cabinet 14 consisting of two side walls 16, a top wall 18, a back wall 20, and a generally flat bottom wall 22. These walls 16, 18, 20 and 22 form a generally enclosed interior chamber 24 that has an access opening 26 at the front of the chamber 24. A sash or door 28 is mounted in the cabinet 14 for up and down movement in a vertical plane to open and close the access opening 26. As best seen in
The cabinet 14 is also formed with an exhaust opening 36 through which air from within the cabinet 14 is exhausted. As is well known in the art, an exhaust system usually consist of a system of conduits and blowers within the building (e.g. a laboratory) in which the fume hood is located, and this system is used to exhaust air from all of the fume hoods and any other equipment that may be generating noxious or harmful gases. However, if desired or required, other equivalent exhaust systems could be used, such as, for example, individual blowers for the fume hoods. In whatever from it takes, the exhaust system is arranged to draw air outwardly from the interior chamber 24 where noxious gases may be produced, and this air is exhausted through the exhaust opening 36 and transported away from the fume hood 10 through conduits (not shown) that transport the air and noxious gases to a safe location away from the user of the fume hood and the environment in which the user is working.
As best seen in
The air foil 12 includes an attachment in portion 40 by which it is attached to the fume hood 10 as described above. The air foil 12 also includes a first generally flat guide surface 42 extending upwardly toward the front edge of the cabinet bottom wall 22 and a second generally flat guide surface 44 extending parallel to the first guide surface 42 and spaced outwardly therefrom. A connecting wall 46 extends generally vertically from the front end of the second wall portion 44 to the rear end of the first wall portion 42 as best seen in
When the sash 28 is raised to create the access opening 26, and when the exhaust system is energized to withdraw air through the exhaust opening 36, the location and construction of the air foil 12 creates a unique air flow pattern that is diagrammatically illustrated in
More specifically, air withdrawn through the exhaust opening 36 creates a negative pressure within the cabinet 14, and outside air, identified as “lab air” in
Accordingly, the unique air flow pattern created by the present invention overcomes the drawbacks of known prior art arrangements described above. First, it will be noted that the air foil 12 is positioned, in its entirety, at or below the plane of the cabinet bottom wall 22, and therefore it does not create any obstacle to the movement of equipment or materials into and out of the interior cabinet 14 along the bottom wall 22. Moreover, even at low air velocities (e.g. less than 70 fpm) the first path of air movement indicated by the open arrows 50 sweeps along the bottom wall 22 to remove noxious gases away from the access opening 26, and the second path of movement indicated by the solid arrows 52 tends to contain or “police” the air flowing along the first path of movement to prevent the formation of undesirable vortexes in the air flowing along the first path of movement. Even if the air flowing inwardly through the access opening is temporarily disrupted, such as by a user walking past the front face of the fume hood 10, the tendency of this movement to create a vortex in the first path of movement is significantly resisted by the policing action of the air flowing along the second path of movement and the tendency of the second path of air movement to resist any tendency of the first path of air movement to separate upwardly from the surface of the bottom wall 22.
In view of the aforesaid written description of the present invention, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to preferred embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.
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